B, N co-doped carbon dots based fluorescent test paper and hydrogel for visual and efficient dual ion detection

It is highly significant to develop water-soluble carbon dots (CDs) for ion detection in the environment via a facile and economical process. Herein, the organic molecules derived boron, nitrogen co-doped CDs (BN-CDs) with water-solubility are solvothermally synthesized towards dual ion detection. The BN-CDs emit bright tangerine fluorescence, and demonstrate a fluorescent quantum yield of 17 %. Besides, the obtained BN-CDs show a good linear relationship with Cu2+/Co2+ in a wide dynamic range of 1–8 μM, along with detection limits of 16 nM (Cu2+) and 24 nM (Co2+). The joint effect of dynamic and static quenching mechanisms is proposed as well for fluorescence quenching by Cu2+/Co2+. Furthermore, two instrument-free BN-CDs-based solid sensors (i.e., test strips and hydrogel beads) are fabricated to sensitively monitor both Cu2+ and Co2+. The paper-based sensors exhibit selective and sensitive response towards Cu2+ and Co2+ in a low-cost manner. The fluorescence hydrogel integrates comprehensive advantages of hydrogel and BN-CDs, which makes it not only conduct as efficient fluorescent sensors to detect Cu2+ and Co2+ but act as the absorbent towards removal of the ions. The simple yet reliable sensing technique developed here favor efficiently detecting and recognizing dual ions in environmental and/or biological samples.