14There is a pressing need for sustainable and sensitive immunodiagnostics for use in public health 15 efforts to understand and combat the threat of endemic and emerging infectious diseases. We 16 describe a novel approach to immunodiagnostics based on virus-like particles (VLPs) attached to 17 magnetic beads. This flexible, innovative immunoassay system, based on the MAGPIX® 18 platform, improves sensitivity by up to 2-logs and has faster sample-to-answer time over 19 traditional methods. As a proof of concept, a retroviral-based VLP, that presents the Venezuelan 20 equine encephalitis virus E1/E2 glycoprotein antigen on its surface, was generated and coupled 21 to magnetic beads to create VLP-conjugated microspheres (VCMs). Using these VCMs, IgG and 22IgM antibodies were detectable in nonhuman primate (NHP) and human clinical serum samples 23 at dilutions of 1 × 10 4 and greater. We extended the VCM methodology to two other New-World 24 alphaviruses, eastern and western equine encephalitis viruses, as well as an Old-World 25 alphavirus, Chikungunya virus, demonstrating the flexibility of this approach toward different 26 VLP architectures. When multiplexed on the MAGPIX platform, the VCMs provided 27 differential diagnosis between Old-World and New-World alphaviruses and well as a route 28 toward assessing the humoral response to both natural infection and vaccination. This VCM 29 system will allow more rapid and efficient detection of endemic and emerging viral pathogens in 30 human populations. 31