Temperature, pH, and Cr(VI) ions sensing with green synthetic carbon dots

In this paper, Syzygium samarangenses were utilized to prepare bio-carbon dots via a one-step hydrothermal protocol. Based on the inner filter effect, this fluorescent nanomaterial enables selective detection of Cr 6+ with a linear range of 10-200 M and a limit of detection of 7.8 M through variation in fluorescence. Meanwhile, it also displays that the carbon dots show excellent reversibility and photostability in pH measurements. The intensity of photoluminescence is linear against pH value from 6 to 12 in the buffer solution. In contrast to most of the reported nanomaterials-based pH sensors that rely on the attachment of additional dyes, this carbon-dotsbased probe is low in toxicity, easy to synthesize, and free from labels. More importantly, due to a significant fluorescence quenching by temperature-induced aggregation of carbon quantum dots (CQDs), the resultant CQDs have commendable potential as an eminent luminescent thermometer sensor, particularly, the fluorescence intensity (FL intensity) is responsive to temperature and approximately linear in the physiological temperature range from 5C to 44C.