Nanoarchitectonics of Congo red dye to biocompatible fluorescent carbon dots for highly sensitive Fe3+ and ferritin detection.

In this work, we have meticulously tuned the carcinogenic Congo red dye to environmentally benign fluorescent carbon dots (CDs) by adopting a typical hydrothermal method without any additives. The as-synthesized CDs were extremely water soluble, exhibited an excitation wavelength independent emission with a high fluorescence quantum yield (46%) and were biocompatible. The microscopy results revealed that the CDs were quasi-spherical with a particle diameter of ∼5 nm. The structure and functional groups of the CDs were comprehensively investigated using Fourier-transform infrared, X-ray photoelectron and Raman spectroscopy analyses. These studies show that the CDs were intrinsically functionalized with -OH, N-H and CO groups. In the sensing experiments, the CDs selectively responded to Fe3+ ions over other analytes with a detection limit of 12 nM. The time-resolved fluorescence quenching measurements were used to decipher the sensing mechanism. For the onsite 'equipment-free' detection of iron, we have developed a CD adsorbed paper-based analytical tool. Furthermore, the selective nature of CDs was highly beneficial for detecting Fe3+ in non-heme metalloprotein (ferritin) and real water samples. Thus, the CDs produced from the Congo red dye could be a prospective asset to the bio-imaging and biosensing research fields.

Fluorescent Carbon Dots Derived from Vehicle Exhaust Soot and Sensing of Tartrazine in Soft Drinks.

Recycling of waste into valuable products plays a significant role in sustainable development. Herein, we report the conversion of vehicle exhaust waste soot into water-soluble fluorescent carbon dots via a simple acid refluxion method. The obtained carbon dots were characterized using microscopic and spectroscopic techniques. Microscopic techniques reveal that the prepared carbon material is spherical in shape with an average particle size of ∼4 nm. Spectroscopic studies exhibited that the carbon dots are emissive in nature, and the emission is excitation-dependent. Further, the prepared carbon dots were successfully utilized as a fluorescent probe for the detection of tartrazine with a limit of detection of 26 nM. The sensitivity of carbon dots has also been realized by the detection of trace amounts of tartrazine in commercial soft drinks. Overall, this work demonstrates the conversion air pollutant soot into value-added fluorescent nanomaterials toward sensing applications.