An opto-acousto-fluidic microchip for efficient Raman spectroscopy of microparticles in aqueous environment

2-D and 3-D Raman mapping are powerful imaging techniques for creating chemical images and compositional analysis of materials. Nevertheless, integration and implementation of Raman mapping on a microfluidic system turns out to be arduous due to several challenges, including the movement of sample, low efficiency of detection, low signal-to-noise ratio, and long measurement times. This study introduces a multimodal microchip for concurrent measurement of Raman signal in both forward- and backward-scattering modes from microparticles (MPs) in an aqueous environment. The microchip integrates microfluidic, acoustic, and optical components, synergistically manipulating and stabilizing a cluster of MPs through the application of precise local acoustic forces. The optical components orchestrate the laser and Raman signals, effectively addressing the total internal reflection challenge and significantly enhancing the Raman signal collection efficiency by a factor of ≈ 32 in comparison to a conventional microfluidic chip. The adoption of dual-mode measurement of Raman signal facilitates the creation of a 2-D Raman image, offering a representative view of a 3-D volume image. This practical methodology not only expedites the measurement process from 4 days to 1.5 hours, but also provides a comprehensive analysis of the clustered entities. To benchmark the versatility and applicability of the developed microchip, the Raman signal of microplastics of different types and human hepatoma HepG2 cells are fully investigated. The meticulous bottom-up approach presented herein holds great promise for advancing efficient and high-throughput sample monitoring in aqueous conditions using Raman spectroscopy.