We have used a nonlithographic deposition process to form single polymeric nanowire chemical sensors. Oriented polyaniline nanowires, with diameters on the order of 100 nm, were deposited on gold electrodes. The devices showed a rapid and reversible resistance change upon exposure to NH 3 gas at concentrations as low as 0.5 ppm. The well-defined single-wire geometry allows for the characterization of the wire material and the device response. The response times of nanowire sensors with various diameters correspond to radius-dependent differences in the diffusion time of ammonia gas into the wires. The nanowire deposition process, utilizing a scanned microfabricated electrospinning source, presents a general method for interfacing polymeric nanowire devices with microfabricated structures.

The ability to detect small amounts of materials, especially pathogenic bacteria, is important for medical diagnostics and for monitoring the food supply. Engineered micro- and nanomechanical systems can serve as multifunctional, highly sensitive, immunospecific biological detectors. We present a resonant frequency-based mass sensor, comprised of low-stress silicon nitride cantilever beams for the detection of Escherichia coli (E. coli)-cell-antibody binding events with detection sensitivity down to a single cell. The binding events involved the interaction between anti-E. coli O157:H7 antibodies immobilized on a cantilever beam and the O157 antigen present on the surface of pathogenic E. coli O157:H7. Additional mass loading from the specific binding of the E. coli cells was detected by measuring a resonant frequency shift of the micromechanical oscillator. In air, where considerable damping occurs, our device mass sensitivities for a 15 μm and 25 μm long beam were 1.1 Hz/fg and 7.1 Hz/fg, respectively. In both cases, utilizing thermal and ambient noise as a driving mechanism, the sensor was highly effective in detecting immobilized anti-E. coli antibody monolayer assemblies, as well as single E. coli cells. Our results suggest that tailoring of oscillator dimensions is a feasible approach for sensitivity enhancement of resonant mass sensors.

We have demonstrated high-sensitivity detection of bacteria using an array of bulk micromachined resonant cantilevers. The biological sensor is a micromechanical oscillator that consists of an array of silicon-nitride cantilevers with an immobilized antibody layer on the surface of the resonator. Measured resonant frequency shift as a function of the additional cell loading was observed and correlated to the mass of the specifically bound Escherichia coli O157:H7 cells. Deposition and subsequent detection of E. coli cells was achieved under ambient conditions.

We present a method for controlled deposition of oriented polymeric nanofibres. The method uses a microfabricated scanned tip as an electrospinning source. The tip is dipped in a polymer solution to gather a droplet as a source material. A voltage applied to the tip causes the formation of a Taylor cone, and at sufficiently high voltages, a polymer jet is extracted from the droplet. By moving the source relative to a surface, acting as a counter-electrode, oriented nanofibres can be deposited and integrated with microfabricated surface structures. For example, we deposited fibres of polyethylene oxide with diameters ranging from 100 to 1800 nm, with the diameter primarily depending on the concentration of the polymeric solution. In addition to the uniform fibre deposition, the scanning tip electrospinning source can produce self-assembled composite fibres of micro-and nanoparticles aligned in a polymeric fibre. We also deposited oriented conductive polymeric fibres of polyaniline and investigated the conductivity of these fibres as components for polymeric nanoelectronics.

Broadband perfect absorber based on one ultrathin layer of the refractory metal chromium without structure patterning is proposed and demonstrated. The ideal permittivity of the metal layer for achieving broadband perfect absorption is derived based on the impedance transformation method. Since the permittivity of the refractory metal chromium matches this ideal permittivity well in the visible and near-infrared range, a silica-chromium-silica three-layer absorber is fabricated to demonstrate the broadband perfect absorption. The experimental results under normal incidence show that the absorption is above 90% over the wavelength range of 0.4-1.4 μm, and the measurements under angled incidence within 400-800 nm prove that the absorber is angle-insensitive and polarization-independent.