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Surface patterns of single-stranded DNA (ssDNA) consisting of nanoscale lines as thin as 40 nm were fabricated on polymer substrates for nanotechnology and bioaffinity sensing applications. Large scale arrays (with areas up to 4 [cm.sup.2]) 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 thiol-modified 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 surfaces 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. 10.1021/ac100362u

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 diffraction measurements at 633 nm. Nanowires with widths varying from 25 to 150 nm were electrodeposited onto nanoscale Ni surfaces created by the undercut etching of a photo-resist 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 d +[DELTA] and d -[DELTA], where d = 25 [micro]m and the asymmetry A varied from 0 to 3.5 [micro]m. 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 diffraction order range were obtained through the use of external reflection (ER) and total internal reflection (TIR) diffraction geometries.

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 CVL 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 CVL 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 HCI, as previously described for massbased 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.

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 [approximately equal to] 6.5 close-packed monolayers of the virus. The properties of this 'covalent virus surface' or CVS 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 CVS 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 HCI 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 HCl rinsing after each exposure. The mass--concentration relationship was linear with a sensitivity of 0.018 [micro]g/([cm.sup.2] 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 [approximately equal to] 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.

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', [Z.sub.Re], 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, [Z.sub.Im], is both a noisier and a less sensitive indicator of this binding compared to [Z.sub.Re]. The specificity of antibody and PSMA binding, and the absence of nonspecific binding to the virus electrode, was confirmed using quartz crystal microbalance gravimetry.

Amorphous silica ribbons are prepared by hydrolyzing SiCl4 at highly oriented pyrolytic graphite surfaces on which water has condensed. Repetitive dosing of the HOPG surface in the human environment with SiCl4 produced nano- and microribbons with a height and width that increased in proportion to square root of the SiCl4 dose.

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]