Ultrasensitive, Multiplexed Buoyant Sensor for Monitoring Cytokines in Biofluids.

Multiplexed quantification of low-abundance protein biomarkers in complex biofluids is important for biomedical research and clinical diagnostics. However, in situ sampling without perturbing biological systems remains challenging. In this work, we report a buoyant biosensor that enables in situ monitoring of protein analytes at attomolar concentrations with a 15 min temporal resolution. The buoyant biosensor implemented with fluorescent nanolabels enabled the ultrasensitive and multiplexed detection and quantification of cytokines. Implementing the biosensor in a digital manner (i.e., counting the individual nanolabels) further improves the low detection limit. We demonstrate that the biosensor enables the detection and quantification of the time-varying concentrations of cytokines (e.g., IL-6 and TNF-α) in macrophage culture media without perturbing the live cells. The easy-to-apply biosensor with attomolar sensitivity and multiplexing capability can enable an in situ analysis of protein biomarkers in various biofluids and tissues to aid in understanding biological processes and diagnosing and treating diverse diseases.