Nanowire-based Biosensors Research Articles

Selective Alignment of Gold Nanowires Synthesized With DNA as Template by Surface-Patterning Technique

The direct and selective assembly of deoxyribonucleic acid (DNA)-templated metal (e.g., Ag, Au, Cu, and Pd) nanowires (NWs) is a key technique for the application to electronic devices and nanowire-based biosensors. In this study, a new technique was developed to carefully control the interval of DNA-templated gold NWs (AuNWs) using surface-patterning techniques. The ?-DNA molecules were stretched and aligned along 3-aminopropyltriethoxysilane (APS) region formed uniformly by self-assembly and patterned by electron beam lithography process, and then treated by positively charged gold nanoparticles to form DNA-templated AuNWs. ?-DNA molecule was verified to be immobilized and stretched into parallel lines only on the surface of APS-coated parallel paths by surface-patterning technique, and it was possible to control the interval of DNA-templated AuNWs. Also, DNAs were confirmed to be assembled not on the bare SiO2 region but on the APS region defined by amine groups.

A Calibration Method for Nanowire Biosensors to Suppress Device-to-Device Variation

Nanowire/nanotube biosensors have stimulated significant interest; however, the inevitable device-to-device variation in the biosensor performance remains a great challenge. We have developed an analytical method to calibrate nanowire biosensor responses that can suppress the device-to-device variation in sensing response significantly. The method is based on our discovery of a strong correlation between the biosensor gate dependence (dI(ds)/dV(g)) and the absolute response (absolute change in current, DeltaI). In(2)O(3) nanowire-based biosensors for streptavidin detection were used as the model system. Studying the liquid gate effect and ionic concentration dependence of strepavidin sensing indicates that electrostatic interaction is the dominant mechanism for sensing response. Based on this sensing mechanism and transistor physics, a linear correlation between the absolute sensor response (DeltaI) and the gate dependence (dI(ds)/dV(g)) is predicted and confirmed experimentally. Using this correlation, a calibration method was developed where the absolute response is divided by dI(ds)/dV(g) for each device, and the calibrated responses from different devices behaved almost identically. Compared to the common normalization method (normalization of the conductance/resistance/current by the initial value), this calibration method was proven advantageous using a conventional transistor model. The method presented here substantially suppresses device-to-device variation, allowing the use of nanosensors in large arrays.

Template Fabrication of Protein-Functionalized Gold−Polypyrrole−Gold Segmented Nanowires

Gold-capped, protein-modified polypyrrole (Ppy) nanowires were grown electrochemically using porous aluminum oxide as a template. The effects of the conditions of electrochemical synthesis on Ppy growth and protein (avidin or streptavidin) incorporation were studied. Streptavidin-modified nanowires grown at constant potential had better electrochemical properties and equilibrated faster when exposed to fluorescently labeled biotin than did nanowires grown by potential cycling. Solution pH had little effect on protein incorporation; however, higher pH provided slower but more reproducible growth rate of the Ppy segments. The best conditions for synthesis of streptavidin-modified Ppy nanowires were constant potential deposition at 0.75 V vs SCE in a phosphate buffer saline solution at pH 9. This method provides a straightforward route to nanowires of controlled length that can incorporate proteins for use in nanowire-based biosensors or in nanoparticle assembly through biomolecular interactions.