A Novel Refractometer Architecture

A novel means for extracting refractive index information from a surface plasmon resonance (SPR) sensor system is presented. Rather than relying on output wavelength (from a polychromatic light source) or angle of incidence (from a monochromatic wave source) to identify the point of SPR, the system presented herein uses the spectral shift induced by varying the drive current on a commercially available red LED to identify resonance. Using appropriate, short duty cycle drive electronics and highly sensitive photodetection circuits, the SPR spectroscopic system demonstrates the ability to detect differences in refractive index among air, water, and various sucrose concentrations in water (representing a total dynamic range from 1.0 to 1.4 RI units). Resulting RI resolution of the SPR system is demonstrated at the portable instrument benchmark of 10
⁻⁴
RI units.