ChapterPDF AvailableLiterature Review

Abstract and Figures

Microfluidic and lab-on-a-chip systems have become increasingly important tools across many research fields in recent years. As a result of their small size and precise flow control, as well as their ability to enable in situ process visualization, microfluidic systems are increasingly finding applications in environmental science and engineering. Broadly speaking, their main present applications within these fields include use as sensors for water contaminant analysis (e.g., heavy metals and organic pollutants), as tools for microorganism detection (e.g., virus and bacteria), and as platforms for the investigation of environment-related problems (e.g., bacteria electron transfer and biofilm formation). This chapter aims to review the applications of microfluidics in environmental science and engineering - with a particular focus on the foregoing topics. The advantages and limitations of microfluidics when compared to traditional methods are also surveyed, and several perspectives on the future of research and development into microfluidics for environmental applications are offered.
Content may be subject to copyright.
Adv Biochem Eng Biotechnol
https://doi.org/10.1007/10_2020_128
©Springer Nature Switzerland AG 2020
Microuidics for Environmental
Applications
Ting Wang, Cecilia Yu, and Xing Xie
Contents
1 Introduction
2 Applications of Microuidics in Environmental Science and Engineering
2.1 Microuidics Used for Contaminant Analysis
2.2 Microuidics Used for Microorganism Detection
2.3 Microuidics Used as Research Platforms
3 Perspectives on MicrouidicsApplications in Environmental Science
and Engineering
References
Abstract Microuidic and lab-on-a-chip systems have become increasingly impor-
tant tools across many research elds in recent years. As a result of their small size
and precise ow control, as well as their ability to enable in situ process visualiza-
tion, microuidic systems are increasingly nding applications in environmental
science and engineering. Broadly speaking, their main present applications within
these elds include use as sensors for water contaminant analysis (e.g., heavy metals
and organic pollutants), as tools for microorganism detection (e.g., virus and bacte-
ria), and as platforms for the investigation of environment-related problems (e.g.,
bacteria electron transfer and biolm formation). This chapter aims to review the
applications of microuidics in environmental science and engineering with a
particular focus on the foregoing topics. The advantages and limitations of
microuidics when compared to traditional methods are also surveyed, and several
perspectives on the future of research and development into microuidics for
environmental applications are offered.
T. Wang, C. Yu, and X. Xie (*)
School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA,
USA
e-mail: xing.xie@ce.gatech.edu
Graphical Abstract
Keywords Bacterial electron transfer, Biolm formation, Contaminant analysis,
Environmental science and engineering, Lab-on-a-chip, Microuidics,
Microorganism detection
1 Introduction
Microuidics, or lab-on-a-chip, is the science and technology of systems that are
made using integrated circuits and/or miniaturized uidic channels designed to
realize different functions via electrical signals and/or ow manipulation
[1]. When feature size and ow volume are shrunk down to microscale, surface
area dramatically increases which signicantly improves the efciency of molec-
ular diffusion and heat transfer [1,2]. As a result of their properties, microuidics are
increasingly nding applications in disparate areas of multidisciplinary research,
including chemical [3,4], biological [5,6], medical (e.g., drug delivery) [2], and
engineering (e.g., material synthesis) [7]elds.
Environmental science and engineering is a discipline for understanding
environment-related processes and dealing with environment-related issues such
as understanding the conditions of environmental contamination and/or nding ways
to affect environment remediation and protection. Some of the most widely studied
environmental topics currently include pollution monitoring and analysis, research
into the effects of pollutants on ecologies and human health, technologies of
pollution treatment and removal, and microorganism-related challenges (such as
the spread of antibiotic resistance).
Microuidic and lab-on-a-chip devices are gaining increasing attention in this
eld due to their usefulness as tools for (by way of example) pollutant sensing,
microorganism detection, and general environment-related process investigation
(Fig. 1). Microuidic devices offer several remarkable advantages over more con-
ventional methods: for instance, they can more readily be used as portable detectors
or analyzers due to their small size, thereby enabling on-site pollution detection and
monitoring. Lab-on-a-chip devices have also provided research platforms for in situ
and real-time observation of microorganisms and for visualization of other
T. Wang et al.
environmental processes. In this chapter, we will review some of the primary
applications of microuidic and lab-on-a-chip devices in environmental science
and engineering. Finally, advantages, limitations, and perspectives on future devel-
opment in this area will be discussed.
2 Applications of Microuidics in Environmental Science
and Engineering
2.1 Microuidics Used for Contaminant Analysis
Conventional methods for conducting water pollutant analysis use advanced and
complex instruments, such as inductively coupled plasma mass spectrometry
(ICP-MS) for metal ions detection; high-performance liquid chromatography
(HPLC) and gas chromatography-mass spectrometry (GC-MS) for organic com-
pounds detection; and ultraviolet-visible spectroscopy (UV-Vis) for nitrate or
nitrite detection. Compared to these traditional analytical techniques, microuidic
systems and lab-on-a-chip sensors possess several signicant advantages, namely,
greater portability for on-site monitoring, smaller required sample volume, shorter
reaction time, and better process control. Optical and electrochemical methods are
the two main approaches that are typically used for pollutant detection in
Fig. 1 Environmental applications of microuidic and lab-on-a-chip devices (some images are
from the Internet)
Microuidics for Environmental Applications
microuidic devices and sensors [8]. Common optical methods include uorescent,
colorimetric, surface plasmon resonance, and surface-enhanced Raman scattering
(SERS) [8]. The detection techniques used in electrochemical sensors consist of
amperometry, voltammetry, conductometry, and potentiometry [9]. With the sensing
device miniaturization and sample volume decrease, electrochemical methods offer
an inherent advantage over optical approaches. Since electrochemical methods rely
on the concentration instead of absolute amount of the analyte, the sensitivity is
independent of the sample volume, and more accurate determinations could be
achieved due to the higher surface-area-to-volume ratios of the small probes [10].
2.1.1 Heavy Metal Ion Analysis
Water contamination by heavy metals is a severe environmental problem with
signicant implications for public health. Indeed, many lab-on-a-chip-based sensors
have been developed specically to facilitate the detection of a variety of metal ions,
including Hg (II) ions [11], Pd (II) ions [12], Cd (II) ions [13,14], Cu (II) ions
[15,16], and other metal ions [17,18].
Wang et al. have developed a microuidic device for quantitative analysis of trace
Hg (II) ions (Hg
2+
) based on surface-enhanced Raman scattering (SERS) [19]. A
sample containing Hg
2+
was mixed with gold nanoparticles while owing through a
wandering channel (Fig. 2a, b). The gold nanoparticles had rhodamine B dye
molecules attached on the surface. Due to the strong afnity between Hg
2+
and
gold nanoparticles, the rhodamine B attached on the gold particles could be replaced
by Hg
2+
(Fig. 2c), causing a change in the SERS signal of rhodamine B in a function
of the concentration of Hg
2+
. The SERS changing was characterized by a Raman
microscope system. The concentration analysis range of Hg
2+
was estimated to be
between 0.1 and 0.5 μg/L.
Another microuidic device has been developed for continuous and on-site
monitoring of Pb (II) ions (Pb
2+
)[20]. The device is composed of cyclic olen
copolymer microuidic channels, with silver working and counter-electrodes. The
Pb
2+
measurement was achieved by square-wave anodic stripping voltammetry
(SWASV) technique. Specically, water sample containing Pb
2+
was rst injected
into the channel through an inlet. Under a certain voltage, Pb (II) ions were deposited
Fig. 2 Schematics of the microuidic system for Hg ions detection. (a) Schematic of the
microuidic device for Hg
2+
detection. (b) Photograph of the channel during operation.
(c) Schematic of Hg
2+
sensing mechanism based on the replacement of RB dye molecules through
the reduction of Hg
2+
on the surface of Au nanoparticles (reprinted by permission from Springer
Nature Customer Service Centre GmbH: Springer, [19]. Copyright (2009))
T. Wang et al.
onto the Ag electrode via electrodeposition, and then plated metal was oxidized off
from the Ag electrode using a square-wave anodic potential sweep. The whole
electrochemical reaction is presented by Pb
2+
+2e
Pb. The current generated
during the stripping process was measured to identify and quantify Pb (II) ions. The
detection limit was 0.55 ppb, and the correlation coefcient is 0.998 within the
concentration range of 11,000 ppb. Furthermore, the detection performance
remained stable after 43 consecutive measurements, demonstrating the sensors
reusability and great potential for real-world applications.
Microuidic systems for water arsenic detection using both colorimetric methods
and electrochemical methods have also been developed [10]. In addition, biological
detection methods have been pioneered as well. A strain of genetically modied
Escherichia coli (E. coli) was used as reporter bacteria for arsenic detection in a
microuidic device [21]. Polydimethylsiloxane (PDMS) was used to fabricate the
microchannels. The bacteria were encapsulated in agarose beads and packed into
small cages in the microchannels. When water sample containing arsenic owed
through the cages, the bacteria exposed to arsenic could produce green uorescent
proteins. The uorescence was imaged with a microscope and processed for inten-
sity analysis. The rate of uorescence signal increase was linearly proportional to the
arsenic concentration within the range of 050 μg/L. More microuidic systems for
arsenic detection were reviewed in [10].
In addition to standard silicon-based sensors, paper-based microuidics have also
been developed for metal analysis (reviewed in [22]). Paper-based microuidics are
paper substrates patterned as channels and barriers to realize different functions.
Compared to traditional PMDS and glass or silicon-based microuidics, the paper-
based microuidic devices are more cost-efcient [22]. By combining eight
pyridylazo compounds, a paper-based microuidic device could discriminate eight
different heavy-metal ions (Hg
2+
,Cd
2+
,Pb
2+
,Ag
+
,Ni
2+
,Cu
2+
,Zn
2+
, and Co
2+
)at
concentrations as low as 50 μM[23].
2.1.2 Organic Compound Analysis
Potentially toxic organic compounds such as phenolic compounds and pesticides
are widely used across many industries. Unfortunately, some of these organic
compounds may also cause water contamination, due to wastewater discharge or
leaching from soil. Microuidic sensors for organic matter have been developed
based on different detection mechanisms, including amperometry [24], enzyme-
based techniques [2527], and electrophoresis [28,29]. A lab-on-a-chip device
with layer-by-layer printing of quantum dot (QD)/enzyme microarrays was fabri-
cated for organophosphorus pesticide (OP) detection [30]. Layer-by-layer
microarrays of QDs/poly (dimethyldiallyl ammonium chloride) (PDDA) and acetyl-
cholinesterase enzyme (AChE) were fabricated on a glass slide using inkjet (Fig. 3).
Water samples and acetylthiocholine (ATCh) were added to the chip for OPs
detection. AChE catalyzes the hydrolysis of ATCh, generating thiocholine (TCh),
which can dissociate the electron-hole pair of QDs and quench the uorescence.
Microuidics for Environmental Applications
When OPs are present, the activity of AChE was inhibited; thus the uorescence of
QDs will not be quenched. A detection limit of 1 μg/L of Ops was achieved with this
device, which was much lower than levels specied by standard tests and other
colorimetric detection methods.
2.1.3 Nitrate and Ammonia Analysis
Nitrate and nitrite are ubiquitous water contaminants in both surface and groundwa-
ter, and they each can impose harmful effects on human health. A miniaturized
microuidic sensor has been developed to facilitate nitrate determination using a
double-potential-step chronocoulometry (DPSC) method [31]. Two potential steps,
E
1
and E
2
, were applied sequentially to obtain oxygen reduction charge Q
1
and both
nitrate and oxygen reduction charge Q
2
. The nitrate reduction charge was calculated
by subtracting Q1 from Q2, which is directly related to nitrate concentration in the
sample. A silver sensing electrode, silver oxide reference electrode, and platinum
counter electrode were then deposited on a silicon substrate. A polyimide passiv-
ation layer was also deposited to prevent short circuit and improve reliability. The
microchannels were fabricated via deep reactive ion etching, which enabled the
ow-through analysis. The lower and upper detection limit for nitrate were 475 μM
and 5002,000 μM, and the linearity (R
2
) was >0.99. Other microuidic-based
sensors for nitrate [32,33] and ammonia [34,35] analysis were also reported.
Lab-on-a-chip systems have also found applications in a wide variety of disparate
environments, including marine pollution analysis [3639], air pollutant detection
[40,41], and bioaerosol monitoring [4244].
Fig. 3 The schematic of the fabrication process of the OPs detection chip and the image of QDs
after OPs are added. (Reprinted from [30]. Copyright (2016), with permission from Elsevier)
T. Wang et al.
2.2 Microuidics Used for Microorganism Detection
Pathogen contamination of drinking water remains a serious public health concern
worldwide, especially in less developed areas. Waterborne pathogens can include
bacteria, viruses, and some protozoa. Some of these biological agents are highly
infectious and resistant to water treatment processes and accordingly pose a severe
risk to human health. Different detection approaches have been developed to
facilitate pathogen detection on-chip, such as nanomechanical cantilever sensing
[45,46]; surface-enhanced Raman spectroscopy [47]; impedance-based sensing
[48]; amplication-based sensing, including PCR [4956] and loop-mediated iso-
thermal amplication [52]; and quartz crystal microbalance-based sensing [57]. Both
optical signals [5861] and electrical signals [62,63] are used in microorganism
sensing techniques. The applications of microuidics in waterborne pathogen detec-
tion are reviewed in [64]. Microuidics for pathogen detection are also being
developed as point-of-care devices, for diagnostic purpose [65]. Although the
samples analyzed in diagnostic devices (e.g., saliva and blood) are different from
environmental samples, the detection techniques and approaches are still valuable as
references.
2.2.1 Virus Detection
An ultrasensitive virus detection sensor based on the Young interferometer has been
reported [66]. The sensor is a silicon chip consisting of four light channels. Si
3
N
4
and SiO
2
layers were deposited on a silicon substrate via chemical vapor deposition.
The SiO
2
layers were etched to form windows for antibody functionalization and
virus detection. The Si
3
N
4
layer beneath served as a pathway for light (Fig. 4a).
Monochromatic light from a laser source was coupled to an optical channel and
guided into the four parallel channels (Fig. 4b). Antibodies for different viruses
detection were coated onto the channels. The light interfered on a screen after exiting
from the four waveguide channels, generating an interference pattern. Virus binding
to the antibody would be probed by the evanescent eld of the guided modes, thus
causing a phase change which could be measured as a change in the interference
pattern. The pattern reects the amount of the viruses bonded on the antibodies.
Figure 4c shows the specic detection of herpes simplex virus type 1 (HSV-1)
realized by the specic reaction between HSV-1 and the antibodies. The sensor
specically and sensitively detected HSV-1 with the concentration as low as 850 par-
ticles/mL and the detection sensitivity of the sensor was estimated to approach one
single HSV-1 particle.
Microuidics for Environmental Applications
Fig. 4 (a) Schematic of the sensor for virus detection. 1, 2, and 3 are the measuring channels, and 4 is the reference channel (reprinted with permission from
[66]). Copyright (2007) American Chemical Society]. (b) Cross section of the chip along the direction of the channels (Adapted form [67]). (c) Specic and
selection detection of HSV-1. The gures indicate phase changes as a function of time. The phase change does not increase when human serum albumin (HSA)
is added but increases only after HSV-1 is added, which is due to the specic interactions between HSV-1 and α-HSV-1gG (reprinted with permission from
[66]. Copyright (2007) American Chemical Society)
T. Wang et al.
2.2.2 Bacteria Detection
Bacteria are another kind of major waterborne pathogen that poses risk to human
health. Mannoor et al. have reported a microuidic system for real-time on-chip
bacteria detection using impedance spectroscopy [68]. A gold electrode array was
deposited onto a silicon substrate via standard microfabrication methods. The ow
channel for real-time monitoring was fabricated using PDMS and bonded to the
substrate. The electrode surface was functionalized with magainin I, which is a kind
of antimicrobial peptide (AMPs) used for bacteria binding. When the bacteria
contained in water samples were recognized by the AMPs and bonded to the
electrode surface, the impedance of the electrode array changed, which was analyzed
by a spectrum analyzer. Since the binding activity was directly proportional to the
variation of impedance, the bacteria concentration could be analyzed. The detection
limit of E. coli was about 1 bacterium/μL. The system showed sufcient selectivity
toward pathogenic and Gram-negative bacteria, and also maintained broad detection
capability for other bacteria. Furthermore, the ow system enabled real-time bacteria
monitoring for a continuous water sample.
2.2.3 Protozoa Detection
In addition to viruses and bacteria, protozoa especially some parasites can pose a
signicant risk to human health. Cryptosporidium is one of the parasites of greatest
concern on this front, due to its low infection dose and resistance to common water
treatment approaches [69]. Several techniques have been integrated to miniaturized
uidic chips for Cryptosporidium detection, including optical methods such as target
trapping combined with immunouorescence or microscopy detection; mass-based
methods such as quartz crystal microbalance sensing and cantilever sensing; and
electrical techniques such as bioimpedance and dielectrophoresis methods. The
detection of cryptosporidium in microuidic devices is reviewed in [69].
2.3 Microuidics Used as Research Platforms
Understanding environmental-related natural processes is another important compo-
nent of environmental science and engineering. These widely studied processes are
encompassed within, but certainly not restricted to, the elds of environmental
microbiology, ecotoxicology, and contaminant transportation. Microuidic and
lab-on-a-chip devices are increasingly being used in environmental research labora-
tories, since they provide ideal research platforms for in situ and real-time observa-
tion. The combination of lab-on-a-chip devices and observation techniques (such as
microscopy) enables in situ visualization,characterization, and simulation of a wide
Microuidics for Environmental Applications
range of environment-related processes, thus becoming a valuable investigation
approach in environmental studies.
2.3.1 Mechanisms of Bacteria Electron Transfer
Microbial fuel cells, which use microorganisms colonizing electrodes to catalyze
electrochemical reactions and convert chemical energy into electrical power, are
being intensively studied in the environmental technology eld since they possess
the potential capability of converting organic or inorganic waste into power via an
environmentally friendly microbiological process [70,71]. Understanding the mech-
anisms of electron transfer from bacteria to electrode is accordingly imperative for
the further development of potential microbial fuel cells.
Three possible electron transfer pathways have been proposed: via direct contact,
via conduct pili, and via diffusion of soluble redox-active molecules serving as
electron shuttles[72]. Jiang et al. have reported a lab-on-a-chip device with
microelectrodes as a platform to investigate the electron transfer between
Shewanella oneidensis and electrodes [73]. Finger-shape electrodes were dened
by photolithography and deposited onto a cover glass using metal evaporation and
lift-off methods. A passive Si
3
N
4
layer was deposited by chemical vapor deposition
and patterned to have nanoscale openings on one electrode and a big opening on the
other electrode (Fig. 5a, b). The nanoholes were small enough to prevent direct
contact between bacteria and the electrode but allowed the indirect contact through
pili or diffusion of extracellular redox-active molecules. A SU-8 (a commonly used
epoxy-based negative photoresist) chamber was fabricated to improve reliability and
environmental control. In situ cell image/tracking with a microscope and current
recording revealed that the currents could be detected even without direct contact
between bacteria and electrodes, suggesting that electron transfer was realized by pili
or a mediators diffusion. In addition, the removal of the diffusible mediators caused
a rapid drop of the current, which further supported that electron transfer occurs
predominantly by diffusion of mediators.
Fig. 5 Schematic of the design of the electrodes for Shewanella electron transfer study. (a) The
silicon nitride insulating layer (blue) with nanoholes or large window openings is deposited over
electrodes (yellow) to prevent or enable direct contact with bacteria (orange). (b) SEM images of the
bacteria cells on the electrodes with nanoholes (left) and large window openings (right). (Reprinted
with permission from [73], Proceedings of the National Academy of Sciences)
T. Wang et al.
For other kinds of bacteria, however, the electron transfer mechanism may need
to be altered. A similar lab-on-a-chip device was fabricated to probe the charge
transport from Geobacter sulfurreducens to electrode [74]. Gold electrodes were
deposited via metal evaporation and lift-off. Thick SU-8 was then fabricated to form
wells around the electrodes to allow direct contact between bacteria and electrodes
(Fig. 6a, b). Simultaneous recording of cell position and currents indicated that the
contact of a cell to the electrode directly caused a stepwise increasing of current
(Fig. 6c). The current of a single Geobacter was 92 fA, and the current density was
estimated to be ~10
6
Am
3
. In addition, when the diffusible redox mediators were
removed, the current was not affected. These measurements together indicated that,
different from Shewanella, the electron transfer between Geobacter and electrode
was mainly due to direct contact. Ding et al. reported a nanoelectronics lab-on-a-chip
system to investigate the electrical conductivity of both Shewanella and Geobacter
and indicated that electrochemical electron transfer at the cell/electrode interface was
the origin of the conductive current for both microbes [75].
As researchers have started to gain a deeper understanding of bacterial electron
transfer, the role of bacterial self-assembled nanostructures for extracellular electron
transfer has also garnered increased attention. For example, to elucidate the effects of
microenvironment on the intercellular microbial nanostructures (nanowires)
Fig. 6 (a) Schematic of experimental design for Geobacter sulfurreducens electron transfer. (b)
SEM image of a well containing two nger electrodes. (c) In situ microscopy images of Geobacter
cells around and on the measured electrode and the current changes at the same time. The cell that
contacts the electrode at the same time with the current increases is marked in red. (Reprinted by
permission from Springer Nature Customer Service Centre GmbH: Springer, [74]. Copyright
(2013))
Microuidics for Environmental Applications
formation, a one-dimensional core/shell bacterial cable has been developed which
allows rational control of the microenvironments [76]. The fabrication method of
this cable was different from common microuidics fabrication processes. The cable
was generated through a ow-focusing device with coaxially aligned glass capil-
laries and multiple inlets for different solutions. Bacteria solution ow was focused
into a narrow stream, and alginate was injected to the device to form the scaffolding
for bacteria encapsulation. A Ca
2+
containing sheath ow was exploited to cross-link
alginate to become a solid hydrogel (Fig. 7a). The results revealed that the formation
of intercellular structures is closely related to the ber diameters. More densely and
closely packed bacteria produced more self-assembling microbial nanowires, which
directly increased the extracellular electron transfer efciency (Fig. 7b). Further-
more, lack of electron acceptors can enhance the production of the nanowires
(Fig. 7b).
2.3.2 Biolm Formation
Biolm formation is a natural process that occurs during bacteria growth. On one
hand, biolms play important roles in some environmental engineering processes,
including in wastewater biological treatment and microbial fuel cells. However,
biolm can also cause environmental and public health problems including by
contaminating or clogging drinking water pipelines or fouling water treatment
systems. As a result, the process of biolm formation is gaining more attention in
environmental science and engineering. Drescher et al. have developed
a microuidic device to investigate biolm formation in uidic channels [77]. A
meandering microuidic channel was fabricated with PDMS and sealed with a cover
glass. Pseudomonas aeruginosa bacterial solution owed through the microuidic
channel and the biolm formation process in the channel was observed with a
microscope. This work demonstrated that the 3D biolm streamers that bridged
the space between obstacles and corners caused major clogging of the channel,
instead of the biolm attached on the inner surface. The 3D biolm streamer was rst
Fig. 7 (a) Schematics of the ow-focusing device for core/shell bacterial ber generation. The
bacteria-containing core stream (brown) is focused before entering the alginate shell stream
(yellow), and then a CaCl
2
sheath ow is introduced to cross-link the alginate to form the cord.
(b) SEM images of high (left) and low (middle) bacteria density networks as well as high-density
networks cultured in electron acceptor rich conditions (right). (Reprinted with permission from
[76]. Copyright (2018) American Chemical Society)
T. Wang et al.
formed by the extracellular matrix shed from the attached bacteria and then worked
as a network to catch the owing bacteria and biomass, leading to a rapid clogging.
With this microuidic chip that enabled in situ observation of the biolm formation,
this work demonstrated a biolm formation process which is independent of and
much faster than bacteria growth. The results also suggested that the biolm
streamers may contribute more to the clogging of ow through systems such as
water pipelines.
During biolm formation, the bacteria within microbial communities can sense
chemical signals from other cells and regulate their own gene expression as a
response. This process is referred to as quorum sensing, and it is an important factor
in regulating biolm formation that is a current subject of intense study in the
environmental microbial eld. Flickinger et al. have reported a lab-on-a-chip plat-
form to study quorum sensing between microbial communities [78]. The lab-on-a-
chip device contained an array of spatially conned chambers fabricated with poly
(ethylene glycol) diacrylate (PEGDA) on a silanized cover glass using a PDMS mold
(Fig. 8a). Pseudomonas aeruginosa (P. aeruginosa) was used as a model bacterial
strain and inoculated in the center chambers for biolm growth (Fig. 8b). The
molecule regulators secreted from the biolm for quorum sensing, homoserine
lactones (HSLs), can diffuse inside (lled with 15% PEGDA) and between the
PEGDA chamber to form spatial and temporal gradients, thus enabling analysis of
the relationship between the diffusion of HSLs and formation of nascent new biolm
(Fig. 8c). The results showed that HSL was detected by the bacteria cells within a
distance of 8 mm. The new biolm growth within 3 mm away from the existing
biolm, where the HSL concentration was higher than 1 μM, was enhanced due to
the detection of HSL, while further biolms were not affected. In addition to regular
on-chip chambers, 3D cavities with various geometries were fabricated using 3D
printing strategy to study the mechanisms of community regulation [79].
Fig. 8 (a) An image of the chamber for quorum sensing study with hydrogel chamber wall (stained
with red dye) on a glass coverslip (upper). An image of the PDMS stamp used to make the chamber
(lower). (b) The center chamber was inoculated with P. aeruginosa.(c) Schematic of the experi-
ment. HSL diffuse through the hydrogel chamber wall, which is detected by biolm in each
chamber. (Reprinted with permission from [78]. Copyright (2011) American Chemical Society)
Microuidics for Environmental Applications
2.3.3 Antibiotic Resistance Gene Transfer
It is now known that horizontal gene transfer is an important pathway by which
antibiotic resistance spreads from one organism to another. Microuidic devices are
promising platforms for facilitating gene transfer study, since they enable the in situ
and real-time monitoring of the process dynamics. A microuidic device was
reported to investigate the plasmid-mediated horizontal gene transfer within the
same species and between different species [80]. The microuidic chip consisted
of a cover glass with a layer of agarose and a PDMS cover on top (Fig. 9a). A drop of
mixed bacteria solution containing the gene donor strain (Pseudomonas putida
harboring an antibiotic resistance plasmid) and recipient strain (E. coli or bacteria
extracted form activated sludge) was sandwiched between the agarose and cover
glass. The PDMS cover had a channel in it for broth delivery and waste removal for
bacteria growth (Fig. 9a). The gene donor bacteria carried plasmid RP4, which was
labeled with GFP, but also tagged with red uorescent genes that repress the
expression of GFP. So, the donor bacteria emitted red uorescence. When the
plasmids were transferred to acceptors, the acceptors would emit green uorescent
from GFP carried with the plasmids. The gene horizontal transfer process on the chip
was monitored with a uorescence microscope. The results showed that the hori-
zontal gene transfer was highly dependent on the structure and composition of the
biolm. The plasmids were rst successfully transferred from donor species Pseu-
domonas putida to acceptor E. coli. Within the pure E. coli colony, the transfer from
the rst transconjugants to other cells was very efcient, leading to a cascading gene
spread within the single-strain biolms (Fig. 9b). In comparison, for the activated
sludge biolm consisting of different species, vertical gene transfer appeared to be
the dominant route instead of horizontal transfer (Fig. 9c). It is also found that many
species that showed horizontal gene transfer were associated with human pathogens.
Fig. 9 (a) Schematic of the device to study antibiotic resistant genes transfer (upper) and the device
setup (lower). (b) Gene spread in pure E. coli culture. (c) Gene spread in activated sludge
community. For both (b) and (c), the donor cells P. putida KT2440 are red; normal E. coli or
active sludge cells are colorless, while transconjugants emit green uorescence. (Reprinted with
permission from [80], https://pubs.acs.org/doi/abs/10.1021/acs.est.8b03281. Copyright (2018)
American Chemical Society. Further permissions related to the material excerpted should be
directed to the ACS)
T. Wang et al.
Other microuidic systems for gene transfer and antimicrobial resistance related
studies were also reported, including using microuidic devices to study gene
transfer on the single-cell level [81], dissect horizontal and vertical gene transfer
[82], test antimicrobial susceptibility [83], and investigate the modulation of antibi-
otics on horizontal gene transfer [84]. More studies are reviewed in [85].
2.3.4 Electroporation
Electroporation is the phenomenon whereby pores form on a cell membrane when
the cell is exposed to an external electric eld. It is commonly used to control cell
membrane permeability when molecular intracellular transfer is desired. In addition,
electroporation is also a widely used method for cell inactivation and lysis.
Researchers in environmental elds are also increasingly exploring the possibility
of using electroporation as a bacteria inactivation approach for drinking water
disinfection [8689] and hazardous wastewater decontamination [90]. Understand-
ing the electroporation process has therefore become another important environmen-
tal study topic. Since the actual formation of these pores is difcult to observe,
Sengel et at. have developed a lab-on-a-chip device to image the dynamics of
individual electropores [91]. The experimental setups are shown in Fig. 10a.A
cover glass was coated with agarose and placed in a recess. Lipid solution was
added and associated with the agarose to form a lipid monolayer. An aqueous droplet
with lipid monolayer was brought onto the cover glass. Two monolayers at the
contact area formed a lipid bilayer, which is similar to cell membrane. Two elec-
trodes were placed at the two sides of the lipid bilayer to monitor the current, and the
pore formation was labeled by a uorescent dye and recorded with a uorescence
microscope (Fig. 10b). With this platform, researchers found several interesting
phenomena of electroporation. When the potential difference across the bilayer
reached 100 mV, the membrane permeability started to change. With higher
Fig. 10 Schematic of the experimental setup. (a) A lipid bilayer is formed on the interface of the
droplet and the substrate. When a pore is formed due to electroporation, Ca
2+
ions ow into the
drop, which could be detected by the Ca
2+
sensitive dye uo-8 and visualized by a microscopy. (b)
A microscopy image of pores formed on lipid bilayer. (Adapted and reprinted with permission form
[91], Proceedings of the National Academy of Sciences)
Microuidics for Environmental Applications
transmembrane potential, larger pores formed, but a large number of small pores still
existed. In addition, the pores uctuated (opened and closed) in a variety of modes,
and higher potential did not lead to more stable pores. Two adjacent pores did not
tend to combine, while anti-combination was found since the potential across the
lipid bilayer would be released when a nearby pore gets larger. A lab-on-a-chip
device to rapidly determine the electroporation threshold for bacteria inactivation
was also reported [92].
2.3.5 On-Chip Toxicity Test
Ecotoxicology focuses on identifying the toxicity level and impact of environmental
pollutants on creatures and human health. Compared to traditional toxicity testing
approaches, the emerging on-chip toxicity tests enabled by microuidics are signif-
icantly more compact, convenient, and labor-efcient and as a result they are
quickly gaining substantial attention in this eld.
Fine particles are major pollutants in the air, which makes them crucial indicators
of general air quality. A microuidic device aiming at recognizing the toxicity of ne
particle matter (PM
2.5
) on human lung epithelial cells was reported [93]. A porous
membrane was bonded to the PDMS chamber, and the human lung epithelial cell
line (BEAS-2B) was cultured on the membrane. Medium owed under the mem-
brane to replenish nutrient for cell growth (Fig. 11). The cell viability remained
above 98% after 21 days of culturing, which demonstrated that this lab-on-a-chip is
capable of retaining the viability of cells for the toxicity test. The air liquid interface
mimicked the pulmonary natural microenvironment, which enabled the in vitro
cytotoxicity test. Particles were added to the cells using an aerosol nebulizer, and
the cytotoxicity was analyzed by several different approaches after exposure. The
results showed that some metabolic pathways of the cells contributing to inamma-
tion reactions were activated after the exposure. The cell apoptosis rate was also
increased from 3.8% to 66.7% after 24 h of exposure. This conguration is also
applicable for cytotoxicity test of other pollutants.
Engineered metal nanoparticles are being used for a variety of applications in
many different elds. However, the potential hazards of these nanoparticles to
human health and environment remain topics of hot debate and active research. To
investigate the effects of silver nanoparticles on microorganismsbehavior, a
Fig. 11 Schematic of the designed microuidic chip for ambient particle toxicity test. (Reprinted
from [93]. Copyright (2019) with permission from Elsevier)
T. Wang et al.
microuidic device was reported to study the swimming response of algae to silver
nanoparticles [94]. PDMS containing microchannels was fabricated via soft lithog-
raphy and bonded to a glass slide, forming the microuidic device. The microuidic
device used in this study was previously designed for a bacterial chemotaxis test,
which contained a concentration-gradient generator and a chemotaxis observation
channel [95]. Solution with and without silver nanoparticles were added to the two
inlets, respectively. After owing through the mixing part, nanoparticle concentra-
tion gradient was created and maintained in the observation channel. Algae was then
added to the observation channel and exposed to the nanoparticle gradient. The algae
swimming response was observed and recorded with a microscope. The results
showed that algae moved away from the area containing 10
8
silver particles/mL,
but no signicant aversive swimming was found to gold nanoparticles at the same
concentration. The toxicity of the released Ag ions may be the main reason leading
to the avoidance behavior.
Microuidics also have applications in aquatic toxicity tests on bacteria [96,97],
nematodes [98], crustacea [99,100], and sh embryo [101]. More applications and
future perspective were discussed in the review paper [102].
3 Perspectives on MicrouidicsApplications
in Environmental Science and Engineering
Microuidic and lab-on-a-chip devices are increasingly being used as tools in the
elds of environmental science and engineering. Miniaturized microuidic or
lab-on-a-chip devices evidence remarkable sensing abilities, because sensing elec-
trodes can be miniaturized without losing sensitivity and the congurations are
compatible with thin layer operations [9]. Flow manipulation and compound sepa-
ration can also be enabled by incorporating additional electrodes in existing chan-
nels, without adding additional parts. When used as detection equipment, lab-on-a-
chip systems offer several comparative advantages over traditional mechanisms
including shorter analysis time, smaller sample volume, and online and real-time
monitoring. All of these benets are attributable to their small size, precise ow
control, and low cost compared to traditional instruments. Some sensors have
already been commercialized, such as test strips based on electrochemistry for
arsenic detection [103] and sensors based on stripping square-wave voltammetry
for metal analysis [104]. A DNA electrochemical biosensor has been combined with
sample processing platforms for online pathogens monitoring in natural water
[105]. IBM is also working on the development of sensors for environmental
pollution detection, such as methane leakage [106]. Since real-world samples are
often complex and signal characterization systems are still required for the systems,
real-world implementation of these detection devices remains limited in some
instances. In addition to further improving the performance of sensors, future studies
will undoubtedly focus on developing more integrated systems that combine
Microuidics for Environmental Applications
sampling, pre-treatment, and signal interpretation on a single chip which will
increase the viability of on-site, real-time applications across a wide variety of real-
world settings. Furthermore, exploring cost-efcient materials (e.g., paper-based
devices), simpler fabrication processes and easier operation approaches will also
undoubtedly continue to bring the cost associated with these devices down, which
will also further facilitate the feasibility of on-site and point-of-use applications.
But compared to their use as sensors and analyzers, microuidic devices offer
even more remarkable advantages as research platforms for environment-related
process investigation. Their miniaturized size and the exible congurations for
realizing various functions provide them with unique capabilities for visualizing and
unveiling the secrets of numerous environmental-related processes, which are not
comparable by other approaches. Therefore, we believe the future growth of lab-on-
a-chip devices as research platforms will be focused on exploring novel and clever
designs to realize more functions based on different investigation purposes. Nano
structures, such as nanoholes, nanoparticles, nanowires, and coating layers with
nanoscale thickness, are providing lab-on-a-chip devices with more features and
functions. Nanofabrication techniques, including electron beam lithography and
atomic layer deposition, are becoming widely used for chip fabrication. In addition,
more and more lab-on-chip devices for research purpose are not restricted to
standard chamber or channel on-chip congurations. Various 3D geometries are
enabled by thriving 3D fabrication techniques, such as 3D printing, two photon
polymerization, and micron/submicron stereolithography. To improve the capabili-
ties of lab-on-a-chip devices, the performance of their basic functions, such as ow
control, cell manipulation, cell culturing, and target tracking, is also worth improv-
ing. Finding the environmental problems and processes that could be investigated
using lab-on-a-chip platforms is also important. In addition to visualizing small-scale
process, such as bacterial-related phenomena mentioned in Sect. 2.3, lab-on-a-chip
systems are also ideal for mimicking and simulating large-scale ecological pro-
cesses, such as fate and transport of nanoparticles in soil and groundwater
[107,108]. The ndings of the on-chip simulations could provide valuable experi-
mental data for modeling and further on-site studies.
Acknowledgments The authors would like to acknowledge the US National Science Foundation
[grant numbers CBET 1845354]. The authors would like to thank Dr. Janina Bahnemann for her
contribution to this chapter.
References
1. Shang L, Cheng Y, Zhao Y (2017) Emerging droplet microuidics. Chem Rev 117
(12):79648040
2. Dittrich PS, Manz A (2006) Lab-on-a-chip: microuidics in drug discovery. Nat Rev Drug
Discov 5(3):210218
3. Demello AJ (2006) Control and detection of chemical reactions in microuidic systems.
Nature 442(7101):394402
T. Wang et al.
4. Janasek D, Franzke J, Manz A (2006) Scaling and the design of miniaturized chemical-
analysis systems. Nature 442(7101):374380
5. Craighead H (2010) Nanoscience and technology: a collection of reviews from nature journals.
World Scientic, Singapore, pp 330336
6. El-Ali J, Sorger PK, Jensen KF (2006) Cells on chips. Nature 442(7101):403411
7. Shih SC, Mufti NS, Chamberlain MD, Kim J, Wheeler AR (2014) A droplet-based screen for
wavelength-dependent lipid production in algae. Energy Environ Sci 7(7):23662375
8. Li M, Gou H, Al-Ogaidi I, Wu N (2013) Nanostructured sensors for detection of heavy metals:
a review. ACS Publications, Washington
9. Kudr J, Zitka O, Klimanek M, Vrba R, Adam V (2017) Microuidic electrochemical devices
for pollution analysisa review. Sensors Actuators B Chem 246:578590
10. Yogarajah N, Tsai SS (2015) Detection of trace arsenic in drinking water: challenges and
opportunities for microuidics. Environ Sci Water Res Technol 1(4):426447
11. Chen K, Lu G, Chang J, Mao S, Yu K, Cui S, Chen J (2012) Hg (II) ion detection using
thermally reduced graphene oxide decorated with functionalized gold nanoparticles. Anal
Chem 84(9):40574062
12. Gao S, Koshizaki N, Koyama E, Tokuhisa H, Sasaki T, Kim J-K, Cho Y, Kim D-S, Shimizu Y
(2009) Innovative platform for transmission localized surface plasmon transducers and its
application in detecting heavy metal Pd (II). Anal Chem 81(18):77037712
13. Jang A, Zou Z, Lee KK, Ahn CH, Bishop PL (2010) Potentiometric and voltammetric polymer
lab chip sensors for determination of nitrate, pH and Cd (II) in water. Talanta 83(1):18
14. Zou Z, Jang A, MacKnight E, Wu P-M, Do J, Bishop PL, Ahn CH (2008) Environmentally
friendly disposable sensors with microfabricated on-chip planar bismuth electrode for in situ
heavy metal ions measurement. Sensors Actuators B Chem 134(1):1824
15. Devadhasan JP, Kim J (2018) A chemically functionalized paper-based microuidic platform
for multiplex heavy metal detection. Sensors Actuators B Chem 273:1824
16. Forzani ES, Zhang H, Chen W, Tao N (2005) Detection of heavy metal ions in drinking water
using a high-resolution differential surface plasmon resonance sensor. Environ Sci Technol 39
(5):12571262
17. Li S, Zhang C, Wang S, Liu Q, Feng H, Ma X, Guo J (2018) Electrochemical microuidics
techniques for heavy metal ion detection. Analyst 143(18):42304246
18. Sudibya HG, He Q, Zhang H, Chen P (2011) Electrical detection of metal ions using eld-
effect transistors based on micropatterned reduced graphene oxide lms. ACS Nano 5
(3):19901994
19. Wang G, Lim C, Chen L, Chon H, Choo J, Hong J, DeMello AJ (2009) Surface-enhanced
Raman scattering in nanoliter droplets: towards high-sensitivity detection of mercury (II) ions.
Anal Bioanal Chem 394(7):18271832
20. Jung W, Jang A, Bishop PL, Ahn CH (2011) A polymer lab chip sensor with microfabricated
planar silver electrode for continuous and on-site heavy metal measurement. Sensors Actuators
B Chem 155(1):145153
21. BufN, Merulla D, Beutier J, Barbaud F, Beggah S, van Lintel H, Renaud P, van der Meer JR
(2011) Development of a microuidics biosensor for agarose-bead immobilized Escherichia
coli bioreporter cells for arsenite detection in aqueous samples. Lab Chip 11(14):23692377
22. Lin Y, Gritsenko D, Feng S, Teh YC, Lu X, Xu J (2016) Detection of heavy metal by paper-
based microuidics. Biosens Bioelectron 83:256266
23. Feng L, Li X, Li H, Yang W, Chen L, Guan Y (2013) Enhancement of sensitivity of paper-
based sensor array for the identication of heavy-metal ions. Anal Chim Acta 780:7480
24. Scampicchio M, Wang J, Mannino S, Chatrathi MP (2004) Microchip capillary electrophore-
sis with amperometric detection for rapid separation and detection of phenolic acids. J
Chromatogr A 1049(12):189194
25. Mayorga-Martinez CC, Cadevall M, Guix M, Ros J, Merkoçi A (2013) Bismuth nanoparticles
for phenolic compounds biosensing application. Biosens Bioelectron 40(1):5762
Microuidics for Environmental Applications
26. Sekretaryova AN, Volkov AV, Zozoulenko IV, Turner AP, Vagin MY, Eriksson M (2016)
Total phenol analysis of weakly supported water using a laccase-based microband biosensor.
Anal Chim Acta 907:4553
27. Song Y, Chen J, Sun M, Gong C, Shen Y, Song Y, Wang L (2016) A simple electrochemical
biosensor based on AuNPs/MPS/Au electrode sensing layer for monitoring carbamate pesti-
cides in real samples. J Hazard Mater 304:103109
28. Castañeda R, Vilela D, González MC, Mendoza S, Escarpa A (2013) SU-8/P yrex microchip
electrophoresis with integrated electrochemical detection for class-selective electrochemical
index determination of phenolic compounds in complex samples. Electrophoresis 34
(14):21292135
29. Ding Y, Ayon A, García CD (2007) Electrochemical detection of phenolic compounds using
cylindrical carbon-ink electrodes and microchip capillary electrophoresis. Anal Chim Acta
584(2):244251
30. Luan E, Zheng Z, Li X, Gu H, Liu S (2016) Inkjet-assisted layer-by-layer printing of quantum
dot/enzyme microarrays for highly sensitive detection of organophosphorous pesticides. Anal
Chim Acta 916:7783
31. Kim D, Goldberg IB, Judy JW (2009) Microfabricated electrochemical nitrate sensor using
double-potential-step chronocoulometry. Sensors Actuators B Chem 135(2):618624
32. Aravamudhan S, Bhansali S (2008) Development of micro-uidic nitrate-selective sensor
based on doped-polypyrrole nanowires. Sensors Actuators B Chem 132(2):623630
33. Nightingale AM, Hassan S-U, Warren BM, Makris K, Evans GW, Papadopoulou E,
Coleman S, Niu X (2019) A droplet microuidic-based sensor for simultaneous in situ
monitoring of nitrate and nitrite in natural waters. Environ Sci Technol 53(16):96779685
34. Fornells E, Murray E, Waheed S, Morrin A, Diamond D, Paull B, Breadmore M (2020)
Integrated 3D printed heaters for microuidic applications: ammonium analysis within envi-
ronmental water. Anal Chim Acta 1098:94101
35. Gallardo-Gonzalez J, Baraket A, Boudjaoui S, Metzner T, Hauser F, Rößler T, Krause S,
Zine N, Streklas A, Alcácer A (2019) A fully integrated passive microuidic lab-on-a-chip for
real-time electrochemical detection of ammonium: sewage applications. Sci Total Environ
653:12231230
36. Fernández-Gavela A, Herranz S, Chocarro B, Falke F, Schreuder E, Leeuwis H, Heideman
RG, Lechuga LM (2019) Full integration of photonic nanoimmunosensors in portable plat-
forms for on-line monitoring of ocean pollutants. Sensors Actuators B Chem 297:126758
37. Geißler F, Achterberg EP, Beaton AD, Hopwood MJ, Clarke JS, Mutzberg A, Mowlem MC,
Connelly DP (2017) Evaluation of a ferrozine based autonomous in situ lab-on-chip analyzer
for dissolved iron species in coastal waters. Front Mar Sci 4:322
38. Grand MM, Clinton-Bailey GS, Beaton AD, Schaap AM, Johengen TH, Tamburri MN,
Connelly DP, Mowlem MC, Achterberg EP (2017) A lab-on-chip phosphate analyzer for
long-term in situ monitoring at xed observatories: optimization and performance evaluation
in estuarine and oligotrophic coastal waters. Front Mar Sci 4:255
39. Han S, Zhang Q, Zhang X, Liu X, Lu L, Wei J, Li Y, Wang Y, Zheng G (2019) A digital
microuidic diluter-based microalgal motion biosensor for marine pollution monitoring.
Biosens Bioelectron 143:111597
40. Ke S, Liu Q, Deng M, Zhang X, Yao Y, Shan M, Yang X, Sui G (2018) Cytotoxicity analysis
of indoor air pollution from biomass combustion in human keratinocytes on a multilayered
dynamic cell culture platform. Chemosphere 208:10081017
41. Sun H, Jia Y, Dong H, Fan L (2019) Graphene oxide nanosheets coupled with paper
microuidics for enhanced on-site airborne trace metal detection. Microsyst Nanoeng 5
(1):112
42. Liu Q, Zhang X, Li X, Liu S, Sui G (2018) A semi-quantitative method for point-of-care
assessments of specic pathogenic bioaerosols using a portable microuidics-based device. J
Aerosol Sci 115:173180
T. Wang et al.
43. Moon H-S, Nam Y-W, Park JC, Jung H-I (2009) Dielectrophoretic separation of airborne
microbes and dust particles using a microuidic channel for real-time bioaerosol monitoring.
Environ Sci Technol 43(15):58575863
44. Shen F, Tan M, Wang Z, Yao M, Xu Z, Wu Y, Wang J, Guo X, Zhu T (2011) Integrating
silicon nanowire eld effect transistor, microuidics and air sampling techniques for real-time
monitoring biological aerosols. Environ Sci Technol 45(17):74737480
45. Burg TP, Godin M, Knudsen SM, Shen W, Carlson G, Foster JS, Babcock K, Manalis SR
(2007) Weighing of biomolecules, single cells and single nanoparticles in uid. Nature 446
(7139):10661069
46. Ndieyira JW, Watari M, Barrera AD, Zhou D, Vögtli M, Batchelor M, Cooper MA, Strunz T,
Horton MA, Abell C (2008) Nanomechanical detection of antibioticmucopeptide binding in a
model for superbug drug resistance. Nat Nanotechnol 3(11):691
47. Premasiri W, Moir D, Klempner M, Krieger N, Jones G, Ziegler L (2005) Characterization of
the surface enhanced Raman scattering (SERS) of bacteria. J Phys Chem B 109(1):312320
48. Pandya HJ, Kanakasabapathy MK, Verma S, Chug MK, Memic A, Gadjeva M, Shaee H
(2017) Label-free electrical sensing of bacteria in eye wash samples: a step towards point-of-
care detection of pathogens in patients with infectious keratitis. Biosens Bioelectron 91:3239
49. Ahmad F, Hashsham SA (2012) Miniaturized nucleic acid amplication systems for rapid and
point-of-care diagnostics: a review. Anal Chim Acta 733:115
50. Azizi M, Zaferani M, Cheong SH, Abbaspourrad A (2019) Pathogenic bacteria detection using
RNA-based loop-mediated isothermal-amplication-assisted nucleic acid amplication via
droplet microuidics. ACS Sens 4(4):841848
51. Leung K, Zahn H, Leaver T, Konwar KM, Hanson NW, Pagé AP, Lo C-C, Chain PS, Hallam
SJ, Hansen CL (2012) A programmable droplet-based microuidic device applied to
multiparameter analysis of single microbes and microbial communities. Proc Natl Acad Sci
109(20):76657670
52. Lin X, Huang X, Zhu Y, Urmann K, Xie X, Hoffmann MR (2018) Asymmetric membrane for
digital detection of single bacteria in milliliters of complex water samples. ACS Nano 12
(10):1028110290
53. Ottesen EA, Hong JW, Quake SR, Leadbetter JR (2006) Microuidic digital PCR enables
multigene analysis of individual environmental bacteria. Science 314(5804):14641467
54. Tsougeni K, Kastania A, Kaprou G, Eck M, Jobst G, Petrou P, Kakabakos S, Mastellos D,
Gogolides E, Tserepi A (2019) A modular integrated lab-on-a-chip platform for fast and highly
efcient sample preparation for foodborne pathogen screening. Sensors Actuators B Chem
288:171179
55. Xie X, Wang S, Jiang SC, Bahnemann J, Hoffmann MR (2016) Sunlight-activated propidium
monoazide pretreatment for differentiation of viable and dead bacteria by quantitative real-
time polymerase chain reaction. Environ Sci Technol Lett 3(2):5761
56. Zhu Y, Huang X, Xie X, Bahnemann J, Lin X, Wu X, Wang S, Hoffmann MR (2018)
Propidium monoazide pretreatment on a 3D-printed microuidic device for efcient PCR
determination of live versus deadmicrobial cells. Environ Sci Water Res Technol 4
(7):956963
57. Bao L, Deng L, Nie L, Yao S, Wei W (1996) Determination of microorganisms with a quartz
crystal microbalance sensor. Anal Chim Acta 319(12):97101
58. Lay C, Teo CY, Zhu L, Peh XL, Ji HM, Chew B-R, Murthy R, Feng HH, Liu W-T (2008)
Enhanced microltration devices congured with hydrodynamic trapping and a rain drop
bypass ltering architecture for microbial cells detection. Lab Chip 8(5):830833
59. Urmann K, Arshavsky-Graham S, Walter J-G, Scheper T, Segal E (2016) Whole-cell detection
of live lactobacillus acidophilus on aptamer-decorated porous silicon biosensors. Analyst 141
(18):54325440
60. Wang C-H, Wu J-J, Lee G-B (2019) Screening of highly-specic aptamers and their applica-
tions in paper-based microuidic chips for rapid diagnosis of multiple bacteria. Sensors
Actuators B Chem 284:395402
Microuidics for Environmental Applications
61. Yamaguchi N, Torii M, Uebayashi Y, Nasu M (2011) Rapid, semiautomated quantication of
bacterial cells in freshwater by using a microuidic device for on-chip staining and counting.
Appl Environ Microbiol 77(4):15361539
62. Mandal HS, Su Z, Ward A, Tang XS (2012) Carbon nanotube thin lm biosensors for sensitive
and reproducible whole virus detection. Theranostics 2(3):251
63. Piekarz I, Górska S, Odrobina S, Drab M, Wincza K, Gamian A, Gruszczynski S (2020) A
microwave matrix sensor for multipoint label-free Escherichia coli detection. Biosens
Bioelectron 147:111784
64. Bridle H, Miller B, Desmulliez MP (2014) Application of microuidics in waterborne
pathogen monitoring: a review. Water Res 55:256271
65. Nasseri B, Soleimani N, Rabiee N, Kalbasi A, Karimi M, Hamblin MR (2018) Point-of-care
microuidic devices for pathogen detection. Biosens Bioelectron 117:112128
66. Ymeti A, Greve J, Lambeck PV, Wink T, van Hövell SW, Beumer TA, Wijn RR, Heideman
RG, Subramaniam V, Kanger JS (2007) Fast, ultrasensitive virus detection using a young
interferometer sensor. Nano Lett 7(2):394397
67. Ymeti A, Kanger JS, Greve J, Lambeck PV, Wijn R, Heideman RG (2003) Realization of a
multichannel integrated Young interferometer chemical sensor. Appl Opt 42(28):56495660
68. Mannoor MS, Zhang S, Link AJ, McAlpine MC (2010) Electrical detection of pathogenic
bacteria via immobilized antimicrobial peptides. Proc Natl Acad Sci 107(45):1920719212
69. Bridle H, Kersaudy-Kerhoas M, Miller B, Gavriilidou D, Katzer F, Innes EA, Desmulliez MP
(2012) Detection of Cryptosporidium in miniaturised uidic devices. Water Res 46
(6):16411661
70. Logan BE, Rabaey K (2012) Conversion of wastes into bioelectricity and chemicals by using
microbial electrochemical technologies. Science 337(6095):686690
71. Xie X, Criddle C, Cui Y (2015) Design and fabrication of bioelectrodes for microbial
bioelectrochemical systems. Energy Environ Sci 8(12):34183441
72. Lovley DR (2012) Electromicrobiology. Annu Rev Microbiol 66:391409
73. Jiang X, Hu J, Fitzgerald LA, Bifnger JC, Xie P, Ringeisen BR, Lieber CM (2010) Probing
electron transfer mechanisms in Shewanella oneidensis MR-1 using a nanoelectrode platform
and single-cell imaging. Proc Natl Acad Sci 107(39):1680616810
74. Jiang X, Hu J, Petersen ER, Fitzgerald LA, Jackan CS, Lieber AM, Ringeisen BR, Lieber CM,
Bifnger JC (2013) Probing single-to multi-cell level charge transport in Geobacter
sulfurreducens DL-1. Nat Commun 4(1):16
75. Ding M, Shiu H-Y, Li S-L, Lee CK, Wang G, Wu H, Weiss NO, Young TD, Weiss PS, Wong
GC (2016) Nanoelectronic investigation reveals the electrochemical basis of electrical con-
ductivity in shewanella and geobacter. ACS Nano 10(11):99199926
76. Hsu L, Deng P, Zhang Y, Jiang X (2018) Core/shell bacterial cables: a one-dimensional
platform for probing microbial electron transfer. Nano Lett 18(7):46064610
77. Drescher K, Shen Y, Bassler BL, Stone HA (2013) Biolm streamers cause catastrophic
disruption of ow with consequences for environmental and medical systems. Proc Natl Acad
Sci 110(11):43454350
78. Flickinger ST, Copeland MF, Downes EM, Braasch AT, Tuson HH, Eun Y-J, Weibel DB
(2011) Quorum sensing between Pseudomonas aeruginosa biolms accelerates cell growth. J
Am Chem Soc 133(15):59665975
79. Connell JL, Ritschdorff ET, Whiteley M, Shear JB (2013) 3D printing of microscopic bacterial
communities. Proc Natl Acad Sci 110(46):1838018385
80. Li B, Qiu Y, Zhang J, Huang X, Shi H, Yin H (2018) Real-time study of rapid spread of
antibiotic resistance plasmid in biolm using microuidics. Environ Sci Technol 52
(19):1113211141
81. Burmeister A, Hilgers F, Langner A, Westerwalbesloh C, Kerkhoff Y, Tenhaef N, Drepper T,
Kohlheyer D, von Lieres E, Noack S (2019) A microuidic co-cultivation platform to
investigate microbial interactions at dened microenvironments. Lab Chip 19(1):98110
T. Wang et al.
82. Li B, Qiu Y, Song Y, Lin H, Yin H (2019) Dissecting horizontal and vertical gene transfer of
antibiotic resistance plasmid in bacterial community using microuidics. Environ Int
131:105007
83. Sun H, Chan C-W, Wang Y, Yao X, Mu X, Lu X, Zhou J, Cai Z, Ren K (2019) Reliable and
reusable whole polypropylene plastic microuidic devices for a rapid, low-cost antimicrobial
susceptibility test. Lab Chip 19(17):29152924
84. Lopatkin AJ, Huang S, Smith RP, Srimani JK, Sysoeva TA, Bewick S, Karig DK, You L
(2016) Antibiotics as a selective driver for conjugation dynamics. Nat Microbiol 1(6):18
85. Liu Z, Banaei N, Ren K (2017) Microuidics for combating antimicrobial resistance. Trends
Biotechnol 35(12):11291139
86. Huo Z-Y, Liu H, Wang W-L, Wang Y-H, Wu Y-H, Xie X, Hu H-Y (2019) Low-voltage
alternating current powered polydopamine-protected copper phosphide nanowire for
electroporation-disinfection in water. J Mater Chem A 7(13):73477354
87. Huo Z-Y, Zhou J-F, Wu Y, Wu Y-H, Liu H, Liu N, Hu H-Y, Xie X (2018) A Cu 3 P nanowire
enabling high-efciency, reliable, and energy-efcient low-voltage electroporation-
inactivation of pathogens in water. J Mater Chem A 6(39):1881318820
88. Zhou J, Wang T, Chen W, Lin B, Xie X (2020) Emerging investigator series: locally enhanced
electric eld treatment (LEEFT) with nanowire-modied electrodes for water disinfection in
pipes. Environ Sci Nano 7:397403
89. Zhou J, Wang T, Xie X (2019) Rationally designed tubular coaxial-electrode copper ionization
cells (CECICs) harnessing non-uniform electric eld for efcient water disinfection. Environ
Int 128:3036
90. Gusbeth C, Frey W, Volkmann H, Schwartz T, Bluhm H (2009) Pulsed electric eld treatment
for bacteria reduction and its impact on hospital wastewater. Chemosphere 75(2):228233
91. Sengel JT, Wallace MI (2016) Imaging the dynamics of individual electropores. Proc Natl
Acad Sci 113(19):52815286
92. Wang T, Chen H, Yu C, Xie X (2019) Rapid determination of the electroporation threshold for
bacteria inactivation using a lab-on-a-chip platform. Environ Int 132:105040
93. Dong H, Zheng L, Duan X, Zhao W, Chen J, Liu S, Sui G (2019) Cytotoxicity analysis of
ambient ne particle in BEAS-2B cells on an air-liquid interface (ALI) microuidics system.
Sci Total Environ 677:108119
94. Mitzel MR, Lin N, Whalen JK, Tufenkji N (2017) Chlamydomonas reinhardtii displays
aversive swimming response to silver nanoparticles. Environ Sci Nano 4(6):13281338
95. Englert DL, Manson MD, Jayaraman A (2010) Investigation of bacterial chemotaxis in ow-
based microuidic devices. Nat Protoc 5(5):864
96. Kim M, Lim JW, Kim HJ, Lee SK, Lee SJ, Kim T (2015) Chemostat-like microuidic
platform for highly sensitive detection of heavy metal ions using microbial biosensors.
Biosens Bioelectron 65:257264
97. Sun P, Liu Y, Sha J, Zhang Z, Tu Q, Chen P, Wang J (2011) High-throughput microuidic
system for long-term bacterial colony monitoring and antibiotic testing in zero-ow environ-
ments. Biosens Bioelectron 26(5):19931999
98. Lockery SR, Hulme SE, Roberts WM, Robinson KJ, Laromaine A, Lindsay TH, Whitesides
GM, Weeks JC (2012) A microuidic device for whole-animal drug screening using electro-
physiological measures in the nematode C. elegans. Lab Chip 12(12):22112220
99. Cartlidge R, Nugegoda D, Wlodkowic D (2017) Milliuidic lab-on-a-chip technology for
automated toxicity tests using the marine amphipod Allorchestes compressa. Sensors Actua-
tors B Chem 239:660670
100. Huang Y, Persoone G, Nugegoda D, Wlodkowic D (2016) Enabling sub-lethal behavioral
ecotoxicity biotests using microuidic lab-on-a-chip technology. Sensors Actuators B Chem
226:289298
101. Zhu F, Wigh A, Friedrich T, Devaux A, Bony S, Nugegoda D, Kaslin J, Wlodkowic D (2015)
Automated lab-on-a-chip technology for sh embryo toxicity tests performed under continu-
ous microperfusion (μFET). Environ Sci Technol 49(24):1457014578
Microuidics for Environmental Applications
102. Campana O, Wlodkowic D (2018) Ecotoxicology goes on a chip: embracing miniaturized
bioanalysis in aquatic risk assessment. Environ Sci Technol 52(3):932946
103. BioNanoConsulting (2020) Bio nano consulting product development page. http://www.bio-
nano-consulting.com/product-developmentdrinksafe
104. PalmSens (2020) PalmSens ItalSensI S-C page. https://www.palmsens.com/product/italsens-
is-c/
105. EarlyWarning (2009) Early warning biohazard water analyzer. https://www.earlywarninginc.
com/products.php
106. IBM (2017) IBM 5 in 5: smart sensors will detect environmental pollution at the speed of light.
https://www.research.ibm.com/5-in-5/environmental-pollutants/
107. Gigault J, Balaresque M, Tabuteau H (2018) Estuary-on-a-chip: unexpected results for the fate
and transport of nanoparticles. Environ Sci Nano 5(5):12311236
108. Seyedpour S, Janmaleki M, Henning C, Sanati-Nezhad A, Ricken T (2019) Contaminant
transport in soil: a comparison of the theory of porous media approach with the microuidic
visualisation. Sci Total Environ 686:12721281
T. Wang et al.
... These miniaturized platforms offer a wide range of advantages, including precise control of fluid dynamics, reduced sample volumes and accelerated reaction times (Hajmohammadi et al., 2018;Li et al., 2019;Feng et al., 2020). In the context of bacterial inactivation studies, these qualities become essential, as they help to improve heat transfer control and overall experiment efficiency (see Patinglag et al., 2021;Pudasaini et al., 2021;Wang et al., 2020). The reduced sample volume in microfluidic devices allows rapid temperature changes, which are essential for obtaining precise, controlled heat transfer conditions. ...
Article
Purpose In the wake of the COVID-19 pandemics, the demand for innovative and effective methods of bacterial inactivation has become a critical area of research, providing the impetus for this study. The purpose of this research is to analyze the AuNPs-mediated photothermal inactivation of E. coli. Gold nanoparticles irradiated by laser represent a promising technique for combating bacterial infection that combines high-tech and scientific progress. The intermediate aim of the work was to present the calibration of the model with respect to the gold nanorods experiment. The purpose of this work is to study the effect of initial concentration of E. coli bacteria, the design of the chamber and the laser power on heat transfer and inactivation of E. coli bacteria. Design/methodology/approach Using the CFD simulation, the work combines three main concepts. 1. The conversion of laser light to heat has been described by a combination of three distinctive approximations: a- Discrete particle integration to take into account every nanoparticle within the system, b- Rayleigh-Drude approximation to determine the scattering and extinction coefficients and c- Lambert–Beer–Bourger law to describe the decrease in laser intensity across the AuNPs. 2. The contribution of the presence of E. coli bacteria to the thermal and fluid-dynamic fields in the microdevice was modeled by single-phase approach by determining the effective thermophysical properties of the water-bacteria mixture. 3. An approach based on a temperature threshold attained at which bacteria will be inactivated, has been used to predict bacterial response to temperature increases. Findings The comparison of the thermal fields and temporal temperature changes obtained by the CFD simulation with those obtained experimentally confirms the accuracy of the light-heat conversion model derived from the aforementioned approximations. The results show a linear relationship between maximum temperature and variation in laser power over the range studied, which is in line with previous experimental results. It was also found that the temperature inside the microchamber can exceed 55 °C only when a laser power higher than 0.8 W is used, so bacterial inactivation begins. Research limitations/implications The experimental data allows to determinate the concentration of nanoparticles. This parameter is introduced into the mathematical model obtaining the same number of AuNPs. However, this assumption introduces a certain simplification, as in the mathematical model the distribution of nanoparticles is uniform. Practical implications This work is directly connected to the use of gold nanoparticles for energy conversion, as well as the field of bacterial inactivation in microfluidic systems such as lab-on-a-chip. Presented mathematical and numerical models can be extended to the entire spectrum of wavelengths with particular use of white light in the inactivation of bacteria. Originality/value This work represents a significant advancement in the field, as to the best of the authors’ knowledge, it is the first to employ a single-phase computational fluid dynamics (CFD) approach specifically combined with the thermal inactivation of bacteria. Moreover, this research pioneers the use of a numerical simulation to analyze the temperature threshold of photothermal inactivation of E. coli mediated by gold nanorods (AuNRs). The integration of these methodologies offers a new perspective on optimizing bacterial inactivation techniques, making this study a valuable contribution to both computational modeling and biomedical applications.
... Automation makes microfluidic systems an attractive option for analysis by minimizing costs and risks, managing high throughput analysis, and lowering contamination risk. It also decreases human errors while increasing precision and reproducibility [9][10][11][12][13]. Microfluidic techniques have been successfully applied in biotechnology [14][15][16]. ...
Article
Full-text available
Microfluidics can process small amounts of fluids by using microscopic channels with microscale dimensions ranging from tens to hundreds of micrometers. Many researchers have recently been working on smaller analytical equipment, such as micro flow cytometers. These gadgets offer numerous advantages, including portability, low cost, and low power consumption. It can also be integrated with other microfluidic devices for multitasking applications. In this study, the fluorescein dye was estimated using a lab-builtfully automated microfluidic fluorometric system. The developed system contained a microfluidic chip with two lines, each four centimetres long and with a volume of 15 µL. In this setup, two Arduino UNO (R3 version) microcontrollers were programmed using homebrew software. The first was to manage the two improvised peristaltic pumps, which successfully introduced the fluorescein dye to the water stream automatically, replacing the manual injection. The volume of the fluorescein sample was modified by varying the fluorescein line's run time. The second one was utilized to record the output signal. The method accurately identified fluorescein concentrations up to 0.01 µg/mL and 0.999 as a regression coefficient for six points. The RSD% (Relative Standard Deviation) for ten 0.08 µg/mL fluorescein measurements was 0%, and the detection limit was 1x10-4 µg/mL. The suggested method can measure 300 samples per hour while decreasing the amounts of reagents and waste. This microfluidic fluorometric system has the potential to be used for fluorescent dye assays in a variety of applications.
... In order to zoom in on the EFT-Cu system and observe the mechanism at work in situ, we can use a lab-on-a-chip (LOAC) device, which allows us to conduct critical mechanism studies at scales unobservable to the naked eye. In addition, we can further reduce the redundancy and tediousness of bulk electroporator based experiments that apply one condition at a time, eliminate the need for wasted materials and chemicals in larger scale studies, and result larger volumes of data with singular, microscale, well-designed experiments [34][35][36][37][38] . In this study, a LOAC device is fabricated and used (Fig. 1a, b) to understand, observe, and quantify the synergistic effect between EFT and Cu inactivation at microscale. ...
Article
Full-text available
As the overuse of chemicals in our disinfection processes becomes an ever-growing concern, alternative approaches to reduce and replace the usage of chemicals is warranted. Electric field treatment has shown promising potential to have synergistic effects with standard chemical-based methods as they both target the cell membrane specifically. In this study, we use a lab-on-a-chip device to understand, observe, and quantify the synergistic effect between electric field treatment and copper inactivation. Observations in situ, and at a single cell level, ensure us that the combined approach has an enhancement effect leading more bacteria to be weakened by electric field treatment and susceptible to inactivation by copper ion permeation. The synergistic effects of electric field treatment and copper can be visually concluded here, enabling the further study of this technology to optimally develop, mature, and scale for its various applications in the future.
... Electrophoresis 16 , microfluidics 17 , magnetic flocculation 18 , centrifugation 19 and filtration 20 have been employed to separate ultrafine particles. However, when applied to the purification of SS-contaminated ...
Article
Full-text available
Removal of suspended solids (SS) is a prerequisite for delivering clean water. However, removal of ultrafine SS during water purification in a cost-effective manner remains a global challenge. Here we develop an injection-driven filter system that integrates a fully bio-based biodegradable nanofibre hydrogel film with a syringe to remove ultrafine SS for portable and sustainable water purification. The hydrogel film features a densely stacked and entangled nanofibre network, enabling it to reject ultrafine SS with a cut-off size of ∼10 nm at a ∼100% rejection efficiency, greatly surpassing commercial filter papers and microporous membranes. During operation, the flux of the injection-driven filter system reaches 90.6 g cm⁻² h⁻¹, which is 7.2 times higher than that of commercial polycarbonate ultrafiltration membrane operated under the same conditions. Moreover, this filter system demonstrates good scalability and reusability, with low cost and reduced environmental footprint. The versatility of this filter system is further proven by successful clean water production from various difficult-to-purify water resources, including muddy water, river water, dirty water from melted snow and nanoplastic-contaminated water. Overall, this work provides a facile yet cost-effective tool for sustainable water purification.
... Highthroughput screening tools test libraries of design variants in parallel. 87,88 Analysing and characterizing the dynamics of engineered networks is non-trivial. Researchers are devising mathematical models and multi-scale computational simulations to predict system behaviours before costly lab work. ...
Article
Full-text available
Bio computing is an emerging interdisciplinary field that harnesses the information processing capabilities of biological substrates like DNA, proteins and cells to perform computational tasks. Rather than relying solely on conventional silicon-based computers, bio computing leverages the innate computational properties of biomolecules to encode, store, process and transmit information in unconventional ways. Core approaches include DNA computing, which uses DNA biochemistry to solve problems in a massively parallel fashion. Protein computing utilizes protein conformational dynamics to implement logic gates and communication modules for molecular information processing. Cellular computing focuses on engineering gene circuits and synthetic biology tools to program computational behaviours in living cells. Neural computing builds artificial neural networks inspired by biological brains. Key application areas include biomedicine, smart drug delivery systems, biosensing, hybrid organic-inorganic electronics, and biomolecular manufacturing. While still facing challenges around biocompatibility, programming complexity and ethical concerns, bio computing has achieved major technical milestones demonstrating its promise. Continued progress at the interface of biology and computing could enable future technologies like bio processors, in-vivo biocomputers, living materials and bio-intelligent systems. With responsible development, bio-inspired computation may catalyse the next revolution in human technological capabilities. This emerging field thus warrants enthusiastic attention as computation further converges with the living world.
Chapter
Because of age-related risk factors and lifestyle choices, the prevalence of chronic disease is rising quickly around the globe in today’s culture. The social and financial toll that inflammatory illnesses and chronic syndromes have on society in terms of direct and indirect medical expenses is substantial. Over the last 10 years, there have been revisions made to the diagnostic criteria in order to enable prompt identification and treatment of inflammatory disorders. Inflammatory markers have developed into biomarkers for several diseases as diagnostic methods have advanced. In both acute and chronic inflammatory illnesses, measurement of inflammatory markers is commonly employed. Information on the primary inflammatory indicators and techniques for diagnosing them is included in this chapter. In particular, electrochemical and optical biosensors work incredibly well for creating diagnostic inflammatory marker systems. The potential applications of sensory systems in the diagnosis of inflammatory indicators are demonstrated.
Article
Full-text available
The existing methods for defect detection in PDMS microfluidic chips typically involve complex image recognition algorithms or manual inspection and still lack efficiency and reliability. Although some automatic defect detection methods have been proposed in recent years, most of them still rely on external computation systems to deploy. To address these challenges, we propose an independent portable defect detection system with embedded computing for microfluidic devices. This portable system is completely self-contained, integrating an image acquisition module, a control panel module, a power module, and an embedded computing control module to realize chip detection, processing, and result display functions. Experimental results show that the system can effectively detect most of the commonly seen defects in PDMS-based microfluidic chips, proving to be more efficient and reliable than manual inspection. With the control of the embedded system, two detection methods: template matching (based on comparison with standard samples) and automatic defect detection (based on surface defect recognition) were used to identify defects in PDMS-based microfluidic chips. The proposed system can automatically inspect and analyze chips without the need for external laboratory support and can provide a promising solution for future microfluidic chip manufacturing and operation.
Article
The handling and analysis of gaseous tritium is of interest for hydrogen isotope separation experiments. In this work, we present an easy-to-handle setup for catalytic oxidation to HTO, recovering all of the initially dosed gaseous tritium as determined by LSC, using CuO as a catalyst at a reaction temperature of 900 °C. Aiming to reduce cocktail waste, the LSC determination was downscaled to a microfluidic setup. The performance was evaluated based on the counting efficiency, which was shown to decrease significantly, as the sample volume was reduced to µl amounts, while no changes were observed over a wide range of sample-to-cocktail ratios.
Article
Full-text available
Electroporation based locally enhanced electric field treatment (LEEFT) is an emerging bacteria inactivation technology for drinking water disinfection. Nevertheless, the lethal electroporation threshold (LET) for bacteria has not been studied, partly due to the tedious work required by traditional experimental methods. Here, a lab-on-a-chip device composed of platinum electrodes deposited on a glass substrate is developed for rapid determination of the LET. When voltage pulses are applied, an electric field with a linear strength gradient is generated on a channel between the electrodes. Bacterial cells exposed to the electric field stronger than the LET are inactivated, while others remain intact. After a cell staining process to differentiate dead and live bacterial cells, the LETs are obtained by analyzing the fluorescence microscopy images. Staphylococcus epidermidis has been utilized as a model bacterium in this study. The LETs range from 10 kV/cm to 35 kV/cm under different pulsed electric field conditions, decreasing with the increase of pulse width, effective treatment time, and pulsed electric field frequency. The effects of medium properties on the LET were also investigated. This lab-on-a-chip device and the experimental approach can also be used to determine the LETs for other microorganisms found in drinking water.
Article
Full-text available
The spread of antibiotic resistance genes (ARGs) has become an emerging threat to the global health. Although horizontal gene transfer (HGT) is regarded as one of the major pathways, more evidence has shown the significant involvement of vertical gene transfer (VGT). However, traditional cultivation-based methods cannot distinguish HGT and VGT, resulting in often contradictory conclusions. Here, single-cell microfluidics with time-lapse imaging has been successfully employed to dissect the contribution of plasmid-mediated HGT and VGT to ARG transmission in an environmental community. Using Escherichia coli with an ARG-coded plasmid pKJK5 with trimethoprim resistance as the donor, we quantified the effects of three representative antibiotics (trimethoprim, tetracycline and amoxicillin) on the ARG transfer process in an activated sludge bacterial community. It was found that HGT was influenced by the inhibitory mechanism of an antibiotic and its targets (donor, recipient alone or together), whereas VGT contributes significantly to the formation of transconjugants and consequently ARG spreading. Trimethoprim is highly resisted by the donor and transconjugants, and its presence significantly increased both the HGT and VGT rates. Although tetracycline and amoxicillin both inhibit the donor, they showed different effects on HGT rate as a result of different inhibitory mechanisms. Furthermore, we show the kinetics of HGT in a community can be described using an epidemic infection model, which in combination with quantitative measure of HGT and VGT on chip provides a promising tool to study and predict the dynamics of ARG spread in real-world communities. Keywords: Cell tracking, Microfluidics, Antibiotics, Antibiotic resistance genes, Horizontal gene transfer, Vertical gene transfer
Article
Full-text available
Though well known for its anti-microbial property, copper is usually not considered for drinking water disinfection because of its health risk to human bodies under efficient biocidal concentration. Herein, we have rationally designed and constructed a tubular coaxial-electrode copper ionization cell (CECIC) that enables superior disinfection performance (~6-log removal of E. coli) with a very low effluent copper concentration (~200 μg/L). A non-uniform electric field with enhanced strength near the center electrode is generated in the chamber attributed to the coaxial center-outer electrode configuration. Exposure to the strong electric field subsequently increases the permeability of cell membrane, the excessive uptake of Cu ions into microbes, and thus the reinforced bacteria inactivation. The in-situ ionization results in a Cu ion concentration gradient with higher concentrations in the regions closer to the center. In addition, being driven by the electrophoresis and dielectrophoresis forces, the bacterial cells are transported to the vicinity of the center electrode, where both the electric field strength and Cu ion concentration are higher. These mechanisms in the CECIC synergistically result in the high inactivation efficiency with low Cu concentration in the effluent. The low-cost, high-efficiency, and disinfection-byproduct-free CECIC has shown significant potential in point-of-use applications.
Article
Chlorine disinfection inevitably generates carcinogenic by-products. Alternative non-chlorine-based techniques in the centralized treatment plants cannot produce residual antimicrobial power in water disinfection systems. Here, we propose locally enhanced electric field treatment (LEEFT) for chemical-free water disinfection in pipes. A tubular LEEFT device with coaxial electrodes is rationally developed for easy adaption to current water distribution system as a segment of the pipelines. The center electrode is modified with perpendicularly grown nanowires, so that the electric field strength near the tips of the nanowires is significantly enhanced for pathogen inactivation. We have demonstrated >6-log inactivation of bacteria with 1 V, a small voltage that can be generated in situ by flowing water.
Article
A multi-material 3D printed microfluidic reactor with integrated heating is presented, which was applied within a manifold for the colorimetric determination of ammonium in natural waters. Graphene doped polymer was used to provide localised heating when connected to a power source, achieving temperatures of up to 120 °C at 12 V, 0.7 A. An electrically insulating layer of acrylonitrile butadiene styrene (ABS) polymer or a new microdiamond-ABS polymer composite was used as a heater coating. The microdiamond polymer composite provided higher thermal conductivity and uniform heating of the serpentine microreactor which resulted in greater temperature control and accuracy in comparison to pure ABS polymer. The developed heater was then applied and demonstrated using a modified Berthelot reaction for ammonium analysis, in which the microreactor was configured at a predetermined optimised temperature. A 5-fold increase in reaction speed was observed compared to previously reported reaction rates. A simple flow injection analysis set up, comprising the microfluidic heater along with an LED-photodiode based optical detector, was assembled for ammonium analysis. Two river water samples and two blind ammonium standards were analysed and estimated concentrations were compared to concentrations determined using benchtop IC. The highest relative error observed following the analysis of the environmental samples was 11% and for the blind standards was 5%.
Article
Marine pollution and monitoring have received more and more concern in recent years. Herein, a fully automatic whole-algae biosensor was designed for low-cost and fast detection of toxic contaminants in seawater. It consists of a digital microfluidic (DMF) diluter chip, an actuation element, a detector element, and a microalgae bioreporter. A feedback-control protocol based on charging-time compensation was introduced. It ensures precise actuation of the droplet with diverse salty concentrations and contents in the marine environment. The two-mixer cross-split dilution engine increases the accuracy of droplet dispensing and concentration diluting. By selecting motility of P. subcordiformis as the sensor signal, the developed biosensor showed good sensitivity and robustness for a wide range of salinity (10-37‰), temperature (0-25 °C), light levels (0-325 μmol photons m-2 s-1), and cell density factor (1.0-4.0). The biosensor responses were examined in the presence of copper, lead, phenol, and nonylphenol (NP). In all cases, toxic responses (i.e. dose-related inhibition of algal motion) were detected with the detection limits of 0.65 μmol.L-1, 1.90 μmol.L-1, 2.85 mmol.L-1, and 5.22 μmol.L-1 respectively. These results were obtained in a much shorter time (2 h for our biosensor vs. 24 h-10 d for growth inhibition test) and the data are consistent with previous classical studies. We thus developed a simple, rapid, and adaptable system for marine routine monitoring and early-warning detection for lab and on-site applications.
Article
Microfluidic-based chemical sensors take laboratory analytical protocols and miniaturise them into field-deployable systems for in situ monitoring of water chemistry. Here we present a prototype nitrate/nitrite sensor based on droplet microfluidics that in contrast to standard (continuous phase) microfluidic sensors, treats water samples as discrete droplets contained within a flow of oil. The new sensor device can quantify the concentrations of nitrate and nitrite within each droplet and provides high measurement frequency and low fluid consumption. Reagent consumption is at a rate of 2.8 ml/day when measuring every ten seconds, orders of magnitude more efficient than the current state of the art. The sensor’s capabilities were demonstrated during a three-week deployment in a tidal river. The accurate and high frequency data (6 % error relative to spot samples, measuring at 0.1 Hz) elucidated the influence of tidal variation, rain events, diurnal effects, and anthropogenic input on concentrations at the deployment site. This droplet microfluidic-based sensor is suitable for a wide range of applications such as monitoring of rivers, lakes, coastal waters, and industrial effluents.
Article
Using antimicrobial susceptibility test (AST) as an example, this work demonstrates a practical method to fabricate microfluidic chips entirely from polypropylene (PP), and the benefits for potential commercial use. Primarily caused by the misuse and abuse of antibiotics, antimicrobial resistance (AMR) is a major threat to modern medicine. AST is a promising technique to help with the optimal use of antibiotics for reducing AMR. However, current phenotypic ASTs suffer from long turnaround time, while genotypic ASTs suffer from low reliability, and both are unaffordable for routine use. New microfluidic based AST methods are rapid, but still unreliable, as well as costly due to the PDMS chip material. Herein, we demonstrate a convenient method to fabricate whole-PP microfluidic chips with high resolution and fidelity. Unlike PDMS chips, the whole-PP chips showed better reliability due to its inertness, are solvent-compatible and can be conveniently reused and recycled, which largely decreases the cost and is environmental-friendly. We specially designed 3D chambers that allow for quick cell loading without valving/liquid exchange; this new hydrodynamic design satisfies the shear stress requirement for on-chip bacteria culture, which, compared to reported designs for similar purposes, allows for simpler, more rapid, and high-throughput operation. Our system allows for reliable tracking of individual cells and acquisition of AST results within 1-3 hours, which is among the group of fastest phenotypic methods. The PP chips are more reliable and affordable than PDMS chips, providing a practical solution to improve current culture-based AST and benefiting the fight against AMR through helping doctors prescribe effective, narrow-spectrum antibiotics; they will also be broadly useful for other applications wherein a reliable, solvent resistant, anti-fouling, and affordable microfluidic chip is needed.
Article
We have developed a photonic nano-immunosensor platform for the on-site analysis of harmful organic ocean pollutants, intended to be allocated in stand-alone buoys. The main aim is bringing the monitoring tools directly to the contaminated place, resulting in cost and time savings as compared to the standard analytical techniques. As sensor we have employed an integrated asymmetric Mach-Zehnder interferometer (aMZI) of micro/nano dimensions, based on silicon photonic technology. In order to obtain a multiplexed system, a four-channel microfluidic cell has been designed, manufactured and incorporated in the miniaturized sensor. Additionally, a microfluidic delivery module enabling automatic sample analysis has been designed, evaluated and assembled. Moreover, we have implemented the optical interconnections of the sensor chip by fiber optics, as well the electronics and the required software and data processing. Pollutant detection is based on a competitive immunoassay using bioreceptors previously biofunctionalized on the aMZI sensor arms and incubation with a specific antibody. As proof of concept, two types of pollutants have been analysed: the biocide Irgarol 1051, and the antibiotic Tetracycline. Results show limits of detection in the range of few ng/mL, accomplished the European legislation.