Tunable sensitivity and linearity of self-assembled carbon nanotube composite based pH biosensors using silica nanoparticles

We describe tunable sensitivity and linearity of layer-by-layer (LbL) self-assembled single-walled carbon nanotube (SWCNT) thin-film composites as a pH sensor by means of silica nanoparticles (SNPs). The SWCNT thin-film devices without and with SNP layer were fabricated with LbL self-assembly and characterized electrochemically in pH buffers. The role of SNPs in SWCNT thin-film chemoresistors and ISFETs is proven to increase and linearize the sensitivity to pH. The linearization in presence of SNP layer is attributed to a positive shift in pH gating voltage in p-type semiconducting SWCNTs. Two types of sensitivity, linear and exponential behaviors found with and without SNP layer, are useful for developing biosensors.