N, Zn-CDs: AgNPs-Induced "Off-On" Fluorescence Sensor for Cysteamine Detection in Biological Media.

Developing efficient, stable cysteamine detection methods is crucial for early toxicity warning and the protection of human health. Herein, we have developed an innovative, highly sensitive, selective, and stable “off-on” composite fluorescent probe composed of N, Zn-CDs and AgNPs. This probe incorporates surface plasmon resonance, the internal filter effect, and photoinduced electron transfer quenching mechanisms, characterized by dual recovery pathways mediated through S-Ag bonds and hydrogen bonding interactions. By employing an orthogonal experimental design to optimize the hydrothermal synthesis process, this study addresses the limitations inherent in existing probes, such as namely low fluorescence quantum yield, inadequate sensitivity, poor resistance to interference, and the release of toxic ions. The synthesized N, Zn-CDs showed a 59.6% fluorescence quantum yield (47.7% higher than undoped CDs). The N, Zn-CDs/AgNPs probe exhibited linear response to cysteamine (0.01–0.1 µM, R²=0.9972) with a detection limit as low as 3 nM. The synthesized N, Zn-CDs demonstrated good stability under continuous ultraviolet irradiation, in high-salinity environments, and at neutral pH conditions. The probe’s selectivity for cysteamine was approximately 3.5 times greater than for other amino acids, indicating good resistance to interference. Recovery experiments in spiked bovine serum samples yielded rates between 95.0 ± 0.92% and 102.8 ± 1.56% (RSD < 2%), further supporting the probe’s reliability. Cytotoxicity assessments confirmed the probe’s low toxicity and favorable biocompatibility. This probe provides a practical method for the efficient and stable quantitative analysis of cysteamine. Furthermore, the synergistic doping of zinc and nitrogen offers novel perspectives for the development of low-toxicity, high-performance carbon dot-based probes.