A concentration-dependent multicolor conversion strategy for ultrasensitive colorimetric immunoassay with the naked...

Colorimetric immunoassays have been attracting more attention for use in practical applications, especially in point-of-care diagnostics. In comparison with a single color immunoassay, the dose-dependent multicolor strategy greatly improves the detection resolution and accuracy of visual inspection. In the current study, a concentration-dependent multicolor conversion strategy was developed based on gold nanoparticle (AuNP)-mediated copper deposition for signal amplification and Prussian blue for color generation. Under optimal conditions, a dose-dependent multicolor from yellow through green to blue were successfully achieved, which was easier to be differentiated from each other by the naked eyes. With rabbit IgG and prostate specific antigen (PSA) as model analytes, semi-quantitative evaluations were demonstrated in lab buffer and serum by direct readout with the naked eyes. Quantitative detections were also accomplished by measurement of absorbance of Prussian blue with a common UV-Vis spectrophotometer. A limit of detection (LOD) down to sub-picogram per milliliter was determined. In addition, this newly developed colorimetric assay method can be easily adapted for the detection of other biomolecules by simply changing the recognition pairs.