We report on a novel label-free biosensor for in situ measurements in liquid. It is comprised of a porous carbon nanotube (CNT) fibre attached to one prong of a quartz tuning fork (QTF) resonator. Only the protruding CNT fibre is immersed into a liquid, while the QTF is kept above the liquid to avoid short circuit of its electrodes. The low density and large surface area of the CNT fibre assure sufficient sensitivity without affecting the performance of the QTF significantly. Efficiency of the sensor was demonstrated experimentally by comparison of the adsorption rate of bovine serum albumin to the CNT fibre at two different pH values; differences in adsorption rates were clearly distinguishable.
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