Novel microfluidic devices for Raman spectroscopy and optical trapping

Abstract

Traditionally, Raman spectroscopy is done in a specialized lab, with considerable requirements in terms of equipment, time and manual sampling of substances of interest. We present the modeling, the design and the fabrication process of a microfluidic device incorporation Raman spectroscopy, from which one enables confocal Raman measurements on-chip. The latter is fabricated using ultra precision diamond tooling and is tested in a proof-of-concept setup, by for example measuring Raman spectra of urea solutions with various concentrations. If one wants to analyze single cells instead of a sample solution, precautions need to be taken. Since Raman scattering is a weak process, the molecular fingerprint of flowing particles would be hard to measure. One method is to stably position the cell under test in the detection area during acquisition of the Raman scattering such that the acquisition time can be increased. Positioning of cells can be done through optical trapping and leads to an enhanced signal-to-noise ratio and thus a more reliable cell identification. Like Raman spectroscopy, optical trapping can also be miniaturized. We present the modeling, design process and fabrication of a mass-manufacturable polymer microfluidic device for dual fiber optical trapping using two counterpropagating singlemode beams. We use a novel fabrication process that consists of a premilling step and ultraprecision diamond tooling for the manufacturing of the molds and double-sided hot embossing for replication, resulting in a robust microfluidic chip for optical trapping. In a proof-of-concept demonstration, we characterize the trapping capabilities of the hot embossed chip.