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.
The key component is a Solenoid 3/2 way valve built by Festo, which can open or close in about 2 ms. I’ve listed all the parts below with photos of how it was all put together. It is controlled by a TTL (5V) signal from a computer, with reliable timing and the ability to produce short puffs down to about 10 ms in duration. I hope you find this description useful.
Valve and Pressure System
Solenoid Valve, Pressure Regulator, Tubing and connectors:
1- Festo Precision Pressure Regulator LRP-1/4-4 (from 0.05 to 4 bar / 0.7 to 58 psi pressure range) Part No: 159501
2- Festo Precision Gauge MAP-40-4-1/8-EN (from 0 to 4 bar / 0.7 to 58 psi pressure range) Part No: 162842
3- Solenoid Valve MHE2-M1H-3/2G-M7 (3/2 way valve) Part No: 196130
4- KMYZ-4-24-2.5-B (plug in cable for valve – not essential) Part No: 193691
5- QSL-1/4-6 Festo Push-in/threaded L-fitting (L fitting to take input from pressure line to regulator port 1, takes 6 mm tube) Part No: 153047
6- QS-1/4-4 Festo Push-in fitting (to screw into port 2 of regulator) Part No: 190644
7- 2x QSM-M7-4-I Festo Push-in fitting (to screw into ports 1 and 2 of the solenoid valve) Part No: 153319
8- B-M7 Festo Blanking plug (blanking plug to block port 3 of valve / ie block exhaust port if required) Part No: 174309 – Update I discovered it is better not to utilise a blanking plug here – ie the pressure is delivered only for the duration of the puff and is released via the exhaust valve straight after
9- 1m of 4mm OD Festo Plastic tubing Part No: 159662
The Festo solenoid valve needs a 24V signal to open. Most computer controlled digiboards generate a 5V signal (TTL) to control components. As such we needed to build a small circuit which converts a 5V signal from the computer/ digiboard to a 24V signal in order to control the valve. This is done by using the 5V TTL signal to open or close the gate of a standard NPN transistor. We used a bit of strip board and the components listed below to build the circuit. It was then shoved in a black plastic box to make it look official!
Q1- Bipolar Transistor – BJT NPN Gen Purpose (Mouser Part No: 610-2N5088)
D1- Zener Diode 5V
D2- Zener Diode 24V
R1- 1K ohm resistor
R2- 0.82 ohm 3W resistor (could use a normal higher resistance resistor) (Mouser Part No: 667-ERX-3SJR82A)
The red lines here indicate the circuit connections via the back.
Power supply and other miscellaneous electronic items
– 24V DC power supply unit, 1.04A (Mantech Part No: 30C0007)
– DC power jack socket panel mount 2.1mm (Mantech Part No: 14C2716)
– BNC male connector socket (Communica Part No: 51K506-200A4)
– Black plastic box (Communica Part No: BTA1B)
– Strip board 100x300mm (Communica Part No: EXCU21-300)
– Wiring and a soldering iron to put it all together
We struggled to wire up the DC socket – the photo above shows what worked in the end.
After soldering the circuit board and and wiring it all up it got placed in a smart looking black plastic box.
And voila! We hope your PuffAdder gives you hours of puffing joy!