The10-fold serial dilutions of p24 in the dilution buffer (PBS containing 1 g/L bovine serum albumin) and spiked in a serum from an HIV-1 negative individual were detected by NLFOA and the conventional ELISA (HIV-1 p24 ELISA). One hundred sera from HIV-1 negative individuals were included as negative controls. The written consent was obtained from all subjects who participated in the study, and the study was approved by the ethics committee of Jilin University. HIV-1 p24 was diluted at low (1 pg/mL), intermediate (10 pg/mL) and high (100 pg/mL) concentrations for determination of the reproducibility and the coefficient of variation (CV). To compare the sensitivity and reproducibility between NLFOA and ELISA, the intra-assay variation was determined with p24 spiked samples (N = 5) analyzed on the same day, and the inter-assay variation was determined with the same samples analyzed on different days. All comparisons were carried out in five independent repeats.
To demonstrate the applicability of NLFOA for detection of other antigens, the capsid protein VP1 of enterovirus 71 (EV71) was analyzed. The procedure for detection of VP1 was similar to that used for p24 detection, with the following changes: mAb 2H2 targeting VP1 was used to coat 96-cell polystyrene microplate, recombinant VP1 expressed in E. coli was spiked in sera, and the biotinylated detection antibody was prepared from VP1-immunized rabbits.