Signal frequency studies of an environmental application of a 65 nm region ion sensitive field effect transistor sensor

A rapid and sensitive novel type of bioelectronic Region Ion Sensitive Field Effect Transistor (RISFET) nanosensor was constructed on a chip with a 65 nm sensing electrode gap. The RISFET nanosensor was demonstrated for the environmental pesticide analysis of neurotoxic organocarbamate/carbofuran. The linear range for carbofuran analysis is ac signal frequency dependent, studied in the range (500 down-0.5 Hz, 50 mV(peak-peak) ac) and a bias voltage applied between the bottom capacitor plate and the electrodes. The signal current response is measured using a low-noise pico ammeter. The inhibition of acetylcholinesterase (AChE) by carbofuran was detectable in a logarithmic linear range (0.1-100nM) at 1.08 Hz, with a lower limit of detection of inhibition 0.1 nM with 10 min incubation time. The sensor is based on the principle of focusing charged reaction products with an electrical field in a region between the sensing electrodes. The current measurement by the sensor electrodes is correlated to the composition of the sample. The carbofuran detection is based on the ability to inhibit the enzyme AChE. The RISFET sensor chip is fabricated using conventional electron beam lithography. The encompassed sensor volume in the "nanocell" is in the attoliter range. (c) 2007 Elsevier B.V. All rights reserved

Long wavelength depolarized light scattering from silver nanoparticles

We report the depolarized light scattering from heterodisperse silver nanoparticles. The profile of the wavelength dependent anisotropy of the colloidal solution of silver nanoparticles extends to the red and near-infrared (NIR) spectral region. For long wavelengths, above 600 nm, the anisotropy drops below 0.5. The presence of such a strong orthogonal component in the scattering opens new opportunities for imaging in dispersive media when polarizers can be used to suppress the background. The anisotropy profile of the scattering of heterodisperse silver nanoparticles can be satisfactorily explained by a theory based on interference between two surface plasmon resonances. (c) 2007 Elsevier B.V. All rights reserved