# Microfluidic Device on Fused Silica for Raman Spectroscopy of Liquid Samples

## TL;DR

A microfluidic device made of fused silica improves Raman spectroscopy for water testing by providing more accurate and consistent results in liquid samples.

## Contribution

A portable microfluidic device on fused silica is developed to enhance Raman spectroscopy for liquid samples.

## Key findings

- The device showed lower standard deviation in Raman signal under continuous flow conditions.
- Background noise was reduced compared to conventional substrates.
- Sample drying issues in static measurements were avoided.

## Abstract

Water testing is becoming increasingly important due to dangerous phenomena such as Harmful Algal Blooms (HABs). Commonly, the content of a water sample is measured for the detection, monitoring and control of these events. Raman spectroscopy is a technique for the molecular characterization of materials in solid, liquid or gaseous form, which makes it an attractive method for analysing materials’ components. However, Raman scattering is a weak optical process and requires an accurate system for detection. In our work, we present, from design to fabrication, a microfluidic device on fused silica adapted to optimise the Raman spectrum of liquid samples when using a Raman probe. The device features a portable design for rapid on-site continuous flow measurements avoiding the use of large, costly and complex laboratory equipment. The main manufacturing technique used was ultrafast laser-assisted etching (ULAE). Finally, the effectiveness of the microfluidic device was demonstrated by comparing the Raman spectra of a known species of cyanobacteria with those obtained using other conventional substrates in laboratory analysis. The results demonstrate that the microfluidic device, under continuous flow conditions, exhibited a lower standard deviation of the Raman signal, reduced background noise and avoided signal variations caused by sample drying in static measurements.