Smartphone-assisted copper nanoclusters fluorescent sensing platform for visual determination of Congo red

In order to realize efficient detection of Congo red, fluorescence analytical method were adopted and investigated systematically. Based on the superior properties of papain and excellent performance of copper nanoclusters, papain stabilized copper nanoclusters (Cu NCs@PP) with blue fluorescence were rapidly synthesized via a one-pot method. The spherical Cu NCs@PP uniformly dispersed with an average size of about 2.5 nm and excellent stability. The as-established Cu NCs@PP emitted stronger fluorescence around 436 nm under the excitation wavelength of 358 nm. Under the optimal measurement conditions, the sensitive detection of Congo red was accomplished with linear range of 0.5–160 μM and detection limit of 0.085 μM. In the light of inner filter effect, Cu NCs@PP displayed excellent selectivity in Congo red detection. More importantly, the regular change of fluorescence color made it possible for visualization determination of Congo red. Coupled with satisfactory recovery tests, this as-developed Cu NCs@PP had prospective future in practical application.