Localized Surface Plasmon Resonance-Modulated Graphene-Based Optical Sensor for Ultrasensitive Immunoassays

Quantitative detection of disease markers at ultralow concentrations has rigorous requirements on the performance of graphene-based optical sensors (GOSs). In this work, a localized surface plasmon resonance-modulated GOS was developed by uniformly dispersing gold nanorods (AuNRs) on the graphene surface. As an optical sensor based on refractive index sensing, the refractive index resolution and sensitivity of the optical sensor reached 2.34 x 10-9 and 2.14 x 107 mV/RIU, respectively. The sensitivity of the optical sensor toward IgG immunoassay reached 6.5 mV (mu g mL-1)-1, a value 7-fold that without the AuNRs. A limit of detection of 1.22 ng/mL toward IgG immunoassay was obtained, a value one-tenth that without the AuNRs. Most critically, it has been demonstrated that the improved performance of the optical sensor was attributed to the enhanced evanescent field on graphene caused by the coupling of the evanescent field and LSRR of AuNRs. The proposed optical sensor in this study has the characteristics of high sensitivity, being label-free, and a simple preparation process. The successful application of the proposed sensor will also greatly promote the development of quantitative detection of disease markers at ultralow concentrations.