This modular biosensor uses genetically engineered bacteriophages bound to graphene oxide to detect pathogen proteins in under one second, even in complex samples like blood, wastewater, or milk. Antibody-free and low-cost, it offers part-per-quadrillion sensitivity without sample purification. Easily adapted to different targets, the device supports real-time, point-of-need diagnostics in clinical, agricultural, and environmental settings. Its speed, resilience, and accessibility make it a powerful tool for global health, food safety, and outbreak response