title: Synthesis and characterization of a stable, label-free optical biosensor from TiO2-coated porous silicon.
abstract: A nanoscale layer of TiO2 is coated on the inner pore walls of a porous silicon (PSi) film by room-temperature infiltration of a TiO2 sol-gel precursor and firing at 500 °C. The PSi:TiO2 composite films are characterized by Fourier transform infrared (FTIR), X-ray diffraction (XRD), energy dispersive X-ray spectral analysis (EDS), scanning electron microscopy (SEM) and reflective interferometric Fourier transform spectroscopy (RIFTS). The analysis indicates that TiO2 conformally coats the inner pore surfaces of the PSi film. The film displays greater aqueous stability in the pH range 2-12 relative to a PSi:SiO2 surface. A label-free optical interference immunosensor based on the TiO2-coated PSi film is demonstrated by real-time monitoring of the physical adsorption of protein A, followed by the specific binding of rabbit anti-sheep immunoglobulin (IgG) and then specific capture of sheep IgG. The time to achieve equilibrium for the physical adsorption of protein A on the surface of TiO2-coated PSi film is significantly greater than that of PSi film. The specificity of the protein A and rabbit anti-sheep IgG construct on the sensor is confirmed by tests with non-binding chicken IgG. The sensitivity of the immunosensor is shown to be 8210 ± 170 nm/refractive index unit (RIU).
authors.affiliation: Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093, USA; Gin College, Nanjing Normal University, Nanjing 210097, Jiangsu, China.
authors.forename: Jianlin
authors.initials: J
authors.lastname: Li
authors.affiliation: Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093, USA. Electronic address: msailor@ucsd.edu.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Sailor
mesh_terms: D000818:Animals; D015374:Biosensing Techniques / Q000295:instrumentation*; D002645:Chickens; D020099:Coated Materials, Biocompatible / Q000138:chemical synthesis*; D004867:Equipment Design; D019544:Equipment Failure Analysis; D007118:Immunoassay / Q000295:instrumentation*; D007074:Immunoglobulin G / Q000032:analysis* / Q000276:immunology; D055096:Optical Devices; D016062:Porosity; D012031:Refractometry / Q000295:instrumentation; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012756:Sheep; D012825:Silicon / Q000737:chemistry*; D013194:Staining and Labeling; D014025:Titanium / Q000737:chemistry*
chemical_list: D020099:Coated Materials, Biocompatible; D007074:Immunoglobulin G; C009495:titanium dioxide; D014025:Titanium; D012825:Silicon
keywords: Chemical modification; Immunosensor; Label-free; Porous silicon; Sol–gel chemistry