Low-cost colorimetric alternative of qPCR for DNA sensing based on intercalation with methylene blue

When methylene blue (MB) dye is added to a test sample containing DNA, a change in absorbance is observed due to intercalation of MB into the DNA base pairs. In this work, we demonstrate a low-cost phase sensitive detection (PSD) system to realize a highly sensitive colorimetric sensor for detecting the change in absorbance. The optical PSD sensor produces a linear response for 1 ng/µL to 15 ng/µL DNA concentration range with a sensitivity of approximately 20 mV/ng/µL. The sensor also produces measurable change in output with progression of number of cycles in PCR, and could be used as a low-cost alternative to quantitative PCR (qPCR).