Non-enzymatic electrochemical impedance sensor for selective detection of electro-inactive organophosphate pesticides using Zr-MOF/ZrO2/MWCNT ternary composite.

The existence of multiple pesticide residues in fruits and vegetables constitutes a direct peril to living organisms. Therefore, it is crucial to develop a low-cost screening method for determining organophosphate pesticides (OPPs) in food samples. This study describes the solvothermal synthesis of a ternary composite comprising multi-walled carbon nanotubes (MWCNT), zirconium oxide, and a zirconium-metal-organic framework (Zr-MOF). The ternary composite was characterised using XRD, FESEM, FTIR, and BET. The ternary composite provides a large surface area (1158 m2/g) compared with the pristine Zr-MOF (868 m2/g). The composite-modified glassy carbon electrode was used to determine nine pesticides, including organophosphate (malathion, dimethoate, chlorpyrifos, monocrotophos, and glyphosate) and non-organophosphate (thiophanate methyl, carbendazim, atrazine, and 2,4, D). In particular, various chemical combinations of OPPs were selected, such as S-P=S, P=S, P=O, and non-OPPs such as C=S (with sulphur), and without sulphur. The sensor results show that the sensor selectivity is high for OPPs containing both phosphorus and sulphur molecules. The low detection limit of the sensor was 2.02, 2.8, 2.5, 1.11, and 2.01 nM for malathion, chlorpyrifos, dimethoate, monocrotophos, and glyphosate, respectively. The electrode exhibited significant chemical stability (93%) after 100 cycles, good repeatability, and a long shelf life. The sensor is reliable for qualitative real-time applications.

Solid electrochemiluminescence sensor by immobilization luminol in Zn-Co-ZIF CNFs for sensitive detection of procymidone in vegetables.

A solid-state electrochemiluminescence (ECL) sensor was fabricated by immobilizing luminol, a classical luminescent reagent, on a Zn-Co-ZIF carbon fiber-modified electrode for the rapid and sensitive detection of procymidone (PCM) in vegetable samples. The sensor was created by sequentially modifying the glassy carbon electrode with Zn-Co-ZIF carbon fiber (Zn-Co-ZIF CNFs), Pt@Au NPs, and luminol. Zn-Co-ZIF CNFs, prepared through electrospinning and high-temperature pyrolysis, possessed a large specific surface area and porosity, making it suitable as carrier and electron transfer accelerator in the system. Pt@Au NPs demonstrated excellent catalytic activity, effectively enhancing the generation of active substances. The ECL signal was significantly amplified by the combination of Zn-Co-ZIF CNFs and Pt@Au NPs, which can subsequently be diminished by procymidone. The ECL intensity decreased proportionally with the addition of procymidone, displaying a linear relationship within the concentration range 1.0 × 10-13 to 1.0 × 10-6 mol L-1 (R2 = 0.993). The sensor exhibited a detection limit of 3.3 × 10-14 mol L-1 (S/N = 3) and demonstrated outstanding reproducibility and stability, making it well-suited for the detection of procymidone in vegetable samples.

Hydrothermal synthesis of iron titanate hexagonal nanoplates for electrochemical detection of nitrofurazone.

An electrochemical sensor is established using an iron titanate (FeTiO3) modified glassy carbon electrode (GCE) to detect nitrofurazone. Various microscopic and spectroscopic analysis was performed to reveal the properties of the prepared FeTiO3 hexagonal nanoplates. The FeTiO3/GCE presents enhanced electrochemical response to nitrofurazone at the peak reduction potential of - 0.471 V with a larger peak current than the bare GCE due to high electrical conductivity, enhanced specific surface area, and abundant active sites. The superior nitrofurazone detection performance includes the low limit of detection of 0.002 µM and the sensitivity of 0.551 µA µM-1 cm-2 in the linear concentration range of 0.01-162.2 µM. The reproducibility and selectivity studies of the FeTiO3/GCE show excellent results with a relative standard deviation of < 5%. The practicability of FeTiO3/GCE is confirmed by monitoring nitrofurazone in actual samples. This work demonstrates that perovskite-type FeTiO3 has great potential in real-world sample analysis, and provides a new way to develop high-performance electrochemical sensors.

Alumina inorganic molecularly imprinted polymer modified multi-walled carbon nanotubes for uric acid detection in sweat.

Alumina inorganic molecularly imprinted polymer (MIP) modified multi-walled carbon nanotubes (MWCNTs) on a glassy carbon electrode (MWCNTs-Al2O3-MIP/GCE) was firstly designed and fabricated by one-step electro deposition technique for the detection of uric acid (UA) in sweat. The UA templates were embedded within the inorganic MIP by co-deposition with Al2O3. Through the evaluation of morphology and structure by Field Emission Scanning Electron Microscope (SEM), Energy Dispersive X-ray Spectroscopy (EDS), X-ray Photoelectron Spectroscopy (XPS) and Transmission Electron Microscopy (TEM), it was verified that the specific recognition sites can be fabricated in the electrodeposited Al2O3 molecular imprinted layer. Due to the high selectivity of molecular imprinting holes, the MWCNTs-Al2O3-MIP/GCE electrode demonstrated an impressive imprinting factor of approximately 2.338 compared to the non-molecularly imprinted glassy carbon electrode (MWCNTs-Al2O3-NIP/GCE) toward uric acid detection. Moreover, it exhibited a remarkable limit of detection (LOD) of 50 nM for UA with wide detection range from 50 nM to 600 µM. The MWCNTs-Al2O3-MIP/GCE electrode also showed strong interference resistance against common substances found in sweat. These results highlight the excellent interference resistance and selectivity of MWCNTs-Al2O3-MIP/GCE sensor, positioning it as a novel sensing platform for non-invasive uric acid detection in human sweat.

Green sonochemical synthesis of ZnCo2O4 decorated with carbon nanofibers for enhanced electrochemical detection of bisphenol A in food products.

The facile sonochemical synthesis is reported of zinc cobalt oxide (ZnCo2O4) composited with carbon nanofiber (CNF). Structural, chemical, and morphological were characterized by X-ray diffraction (XRD), X-ray photoluminescent spectroscopy (XPS), field emission scanning electron microscopy (FESEM), and transmittance electron microscopy (TEM), respectively. ZnCo2O4/CNF-modified GCE was applied to the detection of bisphenol A (BPA). The modified GCE shows enhanced sensing performance towards BPA, which includes a linear range (0.2 to 120 µM L-1) alongside a low limit of detection (38.2 nM L-1), low interference, and good stability. Detection of lower concentrations of BPA enables real sample analysis in the food industries (milk, orange juice, yogurt, tap water, and baby feeding bottles). Surprisingly, the BPA was detected in milk 510 nM L-1, orange juice 340 nM L-1, yogurt 1050 nM L-1, and tap water 140 nM L-1. Moreover, an interaction mechanism between the BPA analyte and ZnCo2O4 was discussed.

Electrochemical detection of poly(3-hydroxybutyrate) production from Burkholderia glumae MA13 using a molecularly imprinted polymer-reduced graphene oxide modified electrode.

The development and application of an electrochemical sensor is reported for detection of poly(3-hydroxybutyrate) (P3HB) - a bioplastic derived from agro-industrial residues. To overcome the challenges of molecular imprinting of macromolecules such as P3HB, this study employed methanolysis reaction to break down the P3HB biopolymer chains into methyl 3-hydroxybutyrate (M3HB) monomers. Thereafter, M3HB were employed as the target molecules in the construction of molecularly imprinted sensors. The electrochemical device was then prepared by electropolymerizing a molecularly imprinted poly (indole-3-acetic acid) thin film on a glassy carbon electrode surface modified with reduced graphene oxide (GCE/rGO-MIP) in the presence of M3HB. Electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), scanning electron microscopy with field emission gun (SEM-FEG), Raman spectroscopy, attenuated total reflection Fourier-transform infrared (ATR-FTIR) and X-ray Photoelectron Spectroscopy (XPS) were employed to characterize the electrode surface. Under ideal conditions, the MIP sensor exhibited a wide linear working range of 0.1 - 10 nM and a detection limit of 0.3 pM (n = 3). The sensor showed good repeatability, selectivity, and stability over time. For the sensor application, the bioproduction of P3HB was carried out in a bioreactor containing the Burkholderia glumae MA13 strain and sugarcane byproducts as a supplementary carbon source. The analyses were validated through recovery assays, yielding recovery values between 102 and 104%. These results indicate that this MIP sensor can present advantages in the monitoring of P3HB during the bioconversion process.

Aptasensor based on gold nanostructure-decorated 2D Cu metal-organic framework nanosheets for highly sensitive and specific electrochemical lipopolysaccharide detection.

Detecting lipopolysaccharide (LPS) using electrochemical methods is significant because of their exceptional sensitivity, simplicity, and user-friendliness. Two-dimensional metal-organic framework (2D-MOF) that merges the benefits of MOF and 2D nanostructure has exhibited remarkable performance in constructing electrochemical sensors, notably surpassing traditional 3D-MOFs. In this study, Cu[tetrakis(4-carboxylphenyl)porphyrin] (Cu-TCPP) and Cu(tetrahydroxyquinone) (Cu-THQ) 2D nanosheets were synthesized and applied on a glassy carbon electrode (GCE). The 2D-MOF nanosheets, which serve as supporting layers, exhibit improved electron transfer and electronic conductivity characteristics. Subsequently, the modified electrode was subjected to electrodeposition with Au nanostructures, resulting in the formation of Au/Cu-TCPP/GCE and Au/Cu-THQ/GCE. Notably, the Au/Cu-THQ/GCE demonstrated superior electrochemical activity because of the 2D morphology, redox ligand, dense Cu sites, and improved deposition of flower-like Au nanostructure based on Cu-THQ. The electron transfer specific surface area was increased by the improved deposition of Au nanostructures, which facilitates enriched binding of LPS aptamer and significantly improved the detection performance of Apt/Au/Cu-THQ/GCE electrochemical aptasensor. The limit of detection for LPS reached 0.15 fg/mL with a linear range of 1 fg/mL - 100 pg/mL. The proposed aptasensor demonstrated the ability to detect LPS in serum samples with satisfactory accuracy, indicating significant potential for clinical diagnosis.

An intense cathodic electrochemiluminescence from carbon-nanosheets in situ grown on glassy carbon electrode and application in immunoanalysis via biometallization strategy.

An intense cathodic electrochemiluminescence (ECL) is reported from a polarized glassy carbon electrode (GCE) in peroxydisulfate solution. After the polarization in 1 M Na2SO4 at the potential of - 3.7 V for 3 s, carbon nanosheets (C-NSs) were in situ grown on the surface of the GCE. Measured in 100 mM K2S2O8 solution, the ECL intensity of the GCE/C-NSs is 112-fold that of a bare GCE. The ECL spectrum revealed that the true ECL luminophore in the GCE/C-NSs-peroxydisulfate system is O2/S2O82- which is promoted by C-NSs. When Cu2+ was electrochemically enriched and reduced to Cu(0) on the catalytic sites of C-NSs, the ECL from GCE/C-NSs/Cu in K2S2O8 solution was decreased with increasing logarithmic concentration of Cu2+ in the range from 10 pM to 1 µM, with a limit of detection (LOD) of 3 pM. An immunoanalysis method is proposed via a biometallization strategy using CuS nanoparticles as the tags and carcinoembryonic antigen (CEA) as the model analyte. After the immune recognition in the microplate, the CuS tags in the immunocomplex were dissolved and the resultant Cu2+ was electrochemically enriched and reduced on the catalytic sites of C-NSs, quenching the ECL intensity of GCE/C-NSs-O2/S2O82- system. The proposed ECL immunoanalysis method was used to quantify CEA in actual serum samples with an LOD of 1.0 fg mL-1, possessing the advantages of simple electrode modification, high sensitivity and good reproducibility.

An electrochemical biosensor for sensitive detection of live Salmonella in food via MXene amplified methylene blue signals and electrostatic immobilization of bacteriophages.

A novel bacteriophage-targeted electrochemical biosensor designed for accurate and quantitative detection of live Salmonella in food samples is presented. The biosensor is simply constructed by electrostatic immobilizing bacteriophages on MXene-nanostructured electrodes. MXene, renowned for its high surface area, biocompatibility, and conductivity, serves as an ideal platform for bacteriophage immobilization. This allows for a high-density immobilization of bacteriophage particles, achieving approximately 71 pcs µm-2. Remarkably, the bacteriophages immobilized MXene nanostructured electrodes still maintain their viability and functionality, ensuring their effectiveness in pathogen detection. Therefore, the proposed biosensor exhibited enhanced sensitivity with a low limit of detection (LOD) of 5 CFU mL-1. Notably, the biosensor shows excellent specificity in the presence of other bacteria that commonly contaminate food and can distinguish live Salmonella from a mixed population. Furthermore, it is applicable in detecting live Salmonella in food samples, which highlights its potential in food safety monitoring. This biosensor offers simplicity, convenience, and suitability for resource-limited environments, making it a promising tool for on-site monitoring of foodborne pathogenic bacteria.

An electrochemical aptasensor for zearalenone detection based on the Co3O4/MoS2/Au nanocomposites and hybrid chain reaction.

An electrochemical aptasensor was used for the fast and sensitive detection of zearalenone (ZEN) based on the combination of Co3O4/MoS2/Au nanocomposites and the hybrid chain reaction (HCR). The glassy carbon electrode was coated with Co3O4/MoS2/Au nanomaterials to immobilize the ZEN-cDNA that had been bound with ZEN-Apt by the principle of base complementary pairing. In the absence of ZEN, the HCR could not be triggered because the ZEN-cDNA could not be exposed. After ZEN was added to the surface of the electrode, a complex structure was produced on the modified electrode by the combination of ZEN and ZEN-Apt. Therefore, the ZEN-cDNA can raise the HCR to produce the long-strand dsDNA structure. Due to the formation of dsDNA, the methylene blue (MB) could be inserted into the superstructure of branched DNA and the peak currents of the MB redox signal dramatically increased. So the concentration of ZEN could be detected by the change of signal intensity. Under optimized conditions, the developed electrochemical biosensing strategy showed an outstanding linear detection range of 1.0×10-10 mol/L to 1.0×10-6 mol/L, a low detection limit (LOD) of 8.5×10-11 mol/L with desirable selectivity and stability. Therefore, the fabricated platform possessed a great application potential in fields of food safety, medical detection, and drug analysis.

An electrochemical immunosensor based on MXene-GQD/AuNPs for the detection of trace amounts of CA-125 as specific tracer of ovarian cancer.

An electrochemical immunoassay system was developed to detect CA-125 using a glassy carbon electrode (GCE) modified with MXene, graphene quantum dots (GQDs), and gold nanoparticles (AuNPs). The combined MXene-GQD/AuNPs modification displayed advantageous electrochemical properties due to the synergistic effects of MXene, GQDs, and AuNPs. The MXene-GQD composite in the modified layer provided strong mechanical properties and a large specific surface area. Furthermore, the presence of AuNPs significantly improved conductivity and facilitated the binding of anti-CA-125 on the modified GCE, thereby enhancing sensitivity. Various analytical techniques such as FE-SEM and EDS were utilized to investigate the structural and morphological characteristics as well as the elemental composition. The performance of the developed immunosensor was assessed using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), square wave voltammetry (SWV), and differential pulse voltammetry (DPV). Under optimized conditions in a working potential range of -0.2 to 0.6 V (vs. Ag/AgCl), the sensitivity, linear range (LR), limit of detection (LOD), and correlation coefficient (R2) were determined to be 315.250 µA pU.mL-1/cm2, 0.1 to 1 nU/mL, 0.075 nU/mL, and 0.9855, respectively. The detection of CA-125 in real samples was investigated using the developed immunoassay platform, demonstrating satisfactory results including excellent selectivity and reproducibility.

Ultrasensitive and specific photoelectrochemical sensor for hydrogen peroxide detection based on pillar[5]arene-functionalized Au nanoparticles and MWNTs hybrid BiOBr heterojunction.

A photoelectrochemical sensor for target detection of hydrogen peroxide was designed based on a new heterojunction nanocomposite which was sulfhydryl-borate ester-modified A1/B1-type pillar[5]arene (BP5)-functionalized Au NPs and multi-walled carbon nanotubes hybridized with bismuth bromide oxide (Au@BP5/MWNTs-BiOBr). The specific sensor was based on the direct induction of oxidation by hydrogen peroxide of the borate ester group of pillar[5]arene. Additionally, the local surface plasmon resonance (LSPR) of Au NPs enhanced visible light capture, the host-guest complexation of BP5 with H2O2 enhanced photocurrent response, the layer-by-layer stacked nanoflower structure of BiOBr provided large specific surface area with more active sites, and the conductivity of MWNTs enhanced the charge separation efficiency and significantly improves the stability of PEC. Their synthesis effect significantly increased the photocurrent signal and further enhanced the detection result. Under the optimal conditions, the linear concentration range of H2O2 detected by the Au@BP5/MWNTs-BiOBr sensor was from 1 to 60 pmol/L. The limit of detection (LOD) and the limit of quantification (LOQ) of the method were 0.333 pmol/L and 1 pmol/L, respectively, and the sensitivity was 6.471 pmol/L. Importantly, the PEC sensor has good stability, reproducibility, and interference resistance and can be used for the detection of hydrogen peroxide in real cells.

One-pot synthesis and hydrogen peroxide electrochemical sensing of 3D TiO2/MnO2 nanorods assembled microspheres.

Nanorods assembled 3D microspheres of TiO2/MnO2 were prepared via a simple one-pot hydrothermal approach. The resultant composite material exhibited remarkable electrocatalytic activity for hydrogen peroxide (H2O2) in comparison to each single component. The electrochemical sensor constructed with TiO2/MnO2 exhibited a linear relationship within the range 0.0001-5.6 mmol·L-1 for H2O2. The limit of detection (LOD) and sensitivity for H2O2 were 0.03 µmol·L-1 (S/N = 3) and 316.6 µA (mmol·L-1)-1 cm-2. Moreover, this sensor can be employed to detect trace amount of H2O2 in serum and urine samples successfully, supporting an insight and strategy for a more sensitive electrochemical sensor.

Electrochemical cytosensor utilizing tetrahedral DNA/bimetallic AuPd holothurian-shaped nanoparticles for ultrasensitive non-destructive detection of circulating tumor cells.

As a real-time fluid biopsy method, the detection of circulating tumor cells (CTCs) provides important information for the early diagnosis, precise treatment, and prognosis of cancer. However, the low density of CTCs in the peripheral blood hampers their capture and detection with high sensitivity and selectivity using currently available methods. Hence, we designed a sandwich-type electrochemical aptasensor that utilizes holothurian-shaped AuPd nanoparticles (AuPd HSs), tetrahedral DNA nanostructures (TDNs), and CuPdPt nanowire networks (NWs) interwoven with a graphdiyne (GDY) sheet for ultrasensitive non-destructive detection of MCF-7 breast cancer cells. CuPdPt NW-GDY effectively enhanced the electron transfer rate and coupled with the loaded TDNs. The TDNs could capture MCF-7 cells with precision and firmness, and the resulting composite complex was combined with AuPd HSs to form a sandwich-type structure. This novel aptasensor showed a linear range between 10 and 106 cells mL-1 and an ultralow detection limit of 7 cells mL-1. The specificity, stability, and repeatability of the measurements were successfully verified. Moreover, we used benzonase nuclease to achieve non-destructive recovery of cells for further clinical studies. According to the results, our aptasensor was more sensitive measuring the number of CTCs than other approaches because of the employment of TDNs, CuPdPt NW-GDY, and AuPd HSs. We designed a reliable sensor system for the detection of CTCs in the peripheral blood, which could serve as a new approach for cancer diagnosis at an early stage.

A molecularly imprinted electrochemical sensor MIP/Cu-MOF/rGO/AuNPs/GCE for highly sensitive detection of electroneutral organophosphorus pesticide residues.

A novel electrochemical sensor, MIP/Cu-MOF/rGO/AuNPs/GCE, was developed by depositing gold nanoparticles, coating Cu-MOF/GO on the surface of glassy carbon electrode (GCE) before electroreducing graphene oxide (GO) to rGO and covering molecularly imprinted membrane by electropolymerization for highly sensitive detection of electroneutral organophosphorus pesticide residues in agricultural product. Cyclic voltammetry, differential pulse voltametry, scanning electron microscopy, energy-dispersive spectroscopy, and atomic force microscopy were used to characterize the imprinted sensor. Several key factors such as chitosan concentration, suspension volume, pH of polymerization solution, and polymerization scanning rate during preparation of the imprinted sensor were optimized in detail. When electroneutral phosmet was used as a template, the linear range of MIP/Cu-MOF/rGO/AuNPs/GCE for detecting phosmet was 1.00 × 10-14-5.00 × 10-7 mol/L with the limit of detection of 7.20 × 10-15 mol/L at working potentials of - 0.2 to 0.6 V. The selectivity, reproducibility, and repeatability of MIP/Cu-MOF/rGO/AuNPs/GCE were all acceptable. The recoveries of this method for determining phosmet in real samples ranged from 94.2 to 106.5%. The MIP/Cu-MOF/rGO/AuNPs/GCE sensor could be applied to detect electroneutral pesticide residues in organisms and agricultural products.

Highly sensitive electrochemical quantification of carbendazim via synergistic enhancement of ring-opening metathesis polymerization and polyethyleneimine modified graphene oxide.

A novel aptamer-based sensor was developed using the signal amplification strategy of ring-opening metathesis polymerization (ROMP) and polyethyleneimine modified graphene oxide to achieve trace detection of carbendazim (CBZ). The dual identification of aptamer and antibody was used to avoid false positive results and improve the selectivity. Polyethyleneimine modified graphene oxide (GO-PEI), as a substrate material with excellent conductivity, was modified on the surface of a glassy carbon electrode (GCE) to increase the grafting amount of aptamer on the electrode surface. Moreover, a large number of cyclopentenyl ferrocene (CFc) was aggregated to form long polymer chains through ring-opening metathesis polymerization (ROMP), so as to significantly improve the detection sensitivity of the biosensor. The linear range of this sensor was 1 pg/mL-100 ng/mL with a detection limit as low as 7.80 fg/mL. The sensor exhibited excellent reproducibility and stability, and also achieved satisfactory results in actual sample detection. The design principle of such a sensor could provide innovative ideas for sensors in the detection of other types of targets.

2D/1D VSe2/MWCNT hybrid-based electrochemical sensor for carbendazim quantification of environmental, food, and biological samples.

For the first time the sensitive determination of carbendatim (CRB) is reported utilizing a well-designed sensing architecture based on vanadium diselenide-multiwalled carbon nanotube (VSMC). FTIR, XRD, FESEM, EDS, and EIS were employed to evaluate the sensor's structural integrity, and the results demonstrated the successful integration of nanomaterials, resulting in a robust and sensitive electrochemical sensor. Cyclic voltammetry (CV) and chronoamperometric (CA) investigations showed that the sensor best performed at pH 8.0 (BRB) with an excellent detection limit of 9.80 nM with a wide linear range of 0.1 to 10.0 µM. A more thermodynamically viable oxidation of CRB was observed at the VSMC/GCE, with a shift of 200 mV in peak potential towards the less positive side compared with the unmodified GCE. In addition, the sensor demonstrated facile heterogeneous electron transfer, favorable anti-fouling traits in the presence of a wide range of interferents, good stability, and reproducible analytical performance. Finally, the developed sensor was validated for real-time quantification of CRB from spiked water, food, and bio-samples, which depicted acceptable recoveries (98.6 to 101.5%) with RSD values between 0.35 and 2.23%. Further, to derive the possible sensing mechanism, the valence orbitals projected density of states (PDOS) for C, H, and N atoms of an isolated CRB molecule, VSe2 + CNT and VSe2 + CNT + CRB were calculated using density functional theory (DFT) calculations. The dominant charge transfer from the valence 2p-orbitals of the C and N atoms of CRB to CNT is responsible for the electrochemical sensing of CRB molecules.

Electrochemical detection of anti-tissue transglutaminase antibody using quantum dots-doped polypyrrole-modified electrode.

A nanohybrid-modified glassy carbon electrode based on conducting polypyrrole doped with carbon quantum dots (QDs) was developed and used for the electrochemical detection of anti-tissue transglutaminase (anti-tTG) antibodies. To improve the polypyrrole conductivity, carrier mobility, and carrier concentration, four types of carbon nanoparticles were tested. Furthermore, a polypyrrole-modified electrode doped with QDs was functionalized with a PAMAM dendrimer and transglutaminase 2 protein by cross-linking with N-hydroxysuccinimide (NHS)/N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (EDC). The steps of electrode surface modification were surveyed via electrochemical measurements (differential pulse voltammetry (DPV), impedance spectroscopy, and X-ray photoelectron spectroscopy (XPS)). The surface characteristics were observed by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and contact angle measurements. The obtained modified electrode exhibited good stability and repeatability. DPV between - 0.1 and 0.6 V (vs. Ag/AgCl 3 M KCl reference electrode) was used to evaluate the electrochemical alterations that occur after the antibody interacts with the antigen (transglutaminase 2 protein), for which the limit of detection was 0.79 U/mL. Without the use of a secondary label, (anti-tTG) antibodies may be detected at low concentrations because of these modified electrode features.

Hollow-like three-dimensional structure of methyl orange-delaminated Ti3C2 MXene nanocomposite for high-performance electrochemical sensing of tryptophan.

Tryptophan(Trp) is being explored as a potential biomarker for various diseases associated with decreased tryptophan levels; however, metabolomic methods are expensive and time-consuming and require extensive sample analysis, making them urgently needed for trace detection. To exploit the properties of Ti3C2 MXenes a rational porous methyl orange (MO)-delaminated Ti3C2 MXene was prepared via a facile mixing process for the electrocatalytic oxidation of Trp. The hollow-like 3D structure with a more open structure and the synergistic effect of MO and conductive Ti3C2 MXene enhanced its electrochemical catalytic capability toward Trp biosensing. More importantly, MO can stabilize Ti3C2 MXene nanosheets through noncovalent π-π interactions and hydrogen bonding. Compared with covalent attachment, these non-covalent interactions preserve the electronic conductivity of the Ti3C2 MXene nanosheets. Finally, the addition of MO-derived nitrogen (N) and sulfur (S) atoms to Ti3C2 MXene enhanced the electronegativity and improved its affinity for specific molecules, resulting in high-performance electrocatalytic activity. The proposed biosensor exhibited a wide linear response in concentration ranges of 0.01-0.3 µM and 0.5-120 µM, with a low detection limit of 15 nM for tryptophan detection, and high anti-interference ability in complex media of human urine and egg white matrices. The exceptional abilities of the MO/Ti3C2 nanocatalyst make it a promising electrode material for the detection of important biomolecules.

Tuning the shell thickness of N-doped interconnected hollow carbon sphere for the electrochemical sensing of antibiotic drug chloramphenicol.

N-doped hollow carbon spheres (NHCSs) with different shell thicknesses are constructed using various amounts of SiO2 precursor. An interconnected framework with diminished wall thickness ensures an efficient and continuous electron transport which helps to enhance the performance of NHCS. Improvement of the electrocatalytic performance was shown in the determination of antibiotic drug chloramphenicol (CAP) due to the unique hollow thin shell morphology, ample defect sites, accessible surface area, higher surface-to-volume ratio and an synergistic effect. Boosted electrocatalytic activity of 1.5 N-doped HCS (1.5 NHCS) was applied to detect CAP with a linear range and detection limit of 1-1150 µM and 0.098 µM (n = 3), respectively, with superior storage stability and considerable sensitivity. These results suggest that the proposed work can be successfully applied to the determination of CAP in milk and water samples.