Mangesh A. Bangar

Polyaniline nanowires-gold nanoparticles hybrid network based chemiresistive hydrogen sulfide sensor

We report a sensitive, selective, and fast responding room temperature chemiresistive sensor for hydrogen sulfide detection and quantification using polyaniline nanowires-gold nanoparticles hybrid network. The sensor was fabricated by facile electrochemical technique. Initially, polyaniline nanowires with a diameter of 250–320 nm bridging the gap between a pair of microfabricated gold electrodes were synthesized using templateless electrochemical polymerization using a two step galvanostatic technique. Polyaniline nanowires were then electrochemically functionalized with gold nanoparticles using cyclic voltammetry technique. These chemiresistive sensors show an excellent limit of detection (0.1 ppb), wide dynamic range (0.1–100 ppb), and very good selectivity and reproducibility.

Conducting polymer nanowires for chemiresistive and FET-based bio/chemical sensors

Conducting polymer nanostructures are emerging materials with tremendous potential for conductometric/field effect transistor (FET) bio/chemical sensors because of their chemical sensitivity and biocompatibility. Herein, we review recent developments in conducting polymer nanowire-based sensors and discuss the impact of several milestones and continuing challenges. Particular attention is given to device fabrication, nanostructure performance enhancement, and functionalization schemes. Several assembly and integration techniques have been developed for single nanowire devices but significant progress is still needed to improve scalability and manufacturability. Future work should focus on high throughput approaches that enable combinatorial screening of conducting polymer nanowires and heterogeneous, high density arrays of conducting polymer nanostructures, deterministically tailored for targeted analytes. The spatial and temporal resolution of conducting polymer nanowires is addressed along with the origin of the sensitivity enhancement. Functionalization routes add another degree of complexity for biosensors and are discussed in the context of nanosensor performance and device fabrication.

Label-Free Chemiresistive Immunosensors for Viruses

We report development, characterization, and testing of chemiresistive immunosensors based on single polypyrrole (Ppy) nanowire for highly sensitive, specific, label free, and direct detection of viruses. Bacteriophages T7 and MS2 were used as safe models for viruses for demonstration. Ppy nanowires were electrochemically polymerized into alumina template, and single nanowire based devices were assembled on a pair of gold electrodes by ac dielectrophoretic alignment and anchored using maskless electrodeposition. Anti-T7 or anti-MS2 antibodies were immobilized on single Ppy nanowire using EDC-NHS chemistry to fabricate nanobiosensor for the detection of corresponding bacteriophage. The biosensors showed excellent sensitivity with a lower detection limit of 10(-3) plaque forming unit (PFU) in 10 mM phosphate buffer, wide dynamic range and excellent selectivity. The immunosensors were successfully applied for the detection of phages in spiked untreated urban runoff water samples. The results show the potential of these sensors in health care, environmental monitoring, food safety and homeland security for sensitive, specific, rapid, and affordable detection of bioagents/pathogens.

Conducting polymer nanowire-based chemiresistive biosensor for the detection of bacterial spores.

Polypyrrole nanowires (Ppy) were assembled onto microfabricated gold interdigitated microelectrodes, to construct a chemiresistive biosensor for the detection of Bacillus globigii, used as simulant of the threatening bioterrorism agent B. anthracis. The fabricated biosensor showed good linear correlation (r(2)=0.992) for low spore concentrations ranging from 1 to 100 CFU (colony forming units)/mL, a concentration that could be used in a bioterrorism attack, with a response time of 30 min, after which the sensor was saturated. The performance of the biosensor was also assessed in the absence of anti-B. globigii antibodies and in the presence of non-target bacterial cells (Escherichia coli) showing no significant non-specific interactions. We believe that Ppy nanowires are a good platform for the detection and also quantification of large molecules and biocomponents even at low concentrations.

Maskless electrodeposited contact for conducting polymer nanowires

This letter reports a simple and scalable method to create mechanical joints and electrical contacts of conducting polymer nanowires to electrodes by selective maskless metal electrodeposition on electrodes. This is an attractive route for contacting nanowires as it bypasses harsh processing conditions of conventional methods. The electrodeposition conditions and initial resistance of the nanowires were found to have a significant impact on the selective maskless deposition. Different dopants were also investigated to understand the polymer reduction during cathodic deposition of metal. A single dodecyl sulfate doped polypyrrole nanowire with maskless electrodeposited nickel contacts was shown to have improved sensitivity toward ammonia gas.

Bioelectronic Light‐Gated Transistors with Biologically Tunable Performance

Light-activated bioelectronic silicon nanowire transistor devices are made by fusing proteoliposomes containing a bacteriorhodopsin (bR) proton pump onto the nanowire surface. Under green-light illumination, bR pumps protons toward the nanowire, and the pH gradient developed by the pump changes the transistor output. Furthermore, co-assembly of small biomolecules that alter the bilayer permeability to other ions can upregulate and downregulate the response of field-effect transistor devices.

Prospective of Conducting Polymer Nanowire for Gas Sensing Application to its Physical Scaling

The effect of physical scaling on one dimensional (1-D) conducting polypyrrole (Ppy) nanowire device has been successfully studied. The synthesis, electrical characterization and ammonia gas sensing with 1-D Ppy nanowire device have been carried out in the present investigation. Ppy nanowires having ~80 to ~200 nm in diameter were synthesized by electrochemical polymerization in alumina template and 1.77 to 3 µm Ppy nanowire length were maintain by varying the distance between electrodes gap. We further demonstrated that gas sensors based on 1-D Ppy nanowire having high aspect ratio (length to diameter ratio, L:D) exhibits good sensitivity towards ammonia, and provided a reliable detection at concentration as low as approximately 1 ppm based on principal of physical scaling co-related to response resistance.

Electrochemically grown single-nanowire sensors

We report a fabrication technique that is potentially capable of producing arrays of individually addressable nanowire sensors with controlled dimensions, positions, alignments, and chemical compositions. The concept has been demonstrated with electrodeposition of palladium wires with 75 nm to 350 nm widths. We have also fabricated single and double conducting polymer nanowires (polyaniline and polypyrrole) with 100nm and 200nm widths using electrochemical direct growth. Using single Pd nanowires, we have also demonstrated hydrogen sensing. It is envisioned that these are the first steps towards nanowire sensor arrays capable of simultaneously detecting multiple chemical species.