A label-free fluorescence method for actin detection based on DNA-templated silver nanoclusters

Actin is the most abundant protein in almost all eukaryotic cells. Due to the important biological properties of actin, it is necessary to develop a specific and sensitive method for actin detection. Herein, a label-free fluorescence assay for the detection of actin based on the digestion ability of deoxyribonuclease I (DNase I) and the formation of DNA-templated silver nanoclusters (DNA-AgNCs) is reported. In this strategy, two particular DNA sequences (Ag-DNA and G-rich DNA) were designed, synthesized, and used for the formation of DNA-AgNCs. Upon addition of DNase I, double-stranded DNA (dsDNA) degraded to form a shorter double-strand or mono-nucleotide that could not be further utilized to synthesize DNA-AgNCs. As a result, the reaction system generated a very low fluorescence signal. However, in the presence of actin, enzymatic digestion could be prevented due to the formation of a stable complex between actin and DNase I, ultimately resulting in an unbroken dsDNA that could be further used as a template for the fluorescent DNA-AgNCs (λex = 570 nm, λem = 620 nm). As a consequence, various actin concentrations could be detected by monitoring the fluorescence intensity variations. Because of good water solubility and excellent fluorescence properties of DNA-AgNCs, this novel fluorescence strategy exhibits several advantages such as being facile, sensitive and environment-friendly. The detection method featured a wide linear range from 0.1 to 20 μg mL−1 and a detection limit of 0.03 μg mL−1 (S/N = 3) under optimized conditions. Besides, this novel fluorescence strategy exhibited a good specificity and gives satisfactory results for biological samples. Overall, the proposed method has promising application potential in the quantification and detection of actin.