Colorimetric determination of staphylococcal enterotoxin B via DNAzyme-guided growth of gold nanoparticles

The authors describe a colorimetric method for the determination of the staphylococcal enterotoxin B (SEB) that also allows for visual readout. The assay is based on the growth of gold nanoparticles (AuNPs) mediated by a hemin/G-quadruplex DNAzyme which generates a color change from red to blue in the presence of SEB. The method is enzyme-free and does not require a label. The kinetics of the formation of the AuNPs is controlled by the hemin/G-quadruplex DNAzyme and this is key to the signal generation mechanism. In the presence of SEB, the reactions between aptamer and target modulated the amount of single probe G strands that form DNAzyme capable of consuming hydrogen peroxide. The growth process of AuNPs is influenced by the resulting concentration of H2O2 and leads to the color change. Under optimal conditions, a linear relationship exists between absorbance and SEB concentration in the range from 0.1 to 500 pg·mL‾1 which covers the clinically relevant range. In case of visual detection, the lower limit of detection is 1 pg·mL−1. The assay described here is sensitive, comparably inexpensive and can detect SEB rapidly without the need for sophisticated equipment. In our perception, the method has a wide scope in that it may be adapted to various nucleic acids, proteins and other biomolecules if respective aptamers are available.