We propose a concept for ligase detection by conversion of aggregation-based homogeneous analysis into surface-tethered electrochemical assay through streptavidin (SA)-biotin interaction. Sortase A (SrtA) served as the model analyte and two biotinylated peptides (bio-LPETGG and GGGK-bio) were used as the substrates. SrtA-catalyzed ligation of the peptide substrates led to the generation of bio-LPETGGGK-bio. The ligation product (bio-LPETGGGK-bio) induced the aggregation and color change of SA-modified gold nanoparticles (AuNPs) through the SA-biotin interactions, which could be assayed by the colorimetric method. Furthermore, we found that the bio-LPETGGGK-bio could trigger the assembly of tetrameric SA proteins with the formation of the (SA-bio-LPETGGGK-bio)n assemblies through the same interactions. The above results were further confirmed by atomic force microscopy and fluorescent imaging. The insulated assemblies were in-situ fabricated at the SA-modified gold electrode, thus hindering the electron transfer of [Fe(CN)6]3−/4− and leading to an increase in the electron-transfer resistance. The capability of the method for the detection of SrtA both in vitro and Staphylococcus aureus (S. aureus) has been demonstrated. SrtA with a concentration down to 1 pmol/L has been determined by the electrochemical analysis, which is lower than that achieved by the colorimetric assay (50 pmol/L). By integrating the advantages of homogeneous reaction and heterogeneous detection, the strategy serves as an ideal means for the fabrication of various sensing platforms by adopting biotin-labeled and sequence-specific peptide or nucleic acid substrates.
| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |