Quantitative Understanding of Charge-Transfer-Mediated Fe³⁺ Sensing and Fast Photoresponse by N-Doped Graphene Quantum Dots Decorated on Plasmonic Au Nanoparticles

Abstract

The formation of a heterostructure with plasmonic nanoparticles drastically alters the optoelectronic properties of graphene quantum dots (GQDs), resulting in exceptional properties. In the present work, we prepare nitrogen-doped GQDs decorated on gold nanoparticles (Au@N-GQDs) by a one-step green reduction method and study its extraordinary fluorescence and photoresponse characteristics. The as-prepared Au@N-GQDs show more than one order of magnitude enhancement in the fluorescence intensity as compared to the bare N-GQDs, which is attributed to hot electron generation and improved absorption in N-GQDs by local field enhancement and the modification of the edge functional groups. Because of the selective coordination to Fe 3+ ions, the Au@N-GQDs exhibit extraordinary quenching of fluorescence, with ultrahigh sensitivity for the detection of Fe 3+ (<1 nM). A new model for the charge-transfer dynamics is developed involving the Langmuir's law of adsorption to explain the unusual quenching, which strongly deviates from the known models of static/dynamic quenching. The proposed sensor is successfully implemented for the ultrasensitive detection of Fe 3+ ions in human serum and Brahmaputra river water samples, representing its high potential applications in clinical as well as environmental diagnosis. Additionally, because of its high absorption in the UV−vis−NIR region and high charge density with long life excitons, the Au@N-GQDs are utilized as photodetectors with ∼10 4 times faster response than that of bare N-GQDs.

High yield synthesis of graphene quantum dots from biomass waste as a highly selective probe for Fe3+ sensing

“…The I D /I G value of GQDs-500-M is ~ 0.98, which show their defective structure, possibly arising from the edge states at the periphery of GQDs 81 . These results are in good agreement with previously reported GQDs 53,54,81 . Figure 7b shows the FTIR spectrum of GQDs-500-M.…”

“…These results suggest that both types of these GQDs are similar in nature. Most of the carbon-based QDs exhibit excitation dependent PL emission 1,8,13,[53][54][55][56] . Their PL emission peak positions change with the change in excitation wavelength.…”

“…Owing to the presence of these functional groups and strong emission, these GQDs are expected to be an ideal candidate for fluorescence sensing. Among the various heavy metal ions, the detection and removal of Fe 3+ ions has always attracted extensive attention 53,92,93 . Generally, iron plays a key role in human life and its deficiency requires considerable attention among the global micronutrient deficiencies.…”

“…Moreover, the iron percentage has to be monitored and balanced in biological and environmental systems 94 . To achieve this, numerous researchers employed the quenching phenomenon of carbon QDs by the addition of Fe 3+4, 53,95 . The quenching percentage is related to the concentration of Fe 3+ .…”

Highly rapid and non-enzymatic detection of cholesterol based on carbon nitride quantum dots as fluorescent nanoprobes

“…These results indicated the formation of the complex between the CNQDs and cholesterol, thus further conrmed that the quenching mechanism was static quenching. 34 In addition, Rong et al veried that the hydrogen bonding could be formed between graphitic carbon nitride (g-C 3 N 4 ) nanosheets and 2,4,6-trinitrophenol, causing the uorescence quenching of g-C 3 N 4 . 35 It was displayed that the hydrogen bonds could be easily formed between carbon nitride nanomaterials and hydroxyl-contained molecules.…”