In the early days of patch clamp electrophysiology, everyone made their own patch clamp amplifiers because there were none commercially available. I was lucky enough to be educated by scientists of such lineage, and in one of my classes, as an exercise, we built a simple patch clamp amplifier with series resistance compensation.

Even after patch clamp amplifiers became commercialized, there were still a few aficionados who insisted on their own designs. But very quickly, companies started building so much technology into the amplifiers, that the amps surpassed what an aficionado could practically engineer in their own labs. Although expensive, the amps were affordable and offered a great deal of functionality.

Perhaps 2-photon laser scanning microscopes (2pLSMs) are approaching a similar turning point. With the expiration of the patent on 2pLSM and the flood of commercial interests in the market, including open source designs like the Janelia Farm scope pictured above (link), we are starting to see much more technology being built into these scopes.

Features such as high speed scanning and wavefront shaping are becoming commonplace. Although both of these can easily be implemented on custom built scopes, the pace of “featurization” of scopes is picking up. Perhaps in five to ten years, no one will be building their own scopes anymore because companies are selling such high tech scopes at very competitive prices.

This website is about open solutions for science, but this is primarily motivated by efficiency, i.e., not reinventing the wheel. We’ll keep covering custom 2pLSM information, for now, but only as long as it is practical. We do not anticipate covering how to build a custom patch clamp amplifier, but it could happen.

On the topic of custom two-photon imaging rigs, what kind of PMTs do you want to go with? Naturally, you’ll order yours to be hand selected for high quantum efficiency and low noise, because you’re such an aficionado, but will you go for the still popular R3896s (pdf) from Hamamatsu, the miniature R6357s (pdf), or the GaAsP H7422s (pdf)?

Increasingly the answer is the latter. It’s hard to compete with GaAsP PMTs. However, the stock versions do have some annoyances: they switch off during transiently high signals and have to be manually reset, they have bulky cooling systems with noisy fans, and the detector is set back into the body so the field of view is quite narrow. Hamamatsu has heard all of this before and has a number of different variants you can order, but this is not widely known. Here is a summary sheet of all the 7422 variations available (pdf, includes models H10770, H10769, H10771 and H8224). Here are the spec sheets for the uncooled, very wide field of view versions (pdf, pdf).

The dark count is what skyrockets when you lose the cooling. From 100 or less per second cooled, to 6000 or more uncooled. Of course, even if your dwell time is a relatively long 10us per pixel, this comes out to one extra count every 17 pixels, which isn’t going to kill you in many applications, particularly those with bright fluorescence. Many people run the MOM scope (aka Denkscope) with no cooling on the H7422 PMTs, and they’re just fine.