A fluorescence AuNPs-LISA: A new approach for Opisthorchis viverrini (Ov) antigen detection with a simple fluorescent enhancement strategy by surfactant micelle in urine samples.

The colorimetric AuNPs-LISA is a new, powerful technique for the detection of Opisthorchis viverrini antigen (OvAg) in urine samples. However, the diagnostic sensitivity of the colorimetric AuNPs-LISA is powerless to screen ultralow concentrations of OvAg in urine samples in cases of early stage liver fluke infection. This work, we aimed to improve the diagnostic sensitivity of the colorimetric AuNPs-LISA by developing a new fluorescence AuNPs-LISA. O-phenylenediamine (OPD) was used as the chromogenic substrate instead of the tetramethylbenzidine (TMB) of the colorimetric AuNPs-LISA. Interestingly, the fluorescence of the OPD oxidation product by the peroxidase-like activity of labelled AuNPs can be extremely enhanced by a non-ionic surfactant, especially the Triton X-100. The proposed assay exhibited a dynamic linear detection of OvAg concentration in the range of 34.18 ng mL to 273.44 ng mL with the limit of detection at 36.97 ng mL which the detection sensitivity enhancement around 1200-fold when comparing with the colorimetric AuNPs-LISA. This model exhibits high diagnosis sensitivity, specificity and accuracy, 91.28%, 91.75%, and 91.59%, respectively, compared to the traditional ELISA. The fluorescence AuNPs-LISA showed excellent potential for the diagnosis of OvAg in urine samples from endemic areas. This will provide an effective tool for the detection, control and elimination of human opisthorchiasis.