Abstract:
Cancer currently stands as the second-leading cause of death worldwide. Studies reveal colorectal cancer (CRC) to be the 4th leading cause of mortality due to cancer. It is estimated that about 30% of CRC cases are hereditary, of which 5% are attributed by known syndromes, particularly Lynch Syndrome. Lynch Syndrome (LS) is caused by loss or malfunction of proteins responsible for DNA mismatch repair proteins (MMR), mostly MLH1 and MSH2, causing increased risks of developing CRC. Despite the small percentage accounted with the disease, the severity of the illness still remains immense since 80% of these patients eventually develop CRC and an overwhelming 40-60 % of female patients develop endometrial cancer, the major of cancer in women in developing nations. Current diagnostic procedures for LS involve testing tumor tissue for microsatellite instability and the presence/absence of MMR proteins by immunohistochemistry (IHC), followed by germine testing for mutations in MMR genes, if warranted. While genetic testing is becoming more cost-effective and accessible, a major problem with this approach is that the functional and pathological consequences of a majority of mutations and small insertions/deletions in MMR genes are unknown, rendering the tests results inconclusive in many cases. Therefore the need for an accurate means of early diagnosis is clearly imminent to prevent the growing threat. This pilot study aims to fabricate a DNA-graphene-polypyrole (DGP) based biosensor to diagnose deficiency of functional MMR proteins present in patients at a scale of less than ng/ ml. Biotinylated DNA probes are immobilized on an avidin film coated over a polypyrole-graphene layer, which in turn is finely deposited over a gold-plated circuit using electrochemical polymerization technique. A detailed morphological characterization has been performed using both scanning electron microscope (SEM) and atomic force microscope (AFM) topography of the DGP biosensor. Quantitative analysis is performed by measuring electrochemical impedance spectroscopy (EIS) where the change in impedance of the samples is recorded by varying frequency between 1MHz- 100 MHz. Though still a work in progress, we assume that the attachment of the MMR proteins onto the mismatched sequences should alter the impedance of the fabricated DGP biosensor. A final analysis is being conducted to confirm our assumptions.
