Re: [DIYbio] What's wrong with open source PCRs

On 1/27/16 6:50 AM, Bryan Jones wrote:

My understanding is that PCR machines typically use solid metal blocks because they make it much easier to heat all the samples evenly and keep a steady temperature. The high heat capacity of the metal minimizes spacial and temporal fluctuations.

Yes, but wasn't that in the dark ages before today's machining could cheaply craft a perfectly shaped *hollow* form which could circulate a more thermally-conductive liquid into a much, much larger capacity mass i.e. external temperature bath?    For example:  newer very highly thermally conductive ceramic epoxies, cast as a PCR tube-shaped mold yet hollow to allow rapid fluid pumping to/from hot & cold baths would be very temp stable and physically light with faster ramp rates; note: temperature sensors embedded during the setting process to algorithmically control this.

Even temperatures across all samples is critically important.  Any thermocycler design must absolutely guarantee this within some very small % tolerance and the design must be verified to work within this tolerance.

On the rant about the use of outdated technology in designs, an analogy, tankless water heaters for home use (showers and kitchen faucets) have been available for some time, yet are still niche products despite their technology superiority, mainly because builders are either not aware of the benefits or are stick-in-the-muds.  So lab device technology is not so different from the same builders of a kitchen toaster in that way either.

## Jonathan Cline  ## jcline@ieee.org  ## Mobile: +1-805-617-0223  ########################      

On Tue, Jan 26, 2016 at 9:09 PM Jonathan Cline <jcline@ieee.org> wrote:

Excellent point about a single-well thermocycler.  Rarely do you want to run 1 tube at a time however.  Need several tubes at a minimum, for experimental controls, redundancy, etc.  OpenPCR is considered personal-pizza-size with only 16.  Apple's USB-C laptop charger is rated at 29W ( 2A @ 14.5V ), for the Macbook which has no other power supply input, only USB-C -- so the supply isn't in either the 60W or 100W class.  Plastic tubes are unfortunately not very thermally conductive.  The liquid volumes are under 100 uL (typical synbio anyway).  I didn't check your math, I do agree that static temperature baths are the cheapest solution - either move the tubes to the bath or move the bath medium to the tubes.  Most of the energy goes into heating/cooling the metal mass holding the tubes, which oddly enough are machined out of large solid metal blocks -- there may be a benefit to this that I can't see, otherwise I consider it a baffling choice (no pun intended).  Some thermocyclers physically halve the heater block mass (I suppose you could call this, decoupling) when ramping temperature down.  Note the use cases may include incubation temperature for long periods of time (37 C typical, or up to 65C in some cases, for up to several hours total), this would result in steady state power draw, not peak power -- this is important regarding the assumption that a battery could be used instead (not sure I'd want to use a battery unless it was remote field use).  Another static temperature use case is 4C for many hours, for example.

The Lava-amp micro thermocycler was under 1W (I think).  Even had it worked out, I'm not sure it would have gained acceptance because it used a different form factor - didn't use "old fashioned" tubes.  Although there could be real experimental differences in results if changing equipment, obviously the ideal thermocycler would increase the surface area of the liquids for maximizing energy transfer -- i.e. not use plastic tubes.  That's one part of the approach the Lava-amp design took.

About this assumption:

>Now suppose I have two water baths, one at 60 degrees, and another at 90 degrees.
>I use a small motor to move the 96 tubes from one bath to the other.
>I can have a small fan that blows over the tubes when they go from the hot bath to the cold bath to speed the cooling, so that when the tubes hit the 60 degree bath they are already at 60 degrees.

Historically there are thermocyclers designs which use fans and electronically controlled vents to direct heated (or room temperature) air for assisted ramping.

Here's an example typical use case (synbio purification-ligation) to contrast to your example.

100 cycles	12 °C	60 s
	22 °C	60 s
	12 °C	60 s
	22 °C	60 s
	12 °C	60 s
	22 °C	60 s
	12 °C	60 s
	22 °C	60 s
Hold	16 °C	infinite

## Jonathan Cline  ## jcline@ieee.org  ## Mobile: +1-805-617-0223  ########################             

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