Bioengineers at the University of California, San Diego have developed an electrical graphene chip capable of detecting mutations in DNA. Researchers say the technology could one day be used in various medical applications such as blood-based tests for early cancer screening, monitoring disease biomarkers and real-time detection of viral and microbial sequences. The advance was published June 13 in the online early edition of Proceedings of the National Academy of Sciences.
“We are at the forefront of developing a fast and inexpensive digital method to detect gene mutations at high resolution—on the scale of a single nucleotide change in a nucleic acid sequence,” said Ratnesh Lal, professor of bioengineering, mechanical engineering and materials science in the Jacobs School of Engineering at UC San Diego.
The technology, which is at a proof-of-concept stage, is a first step toward a biosensor chip that can be implanted in the body to detect a specific DNA mutation—in real time—and transmit the information wirelessly to a mobile device such as a smartphone or laptop.
The team led by Lal, who serves as co-director for the Center of Excellence for Nano-Medicine and Engineering, a subcenter of the Institute of Engineering in Medicine (IEM) at UC San Diego, and Gennadi Glinsky, a research scientist at IEM, developed a new technique to detect the most common genetic mutation called a single nucleotide polymorphism (SNP), which is a variation of a single nucleotide base (A, C, G or T) in the DNA sequence. While most SNPs have no discernable effect on health, some are associated with pathological conditions such as cancer, diabetes, heart disease, neurodegenerative disorders, autoimmune and inflammatory diseases.
Current SNP detection methods are relatively slow, expensive and require the use of cumbersome equipment. “We’re developing a fast, easy, inexpensive and portable way to detect SNPs using a small chip that can work with your cell phone,” said Preston Landon, a research scientist in Lal’s research group and co-first author on the PNAS paper.
The chip consists of a DNA probe embedded onto a graphene field effect transistor. The DNA probe is an engineered piece of double stranded DNA that contains a sequence coding for a specific type of SNP. The chip is specifically engineered and fabricated to capture DNA (or RNA) molecules with the single nucleotide mutation—whenever these pieces of DNA (or RNA) bind to the probe, an electrical signal is produced.
The chip essentially works by performing DNA strand displacement, the process in which a DNA double helix exchanges one strand for another complementary strand. The new complementary strand—which, in this case, contains the single nucleotide mutation—binds more strongly to one of the strands in the double helix and displaces the other strand. In this study, the DNA probe is a double helix containing two complementary DNA strands that are engineered to bind weakly to each other: a “normal” strand, which is attached to the graphene transistor, and a “weak” strand, in which four the G’s in the sequence were replaced with inosines to weaken its bond to the normal strand. DNA strands that have the perfectly matching complementary sequence to the normal strand—in other words, strands that contain the SNP—will bind to the normal strand and knock off the weak strand. Researchers engineered the chip to generate an electrical signal when an SNP-containing strand binds to the probe, allowing for quick and easy SNP detection in a DNA sample.