Conference PaperPDF Available




This work demonstrates the first utilization of virus molecules as nano-scale biotemplates assembled on an electrochemical biosensor, allowing for an 8-times increased signal and an improved biosensing performance of 9.5-fold. The versatile and inexpensive biological Tobacco mosaic virus was integrated as a high aspect ratio, low footprint, low-cost, easy to genetically functionalize, nanostructured three-dimensional scaffold for the synthesis of novel multifunctional electrodes. The biotemplated scaffold allows for an increased surface area resulting in higher electrochemical currents, better signal-to-noise ratio and improved sensitivity when incorporated into miniaturized biosensors.
Hadar Ben-Yoav1*, Adam D. Brown2, Ekaterina Pomerantseva1, Deanna L. Kelly3, James N. Culver2,
and Reza Ghodssi1*
1MEMS Sensors and Actuators Laboratory, Department of Electrical and Computer Engineering, Institute for
Systems Research,
2Institute for Bioscience and Biotechnology Research, University of Maryland, College Park, Maryland, USA
3Maryland Psychiatric Research Center, University of Maryland School of Medicine, Baltimore, Maryland, USA
This work demonstrates the first utilization of virus molecules
as nano-scale biotemplates assembled on an electrochemical
biosensor, allowing for an 8-times increased signal and an
improved biosensing performance of 9.5-fold. The versatile and
inexpensive biological Tobacco mosaic virus was integrated as a
high aspect ratio, low footprint, low-cost, easy to genetically
functionalize, nanostructured three-dimensional scaffold for the
synthesis of novel multifunctional electrodes. The biotemplated
scaffold allows for an increased surface area resulting in higher
electrochemical currents, better signal-to-noise ratio and improved
sensitivity when incorporated into miniaturized biosensors.
Electrochemical Biosensors
Electrochemical biosensors are based on a bioelectrochemical
interaction process, where electrochemical species are consumed
or generated. Most electrochemical measurements detect
oxidation/reduction of the product generated by biological
conversion of the analyte undergoing redox reactions on the
sensor's surface and solely respond to electro-active species.
Electrochemical measurements are classified according to the
variable being measured: amperometry, potentiometry and
conductometry [1, 2].
In recent decades, nanostructured materials have received
much attention due to unique properties they offer as robust
platforms for electronic and optical signal transduction. One of its
major contributions is the design of a new generation of
miniaturized biosensing devices. Furthermore, biofunctional
nanoparticles can produce a synergistic effect between catalytic
activity, conductivity, and biocompatibility to accelerate the signal
transduction, leading to the quick development of stable, specific,
selective and sensitive biosensors in different fields. An important
point besides the biosensing applicability of nanomaterials is the
use of manipulation techniques for their integration in fabrication
techniques [3]. By integrating with electrochemical sensor
fabrication, these materials provide interesting properties such as
increased surface area. The augmented surface area leads to higher
signal-to-noise ratio, increased sensitivity and dynamic range,
short distances for mass transport and charge transfer as well as
their ability to create complex nano-bio-architectures that allow
volume change and unique selective biological functionality.
Nanomaterials allow the development of new architectures applied
in electrochemical sensing and biosensing devices [4, 5]. For
example, Ye and colleagues presented a multi-walled carbon
nanotube (MWNT)-based electrochemical biosensor for glucose
detection [5]. The higher surface area of the well-aligned MWNT
generated higher electrochemical currents that were correlated to a
highly sensitive sensor.
Tobacco mosaic virus
Biological nanomaterials provide a versatile and cost effective
solution for the fabrication of high surface area nanoarchitectures.
One category of these biological nanostructures is plant and
bacteria virus particles consisting of macromolecular assemblies of
nucleic acid packaged by many copies of coat proteins. These
molecules display some unique advantages as they show
exceptional stability in a wide range of temperatures and pH
values, in addition to their surface-exposed functional groups, self-
assembly and tunability [6].
Among the available plant viruses [7], Tobacco mosaic virus
(TMV) is the most extensively studied filamentous plant structure
for nanoscale applications. The TMV virion is a rigid rod
consisting of about 2,130 identical coat protein subunits stacked in
a helix around a single strand of plus sense RNA, forming a 4 nm
diameter channel through the 300 nm long virion axis. Properties
of the TMV system that make it particularly useful as a self-
assembling macromolecular template for nanomaterials include: 1)
its known three-dimensional structure [8]; 2) a wealth of
biophysical information on its self-assembly characteristics [9]; 3)
the availability of creating novel virus structures and surfaces via
established molecular techniques [10]; 4) a wide range of existing
coat protein variants with diverse assembly properties [11], and 5)
the ability to easily purify large quantities of virus and coat protein
from infected plants. TMV-structured metal and metal-oxide
nanowires have been synthesized using several techniques [12, 13],
transport properties have been studied [14], and potential
applications in nano-scale devices have been investigated through
proof-of-concept demonstrations [15].
Previous work with engineered mutations of the TMV has
resulted in enhanced particle coatings and templates that can be
readily integrated into microfabricated devices and has established
a novel patterning process. Efficient templates for metallic
coatings have been achieved through the introduction of one
(TMV-1cys) or two (TMV-2cys) cysteine residues within the coat
protein open reading frame. Cysteines are amino acids with thiol
groups that show enhanced metal binding properties based on
strong, covalent-like interactions. One and two-step electroless
plating methods have been used for the fabrication of TMV-2cys-
based wires coated with gold, silver and palladium clusters that
show more uniform coating compared to the wild-type virus [16].
Additionally, the rod-shaped viruses can be directionally attached
to various surfaces and coated to create high aspect ratio nickel,
cobalt and platinum materials (TMV-1cys). Alternative pathways
were explored for patterning the viral molecules in microfabricated
electrodes as well as controlled environments, utilizing nucleic
acid hybridization [17]. Recent work in our team has focused upon
the development of novel inorganic structures using the TMV and
their application in energy storage devices. A simple and versatile
approach for the selective patterning of both metal-coated and
uncoated TMV using lift-off processing has been developed [18].
The high aspect ratio of the coated TMV in addition to its
robustness was utilized in the development of high surface area
nickel-zinc [19] and Li-ion microbatteries [20, 21]. By the
integration of high aspect ratio biotemplated TMV scaffold in
electrode fabrication process, high surface area electrochemical
sensors can be realized improving the overall biosensing
Mental Health Applications
The medical management of mental health care is one of the
most debilitating and costly of all disorders. A major unmet need
is the ability to have an objective, real time analysis of the disorder
at the point-of-care. Schizophrenia is a common mental health
disorder, has high social and economic impact, and manifests early
mostly during adolescence and early adulthood. It is frequently
preceded by premorbid pattern of rather unspecific but
nevertheless handicapping symptoms that may be present for
several years before clinical manifestation. Schizophrenia is a
complex disorder involving difficulties with reality distortion,
cognitive impairments, and work and social dysfunction. Often, it
is also associated with symptoms of moodiness and anxiety. Once
diagnosed, patients need to remain on antipsychotic medications
lifelong. One of the biggest challenges of treatment is that many
people discontinue their treatment which can lead to relapse and
rehospitalizations, having a major impact on patient and society
healthcare costs [22, 23]. Finding a method for continually
monitoring patient status would allow for psychiatrists to more
effectively treat these mental disorders.
Over the past few years, genetic analysis has found a strong
relation between the gene encoding for Neuregulin-1 (NRG1) and
schizophrenia [24]. Studies have obtained supporting evidence for
NRG1 as a candidate gene for the disorder [25]. Moreover, the
identification of NRG1 receptor ErbB4 as an additional candidate
risk gene for schizophrenia strongly suggests that this signaling
pathway participates in the pathophysiology of the disorder [26].
By monitoring NRG1 concentration during various stages of
schizophrenia, mental health care management can be studied and
Microfluidic lab-on-a-chip (LOC) microsystems provide
numerous advantages in clinical diagnostics, environmental
monitoring and biomedical research fields. These translational
technologies hold potential to improve upon the resolution,
regulation, sensitivity, flexibility, and cost-savings over more
traditional approaches, bringing bench top methods into the point-
of-care. By the integration of MEMS sensing devices with mental
health analysis, pre-clinical assessments and the overall chance of
success of personalized medical care at the point-of-care can be
significantly improved.
One of the challenges with miniaturized biosensing devices is
the high background signal and low signal-to-noise ratio that
decrease the performance of biosensors. By increasing the signal,
electrochemical biosensors can improve their bio-detection
efficiency resulting in higher sensitivity. Here, we used gold
planar square electrodes (20nm Cr/180nm Au, surface area = 0.49
cm2) that were patterned onto a silicon dioxide substrate via DC
sputtering and were realized using both wet etching and lift-off
techniques. Virus modification of the electrode surface was
performed to enhance the total surface area. Fabrication was
carried out by submerging the electrodes in a solution of rod-
shaped 300 x 18 nm TMV vertical viruses in 0.1M phosphate
buffer (pH 7) for 18 hours, allowing for self-assembly of the virus
particles on the microfabricated planar gold electrodes via the
previously mentioned cysteine residues. Following TMV self-
assembly, nickel was electroless deposited for 5 minutes [19].
Sequentially, gold was electroless plated in a gold plating bath
(0.007M KAu(CN)2, 1.4M NH4Cl, 0.2M Sodium citrate, and 1M
NaH2PO2. pH 7.0-7.5) for 45 minutes at 90ºC to form a conformal
gold coating on the virus particles. Fig. 1 shows SEM images of
the surface of the electrode modified with nickel-coated TMV-1cys
after gold deposition (TMV/Ni/Au modified electrode). TMV-
1cys were observed to attach vertically on the electrode surface. A
TEM image of the nanocomposite virus particle (Fig. 2) shows
approximately 67 nm nickel and 46 nm gold coatings. The thin
films of the nickel and the gold maintain the high aspect ratio of
the TMV scaffold after plating, increasing the electrochemically
active surface area of the electrode.
coated with
nickel and gold
Figure 1: Self-assembled TMV-1cys molecules coated with nickel
and gold layers on the surface of planar electrode. (A) Cross
section schematic. (B) Scanning electron micrograph.
(~46 nm)
(~67 nm)
TMV core
(~18 nm)
Figure 2: (A) Schematic of the TMV coatings. (B) Transmission
electron microscopy analysis of the TMV-1cys coated with nickel
and gold layers with EDS profiles of nickel (pink / dark gray) and
gold (orange / light gray).
The modified electrodes were electrochemically characterized
using cyclic voltammetry (CHI660D single channel potentiostat
from CH Instruments, Austin, TX. Commercial Ag/AgCl reference
electrode. Pt wire counter electrode) in the presence of a redox
couple 5mM ferrocyanide, 5mM ferricyanide, 10mM phosphate
buffers saline (PBS) solution. Fig. 3 illustrates the increased signal
from the modified electrodes compared to unmodified electrode
with cyclic voltammograms of the generated electrochemical
reduction and oxidation reactions. The electrodes produced
reversible nernstian characteristics where the TMV/Ni/Au
modified electrode generated the highest electrochemical current
(8-fold higher oxidation peak current in comparison with the
unmodified planar electrode) due to the high active surface area.
The oxidation and the reduction peaks generated by the
TMV/Ni/Au modified electrodes varied in compare to the other
types of electrodes. This variation is may be due to increase with
the uncompensated resistance in the new high aspect ratio
electrochemical interface. Furthermore, the potential presence of
nickel uncoated with gold on the TMV scaffold may result in
changes with the standard reduction potential of the redox couple.
The increased electrochemical activity of the Ni/Au modified
electrode compared to unmodified electrode may be due high
surface roughness resulted by the nickel and the gold electroless
plating. Furthermore, the TMV modified electrode impeded the
generated electrochemical current that was attributed to the non-
conductive virus coating on the electrode surface.
The effective surface area of the unmodified and the modified
electrodes were calculated from Bard and Faulkner [27]:
Ipeak = 0.4463(F3/RT)n3/2AD1/2C*v1/2 (1)
Where F [C mol-1] is the Faraday constant, R [J mol-1 K-1] is the
gas constant, T [K] is the temperature, n is the stoichiometric
number of electrons involved in an electrode reaction, A [cm2] is
the effective surface area of the electrode, D [cm2 s-1] is the
diffusion coefficient of the electro-active species, C* [mol cm-3] is
the bulk concentration of the electro-active species, v [V s-1] is the
linear potential scan rate, and Ipeak [A] is the peak current.
Effective surface area calculations demonstrated that TMV/Ni/Au
resulted in the highest area (Table 1), a characteristic important for
the high performance of electrochemical sensors due to the surface
area limited reaction kinetics.
0.9 0.6 0.3 0.0 -0.3
I (mA)
E vs. Ag/AgCl (V)
Unmodified electrode
Electrode modified with TMV
Electrode modified with Ni/Au
Electrode modified with TMV/Ni/Au
-0.5 0.0 0.5 1.0
I (mA)
E vs. Ag/AgCl (V)
E vs. Ag/AgCl (V)
I (mA)
I (mA)
E vs. Ag/AgCl (V)
Figure 3: Cyclic voltammograms of the planar electrode modified
with either the TMV, the Ni/Au electroless deposition, or both.
Inset shows only the unmodified and the TMV modified electrodes.
Table 1: Measured effective surface area and bio-detection
efficiency analysis for the unmodified and the modified electrodes.
surface area
In this study the target NRG1 polymorphism ssDNA
(SNP8NRG243177) bio-detection efficiency was
electrochemically analyzed using thiolated ssDNA probe to NRG1
assembled on the high surface area TMV/Ni/Au modified
electrode. In short, electrodes were incubated in a solution
containing 10 mM PBS, 100 mM NaCl, 10 µM Tris (2-
carboxyethyl) phosphine (TCEP) and 1 µM probe ssDNA for 3
hour followed by rinsing with PBS. Afterwards, the electrodes
were incubated for 24 hour in PBS solution containing 1 mM of 6-
mercapto-1-hexanol (MCH). MCH is used to passivate any
exposed regions on the surface to reduce non-specific binding
during DNA hybridization. Incubation with either the non-
complementary or the target sequences was performed in a 4x
saline sodium citrate (SSC) buffer containing 1 µM of the target
DNA for 1 hour.
Biosensing performance was studied with cyclic voltammetry
in the presence of the previously described redox
ferrocyanide/ferricyanide solution (Fig. 4). All electrodes
demonstrated reversible nernstian characteristics in the presence of
complementary NRG1 target and non-complementary ssDNA.
Moreover, the TMV/Ni/Au modified electrode demonstrated the
largest current differentiation upon DNA hybridization. DNA
hybridization causes stronger electrostatic repulsion forces with the
negatively charged electro-active species in the electrolyte, hence
impeding the electrochemical reaction at the electrode [28]. Bio-
detection efficiency (ratio of oxidation peak current decrease
between non-complementary and complementary ssDNA) analysis
(Table 1) demonstrated 9.5-fold improved bio-detection
performance for the 3D TMV/Ni/Au modified electrode compared
to the unmodified electrode. This increase is not only due to the
higher effective surface area (factor of 8), but also due to the
inherent properties of nanomaterials improving biosensing
performance, e.g. augmented amount of probes functionalizing the
surface of the electrode and heightened target concentration near
the electrochemically reactive surface.
0.8 0.4 0.0 -0.4
0.8 0.4 0.0 -0.4
0.8 0.4 0.0 -0.4
0.8 0.4 0.0 -0.4
E vs. Ag/AgCl (V)
I (mA)
!"# !"$ !"% !"& !"! '!"& '!"%
)++ 45 ,)6789:
)58;'<8= 60:=:;>?7@)++4 5,
)/ 8=60:=:;>?7@)++ 45, )>?7-:>
Unmodified TMV modified
Ni/Au modified TMV/Ni/Au modified
Figure 4: Cyclic voltammograms of the (A) planar unmodified
electrode, (B) TMV modified electrode, (C) Ni/Au modified
electrode, and (D) TMV/Ni/Au modified electrode following
introduction of ssDNA NRG1 probe (black solid), non-
complementary ssDNA (red dashed), and complementary NRG1
target ssDNA (blue dashed-dot). Arrow indicates current reduction
upon DNA hybridization.
This work demonstrated the first utilization of TMV
molecules coated with nickel and gold as nano-scale biotemplates
assembled on an electrochemical biosensor for schizophrenia
analysis. The biotemplated TMV modified sensor generated
heightened electrochemical activity that improved the biosensing
performance. Given the large set of biological recognition events
that can be detected electrochemically and the innately high
compatibility of TMV-biotemplate integration with conventional
microfabrication technology, we believe this work has broad
applications in biological electrochemical sensing and
transduction. Specifically, we envision the utilization of TMV as a
high aspect ratio nano-scale 3D scaffold for high surface area
microelectrodes integrated in MEMS sensing devices improving
dramatically their performance. We believe TMV-biotemplated
LOC devices leverage electrochemical biosensing reactions that
will lead to the creation of new families of low-cost, rapid and
sensitive miniaturized biosensors for point-of-care analysis.
The authors acknowledge the Robert W. Deutsch Foundation
and National Science Foundation Emerging Frontiers in Research
and Innovation (EFRI) for financial support. The authors also
thank the Maryland Nanocenter and its Fablab for cleanroom
facility support. The authors grateful to Prof. Yosi Shacham-
Diamand and Prof. Alexandra Inberg from the Tel Aviv University
for the fruitful discussion on gold electroless deposition.
[1] A. Le Goff, M. Holzinger, and S. Cosnier, Enzymatic
Biosensors based on SWCNT-Conducting Polymer
Electrodes”, Analyst, 136, 1279 (2011).
[2] W. Siangproh, W. Dungchai, P. Rattanarat, and O.
Chailapakul, Nanoparticle-based Electrochemical Detection
in Conventional and Miniaturized Systems and Their
Bioanalytical Applications: A Review”, Analytica Chimica
Acta, 690, 10, (2011).
[3] R.H. Baughman, A.A. Zakhidov, and W.A. de Heer, “Carbon
Nanotubes - The Route Toward Applications”, Science, 297,
787 (2002).
[4] J. Wang, Carbon-Nanotube based Electrochemical
Biosensors: A Review”, Electroanalysis, 17, 7 (2005).
[5] J.-S. Ye, Y. Wen, W. De Zhang, L. Ming Gan, G.Q. Xu, and
F.-S. Sheu, Nonenzymatic Glucose Detection using Multi-
walled Carbon Nanotube Electrodes”, Electrochemistry
Communications, 6, 66 (2004).
[6] D.J. Evans, The Bionanoscience of Plant Viruses: Templates
and Synthons for New Materials”, Journal of Materials
Chemistry, 18, 3746 (2008).
[7] J.C. Smith, K.-B. Lee, Q. Wang, M.G. Finn, J.E. Johnson, M.
Mrksich, and C.A. Mirkin, Nanopatterning the
Chemospecific Immobilization of Cowpea Mosaic Virus
Capsid”, Nano Letters, 3, 883 (2003).
[8] K. Namba, R. Pattanayek, and G. Stubbs, Visualization of
Protein-Nucleic Acid Interactions in a Virus: Refined
Structure of Intact Tobacco Mosaic Virus at 2.9 Å Resolution
by X-ray Fiber Diffraction”, Journal of Molecular Biology,
208, 307 (1989).
[9] A.C. Durham, J.T. Finch, and A. Klug, States of
Aggregation of Tobacco Mosaic Virus Protein”, Nature New
Biology, 229, 37 (1971).
[10] J.N. Culver, W.O. Dawson, K. Plonk, and G. Stubbs, Site-
Directed Mutagenesis Confirms the Involvement of
Carboxylate Groups in the Disassembly of Tobacco Mosaic
Virus”, Virology, 206, 724 (1995).
[11] J.N. Culver, Tobacco Mosaic Virus Assembly and
Disassembly: Determinants in Pathogenicity and Resistance”,
Annual Review of Phytopathology, 40, 287 (2002).
[12] M. Knez, M. Sumser, A.M. Bittner, C. Wege, H. Jeske, T.P.
Martin, and K. Kern, “Spatially Selective Nucleation of Metal
Clusters on the Tobacco Mosaic Virus”, Advanced Functional
Materials, 14, 116 (2004).
[13] M. Knez, A. Kadri, C. Wege, U. Gösele, H. Jeske, and K.
Nielsch, “Atomic Layer Deposition on Biological
Macromolecules: Metal Oxide Coating of Tobacco Mosaic
Virus and Ferritin”, Nano Letters, 6, 1172 (2006).
[14] M. Knez, M. Sumser, A.M. Bittner, C. Wege, H. Jeske, S.
Kooi, M. Burghard, and K. Kern, Electrochemical
Modification of Individual Nano-Objects”, Journal of
Electroanalytical Chemistry, 522, 70 (2002).
[15] R.J. Tseng, C. Tsai, L. Ma, J. Ouyang, C.S. Ozkan, and Y.
Yang, Digital Memory Device based on Tobacco Mosaic
Virus Conjugated with Nanoparticles”, Nature
Nanotechnology, 1, 72 (2006).
[16] S.-Y. Lee, E. Royston, J.N. Culver, and M.T. Harris,
“Improved Metal Cluster Deposition on a Genetically
Engineered Tobacco Mosaic Virus Template”,
Nanotechnology, 16, S435 (2005).
[17] H. Yi, S. Nisar, S.-Y. Lee, M.A. Powers, W.E. Bentley, G.F.
Payne, R. Ghodssi, G.W. Rubloff, M.T. Harris, and J.N.
Culver, “Patterned Assembly of Genetically Modified Viral
Nanotemplates via Nucleic Acid Hybridization”, Nano
Letters, 5, 1931 (2005).
[18] K. Gerasopoulos, M. McCarthy, P. Banerjee, X. Fan, J.N.
Culver, and R. Ghodssi, “Biofabrication Methods for the
Patterned Assembly and Synthesis of Viral Nanotemplates”,
Nanotechnology, 21, 055304 (2010).
[19] K. Gerasopoulos, M. McCarthy, E. Royston, J.N. Culver, and
R. Ghodssi, “Nanostructured Nickel Electrodes using the
Tobacco mosaic virus for Microbattery Applications”, Journal
of Micromechanics and Microengineering, 18, 104003
[20] E. Pomerantseva, K. Gerasopoulos, X. Chen, G. Rubloff, and
R. Ghodssi, “Electrochemical Performance of the
Nanostructured Biotemplated V2O5 Cathode for Lithium-ion
Batteries”, Journal of Power Sources, 206, 282 (2012).
[21] K. Gerasopoulos, X. Chen, J. Culver, C. Wang, and R.
Ghodssi, “Self-assembled Ni/TiO2 Nanocomposite Anodes
Synthesized via Electroless Plating and Atomic Layer
Deposition on Biological Scaffolds”, Chemical
Communications, 46, 7349 (2010).
[22] R.A. Carlstedt, Handbook of Integrative Clinical Psychology,
Psychiatry, and Behavioral Medicine: Perspectives,
Practices, and Research, Springer Publishing Company, New
York, 2010.
[23] B.J. Sadock, H.I. Kaplan, and V.A. Sadock, Kaplan &
Sadock's Synopsis of Psychiatry: Behavioral
Sciences/Clinical Psychiatry, 10th ed., Lippincott Williams &
Wilkins, Philadelphia, 2007.
[24] B. Rico and O. Marín, “Neuregulin Signaling, Cortical
Circuitry Development and Schizophrenia”, Current Opinion
in Genetics & Development, 21, 262 (2011).
[25] P.J. Harrison and A.J. Law, “Neuregulin 1 and Schizophrenia:
Genetics, Gene Expression, and Neurobiology”, Biological
Psychiatry, 60, 132 (2006).
[26] T. Walsh, J.M. McClellan, S.E McCarthy, A.M. Addington,
S.B. Pierce, G.M. Cooper, A.S. Nord, M. Kusenda, D.
Malhotra, A. Bhandari et al., “Rare Structural Variants
Disrupt Multiple Genes in Neurodevelopmental Pathways in
Schizophrenia”, Science, 320, 539 (2008).
[27] A.J. Bard and L.R. Faulkner, Electrochemical Methods:
Fundamentals and Applications, John Wiley & Sons, New
York, 2001.
[28] E. Katz and I. Willner, “Probing Biomolecular Interactions at
Conductive and Semiconductive Surfaces by Impedance
Spectroscopy: Routes to Impedimetric Immunosensors, DNA-
Sensors, and Enzyme Biosensors”, Electroanalysis, 15, 913
*Reza Ghodssi, tel: +1-301-405-8158;
Hadar Ben-Yoav, tel: +1-301-405-2168;
... The modified probe showed a high surface area with strong current change on DNA hybridization, which lead to an 8-fold increase in signal and 9.5-fold enhancement in biosensing performance. 132 Coating VLPs on the surface of electrodes is a way to increase the electrode surface area, thus allowing for a higher electrochemical signal, decreased signal to noise ratio, and greater sensitivity. For example, a new impedance sensor was developed 133 by Zang et al. that applied FLAG-tagemodified TMV on an electrode surface by capillary action and surface evaporation for label-free antibody detection. ...
We report for the first time fabrication of nanostructured V2O5 thin film cathodes for lithium-ion batteries using Tobacco mosaic virus (TMV) particles as biological templates. TMV-templated V2O5 electrodes showed enhanced electrochemical performance compared to electrodes with a planar configuration demonstrating high specific capacity, excellent rate capability and cycling stability. A specific capacity of 12 μAh cm−2 was achieved for the TMV-templated electrode with a V2O5 layer thickness of ∼30 nm, which is 7–8 times higher than the specific capacity of planar V2O5 electrodes of the same thickness. Higher areal specific capacities are achievable by increasing active battery material loading: electrodes with twice higher V2O5 loading delivered capacities of ∼25 μAh cm−2. Development of the cathode is an important step towards the fabrication of rechargeable lithium-ion batteries with superior virus-templated electrodes for high performance electrochemical energy storage.
The electrocatalytic oxidation of glucose in alkaline medium directly at well-aligned multi-wall carbon nanotubes (MWNTs) electrodes has been investigated in the present study. Compared to glassy carbon electrode, a substantial (+400 mV) decrease in the overvoltage of the glucose oxidation reaction was observed at MWNTs electrodes with oxidation starting at ca. +0.10 V (vs. 3 M KCl–Ag|AgCl). The electrocatalytic effect is mainly attributed to carbon nanotubes with possible minor contributions from the Co catalysts present on the Ta substrate. At an applied potential of +0.20 V, MWNTs electrodes give a high and reproducible sensitivity of 4.36 μA cm−2 mM−1 in the presence of high concentration of chloride ion. The well-aligned MWNTs electrode thus allows highly sensitive, low-potential, stable, and fast amperometric sensing of glucose, promising for the development of nonenzymatic glucose sensors.
At the interface of chemistry, biology, physics, medicine, engineering and materials science sits the field of bionanoscience; this involves the exploitation of biomaterials, devices or methodologies on the nanoscale. One sub-field of bionanoscience explores the exploitation of biomaterials in the fabrication of new nano-materials and/or -devices. This article shows how plant viruses are being used as templates for the production of new materials and how they are being used as building blocks in the construction of new assemblies by a bottom-up approach.
The development of nanostructured nickel–zinc microbatteries utilizing the Tobacco mosaic virus (TMV) is presented in this paper. The TMV is a high aspect ratio cylindrical plant virus which has been used to increase the active electrode area in MEMS-fabricated batteries. Genetically modifying the virus to display multiple metal binding sites allows for electroless nickel deposition and self-assembly of these nanostructures onto gold surfaces. This work focuses on integrating the TMV deposition and coating process into standard MEMS fabrication techniques as well as characterizing nickel–zinc microbatteries based on this technology. Using a microfluidic packaging scheme, devices with and without TMV structures have been characterized. The TMV modified devices demonstrated charge–discharge operation up to 30 cycles reaching a capacity of 4.45 µAh cm −2 and exhibited a six-fold increase in capacity during the initial cycle compared to planar electrode geometries. The effect of the electrode gap has been investigated, and a two-fold increase in capacity is observed for an approximately equivalent decrease in electrode spacing.
This paper presents a flexible approach for using Dip Pen Nanolithography (DPN) to nanopattern mixed monolayers for the selective immobilization of bioassemblies. DPN was used with a binary inksconsisting of a symmetric 11-mercaptoundecyl-penta(ethylene glycol) disulfide and a mixed disulfide substituted with one maleimide groupsto pattern nanoscale features that present functional groups for the chemospecific immobilization of cysteine-labeled biomolecules. This strategy was applied to the chemospecific immobilization of cysteine mutant cowpea mosaic virus capsid particles (cys-VCPs). The combination of DPN for defining nanopatterns and surface chemistries for controlling the immobilization of ligands will be broadly useful in basic and applied biology.
This review addresses recent advances in carbon-nanotubes (CNT) based electrochemical biosensors. The unique chemical and physical properties of CNT have paved the way to new and improved sensing devices, in general, and electrochemical biosensors, in particular. CNT-based electrochemical transducers offer substantial improvements in the performance of amperometric enzyme electrodes, immunosensors and nucleic-acid sensing devices. The greatly enhanced electrochemical reactivity of hydrogen peroxide and NADH at CNT-modified electrodes makes these nanomaterials extremely attractive for numerous oxidase-and dehydrogenase-based amperometric biosensors. Aligned CNT "forests" can act as molecular wires to allow efficient electron transfer between the underlying electrode and the redox centers of enzymes. Bioaffinity devices utilizing enzyme tags can greatly benefit from the enhanced response of the biocatalytic-reaction product at the CNT transducer and from CNT amplification platforms carrying multiple tags. Common designs of CNT-based biosensors are discussed, along with practical examples of such devices. The successful realization of CNT-based biosensors requires proper control of their chemical and physical properties, as well as their functionalization and surface immobilization.
Impedance spectroscopy is a rapidly developing electrochemical technique for the characterization of biomaterial-functionalized electrodes and biocatalytic transformations at electrode surfaces, and specifically for the transduction of biosensing events at electrodes or field-effect transistor devices. The immobilization of biomaterials, e.g., enzymes, antigens/antibodies or DNA on electrodes or semiconductor surfaces alters the capacitance and interfacial electron transfer resistance of the conductive or semiconductive electrodes. Impedance spectroscopy allows analysis of interfacial changes originating from biorecognition events at electrode surfaces. Kinetics and mechanisms of electron transfer processes corresponding to biocatalytic reactions occurring at modified electrodes can be also derived from Faradaic impedance spectroscopy. Different immunosensors that use impedance measurements for the transduction of antigen-antibody complex formation on electronic transducers were developed. Similarly, DNA biosensors using impedance measurements as readout signals were developed. Amplified detection of the analyte DNA using Faradaic impedance spectroscopy was accomplished by the coupling of functionalized liposomes or by the association of biocatalytic conjugates to the sensing interface providing biocatalyzed precipitation of an insoluble product on the electrodes. The amplified detections of viral DNA and single-base mismatches in DNA were accomplished by similar methods. The changes of interfacial features of gate surfaces of field-effect transistors (FET) upon the formation of antigen-antibody complexes or assembly of protein arrays were probed by impedance measurements and specifically by transconductance measurements. Impedance spectroscopy was also applied to characterize enzyme-based biosensors. The reconstitution of apo-enzymes on cofactor-functionalized electrodes and the formation of cofactor-enzyme affinity complexes on electrodes were probed by Faradaic impedance spectroscopy. Also biocatalyzed reactions occurring on electrode surfaces were analyzed by impedance spectroscopy. The theoretical background of the different methods and their practical applications in analytical procedures were outlined in this article.
Tobacco mosaic virus (TMV) is a very stable nanotube complex of a helical RNA and 2130 coat proteins. The special shape makes it an interesting nano-object, especially as a template for chemical reactions. Here we use TMV as a chemically functionalized template for binding metal ions. Different chemical groups of the coat protein can be used as ligands or to electrostatically bind metal ions. Following this activation step, chemical reduction and electroless plating produces metal clusters of several nanometers in diameter. The clusters are attached to the virion without destroying its structure. Gold clusters generated from an ascorbic acid bath bind to the exterior surface as well as to the central channel of the hollow tube. Very high selectivity is reached by tuning PdII and PtII activations with phosphate: When TMV is first activated with PdII, and thereafter metallized with a nickel–phosphinate bath, 3 nm nickel clusters grow in the central channel; when TMV from phosphate-buffered suspensions is employed, larger nickel clusters grow on the exterior surface. Phosphate buffers have to be avoided when 3 nm nickel and cobalt wires of several 100 nm in length are synthesized from borane-based baths inside the TMV channel. The results are discussed with respect to the inorganic complex chemistry of precursor molecules and the distribution of binding sites in TMV.