A comparison of horseradish peroxidase, gold nanoparticles and qantum dots as labels in non-instrumental gel-based immunoassay

We have developed a column gel-based immunoassays for the model analyte benzo[a]pyrene (B[a]P), and have evaluated three different kinds of labels, i.e., horseradish peroxidase, (HRP), colloidal gold (AuNPs), and quantum dots (QDs) with respect to rapid visual on-site testing. In case of HRP, a derivative of B[a]P-BA (benzo[a]pyrenebutyric acid) was directly coupled to HRP. In case of QDs and AuNPs, protein conjugates of B[a]P-BA were synthesized and used for surface functionalization. With the latter, previous coverage of the gold surface with 11-mercaptoundecanoic acid turned out to be advantageous in terms of antibody recognition and of preventing nonspecific binding to the gel layer. The assays based on the use of particle labels requires 4 consecutive working steps only, while those based on HRP require 5 additions of reagent. The lower limit of detection for B[a]P is 5 ng L−1 in case of using HPR or QDs as a label, but 25 ng L−1 when using AuNPs. We believe that the use of QDs constitutes the most promising label for qualitative and semi-quantitative gel-based immunoassays.