Magnetic MXene-based molecularly imprinted electrochemical sensor for methylmalonic acid.

A novel magnetic Ti3C2Tx-MXene/Fe3O4 composite was prepared from Ti3C2Tx and magnetic Fe3O4. The characterizations by electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) exhibited that the Ti3C2Tx/Fe3O4 nanomaterial presented an outstanding conductivity and a large specific area, which could improve the electron transfer rate, leading to the amplification of the sensor's signal. Furthermore, an ultrasensitive molecularly imprinted electrochemical sensor based on MXene/Fe3O4 composites was fabricated for detecting methylmalonic acid (MMA) with high selectivity. The current intensity of differential pulse voltammetry of the sensor presented a good linear relationship with the logarithm of MMA concentration ranging from 9 × 10-15 mol L-1 to 9 × 10-13 mol L-1. The detection limit of the sensor was 2.33 × 10-16 mol L-1. The fabricated sensor was utilized for detecting MMA in human serum samples with excellent recoveries. Therefore, this method significantly improved the sensitivity of detection, and constitutes an  affordable sensing platform for trace detection of organic carboxylic acid.

Electrochemical sensor based on Ti3C2 membrane doped with UIO-66-NH2 for dopamine.

A Ti3C2 membrane was prepared by doping UIO-66-NH2 with Ti3C2 through hydrogen bonds. When the doping mass ratio of Ti3C2 and UIO-66-NH2 was 6:1, the electrochemical performance was optimal. Characterization was done by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electrochemical impedance spectroscopy (EIS) which exhibited hierarchical cave-like physiognomy, large specific area, outstanding electronic conductive network, and excellent film-forming property. Moreover, the Ti3C2 film was analyzed via atomic force microscopy (AFM), which displayed good mechanical properties and rough surface morphology. The fabricated Ti3C2 membrane/GCE sensor was applied to the detection of dopamine (working potential of + 0.264 V vs. Ag/AgCl) with LOD of 0.81 fM and a sensitivity of 14.72 µA fM-1 cm-2. It was demonstrated that the Ti3C2 membrane can be used to construct nonenzymatic sensors with excellent performance. The fabricated sensor has high selectivity and stability and has good practicability with recoveries of 101.2-103.5% and a relative standard deviation (RSD) of 1.2-2.4%.

A novel symmetrical imidazole-containing framework as a fluorescence sensor for selectively detecting silver ions.

In this study, a novel and highly efficient "turn-off" fluorescence imidazole-based sensor (BIB) with a symmetric structure was synthesized by a four-step reaction, from o-phenylenediamine, 6-bromo-2-pyridinecarboxaldehyde, and 1-bromohexane. The sensing mechanism was confirmed via fluorescence titration, HRMS, and 1HNMR techiniques. The results showed that the binding ratio of BIB and Ag+ was 1 : 1 in a DMF-HEPES (pH 7.4) solution (9 : 1, v/v). The fluorescence response of BIB exhibited a good linear response within the Ag+ concentration ranging from 2 × 10-7 to 8 × 10-6 mol L-1, and the limit of detection was calculated to be 4.591 × 10-8 mol L-1. BIB was successfully applied to the detection of Ag+ in water samples with recoveries of 97.25-109.50% and relative standard deviations (RSD) of 1.14-2.45%. In addition, BIB can successfully be applied to qualitatively and quantitatively identify Ag+ in water by test paper strips of BIB, which is fast and convenient. This provides a possible potential for the rapid monitoring of metal ions by sensors in environmental research.

Promising Anodic Electrochemiluminescence of Nontoxic Core/Shell CuInS2/ZnS Nanocrystals in Aqueous Medium and Its Biosensing Potential.

Copper indium sulfide (CuInS2, CIS) nanocrystals (NCs) are a promising solution to the toxic issue of Cd- and Pb-based NCs. Herein, electrochemiluminescence (ECL) of CIS NCs in aqueous medium is investigated for the first time with l-glutathione and sodium citrate-stabilized water-soluble CIS/ZnS NCs as model. The CIS/ZnS NCs can be oxidized to hole-injected states via electrochemically injecting holes into valence band at 0.55 and 0.94 V (vs Ag/AgCl), respectively. The hole-injected state around 0.94 V can bring out efficient oxidative-reduction ECL with a similar color to Ru(bpy)32+ in the presence of tri- n-propylamine (TPrA) and enable CIS/ZnS NCs promising ECL tags with l-glutathione as linker for labeling. The ECL of CIS/ZnS NCs/TPrA can be utilized to determine vascular endothelial growth factor (VEGF) from 0.10 to 1000 pM with the limit of detection at 0.050 pM (S/N = 3). Although the hole-injected state around 0.55 V is generated ahead of oxidation of TPrA and fails to bring out coreactant ECL, annihilation ECL proves that both hole-injected states generated, at 0.55 and 0.94 V, can be involved in electrochemical redox-induced radiative charge transfer by directly stepping CIS/ZnS NCs from electron-injecting potential to hole-injecting potential. CIS/ZnS NCs are promising nontoxic electrochemiluminophores with lowered ECL triggering potential around 0.55 V for less electrochemical interference upon the development of coreactant.

Adjustable Electrochemiluminescence from Highly Passivated CdTe/CdS Nanocrystals by Simple Surface Decoration with Counterions.

Tunable optics and electronics of II-VI nanocrystals (NCs) is mainly achieved by using the traditional size-dependent strategy. Herein, we show that the triggering energy (potential), intensity, and even reductive-oxidation electrochemiluminescence (ECL) spectra of highly passivated CdTe/CdS NCs of the same size can be adjusted by simply decorating the NCs with counterions, which proves that surface chemistry can bring about varied electrostatic interactions between the surface vacancies and electrochemically injected carriers for adjustable electrochemical redox induced radiative charge transfer. Potential-resolved ECL demonstrates that increasing the surface sulfur vacancies and decreasing the surface cadmium vacancies can clearly enhance the ECL intensity and lower ECL triggering energy. All the traditional accumulated ECL spectra of CdTe/CdS NCs with various surface vacancies are close to the photoluminescence spectrum of monodisperse NCs without surface treatment, indicating the ECL spectra are mainly dominated by the CdTe core, whereas the slightly redshifted ECL spectrum of CdTe/CdS NCs with excessive cadmium vacancies indicates that the electrostatic repulsion between surface cadmium vacancies and electrons partially consumes the energy of the electrochemically injected electrons. Interestingly, spooling ECL spectra of CdTe/CdS NCs with varied surface vacancies are slightly blueshifted with negatively scanned potential, indicating electrons can be injected into conduction band of higher energy levels in a potential modulated way.

Synthesis of triangular silver nanoprisms and spectroscopic analysis on the interaction with bovine serum albumin.

The interactions of triangular silver nanoprisms (TAgNPrs) with bovine serum albumin (BSA) were investigated using multiple spectroscopic techniques. A noticeable absorbance increase was noted in the peak ranges of 250 to 300 nm for BSA, and the intensity increased with the increasing concentration of TAgNPrs. Furthermore, a slight blue shift of the surface plasmon resonance band of TAgNPrs occurred, indicating that the protein absorbed on the TAgNPrs surface to form a bio-nano interface. Analysis of fluorescence quenching data using the Stern-Volmer method revealed that static quenching takes place with complex formation. Evaluation of thermodynamic parameter ΔG θ for the binding processes indicated that the binding reaction was exothermic. Furthermore, the values of binding constant K revealed that the size of nanoparticles can affect the binding degree. The order of binding affinity is 43.7 nm > 36.2 nm > 25.1 nm. The competitive experiments of site markers (flufenamic acid and phenylbutazone) suggested that the binding site of TAgNPrs on BSA was located in the region of subdomain IIIA (Sudlow site II). In addition, the conformational changes of BSA by TAgNPrs were analyzed by using synchronous fluorescence spectra, circular dichroism, and three-dimensional fluorescence spectra. Graphical abstract The protein absorbed on the TAgNPrs surface to form a nanoparticle-protein corona.

Electrochemistry and electrocatalysis of myoglobin immobilized in sulfonated graphene oxide and Nafion films.

In this study, sulfonated graphene oxide (SGO) was synthesized and characterized by Fourier transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS). It was used to make Mb-SGO-Nafion composite films by coating myoglobin (Mb) on the glassy carbon electrodes (GCE). Positions of the Soret absorption bands suggested that Mb retained its native conformation in the films. Mb-SGO-Nafion film modified electrode showed a pair of well-defined and nearly reversible cyclic voltammetry peaks at around -0.39 V versus saturated calomel electrode (SCE) in pH 7.0 buffers, characteristic of heme Fe(III)/Fe(II) redox couples. Electrochemical parameters such as electron transfer rate constant (ks) and formal potential (E(o')) were estimated by fitting the data of square-wave voltammetry with nonlinear regression analysis. Experimental data demonstrated that the electron transfer between Mb and electrode was greatly facilitated and showed good electrocatalytic properties toward various substrates, such as H2O2 and NaNO2, with significant lowering of reduction overpotential.

Fabrication and application of a 3D-rGO electrochemical sensor for SO2 detection in ionic liquids.

Sulfur dioxide (SO2) is a common atmospheric pollutant. Currently, most of the detection methods are based on chemical reactions and optical absorption principles. However, these methods have some limitations in their detection range and accuracy, especially in complex environments. In this work, sulfur dioxide was absorbed by an ionic liquid, and a new electrochemical sensor based on 3D-rGO/CB was developed for electrochemical detection. Specifically, carbon black (CB) nanoparticles were incorporated with graphene oxide (GO) sheets using spray drying technology to form a highly porous and interconnected 3D-GO/CB microsphere structure. Then, the 3D-rGO/CB/GCE electrochemical sensor was fabricated by electrochemical reduction of the composite material onto a glassy carbon electrode (GCE) surface and used to detect sulfur dioxide in ionic liquids. The results demonstrated that the sensor had excellent conductivity and mass transfer preferable performance catalytic activity for SO2 in ionic liquids, and a linear detection range of 100-3500 ppm. Besides, the detection limit was 52.3 ppm (S/N = 3). Moreover, it had high selectivity, stability, and repeatability. This work significantly contributed to the development of advanced electrochemical sensors with improved performance for detecting SO2 in ionic liquids and has a potential application prospect in the field of electrochemical gas detection.

Fabrication of nanofluidic biochips with nanochannels for applications in DNA analysis.

With the development of nanotechnology, great progress has been made in the fabrication of nanochannels. Nanofluidic biochips based on nanochannel structures allow biomolecule transport, bioseparation, and biodetection. The domain applications of nanofluidic biochips with nanochannels are DNA stretching and separation. In this Review, the general fabrication methods for nanochannel structures and their applications in DNA analysis are discussed. These representative fabrication approaches include conventional photolithography, interference lithography, electron-beam lithography, nanoimprint lithography and polymer nanochannels. Other nanofabrication methods used to fabricate unique nanochannels, including sub-10-nm nanochannels, single nanochannels, and vertical nanochannels, are also mentioned. These nanofabrication methods provide an effective way to form nanoscale channel structures for nanofluidics and biosensor devices for DNA separation, detection, and sensing. The broad applications of nanochannels and future perspectives are also discussed.

The Reinforced Electromagnetic Interference Shielding Performance of Thermal Reduced Graphene Oxide Films via Polyimide Pyrolysis.

In this work, thin reduced graphene oxide (GO) composite films were fabricated for electromagnetic interference (EMI) shielding application. High solid content GO slurry (7 wt %) was obtained by dispersing GO clay in polymer solution under high-speed mechanical stirring. A composite film with varied thickness (10-150 µm) could be fabricated in pilot scale. After an optimized thermal annealing procedure, the final product showed good conductivity, which reached 500 S·cm-1. The thin sample (thickness < 0.1 mm) containing 10% polymer showed an enhanced EMI shielding performance of 55-65 dB. The outstanding EMI shielding efficiency as well as good suppleness and industrialized potential of thermal reduced graphene oxide polymer composite films could make a progress on their application in flexible devices as an EMI shielding material.

Imidazole Compounds: Synthesis, Characterization and Application in Optical Analysis.

Imidazole is a five-membered heterocyclic ring containing three carbon atoms, two nitrogen atoms, and two double bonds. Among two nitrogen atoms, one of which carries with a hydrogen atom is a pyrrole-type nitrogen atom, another is a pyridine type nitrogen atom. Hence, the imidazole ring belongs to the π electron-rich aromatic ring and can accept strong suction to the electronic group. Moreover, the nitrogen atom of the imidazole ring is coordinated with metal ions to form metal-organic frameworks. In recent years, because of imidazole compounds' unique optical properties, their applications have attracted more and more attention in optical analysis. Thus, this review has summarized the synthesis, characterization, and application with emphasis on the research progress of imidazole compounds in optical analysis, including fluorescence probe, colorimetric probe, electrochemiluminescence sensor, fiber optical sensor, surface plasmon resonance, etc. This paper will suggest the direction for the development of imidazole-containing sensors with high sensitivity and selectivity.

Large-scale preparation of graphene oxide film and its application for electromagnetic interference shielding.

In this work, a large-scale preparation of graphene oxide (GO) film is reported, and the structure and the compositional variation was studied after thermal annealing. The electromagnetic interference (EMI) shielding performance of thermally reduced GO films was also investigated. Commercial GO clay was well dispersed by high-speed shearing and formed a stable slurry with a high solid content in water (5%), and this was chosen rather than organic solvent due to its optimal performance in coating procedures and film quality. The optimized thermal annealing procedure resulted in a significant enhancement of electric conductivity and EMI shielding efficiency, which reached 500 S cm-1 and 32-42 dB with the thickness under 0.1 mm. The excellent EMI shielding efficiency of thermally reduced GO film, as well as the easily amplified pilot manufactoring procedure adaptive to commercial equipment, produce graphene for universal EMI shielding materials.

MXene-based enzymatic sensor for highly sensitive and selective detection of cholesterol.

In this work, the synthesized MXene (Ti3C2Tx) exhibited large specific area, biocompatibility, excellent electronic conductivity, and good dispersion in aqueous phase. The Chit/ChOx/Ti3C2Tx nanocomposite was prepared through the continuous self-assembled process. Its structure is characterized by scanning electron microscopy (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and differential pulse voltammetry (DPV). Moreover, the biosensor for cholesterol detection was fabricated via a one-step dip-coating method. Chit andTi3C2Tx act as a support matrix to immobilize ChOx enzyme, and also play a role in increasing the electrical conductivity. Meanwhile, the addition of redox mediator (Fe(CN)63-/4-) facilitates the electron transport from the analyte to the modified electrode in the oxidation of cholesterol. The DPV response exhibited an increase in current with increasing cholesterol concentration. Under the optimum conditions, the DPV response of the biosensor indicated a good linear relationship with the concentration of cholesterol ranging from 0.3 to 4.5 nM with a low detection limit of 0.11 nM, and a high sensitivity of 132.66 µA nM-1 cm-2. In addition, with favorable selectivity and stability, the biosensor has been used to detect cholesterol in real samples and the results demonstrate that the biosensor has excellent practicability.

Fe-cation Doping in NiSe2 as an Effective Method of Electronic Structure Modulation towards High-Performance Lithium-Sulfur Batteries.

The commercialization of Li-S batteries is hindered by the shuttling of lithium polysulfides (LiPSs), the sluggish sulfur redox kinetics as well as the low sulfur utilization during charge/discharge processes. Herein, a free-standing cathode material was developed, based on Fe-doped NiSe2 nanosheets grown on activated carbon cloth substrates (Fe-NiSe2 /ACC) for high-performance Li-S batteries. Fe-doping in NiSe2 plays a key role in the electronic structure modulation of NiSe2 , enabling improved charge transfer with the adsorbed LiPSs molecules, stronger interactions with the active sulfur species and higher electrical conductivity. Effective promotion of the sulfur redox kinetics and enhanced sulfur utilization were achieved under high areal sulfur loadings. The stronger interactions with LiPSs together with the unique 3D structure of Fe-NiSe2 /ACC also induced the transformation of Li2 S2 /Li2 S growth from conventional 2D films to 3D particles, significantly eliminating the barriers of solid nucleation and growth during the phase transition of liquid LiPSs to solid Li2 S2 /Li2 S. With a high sulfur loading of 9.9 mg cm-2 , the Fe-NiSe2 /ACC cathode enabled a high area capacity of 9.14 mAh cm-2 with a low average decay of 0.11 % per cycle over 200 cycles at 0.1 C.

Synthesis of membrane-type graphene oxide immobilized manganese dioxide adsorbent and its adsorption behavior for lithium ion.

Recently, there has been an urgent need to develop new materials and technologies for extracting lithium ions. Herein, the membrane-type adsorbent of manganese dioxide (MnO2) is prepared by a vacuum filtration method using graphene oxide (GO) as a binder and amino-ß-cyclodextrin (amino-ß-CD) as an adjuvant. The results of thermogravimetric analysis show that MnO2 is successfully immobilized on GO layers with a content of about 24 wt%, which enabled rapid adsorb lithium ions from the ionic solution. In addition, the permeation experiment shows the membrane has specific selectivity for lithium ion transport and adsorption, which is manifested in the selectivity ratios of K+/Li+, Na+/Li+ and K+/Na+ to 2.5, 3.2 and 0.8, respectively. Adsorption experiments show that GO-ß-CD/MnO2 membrane has a high adsorption capacity for lithium ions (37.5 mg g-1). The adsorption kinetic curve indicates that the lithium adsorption process is controlled by the chemical adsorption mechanism. In the enrichment experiment, the concentration of lithium ions from seawater can be enriched to 1.2 mg L-1 after 100 cycles. The results suggest that the developed GO-ß-CD/MnO2 membrane could effectively extract lithium ions from seawater.

Facile synthesis of an aggregation-induced emission (AIE) active imidazoles for sensitive detection of trifluralin.

A novel imidazoles fluorescent probe (2) was synthesized from vanillin, o-phenylenediamine, and N,N-diphenylcarbamyl chloride. Its structure was characterized by fluorescence spectra, UV-Vis spectra, 1H NMR, 13C NMR, and high-resolution mass spectrometry (HRMS). Moreover, its aggregation-induced emission (AIE) feature was investigated in THF/MeOH solution. Furthermore, the fluorescence quenching experimental results suggest that compound 2 is the potential fluorescent probe of small organic molecules showing high selectivity and sensitivity for nitroaromatic compounds. In addition, the probe could be applied in the determination of trifluralin with fast response and stability. The fluorescence response of the probe exhibited a good linear correlation with the concentration of trifluralin ranging from 10 to 100 µM, and the limit of detection (LOD) was as low as 5.066 µM. Finally, the probe was successfully utilized to determine the amount of trifluralin in real samples, and the recoveries were 91.1% to 111.2%, indicating the applicability and reliability of the probe.

l-Cysteine-Modified Graphene Oxide-Based Membrane for Chiral Selective Separation.

A novel chiral separation membrane was fabricated by assembling l-cysteine (l-Cys)-modified graphene oxide sheets. l-Cys modification leads to an enantiomer separation membrane with an accessible interlayer spacing of 8 Å, which allows high solvent permeability. In the racemate separation experiments under isobaric conditions, the enantiomeric excess (ee) values of alanine (Ala), threonine (Thr), tyrosine (Tyr), and penicillamine (Pen) racemates in the permeation solution were 43.60, 44.11, 27.43, and 46.44%, respectively. In the racemate separation experiments under negative pressure, the separation performances of Ala, Thr, and Tyr were still maintained, and the enantiomeric excess (ee) values of the filtrate after separation were 56.80, 54.57, and 32.34%, respectively. These results indicate that the as-prepared GO-Cys membrane has a great practical value in the field of enantiomer separation.

Direct chemical vapor deposition of graphene on plasma-etched quartz glass combined with Pt nanoparticles as an independent transparent electrode for non-enzymatic sensing of hydrogen peroxide.

In this work, chemical vapor deposition (CVD) method-grown graphene on plasma-etched quartz glass supported platinum nanoparticles (PtNPs/eQG) was constructed as an independent transparent electrode for non-enzymatic hydrogen peroxide (H2O2) detection. Graphene grown on quartz glass by the CVD method can effectively reduce the wrinkles and pollution caused by traditional transfer methods. The addition of the CF4 plasma-etched process accelerates the growth rate of graphene on quartz glass. The platinum nanoparticles (PtNPs) prepared by in situ sputtering have favorable dispersibility and maximize exposed active catalytic sites on graphene, providing performance advantages in the application of H2O2 detection. The resulting sensor's detection limit (3.3 nM, S/N = 3), detection linear range (10 nM to 80 µM) and response time (less than 2 s) were significantly superior to other graphene supported PtNPs materials in sensing of H2O2. In addition, the material preparation method was related to the non-transfer CVD method and in situ sputtering technology, allowing for the creation of independent electrodes without additional electrode modification processes. This primitive material preparation and electrode assembly process were promoted for the application and development of practical H2O2 sensors.

Facile synthesis of wavy carbon nanowires via activation-enabled reconstruction and their applications towards nanoparticles separation and catalysis.

We report a facile synthesis of wavy carbon nanowires (WCNWs) derived from polyurethane via KOH activation. The success of this synthesis relies on a carefully designed activation procedure, which involved one pre-activation stage to form suitable precursor and one high-temperature activation stage to allow directional carbon reconstruction. In particular, PU was initially mixed with KOH and thermally treated sequentially at 400 °C and 800 °C for 1 hour, respectively. The resultant products exhibit high purity in the shape of wavy wire, together with a uniform diameter of 51 ± 5.2 nm and the length in the range of 2-8 µm. Systematic studies have been conducted to investigate the effect of reaction parameters in two activation stages on the morphology and structure of final products. It is worth noting that the as-prepared WCNWs could find promising use in the field of both nanoparticle separation and catalysis. For example, they exhibit outstanding separation abilities towards Au nanospheres with different sizes and enhanced catalytic performance when serving as the catalyst support for Pd towards ethanol oxidation reaction. Particularly, the peak current density of Pd/WCNWs catalysts can reach 2126 mA mgPd -1 and the value of its electrochemical active surface area is 60.5 m2 gPd -1.

Solid-Solution Anion-Enhanced Electrochemical Performances of Metal Sulfides/Selenides for Sodium-Ion Capacitors: The Case of FeS2- xSe x.

Transition-metal sulfides/selenides are explored as advanced electrode materials for nonaqueous sodium-ion capacitors, using FeS2- xSe x as an example. A solid solution of S/Se in FeS2- xSe x allows it to combine the high capacity of FeS2 and the good diffusion kinetics of FeSe2 together, thereby exhibiting excellent cycle stability (∼220 mA h g-1 after 6000 cycles at 2 A g-1) and superior rate capability (∼210 mA h g-1 at 40 A g-1) within 0.8-3.0 V. These results are much better than those of FeS2 and FeSe2, confirming the advantages of S/Se solid solution, as supported by EIS spectra, DFT calculations, and electronic conductivity. As FeS2- xSe x is paired with the activated carbon (AC) as Na-ion capacitors, this device is also better than sodium-ion batteries of FeS2- xSe x//Na3V2(PO4)3 and sodium-ion capacitors of metal oxides//AC, particularly at high rates. These results open a new door for the applications of sulfides/selenides in another device of electrochemical energy storage.