Aptamer‐Based Origami Paper Analytical Device for Electrochemical Detection of Adenosine

Here we report a self-powered origami paper analytical device (oPAD) that uses an aptamer to recognize an analyte, a glucose oxidase (GOx) tag to modify the relative concentrations of an electroactive redox couple, and a digital multimeter (DMM) to transduce the result of the assay. The sensor is self-powered in that it self-generates an electrical signal so that the read-out process is similar to testing a battery. The principle of the sensor is illustrated in Scheme 1. Briefly, the device is printed on a single piece of paper, folded into a three-dimensional (3D) configuration, and then laminated in plastic. An aliquot of sample is loaded at the inlet, split into two channels, and then directed to microbeads entrapped within the channels. In one channel, an aptamer immobilized on microbeads binds to the target and releases a GOx-labeled DNA strand that flows downstream. No aptamer is present on the microbeads in the other channel, which is used as a control. The split fluids terminate in an hour-glass-shaped, two-compartment electrochemical cell. The waist of the hour glass serves as a salt bridge between the two half cells. In one of the half cells, GOx catalyzes the oxidation of glucose, which in turn results in conversion of Fe(CN)63− to Fe(CN)64−.The difference in concentrations of Fe(CN)63− and Fe(CN)64− in the sensing half cell and control half cell results in a voltage that is used to charge a capacitor. When the switch (lower part of Scheme 1) is closed, the capacitor discharges through the DMM. The capacitor provides a high instantaneous current, in effect an amplified current, and hence a higher sensitivity than a direct current measurement.