Optical nanothermometers have emerged as powerful tools for non-contact, high-resolution temperature sensing at micro- and nanoscales. Their applications span across micro-opto-electronics, photonics, and biomedical diagnostics, particularly in thermal and pH sensing. However, most existing thermal sensors rely on heavy metals or suffer from low sensitivity. In this study, we present a highly sensitive ratiometric nanothermometer based on colloidal carbon quantum dots (C-dots). These C-dots exhibit dual emission originating from band gap transitions and surface-dominated states, each displaying distinct temperature-dependent photoluminescence (PL) responses. Among various surface-functionalized C-dots, those capped with hydroxyl groups (C-dots@OH) demonstrate an absolute thermal sensitivity of −0.082 °C⁻¹, the highest reported among ratiometric thermosensors to date. This exceptional sensitivity makes C-dots@OH ideal for high-precision, self-calibrated nanoscale thermometry. As a proof-of-concept, C-dots@OH were successfully employed to monitor intracellular temperature variations ranging from 32 to 42 °C within single living cells. The observed trends clearly reflect dynamic temperature changes, underscoring the potential of C-dots as a robust platform for precise intracellular thermal monitoring. Furthermore, their compatibility with nano-electronic and optoelectronic systems highlights their broad applicability beyond biological settings.
Synthesis and Structural Characterization of Functionalized C-Dots
Colloidal C-dots with tailored surface functional groups were synthesized via a hydrothermal method using different organic precursors: phloroglucinol for –OH, N,N-diethyl-para-phenylenediamine for –NR₂, and citric acid/urea for –COOH. The resulting C-dots were purified through silica column chromatography and dialysis (MWCO 3000 Da), yielding high-purity aqueous dispersions. Transmission electron microscopy (TEM) revealed uniform particle sizes below 5 nm, consistent with previous reports. High-resolution TEM (HRTEM) showed lattice fringes of 0.21 nm corresponding to the (100) plane of graphene in C-dots@OH and C-dots@NR₂, while C-dots@COOH exhibited a spacing of 0.34 nm, attributed to the (001) plane of graphite. Selected area electron diffraction (SAED) and X-ray diffraction (XRD) confirmed the graphitic structure in C-dots@OH. Fourier transform infrared (FT-IR) spectroscopy verified the presence of aromatic C=C bonds in C-dots@OH and C-dots@NR₂, while C-dots@COOH displayed characteristic –COOH stretching peaks at 3195 and 1765 cm⁻¹. X-ray photoelectron spectroscopy (XPS) further confirmed the elemental composition and surface chemistry, validating the successful introduction of targeted functional groups.
Optical Properties and Ratiometric Temperature Sensing
The optical properties of the C-dots were strongly influenced by surface functionalization. C-dots@OH and C-dots@NR₂ exhibited dual emission peaks, assignable to band gap emission (shorter wavelength) and surface state emission (longer wavelength), respectively. In contrast, C-dots@COOH displayed a broad, single emission peak due to multiple energy states. Upon excitation at 405 nm, PL intensity increased with decreasing temperature across all samples, indicating suppressed non-radiative recombination at lower temperatures. Crucially, the ratio of integrated PL areas between the two emission bands showed a linear dependence on temperature over the 33–47 °C range, with a correlation coefficient of 0.99. For C-dots@OH, the absolute thermal sensitivity reached −0.082 °C⁻¹, corresponding to a relative sensitivity of 8.2% °C⁻¹—significantly higher than previously reported dual-emission systems such as C-dots–RhB (0.66% °C⁻¹), CdSe–CdS/dye (3.2% °C⁻¹), and PbS/CdS/CdSe (1.22% °C⁻¹). This superior performance is attributed to the pronounced differential temperature response of the two emission components, enabling accurate, self-referenced thermal measurements.IGF-1R Antibody Technical Information
Biocompatibility and Intracellular Thermal Monitoring
To assess biocompatibility, HEK293T cells were exposed to C-dots at concentrations up to 200 mg mL⁻¹ for 24–120 h.MLL Antibody MedChemExpress Cell viability remained above 90% at concentrations ≤75 mg mL⁻¹, indicating minimal cytotoxicity.PMID:34906365 Flow cytometry analysis after 24 h incubation with 100 mg mL⁻¹ C-dots revealed apoptosis rates below 3%, confirming excellent biocompatibility. Confocal microscopy was used to monitor intracellular temperature using C-dots@OH in live HEK293T cells. Two fluorescence channels were set: 500–535 nm (band gap emission) and 566–700 nm (surface emission). Images acquired at temperatures from 32 to 42 °C demonstrated clear intensity changes in both channels, with a linear relationship between the fluorescence intensity ratio and temperature (R² = 0.99). The system showed excellent repeatability and negligible drift over time, confirming its reliability for real-time intracellular thermometry. These results validate the use of C-dots@OH as a promising, non-invasive tool for studying cellular thermal dynamics in physiological environments.
Conclusion and Future Outlook
In conclusion, we have developed a highly sensitive, ratiometric nanothermometer based on colloidal carbon quantum dots functionalized with hydroxyl groups. The system leverages dual emission from band gap and surface states, offering enhanced accuracy and self-calibration capabilities. With an unprecedented thermal sensitivity of 8.2% °C⁻¹ and excellent biocompatibility, C-dots@OH provide a transformative solution for precise, non-invasive temperature monitoring at the single-cell level. This work paves the way for advanced applications in cellular physiology, disease diagnostics, and smart nanodevices. Future efforts will focus on surface engineering to enhance stability in complex biological media and integration into implantable or wearable thermal sensing platforms.MedChemExpress (MCE) offers a wide range of high-quality research chemicals and biochemicals (novel life-science reagents, reference compounds and natural compounds) for scientific use. We have professionally experienced and friendly staff to meet your needs. We are a competent and trustworthy partner for your research and scientific projects.Related websites: https://www.medchemexpress.com