Broadband cavity enhanced UV-VIS absorption spectroscopy for picolitre liquid samples Imogen Fermor-Worth 1,2 and Catalin Chimerel 1 1 Transilvania University of Brasov, Romania, 2 University of Exeter, UK Absorption spectroscopy is a widely used analytical technique due to its label-free nature. However, its application to small liquid samples is hampered by the associated short absorption pathlengths, limiting sensitivity. A concept for the development of an ultrasensitive broadband absorption spectrometer optimised for thin liquid films is presented. We implemented an optical cavity within a fibre-based absorption spectrometer, to enhance sensitivity of the absorbance measurements. In the setup, light propagates multiple times through the sample of interest resulting in greatly increased sensitivity. The bandwidth of the instrument is determined by the choice of two dielectric mirrors forming the optical cavity and, in this implementation, has been set to be optimised for UV detection (250-450 nm). The sensing volume of the spectroscope is prescribed by the choice of optical fibres employed to deliver light to the sample, here we employed 400 µm diameter fibres, giving a sensing volume of 630 picolitres for a thin film of 5 µm in thickness. As a proof-of-concept, we have used our platform for the ultrasensitive detection of the antifungal drug Amphotericin B. Cavity enhancement factors, the equivalent pathlength increase over classical absorption spectroscopy, in the range of 200X have been achieved across a broad wavelength range. Taking advantage of the extended path length the limit of detection for Amphotericin B in a 5 µm thick aqueous film has been dropped from ~125 µg/ml to ~20 µg/ml [1] . We envision multiple applications of our technology ranging from low concentration nucleic acid quantification to label-free cellular drug uptake. References 1. Fermor-Worth, Imogen M., and Catalin Chimerel. "Broadband cavity enhanced UV-VIS absorption spectroscopy for picolitre liquid samples." Analyst (2023).
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