A novel single-particle Raman spectrometer based on switchable dual-wavelength optical trapping: System design and microparticle applications

This study presents the development and application of a novel switchable dual-wavelength optical tweezers micro-confocal Raman spectrometer (DOT-MRS), integrating 532 nm (visible) and 780 nm (near-infrared) lasers into a single confocal optical path. The system addresses key limitations of conventional single-wavelength optical-tweezers Raman systems, such as fluorescence interference and photodamage to organic/biomolecular samples. By enabling independent or combined use of the two wavelengths, DOT-MRS offers enhanced flexibility, as the 532 nm laser provides high Raman scattering efficiency for non-fluorescent samples, while the 780 nm laser minimizes fluorescence background and photodamage for chromophore-containing particles. A series of experiments were performed to validate the system's performance on single-crystal silicon, polystyrene microspheres, fluorescent particles, and potassium oxalate aerosols, demonstrating micrometer-scale spatial resolution, stable trapping, and high-quality Raman spectra. Notably, the dual-wavelength design allows for decoupling of trapping and probing functions, significantly improving sensitivity for weakly scattering samples. This innovation expands the capabilities of optical-tweezers Raman systems for diverse applications in aerosol science, biophysics, and colloidal chemistry.