Label‐Free Spontaneous Raman Sensing in Photonic Crystal Fibers with Nanomolar Sensitivity

Abstract An approach to significantly enhance spontaneous Raman sensitivity through the formation of a thin film via thermophoresis along with evaporation at the facet of a hollow‐core photonic crystal fiber is reported for the first time. Sensitivity of detection is increased by more than 6 orders of magnitude for both organic and inorganic nanoparticles, facilitating the search for trace analytes in solution. Detection of two nanoparticles, alumina and polystyrene, is demonstrated down to 392 nM without the use of surface‐enhanced Raman spectroscopy or other chemical‐based procedures. This new thin‐film deposition approach simplifies the simultaneous detection and analysis of small trace compounds, a previously arduous task using conventional spontaneous Raman.