Abstract

Lactate in humans is believed to provide unique information about the general health status of the individual, including pressure ischemia and insufficient oxidative metabolism [1]. Lactate in form of Lactic acid is widely used as an ingredient in food, cosmetics, and pharmaceuticals, and requires development of cost-effective methods for the determination of lactic acid in human sweat [2]. Optical sensors based on surface plasmon resonance enable label-free optical biosensing method and are used in detection of various chemical and biological species [2]. 2D materials such as graphene and transition metal dichalcogenides have attracted much attention to the possibility of improving the sensitivity of SPR sensors owing to their unique electrical and optical properties. When 2D materials covered on the metal film, the strong coupling occurs at the metal-2D materials due to their high charge carrier mobility, resulting in a significant electric field enhancement at the interface. Also, the high surface-to-volume ratio of 2D materials provides a large surface region for adsorbing biomolecules, which improves the sensitivity of the sensors by increasing the local refractive index change [3]. In this study, a GaSe-based SPR-fiber optic sensor is numerically and experimentally investigated for lactate sensing in human sweat. For this, a multimode optical fiber cable with a core diameter of 220 um is tapered down to a 35 nm core diameter having a 0.22 numerical aperture is used. The tapered part (L= 10mm) of the fiber optic is coated with gold (Au) metal film with a thickness of 20 nm, see Fig.1(b). As a sensing material, 100 nm GaSe film was coated on the metal film using the drop casting method. The configuration of the fiber optic sensor is illustrated in Fig. 1(a). By changing the refractive index of the sensing medium with the 1% intervals, the alterations in the resonance response were observed as graphically illustrated in Fig. 1(c).

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