[Show abstract][Hide abstract] ABSTRACT: Nanocarbon allotropes (NCAs), including zero-dimensional carbon dots (CDs), one-dimensional carbon nanotubes (CNTs) and two-dimensional graphene, exhibit exceptional material properties, such as unique electrical/thermal conductivity, biocompatibility and high quenching efficiency, that make them well suited for both electrical/electrochemical and optical sensors/biosensors alike. In particular, these material properties have been exploited to significantly enhance the transduction of biorecognition events in fluorescence-based biosensing involving Förster resonant energy transfer (FRET). This review analyzes current advances in sensors and biosensors that utilize graphene, CNTs or CDs as the platform in optical sensors and biosensors. Widely utilized synthesis/fabrication techniques, intrinsic material properties and current research examples of such nanocarbon, FRET-based sensors/biosensors are illustrated. The future outlook and challenges for the research field are also detailed.
[Show abstract][Hide abstract] ABSTRACT: The utility of unmanned Micro Underwater Vehicles (MUVs) is paramount for exploring confined spaces, but their spatial agility is often impaired when maneuvers require burst-propulsion. Herein we develop high-aspect ratio (150:1), multi-walled carbon nanotube microarray membranes (CNT-MMs) for propulsive, MUV thrust generation by the decomposition of hydrogen peroxide (H2O2). The CNT-MMs are grown via chemical vapor deposition with diamond shaped pores (nominal diagonal dimensions of 4.5 × 9.0 [µm]) and subsequently decorated with urchin-like, platinum (Pt) nanoparticles via a facile, electroless, chemical deposition process. The Pt-CNT-MMs display robust, high catalytic ability with an effective activation energy of 26.96 [kJ mol-1] capable of producing a thrust of 0.209 ± 0.049 [N] from 50% [w/w] H2O2 decomposition within a compact reaction chamber of eight Pt-CNT-MMs in series.
[Show abstract][Hide abstract] ABSTRACT: Enzymes provide the critical means by which to catalyze almost all biological reactions in a controlled manner. Methods to harness and exploit their properties are of strong current interest to the growing field of biotechnology. In contrast to depending upon recombinant genetic approaches, a growing body of evidence suggests that apparent enzymatic activity can be enhanced when located at a nanoparticle interface. We use semiconductor quantum dots (QDs) as a well-defined and easily bioconjugated nanoparticle along with Escherichia coli-derived alkaline phosphatase (AP) as a prototypical enzyme to seek evidence for this process in a de novo model system. We began by first assessing whether the relatively large dimeric AP protein (∼100 kDa) can be assembled onto two differentially sized green and red CdSe/ZnS core/shell QDs in a ratiometric and structurally controlled manner; such assembly is necessary to minimize heterogeneity within the bioconjugate and provide intimate control over the experimental format. For this, analysis is undertaken using both structural modeling and physicochemical characterization techniques including dynamic light scattering and agarose gel electrophoresis; these all provide strong supporting evidence for controlled AP attachment to the QDs. The enzymatic activity of AP-QD bioconjugates assembled on the different QDs and displaying variable AP:QD ratios was then assayed against equivalent amounts of freely diffusing enzyme controls in both conventional excess substrate formats and a varying enzyme-fixed substrate format that is more amenable in general to concentration-limited nanoparticle conjugates. The resulting experimental data were then analyzed in the context of the Michaelis-Menten model and compared. The results show a general equivalency between the two assay formats while also providing evidence for an increase in apparent AP activity of ca. 25% when attached to the QDs. Some discussion is provided on the underlying mechanisms that may contribute to the enhanced activity along with the implications of this work toward future research.
The Journal of Physical Chemistry C 01/2015; 119(4):2208-2221. DOI:10.1021/jp5110467 · 4.77 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Structural DNA nanotechnology has developed profoundly in the last several years allowing for the creation of increasingly sophisticated devices capable of discrete sensing, locomotion, and molecular logic. The latter research field is particularly attractive as it provides information processing capabilities that may eventually be applied in situ, for example in cells, with potential for even further coupling to an active response such as drug delivery. Rather than design a new DNA assembly for each intended logic application, it would be useful to have one generalized design that could provide multiple different logic gates or states for a targeted use. In pursuit of this goal, we demonstrate a switchable, triangular dye-labeled three-arm DNA scaffold where the individual arms can be assembled in different combinations and the linkage between each arm can be physically removed using toehold-mediated strand displacement and then replaced by a rapid anneal. Rearranging this core structure alters the rates of Förster resonance energy transfer (FRET) between each of the two or three pendant dyes giving rise to a rich library of unique spectral signatures that ultimately form the basis for molecular photonic logic gates. The DNA scaffold is designed such that different linker lengths joining each arm, and which are used as the inputs here, can also be used independently of one another thus enhancing the range of molecular gates. The functionality of this platform structure is highlighted by easily configuring it into a series of one-, two- and three-input photonic Boolean logic gates such as OR, AND, INHIBIT, etc., along with a photonic keypad lock. Different gates can be realized in the same structure by altering which dyes are interrogated and implementation of toehold-mediated strand displacement and/or annealing allows reconfigurable switching between input states within a single logic gate as well as between two different gating devices.
[Show abstract][Hide abstract] ABSTRACT: Platinum nano-urchins supported on microfibrilated cellulose films (MFC) were fabricated and evaluated as hydrogen peroxide catalysts for small-scale, autonomous underwater vehicle (AUV) propulsion systems. The catalytic substrate was synthesized through the reduction of chloroplatinic acid to create a thick film of Pt coral-like microstructures coated with Pt urchin-like nanowires that are arrayed in three dimensions on a two dimensional MFC film. This organic/inorganic nanohybrid displays high catalytic ability (reduced activation energy of 50 - 63% over conventional materials and 13 - 19% for similar Pt nanoparticle-based structures) during hydrogen peroxide (H2O2) decomposition as well as sufficient propulsive thrust ( > 0.5 N ) from low concentration H2O2 (30% w/w) fuel within a small underwater reaction vessel. The results demonstrate that these layered nanohybrid sheets are robust and catalytically effective for green, H2O2-based micro-AUV propulsion where the storage and handling of highly explosive, toxic fuels are prohibitive due to size-requirements, cost limitations, and close person-to-machine contact.
[Show abstract][Hide abstract] ABSTRACT: Luminescent semiconductor nanocrystals or quantum dots (QDs) hold tremendous
promise for in vivo biosensing, cellular imaging, theranostics, and smart molecular sensing
probes due to their small size and favorable photonic properties such as resistance to
photobleaching, size-tunable PL, and large effective Stokes shifts. Herein, we demonstrate how
QD-based bioconjugates can be used to enhance enzyme kinetics. Enzyme-substrate kinetics are
analyzed for solutions containing both alkaline phosphatase enzymes and QDs with enzyme-to-
QD molar ratios of 2, 12, and 24 as well as for a solution containing the same concentration of
enzymes but without QDs. The enzyme kinetic paramters Vmax, KM, and Kcat/KM are extracted from the enzyme progress curves via the Lineweaver-Burk plot. Results demonstrate an
approximate increase in enzyme efficiency of 5 - 8% for enzymes immobilized on the QD
versus free in solution without QD immobilization.
[Show abstract][Hide abstract] ABSTRACT: Real-time monitoring of physiological glucose transport is crucial for gaining new understanding of diabetes. Many techniques and equipment currently exist for measuring glucose, but these techniques are limited by complexity of the measurement, requirement of bulky equipment, and low temporal/spatial resolution. The development of various types of biosensors (eg, electrochemical, optical sensors) for laboratory and/or clinical applications will provide new insights into the cause(s) and possible treatments of diabetes. State-of-the-art biosensors are improved by incorporating catalytic nanomaterials such as carbon nanotubes, graphene, electrospun nanofibers, and quantum dots. These nanomaterials greatly enhance biosensor performance, namely sensitivity, response time, and limit of detection. A wide range of new biosensors that incorporate nanomaterials such as lab-on-chip and nanosensor devices are currently being developed for in vivo and in vitro glucose sensing. These real-time monitoring tools represent a powerful diagnostic and monitoring tool for measuring glucose in diabetes research and point of care diagnostics. However, concerns over the possible toxicity of some nanomaterials limit the application of these devices for in vivo sensing. This review provides a general overview of the state of the art in nanomaterial-mediated biosensors for in vivo and in vitro glucose sensing, and discusses some of the challenges associated with nanomaterial toxicity.
Journal of diabetes science and technology 03/2014; 8(2):403-411. DOI:10.1177/1932296814522799
[Show abstract][Hide abstract] ABSTRACT: We combine quantum dots (QDs) with long-lifetime terbium complexes (Tb), a near-IR Alexa Fluor dye (A647), and self-assembling peptides to demonstrate combinatorial and sequential bionanophotonic logic devices that function by time-gated Förster resonance energy transfer (FRET). Upon excitation, the Tb-QD-A647 FRET-complex produces time-dependent photoluminescent signatures from multi-FRET pathways enabled by the capacitor-like behavior of the Tb. The unique photoluminescent signatures are manipulated by ratiometrically varying dye/Tb inputs and collection time. Fluorescent output is converted into Boolean logic states to create complex arithmetic circuits including the half-adder/half-subtractor, 2:1 multiplexer/1:2 demultiplexer, and a 3-digit, 16-combination keypad lock.
[Show abstract][Hide abstract] ABSTRACT: Luminescent semiconductor nanocrystals or quantum dots (QDs) contain
favorable photonic properties (e.g., resistance to photobleaching,
size-tunable PL, and large effective Stokes shifts) that make them
well-suited for fluorescence (Förster) resonance energy transfer
(FRET) based applications including monitoring proteolytic activity,
elucidating the effects of nanoparticles-mediated drug delivery, and
analyzing the spatial and temporal dynamics of cellular biochemical
processes. Herein, we demonstrate how unique considerations of temporal
and spatial constraints can be used in conjunction with QD-FRET systems
to open up new avenues of scientific discovery in information processing
and molecular logic circuitry. For example, by conjugating both long
lifetime luminescent terbium(III) complexes (Tb) and fluorescent dyes
(A647) to a single QD, we can create multiple FRET lanes that change
temporally as the QD acts as both an acceptor and donor at distinct time
intervals. Such temporal FRET modulation creates multi-step FRET
cascades that produce a wealth of unique photoluminescence (PL) spectra
that are well-suited for the construction of a photonic alphabet and
photonic logic circuits. These research advances in bio-based molecular
logic open the door to future applications including multiplexed
biosensing and drug delivery for disease diagnostics and treatment.
Proceedings of SPIE - The International Society for Optical Engineering 10/2013; 8817. DOI:10.1117/12.2024287 · 0.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Integrating photonic inputs/outputs into unimolecular logic devices can provide significantly increased functional complexity and the ability to expand the repertoire of available operations. Here, we build upon a system previously utilized for biosensing to assemble and prototype several increasingly sophisticated biophotonic logic devices that function based upon multistep Förster resonance energy transfer (FRET) relays. The core system combines a central semiconductor quantum dot (QD) nanoplatform with a long-lifetime Tb complex FRET donor and a near-IR organic fluorophore acceptor; the latter acts as two unique inputs for the QD-based device. The Tb complex allows for a form of temporal memory by providing unique access to a time-delayed modality as an alternate output which significantly increases the inherent computing options. Altering the device by controlling the configuration parameters with biologically based self-assembly provides input control while monitoring changes in emission output of all participants, in both a spectral and temporal-dependent manner, gives rise to two input, single output Boolean Logic operations including OR, AND, INHIBIT, XOR, NOR, NAND, along with the possibility of gate transitions. Incorporation of an enzymatic cleavage step provides for a set-reset function that can be implemented repeatedly with the same building blocks and is demonstrated with single input, single output YES and NOT gates. Potential applications for these devices are discussed in the context of their constituent parts and the richness of available signal.
[Show abstract][Hide abstract] ABSTRACT: Oxygen plays a critical role in plant metabolism, stress response/signaling, and adaptation to environmental changes (Lambers and Colmer, Plant Soil 274:7-15, 2005; Pitzschke et al., Antioxid Redox Signal 8:1757-1764, 2006; Van Breusegem et al., Plant Sci 161:405-414, 2001). Reactive oxygen species (ROS), by-products of various metabolic pathways in which oxygen is a key molecule, are produced during adaptation responses to environmental stress. While much is known about plant adaptation to stress (e.g., detoxifying enzymes, antioxidant production), the link between ROS metabolism, O2 transport, and stress response mechanisms is unknown. Thus, non-invasive technologies for measuring O2 are critical for understanding the link between physiological O2 transport and ROS signaling. New non-invasive technologies allow real-time measurement of O2 at the single cell and even organelle levels. This review briefly summarizes currently available (i.e., mainstream) technologies for measuring O2 and then introduces emerging technologies for measuring O2. Advanced techniques that provide the ability to non-invasively (i.e., non-destructively) measure O2 are highlighted. In the near future, these non-invasive sensors will facilitate novel experimentation that will allow plant physiologists to ask new hypothesis-driven research questions aimed at improving our understanding of physiological O2 transport.
[Show abstract][Hide abstract] ABSTRACT: Hybridization of nanoscale metals and carbon nanotubes into composite nanomaterials has produced some of the best-performing sensors to date. The challenge remains to develop scalable nanofabrication methods that are amenable to the development of sensors with broad sensing ranges. A scalable nanostructured biosensor based on multilayered graphene petal nanosheets (MGPNs), Pt nanoparticles, and a biorecognition element (glucose oxidase) is presented. The combination of zero-dimensional nanoparticles on a two-dimensional support that is arrayed in the third dimension creates a sensor platform with exceptional characteristics. The versatility of the biosensor platform is demonstrated by altering biosensor performance (i.e., sensitivity, detection limit, and linear sensing range) through changing the size, density, and morphology of electrodeposited Pt nanoparticles on the MGPNs. This work enables a robust sensor design that demonstrates exceptional performance with enhanced glucose sensitivity (0.3 µM detection limit, 0.01–50 mM linear sensing range), a long stable shelf-life (>1 month), and a high selectivity over electroactive, interfering species commonly found in human serum samples.
[Show abstract][Hide abstract] ABSTRACT: Bullets and rockets: Ultrasound-triggered vaporization of a perfluorocarbon compound loaded into microbullets provides the necessary force for the microbullets to penetrate, cleave, and deform cellular tissue for potential targeted drug delivery and precision nanosurgery. The microbullets have an inner Au layer that allows conjugation of a monolayer of thiolated cysteamine (green in picture) for electrostatic attachment of perfluorocarbon droplets (purple droplets).
[Show abstract][Hide abstract] ABSTRACT: We report on the development of a microneedle-based multiplexed drug delivery actuator that enables the controlled delivery of multiple therapeutic agents. Two individually-addressable channels on a single microneedle array, each paired with its own reservoir and conducting polymer nanoactuator, are used to deliver various permutations of two unique chemical species. Upon application of suitable redox potentials to the selected actuator, the conducting polymer is able to undergo reversible volume changes, thereby serving to release a model chemical agent in a controlled fashion through the corresponding microneedle channels. Time-lapse videos offer direct visualization and characterization of the membrane switching capability and, along with calibration investigations, confirm the ability of the device to alternate the delivery of multiple reagents from individual microneedles of the array with higher precision and temporal resolution than conventional drug delivery actuators. Analytical modeling offers prediction of the volumetric flow rate through a single microneedle and accordingly can be used to assist in the design of subsequent microneedle arrays. The robust solid-state design and lack of mechanical components circumvent reliability issues that challenge fragile conventional microelectromechanical drug delivery devices. This proof-of-concept study demonstrates the potential of the drug delivery actuator system to aid in the rapid administration of multiple therapeutic agents and indicates the potential to counteract diverse biomedical conditions.
Sensors and Actuators B Chemical 01/2012; 161(1). DOI:10.1016/j.snb.2011.11.085 · 4.10 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: New template-based self-propelled gold/nickel/polyaniline/platinum (Au/Ni/PANI/Pt) microtubular engines, functionalized with the Concanavalin A (ConA) lectin bioreceptor, are shown to be extremely useful for the rapid, real-time isolation of Escherichia coli (E. coli) bacteria from fuel-enhanced environmental, food, and clinical samples. These multifunctional microtube engines combine the selective capture of E. coli with the uptake of polymeric drug-carrier particles to provide an attractive motion-based theranostics strategy. Triggered release of the captured bacteria is demonstrated by movement through a low-pH glycine-based dissociation solution. The smaller size of the new polymer-metal microengines offers convenient, direct, and label-free optical visualization of the captured bacteria and discrimination against nontarget cells.
[Show abstract][Hide abstract] ABSTRACT: Nascent nanofabrication approaches are being applied to reduce electrode feature dimensions from the microscale to the nanoscale, creating biosensors that are capable of working more efficiently at the biomolecular level. The development of nanoscale biosensors has been driven largely by experimental empiricism to date. Consequently, the precise positioning of nanoscale electrode elements is typically neglected, and its impact on biosensor performance is subsequently overlooked. Herein, we present a bottom-up nanoelectrode array fabrication approach that utilizes low-density and horizontally oriented single-walled carbon nanotubes (SWCNTs) as a template for the growth and precise positioning of Pt nanospheres. We further develop a computational model to optimize the nanosphere spatial arrangement and elucidate the trade-offs among kinetics, mass transport, and charge transport in an enzymatic biosensing scenario. Optimized model variables and experimental results confirm that tightly packed Pt nanosphere/SWCNT nanobands outperform low-density Pt nanosphere/SWCNT arrays in enzymatic glucose sensing. These computational and experimental results demonstrate the profound impact of nanoparticle placement on biosensor performance. This integration of bottom-up nanoelectrode array templating with analysis-informed design produces a foundation for controlling and optimizing nanotechnology-based electrochemical biosensor performance.
The Journal of Physical Chemistry C 10/2011; 115(43). DOI:10.1021/jp205569z · 4.77 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This work addresses the comparison of different strategies for improving biosensor performance using nanomaterials. Glucose biosensors based on commonly applied enzyme immobilization approaches, including sol-gel encapsulation approaches and glutaraldehyde cross-linking strategies, were studied in the presence and absence of multi-walled carbon nanotubes (MWNTs). Although direct comparison of design parameters such as linear range and sensitivity is intuitive, this comparison alone is not an accurate indicator of biosensor efficacy, due to the wide range of electrodes and nanomaterials available for use in current biosensor designs. We proposed a comparative protocol which considers both the active area available for transduction following nanomaterial deposition and the sensitivity. Based on the protocol, when no nanomaterials were involved, TEOS/GOx biosensors exhibited the highest efficacy, followed by BSA/GA/GOx and TMOS/GOx biosensors. A novel biosensor containing carboxylated MWNTs modified with glucose oxidase and an overlying TMOS layer demonstrated optimum efficacy in terms of enhanced current density (18.3 ± 0.5 µA mM(-1) cm(-2)), linear range (0.0037-12 mM), detection limit (3.7 µM), coefficient of variation (2%), response time (less than 8 s), and stability/selectivity/reproducibility. H(2)O(2) response tests demonstrated that the most possible reason for the performance enhancement was an increased enzyme loading. This design is an excellent platform for versatile biosensing applications.