Colorimetric determination of Cu2+ ions with a desktop scanner using silica nanoparticles via formation of a quinonediimine dye

- A Si nanoparticle-based Cu2+-selective colorimetric signaling probe was developed.
- Signaling is based on Cu2+-assisted oxidative coupling to yield quinonediimine dye.
- Selective and sensitive sensing was possible with a detection limit of 2.13 μM.
- The probe system could easily determine Cu2+ levels in wastewater using a scanner.

A new Cu2+-selective chromogenic reaction-based probe system that functions via Cu2+-assisted quinonediimine dye formation has been investigated. Aniline-functionalized silica nanoparticles showed a pronounced selectivity and a colorimetric Cu2+ signaling behavior that could be discerned with the naked eye upon Cu2+-induced oxidative coupling with 4-aminoantipyrine in aqueous solution. The selectivity of the method was readily established by the vivid colorimetric responses shown by signaling experiments conducted in a microwell plate. Cu2+ signaling by the silica nanoparticles was most pronounced at pH 7.0, but was not significantly affected by solution pH values between 5.0 and 7.0. The marked color change from colorless to violet could be easily detected with a desktop office scanner as a readily available signal-capturing tool. Using the scanner, the detection limit for Cu2+ in simulated wastewater by the probe was found to be 2.13 μM. The use of nanoparticle-immobilized aniline minimizes the possibility of human exposure to this toxic substance. Finally, a practical application of the designed method in the convenient determination of Cu2+ in simulated wastewater samples using an office scanner was demonstrated.

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