Preparation and utilization of carbon dots as a nanoprobe for sensitive detection of tartrazine and palladium (II).

We prepared novel green, eco-friendly carbon dots as a dual-channel probe for highly sensitive and selective detection of tartrazine (Trz) and palladium(II) (Pd(II)) involving, respectively, FRET and electron transfer mechanisms. Furthermore, the successful utilization of the carbon dots for detecting Trz and Pd(II) in actual samples implies its potential application prospects in analysis.

Selective identification of p-nitroaniline by bromine-mediated polarization of carbon dots.

A fluorometric method based on boron, bromide-codoped carbon dots (BBCNs) was developed for the first time for the highly selective detection of p-nitroaniline (PNA) in wastewater samples. It should be noted that the introduction of bromine greatly increases the molecular polarizability of the probe, which can regulate the energy level matching between the probe and PNA, resulting in the interaction between BBCNs and PNA. In the presence of PNA, the fluorescence of BBCNs is obviously quenched and accompanied by a red shift of the fluorescence band, which might be attributed to the formation of aggregates caused by the polar adsorption of BBCNs and PNA. It is beneficial for constructing a highly selective sensing platform for PNA determination compared to its isomers (o-nitroaniline and m-nitroaniline) through atomic bromine-mediated polarization of the BBCNs. With the help of this mechanism, an excellent linear range of 0.5-300 µM with a low detection limit of 0.24 µM toward PNA was obtained. This work further confirms that there is a significant relationship between the nature of doping elements and the optical and physicochemical properties of fluorescent materials.

Photoelectrochemical detection of copper ions based on a covalent organic framework with tunable properties.

Copper ions (Cu2+) play an essential role in various cellular functions, including respiration, nerve conduction, tissue maturation, oxidative stress defense, and iron metabolism. Covalent organic frameworks (COFs) are a class of porous crystalline materials with directed structural designability and high stability due to the combination of different monomers through covalent bonds. In this study, we synthesized a porphyrin-tetrathiazole COF (TT-COF(Zn)) with Zn-porphyrin and tetrathiafulvalene (TTF) as monomers and used it as a photoactive material. The strong light absorption of metalloporphyrin and the electron-rich properties of supplied TTF contribute to its photoelectrochemical performance. Additionally, the sulfur (S) in the TTF can coordinate with Cu2+. Based on these properties, we constructed a highly sensitive photoelectrochemical sensor for detecting Cu2+. The sensor exhibited a linear range from 0.5 nM to 500 nM (R2 = 0.9983) and a detection limit of 0.15 nM for Cu2+. Notably, the sensor performed well when detecting Cu2+ in water samples.

An eco-friendly fluorometric assay for high-sensitive meloxicam quantitation in biological matrices.

Meloxicam (Mel), as a powerful and effective anti-inflammatory drug, is commonly employed for the treatment of various inflammatory diseases; however, the use of Mel at high doses or for extended periods could cause severe side effects in human visceral organs. Therefore, a simple, rapid, and reliable method is urgently needed to monitor Mel in biological samples. Herein, novel water-soluble luminescent nano-carbon dots (nano-Cdots) with outstanding physicochemical properties were prepared by a one-pot high-temperature hydrothermal process of ellagic acid and guanidine. The nano-Cdots were further used as an optical probe for the sensitive detection of Mel in serum samples through the cooperative mechanisms of the inner filter effect and photoelectron transfer. By employing this sensor, an excellent linear correlation was achieved between the relative luminescent intensity [(PL0 - PL)/PL0] and the concentration of Mel in the range of 0.1 to 200 µM, with a limit of detection of 34.68 nM (3σ/k). This sensor was effectively employed for the analysis of Mel in real serum samples, implying its potential development prospects for the advancement of drug analysis with carbon-based probes.

Green synthesis of a deep-ultraviolet carbonized nanoprobe for ratiometric fluorescent detection of feroxacin and enrofloxacin in food and serum samples.

Recently, the development of a novel fluorescent (FL) nanoprobe for ratiometric detection of antibiotics in real-world samples has received more and more attention. In this article, the distinctive optical properties of deep-ultraviolet emission, a narrowed full width at half maximum (∼20 nm) and excitation-independent emission of a carbonized nanoprobe (CNP) were easily prepared by an environmentally friendly approach of solvothermal treatment using melamine as the precursor and H2O as the solvent. The obtained CNP can be further utilized as an efficient ratiometric FL nanoprobe for enrofloxacin (EFC) and feroxacin (FXC) detection based on the fact that the FL quenching of the CNP was accompanied by an FL increase with EFC/FXC based on the inner filter effect (IFE). Under the optimal conditions, excellent linear relationships existed between the relative FL intensity (FL290 nm/FL412 nm, CNP for FL290 nm and antibiotics for FL412 nm) and the concentrations of FXC and EFC in the range of 0.05-500.0 µM and 0.05-200.0 µM, with limits of detection of 21.74 and 22.43 nM (3σ/k), respectively. With the proposed ratiometric FL sensor, FXC and EFC in milk and serum samples can be rapidly and selectively analyzed without tedious pretreatment processes for real-world samples.

Ratiometric detection of p-nitrophenol and its derivatives using a dual-emissive neuron cell-like carbonized probe based on a ππ stacking quenching mechanism.

p-Nitrophenol and its derivatives can cause serious harm to the health of mankind and the earth's ecosystem. Therefore, it is necessary to develop a novel and rapid detection technology for p-nitrophenol and its derivative. Herein, excellent water-soluble, large-size and dual-emissive neuron cell-analogous carbon-based probes (NCNPs) have been prepared via a solvothermal approach, using o-phenylenediamine as the only precursor, which exhibit two distinctive fluorescence (FL) peaks at 420 and 555 nm under 345 nm excitation. The NCNPs show a neuron cell-like branched structure, are cross-connected, and are in the range of 10-20 nm in skeleton diameter. Interestingly, their blue-green dual-colour fluorescence is quenched by p-nitrophenol or its derivative due to the specific mechanism of the ππ stacking interactions or internal filtration effect. Accordingly, a simple, rapid, direct and free-label ratiometric FL detection of p-nitrophenol is proposed. An excellent linear relationship shows linear regions over the range of 0.1-50 µM between the ratio of the FL intensity (FL555 nm/FL420 nm) and the concentrations of p-nitrophenol. The detection limit is as low as 43 nM (3σ). Importantly, the NCNP-based probe also shows acceptable repeatability and reproducibility for the detection of p-nitrophenol and its derivatives, and the recovery results for p-nitrophenol in real wastewater samples are favourable.

Au-Hg/rGO with enhanced peroxidase-like activity for sensitive colorimetric determination of H2O2.

The Au-Hg amalgam anchored on the surface of reduced graphene oxide nanosheets (Au-Hg/rGO) has been synthesized successfully and characterized by various techniques such as transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The Au-Hg/rGO nanocomposites were found to possess excellent peroxidase-like catalytic activity and can quickly catalyze the oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) to blue oxTMB in the presence of H2O2. The obvious color change offered accurate determination of the H2O2 concentration by recording the absorbance at 652 nm using a UV-vis spectrophotometer. The linear response range for H2O2 was from 5 µM to 100 µM and the detection limit was 3.25 µM (S/N = 3). Furthermore, a kinetic study indicated that the catalytic behavior of Au-Hg/rGO nanocomposites followed the typical Michaelis-Menten theory and Au-Hg/rGO nanocomposites showed good affinity for H2O2. We envision that the simple and sensitive colorimetric detection system holds great promising applications in clinical diagnostics and food and environment monitoring.

UV-assisted one-pot synthesis of bimetallic Ag-Pt decorated reduced graphene oxide for colorimetric determination of hydrogen peroxide.

Bimetallic Ag-Pt nanoparticles decorated on the surface of reduced graphene oxide (Ag-Pt/rGO) were designed and selected as a nanozyme for the assay of hydrogen peroxide. The nanocomposites were prepared through a one-pot reduction of potassium chloroplatinate, silver nitrate, and graphene oxide under ultraviolet irradiation without using any extra chemical reducing agents or surfactants. The successful formation of Ag-Pt/rGO nanocomposites was confirmed by transmission electron microscopy, energy disperse spectroscopy mapping, X-ray photoelectron spectroscopy, and X-ray diffraction analysis. Significantly, Ag-Pt/rGO nanocomposites possessed excellent peroxidase-like activity toward the catalytic oxidation of 3,3',5,5'-tetramethylbenzidine to form a blue product in the presence of hydrogen peroxide. Steady-state kinetics studies suggested that Ag-Pt/rGO nanocomposites had high affinity to hydrogen peroxide. Based on these properties, a convenient and sensitive method for the colorimetric determination of hydrogen peroxide was developed. Under optimal conditions, the absorbance at 652 nm increases linearly in the 10-100 µM and 100 µM-1 mM ranges of hydrogen peroxide concentration, and the detection limit is 0.9 µM (S/N = 3). The method was successfully applied to the determination of hydrogen peroxide in real water samples. Graphical abstract Ag-Pt/rGO nanocomposites were prepared by a one-pot UV irradiation method and used as a novel nanozyme for colorimetric determination of H2O2.

Nanoporous Semiconductor Electrode Captures the Quantum Dots: Toward Ultrasensitive Signal-On Liposomal Photoelectrochemical Immunoassay.

Liposomal photoelectrochemical (PEC) bioanalysis has recently emerged and exhibited great potential in sensitive biomolecular detection. Exploration of the facile and efficient route for advanced liposomal PEC bioanalysis is highly appealing. In this work, we report the split-type liposomal PEC immunoassay system consisting of sandwich immunorecognition, CdS quantum dots (QDs)-loaded liposomes (QDLL), and the release and subsequent capture of the QDs by a separated TiO2 nanotubes (NTs) electrode. The system elegantly operated upon the protein binding and lysis treatment of CdS QDLL labels within the 96-well plate, and then the CdS QDs-enabled sensitization of TiO2 NTs electrode. Exemplified by cardiac markers troponin I (cTnI) as target, the proposed system achieved efficient activation of TiO2 NTs electrode and thus the signal generation toward the split-type PEC immunoassay. This work features the first use of QDs for liposomal PEC bioanalysis and is expected to inspire more interests in the design and implementation of numerous QDs-involved liposomal PEC bioanalysis.

Self-Assembled Peptide Nanostructures for Photoelectrochemical Bioanalysis Application: A Proof-of-Concept Study.

Currently, one of important research directions of photoelectrochemical (PEC) bioanalysis is to exploit innovative photoactive species and their elegant implementations for selective detection and signal transduction. Different from existing candidates for photoelectrode development, this study, exemplified by the cationic dipeptide nanoparticles (CDNPs), reports the first demonstration of self-assembled peptide nanostructures (SAPNs) for the PEC bioanalysis. Specifically, the CDNPs were prepared as representative materials and then immobilized onto the indium tin oxide (ITO) electrode for the PEC differentiation of several commonly involved biomolecules such as ascorbic acid (AA) and l-cysteine. Significantly, the experimental results disclosed that the CDNPs possessed unique photocathodic responses and good analytical performance toward AA detection in terms of rapid response, high stability, and excellent selectivity. This work demonstrates the great potential of the large SAPN family for the future PEC bioanalysis development and has not been reported to our knowledge.

An OFF-ON detection method for copper(ii) ions using a AgAu-NG nanocomposite modified electrode.

An OFF-ON detection method for Cu2+ was developed at the AgAu bimetallic nanoparticle decorated nitrogen-doped graphene (AgAu-NG) nanocomposite modified electrode. The measurement was based on the copper-catalyzed oxidation of cysteamine (Cys) to regulate the oxidation peak current of Ag. In the absence of Cu2+, Cys can bind to the surface of AgAu-NG via the Ag-S or Au-S bond, thus leading to an obvious decrease of the oxidation peak current of Ag. However, in the presence of Cu2+, Cu2+ can greatly catalyze the oxidation of Cys by dissolved O2 to form cystamine, which would fall off the surface of AgAu-NG nanocomposites, leading to the partial recovery of the oxidation peak current of Ag. With the increase in the concentration of Cu2+, the oxidation peak current of Ag in the presence of Cys increases accordingly. So, the concentration of Cu2+ can be measured. By using the optimum conditions, this method can detect Cu2+ concentrations down to 0.3 nM (S/N = 3) with a linear response range of 1 nM-1 mM. Furthermore, this method was applied to determine Cu2+ concentrations in river water samples and showed excellent analytical performance.

A novel electrochemical sensor based on Au nanoparticles/8-aminoquinoline functionalized graphene oxide nanocomposite for paraquat detection.

In this paper, a novel electrochemical sensor based on Au nanoparticles/8-aminoquinoline functionalized graphene oxide (AuNPs/GAQ) nanocomposite was developed and tested for the first time for detection of paraquat (PQ). The morphology and composition of AuNPs/GAQ nanocomposite were characterized by various techniques, including transmission electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, and x-ray photoelectron spectroscopy. Cyclic voltammetry and differential pulse voltammetry were utilized to investigate the electrochemical performances of AuNPs/GAQ nanocomposite modified glassy carbon electrode. The obtained modified electrode exhibited excellent electrocatalytic activity towards detection of PQ. Under the optimized conditions, the proposed sensor showed low detection limit (6 nM, S/N = 3), wide linear range (0.02-24 µM), high selectivity and good stability. In addition, it was successfully applied for detection of PQ in natural water samples with satisfactory results.

Voltammetric simultaneous determination of catechol and hydroquinone using a glassy carbon electrode modified with a ternary hybrid material composed of reduced graphene oxide, magnetite nanoparticles and gold nanoparticles.

An electrochemical sensor is described for the simultaneous determination of the pollutants catechol (CC) and hydroquinone (HQ). A glassy carbon electrode (GCE) was modified with reduced graphene oxide, Fe3O4 and gold nanoparticles and then showed a pair of well-defined voltammetric peaks for CC and HQ. Its oxidation peak potentials (located at 0.21 and 0.10 V vs. Ag/AgCl) are well separated, and this makes it suitable for simultaneous determination of the two isomers. Under optimal conditions, the oxidation peak currents of CC and HQ increase linearly in the 0.05-550 µM and 0.1-500 µM concentration ranges, even in the presence of 0.1 mM of the respective other isomer. The detection limits are 0.02 and 0.17 µM (at S/N = 3), respectively. The modified GCE exhibits good selectivity and recovery when applied for the analysis of spiked wastewater. Graphical abstract Ternary hybrid nanomaterials of rGO-Fe3O4-Au was developed for simultaneous electrochemical determination of catechol (CC) and hydroquinone (HQ).

Long-term stable electrochemiluminescence of perovskite quantum dots in aqueous media.

We develop a novel electrochemiluminescence (ECL) emitter of aqueous-based perovskite quantum dots, with long-term stable ECL emission in aqueous media. Moreover, an electron transfer annihilation mechanism of ECL generation is proposed, revealed by the experimental results. This study opens a door for exploring efficient perovskite-based ECL emitters.

Porous calix[4]pyrrole-based polymers with high surface area for efficient removal of polar organic micropollutants from water.

Herein, effort was made to construct innovative adsorbent for the removal of polar organic micropollutants (OMPs) from water. Tetra-meso resorcinol-functionalized calix[4]pyrrole (CP) featured with endo-functionalized attribute and polyphenol hydroxyl structure was crosslinked by π-electron-rich 4,4'-bis(chloromethyl)biphenyl (BCMBP) through Friedel-Crafts reaction to generate porous calix[4]pyrrole-based polymers (PCPPs) with high surface area. The porosity of the PCPPs could be tuned by adjusting the molar ratio of hydrophilic CP to hydrophobic BCMBP, and diversified binding sites were integrated together. Based on adsorption kinetics and isotherm studies, PCPP(1-16) showed rapid adsorption rate and high removal efficiency (RE) as well as advanced adsorption capacity. The REs towards the tested polar OMPs by PCPP(1-16) were all above 95% in 30 min. Compared with granular activated carbon (GAC), the rate constant of pseudo-second-order model (k2) and adsorption capacity upon PCPP(1-16) were 8-230 times and 1.3-3.1 times greater than those by GAC. Adsorption mechanism studies confirmed the presence of multiple interactions and thermodynamic investigation revealed the spontaneous and physical adsorption nature. Besides, PCPP(1-16) showed excellent adsorption performance in real water samples at environmental levels and exhibited advanced absorption ability in flow-through mode. Accompanied by facile regeneration under eluting with methanol and cost-effective preparation, PCPP(1-16) demonstrated great potential as promising adsorbent for water treatment.

A MELET- and IFE-based UV-visible luminescent ratiometric probe for quantization of mercury(II) and nitrofurantoin in environmental sewage.

A novel fluorimetric ratiometric probe of green and eco-friendily nitrogen-enriched, oxygen-doped carbon nanodots (Cnanodots) was prepared for the quantitative analysis of mercury(II) (HgII) and nitrofurantoin (Nit) in the environmental sewage. The Cnanodots exhibits dual-emission peaks respectively at 345 and 445 nm under 285 nm excitation, with excitation-independent properties. Unexpectedly, this Cnanodots displays two obvious ratiometric responses to HgII and Nit through decreasing the signal at 345 nm and remaining invariable at 445 nm. Experimental results confirm that the highly sensitive analysis of HgII and Nit are achieved respectively based on matching energy-level electron transfer and inner filter effect mechanisms. The fluorescence (FL) ratiometric intensity of [FL345nm/FL445nm] expresses a good linear relationship with the concentration of HgII in the scope of 0.01-20 µM, while the logarithm of [Log(FL0345nm-FL345nm)] on the quenching degree of the probe by Nit also shows a good linear correlation within the range of 0.01-100 µM. The detection limits were calculated to be 4.14 nM for HgII, and 7.84 nM for Nit. Moreover, recovery experiments of Cnanodots for HgII and Nit sensing in real sewage samples obtained satisfactory results, comfirming the feasibility of practical application.

A nickel porphyrin-based covalent organic framework modified electrode for the electrochemical detection of acetaminophen.

Covalent organic frameworks (COFs) can be rationally designed with functional organic ligands to improve the electrochemical responsiveness of the electrode toward certain medicinal compounds. In this study, we synthesized a COF-Ni electrocatalyst material, which is formed by covalent coupling of electron-rich 2,3,6,7-tetrakis (4-formylphenyl) tetrakis (4-imidazolyl) (TTF-4CHO) and hole-rich 5,10,15,20-tetrakis (4-aminophenyl) porphyrin nickel(II) (TAPP-Ni). The reasonable electron transfer path design, the large specific surface area of the COF and the physical properties of ordered nanopores, as well as the Ni-N4 bond as a highly active catalytic center, allow the COF-Ni material modified electrode to exhibit excellent sensing performance for acetaminophen (ACOP). The detection limit for ACOP is as low as 47.6 nM, with a linear range of 1-1500 µM, which is better than for most of the reported sensors. With superior interference resistance and good stability performance, COF-Ni is a highly suited electrode modification material for real-world sample detection, which provided a new perspective for application of COF materials in drug analysis.

Porous ß-cyclodextrin polymers for rapid and efficient removal of organic micropollutants from water: The role of sulfonation and porosity on adsorption performance.

Removal of organic micropollutants (OMPs) from water, especially hydrophilic and ionized ones, is challenging for water remediation. Herein, porous ß-cyclodextrin polymers (PCPs) with tailored functionalization were prepared based on molecular expansion strategy and sulfonation. Partially benzylated ß-cyclodextrin was knotted by external crosslinker to form PCP1, and knotting PCP1 by expansion molecule generated PCP2. PCP1 and PCP2 were sulfonated to achieve PCP1-SO3H and PCP2-SO3H. Based on systematical adsorption evaluation toward multiple categories of OMPs, it was found that the introduced strong polar -SO3H group could bring strong hydrogen bonding and electrostatic interactions. PCP2 showed the highest surface (998.97 m2/g) displayed more excellent adsorption performance toward neutral and anionic OMPs, and the adsorption mechanism for this property of PCP2 was dominated by hydrophobic interactions. In addition, the PCP1-SO3H with the lowest surface area (39.75 m2/g) rather than PCP2-SO3H with higher surface (519.28 m2/g) exhibited more superior adsorption towards hydrophilic and cationic OMPs, benefiting by hydrogen bonding and electrostatic interactions as well as appropriate porosity. These results not only confirmed the performance enhancement of PCPs through the integration of novel preparation strategy, but also provided fundamental guidance for PCPs design for water remediation.

Probing the interactions between boronic acids and cis-diol-containing biomolecules by affinity capillary electrophoresis.

The affinity of boronic acids to cis-diol-containing biomolecules has found wide applications in many fields, such as sensing, separation, drug delivery, and functional materials. A sound understanding of the binding interactions will greatly facilitate exquisite applications of this chemistry. Although a few analytical tools have been available for the characterization of the interactions, these techniques are associated with some apparent drawbacks, so they are only applicable to a limited range of boronic acids and cis-diol-containing biomolecules. Therefore, a widely applicable method is still greatly needed. In this work, an affinity capillary electrophoresis (ACE) method was established and validated to probe the interactions between boronic acids and cis-diol-containing biomolecules. The method was proven to be applicable to almost all types of cis-diol-containing biomolecules and boronic acids. Based on this method, a quantitative, comparative study on the interactions between 14 boronic acids that have important potentials for application with 5 typical monosaccharides of biological importance was carried out. The findings provided new insights into boronate affinity interactions, particularly the relationship between the binding strength with the molecular structures of the binding species. Besides, effects of pH and temperature on the binding strength were also investigated. This method exhibited several significant advantages, including (1) possibility of simultaneous study of multiple interactions, (2) low requirement on the purity of the binding species, (3) wide applicability, and (4) high accuracy and precision.

Separation and analysis of cis-diol-containing compounds by boronate affinity-assisted micellar electrokinetic chromatography.

Cis-diol-containing compounds (CDCCs) are usually highly hydrophilic compounds and are therefore difficult to separate by conventional reversed-phase-based micellar electrokinetic chromatography (MEKC) due to poor selectivity. Here, we report a new method, called boronate affinity-assisted micellar electrokinetic chromatography (BAA-MEKC), to solve this issue. A boronic acid with a hydrophobic alkyl chain was added to the background electrolyte, which acted as a modifier to adjust the selectivity. CDCCs can covalently react with the boronic acid to form negatively charged surfactant-like complexes, which can partition into micelles formed with a cationic surfactant. Thus, CDCCs can be separated according to the differential partition constants of their boronic acid complexes between the micellar phase and the surrounding aqueous phase. To verify this method, eight nucleosides were employed as the test compounds and their separation confirmed that the combination of boronate affinity interaction with MEKC can effectively enhance the separation of CDCCs. The effects of experimental conditions on the separation were investigated. Finally, the BAA-MEKC method was applied to the separation and analysis of nucleosides extracted from human urine. BAA-MEKC exhibited better selectivity and improved separation as compared with conventional MEKC and CZE. Successful quantitative analysis of urinary nucleosides by BAA-MEKC was demonstrated.