Nanoparticle-based colorimetric biosensor for the detection of telomerase activity based on the peroxidase-mimicking activity of nanogold.

The early detection of cancers can be done by monitoring telomerase activity as it is considered a cancer biomarker. Several strategies for detecting telomerase have been developed, including polymerase chain reaction (PCR)-based and PCR-free assays. Despite various advantages of these strategies such as high sensitivity and accuracy, they have many limitations such as being time consuming and labor-intensive; they are also prone to provide false negatives and unsuitable for onsite testing. This study suggests a simple, fast, and low-cost method for the ultrasensitive detection of telomerase by exploiting the selective cleavage of exonuclease III and catalytic activity of nanogold. In the presence of telomerase, the primer is elongated and hybridized with its complementary strand, resulting in the formation of dsDNA with a blunt end. The dsDNA is then cleaved by exonuclease III to release the elongated primers. Once released, these primers get adsorbed on nanogold and suppress its catalytic activity. In the absence of telomerase, exonuclease III completely digests the dsDNA, resulting in the uninhibited catalytic activity of nanogold that can oxidize TMB into a blue-colored product. The proposed method enabled the detection of telomerase in 100 MCF-7 cells by the naked eye. Absorbance measurements revealed a detection limit of ∼0.3 MCF-7 cells with a wide linear range from 102 to 106 cells. This sensing approach provided a simple PCR-free method for the detection of telomerase with high sensitivity and specificity, demonstrating its potential utility as a proof-of-concept platform for telomerase-related cancer research, with future diagnostic development contingent upon further validation.