Sensitive detection of protein biomarkers using silver nanoparticles enhanced immunofluorescence assay

Detection of biomarkers is extremely important for the early diagnosis of diseases. Here, we developed an easy and highly sensitive fluorescence detection system for the determination of biomarkers by combining the rapid separation of magnetic beads and silver nanoparticles labeled antibodies. An ultrasensitive silver ions fluorescence probe 3', 6'-bis (diethylamino)-2-(2-iodoethyl) spiro[isoindoline-1, 9'-xanthen]-3-one (Ag⁺-FP) was applied to immunoassay. A significant signal amplification was achieved as the AgNPs can be dissolved by H₂O₂ and generate numerous Ag⁺, which would turn "on" the fluorescence of Ag⁺-FP. Using α-fetoprotein (AFP) and C-reactive protein (CRP) as target analytes, good linear responses were obtained from 0.1 to 10 ng mL^-1 and the limits of detection (LOD) were as low as 70 pg·mL^-1 and 30 pg·mL^-1, respectively. In addition, the developed system was further evaluated for the detection of real samples including 30 positive serum specimens obtained from hepatocarcinoma patients and 20 negative serum samples, and performs as well as the commercial electrochemiluminescence immunoassay (ECLI) method with less cost and more convenience. Thus, the designed detection system can be used as a promising platform for the detection of a variety of biomarkers and served as a powerful tool in clinical diagnosis.