Ultra-Low-Cost Integrated Silicon-based Transducer for On-Site, Genetic Detection of Pathogens

Estefania Nunez-Bajo; Michael Kasimatis; Yasin Cotur; Tarek Asfour; Alex Collins; Ugur Tanriverdi; Max Grell; Matti Kaisti; Guglielmo Senesi; Karen Stevenson; Firat Guder

First, we characterized the electrochemical redox processes for methylene blue (MB) using cyclic voltammetry (Figure 4A) . We chose MB because the electrochemical approach we used for the detection of DNA involves the use of MB [23] [24] [25] as an intercalating redox reporter. During NA amplification, MB is intercalated between guanine-cytosine base pairs of the double-stranded DNA (ds-DNA) which provides an electroanalytical signal correlated with the concentration of ds-DNA in the sample. We prepared a 125 µg mL -1 solution of MB in 10 mM phosphate-buffered saline pH 7 (PBS) and swept across a range of potentials between -400 to 200 mV at a scan rate of 100 mV s −1 to characterize the electrochemical processes involving MB and electrodes. We determined that the anodic peak current, originating from the oxidation of MB on the electrode surface, appears at −67±2 and cathodic peak (due to reduction) at −97±4 mV versus Ag ( Figure 4A ). The absence of peaks with nearly overlapping anodic and cathodic curves in buffer alone indicates that the electrodes are electrochemically and mechanically stable and high performance (e.g., low capacitive current). We have performed ( Figure 4B ) square wave voltammetry (SWV), a substantially more sensitive electroanalytical method, to measure the concentration of MB in PBS in a range between 0 -125 µg mL -1 using a potential window from -500 mV to -250 mV versus Ag (corresponding to the anodic process). The SWV measurements using TriSilix produces an electroanalytical signal (peak current intensity) that is linearly related to the concentration of MB in the range 0.5 µg mL −1 -80 µg mL −1 with an R 2 = 0.9963 ( Figure 4C curve denoted by 'RT'). We have also characterized the analytical performance of TriSilix for performing SWV measurements when the chip was operated at elevated temperatures. To prevent evaporation of the solvent (i.e. water) from the sample solution, a small amount (10 µL) of mineral oil was added to the reservoir. Since both isothermal and cyclic NA amplification reactions require heating; the effect of temperature on the electrochemical measurements is important. As shown in Figure 4C , the peak current intensity (measured from the recorded SWVs) increased two to four times in comparison to room temperature when operated at higher temperatures; this is due to enhanced transport of the analyte to the surface of the electrode. 26- author/funder. All rights reserved. No reuse allowed without permission.