Functionalized Quantum Dot Fluorescent Probes with Dopamine Quinone: Construction and pH Response

Quantum dots (QDs) have demonstrated significant potential in the field of biological detection due to their excellent photoluminescence properties. As one of the key parameters in regulating physiological functions, pH response with high sensitivity is of great significance. However, conventional pH fluorescent probes are frequently limited by insufficient sensitivity or poor stability. In this work, band gap engineering was used to design and construct a CdSe/CdS/ZnS core-shell structured QD to improve the fluorescence quantum yield and stability. Additionally, the modification with mercaptoethylamine (MEA) and dopamine-isothiocyanate (DA-ITC) results in improved QD fluorescent probe exhibiting a highly sensitive pH response. Experimental results indicate that the amino-protected CdSe/CdS/ZnS QDs possess excellent optical properties. Following modification with DA-ITC, the probe exhibits highly sensitive pH response. The underlying response mechanism is attributed to fluorescence quenching effect of the dopamine quinone (DQ), which is formed by oxidation in surface ligands on the QDs under alkaline conditions. For 1 nmol QDs, when the input amount of DA-ITC is in the range of 4-40 μg/nmol, the fluorescence intensity of the probe reveals a linear decreasing trend with increasing pH from 5.0 to 10.0 (R2>0.90). Notably, when the addition of DA-ITC is set at 20 μg/nmol, the probe demonstrates optimal pH responsiveness (R2=0.9869). Moreover, this probe has good cytocompatibility, allowing for effective application in fluorescence imaging for monitoring of cell pH.