Whole virus detection using aptamers and paper-based sensor potentiometry

Paper-based sensors, microfluidic platforms and electronics have attracted attention in the past couple of decades because they are flexible, can be recycled easily, environmentally friendly and inexpensive. Here, we report a paper-based potentiometric sensor to detect the whole Zika virus with a minimum sensitivity of 0.26 nV/Zika and a minimum detectable signal (MDS) of 2.4x10⁷ Zika. Our paper sensor works very similar to a P-N junction where a junction is formed between two different regions with different electrochemical potentials on the paper. These two regions with slightly different ionic contents, ionic species and concentrations, produce a potential difference given by the Nernst equation. Our paper sensor consists of 2-3 × 10 mm segments of paper with conducting silver paint contact patches on two ends. The paper is dipped in a buffer solution containing aptamers designed to bind to the capsid proteins on Zika. We then added the Zika (in its own buffer) to the region close to one of the silver paint contacts. The Zika virus (40 nm diameter with 43 kDa or 7.1 × 10^-20 gm weight) became immobilized in the paper's pores and bonded with the resident aptamers creating a concentration gradient. Atomic force microscopy and Raman spectroscopy were carried out to verify that both the aptamer and Zika become immobilized in the paper. The potential measured between the two silver paint contacts reproducibly became more negative upon adding the Zika. We also showed that a liquid crystalline display (LCD) powered by the sensor can be used to read the sensor output.