Your Science Zine

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

0 Comments

  1. Mahmud April 10, 2011 Reply

    Where do you put your samples?

  2. Russell Durrett April 10, 2011 Reply

    The tubes go inside the circle of small holes on the top, tapering portion of the machine. This brings them in proximity of the light bulb and in the air flow of the fan.

  3. Philip April 11, 2011 Reply

    Neat and simple, though you should watch your circuit diagram symbols. The symbols you have labeled as “relays” are transistor symbols. Transistors would not work with AC. The symbol used for a “thermistor” is actually for a potentiometer.

  4. Shyamveer March 26, 2012 Reply

    Above you mentioned that you used “PVC pipe” and for PCR machine the temperature range should be minimum RT to 100 c but do you think that your outer PVC pipe will stay on this temp.

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