A planar on-chip micro-nib interface for NanoESI–MS microfluidic applications

We present a novel nanoelectrospray emitter tip based on the principle of a nib rather than a nozzle for nano-electrospray ionization-mass spectrometry (ESI-MS) applications. The fabrication of the micro-nibs relies on micromachining techniques using the epoxy-based negative photoresist SU-8. A double exposure photolithographic process has been employed to form a nib in a membrane-like structure. The nibs contained a capillary slot measuring 20 µm at the tip end. The nib sources were successfully tested on an ion trap mass spectrometer using standard peptide samples at low concentrations, down to 1 µM. High voltage (HV) supply was achieved using platinum wire inserted in a liquid reservoir. A Taylor cone was clearly seen protruding from the nib tip and was determined by the dimensions of the capillary slot.