Upconversion nanoprobe counting analysis for specific detection of insulin-like growth factor-1 in Milk products

There is rapidly growing interest in food nutrition assessment, particularly for nutrients present at low abundance. Here, an upconversion nanoprobe counting analysis (UNCA) is designed for ultra-sensitive detection of insulin-like growth factor-1 (IGF-1). The high sensitivity is attributed to the strong fluorescent intensity of upconversion nanoparticles (UCNPs) and highly specific antibody-antigen binding. Core-shell structured UCNPs are synthesized via co-precipitation followed by layer-by-layer epitaxial growth, and detection probes are constructed through hydrophilic ligand exchange and antibody conjugation. Two detection methods, traditional fluorescent intensity detection and single-molecule counting, are established with linear working ranges of 0.05-5000 ng/mL, which reach limit of detections (LODs) of 21.23 and 6.04 pg/mL, respectively. UNCA is further employed for analyzing three representative milk products, achieving recovery of 73.90%-107.09% with coefficients of variation (CVs) between 2.24% and 7.57%. This method demonstrates quantitative detection of trace-level IGF-1, especially via single-molecule counting.