Three dimensional conductivity modulation in biocompatibly functionalized nano-engineered structures
The objective of this work is to fabricate a biosensor consisting of a boron doped silicon nanopillar array whose surface when modified with biotin exhibits a three dimensional modulation in conductivity upon the addition of streptavidin. For this purpose, direct write e-beam lithography technique is used to print a dot array on 950k PMMA C7 resist and the nickel dots obtained after lift-off are used as an etch mask to etch into silicon to realize the nanopillar array. A number of experiments are conducted to optimize the exposure dose for the dot array pattern and understand the effect of various parameters of the beam substrate and pattern on the dose required. A 25 X 25 silicon pillar array consisting of pillars with diameters 150-200nm and a spacing 1µm between the pillars is fabricated. Surface modification experiments are done to immobilize streptavidin on biotinylated silicon surface. An approach to the fabrication of the top electrode has been suggested. A theoretical model is developed to explain the conductivity modulation.