Sensing absorptive fluids with backside illuminated grating coupled SPR sensor fabricated by nanoimprint technology

Grating coupled surface plasmon resonance (GC-SPR) sensors are widely used in analyzing gases, aqueous solutions, proteins and environmental pollutants. However, traditional GC-SPR sensors are difficult to detect absorptive fluids because the spectra of the light will be distorted after passing through the absorptive fluids. Here, we propose and experimentally demonstrate a backside illuminated GC-SPR (BIGC-SPR) sensor, where the light is incident from the transparent substrate side of the sensor chip. The grating chip is fabricated by a simple and cost-effective procedure. DVD-R disc is used as a template to imprint the grating structure onto a polydimethylsiloxane (PDMS) substrate, then a thin Au layer of 35 nm thickness is evaporated on it. By calibrating the sensor with glucose solutions, the sensitivity and refractive index resolution are measured to be 311.97 nm/ RIU and 0.00043 RIU, respectively. Moreover, the BIGC-SPR sensor is demonstrated to monitor the concentration of blue engine coolant, green antirust cutting fluid and white antirust emulsified oil solutions. The designed sensor is able to detect colored or highly scattering solutions, and can be potentially used in the fields of medical diagnosis, environmental monitoring and biological protein detection.

Automated summary

A backside illuminated GC-SPR (BIGC-SPR) sensor is proposed and experimentally demonstrated in this study. It can detect absorptive fluids and colored or highly scattering solutions, and has potential applications in medical diagnosis, environmental monitoring, and biological protein detection.