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Conspectus Hydrogen gas (H2) is odorless and flammable at concentrations above 4% (v/v) in air. Sensors capable of detecting it rapidly at lower concentrations are needed to "sniff" for leaked H2 wherever it is used. Electrical H2 sensors are attractive because of their simplicity and low cost: Such sensors consist of a metal (usually palladium, Pd) resistor. Exposure to H2 causes a resistance increase, as Pd metal is converted into more resistive palladium hydride (PdHx). Sensors based upon Pd alloy films, developed in the early 1990s, were both too slow and too insensitive to meet the requirements of H2 safety sensing. In this Account, we describe the development of H2 sensors that are based upon electrodeposited nanomaterials. This story begins with the rise to prominence of nanowire-based sensors in 2001 and our demonstration that year of the first nanowire-based H2 sensor. The Pd nanowires used in these experiments were prepared by electrodepositing Pd at linear step-edge defects on a graphite electrode surface. In 2005, lithographically patterned nanowire electrodeposition (LPNE) provided the capability to pattern single Pd nanowires on dielectrics using electrodeposition. LPNE also provided control over the nanowire thickness (±1 nm) and width (±10-15%). Using single Pd nanowires, it was demonstrated in 2010 that smaller nanowires responded more rapidly to H2 exposure. Heating the nanowire using Joule self-heating (2010) also dramatically accelerated sensor response and recovery, leading to the conclusion that thermally activated H2 chemisorption and desorption of H2 were rate-limiting steps in sensor response to and recovery from H2 exposure. Platinum (Pt) nanowires, studied in 2012, showed an inverted resistance response to H2 exposure, that is, the resistance of Pt nanowires decreased instead of increased upon H2 exposure. H2 dissociatively chemisorbs at a Pt surface to form Pt-H, but in contrast to Pd, it stays on the Pt surface. Pt nanowires showed a faster response to H2 exposure than Pd nanowires operating at the same elevated temperature, but they had a surprising disadvantage: The resistance change observed for Pt nanowires was exactly the same for all H2 concentrations. Electron surface scattering was implicated in the mechanism for these sensors. Work on Pt nanowires lead in 2015 to the preparation of Pd nanowires that were electrochemically modified with thin Pt layers (Pd@Pt nanowires). Relative to Pd nanowires, Pt@Pd nanowires showed accelerated response and recovery to H2 while retaining the same high sensitivity to H2 concentration seen for sensors based upon pure Pd nanowires. A new chapter in H2 sensing (2017) involves the replacement of metal nanowires with carbon nanotube ropes decorated with electrodeposited Pd nanoparticles (NPs). Even higher sensitivity and faster sensor response and recovery are enabled by this sensor architecture. Sensor properties are strongly dependent on the size and size monodispersity of the Pd NPs, with smaller NPs yielding higher sensitivity and more rapid response/recovery. We hope the lessons learned from this science over 15 years will catalyze the development of sensors based upon electrodeposited nanomaterials for gases other than H2. [ABSTRACT FROM AUTHOR]

The article discusses phage display mechanisms and phage-based biosensors. Topics include the: advantages of using the bacteriophage called filamentous phage; manipulation of polypeptides on virus particle surfaces; selection of a polypeptide receptor and affinity screening; methods for immobilizing filamentous phage on biosensor surfaces; antibody binding on a covalent virus surface; prostate-specific membrane antigen--a cancer biomarker; biosensor transducer--electrochemical impedance spectroscopy; and binding of target molecules to macroscopic gold electrodes.

Examines the imaging of silver nanoparticles on graphite basal plane surfaces. Use of electrostatic force microscopy; Determination of the lateral resolution of the images; Accumulation of a positive charge on the silver particles.

Examines the deposition of metal nanostructures onto silicon (111) surfaces by field evaporation. Induction of metal field emission by the application of tip-negative bias pulses; Use of scanning tunneling microscope; Confirmation of the metallic composition of the structures.

Reports that pulse-induced nanometer-scale lithography has been performed on graphite surfaces that were in contact with pure water or other organic liquids. Observation of reproducible control over the pit diameter in aqueous solutions.

Procedures are described for insulating metal scanning tunneling microscope (STM) tips with either glass or polymer coatings. In solutions containing 0.10 M of a reversible redox couple, Fe(CN)-3/-46 , the faradaic limiting current to polymer coated tips was 200–500 pA and that for glass coated tips was <10 pA. For polymer insulated tips, steady-state currents of 10–100 pA were observed at tip-sample displacements less than 0.3 μm. The suppression of faradaic current achieved by these coating procedures enabled the collection of the first atomic resolution STM images of highly ordered pyrolytic graphite electrodes in contact with redox-active electrolytes. Preliminary data for the in situ electrochemical characterization of these tips are also discussed. [ABSTRACT FROM AUTHOR]

The article informs that electrochemistry has found a new move for controlling the power of hydrogen of a solution by reversible reduction and oxidation of an electrode coating formed from three-dimensional hybrid aniline gold nanoparticles. A variety of electrodes were coated with molecular monolayers and intensively studied to elucidate chargetransport mechanism in these materials. The power of hydrogen-switching amplitude is large enough to influence the activity of many enzymes and the association and dissociation reactions are controlled by the electrochemically induced power of hydrogen changes to the solution.

[Display omitted] Electrodeposition and electropolymerization have emerged as versatile tools for the fabrication of chemical and biosensors. The literature in this area, published since 2017, is the main focus of this review. Electropolymerization has played a particularly prominent role in sensor development since its discovery in 1980 by Diaz at IBM. The ability to entrain receptors such as antibodies, engineered virus particles, and metal chelating agents into a conductive polymer sensing element during electropolymerization has proven to be a powerful means of preparing chemiresistors for a variety of analyses. Electrodeposition has also been used to prepare nanostructured metal indicator microelectrodes, enabling of a new modality for transducing biosensors. Electrodeposited metal nanowires have formed the basis for rapid and sensitive sensors for hydrogen gas. Electrodeposition has also been exploited as a powerful means for amplifying weak biosensor signals, extending their dynamic range. Opportunities for the application of electrodeposition and electropolymerization for chemical and biological sensor fabrication and function are discussed. [ABSTRACT FROM AUTHOR]

Wafer scale (cm2) arrays and networks of nanochannels were created in polydimethylsioxane (PDMS) from a surface pattern of electrodeposited gold nanowires in a master-replica process and characterized with scanning electron microscopy (SEM), atomic force microscopy (AFM), and fluorescence imaging measurements. Patterns of gold nanowires with cross-sectional dimensions as small as 50 nm in hnight and in, tins in width were prepared on silica subsirates using the process of lithographically patterned nanowire electrodeposition (LPNE). Thtie nanowire patterns were then employed at masters for the fabrication of inverse replica nanochannels in a special formulation of PDMS. SEM and AFM measurements verified a linear correlation between the widths and heights of the nanowires and nanochannels over a range of 50 to 500 nm. The PDMS replica was then oxygen plasma-bonded to a glass substrate in order to create a linear array of nanofluidic channels (up to 1 mm in length) filled with solutions of either fluorescent dye or 20 nm diameter fluorescent polymer nanoparticles. Nanochannel continuity and a 99% fill success rate was determined from the fluorescence imaging measurements, and the electrophoretic injection of both dye and nanoparticles in the nanochannel arrays was also demonstrated. Employing a double LPNE fabrication method, this master-replica process was also used to create a large two-dimensional network of crossed nanofluidic channels. [ABSTRACT FROM AUTHOR]

The electrical resistance, R, of an array of 30 palladium nanowires is used to detect the concentration of dissolved hydrogen gas (H2) in transformer oil over the temperature range from 21 to 70°C. The palladium nanowire array (PdNWA), consisting of Pd nanowires 100 nm (width), 20 nm (height), and ∼100 μm (length), was prepared using the lithographically patterned nanowire electrodeposition (LPNE) method. The R of the PdNWA increased by up to 8% upon exposure to dissolved H2 at concentrations above 1.0 ppm and up to 2940 ppm at 21 °C. The measured limit-of-detection for dissolved H2 was 1.0 ppm at 21 °C and 1.6 ppm at 70 °C. The increase in resistance induced by exposure to H2 was linear with [H2]oil1/2 across this concentration range. A PdNWA sensor operating in flowing transformer oil has functioned continuously for 150 days. [ABSTRACT FROM AUTHOR]

A protocol is described for forming reconnectable sub-5 nm nanogaps in single ultralong (>100 μm) gold nanowires fabricated by lithographically patterned nanowire electrodeposition (LPNE). During an initial computer-controlled electromigration process, gold nanowires with a rectangular cross-section were transformed by the formation of a constriction at a single point along the 250 μm length of the nanowire, and within this constriction a nanogap of width <5 nm. After this initial nanogap formation, 42% (19 of 45) of the gaps could be reconnected by applying a voltage ramp, restoring the electrical resistance of the original nanowire to within 10%. The voltage threshold for nanogap reconnection was narrowly distributed across multiple wires and nanogaps and in the range from 2 to 3 V. Using voltage programming, it was possible to cycle between the open and closed states for some nanogaps more than 100 times. We propose that the mechanism for reconnection involves the field evaporation of gold, qualitatively as observed previously for metal transfer from the tip of a scanning tunneling microscope. [ABSTRACT FROM AUTHOR]

Reports on the preparation of metallic molybdenum nanowires by electrodeposition. Uniformity of the hemicylindrical wires; Correlation of the mean wire diameter to the square root of the electrolysis time; Similarity of the conductivity and resiliency of the embedded wires to those of bulk molybdenum.

Investigates the time evolution of the topography of an oxidized silicon (Si) surface immersed in an aqueous 40% NH[sub 4]F etching solution. Use of scanning tunneling microscopy; Production of Si pillars at shielded surface locations; Suppression of gas evolution and roughening by reductant addition.

The virus bioresistor (VBR) is a chemiresistor that directly transfers information from virus particles to an electrical circuit. Specifically, the VBR enables the label-free detection of a target protein that is recognized and bound by filamentous M13 virus particles, each with dimensions of 6 nm (w) × 1 μm (l), entrained in an ultrathin (~250 nm) composite virus-polymer resistor. Signal produced by the specific binding of virus to target molecules is monitored using the electrical impedance of the VBR: The VBR presents a complex impedance that is modeled by an equivalent circuit containing just three circuit elements: a solution resistance (Rsoln), a channel resistance (RVBR), and an interfacial capacitance (CVBR). The value of RVBR, measured across 5 orders of magnitude in frequency, is increased by the specific recognition and binding of a target protein to the virus particles in the resistor, producing a signal ΔRVBR. The VBR concept is demonstrated using a model system in which human serum albumin (HSA, 66 kDa) is detected in a phosphate buffer solution. The VBR cleanly discriminates between a change in the electrical resistance of the buffer, measured by Rsoln, and selective binding of HSA to virus particles, measured by RVBR. The ΔRVBR induced by HSA binding is as high as 200 Ω, contributing to low sensor-to-sensor coefficients-of-variation (<15%) across the entire calibration curve for HSA from 7.5 nM to 900 nM. The response time for the VBR is 3-30 s. [ABSTRACT FROM AUTHOR]

The influence of hexamethylenetetraamine (HMTA) on the morphology of δ-MnO2 and its properties for electrical energy storage are investigated, specifically for ultrathick δ-MnO2 layers in the micron scale. Planar arrays of gold@δ-MnO2, core@shell nanowires, were prepared by electrodeposition with and without the HMTA and their electrochemical properties were evaluated. HMTA alters the MnO2 in three ways: First, it creates a more open morphology for the MnO2 coating, characterized by "petals" with a thickness of 6 to 9 nm, rather than much thinner δ-MnO2 sheets seen in the absence of HMTA. Second, the electronic conductivity of the δ-MnO2 is increased by an order of magnitude. Third, δ-MnO2 prepared in HMTA shows a (001) interlayer spacing that is expanded by ≈30% possibly accelerating Li transport. The net effect of "HTMA doping" is to dramatically improve high rate performance, culminating in an increase in the specific capacity for the thickest MnO2 shells examined here by a factor of 15 at 100 mV/s. [ABSTRACT FROM AUTHOR]

The label-free detection of human serum albumin (HSA) in aqueous buffer is demonstrated using a simple, monolithic, two-electrode electrochemical biosensor. In this device, both millimeter-scale electrodes are coated with a thin layer of a composite containing M13 virus particles and the electronically conductive polymer poly(3,4-ethylenedioxy thiophene) or PEDOT. These virus particles, engineered to selectively bind HSA, serve as receptors in this biosensor. The resistance component of the electrical impedance, Zre, measured between these two electrodes provides electrical transduction of HSA binding to the virus-PEDOT film. The analysis of sample volumes as small as 50 μL is made possible using a microfluidic cell. Upon exposure to HSA, virus-PEDOT films show a prompt increase in Zre within 5 s and a stable Zre signal within 15 min. HSA concentrations in the range from 100 nM to 5 μM are detectable. Sensor-to-sensor reproducibility of the HSA measurement is characterized by a coefficient-of-variance (COV) ranging from 2% to 8% across this entire concentration range. In addition, virus-PEDOT sensors successfully detected HSA in synthetic urine solutions. [ABSTRACT FROM AUTHOR]

Arrays of nanowires of an electronically conductive polymeric affinity medium tailored to the detection of Fe(III) are prepared, and their properties for detecting Fe(III) are evaluated. This polymeric affinity medium consists of poly(3,4-ethylenedioxythiophene) (PEDOT) into which an iron chelator, deferoxamine (DFA), has been doped during the polymerization process. PEDOT-DFA nanowires are potentiostatically deposited from a solution containing both EDOT and DFA using lithographically patterned nanowire electrodeposition (LPNE). The through-nanowire electrical resistance of PEDOT-DFA nanowires is measured as a function of the Fe(III) concentration. In parallel with measurements on PEDOT-DFA nanowire arrays, the electrochemical impedance of PEDOT-DFA films is characterized as a function of the Fe(III) concentration and the frequency of the impedance measurement in order to better understand the mechanism of transduction. PEDOT-DFA nanowires detect Fe(III) from 10-4 to 10-8 M with a limit of detection of 300 pM (calculated) and 10 nM (measured). [ABSTRACT FROM AUTHOR]

The sensitive detection of cancer biomarkers in urine could revolutionize cancer diagnosis and treatment. Such detectors must be inexpensive, easy to interpret, and sensitive. This report describes a bioaffinity matrix of viruses integrated into PEDOT films for electrochemical sensing of prostate-specific membrane antigen (PSMA), a prostate cancer biomarker. High sensitivity to PSMA resulted from synergistic action by two different ligands to PSMA on the same phage particle. One ligand was genetically encoded, and the secondary recognition ligand was chemically synthesized to wrap around the phage. The dual ligands result in a bidentate binder with high-copy, dense ligand display for enhanced PSMA detection through a chelate-based avidity effect. Biosensing with virus–PEDOT films provides a 100 pM limit of detection for PSMA in synthetic urine without requiring enzymatic or other amplification. [ABSTRACT FROM AUTHOR]

Electroluminescent (EL) metal-semiconductor-metal nanojunctionsare prepared by electrodepositing nanocrystalline cadmium selenide(nc-CdSe) within ∼250 nm gold (Au) nanogapsprepared by focused ion beam milling. The electrodeposition of nc-CdSe is carried out at two temperatures: 20 °C (“cold”)and 75 °C (“hot”), producing mean grain diametersof 6 ± 1 nm and 11 ± 2 nm, respectively, for the nc-CdSe. Light-emitting nanojunctions (LEnJs) prepared atboth temperatures show a low threshold voltage for light emissionof <2 V; just above the 1.74 eV bandgap of CdSe. The EL intensityincreases with the injection current and hot-deposited LEnJs produceda maximum EL intensity that is an order of magnitude higher than thecold-deposited LEnJs. Emitted photons are bimodal in energy with emissionnear the band gap of CdSe, and also at energies 200 meV below it;consistent with a mechanism of light emission involving the radiativerecombination of injected holes with electrons at both band-edge anddefect states. The quantum yield for “hot” electrodeposited nc-CdSe LEnJs is comparable to devices constructed fromsingle crystalline nanowires of CdSe, and the threshold voltage of1.9 (±0.1) V (cold) and 1.5 (±0.2) V (hot) is at the lowend of the range reported for CdSe nanowire based devices. [ABSTRACT FROM AUTHOR]

Virus-poly(3,4-ethylenedioxythiophene) (virus-PEDOT)biocompositefilms are prepared by electropolymerizing 3,4-ethylenedioxythiophene(EDOT) in aqueous electrolytes containing 12 mM LiClO4andthe bacteriophage M13. The concentration of virus in these solutions,[virus]soln, is varied from 3 to 15 nM. A quartz crystalmicrobalance is used to directly measure the total mass of the biocompositefilm during its electrodeposition. In combination with a measurementof the electrodeposition charge, the mass of the virus incorporatedinto the film is calculated. These data show that the concentrationof the M13 within the electropolymerized film, [virus]film, increases linearly with [virus]soln. The incorporationof virus particles into the PEDOT film from solution is efficient,resulting in a concentration ratio of [virus]film:[virus]soln≈ 450. Virus incorporation into the PEDOT causesroughening of the film topography that is observed using scanningelectron microscopy and atomic force microscopy (AFM). The electricalconductivity of the virus-PEDOT film, measured perpendicular to theplane of the film using conductive tip AFM, decreases linearly withvirus loading, from 270 μS/cm for pure PEDOT films to 50 μS/cmfor films containing 100 μM virus. The presence on the virussurface of displayed affinity peptides did not significantly influencethe efficiency of incorporation into virus-PEDOT biocomposite films. [ABSTRACT FROM AUTHOR]

We describe the fabrication of arrays of nanowires onglass inwhich a gold core nanowire is encapsulated within a hemicylindricalshell of manganese dioxide. Arrays of linear gold (Au) nanowires arefirst prepared on glass using the lithographically patterned nanowireelectrodeposition (LPNE) method. These Au nanowires have a rectangularcross-section with a width and height of ≈200 and 40 nm, respectively,and lengths in the 1 mm to 1 cm range. Au nanowires are then usedto deposit MnO2by potentiostatic electrooxidation fromMn2늉溶⨧, forming a conformal, hemicylindrical shellwith a controllable diameter ranging from 50 to 300 nm surroundingeach Au nanowire. This MnO2shell is δ-phase andmesoporous, as revealed by X-ray diffraction and Raman spectroscopy.Transmission electron microscopy (TEM) analysis reveals that the MnO2shell is mesoporous (mp-MnO2),consisting of a network of ≈2 nm fibrils. The specific capacitance, Csp, of arrays of gold:mp-MnO2nanowires is measured using cyclic voltammetry.For a mp-MnO2shell thickness of 68 ±3 nm, core:shell nanowires produce a Cspof 1020 ± 100 F/g at 5 mV/s and 450 ±70 F/g at 100 mV/s. The cycle stability of this Csp, however, is extremely limited inaqueous electrolyte, decaying by >90% in 100 scans, but after ovendrying and immersion in dry 1.0 M LiClO4, acetonitrile,dramatically improved cycle stability is achieved characterized bythe absence of Cspfadefor 1000 cycles at 100 mV/s. Core:shellnanowires exhibit true hybridenergy storage, as revealed by deconvolution of Cspinto insertion and noninsertion components. [ABSTRACT FROM AUTHOR]

The performance of a single platinum (Pt) nanowire fordetecting H2in air is reported. A Pt nanowire shows noresistance change upon exposure to H2in N2,but H2exposure in air causes a reversible resistance decreasefor H2concentrations above 10 ppm. The amplitude of theresistance change induced by H2exposure and the time rateof change of the nanowire resistance both increased with increasingtemperature from 298 to 550 K. This resistance decrease of the Ptnanowire in the presence of H2results from reduced electrondiffuse scattering at hydrogen-covered Pt surfaces as compared withoxygen-covered platinum surfaces, we hypothesize. The properties forthe detection of H2in air of single Pt and Pd nanowiresof similar size are compared in this study. Pt nanowires have a limit-of-detectionfor H2(LODH2) of 10 ppm; 3 ordersof magnitude lower than for Pd nanowires of the same size, as wellas a response time that is 1/100th of Pd for [H2] ≈1%. [ABSTRACT FROM AUTHOR]

We demonstrate the de novo fabrication of a biosensor, based upon virus-containing poly(3,4-ethylene-dioxythiophene) (PEDOT) nanowires, that detects prostate-specific membrane antigen (PSMA). This development process occurs in three phases: (1) isolation of a M13 virus with a displayed polypeptide receptor, from a library of ≈1011 phage-displayed peptides, which binds PSMA with high affinity and selectivity, (2) microfabrication of PEDOT nanowires that entrain these virus particles using the lithographically patterned nanowire electrodeposition (LPNE) method, and (3) electrical detection of the PSMA in high ionic strength (150 mM salt) media, including synthetic urine, using an array of virus-PEDOT nanowires with the electrical resistance of these nanowires for transduction. The electrical resistance of an array of these nanowires increases linearly with the PSMA concentration from 20 to 120 nM in high ionic strength phosphate-buffered fluoride (PBF) buffer, yielding a limit of detection (LOD) for PSMA of 56 nM. [ABSTRACT FROM AUTHOR]

The formation of a nanometer-scale chemically responsivejunction(CRJ) within a silver nanowire is described. A silver nanowire wasfirst prepared on glass using the lithographically patterned nanowireelectrodeposition method. A 1–5 nm gap was formed in this wireby electromigration. Finally, this gap was reconnected by applyinga voltage ramp to the nanowire resulting in the formation of a resistive,ohmic CRJ. Exposure of this CRJ-containing nanowire to ammonia (NH3) induced a rapid (<30 s) and reversible resistance changethat was as large as ΔR/R0= ()138% in 7% NH3and observable down to 500ppm NH3. Exposure to water vapor produced a weaker resistanceincrease of ΔR/R0,H2O= ()10–15% (for 2.3% water) while nitrogen dioxide (NO2) exposure induced a stronger concentration-normalized resistancedecrease of ΔR/R0,NO2= (−)10–15% (for 500 ppm NO2). The proposed mechanism of the resistance response for a CRJ, supportedby temperature-dependent measurements of the conductivity for CRJsand density functional theory calculations, is that semiconductingp-type AgxO is formed within the CRJ andthe binding of molecules to this AgxOmodulates its electrical resistance. [ABSTRACT FROM AUTHOR]

Composite films composed of poly(3,4-ethylenedioxythiophene), PEDOT, and the filamentous virus M13-K07 were prepared by electrooxidation of 3,4-ethylenedioxythiophene (EDOT) in aqueous solutions containing 8 nM of the virus at planar gold electrodes. These films were characterized using atomic force microscopy and scanning electron microscopy. The electrochemical impedance of virus-PEDOT films increases upon exposure to an antibody (p-Ab) that selectively binds to the M13 coat peptide. Exposure to p-Ab causes a shift in both real (ZRE) and imaginary (ZIM) impedance components across a broad range of frequencies from 50 Hz to 10 kHz. Within a narrower frequency range from 250 Hz to 5 kHz, the increase of the total impedance (Ztotal) with p-Ab concentration conforms to a Langmuir adsorption isotherm over the concentration range from from 6 to 66 nM, yielding a value for Kd = 16.9 nM at 1000 Hz. [ABSTRACT FROM AUTHOR]

The Seebeck coefficient, S, and the electrical conductivity, σ, of electrodeposited poly(3,4-ethylenedioxythiophene) (PEDOT) nanowires and thin films are reported. PEDOT nanowires were prepared by electropolymerizing 3,4-ethylenedioxythiophene (EDOT) in aqueous LiClO4 within a template prepared using the lithographically patterned nanowire electrodeposition (LPNE) process. These nanowires were 40−90 nm in thickness, 150−580 nm in width, and 200 μm in length. σ and S were measured from 190 K to 310 K by fabricating heaters and thermocouples on top of arrays of 750 PEDOT nanowires. Such PEDOT nanowire arrays consistently produced S values that were higher than those for PEDOT films: up to −122 μV/K (310 K) for nanowires and up to −57 μV/K (310 K) for films. The sample-to-sample variation in S for 14 samples of PEDOT nanowires and films, across a wide range of critical dimensions, is fully explained by variations in the carrier concentrations in accordance with the Mott equation. In spite of their higher |S| values, PEDOT nanowires also had higher σ than films, on average, because electron mobilities were greater in nanowires by a factor of 3. [ABSTRACT FROM AUTHOR]

Surface patterns of single-stranded DNA (ssDNA) consisting of nanoscale lines as thin as 40 nan were fabricated on polymer substrates for nanotechnology and bioaffinity sensing applications. Iarge scale arrays (with areas up to 4 cm2) of ssDNA "nanolines" were created on streptavidin-coated polymer (PDMS) surfaces by transferring biotinylated ssDNA from a master pattern of gold nanowires attached to a glass substrate. The gold nanowires were first formed on the glass substrate by the process of lithographically patterned nanowire electrodeposition (LPNE), and then "inked" with biotinylated ssDNA by hybridization adsorption to a thiolmodified ssDNA monolayer attached to the gold nanowires. The transferred ssDNA nanolines were capable of hybridizing with ssDNA from solution to form double-stranded DNA (dsDNA) patterns; a combination of fluorescence and atomic force microscopy (AFM) measurements were used to characterize the dsDNA nanoline arrays. To demonstrate the utility of these surices for biosensing, optical diffraction measurements of the hybridization adsorption of DNA-coated gold nanoparticles onto the ssDNA nanoline arrays were used to detect a specific target sequence of unlabeled ssDNA in solution. [ABSTRACT FROM AUTHOR]

Parallel arrays of either Au or Pd nanowires were fabricated on glass substrates via the electrochemical process of lithographically patterned nanowire electrodeposition (LPNE) and then characterized with scanning electron microscopy (SEM) and a series of optical dithaction measurements at 633 nm. Nanowires with widths varying from 25 to 150 tim were electrodeposited onto nanoscale Ni surfaces created by the undercut etching of a photoresist pattern on a planar substrate. With the use of a simple transmission grating geometry, up to 60 diffraction orders were observed from the nanowire gratings, with separate oscillatory intensity patterns appearing in the even and odd diffraction orders. The presence of these intensity oscillations is attributed to the LPNE array fabrication process, which creates arrays with alternating interwire spacings of distances Δ+A and d -Δ, where d =25 μm and the asymmetry Δ varied from 0 to 3.5 μm. The amount of asymmetry could be controlled by varying the LPNE undercut etching time during the creation of the nanoscale Ni surfaces. The Fourier transform of a mathematical model of the nanowire array was used to predict the diffraction intensity patterns and quantitatively determine A for any grating. Additional sensitivity and an expanded dithaction order range were obtained through the use of external reflection (ER) and total internal reflection (TIR) diffraction geometries. [ABSTRACT FROM AUTHOR]

Abstract: Cadmium sulfide (CdS) is a well-known wide bandgap semiconductor for solar cell applications. In this work we report an electrochemical/chemical method to prepare CdS thin films on gold (Au)-coated glass substrates. 10nm thick of titanium (Ti) film was first sputtered on glass surface to improve the adhesion between the subsequent sputtered Au film and the glass surface. Cadmium films were then electrochemically deposited on Au surface in an acidic solution with negative potential, and the obtained glass/Ti/Au/Cd samples were annealed in H2S atmosphere to convert Cd into CdS. XRD pattern of H2S-annealed Cd samples shows a hexagonal wurtzite phase in CdS with (002) as the preferential crystalline plane. Photovoltaic properties were clearly shown in hybrid heterojunctions of CdS and poly3-octylthiophene (P3OT) with Au as the top and the back metal contacts. [Copyright &y& Elsevier]

Electrochemical impedance spectroscopy is used to detect the binding of a 148.2 kDa antibody to a "covalent virus layer" (CVL) immobilized on a gold electrode. The CVL consisted of M13 phage particles covalently anchored to a 3 mm diameter gold disk electrode. The ability of the CVL to distinguish this antibody ("p-Ab") from a second, nonbinding antibody ("n-Ab") was evaluated as a function of the frequency and phase of the measured current relative to the applied voltage. The binding of p-Ab to the CYL was correlated with a change in the resistance, reducing it at low frequency (1-40 Hz) while increasing it at high frequency (2-140 kHz). The capacitance of the CYL was virtually uncorrelated with p-Ab binding. At both low and high frequency, the electrode resistance was linearly dependent on the p-Ab concentration from 20 to 266 nM but noise compromised the reproducibility of the p-Ab measurement at frequencies below 40 Hz. A "signal-to-noise" ratio for antibody detection was computed based upon the ratio between the measured resistance change upon p-Ab binding and the standard deviation of this change obtained from multiple measurements. In spite of the fact that the impedance change upon p-Ab binding in the low frequency domain was more than 100 times larger than that measured at high frequency, the S/N ratio at high frequency was higher and virtually independent of frequency from 4 to 140 kHz. Attempts to release p-Ab from the CVL using 0.05 M HCl, as previously described for mass-based detection, caused a loss of sensitivity that may be associated with a transition of these phage particles within the CVL from a linear to a coiled conformation at low pH. [ABSTRACT FROM AUTHOR]

M13 virus particles were covalently attached to a planar gold-coated quartz crystal microbalance (QCM) through reaction with a self-assembled monolayer of N-hydroxysuccinimide thioctic ester, followed by incorporation of the blocking agent bovine serum albumin. This immobilization chemistry produced a phage multilayer having a coverage equivalent to ≈6.5 close-packed monolayers of the virus. The properties of this "covalent virus surface" or CYS for the mass-based detection of a 148.2 kDa antibody were then evaluated in a phosphate buffer using a flow injection analysis system. The mass of the CYS increased with exposure to an antibody (p-Ab) known to bind the phage particles with high affinity. Bound p-Ab was removed by washing with 0.5 M HCl thereby regenerating the sensor surface. A calibration plot for p-Ab binding was constructed by repetitively exposing the surface to p-Ab at concentrations between 6.6 and 200 nM and HCI rinsing after each exposure. The mass-concentration relationship was linear with a sensitivity of 0.0 18 μg/(cm2 nM) and a limit of detection of 7 nM or 1.3 pmol. The CVS could be saturated with high doses of p-Ab enabling the determination that an average of ≈140 binding sites are available per M13 phage particle. Exposure of the CVS to a second, nonbinding antibody (n-Ab) did not cause a measurable mass change. These results demonstrate that the covalent virus layer is a rugged, selective, and sensitive means for carrying out mass-based biodetection. [ABSTRACT FROM AUTHOR]

A dense virus layer, readily tailored for recognition of essentially any biomarker, was covalently attached to a gold electrode surface through a self-assembled monolayer. The resistance of this ‘virus electrode’, ZRe, measured in the frequency range from 2 to 500 kHz in a salt-based pH 7.2 buffer, increased when the phage particles selectively bound either an antibody or prostate-specific membrane antigen (PSMA), a biomarker for prostate cancer. In contrast to prior results, we show the capacitive impedence of the virus electrode, Zlm, is both a noisier and a less sensitive indicator of this binding compared to ZRe. The specificity of antibody and PSMA binding, and the absence of nonspecific binding to the virus electrode, was confirmed using quartz crystal microbalance gravimetry. [ABSTRACT FROM AUTHOR]

Focuses on the fabrication of hydrogen sensors and hydrogen-activated switches from arrays of mesoscopic palladium wires. Preparation of palladium mesowire arrays by electrodeposition onto graphite surfaces; Impact of exposure to hydrogen gas on array resistance; Involvement of sensor response in the closing of nanoscopic gaps or break junctions in wire.

Single crystal ZnO nanowires are synthesized and configured as field-effect transistors. Photoluminescence and photoconductivity measurements show defect-related deep electronic states giving rise to green-red emission and absorption. Photocurrent temporal response shows that current decay time is significantly prolonged in vacuum due to a slower oxygen chemisorption process. The photoconductivity of ZnO nanowires is strongly polarization dependent. Collectively, these results demonstrate that ZnO nanowire is a remarkable optoelectronic material for nanoscale device applications. [ABSTRACT FROM AUTHOR]