Fabrication Of Optical Biosensor Based On Porous Silicon And Its Application

In recent years, optical biosensors are widely used for biomolecular analyses inbiomedical needs, health care, food quality and environmental issues. Laboratory andcommercial research is attempting to address these needs for small, fast, efficient andlabel-free optical biosensors. Porous silicon (PS) is cheap and easy to obtain, and its largeinternal surface area (up to800m2/g) allows immobilization of more probe molecules，which increases the possibility of capturing low concentration target molecules in solutionand is fully compatible for integrated circuit technology.In this paper, to increase the accuracy and efficiency of label-free biosensor, severalmethods have been developed for the detection of both small and big biomolecules separately.Based on these techniques, we have successfully fabricated optical biosensors based on PS.The main results of this thesis are as follows:1. It is the first time to evaluate the performance of label-free PS optical biosensor for thedetection of VHH antibody on the N-type silicon with small resistivity (0.02-0.03·cm).We fabricate PS by electrochemical etching and hen egg white lysozyme (HEWL) isimmobilized into the PS pore using a standard cross-link chemistry method. The binding ofHEWL and VHH causes a red shift in the reflection spectrum of the biosensor. The red shift isproportional to the VHH concentration in the range from14μgï¹'ml-1to30μgï¹'ml-1with adetection limit of0.648ngï¹'ml-1. The small molecules and the low antibody concentrationcan be detected by PS biosensor. As a biosensor platform, PS can be used for the developmentof label-free biosensor for rapid and sensitive determination of small molecules.2. Based on our simulations to obtain appropriate optical properties of a porous siliconmicrocavity (PSM), it is the first time for us to have successfully fabricated a highly efficientPSM on SOI wafer by electrochemical etching for DNA detection. The narrow resonancepeak in the reflectance spectrum, located at optical wavelength1555.0nm, very near theoptical communication widow, gives a high Q factor which causes high sensitivity for sensingperformance. The sensitivity of this sensor is investigated through19-base pair DNAhybridization in the PSM by surface modification using a standard cross link chemistry method. The red shift of the reflectance spectra shows that the detection limit is43.9nM,which is comparable to that reported for other favorable PS biosensor techniques based onsilicon wafer. This optical PSM on SOI is highly sensitive, fast responsive, easy to fabricateand low-costly, that will broadly benefit to develop a new optical label-free biosensor on SOIwafer and has a great potential for biochips based on integrated optical devices.3. A novel method is demonstrated to detect Antifreeze proteins (AFPs) based onphotoluminescence (PL), using N-type (1-10·cm in resistivity) PS coated with silver as asubstrate. Ag/PS substrate is obtained through immersion of PS in silver nitrate (AgNO3)solutions and is incubated with Rhodamine B (RB) as PL label. This substrate is easy to befabricated and the pore size of PS is large enough for biological molecules to infiltrate, whichis an ideal platform for biological molecule detection. Based on PS coated with silver as asubstrate, the RB-based PL biosensor makes it possible to address detection of numerous bigbiomolecules even with high concentration. Thus this could be a new method to developlabel-free biosensors and applied for rapid and sensitive detections of big biomolecules.4. Highly active and sensitive Surface Enhance Raman Scattering (SERS) substrates areprepared based on N-type (1-10·cm in resistivity) PS substrates of Ag nanoparticles.SERS studies are carried on these substrates with R6G as a test molecule. We optimize thefabrication procedure, which is easy and rapid, for nanostructured silver particles on thesurface of PS. The maximum of SERS enhancement for R6G has been observed. SERSspectra show that the Ag-PS substrate has high SERS activity. The larger pore diameter ofthis new Ag-PS substrate is obtained and the large size of pore permits better biomoleculeinfiltration. It is suggested that this N-type PS can be a new material for the fabrication ofsensitive substrates for SERS. This new Ag-PS substrate can be applied in SERS inbiochemical and biomedical fields.