The Light Bulb PCR Machine

This clever device shatters the cost of current thermal cyclers and increases the accessibility of this integral piece of bioware. For less than $50, it could be yours.

Citizen Scientists have already begun to empower themselves and others by making biology more accessible. The first wave of change, it seems, is coming in the form of cleverly-built hardware – PCR machines, incubators and centrifuges made from materials one normally wouldn’t  think to employ.

A few weeks ago I struck on a 2002 publication by Brian Blais describing a working PCR machine he built using a light bulb as its heating element.

Ingenius.

Since then, it seems there has been no further development in this potentially revolutionary type of machine – so I decided to build one myself. I had almost no prior electrical experience, but I was willing to learn. If I was able to build this machine in less than a week, then you can too (and it will probably blow this one out of the water).

Using only Home Depot and Radio Shack products accessible to anyone, I built this PCR machine for less than $20. This prototype requires a $30 Arduino Uno to operate (which was already available), but the control system in future models can be scaled down to a much simpler circuit, an LCD screen and a few buttons.

I decided to use 4’’ PVC pipe and couplings for the enclosure because of the range of attachments available. The machine consists of three layers: the top is a 3’’ to 4’’ adapter with holes to house the PCR tubes, the middle is a coupling that holds the fan and light bulb in place and the bottom is a coupling that shelters the arduino and a safety switch. The 110V AC is wired with a simple two-wire connector.

The arduino monitors the temperature  by using a thermistor, basically a resistor that lowers the resistance the hotter it gets. The thermistor is wired in-line with a 5V potential and an analog input pin of the Arduino. The hotter the thermistor gets, the higher the potential flows to the input pin.

During a run, the thermistor is placed inside one of the tube holes. For more accurate readings in the future, the thermistor can be submerged in water and mineral oil inside a PCR tube.

The thermistor can be substituted for a more consistent IC temperature sensor, such as the LM335, in future models.

The schematic for the machine is extremely simple – due to the Arduino’s simple interface requirements, many hardware components can easily be subbed for software programming.

5V relays are used to control the fan and light bulb. These relays  can be switched on and off using the native output of the Arduino – no amplification required.

 

The entire control module could fit onto the arduino using a prototyping shield called the makershield. I programmed the arduino to control the relays and sense the temperature through the thermistor, then wrote some code to allow the machine to cycle through the three designated temperatures for the PCR reaction.

The machine cycles quickly – a standard 1KB run takes less than 2 1/2 hours to complete. I am in the process of testing the machine using PCR reagents, but given Mr. Blais’s success in the 2002 model I am confident it will work.

Instead of buying a thermal cycler for your lab, I encourage you to go out and build your own machine! This entire system took about $50 (+ a computer to program it) and less than 5 manhours to construct.

My arduino code and more details about the machine to help get you started are available RusselDurret.com.

Russell Durrett is a Research Specialist in Bioinformatics and Genetic Engineering in the Mason lab at Weill-Cornell Medical College and is a cofounder of GenSpace NYC, the world’s first community biology lab.

You can find this article and many more in Issue 01 of Citizen Science Quarterly

The $25 Thermal Cycler

Using a thermal cycler of his own design(circuit below) Brian Blais of Bryant College was able to achieve successful pcr.  It’s important to note, because using a simple incandescent light bulb he got ramping of 1C/sec for heating and .25C/sec for cooling which is only about 3 times slower than lab quality PCR machines. Not to mention his cost $25 and most pcr machines are in the >$1k range.

If you are a diybiologist and are planning on adapting Brians lightbulb pcr for your home lab, I’d recommend you adapt the circuit to utilize an arduino (or any prototyping platform with an ADC), that way you wont need to dedicate a laptop to run your thermalcycler as Brian did. My other thought is that by adding a computer fan during the cooling cycle it might help to improve the cooling rate.  Either way, if you try doing pcr using a lightbulb, let us know how it works and if you did anything to improve the technique.

Design and circuit via: http://web.bryant.edu/~bblais/projects/cycler/cycler-Feb02.pdf