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

Abstract

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 CO 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.