EBCatch: A label-free electrochemical biosensor for non-invasive at-home monitoring of viral infection and infectivity via exhaled breath condensate.

The ongoing threat of emerging "Disease X″, exemplified by SARS-CoV-2, emphasizes the urgent need for non-invasive, rapid, and accurate diagnostic platforms suitable for home use. Here, we present EBCatch, an integrated system for the label-free electrochemical detection of respiratory viruses directly from exhaled breath condensate (EBC). The platform combines a semiconductor-based condenser for efficient EBC collection within 1 min, a carbon nanotube-based electrochemical biosensor functionalized with ACE2 receptors for specific virus recognition, and a smartphone application for automated result interpretation. Without the need for exogenous reagents or complex sample pretreatment, EBCatch achieves femtogram-level sensitivity (limit of detection = 1.6 fg/mL for pseudovirus, substantially below the viral load in EBC samples of infected individuals with SARS-CoV-2) and delivers results within 8 min from sample collection to readout. Clinical validation with total 155 samples demonstrated high diagnostic accuracy with sensitivity of 95.06%, specificity of 97.30% and overall accuracy of 96.13%, enabling detection in pre-symptomatic and antigen-negative stages. Notably, the EBCatch response reflects not only viral load but also viral activity, providing valuable insight into infectivity status and transmission risk. This versatile and user-friendly platform represents a significant advance toward decentralized, real-time monitoring of respiratory infections at home, enabling timely intervention during emerging outbreaks.