A More Efficient Polymerase Chain Reaction Procedure Through Interactions Between Light and Free Electrons

Kristine Wong

What would you say if someone told you that you could generate millions of copies of DNA samples in a matter of minutes with just the switch of a light?  It seems pretty unrealistic, right?  Well, bioengineers at the University of California, Berkeley have recently developed new technology that can make the PCR procedure much faster, more portable, and less costly with the help of light and free electrons.

The polymerase chain reaction, more commonly referred to as PCR, is an essential component in a variety of scientific research ranging from cloning experimentation to the diagnosis of genetic diseases to the analysis of ancient DNA samples.  Developed by Chemistry Nobel laureates Kary Mullis and Michael Smith in the 1980s, this revolutionary procedure lifted the barriers of genetic research by allowing scientists to amplify specific regions of a DNA sequence, resulting in thousands to millions and even billions of copies available for use in scientific experiments (Yang, 2015).  Because of this, PCR is especially applicable to genomic studies which frequently involve the use of DNA templates.

One drawback to the procedure, however, is the turnaround time – the PCR process can take up to an hour or longer to complete which can be cumbersome in time-sensitive experiments.  The problem lies in the time required to heat and cool the DNA samples.  The amplification process involves multiple cycles and repeated temperature changes in order to denature and separate the two strands of DNA and then subsequently bind the correct primer to a single strand in order to synthesize new DNA.  At the end of each thermal cycle, the amount of DNA is doubled.

PCR is powerful, and it is widely used in many fields, but existing PCR systems are relatively slow,” said study senior author Luke Lee, a professor of bioengineering at UC Berkeley. “It is usually done in a lab because the conventional heater used for this test requires a lot of power and is expensive. Because it takes an hour or longer to complete each test, it is not practical for use for point-of-care diagnostics” (Yang, 2015).

Therefore, to solve this problem, Lee and his research team developed a system that uses light-emitting diodes, also known as LEDs, to heat up free electrons on the surface of thin films of gold.  When the LEDs are on, they generates heat by causing free electrons in the gold foil to become excited and oscillate rapidly; once the LEDs are turned off, heat is no longer generated and the electrons stop oscillating.  Gold film was used because gold has properties that make it very efficient at absorbing light (Yang, 2015).

The researchers used thin films of gold that were 120 nm thick and an array of commercial LEDs in their experiments.  The LEDs were placed under microfluidic wells in a plastic chip that held the DNA sample and PCR mixture, and the gold foil was placed on the plastic chip.  The LEDs produced blue light with a peak wavelength of 450 nm for the most efficient light-to-heat conversion (Yang, 2015).

When this photonic PCR method was compared to the conventional PCR method, the results of the new test were much faster, completing thermal cycling in less than five minutes (Yang, 2015).

With this new, ultrafast photonic PCR test, point-of-care diagnostics will be dramatically improved, and the new test can be used in a variety of different settings unimpeded by time restraints.  By utilizing the interaction between light and free electrons on the surface of a metal, the time it takes to complete thermal cycling during PCR is drastically decreased from hours to mere minutes.  The system is also efficient and inexpensive, which will make DNA sample amplification in research much easier and more affordable for scientists.

Lee and his team of researchers are currently working on developing an ultrafast genomic diagnostic chip which photonic PCR can be integrated into for everyday use in the field of scientific research (Yang, 2015).

Reference List:

Yang, Sarah.  (2015, July 31).  Heating and cooling with light leads to ultrafast DNA diagnostics.  Retrieved from http://news.berkeley.edu/2015/07/31/light-speeds-up-pcr-test/

Editor: Ruby Halfacre