Streptavidin labelled fluorescent ZnO nanoparticles have been surface engineered to develop a fluorescent ZnO nanoparticle linked immunoassay (FZLIA) for the sensitive detection of HIV infection. ZnO nanoparticles were synthesized by a single step chemical precipitation method. Cysteine was used to graft carboxyl groups on to the surface of nanoparticles in a single step. Cysteine capped ZnO nanoparticles exhibited fluorescence at 546 nm when excited with 358 nm and FESEM confirmed the particle size to be 50-70 nm. FTIR and TGA confirmed the functionalisation of carboxyl groups by cysteine. The amount of cysteine grafted on the ZnO nanoparticles calculated as 68.1% from TGA analysis indicated the presence of large amount of carboxyl groups. ZnO nanoparticles were conjugated to streptavidin and the same were deployed as fluorescent probes in the development of the FZLIA platform for the early and accurate detection of HIV infection. The linear dose dependent detection range was from 25 pg/mL to 1000 pg/mL. HIV positive and HIV negative plasma samples were tested using FZLIA for the presence of HIV-1 p24 antigen. This immunoassay exhibited no false positive and false negative results with the clinical samples tested. This highly sensitive HIV-1 p24 antigen assay may be useful to improve blood safety by reducing the antibody negative window period in blood donors in resource limited settings where nucleic acid testing is not practical or feasible. This technology can be transferred to a lab-on-chip platform for use in resource limited settings and can also be easily adopted for the detection of other antigens.