Multicolor visual biosensor based on dual-functional aptamer-mediated gold nanorod etching for point-of-care testing of β-lactoglobulin

Abstract

β-Lactoglobulin (BLG) is considered the main sensitizing protein that causes milk allergy and has become one of the hot spots in food safety research. Here, a simple multicolor visualization sensing strategy was constructed by hemin/G-quadruplex (G4) DNAzyme and 3,3′,5,5′-tetramethylbenzidine (TMB)-mediated etching of gold nanorods (GNRs). A dual-functional aptamer enlg2-pl3 was used as the recognition element of BLG and the skeleton of hemin/G4 DNAzyme. Hemin/G4 DNAzyme catalyzed H₂O₂-mediated oxidation of TMB to produce TMB²⁺ under acidic conditions. The GNRs were etched by TMB²⁺ with a change in the aspect ratio, accompanied by a multicolor change. The combination of BLG and enlg2-pl3 reduced the catalytic activity of hemin/G4 DNAzyme, thus inhibiting the etching reaction. The concentration gradient of the BLG can be identified by the difference in the plasmon resonance wavelength signal and the color change generated by the GNRs with different aspect ratios. Compared to previous colorimetric methods for BLG determination, multiple colors corresponding to the concentration of BLG was the most attractive virtue of our approach. This aptasensor can easily detect BLG within 50 min. Combined with the smartphone detection platform, it can realize convenient quantitative analysis without instruments and meet the requirements of point-of-care testing (POCT).