Two strategies for rapid and sensitive detection of procalcitonin using carbon dots-encapsulated nanocapsule and magnetic carbon dots as coupled labels

Procalcitonin (PCT) is a crucial biomarker for diagnosing bacterial infections in clinical settings. Here, a biosensing system utilizing a fluorescence amplification system of nanocapsules and magnetic carbon dots was developed. The system incorporated two PCT sensing strategies: highly sensitive immunomagnetic separation and rapid homogeneous immunoassay. In these strategies, nanocapsules modified with antibodies function as immunosensors and energy transmitters, while magnetic carbon dots modified with antibodies serve as capture probes and immunosensors. The immunomagnetic separation analysis strategy utilized immunonanocapsules as sensors and immunomagnetic carbon dots as capture probes. This strategy demonstrated the capability to achieve ultrasensitive trace detection of PCT within the range of 1–1000 pg/mL, following normal immunoreactivity and magnetic separation. The limit of detection to 0.3 pg/mL (serum) and 0.33 pg/mL (plasma). Via the fluorescence resonance energy transfer principle, the homogeneous immunoassay strategy used immunonanocapsules as energy transmitters and immunomagnetic carbon dots as sensors. This enabled direct and rapid detection of PCT in a wide range of 0–100 ng/mL in diluted serum, with a limit of detection of 0.41 ng/mL. Both strategies demonstrated high recoveries (93.5%-104.6% and 98.4%-103.8%) and exhibited reliability in achieving accurate quantitative PCT detection. Such a novel analytical approach to PCT may broaden the potential uses of carbon dots-based immunofluorescent sensing. Furthermore, it was direct implications for ultrasensitive and rapid point-of-care detection of various serum biomarkers in clinical settings.