Detection of viral infection is commonly performed using serological techniques like the enzymelinked immunosorbent assay (ELISA) to detect antibody responses. Such assays may also be used to determine the infection phase based on isotype prevalence. However, ELISAs demonstrate limited sensitivity and are difficult to perform at the point of care. Here, we present a novel technique for label-free, rapid detection of ultra-low concentrations of virus specific antibodies. We have developed a simple, robust capacitive biosensor using microwires coated with Zika or Chikungunya virus envelope antigen. With little discernable nonspecific binding, the sensor can detect as few as 10 antibody molecules in a small volume (10 molecules/30μL) within minutes. It can also be used to rapidly, specifically, and accurately determine the isotype of antigen-specific antibodies. Finally, we demonstrate that anti-Zika virus antibody can be sensitively and