A very neat picospritzer has been created by Joseph Raimondo using basically a solenoid valve, microcontroller and a power source. You can find more description of the project on the lab website or read a transcript below:
Many laboratories require a means to deliver picolitre or nanolitre volumes. We use a picospritzer for delivering small puffs of GABA or other neurotransmitters to activate receptors on single neurons within brain slices. Commercial Picospritzers can cost roughly $3000 or in South African terms about R30 000. Inspired by a post describing a custom built Picospritzer on Labrigger, we built our very own custom made DIY picospritzer for about R4000. It’s African and decidedly less dangerous than the local snake it’s named after: the Puff Adder.