Application of Silicon Nanowire in Biosensor Student: HongPhan ID: Professor: Cheng-Hsien Liu

Outline Introduction The SiNW detector for protein The SiNW detector for DNA The SiNW detector for single molecule. Conclusions

Introduction One dimensional silicon nanostructures (SiNW) have attracted remarkable attentions due to their unique electronic, optoelectronic and thermal properties. Recently, SiNWs became the promising architecture in the present miniaturization of silicon-based devices, enabling many potential applications for the new generation nano-scale device including field-effect transistors (FET), optoelectronics, solar cell and especially biosensor Using SiNW to detect protein, DNA and single molecules.

The SiNW detector for Protein *The nanowires are modified with different (1, green;2, red) antibody receptors. A cancer maker protein that binds to its receptor (on nanowire-1) will product change characteristic of the surface charge on nanowire-1. *Device 1,2,3 fabricated from similar nanowires. Using them to detect three different cancer maker protein. Nat.Biotechnol.2008, 23, 1294

The SiNW detector for DNA Nanoletters, 8, (2009)

Establishment of SiNW with PNA capture probes Fabricated SiNWs by LPCVD. The PNA (peptide nucleic acid) capture probes with amine groups at their N ends are covalently immobilized on the SiNW surface by means of photochemical hydrosilation. PNA

Advantage of PNA instead of DNA capture probes PNA_ neutral and to increase the hybridization efficiency. Hybridization target DNAs to take place at low ionic strength. Minimized the build-up of a strong electrical field at the SiNW surface. Producing a high signal/noise ratio

Experiment (1) Using seven 22-nucleotide (nt) target DNAs to hybridize PNA of SiNW sensor. Anal.Chem. 2007, 79, 3291

Experiment (2) The varied distance of the hybridization sites of DNAs to PNA capture probes while maintaining the total number of charges unchanged.

Results (1) Complementary target DNAs were completely hybridized to immobilized PNA. Therefore, the PNA capture probes are highly selective. (epi-fluorescence microscopy) Cy 3-labeled fully cDNACy 3-labeled seven-base cDNANoncomplementary DNA

Result (2) The resistance changes decreases with the hybridization sites moving away from the SiNW surface.

Conclusions Demonstrated the significance of charge layer distance to ensure SiNW biosensing sensitivity Understanding the response of the SiNWs biosensors to the location of charge layer.

The SiNW detector for single molecules Chem.Mater.2009

Introduction A facile method is demonstrated to metallize a SiNW array just by dipping it into a deposition solution (such as AgNO 3 & HF). The deposited AgNPs uniformly self-assembled along the SiNW and developed into a metal covering with the NW as its core. The metallized NW with a uniform distribution of AgNPs tested as a SERS substrate and a high enhancement is observed even from a single metallized NW alone.

Experiment Fabricated the SiNW chip ( NW and conductive circuit) The whole of SiNW chip will be dipped into the aqueous deposition solution ( metal ion and HF) for several minutes Not only could Ag + be reduced and deposited onto the SiNW surface, but Cu 2+, Pd 2+, Co 2+, Au 3+ and Pt 4+ were also employed to metallize the SiNW

The metallization process The metallization process includes nucleation and growth process. – The nucleation process is a redox reaction, which includes: The reduction of metal ions to be deposited as NPs. The oxidation of Si to provide the needed electrons. – SiO 2 is momentarily formed but quickly removed again by HF – There are two growth processes: coarsening and aggregation. The growth of the NPs was faster along some particular crystallographic directions than along the rest. This is reason for the appearance of nanostick. The dendrite structures originate from the nanostick stem when the growth time has been prolonged.

Results The highest intensity of Raman signal was collected from the Ag NP substrate with a deposition time of ~ 5 min. Other Ag NP arrays with longer or shorter deposition time led to a decreased intensity. A limit of detection of ~ 1nM R6G was reached when incubation in the same solution was employed to load the Raman scattered. The signal was significantly enhanced when the laser was focused on the AgNPs assembled along the SiNWs. The blue background indicates that there is little or no Raman response from the gap area. The Raman signal collected along the NW is much stronger than that from the gap area, from green to yellow spots, the intensity of which is uniform because of the close intensity of Raman signal.

Conclusions A strong SERS signal could be collected from only one metallized NW. This approach holds promise for trace-level and perhaps single molecule detection.