Assay of Biothiols by Regulating the Growth of Silver Nanoparticles with C-Dots as Reducing Agent

Difunctional Cu-doped carbon dots: catalytic activity and fluorescence indication for the reduction reaction of p-nitrophenol

The reduction reaction ofp-nitrophenol was catalyzed and monitored using the fluorescence of Cu-doped CDs.

Simple and Cost-Effective Glucose Detection Based on Carbon Nanodots Supported on Silver Nanoparticles

We present a new glucose oxidase (GOx)-mediated strategy for detecting glucose based on carbon nanodots supported on silver nanoparticles (C-dots/AgNPs) as nanocomplexes. The strategy involves three processes: quenching of C-dots' fluorescence by AgNPs, production of H₂O₂ from GOx-catalyzed oxidation of glucose, and H₂O₂-induced etching of AgNPs. In the C-dots/AgNPs complex, AgNPs act as a "nanoquencher" to decrease C-dots fluorescence by surface plasmon-enhanced energy transfer (SPEET) from C-dots (donor) to AgNPs (acceptor). The H₂O₂ formed by GOx-catalyzed oxidation of glucose etches the AgNPs to silver ions, thus freeing the C-dots from the AgNPs surfaces and restoring the C-dots' fluorescence. Therefore, the increase in fluorescence depends directly on the concentration of H₂O₂, which, in turn, depends on the concentration of glucose. The strategy allows the quantitative analysis of glucose with a detection limit of 1.39 μM. The method based on C-dots/AgNPs offers the following advantages: simplicity of design and facile preparation of nanomaterials, as well as low experimental cost, because chemical modification and separation procedures are not needed.

Graphitic carbon nitride nanodots: As reductant for the synthesis of silver nanoparticles and its biothiols biosensing application

The graphitic carbon nitride nanodots (g-C₃N₄-dots) were synthesized by a simple electrochemical "tailoring" process from bulk graphitic carbon nitride (g-C₃N₄) under alkaline solution for the first time. Compared with the bulk g-C₃N₄, the novel g-C₃N₄-dots not only exhibit enhanced fluorescence and excellent dispersion stability in water but also show the reducibility for the reduction of Ag⁺ to AgNPs at 60°C. The biothiols can bound with Ag⁺ through formation of biothiol-Ag⁺ complex to consume the Ag⁺ and act as capping agent to prevent the growth of AgNPs, which cause the decrease of the absorption peak of the AgNPs. Therefore, an optical sensor was developed for the detection of biothiols based on the change of the plasmon resonance absorption peak of the AgNPs. The proposed method exhibits excellent sensitivity and selectivity to biothiols with low detection limit for cysteine (Cys), homocysteine (Hcy), and glutathione (GSH) with 11.5, 16.1, and 15.5nM, respectively. This method also has been successfully applied for the detection of biothiols in human serum with satisfactory results.

Facilely prepared Fe3O4/nitrogen-doped graphene quantum dot hybrids as a robust nonenzymatic catalyst for visual discrimination of phenylenediamine isomers

In this work, we report a reducing agent-free strategy for the synthesis of Fe3O4 nanoparticle/nitrogen-doped graphene quantum dot (Fe3O4/N-GQD) hybrids, and constructed a sensing platform based on Fe3O4/N-GQDs for the visual discrimination of phenylenediamine isomers. Fe3O4/N-GQDs were facilely prepared by hydrothermal treatment of Fe(3+)/N-GQD solutions under alkaline conditions without other reagents. The prepared Fe3O4/N-GQDs exhibited outstanding peroxidase-like activity and were stable under a wide range of pH values and temperatures. The phenylenediamine isomers (o-phenylenediamine, m-phenylenediamine, and p-phenylenediamine) were discriminated through the H2O2-mediated oxidation reaction using Fe3O4/N-GQDs as novel peroxidase mimics, which resulted in appreciable color changes. The proposed method is simple, economical, and effective for discrimination of isomers, and can be used for sensitive and selective quantitative analysis of o-phenylenediamine and p-phenylenediamine. A good linear relationship from 1 to 90 μM and a detection limit of 230 nM for o-phenylenediamine were achieved, and the linear relationship for p-phenylenediamine was from 2 to 70 μM with a detection limit of 530 nM. The proposed method may open new applications of Fe3O4/N-GQDs in biomedicine and environmental chemistry.

New development in carbon quantum dots technical applications

As a newly emerged member in carbon nanomaterials family, carbon quantum dots (CQDs) attracted everincreasing attention owing to their ultracompact size, excellent photoluminescence, favorable biocompatibility, versatile surface and superior electron transfer ability. The past decade has witnessed continuous advancements in the production of CQDs with high photoluminescence quantum yields for various applications. Herein, we track the newest development of CQDs with advanced physicochemical properties and their applications in sensing, bioimaging, nanomedicine and catalysis, and propose the challenges and perspectives in this exciting and promising field.

Fluorescent carbon quantum dot hydrogels for direct determination of silver ions

The paper reports for the first time the direct determination of silver ion (Ag(+)) using luminescent Carbon Quantum Dot hydrogels (CQDGs). Carbon Quantum Dots (CQDs) with different superficial moieties (passivate-CQDs with carboxylic groups, thiol-CQDs and amine-CQDs) were used to prepare hybrid gels using a low molecular weight hydrogelator (LMWG). The use of the gels results in considerable fluorescence enhancement and also markedly influences selectivity. The most selective CQDG system for Ag(+) ion detection proved to be those containing carboxylic groups onto their surface. The selectivity towards Ag(+) ions is possibly due to its flexible coordination sphere compared with other metal ions. This fluorescent sensing platform is based on the strong Ag-O interaction which can quench the photoluminescence of passivate-CQDs (p-CQDs) through charge transfer. The limit of detection (LOD) and quantification (LOQ) of the proposed method were 0.55 and 1.83µgmL(-1), respectively, being applied in river water samples.

Fluorescence “turn on” detection of Cr3+ using N-doped-CDs and graphitic nanosheet hybrids

N-doped CDs and graphitic nanosheet hybrids were prepared and used for fluorescence “turn on” detection of Cr³⁺ based on FRET.

Green synthesis of nitrogen-doped carbon dots from lentil and its application for colorimetric determination of thioridazine hydrochloride

A simple and green hydrothermal method is introduced for synthesis of nitrogen-doped carbon dots (N-CDs) by using lentil. The interaction of as-prepared N-CDs with AgNPs was utilized for colorimetric detection of thioridazine hydrochloride.

Visual discrimination of dihydroxybenzene isomers based on a nitrogen-doped graphene quantum dot-silver nanoparticle hybrid

A room temperature reducing agent-free strategy for the synthesis of a nitrogen-doped graphene quantum dot-silver nanoparticle (N-GQD/AgNP) hybrid was presented. In this strategy, N-GQDs were used as a reducing agent and stabilizer for the formation of the N-GQD/AgNP hybrid, and the formation of the N-GQD/AgNP hybrid may result from the extraordinary reduction properties of N-GQDs, which are attributed to the nature of the surface oxygen-containing functional groups. The N-GQD/AgNP hybrid exhibits good dispersity and outstanding catalytic ability toward the oxidation of catechol (CC) and hydroquinone (HQ) by Ag(+). In the presence of the N-GQD/AgNP hybrid, the reduction of Ag(+) by CC and HQ was improved. CC enhanced the absorbance of the N-GQD/AgNP-Ag(+) system the most, and HQ followed, while resorcinol (RC) had only a little effect on the absorption intensity of the system. Thus, a sensitive and selective colorimetric sensing method based on the N-GQD/AgNP-Ag(+) system was developed for the discrimination of CC, HQ and RC. A good linear relationship was obtained from 0.1 to 15.0 μM for CC and from 0.3 to 20.0 μM for HQ. The detection limits of CC and HQ were 0.03 and 0.1 μM, respectively. In addition, the proposed method also shows a high selectivity for the detection of CC and HQ, and appreciable changes in color of the N-GQD/AgNP-Ag(+) system toward CC, RC and HQ were observed.

A rapid fluorescence "switch-on" assay for glutathione detection by using carbon dots-MnO2 nanocomposites

Glutathione (GSH) serves many cellular functions and plays crucial roles in human pathologies. Simple and sensitive sensors capable of detecting GSH would be useful tools to understand the mechanism of diseases. In this work, a rapid fluorescence "switch-on" assay was developed to detect trace amount of GSH based on carbon dots-MnO2 nanocomposites, which was fabricated through in situ synthesis of MnO2 nanosheets in carbon dots colloid solution. Due to the formation of carbon dots-MnO2 nanocomposites, fluorescence of carbon dots could be quenched efficiently by MnO2 nanosheeets through fluorescence resonance energy transfer (FRET). However, the presence of GSH would reduce MnO2 nanosheets to Mn(2+) ions and subsequently release carbon dots, which resulted in sufficient recovery of fluorescent signal. This proposed assay demonstrated highly selectivity toward GSH with a detection limit of 300nM. Moreover, this method has also shown sensitive responses to GSH in human serum samples, which indicated its great potential to be used in disease diagnosis. As no requirement of any further functionalization of these as-prepared nanomaterials, this sensing system shows remarkable advantages including very fast and simple, cost-effective as well as environmental-friendly, which suggest that this new strategy could serve as an efficient tool for analyzing GSH level in biosamples.

Scale-Up Synthesis of Fragrant Nitrogen-Doped Carbon Dots from Bee Pollens for Bioimaging and Catalysis

Fragrant nitrogen-doped carbon dots of gram scale can be prepared from commercial bee pollens by a hydrothermal process. These carbon dots of 1-2 nm in size show promising applications in cellular imaging and catalysis/photocatalysis.

Reduced carbon dots employed for synthesizing metal nanoclusters and nanoparticles

Reduced carbon dots (r-CDs) were creatively and successfully employed for preparing Au nanoclusters and nanoparticles.

Detection of glutathione with an “off–on” fluorescent biosensor based on N-acetyl-l-cysteine capped CdTe quantum dots

This paper reports a quantum dot (QD)-based “off–on” fluorescent biosensor specifically for the determination of glutathione (GSH) with high sensitivity.