A competitive immunoassay using hapten-modified polydiacetylene vesicles for homogeneous and sensitive detection of sodium benzoate

Abstract Polydiacetylene (PDA) vesicles-based chromatic biosensor could present a unique color change in response to a particular analyte or circumstance. However, its application in recognition of small molecules still remains a big challenge. In this paper, we describe a new strategy to build a competitive colorimetric immunoassay for detection of small molecules by employing hapten-modified PDA vesicles. A commonly used chemical food additive, sodium benzoate, was used as the model analyte. We coupled benzoate analog, 4-aminobenzioic acid, with PDA monomer to facilitate blue-to-red color transition after adding antibodies of sodium benzoate. In the presence of sodium benzoate, the interaction of its antibodies with 4-aminobenzioic acid would be inhibited and the extent of color change was reduced. The inhibition effect correlated well with sodium benzoate concentration, and the lowest distinguishable concentration of sodium benzoate was 100 ng mL −1 by naked-eye readout, and 0.01 ng mL −1 by UV–vis spectrometry. This assay was highly specific and as accurate as HPLC method. It could be also applied in foodstuffs of vinegar and soy sauce diluted by 100 or 200 times. The proposed method showed a great potential in benzoate analysis in these samples, and hapten-modified PDA vesicles was a promising approach in colorimetric detection of other chemical food additives.