The Mullis (named after Kary Mullis, winner of the Nobel Prize for PCR) is a project of the State College Reprap Users Group. It is an open source, RepRap based PCR machine. The design uses a readily available tray for PCR, which is carried back and forth between two heated containers. It is easily converted from an Open Hybrid Mendel, or any Mendel Derivative.
UPDATE 2/27/12: First PCR reaction was successful, but had a lot of room for improvement. Pictures and results soon.
Mullis v. 1
The Mullis v.1 is designed to be built from the Open Hybrid Mendel (OHM) with as little modification as possible. It uses a combination of the open x carriage and the y axis motor assembly. The PCR tray is raised and lowered by a winch system into two separate heated water baths. The tray moves on an extended x axis between the two water baths.
|X Carriage||1||Carriage Base|
|1||X Angled Arm|
|Extruder||1||Herringbone Drive Gear|
|1||Herringbone Driven Gear|
|1||Bearing and Motor Bracket|
|4||Y Bar Clamp|
|1||Y Motor Bracket|
|1||Y Idler Bracket|
- Two smooth rods, approximately 36 inches in length.
- One PCR tray, loaded with samples.
- One tall laboratory stand to mount the axis well above the water baths.
- Two independently heated, temperature controlled water baths. The baths need to be significantly larger than the tray.
The Gcode for the Mullis consists of a header, then code for one cycle which is repeated for the desired number of cycles. Here is the commented code that we used. Values need to be adjusted based on distances, materials, and extruder design. Due to the limited processing power of the electronics for the Reprap, I recommend deleting the comments before running the code. A python script to generate this code is coming soon.
M28 X18 ; home x axis
G91 ; use relative positioning
G1 X10 F2200 ; these three lines are the header
G1 F50000 ; this is the speed of the motor, adjust it to make the extruder go faster or slower.
G1 E2500 ; Lower tray for a length of units. To go farther, adjust the number after the E (extrude).
G4 P30000 ; this is the pause command. P is the time paused in milliseconds.
G1 E-2500 ; this moves the extruder backwards, retracting the PCR tray
G1 X250 F2200 ; this moves the x carriage to the next bath. the number after the F controls the speed (feedrate).
G1 E2500 F50000 ; Lower PCR tray 2500 steps
G4 P30000 ; pause for 30 seconds
G1 E-2500 F50000 ; Raise PCR tray by 2500 steps
G1 X-250 F2200; move PCR tray to first bath.
- this sequence will be repeated for each cycle of the PCR process.
PCR (Polymerase Chain Reaction)
PCR (Polymerase Chain Reaction) is a DNA replicationg technique. A DNA sample is set in a solution containing primers and nucleotides (A,T,C,G). The DNA is heated up quickly, so that it denatures (untwists) and then separates. It is then annealed (cooled), allowing the primers to attach to the open halves of the DNA strands. Next, an enzyme (Taq polymerase) extends the strands by allowing complimentary nucleotides to become attached to each open strand of DNA. This results in two separate but identical strands. The process is repeated until millions of copies of the sample are made. (For more on PCR, see http://en.wikipedia.org/wiki/PCR ).
Normally, PCR machines cost several thousands of dollars. Our goal is to make this technology available open source. All you will need is a RepRap, a PCR tray (which can be printed), and heating.