Fabrication of thermoplastic microfluidic probes for nanospray desorption electrospray ionization mass spectrometry

Nanospray desorption electrospray ionization mass spectrometry (nano-DESI MS) uses specially designed probes to achieve a stable liquid bridge on the sample surface, ensuring consistent analyte extraction. Here, we present a mold-based fabrication protocol for cyclic olefin copolymer (COC) microfluidic probes (MFPs). We describe mold design, probe fabrication, and probe setup for nano-DESI MS. Four mold fabrication methods, including computer numerical control (CNC) machining, metal 3D printing, photolithography, and selective laser-assisted etching (SLE), were evaluated, with SLE providing the highest structural precision and enabling reproducible channel fabrication. Performance evaluation using lysophosphatidylethanolamine (LPE) 17:1 standard demonstrated stable liquid bridge formation, clear spatial separation, reproducible signal response, and low background interference. This mold-based fabrication strategy produces reproducible, low-cost probes and offers an accessible approach for nano-DESI MS.