A dual-emitting Fluorescence and Absorption Spectrophotometric Dual-Mode Carbon Dots Probe for Cadmium Detection

Herein, we developed a facile route via a calcination method for the synthesis of dual-emission carbon dots (D-CDs). The synthesized D-CDs exhibit dual emission bands at 340 nm and 450 nm under single-wavelength excitation at 250 nm, respectively, and can be used to detect cadmium ions. The fluorescence intensity of the synthesized D-CDs probe at 450 nm is enhanced in the presence of cadmium ions. This probe boasts advantages such as simple preparation, high sensitivity, and good accuracy for detecting cadmium ions. Furthermore, when a certain amount of cadmium ions is added to the methanol solution of D-CDs, the D-CDs precipitate out, which in turn leads to a decrease in the absorbance of the solution. Satisfactory results for cadmium detection are also achieved via absorption spectrophotometry in the methanol system. Under optimized experimental conditions, the linear response to Cd²⁺ covers a concentration range of 10 to 150 µM (with a lower detection limit of 4.05 µM) for fluorophotometry, and a range of 2.0 to 10.0 mM (with a lower detection limit of 30 µM) for absorption spectrophotometry, respectively. The as-synthesized D-CDs probe was characterized using multiple analytical techniques, including transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and infrared spectroscopy. To explore the mechanism underlying the fluorescence enhancement of D-CDs by cadmium ions, D-CDs were characterized by X-ray absorption fine structure (XAFS) spectroscopy after interacting with cadmium ions. The as-synthesized D-CDs were applied as a ratiometric fluorescent probe for the determination of Cd²⁺ ions in real samples. This study provides promising opportunities for the application of D-CDs in detecting Cd²⁺ ions in solutions.