In-situ growth of gold nanoparticles on a 3D-network consisting of a MoS2/rGO nanocomposite for simultaneous voltammetric determination of ascorbic acid, dopamine and uric acid

3D-printed MoS2/Ni electrodes with excellent electro-catalytic performance and long-term stability for dechlorination of florfenicol

Here, we report the production of 3D-printed MoS2/Ni electrodes (3D-MoS2/Ni) with long-term stability and excellent performance by the selective laser melting (SLM) technique. As a cathode, the obtained 3D-MoS2/Ni could maintain a degradation rate above 94.0% for florfenicol (FLO) when repeatedly used 50 times in water. We also found that the removal rate of FLO by 3D-MoS2/Ni was about 12 times higher than that of 3D-printed pure Ni (3D-Ni), attributed to the improved accessibility of H*. In addition, the electrochemical characterization results showed that the electrochemically active surface area of the 3D-MoS2/Ni electrode is about 3-fold higher than that of the 3D-Ni electrode while the electrical resistance is 4 times lower. Based on tert-butanol suppression, electron paramagnetic resonance and triple quadrupole mass spectrometer experiments, a "dual path" mechanism and possible degradation pathway for the dechlorination of FLO by 3D-MoS2/Ni were proposed. Furthermore, we also investigated the impacts of the cathode potential and the initial pH of the solution on the degradation of FLO. Overall, this study reveals that the SLM 3D printing technique is a promising approach for the rapid fabrication of high-stability metal electrodes, which could have broad application in the control of water contaminants in the environmental field.

Applicability of a graphene oxide nanocomposite for fabrication of an electrochemical sensor for simultaneous detection of sunset yellow and rhodamine B in food samples

Developing a sensitive portable sensor for the determination of food additives is very important. Herein, a simple and sensitive electrochemical sensor has been constructed based on a carbon paste electrode (CPE) modified with graphene oxide (GO) nanosheets for the simultaneous determination of sunset yellow (SY) and rhodamine B (RhB) in phosphate buffer solution (pH = 4). The cyclic and differential pulse voltammetry (CV and DPV) results revealed two well-resolved anodic peaks for SY and RhB with a remarkable increase in oxidation signals of these colorants. Based on this, an electrochemical method was developed for the first time for the simultaneous detection of SY and RhB. Applicability of the sensor was confirmed in various concentrations of two analytes in two linear ranges of 1-20 μM for SY and 1-30 μM for RhB with a limit of detection (LOD) of 10.0 nM and 20.0 nM, respectively. Furthermore, the proposed sensor was successfully employed for the simultaneous detection of SY and RhB in food samples with recoveries of 93.1-106.0% indicating promising potential in practical application.

Facile fabrication of screen-printed MoS2 electrodes for electrochemical sensing of dopamine

Molybdenum disulfide (MoS₂) screen-printed working electrodes were developed for dopamine (DA) electrochemical sensing. MoS₂ working electrodes were prepared from high viscosity screen-printable inks containing various concentrations and sizes of MoS₂ particles and ethylcellulose binder. Rheological properties of MoS₂ inks and their suitability for screen-printing were analyzed by viscosity curve, screen-printing simulation and oscillatory modulus. MoS₂ inks were screen-printed onto conductive FTO (Fluorine-doped Tin Oxide) substrates. Optical microscopy and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM/EDX) analysis were used to characterize the homogeneity, topography and thickness of the screen-printed MoS₂ electrodes. The electrochemical performance was assessed through differential pulse voltammetry. Results showed an extensive linear detection of dopamine from 1 µM to 300 µM (R² = 0.996, sensitivity of 5.00 × 10^-8 A μM^-1), with the best limit of detection being 246 nM. This work demonstrated the possibility of simple, low-cost and rapid preparation of high viscosity MoS₂ ink and their use to produce screen-printed FTO/MoS₂ electrodes for dopamine detection.

Two-Dimensional Material-Based Electrochemical Sensors/Biosensors for Food Safety and Biomolecular Detection

Two-dimensional materials (2DMs) exhibited great potential for applications in materials science, energy storage, environmental science, biomedicine, sensors/biosensors, and others due to their unique physical, chemical, and biological properties. In this review, we present recent advances in the fabrication of 2DM-based electrochemical sensors and biosensors for applications in food safety and biomolecular detection that are related to human health. For this aim, firstly, we introduced the bottom-up and top-down synthesis methods of various 2DMs, such as graphene, transition metal oxides, transition metal dichalcogenides, MXenes, and several other graphene-like materials, and then we demonstrated the structure and surface chemistry of these 2DMs, which play a crucial role in the functionalization of 2DMs and subsequent composition with other nanoscale building blocks such as nanoparticles, biomolecules, and polymers. Then, the 2DM-based electrochemical sensors/biosensors for the detection of nitrite, heavy metal ions, antibiotics, and pesticides in foods and drinks are introduced. Meanwhile, the 2DM-based sensors for the determination and monitoring of key small molecules that are related to diseases and human health are presented and commented on. We believe that this review will be helpful for promoting 2DMs to construct novel electronic sensors and nanodevices for food safety and health monitoring.

A Simple, Cost-Effective, and Green HPTLC Method for the Estimation of Ascorbic Acid in Solvent and Ultrasound-Assisted Extracts of Phyllanthus emblica, Capsicum annuum, and Psidium guajava

Greener analytical methodologies for the estimation of ascorbic acid (AA) are poorly reported in the literature. Furthermore, the green indexes of the literature’s analytical assays of AA estimation have not been assessed. As a consequence, the aim of this research is to invent and validate a simple, cost-effective, and green reverse-phase “high-performance thin-layer chromatography (HPTLC)” method for the estimating AA in the solvent extracts (SE) and ultrasound-assisted extracts (UAE) of Phyllanthus emblica, Psidium guajava, and Capsicum annuum. The greener mobile phase for AA estimation was a binary mixture of water and ethanol (70:30, v/v). At a wavelength of 265 nm, the detection of AA was carried out. The greener HPTLC technique was linear in the 25–1200 ng/band range. In addition, the method was simple, cost-effective, accurate, precise, robust, sensitive, and green. The amount of AA was highest in the SE and UAE of P. emblica compared to the SE and UAE of P. guajava and C. annuum. The amount of AA in the SE of P. emblica, P. guajava, and C. annuum was found to be 491.16, 168.91, and 144.30 mg/100 g, respectively. However, the amount of AA in the UAE of P. emblica, P. guajava, and C. annuum was found to be 673.02, 218.71, and 199.30 mg/100 g, respectively. Using the “analytical GREEnness (AGREE)” methodology, the greenness index for the developed method was calculated to be 0.88, showing that the developed method has an excellent green profile. When it came to extracting AA, the UAE method outperformed the SE method. These findings suggested that the developed method might be used to estimate the AA in a variety of vegetable crops, plant-based extracts, and commercial formulations. Furthermore, because of the use of greener solvent systems against the commonly utilized hazardous solvent systems for AA determination, this technique is also safe and sustainable.

Electrospun porous poly(3-hydroxybutyrate-co-4-hydroxybutyrate)/lecithin scaffold for bone tissue engineering

Bone tissue engineering has emerged as a promising restorative strategy for bone reconstruction and bone defect repair. It is challenging to establish an appropriate scaffold with an excellent porous microstructure for bone defects and thereby promote bone repair. In this study, electrospinning as a simple and efficient technology was employed to fabricate a porous poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P34HB) scaffold coated with lecithin. The morphology, phase composition, and physical properties of the electrospun P34HB/lec scaffold were characterized. Meanwhile, cellular behaviors of bone marrow mesenchymal stem cells (BMSCs), including proliferation, adhesion, migration, osteogenic differentiation, and related gene expression, were also investigated. Finally, a rat subcutaneous implant model and a calvarial defect model were used to evaluated the biocompatibility and effect of these scaffolds on bone repair, respectively. The in vitro results demonstrated that these electrospun fibers were interwoven with each other to form the porous P34HB/lec scaffold and the addition of lecithin improved the hydrophilicity of the pure P34HB scaffold, enhanced the efficiency of cell migration, and decreased inflammatory response. Furthermore, the in vivo results showed that P34HB/lec scaffold had excellent biocompatibility, improved the vascularization, and promoted the bone regeneration. All these results indicated that nanofibers of P34HB scaffolds in combination with the lecithin could exert a synergistic effect on promoting osteogenesis and regeneration of bone defects; thus, the P34HB scaffold with lecithin showed great application potential for bone tissue engineering.

A label-free amperometric immunosensor with improved electrocatalytic 3D braided AuPtCu-SWCNTs@MoS2-rGO for human growth differentiation factor-15 detection

Growth differentiation factor-15 (GDF-15) is a member of the transforming growth factor-β family. GDF-15 is overexpressed in cardiovascular diseases and has become a novel biomarker for these diseases. In this study, we fabricated a label-free electrochemical immunosensor for sensitive detection of GDF-15. Briefly, a three-dimensional braided composite of AuPtCu-SWCNTs@MoS₂-rGO (denoted A@M), which served as a label-free immunosensor platform, was obtained by wrapping single-walled carbon nanotubes (SWCNTs) with trimetallic nanoflowers (AuPtCu NFs) woven on a three-dimensional network nanostructure composed of Molybdenum disulfide (MoS₂) and reduced graphene oxide (rGO) nanosheets. This optimization improved the ability of the platform to immobilize antibodies, accelerated the reduction of hydrogen peroxide, and promoted the migration rate of electrons on the electrode surface, thereby further amplifying the electrical signal and improving the sensitivity. The constructed sensor exhibited high sensitivity over a wide linear range from 1 pg mL^-1 to 50 ng mL^-1, with a low detection limit of 0.825 pg mL^-1 for GDF-15. The fabricated label-free immunosensor exhibits satisfactory reproducibility, selectivity, and stability. The detection of actual samples was successful, enabling a broad scope of application in the early diagnosis, prognosis, and treatment of cardiovascular diseases.

The Effect of the 3D Nanoarchitecture and Ni-Promotion on the Hydrogen Evolution Reaction in MoS2 /Reduced GO Aerogel Hybrid Microspheres Produced by a Simple One-Pot Electrospraying Procedure

The transition toward renewable energy sources requires low-cost, efficient, and durable electrocatalysts for green H₂ production. Herein, an easy and highly scalable method to prepare MoS₂ nanoparticles embedded in 3D partially reduced (pr) graphene oxide (GO) aerogel microspheres (MoS₂ /prGOAMs) with controlled morphology and composition is described. Given their peculiar center-diverging mesoporous structure, which allows easy access to the active sites and optimal mass transport, and their efficient electron transfer facilitated by the intimate contact between the MoS₂ and the 3D connected highly conductive pr-GO sheets, these materials exhibit a remarkable electrocatalytic activity in the hydrogen evolution reaction (HER). Ni atoms, either as single Ni atoms or NiO aggregates are then introduced in the MoS₂ /prGOAMs hybrids, to facilitate water dissociation, which is the slowest step in alkaline HER, producing a bifunctional catalyst. After optimization, Ni-promoted MoS₂ /prGOAMs obtained at 500 °C reach a remarkable η₁₀ (overpotential at 10 mA cm^-2 ) of 160 mV in 1 m KOH and 174 mV in 0.5 m H₂ SO₄ . Moreover, after chronopotentiometry tests (15 h) at a current density of 10 mA cm^-2 , the η₁₀ value improves to 147 mV in alkaline conditions, indicating an exceptional stability.

Graphene oxide modified screen-printed electrode for highly sensitive and selective electrochemical detection of ciprofloxacin residues in milk

The monitoring of antibiotic residues in foodstuffs by using rapid detection method is essential for food safety. In this work, the electrochemical sensor was developed by modification of screen-printed carbon electrode with graphene oxide, and then the ciprofloxacin (CIP) was detected based on the complexation of CIP with Mn2+. On modified electrode, the anodic stripping peak current response of Mn2+ was prohibited in the presence of CIP, and a peak current response of the complex was occurred. Thus, the peak current response of the complexation peak was employed as the indicating signal for CIP determination, which was more sensitive than the direct electrochemical oxidation response of CIP. Parameters that affect the signal response have been investigated in method. Under the optimum conditions, the peak current of the complexation peak was linearly correlated with the CIP content in the milk sample solution at 1.0 to 8.0 μM, and the linear correlation coefficients (R2) was 0.994. The limits of detection (LOD) was 0.30 μM. Recoveries of CIP in milk sample were ranged from 81.0 to 95.4% with relative standard deviations (RSDs) below 4.6%. The method showed high selectivity and sensitive, good reproducibility, indicated that this method has potential to be applied in CIP residue analysis.

Disposable Voltammetric Sensor Modified with Block Copolymer-Dispersed Graphene for Simultaneous Determination of Dopamine and Ascorbic Acid in Ex Vivo Mouse Brain Tissue

Dopamine (DA) and ascorbic acid (AA) are two important biomarkers with similar oxidation potentials. To facilitate their simultaneous electrochemical detection, a new voltammetric sensor was developed by modifying a screen-printed carbon electrode (SPCE) with a newly synthesized block copolymer (poly(DMAEMA-b-styrene), PDbS) as a dispersant for reduced graphene oxide (rGO). The prepared PDbS–rGO and the modified SPCE were characterized using a range of physical and electrochemical techniques including Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, cyclic voltammetry, electrochemical impedance spectroscopy, and linear sweep voltammetry. Compared to the bare SPCE, the PDbS–rGO-modified SPCE (PDbS–rGO/SPCE) showed better sensitivity and peak-to-peak separation for DA and AA in mixed solutions. Under the optimum conditions, the dynamic linear ranges for DA and AA were 0.1–300 and 10–1100 µM, and the detection limits were 0.134 and 0.88 µM (S/N = 3), respectively. Furthermore, PDbS–rGO/SPCE exhibited considerably enhanced anti-interference capability, high reproducibility, and storage stability for four weeks. The practical potential of the PDbS–rGO/SPCE sensor for measuring DA and AA was demonstrated using ex vivo brain tissues from a Parkinson’s disease mouse model and the control.

A highly sensitive flow injection amperometric glucose biosensor using a gold nanoparticles/polytyramine/Prussian blue modified screen-printed carbon electrode

A novel oxidase enzyme sensor was fabricated based on the chemisorption of highly active glucose oxidase (GOx) on gold nanoparticles that were adsorbed on a polytyramine layer (AuNPs/Pty). The GOx/AuNPs/Pty assembly was coated on a Prussian blue (PB)-modified screen-printed carbon electrode (SPCE) to produce the GOx/AuNPs/Pty/PB/SPCE biosensor. The amperometric glucose biosensor response was measured at -0.10 V using a Ag pseudo-reference electrode through the reduction current of the PB mediator in a flow injection analysis system. Under optimised experimental conditions, the developed biosensor displayed linearity over the 1.0 μM-1.0 mM glucose concentration range and a limit of detection of 1.0 μM (S/N ≥ 3). A low value for the Michaelis constant of 0.21 mM indicated that the immobilised GOx had high affinity for glucose. The developed biosensor exhibited excellent operational stability over 374 injections, long-term stability over 3 weeks, good reproducibility (relative standard deviations = 1.9%-4.3%) and high selectivity. The results obtained analysing glucose in blood plasma samples were satisfactory when compared with the corresponding results recorded implementing the standard hexokinase-spectrophotometric method (P > 0.05).

Gold nanoparticles modified graphene platforms for highly sensitive electrochemical detection of vitamin C in infant food and formulae

An easy and reliable method based on a novel electroanalytical nanostructured sensor has been developed to perform quantification of vitamin C in commercial and fortified cow-milk-based formulae and foods for infants and young children. The work is motivated by the need of a reliable analytical tool to be applied in quality control laboratories for the quantitative assessment of vitamin C where its rapid and cost-effective monitoring is essential. The ad hoc designed sensor, based on disposable screen-printed carbon electrodes modified with Au nanoparticles decorated reduced graphene oxide flakes, exhibits a LOD of 0.088 mg L^-1. The low cost, easy sample preparation, fast response and high reproducibility (RSD ≈ 8%) of the proposed method highlight its suitability for usage in quality control laboratories for determining vitamin C in real complex food matrices, envisaging the application of the sensing platform in the determination of other compounds relevant in food chemistry and food manufacturing.

Electrochemical detection of ascorbic acid in artificial sweat using a flexible alginate/CuO-modified electrode

A flexible sensor is presented for electrochemical detection of ascorbic acid in sweat based on single-step modified gold microelectrodes. The modification consists of electrodeposition of alginate membrane with trapped CuO nanoparticles. The electrodes are fabricated at a thin polyimide support and the soft nature of the membrane can withstand mechanical stress beyond requirements for skin monitoring. After characterization of the membrane via optical and scanning electron microscopy and cyclic voltammetry, the oxidative properties of CuO are exploited toward ascorbic acid for amperometric measurement at micromolar levels in neutral buffer and acidic artificial sweat, at ultralow applied potential (- 5 mV vs. Au pseudo-reference electrode). Alternatively, measurement of the horizontal shift of redox peaks by cyclic voltammetry is also possible. Obtaining a limit of detection of 1.97 μM, sensitivity of 0.103 V log (μM)^-1 of peak shift, and linear range of 10-150 μM, the effect of possible interfering species present in sweat is minimized, with no observable cross-reaction, thus maintaining a high degree of selectivity despite the absence of enzymes in the fabrication scheme. With a lateral flow approach for sample delivery, repeated measurements show recovery in few seconds, with relative standard deviation of about 20%, which can serve to detect increased loss or absence of vitamin, and yet be improved in future by optimized device designs. This sensor is envisioned as a promising component of wearable devices for e.g. non-invasive monitoring of micronutrient loss through sweat, comprising features of light weight, low cost, and easy fabrication needed for such application. Graphical Abstract Schematic depiction of the cyclic voltammetry signal change as the sweat flows over the sensor surface.

Single-atom doping of MoS2 with manganese enables ultrasensitive detection of dopamine: Experimental and computational approach

Two-dimensional transition metal dichalcogenides (TMDs) emerged as a promising platform to construct sensitive biosensors. We report an ultrasensitive electrochemical dopamine sensor based on manganese-doped MoS2 synthesized via a scalable two-step approach (with Mn ~2.15 atomic %). Selective dopamine detection is achieved with a detection limit of 50 pM in buffer solution, 5 nM in 10% serum, and 50 nM in artificial sweat. Density functional theory calculations and scanning transmission electron microscopy show that two types of Mn defects are dominant: Mn on top of a Mo atom (MntopMo) and Mn substituting a Mo atom (MnMo). At low dopamine concentrations, physisorption on MnMo dominates. At higher concentrations, dopamine chemisorbs on MntopMo, which is consistent with calculations of the dopamine binding energy (2.91 eV for MntopMo versus 0.65 eV for MnMo). Our results demonstrate that metal-doped layered materials, such as TMDs, constitute an emergent platform to construct ultrasensitive and tunable biosensors.

Electrostatic repulsion strategy for high-sensitive and selective determination of dopamine in the presence of uric acid and ascorbic acid

In this work, poly(sodium 4-styrenesulfonate)-functionalized three-dimensional graphene (PFSG) composites were realized via a facile and green strategy. The nanocomposite was characterized by scanning electron microscopy, ultraviolet and visible spectroscopy, X-ray photoelectron spectroscopy, and electrochemical method. An electroanalytical sensor of dopamine (DA) with high sensitivity and selectivity was fabricated based on PFSG modified glassy carbon electrode (GCE). Under the optimum conditions, the negatively charged PFSG composites exhibit strong electrostatic attraction for DA and electrostatic repulsion to the negatively charged ascorbic acid (AA) and uric acid (UA) molecules. Such electrostatic interaction hindered the enrichment of AA and UA on the surface of PSFG/GCE, which make a higher selectivity for the DA even in the presence of 120-fold AA and UA. Owing to the enhanced electron transfer rate and the stronger surface attraction, the current signal of DA on PFSG/GCE was about 160 times enhanced compared with the bare electrode. There was a good linear relationship between the reduction peak current of DA and concentration across the range of 0.002-2.0 μmol L^-1 and 2.0-10.0 μmol L^-1 with the limit of 0.8 nmol L^-1. Further, the PFSG/GCE was applied to the detection of DA in human serum samples. This biosensor is simple, sensitive, selective and highly stable, which provided a new design strategy and a valuable tool to detect DA in complex samples.

A sensitive method to determine dopamine in the presence of uric acid based on In2O3 nanosheet arrays grown on 3D graphene

A nonenzymatic voltammetric assay for dopamine (DA) was developed based on the combination of three-dimensional graphene (3D Gr) and indium oxide nanosheet arrays (In₂O₃ NSAs). 3D Gr was prepared by chemical vapor deposition (CVD), and In₂O₃ NSAs were grown on its surface by hydrothermal synthesis. The results show that 3D Gr maintains a good porous structure (200 μm), and the pore size of In₂O₃ NSAs is 0.50 μm. Differential pulse voltammetry (DPV) is mainly used to determine the electrochemical properties of In₂O₃ NSAs/3D Gr. It possesses a sensitivity of 2.69 μA·μM^-1·cm^-2 towards DA (5-60 μM) at 0.14 V, and the detection limit (LOD) is 0.10 μM (S/N = 3). The recoveries obtained for spiked samples in the real sample detection is 105 (± 8)%. Graphical abstractSchematic representation of DA sensitive detection by growing In₂O₃ nanosheets arrays on three-dimentional graphene modified ITO.

Photoelectrochemical assay for DNA hydroxymethylation determination based on the inhibited photoactivity of black TiO2 nanosphere by ZnO

A photoelectrochemical method was proposed for DNA hydroxymethylation determination using black TiO₂ (B-TiO₂) nanosphere as photoactive material and ZnO as photoactivity inhibitor. After hydroxymethylated DNA (5hmC-DNA) was captured on the probe modified B-TiO₂/ITO electrode surface through hybridization, a glycosyl can be then transferred from uridine diphosphoglucose to 5hmC-DNA and formed a covalent structure with -CH₂OH in the presence of T4 β-glucosyltransferase (β-GT). Afterwards, based on a series of covalent reaction, amino functionalized ZnO nanoparticles are further immobilized to the surface of the electrode. Due to the capacity to expend the irradiation light and the photogenerated electron of electron donor, the modified ZnO nanoparticles can result in a decreased photocurrent. The developed method shows wide linear ranges from 0.05-200 nM for hydroxymethylated DNA and 1-220 unit·mL^-1 for T4-β-glucosyltransferase. The corresponding determination limits were 0.013 nM and 0.24 unit·mL^-1, respectively. The enzyme activity inhibited by 4-phenylimidazole was evaluated. This photoelectrochemical method shows high specificity for 5hmC-DNA (compared to 5fC, 5mC, m6A, control) and β-GT (compared to β-AGT, UGT2B7), and shows excellent stability for testing 5hmC (RSD = 2.75%). Graphical abstractSchematic representation of photoelectrochemical method for DNA hydroxymethylation and β-glucosyltransferase detection based on the glycosylation reaction of -CH₂OH in 5-hydroxymethylcytosine and the inhibition activity of ZnO to the photoactivity of black TiO₂ nanospheres.

In situ formation and immobilization of gold nanoparticles on polydimethylsiloxane (PDMS) exhibiting catalase-mimetic activity

We used needles to prepare immobilized AuNPs on the surface of PDMS in situ with catalase-mimetic activity.

A composite film prepared from titanium carbide Ti3C2Tx (MXene) and gold nanoparticles for voltammetric determination of uric acid and folic acid

In this study, a solution-processing based galvanic deposition approach is described for in-situ deposition of gold nanoparticles (AuNP) on delaminated titanium Ti₃C₂T_x nanosheets under ultrasonication. The nanocomposite (AuNP@Ti₃C₂T_x) was placed on a glassy carbon electrode (GCE) and then applied to electrochemically with label-free, and simultaneously sense uric acid (UA), and folic acid (FA) at physiological pH. The modified GCE has attractive figures of merit: (i) The working potentials for UA and AA are well separated (+0.35 V and 0.70 V vs. Ag|AgCl); (ii) wide linear responses (from 0.03-1520 μM for UA and from 0.02-3580 μM for FA; (iii) good electrochemical sensitivities for both UA and FA (0.53 and 0.494 μAμM^-1.cm^-2, respectively), and (iv) detection limits of 11.5 nM (UA) and 6.20 nM (FA). The electrode exhibited good repeatability (RSD = 4.4%), acceptable reproducibility (RSD = 4.1%), and excellent stability (91.8% over one-month storage). The method was applied to analyze spiked serum samples, and modified GCE is shown appreciable recoveries (97.1-98.8% and 96.8-98.0% for UA, and FA, respectively). Graphical abstractA photograph (top left) of colloidal suspension of gold nanoparticles (AuNPs). They were grown on the delaminated titanium carbide Ti₃C₂T_x MXene nanosheet via galvanic displacement deposition method, and their corresponding a low-resolution transmission electron microscopy micrograph (top right) of AuNP@Ti₃C₂T_x. The graphical representation of AuNP@Ti₃C₂T_x drop-casted on glassy carbon electrode (GCE) (bottom left), and their voltammetric measurement were applied in the presence of both uric acid and folic acid with increasing the concentration of both analytes (bottom right).

A review on recent advancements in electrochemical biosensing using carbonaceous nanomaterials

This review, with 201 references, describes the recent advancement in the application of carbonaceous nanomaterials as highly conductive platforms in electrochemical biosensing. The electrochemical biosensing is described in introduction by classifying biosensors into catalytic-based and affinity-based biosensors and statistically demonstrates the most recent published works in each category. The introduction is followed by sections on electrochemical biosensors configurations and common carbonaceous nanomaterials applied in electrochemical biosensing, including graphene and its derivatives, carbon nanotubes, mesoporous carbon, carbon nanofibers and carbon nanospheres. In the following sections, carbonaceous catalytic-based and affinity-based biosensors are discussed in detail. In the category of catalytic-based biosensors, a comparison between enzymatic biosensors and non-enzymatic electrochemical sensors is carried out. Regarding the affinity-based biosensors, scholarly articles related to biological elements such as antibodies, deoxyribonucleic acids (DNAs) and aptamers are discussed in separate sections. The last section discusses recent advancements in carbonaceous screen-printed electrodes as a growing field in electrochemical biosensing. Tables are presented that give an overview on the diversity of analytes, type of materials and the sensors performance. Ultimately, general considerations, challenges and future perspectives in this field of science are discussed. Recent findings suggest that interests towards 2D nanostructured electrodes based on graphene and its derivatives are still growing in the field of electrochemical biosensing. That is because of their exceptional electrical conductivity, active surface area and more convenient production methods compared to carbon nanotubes. Graphical abstract Schematic representation of carbonaceous nanomaterials used in electrochemical biosensing. The content is classified into non-enzymatic sensors and affinity/ catalytic biosensors. Recent publications are tabulated and compared, considering materials, target, limit of detection and linear range of detection.

In-situ graft-crosslinked gold nanoparticles with high-density surface defects and coated with a polytaurine membrane for the voltammetric determination of dopamine

Well-dispersed and graft-crosslinked gold nanoparticles (AuNPs) were synthesized by the reduction of tetrachloroaurate with hydrazine at room temperature. The AuNPs possess a high density of surface defects which is due to grafting of n-octanoic acid to polyvinylpyrrolidone. The physical and chemical properties of the resulting AuNPs were characterized by UV-vis, XRD, TEM/HRTEM, SAED, and XPS, respectively. The modified AuNPs were placed on a glassy carbon electrode (GCE) in an electropolymerized taurine layer to obtain a sensitive, selective, stable and rapid electrochemical dopamine sensor. The peak current, typically measured at 0.17 V (vs. SCE), increases linearly in the 1.0 to 120 μM dopamine concentration range, and the limit of detection (at S/N = 3) is 0.16 μM with a sensitivity of 2.94 μA·μM^-1·cm^-2. The sensor was successfully applied to the determination of dopamine in injections and spiked serum samples. The recoveries from spiked serum samples range from 97.5 to 102.4%, with RSDs ranging between 2.8 and 3.4%. Graphical abstract Schematic representation of a glassy carbon electrode modified with in-situ graft-crosslinked gold nanoparticles combined with an electropolymerized polytaurine membrane. The sensor exhibits excellent features towards dopamine determination.

Fabrication of Au Nanoparticle-Decorated MoS2 Nanoslices as Efficient Electrocatalysts for Electrochemical Detection of Dopamine

Herein, MoS2 nanoslices were simply prepared by using ultrasonic treatment, and were further decorated with Au nanoparticles (AuNPs) through an electrodeposition process to obtain the MoS2/Au nanocomposites. The obtained nanocomposites display synergetic electrocatalytic effect for the oxidation of dopamine due to the large surface area and two-dimensional structure of the MoS2 nanoslices, combining with the high catalytic activity and good conductivity of AuNPs. An electrochemical sensor was constructed based on MoS2/Au-modified carbon paste electrode, for sensitive and quantitative determination of dopamine. The prepared electrochemical sensor proves excellent analytical performances: very high sensitivity, wide linear ranges (0.5–300 μM), and low detection limit (76 nM). Moreover, the dopamine sensor also displays high selectivity, good reproducibility and stability, and can be used in real sample analysis. The method of fabricating high-efficiency electrocatalysts and electrochemical sensors proposed in this study provides a good reference for developing more functionalized nanocomposites and for extending practical applications.

Targeted and effective glioblastoma therapy via aptamer-modified tetrahedral framework nucleic acid-paclitaxel nanoconjugates that can pass the blood brain barrier

Targeted DNA nanoparticles have been identified as one of the most promising nanocarriers in anti-glioma drug delivery. We established a multifunctional nanosystem for targeted glioma therapy. Tetrahedral framework nucleic acid (tFNA), entering U87MG cells and bEnd.3 cells, was chosen to deliver two aptamers, GMT8 and Gint4.T, and paclitaxel. GMT8 and Gint4.T, which specifically bind with U87MG cells and with PDGFRβ, were linked with tFNA, to form Gint4.T-tFNA-GMT8 (GTG). GTG was efficiently internalized by U87MG and bEnd.3 cells and penetrated an in-vitro blood-brain-barrier model. GTG loaded with paclitaxel (GPC) had potentiated anti-glioma efficacy. It inhibited the proliferation, migration, and invasion of U87MG cells, and enhanced apoptosis induction in these cells. The expression of apoptosis-related proteins was significantly changed after treatment with GPC, confirming apoptosis induction. Our study demonstrated that the combination of GTG and paclitaxel has great potential for glioma treatment and tFNA shows great promise for use in drug delivery.

Copper Nanowires Modified with Graphene Oxide Nanosheets for Simultaneous Voltammetric Determination of Ascorbic Acid, Dopamine and Acetaminophen

Copper nanowires (Cu NWs) were modified with graphene oxide (GO) nanosheets to obtain a sensor for simultaneous voltammetric determination of ascorbic acid (AA), dopamine (DA) and acetaminophen (AC). The nanocomposite was obtained via sonication, and its structures were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS). The electrochemical oxidation activity of the materials (placed on a glassy carbon electrode) was studied by cyclic voltammetry and differential pulse voltammetry. Due to the synergistic effect of Cu NWs and GO, the specific surface, electrochemical oxidation performance and conductivity are improved when compared to each individual component. The peaks for AA (-0.08 V), DA (+0.16 V), and AC (+0.38 V) are well separated. The sensor has wide linear ranges which are from 1-60 μM, 1-100 μM, and 1-100 μM for AA, DA, and AC, respectively, when operated in the differential pulse voltammetric mode. The detection limits are 50, 410 and 40 nM, respectively. Potential interferences by uric acid (20 μM), glucose (10 mM), NaCl (1 mM), and KCl (1 mM) were tested for AA (1 μΜ), DA (1 μΜ), and AC (1 μΜ) and were found to be insignificant. The method was successfully applied to the quantification of AA, DA, and AC in spiked serum samples.

Tetrahedral Framework Nucleic Acids Promote Corneal Epithelial Wound Healing in Vitro and in Vivo

Poor post-traumatic wound healing can affect the normal function of damaged tissues and organs. For example, poor healing of corneal epithelial injuries may lead to permanent visual impairment. It is of great importance to find a therapeutic way to promote wound closure. Tetrahedral framework nucleic acids (tFNAs) are new promising nanomaterials, which can affect the biological behavior of cells. In the experiment, corneal wound healing is used as an example to explore the effect of tFNAs on wound healing. Results show that the proliferation and migration of human corneal epithelial cells are enhanced by exposure to tFNAs in vitro, possibly relevant to the activation of P38 and ERK1/2 signaling pathway. An animal model of corneal alkali burn is established to further identify the facilitation effect of tFNAs on corneal wound healing in vivo. Clinical evaluations and histological analyses show that tFNAs can improve the corneal transparency and accelerate the re-epithelialization of wounds. Both in vitro and in vivo experiments show that tFNAs can play a positive role in corneal epithelial wound healing.