We have fabricated label-free protein biosensors based on aptamer-modified carbon nanotube field-effect transistors (CNT-FETs) for the detection of immunoglobulin E (IgE). After the covalent immobilization of 5'-amino-modified 45-mer aptamers on the CNT channels, the electrical properties of the CNT-FETs were monitored in real time. The introduction of target IgE at various concentrations caused a sharp decrease in the source-drain current, and a gradual saturation was observed at lower concentrations. The amount of the net source-drain current before and after IgE introduction on the aptamer-modified CNT-FETs increased as a function of IgE concentration. The detection limit for IgE was determined as 250 pM. We have also prepared CNT-FET biosensors using a monoclonal antibody against IgE (IgE-mAb). The electrical properties of the aptamer- and antibody-modified CNT-FETs were compared. The performance of aptamer-modified CNT-FETs provided better results than the ones obtained using IgE-mAb-modified CNT-FETs under similar conditions. Thus, we suggest that the aptamer-modified CNT-FETs are promising candidates for the development of label-free protein biosensors.

We have fabricated local-electrolyte-gated carbon nanotube field-effect transistors (CNTFETs), in which the electrolyte functions as a local top gate. The local-electrolyte-gated CNTFETs in the electrolyte solution provided high performance in terms of subthreshold slope and transconductance, resulting from the modulation of the conduction in the carbon nanotube channel and the large gate capacitance. Using the local-electrolyte-gated CNTFETs, real-time protein detection based on the channel conductance modulation was successfully demonstrated. Our local-electrolyte-gated CNTFETs are promising candidates for the development of nanoscale electronic and molecular-sensing device applications.

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