Dual-parameter monitoring of HSA and ALT <i>via</i> an albumin-responsive carbon dot fluorescence signal amplification system

Human serum albumin (HSA) and alanine aminotransferase (ALT) are critical biomarkers for monitoring various health conditions. Here, a novel dual-functional fluorescent nano-sensor platform was developed for monitoring HSA and ALT using carbon dots (CDs) and Au@MnO₂ nano-heterojunctions. Water-soluble red-emitting CDs were synthesized <i>via</i> a solvothermal method, which enabled direct HSA detection with exceptional sensitivity (LOD: 0.0104 mg mL^-1) and a wide linear range (0.013-3.3 mg mL^-1), while intracellular HSA imaging was simultaneously achieved. The Au@MnO₂ nano-heterojunctions were further synthesized and non-internal-filtering specific and efficient quenching of CD fluorescence was achieved, and an Au@MnO₂-CD fluorescence quenching system was designed for ALT detection by combining the specific interaction of tiopronin with Au@MnO₂ and ALT. Ultrahigh sensitivity (LOD: 0.00137 U mL^-1) across a broad dynamic range (0.00274-0.667 U mL^-1) was demonstrated by this system. The reliability of this nanosensor was established through recovery studies in serum matrices, thereby demonstrating the measurement accuracy and potential for diagnostic applications.