High-resolution surface plasmon resonance sensors based on a dove prism

Wavelength interrogation surface plasmon resonance (SPR) spectroscopy using a dove prism combines a simple and inexpensive optical design with high-resolution refractive index monitoring and biosensing. A BK7 dove prism inverts an optical image with a total internal reflection angle of 72.8°, an angle active in SPR. Hence, a unique system can accomplish SPR biosensing using wavelength interrogation and also perform SPR imaging. This optical configuration advantageously uses a single axis optical path between each optical component, simplifying the optical design of SPR instruments without compromise of the analytical performance. Fluidics were also incorporated to the instrument design for efficient sample delivery. The SPR instrument is characterized in terms of refractive index (RI) sensitivity, RI resolution, reproducibility, and application for monitoring low concentration biological events. Data analysis methodologies are compared for improved resolution of the measured response. Raw data analyzed using a minimum hunting procedure results in RI resolution in the 10⁻⁶ range, while pre-treating data with singular value decomposition improves the resolution by one order of magnitude. Depending on the spectrophotometer employed, the RI range accessible can be easily tuned; examples with a 550-850 nm and a 550-1100 nm spectrophotometers are shown and results respectively in RI ranges of 1.32-1.39 RIU and 1.32-1.42 RIU. Monitoring of μM concentration of β-lactamase is performed using the wavelength interrogation configuration of the biosensor. Finally, a SPR image of a surface with a water droplet (volume = 500 nL) was obtained using the dove prism SPR with a band pass filter and a CCD camera. SPR using a dove prism configuration combines advantages of portable SPR instruments, SPR imagers and research-grade SPR instruments in a unique platform.