Polymeric grating prism-based dual-mode miniature surface plasmon resonance sensor chip†

In this study, we demonstrate the fabrication of a dual-mode miniature surface plasmon resonance (SPR) sensor using a polymeric grating prism made from a UV-curable adhesive, specifically Norland Optical Adhesive 61 (NOA 61), employing a confined sessile drop technique. The SPR excitation of the dual-mode SPR sensor chip was observed through wavelength modulation at incident angles ranging from 45° to 75° in air. The results demonstrated SPR reflectivity curves spanning the vis-NIR region. The mode of each SPR reflectivity curve was elucidated by comparing the SPR dip of the experimental results with the calculated surface plasmon (SP) dispersions. Two types of SPR modes were identified: prism-coupling SPR mode (PC-SPR mode, corresponding to +SP⁰ of the gold–NOA 61 interface) and grating-coupling SPR mode (GC-SPR mode, corresponding to −SP⁺¹ of the gold–air and gold–NOA 61 interfaces). In deionized water (n ∼ 1.33300), PC-SPR and GC-SPR modes at the gold–air interface were observed using a larger incident angle, whereas only the GC-SPR mode of the gold–NOA 61 interface was obtained at all incident angles. Additionally, the dual-mode SPR property was studied using different concentrations of ethylene glycol in aqueous solution (n ∼ 1.33300–1.38313). The refractive index sensitivity obtained for the PC-SPR and GC-SPR modes at the gold–air interface was 1853 and 489.6 nm per RIU, respectively. Furthermore, the dual-mode SPR sensor demonstrated selective sensitivity by incorporating materials onto a gold-coated grating prism that matched the refractive index of the target analyte and exhibited overlapping absorption at the specific SPR excitation wavelength. Its enhanced response and significant wavelength amplification allow accurate performance in selective sensing situations. These findings underscore the dual-mode SPR sensor's potential as a powerful tool for future advanced sensing and detection applications.