High-sensitivity optical imaging for biomedical applications using superconducting nanowire single-photon detectors: confocal fluorescence microscopy and Raman Spectroscopy

We present two independent high sensitivity optical imaging platforms: fluorescence confocal microscopy and swept source Raman spectroscopy, both enabled by a superconducting nanowire single photon detector (SNSPD). With SNSPD’s superior quantum efficiency and low dark counts, our confocal setup successfully visualizes weak NIR-II fluorescence from indocyanine green (ICG) in deep tissue area (up to 512 μm) under low excitation power (~1 mW). Separately, the Raman system integrates SNSPDs with a swept-source and narrowband filtering to detect femtomolar concentrations of tumor-targeted SERS nanoparticles using just 30 mW excitation and 40 ms point exposure. While distinct, both modalities share a common SNSPD detection backbone, demonstrating its versatility across fluorescence and Raman imaging. This work highlights the potential of SNSPD technology for broader adoption in more low-light biomedical imaging applications.