A localized surface plasmon resonance (LSPR) refractometer based on Au nanoparticles (NPs) was demonstrated in this paper. By immobilizing Au NPs onto the inner wall of micro-capillary, a LSPR-based refractometer was obtained. This sensor was highly sensitive to refractive index (RI) and offers a wide dynamic detection range, and it was sensitivitie-tunable caused by the extinction efficiency of the Au NPs in the evanescent field of micro-capillary inner surface. Then the micro-capillary can be used as both a sensing element and a flow cell, so that micro-measurement can be achieved. The response of LSPR to RI was verified experimentally and the results demonstrated that the absorbance of Au NPs increases between 1.328–1.451, and decreases between 1.451–1.470 with the increasing RI. The sensitivities were 109.6%/RIU in the RI of 1.328–1.394RIU, 395.7%/RIU in the RI of 1.394–1.397RIU and 1035.7%/RIU in the RI range of 1.451–1.470RIU. This refractometer was cost-effective, small-size and highly sensitive to be used for refractometer and can be extended for other physical or chemical parameter measurement for further investigations.
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