Bottom-up assembly of silicon nanowire conductometric sensors for the detection of apolipoprotein A1, a biomarker for bladder cancer

The authors describe highly sensitivity nanowire sensors that can be prepared by a bottom-up approach. The sensors were incorporated into microchannels and used for the quantitative conductometric detection of apolipoprotein A1 (APOA1), a bladder cancer protein biomarker. Silicon nanowires were placed in the gap between nickel electrodes by using dielectrophoretic forces, which improved the yield of the assembly. Then, the nanowires were clipped by another nickel layer to form a nickel/nanowire/nickel sandwich-like structure using photolithography and a lift-off process. The results show that this structure exhibits reduced contact resistance at the interface between the nickel layer and the silicon nanowires, which is an ohmic contact. Thus, a stable nanowire sensor was obtained. It was found that the contact resistance can be further decreased by using a hot plate annealing process. An SU-8 photoresist was used to insulate the electrodes to allow for applications in wet environments. An antibody against APOA1 was covalently conjugated to the surface of the silicon nanowires. Antibody conjugation was verified via the decrease in the conductance of the nanowires after conjugation. The sensor has a dynamic range that covers the 0.2 ng·mL⁻¹ to 10 μg·mL⁻¹ APOA1 concentration range and a detection limit of approximately 1 ng·mL⁻¹.