Antibody-responsive signal-off fluorescence of DNA-harbored silver nanoclusters for direct, rapid and sensitive immunoassay

Specific DNA sequence-templated silver nanoclusters (AgNCs) are extremely promising fluorescent emitters in biosensing and bioanalysis. Here, based on the targeted antibody-responsive fluorescent quenching of AgNCs harbored in a unique DNA-based nanoassembly, we propose a specific, sensitive and one-step immunoassay of bivalent anti-digoxigenin (Dig) antibody (antiDA) as a model analyze. For proof-of-concept, this functional nanoassembly (CS1/RS/CS2) consists of a reporter strand tethering Ag-nucleable template (RS) and two capture strands (CS1 and CS2) labeled with hapten Dig, in which two tethered Dig haptens are closely positioned, and brightly emissive AgNCs can be accommodated and stabilized in the unpaired Ag-nucleable scaffold to produce significant fluorescent emission (CS1/RS/CS2-AgNCs). In the presence of antiDA, the specific conjugation of antiDA with two Dig haptens results in the conformation stretch of CS1/RS/CS2, and simultaneously the harbored AgNCs are destabilized to aggregate each other into larger non-fluorescent silver nanoparticles (AgNPs). The remarkable decreasing of AgNCs fluorescence emission is linearly proportional to the antiDA concentration with a high sensitivity down to 4.5 pM. With this regulatory antibody-dependent signal off scheme, the advantageous rapidness and simplification would be attractive and promising for highly specific detection of diverse bivalent antibodies or small molecules.