Advancing Raman imaging in opto-acousto-fluidic microchips

Two-dimensional (2D) and three-dimensional (3D) Raman mapping are powerful techniques for chemical imaging and compositional analysis of materials. However, their integration with microfluidic systems faces challenges such as low signal collection efficiency, sample movement, long measurement times, and suboptimal detection in aqueous environments. In this study, we present a multimodal opto-acousto-fluidic microchip that enables simultaneous acquisition of forward- and backward-scattering Raman signals from microparticles (MPs) in liquid samples. The microchip combines microfluidic, acoustic, and optical components to achieve stable particle trapping and enhanced signal detection. Acoustic forces are used to manipulate and cluster MPs within the microchannel, ensuring their stable positioning during Raman measurements. To address optical signal losses caused by total internal reflection, the chip is equipped with half-ball lenses and a spherical reflector, significantly improving the Raman signal collection efficiency by a factor of ≈32 compared to conventional microfluidic chips. The dual-scattering mode allows for rapid 2D Raman mapping that accurately represents a 3D Raman image, reducing the total measurement time from four days to 1.5 hours. To evaluate the chip’s performance, the Raman spectra of various microplastics and human hepatoma (HepG2) cells were analyzed. The results demonstrate the capability of the chip for high-throughput and non-destructive analysis of samples in aqueous environments. This approach shows potential for a broad range of applications, including environmental monitoring and biomedical research, where efficient and accurate Raman imaging is essential.