Ultrasensitive Protein Detection Using Luminescent Eu-Ion-Doped Vanadate Nanoparticles

Disease prevention, diagnosis, and treatment monitoring in some cases require ultrasensitive (sub-)femtomolar biomarker detection and quantification. While standard ELISA assays yield picomolar sensitivity, existing ultrasensitive approaches reach fM, aM, or even zM sensitivity. This, however, is obtained at the expense of increased complexity and cost which hamper their biomedical applications. We propose a novel approach, nanoparticle-linked immunosorbent assay (NLISA), combining ultrasensitive, fM/sub-fM, detection with simplicity and ease of use based on 38-nm YVO₄:Eu (20%) crystalline nanoparticles used as detection probes. These particles possess an extremely strong absorption in the UV leading to bright Eu³⁺-ion emission. We developed a transportable, multi-well plate reader providing LED excitation and detection with a photomultiplier enabling detection down to 16,000 nanoparticle probes/well. We obtained sensitivity gain factors with respect to ELISA ranging from 65 to 35,000 for insulin, IFN-γ, and HIV-GAG-p24 while maintaining the same antibodies. We demonstrated femtomolar LOD and a dynamic range of 4-5 orders of magnitude and NLISA efficiency for HIV-positive patient diagnosis. This approach for straightforward, ultrasensitive polypeptide/protein detection is easily generalizable paving the way for a new generation of diagnostic tests.