Determination of parathion by time-resolved fluorescence immunochromatographic assay based on nanobody: Aiming at improving strip sensitivity.

The label probe plays a crucial role in enhancing the sensitivity of immunochromatographic assay. Time-resolved fluorescent microspheres (TRFMs) have provided accurate and reliable results for fast and immediate detection. In this study, parathion was used as a model molecule in the time-resolved fluorescence immunochromatographic assay (TRFICA) strip establishment using recognition element of anti-parathion nanobody (VHH9). Under the optimal conditions, this TRFICA demonstrated good analytical performance for the detection of parathion with a cut-off value of 30 ng/mL and the limit of detection (LOD) of 0.016 ng/mL. Meanwhile, the sensitivity of the nanobody-based TRFICA was 10-fold and 480-fold higher than that of the VHH9 based colloidal gold ICA (CGICA) and commercial mAb-ICA. Moreover, this method exhibited good recoveries for the detection of cabbage, cucumber, and orange samples with no obvious cross-reactions with the other analogs observed and showed strong correlation with UPLC-MS/MS results in spiked samples. In summary, the proposed method is feasible, rapid, and could serve as a highly sensitive platform to meet practical samples detection for parathion.