Integrated-optic biosensor by electro-optically modulated surface plasmon resonance.

We present a new integrated-optic surface plasmon resonance (SPR) biosensor based on electro-optical modulation. The SPR characteristics for the analyte concentration detection can be electro-optically modulated by applying the voltage on the electrodes of the biosensor fabricated on lithium niobate, which is an excellent electro-optic material. Two measurement methods, electro-optically modulated SPR spectral measurement and electro-optically modulated SPR intensity measurement, are demonstrated and their measurands are the SPR wavelength and the output optical intensity, respectively. Human serum albumin is coated on the gold film surface of the proposed biosensor to detect the concentration of beta-blocker, which is a remedy for heart disease. As the applied voltage increases such that the effective index of guided mode rises, the SPR wavelength shifts toward the long wavelength side and the output optical intensity at the wavelength of 632.8 nm diminishes. The linear regression slope of the relation between the measurand and the applied voltage is dependent on the analyte concentration and can be used to determine the concentration variation. Experimental results measured by the electro-optically modulated SPR methods are compared with those measured by the conventional spectral and intensity methods, and the effects of waveguide width on the biosensor performance are discussed.