Re: [DIYbio] Electronic requirements for redesign of Arduino PCR thermal cycler

The reaction mixture will condense on the coldest part of the pcr tube, for instance, any surface not enclosed in the main heated block and exposed to ambient air.

One solution is to establish a temperature gradient from the top of the cap to the block by touching the cap with a second hot surface, preferably hotter than the main block such radiative and conductive heat transfer from the heated lid raises the temperature of all surfaces of the pcr tube exposed to air above the current temperature of the block. 

But you don't need s Peltier to do this. You just need a heat source you can keep at a constant temperature guaranteed to be hotter than any of the pcr temps.

It would be interesting to explore a hybrid design combining dynamic conductive heating in the tube block with constant radiative heating from a lamp or hot air flow positioned at just the right distance, instead of a heated lid in constant contact with the cap. Can the radiative heat source be set up to always add +20C to the exposed cap and 5-10 C to the reaction mixture? If so, perhaps such a design could lead to faster ramp times, by switching the radiator off during cooling.

Does the transparent plastic most pcr tubes are made from absorb IR?

Or maybe all that matters is if the reaction mixture absorbs the radiative energy. Not sure. Would pcr work in a transparent Quartz vessel in a freezer that was pulsed by a powerful IR source? Or would that be condensation city?

Cheers

Mac

On Thursday, February 26, 2015, Andy Morgan <andrew.r.morgan@gmail.com> wrote:

Thanks for the heads up Josiah.

That's a bit annoying, I was hoping that I could have the lid at the same temperature as the tubes, allowing me to run the whole thing off of just the one simple circuit described in the original instructable.

Perhaps I'll look into using one peltier element for the base and another smaller one for the lid, although that might mean I'd have to hook up a whole other arduino board and solid state relay. Not to mention that all sounding a wee bit over my head. If I could hook them both up to the one arduino board that might be a little bit simpler though.

I came across this design (http://2013.igem.org/Team:Paris_Saclay/PS-PCR/detailed_description) that was build (and apparently for only 30 euros!) using peltier elements, but the electronic schematics look intense.

On Friday, February 27, 2015 at 2:12:14 PM UTC+13, Josiah Zayner wrote:

Keeping the lid at a constant temp of ~90C will generally suffice. Most PCR machines hold the lid at 90C - 105C.

I have tried doing the lid at same temperature as the tubes but received condensation. I think this might have been because of the different heat transfer rates? Maybe you can figure it out?

Looking on eBay these days you can buy most of the parts for the Arduino thermalcycler for much cheaper than the $85USD pricetag (inexpensive Arduino boards &c). Also, keep on eye out on eBay for thermal cyclers. Sometimes people don't know what the actual equipment is so they just list it as brand and product names so searching directly for brand names help. I have found some for under $100 that work great though this is from the US, so who knows what you might find?



Josiah




On Thursday, February 26, 2015 at 3:02:09 PM UTC-8, Andy Morgan wrote:

Ah it all becomes clear, I was wondering why they listed a 12V power supply AND a regular power cable.

Thanks Simon.

On Friday, February 27, 2015 at 8:22:16 AM UTC+13, Simon Field wrote:

I presume the power supply is simply for the Arduino part of the project, which is unchanged from the original. In fact, the only thing that has changed is the heater. It's like swapping a 40 watt light bulb for a 100 watt light bulb. You don't have to change anything else.

-----

Get a free science project every week! "http://scitoys.com/newsletter.html"

--
-- You received this message because you are subscribed to the Google Groups DIYbio group. To post to this group, send email to diybio@googlegroups.com. To unsubscribe from this group, send email to diybio+unsubscribe@googlegroups.com. For more options, visit this group at https://groups.google.com/d/forum/diybio?hl=en
Learn more at www.diybio.org
---
You received this message because you are subscribed to the Google Groups "DIYbio" group.
To unsubscribe from this group and stop receiving emails from it, send an email to diybio+unsubscribe@googlegroups.com.
To post to this group, send email to diybio@googlegroups.com.
Visit this group at http://groups.google.com/group/diybio.
To view this discussion on the web visit https://groups.google.com/d/msgid/diybio/ba876564-210f-4558-8968-78c096bb5d2f%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

--
Sent from my Rotary Phone