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Gold Nanoparticles Coated Optical Fiber for Real-time Localized Surface Plasmon Resonance Analysis of In-situ Light-Matter Interactions

In situ measurement of analytes for in vivo or in vitro systems has been challenging due to the bulky size of traditional analytical instruments. Also, frequent in vitro concentration measurements rely on fluorescence-based methods or direct slicing of the matrix for analyses. These traditional approaches become unreliable if localized and in situ analyses are needed. In contrast, for in situ and real-time analysis of target analytes, surface-engineered optical fibers can be leveraged as a powerful miniaturized tool, which has shown promise from bio to environmental studies. Herein, we demonstrate an optical fiber functionalized with gold nanoparticles using a dip-coating process to investigate the interaction of light with molecules at or near the surface of the optical fiber. Localized surface plasmon resonance from the light-matter interaction enables the detection of minute changes in the refractive index of the surrounding medium. We used this principle to assess the in situ molecular distribution of a synthetic drug (methylene blue) in an in vitro matrix (agarose gel) having varying concentrations. Leveraging the probed Z-height in diffused analytes, combined with its in silico data, our platform shows the feasibility of a simple optofluidic tool. Such straightforward in situ measurements of analytes with optical fiber hold potential for real-time molecular diffusion and molecular perturbation analyses relevant to biomedical and clinical studies.