A novel “on–off–on” fluorescence assay for the discriminative detection of Cu(ii) and l-cysteine based on red-emissive Si-CDs and cellular imaging applications

Copper ions (Cu²⁺) and l-cysteine (l-Cys) in the human body always play critical roles in various physiological processes, while abnormal Cu²⁺ and l-Cys concentrations in the biological system lead to many diseases.