Fabrication of a polymer nozzle array in a microstructured fibre as a nanoelectrospray emitter for mass spectrometry

We report a modified silica microstructured fibre (MSF) as a multiple electrospray (MES) emitter, with dimensional compatibility with conventional liquid chromatography and mass spectrometry equipment, to generate stable electrospray from a wide range of applied potentials and flow rates. An array of polymer nozzles is fabricated in the MSF by a procedure involving templated polymerization of microtubes and wet chemical etching of the silica at the tip. The structure of the emitting end of the MSF was optimized with respect to the etching process, and the morphology of the polymer nozzles was optimized with respect to polymerization conditions. The mechanisms of the etching and of the templated polymerization of the microtubes were explored. Optimization experiments were performed using commercially available MSF having 126 tubular air channels arranged in a hexagonal pattern with channel diameter of ∼5.6 μm. However, the flexibility and versatility in the pattern, shape, and size of channels in MSFs allowed a custom-designed MSF to be fabricated and tested for MES. In the new design, six channels were evenly spaced in a radial pattern, and when polymer nozzles were made, six stable electrosprays were observed over a wide range of electrospray conditions. Using these MES emitters, the spray current is enhanced by a factor related to the number of nozzles.