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Graphene oxide (GO) is an excellent chemical tunable optical platform for imaging and sensing. The photoluminescence (PL) quantum yield of GO is relatively low, which limited the application of the intrinsic and tunable fluorescence from GO. Here, we report the first case of metal-enhanced fluorescence (MEF) of GO. A significant enhancement (~10-fold) in fluorescence intensity is observed from GO on the Ag substrate as compared to that on the glass. FL, Raman, and SEM images are used to investigate the MEF behavior and are coincident with each other. The influence of the metal particle size of Ag substrate is investigated. The fluorescence is also found to be responsive when adding different metal ions into GO solution. GO contacting directly with metal substrate exhibits strong MEF without quenching, which makes it possible to use GO sheets for three-dimension optical imaging and sensing.

A photo-induced uranium extraction method without an external photocatalyst and inert atmosphere would greatly reduce the energy consumption and operation equipment in the treatment of nuclear wastewater.

Surface-initiated activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) integrated with mussel-inspired polydopamine (PDA) chemistry was, for the first time, employed for controlled grafting of poly(glycidyl methacrylate) (PGMA) brushes from carbon nanotubes (CNTs). The strategy initially involved deposition of a PDA layer by spontaneous self-polymerization, which is a benign and nonsurface specific way for anchoring 2-bromoisobutyryl bromide to form initiators on the CNTs. Dense and uniform PGMA brushes were then grown via ARGET ATRP using low concentration of Cu catalyst in different solvents. With abundant highly reactive epoxy groups, the PGMA-grafted CNTs could serve as a versatile platform for further modification or functionalization. Ethylenediamine ligands were facilely introduced, imparting the functionalized CNTs with record-high adsorption ability toward uranium ions among CNTs composites. The integrated strategy combining surface-initiated ARGET ATRP technique and PDA chemistry would provide new opportunities for surface engineering of nanomaterials for advanced applications.

Ultrasmall metal nanoparticles (MNPs) and atomically dispersed metal sites (ADMSs) exhibit excellent catalytic activity and selectivity. However, they tend to aggregate into large particles during synthesis and catalysis due to high surface free energy. Aiming to break out of this dilemma, zeolite imidazolate frameworks (ZIFs) have proved to be ideal substrates for stabilizing the ultrafine metal nanostructures. The stabilizing mode includes confining MNPs inside their pore structures and converting intrinsic metal nodes into coordinately unsaturated metal sites (i.e., ZIF‐confined metal catalysts). Furthermore, various MNPs and ADMSs can also be immobilized into ZIF‐derived porous carbon through high‐temperature pyrolysis (i.e., ZIF‐derived carbon‐supported metal catalysts). In brief, ZIFs and their derivatives have gradually emerged as good platforms for designing metal catalysts at nanoscale and even atomic level. In this review, recent progress in the structural analysis and synthetic strategies of metal catalysts supported by ZIFs and their derivatives is presented. Besides, current challenges and future directions of atomically dispersed metal catalysts are discussed. This article will provide valuable insights into rational design of metal catalysts with exquisite nanostructure and high catalytic performance to meet further material requirements in the catalytic field.

Due to a lack of focus on China’s financial decentralization system, the existing research does not pay attention to the beneficial contribution of Chinese local governments to carbon emission reduction through their actions in the financial field. In this study, we collected 16 years of data from 30 provinces in China and utilized a two-way fixed-effects model to empirically test the impact of China’s financial decentralization on carbon emission reduction. The regression results show that China’s financial decentralization system has a significant carbon-emission reduction effect. A heterogeneity analysis shows that this effect is common in different regions of China and that fiscal decentralization will negatively moderate it. A mechanism analysis shows that under China’s financial decentralization system, the active intervention of local governments in local finance will significantly upgrade the energy consumption structure and ease the financing constraints of enterprises. The regression results of the spatial econometric model show that the carbon emission reduction effect of China’s financial decentralization still has a spatial spillover effect. Finally, we put forward corresponding policy recommendations.

Radioactive ions with high-heat release or long half-life could cause long-term influence on environment and they might enter the food chain to damage human body for their toxicity and radioactivity. It is of great importance to develop methods and materials to detect and remove radioactive ions. Carbon dots and their composite materials has been applied widely in many fields due to their plentiful raw materials, facile synthesis and functional process, unique optical property and abundant functional groups. This comprehensive review focuses on the preparation of CDs and composite materials for the detection and adsorption of radioactive ions. Firstly, the recent-developed synthetic methods for CDs were summarized briefly, including hydrothermal/solvothermal, microwave, electrochemistry, microplasma, chemical oxidation methods, focusing on the influence of CDs properties. Secondly, the synthetic methods for CDs composite materials were classified to four categories and summarized generally. Thirdly, the application of CDs for radioactive ions detection and adsorption were explored and concluded including uranium, iodine, europium, strontium, samarium et al. Finally, the detection and adsorption mechanism for radioactive ions were searched and the perspective and outlook of CDs for detection and adsorption radioactive ions have been proposed based on our understanding.

The authors have studied the role of different ligands on the surfaces of silver nanoplates for regulating their analytical applications. Citrate-capped silver nanoplates are applied for the detection of chromium ions (Cr3+) based on aggregation of silver nanoplates. Cr3+ can cause aggregation through high affinity between Cr3+ and carboxylate groups of citrates, resulting in a color change from dark yellow to purple and at last colorless. The detection limit is 8.0 nM. This system shows excellent selectivity in the presence of a variety of other metal ions. Further, silver nanoplates coupled with iodide ions are employed for the colorimetric determination of copper ions (Cu2+) based on a new strategy of fusion/oxidation etching nanoplates. When Cu2+ is introduced into this silver nanoplate system, Cu2+ can oxidize I− to iodine (I2), which can further oxidize silver to form silver iodide (AgI). Simultaneously, the solution color changes from dark yellow to colorless. The lower limit detection is 0.27 μM. This assay exhibits excellent selectivity for Cu2+ over other environmental metal ions. It is perceived that this design concept will open up a fresh insight of simple, rapid and reliable detection of other heavy metal ions in drinking water and environmental samples.

A key challenge of photoregulated living radical polymerization is developing efficient and robust photocatalysts. Now carbon dots (CDs) have been exploited for the first time as metal-free photocatalysts for visible-light-regulated reversible addition-fragmentation chain-transfer (RAFT) polymerization. Screening of diverse heteroatom-doped CDs suggested that the P- and S-doped CDs were effective photocatalysts for RAFT polymerization under mild visible light following a photoinduced electron transfer (PET) involved oxidative quenching mechanism. PET-RAFT polymerization of various monomers with temporal control, narrow dispersity (Đ≈1.04), and chain-end fidelity was achieved. Besides, it was demonstrated that the CD-catalyzed PET-RAFT polymerization was effectively performed under natural solar irradiation.

Artificial enzyme mimics based on nanomaterials have attracted sustained attention owing to their multiple advantages compared with natural enzymes. However, there are a few enzyme self-cascade systems for the highly sensitive detection of analytical targets. Herein, we have described a self-cascade catalytic system based on single-component cupric oxide nanoparticles (CuO NPs) for an ultrasensitive fluorescent detection toward glutathione (GSH) and Ag+ ions. The limit of detection is lower for nanomolar (nM) and picomolar (pM) levels for GSH and Ag+, respectively. To the best of our knowledge, for the first time, we find that CuO NPs possess the intrinsic GSH-oxidase and peroxidase-like activity as a dual-functional nanozyme, coupling with terephthalic acid (TA) and GSH to construct a self-cascade fluorescent system. The turn-on fluorescence signal of oxidation hydroxyterephthalate (TAOH) is generated in the presence of GSH. Then, the fluorescence of a reaction mixture is quenched after the addition of A...

A fluorescence method for the determination of inorganic pyrophosphatase (PPase) activity has been established based on copper nanoclusters (CuNCs). The polythymine of 40 mer (T40) acts as a template for the reduction reaction from Cu2+ to Cu0 by ascorbic acid (AA). This reaction leads to the formation of fluorescent CuNCs with excitation/emission peaks at 340/640 nm. However, the higher binding affinity between inorganic pyrophosphate (PPi) and Cu2+ hinders the effective formation of CuNCs. This shows low fluorescence intensity. PPase catalyzes the hydrolysis of PPi into Pi during which free Cu2+ ions are produced. This facilitates the formation of fluorescent CuNCs. Thus, the fluorescence intensity was restored. The fluorescence enhancement of the system has a linear relationship with PPase activity in the range 0.3 to 20 mU·mL−1, and the detection limit is0.2 mU·mL−1. The relative intensity (I/I0) at 640 nm for the analytical solution versus system is also employed to screen the inhibitor for PPase with high efficiency.

Fluorescent polydopamine nanoparticles (FPD) are a kind of promising fluorescent nanoparticles for biosensing and imaging, while the rapid and controllable synthesis of FPD is still challenging. In this paper, we developed a microplasma electrochemistry strategy to regulate the oxidative polymerization process of dopamine, resulting in a controlled formation of FPD. Treating the dopamine solution with microplasma anode could not only generate oxidative species to trigger the nucleation of polydopamine nanoparticles at the plasma-liquid interface, but also provide an acidic environment to inhibit their further growing up during the diffusion process. Thus, uniform FPD with a diameter of 3.1 nm could be prepared within minutes. And, continuous generation of FPD could be achieved without the formation of aggregates when prolonging the reaction time. The obtained FPD had abundant functional groups on the surfaces, showing tunable fluorescent emission properties. These luminescent nanoparticles were demonstrated for highly selective detection of uranium with a detection limit of 2.1 mg/L. The novel microplasma electrochemistry strategy established in this work provided better opportunity for controllable synthesis of FPD, as well as other luminescent nanoparticles, and broadened their application in chemical sensing area.

Oxidant-regulated polymerization of dopamine was exploited, for the first time, for effective surface engineering of the well-defined cylindrical pores of nuclear track-etched membranes (NTEMs) to develop novel catalytic membrane reactor. First, in the presence of a strong oxidant, controlled synthesis of polydopamine (PDA) with tunable particle size was achieved, allowing a homogeneous deposition to the confined pore channels of NTEMs. The PDA interfaces rich in catechol and amine groups provided enhanced hydrophilicity to promote mass transport across the membrane and abundant nucleation sites for formation and stabilization of metallic nanoparticles (NPs). In-situ reductive growth of multiple metallic NPs, including Pd, Ag, and Au, was then achieved inside the cylindrical pores of NTEMs. Using the functionalized membrane as a catalytic reactor, efficient reduction of 4-nitrophenol (4-NP) was demonstrated in a flow-through mode. Moreover, after dissolution removal of the NTEMs, self-sustained one-dimensional (1D) PDA/M (M = Pd, Ag, or Au) hybrid nanotubes (NTs), with determined aspect ratio and a length reaching up to 10 μm, were obtained for catalysis of 4-NP in a batch reaction mode. This study established a facile and versatile method, by rational tuning of the polymerization behavior of dopamine, for effective modification of confined microscale/nanoscale cavities with different surface characteristics. The integration of PDA chemistry with NTEMs would provide more opportunities for development of novel catalytic membrane reactors as well as for the tailored synthesis of functional 1D nanotubes for broadened applications.

A novel colorimetric nanosensor based on stable aggregation of gold nanoparticle (AuNP) triggered by carbon quantum dots (CDs) has been developed for detection of Ag+ ions in the presence of glutathione (GSH). First, the nanosensor is constructed by assembling carbon quantum dots (CDs) “shell” on the surface of gold nanoparticle (AuNP), resulting in the generation of the stable aggregation of CDs/AuNP. The solution color changes from red to blue. In the absence of target, the addition of GSH into the aggregated CDs/AuNP exhibits the dispersion state corresponding to the color change from blue to red, because GSH can prefer to binding with AuNP comparing with CDs. On the contrary, the aggregated CDs/AuNP has been again observed with the color change from red to blue after the target analyte Ag+ ions are added. Therefore, the new sensing strategy based on “aggregation-dispersion-aggregation” or “blue-red-blue” mode can be established for Ag+ detection. This method can selectively detect Ag+ in a linear rang...

We described a rapid and highly sensitive colorimetric method for the detection and quantification of silver ions employing glutathione (GSH)-mediated MnO 2 nanosheets as an artificial oxidase. In this assay,the absorption intensity of the chromogenic reaction system enabled the quantification of silver ions. Under the optimum conditions, the linear response ranged for Ag + was from 10 nM to 800 nM with a correlation coefficient of 0.996. Remarkably, limit of detection in aqueous solutions was 4.23 nM, which was well below United States Environmental Protection Agency (USEPA) permissible limit in drinking water (460 nM). This sensing assay had highly specificity because no significant interference occurred with 10-fold concentration of other metal ions. Moreover, the approach also could be employed to the Ag + detection in real samples. And the recovery of Ag + spiked in tap water ranged from 99.62% to 108.01%. Importantly, the oxidation reaction of TMB to oxTMB by MnO 2 nanosheets completed instantaneously even by naked-eye readout. Therefore, the assay based on GSH-mediated MnO 2 nanosheets is simple, rapid, highly sensitive and selective for the quantification of Ag + in water and practical samples.

Mercury is a common heavy metal element in natural systems and is highly toxic to the human body. Herein, a novel colorimetric detection of Hg2+ ions is proposed based on the aggregation of gold nanoparticles (AuNPs) induced by carbon quantum dots (CDs) with the assistance of glutathione (GSH). In this sensing system, the AuNP/CDs composite forms through Au–N bonds. Simultaneously, the color of the solution turns from wine red to blue. The well-dispersed AuNPs can be restored after the addition of GSH, because GSH competes with CDs to bind onto the surface of AuNPs and protect AuNPs from aggregation. In the presence of Hg2+ ions, GSH can chelate with Hg2+ to form a complex, which subsequently enables CDs to facilitate the aggregation of the AuNPs again. Therefore, according to the red-to-blue color change, a colorimetric sensor is established for the sensitive and selective detection of Hg2+ with a detection limit of 7.5 nM. Moreover, this sensor is successfully used to detect Hg2+ spiked in environmental water. This very simple and cost-effective strategy will promote the development of a colorimetric sensor for the determination of other metal ions in biological and environmental fields.

This study presents a facile hydrothermal approach in a “Tris” buffer solution for fabricating polydopamine (PDA) nanostructures with different morphologies (core–shell, yolk–shell, and hollow spheres), while concurrently tuning their stability, permeability, and reactivity. Structural and morphological transformation of PDA induced by hydrothermal treatments is described in detail. Surface-initiated growth of poly(N-isopropylacrylamide) (PNIPAM), a thermally responsive polymer, was then achieved from the hydrothermally treated PDA by using the activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP). Interestingly, inward and outward growth of polymer chains from PDA hollow spheres could be manipulated depending on the solvation effect and hydrothermally induced regulation of the pore network in the PDA structure. Hybrid PDA/PNIPAM nanocapsules with tunable morphologies could be obtained. This study provides new insights into PDA’s structural evolution under hydrother...

This study presents a new strategy by integrating surface-initiated atom transfer radical polymerization (SI-ATRP) with bio-inspired polydopamine chemistry to prepare well-defined glass fiber/polymer composites. Firstly, a homogenous PDA layer, which served as a favorable platform facilitating ATRP initiators anchoring, was deposited onto the glass fibers. Controlled growth of poly(glycidyl methacrylate) (PGMA) brushes from the glass fibers were then performed using the initiators for continuous activator regeneration (ICAR) ATRP method. PGMA brushes with defined structure, grafting density (5 wt.% ~ 25 wt.%) and well preservation of chain end-functionality could be obtained by reducing radical initiator ratio and using a high dilution strategy (solvent: monomer=10:1 (V:V)). And, a narrow distribution of molecular weight (PDI≤1.2) could be attained within reduced polymerization time. Laccase, as an enzyme model, was then covalently immobilized to the glass fiber/PGMA composites. The developed bio-composit...

We report on a method for sensitive detection and discrimination of multiple proteins. The peroxidase-like activity of gold nanoparticles (AuNPs) is employed to catalyze the oxidation of 3′,3′,5′,5′-tetramethylbenzidine (TMB) in the presence of H2O2. Depending on the protein, this produces colorations with different absorbance. The catalytic activity of the reaction system is affected because different proteins are absorbed onto the surface of the AuNPs. The absorbance values at 370, 450, and 650 nm are different in the presence of different proteins. The array can discriminate 8 proteins at 50 nM concentration levels with 100% accuracy. It also can discriminate proteins being present in different concentrations and mixtures with different molar ratios of proteins. Human urine spikes with 8 proteins (Concanavalin A), Cytochrome C, Horseradish peroxidase, Human serum albumin, Myoglobin, Pepsin, Trypsin, Papain) can be differentiated by applying hierarchical cluster analysis. The system also can discriminate proteins at different concentrations and the mixtures with different molar ratios in bovine serum. This indicates that the array has a great potential in terms of analyzing biological fluids.

We proposed a colorimetric sensor array for proteins discrimination based on the tunable catalytic activity of AuNPs-DNA conjugates. The peroxidase-like activity of AuNPs could be enhanced by the attachment of single-stranded oligonucleotides on its surface, resulting in highly sensitive colorimetric signal by catalyzing the oxidization of TMB. In the presence of different proteins, the AuNPs-DNA conjugates showed tunable catalytic activity, inducing differential colorimetric response. At the same time, the same protein could tune the catalytic activity of AuNPs decorated by different DNA with different degree. The fingerprint response generated from the sensor array was used for proteins discrimination. Compared to the colorimetric sensor array based on salt-induced AuNPs aggregation, this strategy exhibited much improved discrimination power for proteins at the low concentration. Seven proteins at the concentration of 10 nM could be successfully identified and proteins spiked in human urine at the final concentration of 100 nM could also be well distinguished. The discrimination accuracy of unknown samples was all 100% for these experiments. The current colorimetric array demonstrated its potential for highly sensitive diagnostic applications.

Developing green and efficient technologies for surface modification of magnetic nanoparticles (MNPs) is of crucial importance for their biomedical and environmental applications. This study reports, for the first time, a novel strategy by integrating metal-free photoinduced electron transfer-atom transfer radical polymerization (PET-ATRP) with the bioinspired polydopamine (PDA) chemistry for controlled architecture of functional polymer brushes from MNPs. Conformal PDA encapsulation layers were initially generated on the surfaces of MNPs, which served as the protective shells while providing an ideal platform for tethering 2-bromo-2-phenylacetic acid (BPA), a highly efficient initiator. Metal-free PET-ATRP technique was then employed for controlled architecture of poly(glycidyl methacrylate) (PGMA) brushes from the core-shell MNPs by using diverse organic dyes as photoredox catalysts. Impacts of light sources (including UV and visible lights), photoredox catalysts, and polymerization time on the composition and morphology of the PGMA brushes were investigated. Moreover, the versatility of the PGMA-functionalized core-shell MNPs was demonstrated by covalent attachment of ethylenediamine (EDA), a model functional molecule, which afforded the MNPs with improved hydrophilicity, dispersibility, and superior binding ability to uranyl ions. The green methodology by integrating metal-free PET-ATRP with facile PDA chemistry would provide better opportunities for surface modification of MNPs and miscellaneous nanomaterials for biomedical and electronic applications.

Developing facile and robust technologies for effective enrichment of uranium from seawater is of great significance for resource sustainability and environmental safety. By exploiting mussel-inspired polydopamine (PDA) chemistry, diverse types of PDA-functionalized sorbents including magnetic nanoparticle (MNP), ordered mesoporous carbon (OMC), and glass fiber carpet (GFC) were synthesized. The PDA functional layers with abundant catechol and amine/imine groups provided an excellent platform for binding to uranium. Due to the distinctive structure of PDA, the sorbents exhibited multistage kinetics which was simultaneously controlled by chemisorption and intralayer diffusion. Applying the diverse PDA-modified sorbents for enrichment of low concentration (parts per billion) uranium in laboratory-prepared solutions and unpurified seawater was fully evaluated under different scenarios: that is, by batch adsorption for MNP and OMC and by selective filtration for GFC. Moreover, high-resolution X-ray photoelectron spectroscopic and extended X-ray absorption fine structure studies were performed for probing the underlying coordination mechanism between PDA and U(VI). The catechol hydroxyls of PDA were identified as the main bidentate ligands to coordinate U(VI) at the equatorial plane. This study assessed the potential of versatile PDA chemistry for development of efficient uranium sorbents and provided new insights into the interaction mechanism between PDA and uranium.

The development of convenient method for detection and identification of toxic metals ions is of great interest. In this work, we have developed a facile fluorescent sensor array based on luminescence carbon dots for detecting and differentiating a set of metal ions. Three kinds of nitrogen-doped carbon dots were synthesized by hydrothermal treatment of citric acid with three different amino acids ( l -glycine, l -lysine and l -serine). These carbon dots had various surface states and thus exhibited diverse quenching responses to different metal ions. Six metal ions can be well distinguished at various concentrations (100, 50, 20 and 10 μM). The discrimination accuracy of unknown samples was found to be 100% at a concentration as low as 10 μM. In addition, the binary and ternary mixtures of three metal ions (Hg2+, Cu2+, Fe3+) could also be well recognized with this sensor array. This method is simple, label-free, and the sensor arrays could be obtained and expanded easily with large-scale and low-cost. It will broaden the application field of carbon dots sensors and give a new direction of developing sensitive array sensing systems.

The removal and separation of uranium from aqueous solutions are quite important for resource reclamation and environmental protection. Being one of the most effective techniques for metal separation, adsorption of uranium by a variety of adsorbent materials has been a subject of study with high interest in recent years. However, current methods for monitoring the adsorption process require complicated procedures and tedious measurements, which hinders the development of processes for efficient separation of uranium. In this work, we prepared a type of luminescent mesoporous silica-carbon dots composite material that has high efficiency for the adsorption of uranium and allows simultaneous in situ monitoring of the adsorption process. Carbon dots (CDs) were prepared in situ and introduced onto amino-functionalized ordered mesoporous silica (SBA-NH2) by a facile microplasma-assisted method. The prepared CDs/SBA-NH2 nanocomposites preserved the high specific surface area of the mesoporous silica, as well as...

Single nucleotide polymorphisms (SNPs) are the most fundamental internal causes for many genetic diseases. However, the location information on SNPs in a specific DNA sequence is not well acquired through current SNPs detection methods, except for accurate DNA sequencing. Here we report a fluorescence enhancement phenomenon in the process of two silver nanoclusters (AgNCs) approaching closely to form a nanocluster dimer (NCD). The fluorescence intensity is sensitive to the distance between two AgNCs; therefore, the NCD lights into different fluorescence intensities upon binding SNPs targets with mismatched bases at different positions. Interestingly, the fluorescence intensities of the NCD decrease linearly when the position of single mismatched base moves gradually from the middle point to the end of the target DNA. The NCD is a single probe acting as a universal platform to pinpoint various SNP positions. With this single probe, we cannot only identify the existence of SNPs but also pinpoint the location of a specific single mismatched base in the adjacent positions. This strategy is feasible to detect specific gene point mutations in clinical samples.

An extensible multidimensional colorimetric sensor array for the detection of protein is developed based on DNA functionalized gold nanoparticles (DNA-AuNPs) as receptors. In the presence of different proteins, the aggregation behavior of DNA-AuNPs was regulated by the high concentrations of salt and caused different color change; while DNA-AuNPs grew induced by the reduction of HAuCl4 and NH2OH as a reductant on the surface of nanoparticles exhibited different morphologies and color appearance for different proteins. The transducers based on AuNPs modified by specific and nonspecific DNA enables naked-eye discrimination of the target analytes. This extensible sensing platform with only two receptors could simultaneously discriminate ten native proteins and their thermally denatured conformations using hierarchical cluster analysis (HCA) at the concentration of 50nM with 100% accuracy. This opens up the possibility of the sensor array to investigate the different conformational changes of biomacromolecules, and it gives a new direction of developing multidimensional transduction principles based on plasmonic nanoparticle conjugates. Furthermore, the sensing system could discriminate proteins at the concentration of 500nM in the presence of 50% human urine, which indicated this sensor array has great potential ability in analyzing real biological fluids. In addition, the multidimensional colorimetric sensor array is suitable for analysis of target analytes in the resource-restricted regions because of rapid, simple, low cost, and in-field detection with the naked eye.

A fluorometric and colorimetric method are described for the determination of hydrogen peroxide and glucose by integrating copper nanoclusters (CuNCs) into a Fenton-like reaction. The mechanism mainly depends on the fast formation of long-strand DNA-templated CuNCs with strong red fluorescence (with excitation/emission maxima at 340/640 nm) in the absence of H2O2. The DNA can be cleaved into short-oligonucleotide fragments by hydroxy radicals as formed in the Ce(III)-triggered Fenton-like reaction in the presence of H2O2. As a result, short-strand DNA loses the ability as a template for the formation of CuNCs. This leads to a decrease of fluorescence. The colorimetric assay, in turn, is based on the oxidation of colorless Ce(III) ions to the distinctly yellow Ce(IV) ions (with an absorption maximum at 400 nm) by H2O2. Compared with those assays based on the use of enzyme mimics, this method does not require any chromogenic substrates such as ABTS and TMB. Based on the dual-signal readout platform, we successfully achieved the detection of H2O2 and glucose. LODs are as low as 0.266 μM and 2.92 μM. The methods were applied to the sensitive determination of glucose by using glucose oxidase (GOx) which catalyzes the oxidization of glucose to produce H2O2. The practical application was demonstrated by determination of glucose in human serum, with apparent recoveries of 98.4–101.9% and 99.1–105.6%, respectively. The concentration of glucose ranges from 1 to 500 μM and 50 to 600 μM based on the dual-signal readout platform, respectively. This fluorometric and colorimetric dual-mode strategy will pave a new avenue for constructing effective assays for H2O2-related analytes in biochemical and clinical applications.

Carbon dots (CDs) possess abundant functional groups on their surface which are related to their application in various fields such as sensing, imaging, and catalysis. Understanding the amount and properties of these functional groups and their interaction with metal ions is essential but has posed longstanding challenges because of the diverse and complex structures of CDs. In this work, potentiometric titration is demonstrated as an effective method to figure out the categories and amounts of functional groups. Surface complexation modeling with the FITEQL program was applied to the quantification of the surface sites on CDs with the titration data. Then with the obtained molar concentrations of the surface sites, the pKas of these surface sites were calculated with the Hyperquad program. Finally, titration experiments of CDs with and without Fe(III) were carried out and the stability constants of Fe(III) and ArgCDs were simulated on the Hyperquad program. By utilizing the stability constants, the distribution of Fe(III) species at different pHs and the concentrations of Fe(III) and CDs were also investigated. This potential method might be used for characterizing the surface sites on other CDs or even other soluble nanoparticles as well as for investigating the interactions of the surface sites with different metal ions.