Intramolecular hydrogen bond-tuned thermal-responsive carbon dots and their application to abnormal body temperature imaging

A steric hindrance strategy was used to prepare intramolecular hydrogen bond-controlled thermosensitive fluorescent carbon dots (CDs) via the solvothermal treatment of o-phenylenediamine respectively with three dihydroxybenzene isomers. The CDs obtained from different isomers have very similar morphology, surfaces, and photophysical properties but exhibited different thermal sensitivities. Meanwhile, the orange-emitting CDs (p-CDs) obtained from o-phenylenediamine and p-hydroquinone exhibited an optimal thermal sensitivity of 1.1%/degrees C. Comprehensive experimental characterizations and theoretical calculations revealed that even a small difference in substituent locations in the phenyl ring of the precursors can considerably affect the formation of intramolecular hydrogen bonds and that the CDs with strong intramolecular hydrogen bonds exhibited poor thermosensitivity. The p-CDs were incorporated with reference CDs (B-CDs) that exhibited heating-quenching blue emission through electrostatic selfassembly to construct a dual-emission probe (p-CDs/B-CDs), which exhibited a thermal sensitivity of 2.0%/degrees C. Test strips based on the p-CDs/B-CDs were prepared to measure temperature fluctuations based on sensitive and instant fluorescence color evolution. Further, this fluorescent colorimetry was successfully applied to a test strip-integrated wearable wristband to measure the body temperature. This study establishes an inherent relationship between precursors and the resulting intramolecular hydrogen bonds for precisely tuning the thermal sensitivity of CDs. It also offers a visual quantitative strategy for the early warning of abnormal body temperatures.

Automated summary

The study uses a steric hindrance strategy to prepare intramolecular hydrogen bond-controlled thermosensitive fluorescent carbon dots (CDs). CDs obtained from different isomers have similar morphology, surfaces, and photophysical properties but exhibit different thermal sensitivities. By incorporating the obtained CDs with reference CDs, a dual-emission probe is constructed, which can be used for sensitive and instant fluorescence color evolution to measure temperature fluctuations. This study establishes a relationship between precursors and intramolecular hydrogen bonds, allowing precise tuning of the thermal sensitivity of CDs, and provides a visual quantitative strategy for early warning of abnormal body temperatures.