Fig. 1. Principle of Cu²⁺ detection by GSH-AuNCs fluorescence sensor

Fig. 2. GSH-AuNCs transmission electron microscope image, illustrated with particle size distribution

Fig. 3. Infrared spectra of GSH-AuNCs

Fig. 4. Fluorescence spectra of GSH-AuNCs

Fig. 5. Relationship between GSH-AuNCs fluorescence intensity and Cu²⁺ concentration

Fig. 6. Fluorescence attenuation curves of GSH-AuNCs and GSH-AuNCs /Cu²⁺

Fig. 7. Fluorescence emission spectra of GSH-AuNCs under different wavelengths of excitation light

Fig. 8. Effect of pH on fluorescence intensity of GSH-AuNCs

Fig. 9. Effect of different Cu²⁺ concentrations on fluorescence intensity of GSH-AuNCs, embedded images a and b are the photos of GSH-AuNCs before and after fluorescence is quenched by Cu²⁺ under ultraviolet light

Fig. 10. Relationship between Cu²⁺ concentration and natural logarithm of GSH-AuNCs fluorescence intensity ratios before and after quenching

Fig. 11. Specificity analysis of fluorescence sensor