The feasibility of liquid sample microanalysis using polydimethylsiloxane microfluidic chips with in-channel and in-port laser-induced breakdown spectroscopy detection

This study describes the direct interfacing of polydimethylsiloxane (PDMS) microfluidic chips with laser-induced breakdown spectroscopy (LIBS) detection. The changes induced in the PDMS material by nanosecond laser ablation are briefly documented by using optical microscopy and scanning profilometry. The main part of the study focuses on the solution of technical and analytical problems of coupling single-pulse LIBS detection with PDMS microfluidic chips in order to assess the feasibility and performance of the concept of creating a lab-on-a-chip device with LIBS detection (LOC-LIBS). Multiple optical and sample presentation schemes including in-channel and in-port detection were tested, but it was found that LOC-LIBS is only viable and practical with in-port detection outside the chip. It was shown that LOC-LIBS in this configuration is capable of the trace speciation analysis of chromium using as little as 0.5 μL solution volume. The achieved absolute limit of detection was 2 ng. - Highlights: • The laser ablation properties of polydimethylsiloxane polymer are documented. • Multiple coupling and sample presentation schemes were tested. • In-port LIBS detection in an outside pocket was found to be the most practical approach. • The speciation analysis of Cr(III)/Cr(VI) using only 0.5 μL solution is demonstrated.