Fig 1.
Top-down nanofabrication process steps of silicon nanowires using EBL.
Table 1.
ma-N2400 series coating process parameters.
Fig 2.
The overall design for silicon nanowires.
(a) Array and (b) single, with the drain and source electrode pads.
Table 2.
Exposure parameters.
Fig 3.
(a) Silicon nanowires produced by EBL and ICP-RIE, (b) size reduction by thermal oxidation, (c) BOE etching of the oxidized surface reduces the size of silicon nanowires, (d) silicon nanowires with the corresponding contact pads and (e) the sensor consisting of silicon nanowires integrated with the microfluidic channel.
Fig 4.
Schematic diagram of a cross-sectional view of the silicon nanowires integrated with the microfluidic channel.
(a) Open chamber with a spin-coated resist (SU-8 or PR1-2000A) and (b) closed PDMS microfluidic channel.
Fig 5.
Schematic illustration of the surface functionalization.
Surface modification by APTES and glutaraldehyde, DNA immobilization and DNA hybridization on the silicon nanowire surface.
Fig 6.
ma-N 2400 series resist characteristics.
(a) The resist thickness curve decreasing with the spin speed (rpm), SEM and AFM images of resist pattern after development process (b) 100 nm width exposed with an electron dose of 200 μC/cm2 and (c) 70 nm width exposed with an electron dose of 150 μC/cm2.
Fig 7.
SEM and AFM images of the silicon nanowires.
(a) 60 nm width and 50 nm height. The inset is the cross-section of the silicon nanowires. EDX spectrum shows the purity of silicon (Si) on the nanowire. (b) The silicon nanowires were oxidized to a width of 100 nm and then (c) etched in BOE to remove the SiO2, thus producing 20-nm-wide and 30-nm-high silicon nanowires. The inset is the SEM image of silicon nanowires at 15 keV with 100 000 magnification. (d) The size (width) of silicon nanowire for three samples (before and after size reduction process).
Fig 8.
Electrical properties of silicon nanowires.
(a) Ids-Vds characteristic shows p-type ohmic behavior and (b) the resistance and conductance histograms for 20 nm and 60 nm nanowires. The arrow highlights the direction from low to high width of the silicon nanowires.
Fig 9.
(a) Ids-Vds characteristic, (b) the average resistance values after various surface functionalizations, (c) hybridization specificity demonstrated by the response (i.e., resistance change) to the complementary and non-complementary DNA sequences and (d) the electrical conductance by different steps of surface functionalization.
Fig 10.
Response of the immobilized DNA silicon nanowires biosensor to the complementary DNA of varying concentrations from 10 μM down to 10 fM.
(a) Ids-Vds characteristic and (b) resistance changes versus concentration (i.e., relative change in resistance).
Table 3.
Analytical performance of p-type silicon nanowire in DNA biosensor technologies.