(295n) Multiplex Electrochemistry: Translation to Quantitative Microarray for Medicine

Immobilization of DNA oligomers on Au has been pervasively applied to a broad range studies. Primary motivation has been the possibility of electrochemical detection to quantify DNA binding to microarray for early diagnosis of cancer, cardiovascular and neurological diseases. However, the tantalizing fundamental results of a “perfect switch” between ssDNA versus dsDNA signal for the electrochemical beacon (EcB) method discovered two decades ago (Fig. 1(a)) has not been translated. We studied EcB by local electrochemistry on 10 to 100 µm spot by an instrument developed by Vajra Instruments called SEED.¹ We observe a distribution of conformation making the switch imperfect (Fig. 1(b)). We observed that,

• before, MCH backfilling the MB on ssDNA has total freedom to undergo redox but contrary to “perfect switch” mechanism redox appears after (Fig. 2); and
• the peaks (R_max) for oxidation and reduction measured by SEED on the same chip shows that the decrease in the signal on binding depends on the length of the probe (Fig. 3).

Based on these observations we have developed a strategy to increase the Limit of Quantification (LOQ) from 1 picomolar in previous studies to 10 attomolar that is significantly better than qPCR for short chain nucleic acids such as, microRNA (Fig. 4). We will describe the modified mechanism leading to the strategy that improved the performance by orders of magnitude.

1. Tevatia, R.; Prasad, A.; Saraf, R. F. Electrochemical Characteristics of a DNA Modified Electrode as a Function of Percent Binding. Analytical Chemistry 2019, 91, 10501-10508.