Ultrasensitive nanoelectrospray ionization-mass spectrometry using poly(dimethylsiloxane) microchips with monolithically integrated emitters.

Poly(dimethylsiloxane) (PDMS) is a widely used substrate for microfluidic devices, as it enables facile fabrication and has other distinctive properties. However, for applications requiring highly sensitive nanoelectrospray ionization mass spectrometry (nanoESI-MS) detection, the use of PDMS microdevices has been hindered by a large chemical background in the mass spectra that originates from the leaching of uncross-linked oligomers and other contaminants from the substrate. A more general challenge is that microfluidic devices containing monolithically integrated electrospray emitters are frequently unable to operate stably in the nanoflow regime where the best sensitivity is achieved. In this report, we extracted the contaminants from PDMS substrates using a series of solvents, eliminating the background observed when untreated PDMS microchips are used for nanoESI-MS, such that peptides at concentrations of 1 nM were readily detected. Optimization of the integrated emitter geometry enabled stable operation at flow rates as low as 10 nL min(-1).