Study of Mesoporous-SiO2-Film-Modified Surface Plasmon Resonance Sensors with Wavelength Interrogation in Near Infrared Region

An infrared surface plasmon resonance (SPR) sensor with wavelength interrogation was prepared based on Kretschmann configuration. The SPR chips were fabricated by sputtering a 45-nm gold layer on the glass substrate followed by sol-gel template synthesis of a 45-nm-thick mesoporous silica film. The experimental results indicate that with a broadband collimated incident beam both the resonance wavelength (lambda(R)) and the refractive-index sensitivity (S) increase with decreasing the incident angle (theta). The refractive-index sensitivity was measured as S=24241 nm/RIU at theta=8 degrees, being 9.6 times as high as S=2524.2 nm/RIU obtained at theta=15 degrees. Compared with a conventional SPR sensor with a naked gold film, the modification of SPR chips with mesoporous silica thin films makes the resonance absorption band narrower and consequently offers a higher SPR spectrum resolution. The results measured at theta=10 degrees using low concentrations of aqueous lysozyme solutions indicate a linear dependence of the resonance wavelength on the protein concentration with a slope of Delta lambda(R)/C=1.5x10(7) nm.L/mol, implying that an increase of 6.67x10-8 mol/L in protein concentration can causes a redshift of Delta lambda(R)=1 nm. For the detection of Cu2+ ions, the results indicated that adsorption of Cu2+ ions from the 1x10(-7) mol/L aqueous solution can make the resonance wavelength redshift 3 nm.