Highly Selective and Instant Ratio Fluorescence-Scattering Sensor for Phosphate Detection in a Water Environment by a Stable Eu3+/Y3+-Modified Nitrogen-Doped Carbon Quantum Dot

Developing an accurate sensor for the detection of phosphate ions (Pi, a crucial indicator of water quality) in water environments is of great significance. Fluorescence-scattering ratiometric probes with great promise to achieve sensitive and selective detection are still hindered by the poor solubility and stability and complex construction of fluorescence composites. In this paper, a simple ratio fluorescence-scattering sensor based on Eu³⁺- and Y³⁺-modified nitrogen-doped carbon quantum dots (NCQDs) was developed for Pi rapid detection. It is found that Eu³⁺ can specifically recognize Pi and form ternary ion chelates with Pi and NCQDs, resulting in decreased fluorescence signals of NCQDs at 420 nm and increased second-order scattering (SOS) signals at 640 nm. Y³⁺ as the sensitizer of Eu³⁺ promotes the aggregation of NCQDs, thereby enhancing the sensitivity of the sensor. The ratio fluorescence-scattering probe based on NCQDs-Eu³⁺-Y³⁺ shows a high sensitivity, a low detection limit of 0.08 μM, a rapid response time of within 2 s, and a wide detection range from 1 to 150 μM. Moreover, the proposed probe showed excellent selectivity and stability, and the relative standard deviation (RSD) of seven cycles of Pi detection is only 0.559%. Furthermore, the accurate detection of Pi (RSD < 5%) in real environmental water samples confirmed the practicality of the proposed sensor. This ratio fluorescence-scattering sensor provides a novel method for the detection of Pi with a simple preparation process and excellent detection performance, having great application potential for the fast on-site detection of Pi.