Fig. 2.

SARS-CoV-2 aptamers: a 51-bp aptamer with 3 hair-pined structures selective to RBD [17], 67-bp 2 hairpin sequences [17], 20-bp aptamer with 1 loop (www.basepairbio.com), 58-bp aptamer [30]. b Differential pulse voltammograms (DPVs) of a gold electrode functionalized with a cysteine-modified 20-bp COVID-19 aptamer (10 μg mL⁻¹ for 2 h) using three different electrochemical mediators (1 mM in 0.1 M PBS, pH 7.4). DPV parameters: E_step = 0.01 V; E_pulse = 0.06 V, t = 0.02 s, scan rate = 0.06 V/s