Carbon dots, an emerging class within the carbon allotrope family, have gained significant attention largely due to their versatile and tunable physico-chemical and optical properties.

Classical methods for the detection of heavy metal ions in water are tedious and time consuming.

A review of the green carbon dot synthesis literature outlining the various precursors used, synthesis and purification methods employed, the resulting physicochemical properties of the carbon dots, and their applications.

Highly sensitive non-invasive temperature sensing is critical for studying fundamental biological processes and applications in medical diagnostics. Nanoscale-based thermometers are promising non-invasive probes for precise temperature sensing with subcellular resolution. However, many of these systems have limitations as they rely on fluorescence intensity changes, deconvolution of peaks, or the use of hybrid systems to measure thermal events. To address this, we developed a fluorescence-based ratiometric temperature sensing approach using carbon dots prepared via microwave synthesis. These dots possess dual fluorescence signatures in the blue and red regions of the spectrum. We observed a linear response as a function of temperature in the range of 5-60 C with a thermal resolution of 0.048 K À1 and thermal sensitivity of 1.97% C À1 . Temperature-dependent fluorescence was also observed in HeLa cancer cells over a range of 32-42 C by monitoring changes in the red-to-blue fluorescence signatures. We demonstrate that the ratiometric approach is superior to intensity-based thermal sensing because it is independent of the intracellular concentration of the optical probe. These findings suggest that dual-emitting carbon dots can be an effective tool for in vitro and possibly in vivo fluorescence nanothermometry.