Quantum dots colorimetric sensing system based on paper-based aptasensor coupled with smartphone-based device

Quantum dots colorimetric sensing systems (QDs-CSSs) are promising tools for on-site monitoring or point-ofcare testing, owing to their high sensitivity, low cost, and direct visual readout. Despite these advantages, a notable challenge hindering their practical applications lies in the limited selectivity. To date, scant attention has been devoted to addressing this issue. In this study, we designed a ternary colorimetric probe integrating aptamer recognition with a QDs-based photocatalytic reaction. The target can specifically modulate the photocatalytic oxidation of o-phenylenediamine through its specific aptamer, thereby triggering a color change within the probe. We fabricated a multi-layer paper chip to load the probe and perform multi-target detection. We manufactured a multi-functional smartphone-based device to support the chip and provide automatic readout of the colorimetric sensing results. By putting these elements together, we obtained a QDs-CSS with high selectivity, good reproducibility, and low consumption. To prove its practical performance, this system was used for the simultaneous sensing of Pb(II), As(III), and Cd(II). A nM level detection limit was achieved and the testing results in actual samples agreed with those from the standard method. The proposed system opens up a new avenue to develop QDs-CSSs with high selectivity. Moreover, it shows promising prospects to be a general sensing system for various targets.