NIR-II Dyad-Doped Ratiometric Nanosensor with Enhanced Spectral Fidelity in Biological Media for In Vivo Biosensing.

Ratiometric fluorescence nanosensors provide quantitative biological information. However, spectral shift and distortion of ratiometric nanosensors in biological media often compromise sensing accuracy, limiting in vivo applications. Here, we develop a fluorescent dyad () in the second near-infrared (NIR-II) window by covalently linking an asymmetric aza-BODIPY with a ONOO-responsive -thiocyanine. The dyad encapsulated in the PEGylated nanomicelle largely improves spectral fidelity in serum culture by >9.4 times compared to that of its noncovalent counterpart. The increased molecular weights (>1480 Da) and hydrophobicity (Log of 7.87-12.36) lock dyads inside the micelles, which act as the shield against the external environment. ONOO-altered intramolecular Förster resonance energy transfer (FRET) generates linear ratiometric response with better serum tolerance, enabling us to monitor the dynamics of oxidative stress in traumatic brain injury and evaluate therapeutic efficiency. The results show high correlation with in vitro triphenyltetrazolium chloride staining, suggesting the potential of NIR-II dyad-doped nanosensor for in vivo high-fidelity sensing applications.