A Simple Method for Developing a Hand‐Drawn Paper‐Based Sensor for Mercury; Using Green Synthesized Silver Nanoparticles and Smartphone as a Hand‐Held‐Device for Colorimetric Assay

Mercury ions are highly toxic at trace levels, and its pollution has posed a significant threat to the environment and public health, where current detection methods mainly require laborious operation and expensive instrumentation. Herein, a simple, cost‐effective, instrument‐free approach for selective detection of Hg(2+) based on a hand‐drawn paper‐based naked‐eye colorimetric device is developed. To develop a hand‐drawn paper‐based device, a crayon is used to build hydrophobic barriers and a paper puncher is applied to obtain patterns as a sensing zone. A green method for the synthesis of silver nanoparticles (AgNPs) is applied using Achillea Wilhelmsii (Aw) extract. The sensing ability of Aw‐AgNPs toward Hg(2+) is investigated in both solution‐phase and paper substrate loaded with Aw‐AgNPs using colorimetric methods. For the paper‐based sensor, the quantification of the target relies on the visual readout of a color‐changed sensing zone modified with Aw‐AgNPs. Under optimal conditions, the color of Aw‐AgNPs in aqueous solution and on the coated paper substrate can change from brown to colorless upon addition of target, with a detection limit of 28 × 10(−9) m and 0.30 × 10(−6) m, respectively. In conclusion, the present study indicates the potential of this hand‐drawn eco‐friendly paper‐based sensor for monitoring of mercury.