Dielectric over-layer assisted graphene, its oxide and MoS2-based fibre optic sensor with high field enhancement

A high-index fibre-core-based surface plasmon resonance (SPR) sensor using 2D materials such as graphene, graphene oxide (GO) and molybdenum disulphide (MoS2) on a silicon (Si) over-layer in visible and near infrared is reported. Si was used on silver (Ag) followed by different 2D materials of appropriate thickness on a 600 µm core multimode fibre. Here Si is used to tune the resonance to a higher wavelength, and different 2D materials are used to enhance the performance as well as address the oxidation problem of Si. Moreover, a high-index chalcogenide core helps to decrease the full width at half maxima of the SPR spectra, hence increasing the detection accuracy of the sensor. Both the Ag and Si thickness are optimized, and the effects of different 2D materials on the performance of sensor are studied using the transfer matrix method in terms of electric field intensity, sensitivity, figure of merit (FOM) and resolution. We found that the percentage electric field enhancement for the Ag–Si-GO system is 4.65 × 104 in the presence of GO. The GO-based sensor is found to have a sensitivity of 202.2 nm RIU−1 in comparison to the graphene based sensor with a sensitivity of 189.4 nm RIU−1. Moreover, the FOM values are found to be as high as 5.57 RIU−1 for GO, and 5.18 RIU−1 and 2.29 RIU−1 for the MoS2 and graphene respectively. We believe that the proposed 2D-material-based sensors will open a new window for the development of high-performance fibre biosensors by utilizing the biocompatibility aspect of different 2D materials along with its high electric field value in the presence of a dielectric over-layer.