Abstract
In this paper, an interdigitated electrode-less, high- performance macroporous silicon-based impedance biosensor has been reported first time for the detection of E.ColiO157. Macroporous silicon of three different pore thickness of around 3, 8, and 12 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$ \mu{\rm m}$</tex></formula> and 55% porosity have been fabricated on a 10–20 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\ \Omega \mathchar"702D {\rm cm}$</tex> </formula> wafer using hydrofluoric acid (HF) and dimethyl sulfoxide (DMSO). The samples are next thermally oxidized for partial oxidation of silicon crystallites followed by optimized silanization and antibody immobilization. Two simple gold coated aluminium electrodes of 2 mm by 1 mm dimensions and 1 mm spacing have been fabricated similar to our previous report. It has been observed that the macroporous silicon with 8 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$ \mu{\rm m}$</tex></formula> thickness exhibits the maximum sensitivity of 30% corresponding to <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$10 ^{4}~{\rm CFU}/{\rm ml}$</tex></formula> which is twice compared to the earlier report on macroporous silicon and also it is higher than most of the other reports using IDE structures. The optimized sensor has been found to be reproducible, specific and capable of detecting down to <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$10 ^{3}~{\rm CFU}/{\rm ml}$</tex></formula> with a simple structure. A distributed transmission line model has been developed for macroporous silicon in presence of solution to explain the nature of variation of sensitivity with thickness from the current line confinement effects.
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