Ballpoint pen tips as robust cone-jet electrospray emitters

This technical note documents the use of ballpoint pen tips as robust electrospray emitters. The embedded microsphere helps stabilize Taylor cones by effectively reducing the height of the liquid meniscus and significantly decreasing the viscous damping time of the Taylor cone. The microsphere also provides a mechanism for the Taylor cone to continuously adapt its base diameter to match the voltage applied. As a result, the ballpoint pen electrospray emitter noticeably expands the operation envelope in the flow rate-voltage space.