Smartphone-based nanozyme immunosensor for rapid quantification of rabies neutralizing antibody

• Smartphone-based immunosensor device (SPIS) was designed and fabricated. • Custom-designed app was in-stored in smartphone for reading immunoassay signals. • Nanozyme engaged competitive immunoassay (CIV) was developed on SPIS platform. • SPIS-CIV was used for rapid quantification of rabies neutralizing antibody. The level of rabies virus neutralizing antibody (RVNA) is a critical indicator to evaluate the protective immunity of vaccinees against rabies virus (RABV) infection. The fluorescent antibody virus neutralization test (FAVN) and the rapid fluorescent focus inhibition test (RFFIT) are the WHO recommended assays for determining the RVNA level after vaccination, but both methods are complicated and time-consuming for 1-5 days. Here we developed a smartphone-based immunosensor platform (SPIS), intelligently integrated with the nanozyme (Au@PtNPs) engaged competitive immunoassay (CIA) in the heavy ion microporous membrane (HIM) filtration microplate and PMMA optical fiber signal transmission (SPIS-CIV) for quantitatively surrogate virus neutralization testing (sVNT) of the surrogate RVNA (sRVNA) in blood samples during 50 min. The highest intra-assay and inter-assay coefficient variations (CV) of SPIS-CIA varied < 13% or 14%, respectively. The linear range of quantification was between 0.4 IU/mL and 10 IU/mL RVNA. The nearly full agreement was found between SPIS-CIA and FAVN for measuring sRVNA or RVNA titers in serum/plasma samples from 27 rabies vaccinees and 64 non-rabies vaccinees (R 2 =0.9941, P< 0.0001), especially SPIS-CIV was accurate for quantification of sRVNA at the border line of protection level (0.5 IU/mL). The limit of detection or quantification (LOD/LOQ) was determined to be 0.25 IU/mL and 0.4 IU/mL, respectively. In conclusion, SPIS-CIA is a rapid, quantitative and precise point-of-care testing for serum sRVNA level, which can be used to predict the protection efficacy against RABV infection in human rabies vaccinees in clinical diagnosis.