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In this paper we demonstrate an efficient and non-interfering computational method for sub-femtomolar food toxin detection in complex mixture based on nanoporous silicon oxide impedance immunosensor by employing noise spectroscopy analysis at the peak frequency. It has been observed that the peak frequency (fp) values obtained from steady state impedance measurements cannot distinguish between solution with only the specific toxin, which is aflatoxin B1 (AfB1) and mixture of AfB1 with other non-specific toxins (NSTs), thus leading to erroneous quantification of AfB1 in complex mixture. On the other hand, the first cut-off frequency (fc) ranges obtained from noise spectroscopy analysis can qualitatively differentiate between solution containing only AfB1, AfB1 and NSTs and no AfB1. However fc values being very close for different concentration of AfB1 in pure solution and being overlapping for different mixtures cannot quantify AfB1 either in pure solution or in complex mixture. To address this problem, the proposed computational method first clusters the fp and fc values in 11 categories each using k-means clustering algorithm and then applies a simple combinational digital logic on the clusters of fps and fcs to obtain the final output, realizable with standard NAND-NOR gates. The output digital word differs only with AfB1 concentration and not with concentration of NSTs and is found to be capable of detecting sub-femtomolar AfB1 range down to 0.1 fg/ml not only in pure solution but also in complex mixture with as high as 1000 ng/ml NSTs. This is the most sensitive and selective report so far on electrochemical food toxin immunosensors., (Copyright © 2014 Elsevier B.V. All rights reserved.)

A thermally oxidized macroporous silicon substrate with simple electrode structure without interdigitated electrode configuration has been reported for the detection of Salmonella typhimurium pathogens by electrical impedance measurement using antibody-antigen binding method. Macroporous silicon which has been fabricated by anodizing silicon in HF and DMF solution is a regular network of pores of 1-2 microm diameters. This has been thermally oxidized to yield the surface hydrophilic for antibody immobilization as well as provide suitable electrical insulation of the metal contacts from the underlying conducting silicon substrate. The macroporous silicon surface has been immobilized by Salmonella specific antibody and has been tested with different concentration of S. typhimurium pathogens in phosphate buffer solution (PBS). It has been found that such macroporous silicon substrates is capable of detecting down to 10(3)CFU/ml in pure culture using a 3 mm x 1 mm electrode structure with a wide spacing of 1mm. The selectivity of the macroporous silicon substrates with reference to S. typhimurium has been tested to be satisfactory by carrying out controlled experiments with Escherichia coli O157:H7.

This article investigates the impact of incorporating silica nanoparticles of varying diameters in label free impedance immunosensor. It has been observed that even if the surface area improvement has been adjusted to be similar for all the diameters, the sensitivity is enhanced by five times at a particular diameter of 100 nm due to the optimum combination of intersection with electric field lines and surface convexity. This study has enabled the detection of 0.1 fM Hep-B surface antigen with a reliable sensitivity of around 75%. Further, it has been observed that the SNR corresponding to 0.1 fM is 20 dB only for 100 nm particle. This SNR is comparable to a recent report on Hep-B virus detection but the limit of detection in the proposed sensor is lowered by more than three orders of magnitude. [ABSTRACT FROM AUTHOR]

This paper reports the optimization of electrode geometry on macroporous silicon biosensor for improved bacteria detection. Macroporous silicon of 8 μm thickness and 55% porosity has been fabricated on a 10-20 Ω-cm wafer using hydrofluoric acid and dimethyl sulfoxide. The electrode configurations selected for optimization are coplanar rectangular types with simple two-electrode, interdigitated comb finger-like electrode, and a combination of simple electrode and comb-shaped electrode designs. With these configurations, 14 different patterns have been generated with varying lengths and spacing within the technological constraints of low cost screen printing method of electrode fabrication with a wide range of effective exposed area from 0.04 to 0.6 mm2 by techniques from design of experiments. The sensitivity toward bacteria detection for all the patterns has been estimated by computation of an area utilization factor (AUF) which has been defined as the ratio of the effective area occupied by the captured bacteria to the effective exposed area available for capture. From the AUF values, eight patterns have been selected which are above a lower cut-off threshold for experimentation with E.coli O157 in the range of 102CFU/ml to 106 CFU/ml. It has been observed that the pattern with the highest AUF is capable of detecting 102CFU/ml E.coli O157 with a sensitivity of 11% without any pre-concentration which was not possible in the earlier reports of macroporous silicon. [ABSTRACT FROM PUBLISHER]

The paper focuses on the design of a CMOS analog ASIC for temperature-drift compensation of a high sensitivity piezoresistive micro-machined porous silicon pressure sensor to avoid analog-to-digital conversion, limit chip area and reduce power consumption. For implementing the compensation circuitry, multilayered perceptron (MLP) based artificial neural network (ANN) with inverse delayed function model of neuron has been optimized. The temperature drift compensation CMOS ASIC has been implemented to make porous silicon pressure sensor an excellent SMART porous silicon pressure sensor. Using the compensation circuit, the error in temperature-drift has been minimized from 93% to about 0.5% as compared to 3% using conventional neuron model in the temperature range of 25-80°C. The entire circuit has been designed using 0.35 μm AMS technology model and simulated using mentor graphics ELDO Simulator. [ABSTRACT FROM AUTHOR]

The authors would like to make corrections to [1, Fig. 7(b) and (c)] due to some post-processing carried out in these figures. After capturing the SEM images—top view [Fig. 7(b)] and cross section [Fig. 7(c)] in [1], we started measuring the pore dimensions with image processing software. We wanted to measure both the lateral and the vertical diameters of the pores in Fig. 7(b) (since they are not exactly circular). For this purpose, a boundary was constructed around some of the pores with textured lines but mistakenly these lines were not removed during transferring the pictures to the manuscript, which is responsible for the distortion in [1, Fig. 7(b)]. In Fig. 7(c) also, we wanted to measure the pore length, for which textured lines were drawn along the length of the pore, leading to some changes in the color contrast at the mouth of the pore from the original SEM picture. These lines also should have been removed from [1, Fig. 7(c)]. [ABSTRACT FROM AUTHOR]