Side-polished flexible SPR sensor modified by graphene with in situ temperature self-compensation

Fiber-based techniques make it possible to implant a miniaturized and flexible surface plasmon resonance (SPR) sensor into the human body. However, for implantable applications, the miniaturization of fiber SPR sensors results in low sensitivity compared with traditional prism-type SPR sensors due to limited space and the effects of temperature fluctuations. Therefore, it is necessary to compensate for temperature drift in the measurements, such as the case of the quantification of the relationship between glucose concentration and SPR resonance wavelength. In this report, we proposed a highly sensitive fiber SPR sensor based on a side-polished structure modified by graphene for implantable continuous glucose monitoring with in situ temperature self-compensation using a long-period fiber grating (LPFG). The results demonstrate that the sensor with monolayer graphene achieved the best sensitivity of 3058.22 nm/RIU, and the LPFG achieves a maximum resolution of 0.042 nm/°C. The proposed SPR sensor enabled the detection of hypoglycemia, which is still a significant challenge for continuous glucose monitoring in a clinical setting.