Si NanoWire Biosensor

Silicon nanowire SiNW FETs could be used to detect binding and unbinding of proteins to their corresponding ligands linked to nanowire surfaces in aqueous solutions. Proteins and nucleic acids also have been detected by using carbon nanotubes and SiNW FETs, respectively.



fig 1 - Detection of ATP binding. (A) Conductance (G) vs. ATP concentration for SiNWs modified with Abl (red curve) and a device prepared in an identical fashion, except Abl was not coupled to the surface (black curve). Regions 1, 2, and 3 correspond to 0.1, 3, and 20 nM ATP, respectively. Arrows indicate the points where solution is changed. (Inset) Scanning electron micrograph of a typical SiNW FET device. The nanowire is highlighted by a white arrow and is contacted on either end with Ti/Au metal electrodes. (Scale bar: 500 nm.) (B) Change in conductance (ΔG) vs. ATP concentration for Abl-modified SiNW (red) and SiNW without Abl (black).


ATP Sensing. Typical time-dependent data recorded from an Abl-modified SiNW device (Fig. 1) exhibited reversible, concentration-dependent increases in conductance upon introducing buffer solutions containing ATP. The reversibility of these concentration-dependent increases was evident from the corresponding decreases in conductance to baseline value upon introducing buffer solution without ATP. The observed increases in conductance are consistent with the binding of negatively charged ATP to Abl. Specifically, a p-type SiNW FET will exhibit an increase (decrease) in conductance when the gate-voltage is negative (positive) because of the accumulation (depletion) of carriers. Binding of negatively charged ATP to the Abl kinase increases the negative surface-charge density and increases conductance similar to a negative gate voltage.

Wang U W et al, Label-free detection of small-molecule–protein interactions by using nanowire nanosensors, PNAS March 1, 2005 vol. 102 no. 9 3208-3212




Fig 2-Nanowire with excitation at the bottom end and top end (no plasmon excitement)


Nanowire Nanosensors for Highly Sensitive and Selective Detection of Biological and Chemical Species



fig 3- NW nanosensor for pH detection. (A) Schematic illustrating the conversion of a NW FET (field effect transistor) into NW nanosensors for pH sensing. The NW is contacted with two electrodes, a source (S) and drain (D), for measuring conductance. Zoom of the APTES-modified SiNW surface illustrating changes in the surface charge state with pH. (B) Real-time detection of the conductance for an APTES-modified SiNW for pHs from 2 to 9; the pH values are indicated on the conductance plot. (inset, top) Plot of the time-dependent conductance of a SiNW FET as a function of the back-gate voltage. (inset, bottom) Field-emission scanning electron microscopy image of a typical SiNW device. (C) Plot of the conductance versus pH; the red points (error bars equal ± 1 SD) are experimental data, and the dashed green line is linear fit through this data. (D) The conductance of unmodified SiNW (red) versus pH. The dashed green curve is a plot of the surface charge density for silica as a function of pH.