A Nanoparticle Autocatalytic Sensor for Ag⁺ and Cu²⁺ Ions in Aqueous Solution with High Sensitivity and Selectivity and Its Application in Test Paper

A novel nanoparticle autocatalytic sensor for the detection of Ag(+) and Cu(2+) has been constructed based on the oxidative ability of Ag(+) and Cu(2+) toward o-phenylenediamine (OPDA). Ag(+) and Cu(2+) can be reduced to zerovalent silver and copper, respectively, and then such zerovalent Ag and Cu species form silver and copper nanoparticles that can catalyze the reaction between OPDA and Ag(+) and Cu(2+). In the reaction, OPDA is oxidized to 2,3-diaminophenazine (OPDAox), which has a fluorescence emission at 568 nm. Under the optimal conditions, Ag(+) and Cu(2+) can be detected in the concentration ranges from 60 nM to 60 μM and from 2.5 nM to 25 μM, respectively. Through this facile approach, Ag(+) and Cu(2+) can be detected down to 60 nM and 2.5 nM, respectively. In addition, the sensor is utilized for the detection of Ag(+) and Cu(2+) in sewage, and we have obtained very good results that are consistent with those of inductively coupled plasma-mass spectroscopy (ICP-MS). Moreover, such a nanoparticle autocatalytic sensor is applied to test paper for the detection of Ag(+) and Cu(2+) with the naked eye. With such test paper, Ag(+) and Cu(2+) could be detected at levels as low as 0.06 nmol and 0.3 nmol, respectively, with detection ranges of 0.06-60 nmol for Ag(+) and 0.3-60 nmol for Cu(2+), under the irradiation of UV light (365 nm). The test paper could be potentially used in the rapid detection of Ag(+) and Cu(2+) in real samples.