Superlattice stacking by hybridizing layered double hydroxide nanosheets with layers of reduced graphene oxide for electrochemical simultaneous determination of dopamine, uric acid and ascorbic acid

Disposable paper electrodes for detection of changes in dopamine concentrations in rat brain homogenates

Dopamine, the main catecholamine neurotransmitter plays an important role in renal, cardiovascular, central nervous systems, and pathophysiological processes. The abnormal dopamine levels can result in neurological disorders such as Parkinson's, Alzheimer's, schizophrenia, acute anxiety, neuroblastoma and also contribute to cognitive dysfunctions. Given the widespread importance of dopamine concentration levels, it is imperative to develop sensors that are able to monitor dopamine. Herein, we have developed pre-anodized disposable paper electrode modified with 1-pyrenebutyric acid, for the selective and sensitive determination of dopamine. The sensor was characterized with Fourier transform infrared spectroscopy, Energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and electrochemical techniques for addressing the robust formation and electrochemical activity. The modified electrode exhibited excellent electrocatalytic activity towards dopamine without the common interference from ascorbic acid. The calibration plot for the dopamine sensor resulted linear range from 0.003 μM to 0.5 μM with a detection limit of 0.11 nM. The sensor's potential utility was tested by monitoring dopamine concentration changes in rat brain homogenates when subjected to neurotoxicity. The developed sensor was validated with gold-standard UV-Vis spectroscopy studies and computational studies were performed to understand the interaction between 1-pyrenebutyric acid and dopamine.

Co4+ in porous ZIF-67-derives intercalating-bridging adsorption of 2-reaction sites for simultaneous 2-electron transfer toward sensitive detection of uric acid

Metal-organic frameworks (MOFs) have been used to detect uric acid (UA), but still very challenging to achieve a low detection limit due to the low inferior conductivity of MOFs. Herein, three different N-doped ZIF-67-derived carbons were synthesized for the first time by one-step co-pyrolysis of 2-methylimidazole with cobalt nitrate (CN), cobalt acetate (CA) or cobalt chloride (CC) toward UA sensing. Afterwards, the cobalt nitrate-derived Co particle (Co/CN) supported by N-doped ZIF-67-derived carbon displays extremely low detection limit and high sensitivity for UA, outperformed all reported MOFs-based UA sensors. More interestingly, it was discovered that the high valence Co4+ within the Co/CN sample produced in high-acidic environment can intercalate in the frame for a bridge adsorption between two reaction sites, which boosted simultaneous 2-electron transfer, while Co3+ only allows an end-adsorption structure for one-electron transfer being the rate determining step. Furthermore, the bridge adsorption mode of UA on Co4+ -based catalyst was also verified by theoretical DFT calculations and XPS experiment. This work holds great promise for a selective and sensitive UA sensor for practical bioscience and clinic diagnostic applications while shedding lights in fundamental research for innovative designs and developments of high-sensitive electrochemical sensors.

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.

Simultaneous determination of environmental endocrine disruptors bisphenol A and 4-nitrophenol bleached from food-contacting materials using the spin-ladder compound La2Cu2O5 modified glassy carbon electrode

Environmental endocrine-disrupting chemicals, Bisphenol A (BPA) and 4-Nitrophenol (4-NP), pose significant risks to reproductive health in both animals and humans. Here, we introduce the first utilization of the 4-leg spin ladder compound La2Cu2O5 as an electrode material for electrochemical sensor. Nanostructured La2Cu2O5 was synthesized via a straightforward Sol-Gel method and thoroughly characterized using X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, and powder X-ray diffraction. La2Cu2O5 nanoparticles modified glassy carbon electrode (GCE) exhibited a significant electrocatalytic activity towards the oxidation of BPA and 4-NP in phosphate buffer saline (pH 7.0). Square wave voltammetry studies revealed lowest detection limits of 3 nM for BPA and 2.6 nM for 4-NP over a wider concentration range of 0.01-500 μM. Notably, this study marks the first utilization of La2Cu2O5 for simultaneous electrochemical detection of BPA and 4-NP, demonstrating its potential in this field. Furthermore, the sensor exhibited good sensitivity, reproducibility, and selectivity towards BPA and 4-NP, even in the presence of similar potential organic and inorganic interferents. Additionally, the newly developed sensor enabled simultaneous quantification of BPA and 4-NP in real samples such as packaged milk, river water, and plastic bottles, achieving recovery rates above 95%. Importantly, our results underscore the leaching of BPA into water from thin and thick plastics at elevated temperatures (40 °C-80 °C), emphasizing the utility of the proposed sensor for rapid and simultaneous detection of BPA and 4-NP in environmental and food matrices.

Recent advances in biological molecule detection based on a three-dimensional graphene structure

Graphene has become an attractive material in the field of electrochemical detection owing to its unique electrical properties. Although the simple stacking structures of two-dimensional (2D) graphene sheets can provide excellent detection properties, a macroscopic three-dimensional (3D) structure needs to be constructed to enhance its functional properties. Graphene with a 3D structure has elegant functions, unlike graphene with a 2D structure. These properties include a large specific surface area, easy loading of nanomaterials with electrocatalytic and redox functions, and so on. Herein, we outline the preparation methods (self-assembly, chemical vapor deposition, templates, and 3D printing) for 3D graphene structures for obtaining excellent detection performance and applications in detecting biological molecules, bacteria, and cells. Furthermore, this review focuses on the improvement of the detection performance and enhancement of the applicability of graphene-based electrochemical sensors. We hope that this article will provide a reference for the future development of electrochemical sensors based on 3D graphene composites.

Unlocking the future of brain research: MOFs, TMOs, and MOFs/TMOs for electrochemical NTMs detection and analysis

The central nervous system relies heavily on neurotransmitters (NTMs), and NTM imbalances have been linked to a wide range of neurological conditions. Thus, the development of reliable detection techniques is essential for advancing brain studies. This review offers a comprehensive analysis of metal-organic frameworks (MOFs), transition metal oxides (TMOs), and MOFs-derived TMOs (MOFs/TMOs) as materials for electrochemical (EC) sensors targeting the detection of key NTMs, specifically dopamine (DA), epinephrine (EP), and serotonin (SR). The unique properties and diverse families of MOFs and TMOs, along with their nanostructured hybrids, are discussed in the context of EC sensing. The review also addresses the challenges in detecting NTMs and proposes a systematic approach to tackle these obstacles. Despite the vast amount of research on MOFs and TMOs-based EC sensors for DA detection, the review highlights the gaps in the literature for MOFs/TMOs-based EC sensors specifically for EP and SR detection, as well as the limited research on microneedles (MNs)-based EC sensors modified with MOFs, TMOs, and MOFs/TMOs for NTMs detection. This review serves as a foundation to encourage researchers to further explore the potential applications of MOFs, TMOs, and MOFs/TMOs-based EC sensors in the context of neurological disorders and other health conditions related to NTMs imbalances.

Electrospun cobalt-doped 2D-MoSe2/polypyrrole hybrid-based carbon nanofibers as electrochemical sensing platforms

A novel cobalt-doped two-dimensional molybdenum diselenide/polypyrrole hybrid-based carbon nanofiber (Co/MoSe2/PPy@CNF) was prepared using the hydrothermal method followed by electrospinning technique. The structural and morphological properties of the 2D-TMD@CNF-based hybrids were characterized through X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS), and transmission electron microscopy (TEM). The Co-MoSe2/PPy@CNF exhibited large surface area, porous structure, and improved active sites due to the synergistic effect of the components. The electrochemical and electrocatalytic characteristics of the 2D-TMD@CNF-modified electrodes were also investigated using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques. The Co/MoSe2/PPy@CNF electrode was used as an electrochemical sensor for simultaneous detection of ascorbic acid (AA), dopamine (DA), and uric acid (UA) and showed enhanced catalytic activity and sensitivity. Using DPV measurements, the Co/MoSe2/PPy@CNF demonstrated wide linear ranges of 30-3212 μM for AA, 1.2-536 μM for DA, and 10-1071 μM for UA with low detection limits of 6.32, 0.45, and 0.81 μM, respectively. The developed sensor with the Co/MoSe2/PPy@CNF-modified electrode was also applied to a human urine sample and gave recoveries ranging from 94.0 to 105.5% (n = 3) for AA, DA, and UA. Furthermore, the Co/MoSe2/PPy@CNF-based sensor exhibited good selectivity and reproducibility for the detection of AA, DA, and UA.

Hybridizing Ti3C2Tx Layers with Layered Double Hydroxide Nanosheets at the Molecular Level: A Smart Electrode Material for H2O2 Monitoring in Cancer Cells

Vertically stacked artificial 2D superlattice hybrids fabricated through molecular-level hybridization in a controlled fashion play a vital role in scientific and technological fields, but developing an alternate assembly of 2D atomic layers with strong electrostatic interactions could be much more challenging. In this study, we have constructed an alternately stacked self-assembled superlattice composite through integration of CuMgAl layered double hydroxide (LDH) nanosheets having positive charge with negatively charged Ti₃C₂T_x layers using well-controlled liquid-phase co-feeding protocol and electrostatic attraction and investigated its electrochemical performance in sensing early cancer biomarkers, i.e., hydrogen peroxide (H₂O₂). The molecular-level CuMgAl LDH/Ti₃C₂T_x superlattice self-assembly possesses superb conductivity and electrocatalytic properties, which are significant for obtaining a high electrochemical sensing aptitude. Electron penetration in Ti₃C₂T_x layers and rapid ion diffusion along 2D galleries have shortened the diffusion path and enhanced the charge transferring efficacy. The electrode modified with the CuMgAl LDH/Ti₃C₂T_x superlattice has demonstrated admirable electrocatalytic abilities in H₂O₂ detection with a wide linear concentration range and low real-time limit of detection (LOD) of 0.1 nM with signal/noise ratio (S/N) = 3. Practically, an electrochemical sensing podium based on the CuMgAl LDH/Ti₃C₂T_x superlattice has been effectively applied in real-time in vitro tracking of H₂O₂ effluxes excreted from different live cancer cells and normal cells after being encouraged by stimulation. The results exhibit that molecular-level heteroassembly holds great potential in electrochemical sensors to detect promising biomarkers.

Dual-modification strategy of Co(II) and g-C3N4 to CuS for efficient colorimetric determination of thioglycolic acid in daily cosmetics

A conventional colorimetric method based on CuS-catalyzed H₂O₂ is improved by a dual-modification strategy and employed for thioglycolic acid (TGA) determination. The doping of Co(II) can enhance ion exchange efficiency. Meanwhile, the modification of g-C₃N₄ can increase specific surface area and decrease unspecific aggregation. The constructed g-C₃N₄/Co-CuS nanocomposite exhibited a favorable catalytic feature. A Michaelis constant (K_m) value of 0.02 mM has been achieved, which is 1/160 of those of CuS and horseradish peroxidase (HRP). The g-C₃N₄/Co-CuS displays a rapid color response in 3 min and resulted in a stable measurable signal within 10 min. In the determination procedure, the sulfhydryl contained in TGA is capable of preventing TMB oxidation via competing the ·OH produced by catalysis and caused a color distinction that is related to the TGA amount. The distinctions of absorbance (λ_max = 652 nm) of different concentrations of TGA are recorded. Linearity is obtained in the ranges of 2.5 - 20 µM and 20 - 160 µM, and the LOD is 0.14 µM. In the real sample assays of perm agent and Qianhu lake water, the recoveries were 96.70 - 106.84% and 100.21 - 101.90%, respectively. This demonstrates that the proposed dual-modification strategy for CuS contributes to highly efficient and convenient determination of TGA in daily cosmetics and water analysis.

A signal "on-off-on"-type electrochemiluminescence aptamer sensor for detection of sulfadimethoxine based on Ru@Zn-oxalate MOF composites

An "on-off-on"-type electrochemiluminescence (ECL) aptamer sensor based on Ru@Zn-oxalate metal-organic framework (MOF) composites is constructed for sensitive detection of sulfadimethoxine (SDM). The prepared Ru@Zn-oxalate MOF composites with the three-dimensional structure provide good ECL performance for the "signal-on." The MOF structure with a large surface area enables the material to fix more Ru(bpy)₃²⁺. Moreover, the Zn-oxalate MOF with three-dimensional chromophore connectivity provides a medium which can accelerate excited-state energy transfer migration among Ru(bpy)₃²⁺ units, and greatly reduces the influence of solvent on chromophore, achieving a high-energy Ru emission efficiency. The aptamer chain modified with ferrocene at the end can hybridize with the capture chain DNA1 fixed on the surface of the modified electrode through base complementary pairing, which can significantly quench the ECL signal of Ru@Zn-oxalate MOF. SDM specifically binds to its aptamer to separate ferrocene from the electrode surface, resulting in a "signal-on" ECL signal. The use of the aptamer chain further improves the selectivity of the sensor. Thus, high-sensitivity detection of SDM specificity is realized through the specific affinity between SDM and its aptamer. This proposed ECL aptamer sensor has good analytical performance for SDM with low detection limit (27.3 fM) and wide detection range (100 fM-500 nM). The sensor also shows excellent stability, selectivity, and reproducibility, which proved its analytical performance. The relative standard deviation (RSD) of SDM detected by the sensor is between 2.39 and 5.32%, and the recovery is in the range 97.23 to 107.5%. The sensor shows satisfactory results in the analysis of actual seawater samples, which is expected to play a role in the exploration of marine environmental pollution.

In situ generated PANI promoted flexible photoelectrochemical biosensor for ochratoxin A based on GOx-stuffed DNA hydrogel as enhancer

A flexible photoelectrochemical (PEC) biosensor is proposed for the sensitive detection of ochratoxin A (OTA) based on glucose oxidase (GOx)-encapsulated target-responsive hydrogel, using Fenton reaction-mediated in situ formation of polyaniline (PANI) as signal amplified strategy. The target-responsive DNA hydrogels with high loading capacity can carry a large amount of GOx, which not only avoids laborious labeling process but also enhances the analytical performance. Upon introduction of target molecules, the hydrogel can be opened, and multiple GOx was released, thus producing lots of H₂O₂ via catalytic reduction of glucose. As a component of the Fenton reagent, H₂O₂ can react with the Fe²⁺ on the graphene oxidase-PAMAM-Fe²⁺ (GO-PAMAM-Fe²⁺) to generate Fe³⁺ and ·OH. This in turn can oxidize aniline and generate polyaniline (PANI), resulting in the enhancement of the photocurrent signal of GO-MoS₂-CdS photoelectrode. The GO-PAMAM-Fe²⁺ as the neighborhood component of GO-MoS₂-CdS-based photoactive material not only can increase the loading amount of Fe²⁺, but also can inhibit the decrease of photocurrent of GO-MoS₂-CdS by direct modification of Fe²⁺ on the photoactive material. Moreover, the high loading capacity of DNA hydrogel can efficiently promote the performance of the PEC biosensor. The PEC biosensor exhibited satisfactory analytical performance for OTA with a linear range of 0.0001-0.1 ng/mL and a low detection limit of 0.05 pg/mL. It presents recommendable specificity, stability, and practical applications. Importantly, the PEC biosensor provides a new concept for construction of PEC biosensing platform.

A Carbon Paste Electrode Modified by Bentonite and l-Cysteine for Simultaneous Determination of Ascorbic and Uric Acids: Application in Biological Fluids

A novel modification of a paste carbon electrode by Bentonite (Bent) and l-Cysteine (l-Cyst) was carried out for uric acid (UA) and ascorbic acid (AA) detection and quantification. Morphological and compositional characterization of the electrode surface were carried out using electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopic analysis (EDS). Cyclic voltammetry (CV) and square wave voltammetry (SWV) techniques were used to analyze UA and AA. The obtained sensor shows a good stability, sensibility, selectivity, and regeneration ability. Accordingly, the limit of detection (LOD) is found to be 0.031 μm and 9.6 μm for UA and AA, respectively. A good linearity in the range of 0.1 to 100 μm for UA and 10 to 1000 μm for AA was obtained. The peak-to-peak separation of UA-AA (ΔE_UA-AA ) was determined to be 330 mV. In addition, the sensor is applied successfully to monitor UA and AA in serum samples.

Ultra-sensitive detection of multiplexed heavy metal ions by MOF-derived carbon film encapsulating BiCu alloy nanoparticles in potable electrochemical sensing system

In this work, we report the development of a new type of highly active and stable Bi-based electrode material, i.e., BiCu metal-organic frames (MOF) derived carbon film (CF) encapsulating BiCu alloy nanoparticles (BiCu-ANPs) for electrochemical sensing. The integration of Bi with Cu to form BiCu-ANPs can improve their electrocatalytic activity as well as the acid resistance. Meanwhile, the carbon film that encapsulates BiCu-ANPs not only guarantees the BiCu-ANPs with high electrical conductivity and fast electrochemical kinetics but also effectively alleviates the volume change during the adsorption and desorption of heavy metal (HM) ions. Therefore, the as-obtained CF encapsulating BiCu-ANPs (BiCu-ANPs@CF) exhibits fully exposed active sites, facile charge transfer, high stability and conductivity, which gives rise to enhanced sensitivity and stability for the electrochemical detection of HM ions. When integrated into a potable electrochemical sensing system for simultaneous detection of Pb²⁺, Cd²⁺ and Zn²⁺, the BiCu-ANPs@CF modified electrode exhibits low detection limit (i.e., 0.081 ppb for Pb²⁺, 0.95 ppb for Cd²⁺, 35 ppb for Zn²⁺), wide detection range (i.e., 0.5-700 ppb for Pb²⁺, 5-900 ppb for Cd²⁺, 150-600 ppb for Zn²⁺) and good anti-interference. Finally, the system has been used for on-site detection of multiplexed HM ions in human biological liquids and environmental water with a good spiked recovery rate, which demanstrates its promise application in the future for on-site monitoring of human health and pollutants in water quality.

Magnetic RuCo aerogels with enhanced peroxidase-like activity by regulation of boron and oxygen vacancies for colorimetric biosensing applications

Metallic aerogels (MAs) are self-supported porous nanomaterials with excellent catalytic activity, which could be a promising candidate for high-performance nanozymes. The interface regulation by heteroatom and vacancies is an effective strategy for boosting the enzyme-mimicking activity. Herein, magnetic RuCo aerogels with doping of boron and oxygen vacancies were prepared by a one-pot spontaneous NaBH₄ gelation method under a low temperature. The three-dimensional network structure with high specific surface area and interlinked pores of RuCo aerogels afford abundant active sites to facilitate the interaction with substrates. Moreover, the monolithic structure avoided conventional aggregation, thus enhancing stability during catalysis. Introducing elemtal boron and oxygen vacancies adjusted the electronic structure of RuCo aerogels to achieve enhanced enzyme-like performances. It is found that the RuCo aerogel nanozyme can mimic nature peroxidase, demonstrating their viable applications in the bioassay of H₂O₂ and glucose. The constructed glucose sensor possesses acceptable sensitivity and stability with a linear range of 0.002 ~ 5 mM and a low detection limit (1.66 μM). This work provides insights into the rational design of advanced nanozymes and paves the avenue for the applications of metallic aerogels in the bioassay field. A boron-doped RuCo bimetallic aerogel with rich oxygen vacancies was prepared by a facile self-assembly method under an ice bath. The unique physical and electronic structure of RuCo aerogel results in the improvement of the intrinsic peroxidaselike activity, and thus, a sensitive and robust colorimetric glucose sensor could be developed.

The Roadmap of Graphene-Based Sensors: Electrochemical Methods for Bioanalytical Applications

Graphene (GR) has engrossed immense research attention as an emerging carbon material owing to its enthralling electrochemical (EC) and physical properties. Herein, we debate the role of GR-based nanomaterials (NMs) in refining EC sensing performance toward bioanalytes detection. Following the introduction, we briefly discuss the GR fabrication, properties, application as electrode materials, the principle of EC sensing system, and the importance of bioanalytes detection in early disease diagnosis. Along with the brief description of GR-derivatives, simulation, and doping, classification of GR-based EC sensors such as cancer biomarkers, neurotransmitters, DNA sensors, immunosensors, and various other bioanalytes detection is provided. The working mechanism of topical GR-based EC sensors, advantages, and real-time analysis of these along with details of analytical merit of figures for EC sensors are discussed. Last, we have concluded the review by providing some suggestions to overcome the existing downsides of GR-based sensors and future outlook. The advancement of electrochemistry, nanotechnology, and point-of-care (POC) devices could offer the next generation of precise, sensitive, and reliable EC sensors.

Heterostructure Engineering of 2D Superlattice Materials for Electrocatalysis

Exploring low-cost and high-efficient electrocatalyst is an exigent task in developing novel sustainable energy conversion systems, such as fuel cells and electrocatalytic fuel generations. 2D materials, specifically 2D superlattice materials focused here, featured highly accessible active areas, high density of active sites, and high compatibility with property-complementary materials to form heterostructures with desired synergetic effects, have demonstrated to be promising electrocatalysts for boosting the performance of sustainable energy conversion and storage devices. Nevertheless, the reaction kinetics, and in particular, the functional mechanisms of the 2D superlattice-based catalysts yet remain ambiguous. In this review, based on the recent progress of 2D superlattice materials in electrocatalysis applications, the rational design and fabrication of 2D superlattices are first summarized and the application of 2D superlattices in electrocatalysis is then specifically discussed. Finally, perspectives on the current challenges and the strategies for the future design of 2D superlattice materials are outlined. This review attempts to establish an intrinsic correlation between the 2D superlattice heterostructures and the catalytic properties, so as to provide some insights into developing high-performance electrocatalysts for next-generation sustainable energy conversion and storage.

Engineering MOFs derived metal oxide nanohybrids: Towards electrochemical sensing of catechol in tea samples

In this work, we have successfully developed Cu-MOF/CuO/NiO nanocomposites (NCs) and employed as a novel electrochemical sensing platform in catechol (CC) detection. The Scanning electron microscopy (SEM) along Energy dispersive X-ray Analysis (EDX), Transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) are carried out to characterize the as-fabricated Cu-MOF/CuO/NiO NCs. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques have used to obtain oxidation peak currents of CC. Glassy carbon electrode (GCE) modified with Cu-MOF/CuO/NiO has exposed the superb EC properties representing low limit of detection (LOD) of 0.0078 µM (S/N = 3). To assess the practicability of Cu-MOF/CuO/NiO based sensing medium, it has been used to detect CC from two varieties of tea, namely black and green. Thus, we anticipate that this structural integration strategy possesses encouraging application potential in sensing podium and material synthesis.

A Hemin-Graphene Nanocomposite-Based Aptasensor for Ultrasensitive Colorimetric Quantification of Leukaemia Cells Using Magnetic Enrichment

Diagnostic blood cell counting is of limited use in monitoring a minimal number of leukaemia cells, warranting further research to develop more sensitive and reliable techniques to identify leukaemia cells in circulation. In this work, a hemin-graphene nanocomposite-based aptasensor was developed for ultrasensitive colorimetric detection of leukaemia cells (CEM) using magnetic enrichment. Hemin-conjugated graphene oxide nanocomposites (HGNs) were prepared by hydrazine reduction using graphene oxide nanosheets and hemins. Hence, the prepared HGNs become able to absorb single-stranded DNA and acquire peroxidase-like activity. The aptamer sgc8c, which recognizes a specific target on leukaemia cells, was absorbed onto HGNs to capture the target CEM cancer cells. The captured target cells that associated with the HGNs were then concentrated and separated by magnetic beads (MBs) coated with sgc8c aptamers, forming a HGN-cell-MB sandwich structure. These sandwich structures can be quantified via an oxidation reaction catalysed by HGNs. By utilizing dual signal amplification effects generated by magnetic enrichment and the improved peroxidase activity of HGNs, the biosensor allowed for highly sensitive detection of 10 to 10⁵ CEM cells with an ultra-low limit of detection (LOD) of 10 cells under optimal conditions. It is expected that the proposed aptasensor can be further employed in monitoring the minimal residual disease during the treatment of leukaemia.

Electrochemical fabrication of Co(OH)2 nanoparticles decorated carbon cloth for non-enzymatic glucose and uric acid detection

Cobalt hydroxide nanoparticles (Co(OH)₂ NPs) were uniformly deposited on flexible carbon cloth substrate (Co(OH)₂@CC) rapidly by a facile one-step electrodeposition, which can act as an enzyme-free glucose and uric acid sensor in an alkaline electrolyte. Compositional and morphological characterization were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS), which confirmed the deposited nanospheres were Co(OH)₂ nanoparticles (NPs). The electrochemical oxidation of glucose and uric acid at Co(OH)₂@CC electrode was investigated by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), differential pulse voltammetry (DPV), and chronoamperometry methods. The results revealed a remarkable electrocatalytic activity toward the single and simultaneous determination of glucose and uric acid at about 0.6 V and 0.3 V (vs. Ag/AgCl), respectively, which is attributed to a noticeable synergy effect between Co(OH)₂ NPs and CC with good repeatability, satisfactory reproducibility, considerable long-term stability, superior selectivity, outstanding sensitivity, and wide linear detection range from 1 uM to 2 mM and 25 nM to 1.5 uM for glucose and UA, respectively. The detection limits were 0.36 nM for UA and 0.24 μM for glucose (S/N = 3). Finally, the Co(OH)₂@CC electrode was utilized for glucose and uric acid determination in human blood samples and satisfying results were obtained. The relative standard derivations (RSDs) for glucose and UA were in the range 6 to 14% and 0 to 3%, respectively. The recovery ranges for glucose an UA were 97 to 103% and 95 and 101%, respectively. These features make the novel Co(OH)₂@CC sensor developed by a low-cost, efficient, and eco-friendly preparation method a potentially practical candidate for application to biosensors.

Application of functionalized layered double hydroxides for heavy metal removal: A review

Layered double hydroxides (LDHs) are ionic laminar composites composed of positively charged brucite-like layers with an interlayered region containing charged compensating anions and solvation molecules. Such functional LDHs materials present a strong potential for heavy metal treatment especially for wastewater and soil, due to the large surface area and layered structure. This paper started with the background of techniques for heavy metals treatment and then discussed the potential environmental toxic effects, feasibility, stability of LDH composites. The preparation strategies of LDHs composites, and their application were summarized, followed by main mechanisms involving chelation, complexation, surface precipitation, ion exchange. This work also presented the potential environmental toxic effects, feasibility, stability of LDHs composites, reuse of waste liquid and the ratio adjustment of M²⁺ and N³⁺ for LDHs synthesis. While most efforts focused on improving the absorption capacity of LDHs by composites construction, ignoring the toxicity effects and detailed mechanism investigation. Based on a thorough review of the latest development, the challenges and perspectives would be proposed, offering promising insights on environmental purification via LDHs based materials.

A comprehensive review on electrochemical and optical aptasensors for organophosphorus pesticides

There has been a rise in pesticide use as a result of the growing industrialization of agriculture. Organophosphorus pesticides have been widely applied as agricultural and domestic pest control agents for nearly five decades, and they remain as health and environmental hazards in water supplies, vegetables, fruits, and processed foods causing serious foodborne illness. Thus, the rapid and reliable detection of these harmful organophosphorus toxins with excellent sensitivity and selectivity is of utmost importance. Aptasensors are biosensors based on aptamers, which exhibit exceptional recognition capability for a variety of targets. Aptasensors offer numerous advantages over conventional approaches, including increased sensitivity, selectivity, design flexibility, and cost-effectiveness. As a result, interest in developing aptasensors continues to expand. This paper discusses the historical and modern advancements of aptasensors through the use of nanotechnology to enhance the signal, resulting in high sensitivity and detection accuracy. More importantly, this review summarizes the principles and strategies underlying different organophosphorus aptasensors, including electrochemical, electrochemiluminescent, fluorescent, and colorimetric ones.

Layered double hydroxide-based nanomaterials for biomedical applications

Against the backdrop of increased public health awareness, inorganic nanomaterials have been widely explored as promising nanoagents for various kinds of biomedical applications. Layered double hydroxides (LDHs), with versatile physicochemical advantages including excellent biocompatibility, pH-sensitive biodegradability, highly tunable chemical composition and structure, and ease of composite formation with other materials, have shown great promise in biomedical applications. In this review, we comprehensively summarize the recent advances in LDH-based nanomaterials for biomedical applications. Firstly, the material categories and advantages of LDH-based nanomaterials are discussed. The preparation and surface modification of LDH-based nanomaterials, including pristine LDHs, LDH-based nanocomposites and LDH-derived nanomaterials, are then described. Thereafter, we systematically describe the great potential of LDHs in biomedical applications including drug/gene delivery, bioimaging diagnosis, cancer therapy, biosensing, tissue engineering, and anti-bacteria. Finally, on the basis of the current state of the art, we conclude with insights on the remaining challenges and future prospects in this rapidly emerging field.

Gas Sensing Mechanism and Adsorption Properties of C2H4 and CO Molecules on the Ag3–HfSe2 Monolayer: A First-Principle Study

The detection of dissolved gases in oil is an important method for the analysis of transformer fault diagnosis. In this article, the potential-doped structure of the Ag₃ cluster on the HfSe₂ monolayer and adsorption behavior of CO and C₂H₄ upon Ag₃–HfSe₂ were studied theoretically. Herein, the binding energy, adsorption energy, band structure, density of state (DOS), partial density of state (PDOS), Mulliken charge analysis, and frontier molecular orbital were investigated. The results showed that the adsorption effect on C₂H₄ is stronger than that on CO. The electrical sensitivity and anti-interference were studied based on the bandgap and adsorption energy of gases. In particular, there is an increase of 55.49% in the electrical sensitivity of C₂H₄ after the adsorption. Compared to the adsorption energy of different gases, it was found that only the adsorption of the C₂H₄ system is chemisorption, while that of the others is physisorption. It illustrates the great anti-interference in the detection of C₂H₄. Therefore, the study explored the potential of HfSe₂-modified materials for sensing and detecting CO and C₂H₄ to estimate the working state of power transformers.

Tuning the Redox Chemistry of Copper Oxide Nanoarchitectures Integrated with rGOP via Facet Engineering: Sensing H2S toward SRB Detection

The ultrasensitive determination of sulfate reducing bacteria (SRB) is of great significance for their crucial roles in environmental and industrial harms together with the early detection of microbial corrosion. In this work, we report the development of highly efficient electrocatalysts, i.e., Cu₂O-CuO extended hexapods (EHPs), which are wrapped on homemade freestanding graphene paper to construct a flexible paper electrode in the electrochemical sensing of the biomarker sulfide for SRB detection. Herein Cu₂O-CuO EHPs have been synthesized via a highly controllable and facile approach at room temperature, where the redox centers of copper oxide nanoarchitectures are tuned via facet engineering, and then they are deposited on the graphene paper surface through an electrostatic adsorption to enable homogeneous and highly dense distribution. Owing to the synergistic contribution of high electrocatalytic activity from the Cu mixed oxidation states and abundant catalytically active facets of Cu₂O-CuO EHPs and high electrical conductivity of the graphene paper electrode substrate, the resultant nanohybrid paper electrode has exhibited superb electrochemical sensing properties for H₂S with a wide linear range up to 352 μM and an extremely low detection limit (LOD) of 0.1 nM with a signal-to-noise ratio of 3 (S/N = 3), as well as high sensitivity, stability, and selectivity. Furthermore, taking advantage of the good biocompatibility and mechanical flexibility, the electrochemical sensing platform based on the proposed electrode has been applied in the sensitive detection of SRB in environmental samples through the sensing of sulfide from SRB, which holds great promise for on-site and online corrosion and environmental monitoring.

A Multicomponent Polymer-Metal-Enzyme System as Electrochemical Biosensor for H2O2 Detection

Herein, an Au nanoparticles-polydopamine-poly acrylic acid-graphene (Au NPs-PDA-PAA-graphene) multicomponent nanohybrid is fabricated by surface functionalization of graphene alongside extensive in-situ growth of Au nanoparticles. The as-obtained nanocomposite possesses good hydrophilicity, excellent biocompatibility and high biomolecules loading capacity, which acts as an ideal platform for enzyme modification. Considering this fact, Horseradish peroxidase is expressively immobilized upon Au NPs-PDA-PAA-graphene surface, in order to lay the foundations of a biosensor that is majorly based on enzymatic activity. The biosensor exhibits higher sensitivity towards the determination of H2O2 with linearity ranging from 0.1 μm upto 20 mm, and the limit of detection going down to 0.02 μm. Encouraged by its acceptable electrocatalytic performance, this multicomponent system can also be easily employed for carrying out the real-time tracking of H2O2 coming out of Macrophage cells. Therefore, this work designs an extraordinarily updated platform for biosensing related applications, and also presents a reliable platform for the direct detection of H2O2in vivo and in vitro, which show great potential in bioelectroanalytical chemistry, cellular biology, and pathophysiology.

Surfactant-Assisted Synthesis of Praseodymium Orthovanadate Nanofiber-Supported NiFe-Layered Double Hydroxide Bifunctional Catalyst: The Electrochemical Detection and Degradation of Diphenylamine

Physiological storage disorders are caused by ineffective post-harvest handling of horticultural crops, particularly fruits. To address these post-harvest concerns, diphenylamine (DPAH^•+) is widely used as a preservative to prevent fruit degradation and surface scald during storage around the world. Humans are negatively affected by the use of high concentrations of DPAH^•+ because of the various health complications related to its exposure. As a result, accurate detection and quantification of DPAH^•+ residues in treated fruits are critical. Rare earth metal orthovanadates, which have excellent physical and chemical properties, are potential materials for electrochemical sensors in this area. Herein, we present a simple and direct ultrasonication technique for the surfactant-assisted synthesis of praseodymium orthovanadate (PrVO₄ or PrV) loaded on nickel iron layered double hydroxide (NiFe-LDH) synthesized with deep eutectic solvent assistance, as well as its application as an effective catalyst in the detection and degradation of DPAH^•+ in fruits and water samples. The current work presents supreme electrochemical features of a PrV@NiFe-LDH-modified screen-printed carbon electrode (SPCE) where cetyltrimethylammonium bromide (CTAB) surfactant-driven fabrication of PrV directs the formation of highly qualified engineered structures and the deep eutectic solvent based green synthesis of NiFe-LDH creates hierarchical lamellar structures following the principles of green chemistry. PrV and NiFe-LDH combine to produce a synergistic effect that improves the number of active sites, charge transfer kinetics, and electronic conductivity. Differential pulse voltammetry analysis of PrV@NiFe-LDH/SPCE reveals a dynamic working range (0.005-226.26 μM), increased sensitivity (133.13 μA μM^-1 cm^-2), enhanced photocatalytic activity, and low detection limit (0.001 μM), which are considered significant when compared with the former reported electrodes in the literature for the determination of DPAḢ⁺ for its real-time applications.

Layered double hydroxide based materials applied in persulfate based advanced oxidation processes: Property, mechanism, application and perspectives

Recently, persulfate-based advanced oxidation processes (persulfate-AOPs) are booming rapidly due to their promising potential in treating refractory contaminants. As a type of popular two-dimensional material, layered double hydroxides (LDHs) are widely used in energy conversion, medicine, environment remediation and other fields for the advantages of high specific surface area (SSA), good tunability, biocompatibility and facile fabrication. These excellent physicochemical characteristics may enable LDH-based materials to be promising catalysts in persulfate-AOPs. In this work, we make a summary of LDHs and their composites in persulfate-AOPs from different aspects. Firstly, we introduce different structure and important properties of LDH-based materials briefly. Secondly, various LDH-based materials are classified according to the type of foreign materials (metal or carbonaceous materials, mainly). Latterly, we discuss the mechanisms of persulfate activation (including radical pathway and nonradical pathway) by these catalysts in detail, which involve (i) bimetallic synergism for radical generation, (ii) the role of carbonaceous materials in radical generation, (iii) singlet oxygen (¹O₂) production and several special nonradical mechanisms. In addition, the catalytic performance of LDH-based catalysts for contaminants are also summarized. Finally, challenges and future prospects of LDH-based composites in environmental remediation are proposed. We expect this review could bring new insights for the development of LDH-based catalyst and exploration of reaction mechanism.

Boosting the Electrochemical Performance of PI-5-CA/C-SWCNT Nanohybrid for Sensitive Detection of E. coli O157:H7 From the Real Sample

Redox activity is an important indicator for evaluating electrochemical biosensors. In this work, we have successfully polymerized indole-5-carboxylic acid into poly-5-carboxyindole nanomaterials (PI-5-CA), using its superior redox activity, and introduced carboxylated single-walled carbon nanotubes (C-SWCNTs) to synthesize a composite material. Finally, a synthesized composite material was used for the modification of the glass carbon electrode to fabricate the PI-5-CA/C-SWCNTs/GCE-based immunosensor and was successfully applied for the sensitive detection of E. coli O157:H7. The fabricated immunosensor exhibited an outstanding electrocatalytic activity toward the detection of E. coli O157:H7 with a remarkably lowest limit of detection (2.5 CFU/ml, LOD = 3 SD/k, n = 3) and has a wide linear range from 2.98×101 to 2.98×107 CFU/ml. Inspired from the excellent results, the fabricated electrode was applied for the detection of bacteria from real samples (water samples) with a good recovery rate (98.13–107.69%) as well as an excellent stability and specificity. Owing to its simple preparation, excellent performance, and detection time within 30 min, our proposed immunosensor will open a new horizon in different fields for the sensitive detection of bacteria from real samples.

Molybdenum Disulfide-Based Nanoprobes: Preparation and Sensing Application

The use of nanoprobes in sensors is a popular way to amplify their analytical performance. Coupled with two-dimensional nanomaterials, nanoprobes have been widely used to construct fluorescence, electrochemical, electrochemiluminescence (ECL), colorimetric, surface enhanced Raman scattering (SERS) and surface plasmon resonance (SPR) sensors for target molecules' detection due to their extraordinary signal amplification effect. The MoS₂ nanosheet is an emerging layered nanomaterial with excellent chemical and physical properties, which has been considered as an ideal supporting substrate to design nanoprobes for the construction of sensors. Herein, the development and application of molybdenum disulfide (MoS₂)-based nanoprobes is reviewed. First, the preparation principle of MoS₂-based nanoprobes was introduced. Second, the sensing application of MoS₂-based nanoprobes was summarized. Finally, the prospect and challenge of MoS₂-based nanoprobes in future were discussed.

Boosting electrocatalytic activity of carbon fiber@fusiform-like copper-nickel LDHs: Sensing of nitrate as biomarker for NOB detection

Morphological evolution of layered double hydroxides (LDHs) with preferential crystal facets has appealed gigantic attention of research community. Herein, we prepare hierarchical hybrid material by structurally integrating fusiform-like CuNiAl LDHs petals on conductive backbone of CF (CF@CuNiAl LDHs) and investigate electrocatalytic behavior in nitrate reduction over a potential window of -0.7 V to +0.7 V. The CF@CuNiAl LDHs electrode exhibits remarkable electrocatalytic aptitude in nitrate sensing including broad linear ranges of 5 nM to 40 µM and 75 µM to 2.4 mM with lowest detection limit of 0.02 nM (S/N = 3). The sensor shows sensitivity of 830.5 ± 1.84 µA mM^1- cm^2- and response time within 3 s. Owing to synergistic collaboration of improved electron transfer kinetics, specific fusiform-like morphology, presence of more catalytically active {111} facets and superb catalytic activity of LDHs, CF@CuNiAl LDHs electrode has outperformed as electrochemical sensor. Encouraged from incredible performance, CF@CuNiAl LDHs flexible electrode has been applied in real-time in-vitro detection of nitrite oxidizing bacteria (NOB) through the sensing of nitrate because NOB convert nitrite into nitrate by characteristic metabolic process to obtain their energy. Further, CF@CuNiAl LDHs based sensing podium has also been employed in in-vitro detection of nitrates from mineral water, tap water and Pepsi drink.

Construction of cationic polyfluorinated azobenzene/reduced graphene oxide for simultaneous determination of dopamine, uric acid and ascorbic acid

A highly sensitive cationic polyfluorinated azobenzene/reduced graphene oxide (C₃F₇-azo⁺/RGO) nanocomposite electrochemical sensor for simultaneous detection of dopamine (DA), ascorbic acid (AA) and uric acid (UA) was successfully synthesized using a facile exfoliation/restacking method. The nanocomposite is self-assembled from oppositely charged graphene oxide nanosheets (GO) and polyfluorinated azobenzene cations (C₃F₇-azo⁺), and then obtained by electrochemical reduction. The structure and electrochemical properties were characterized by X-ray diffraction (XRD), energy dispersive spectrometer analysis (EDS), transmission electron microscope (TEM) and scanning electron microscope (SEM). The electrochemical property of C₃F₇-azo⁺/RGO was characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and differential pulse voltammetry (DPV). It can be clearly seen from experimental results that C₃F₇-azo⁺/RGO-modified electrode (C₃F₇-azo⁺/RGO/GCE) can detect DA, AA and UA simultaneously, and has good stability and anti-interference performance. The detection limits are 65 nM, 8 nM and 11 nM for DA, AA and UA in the ranges 57.28-134.28 μM, 0.04-6.01 μM, 9.23-23.45 μM, respectively.

A Simple Colorimetric Assay for Sensitive Cu2+ Detection Based on the Glutathione-Mediated Etching of MnO2 Nanosheets

In this paper, we developed a quick, economical and sensitive colorimetric strategy for copper ions (Cu²⁺) quantification via the redox response of MnO₂ nanosheets with glutathione (GSH). This reaction consumed MnO₂ nanosheets, which acted as a catalyst for the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to a blue product (oxTMB). In the presence of Cu²⁺, the GSH was catalyzed to GSSG (oxidized glutathione), and the solution changed from colorless to deep blue. Under the optimum conditions, the absorption signal of the oxidized product (oxTMB) became proportional to Cu²⁺ concentration in the range from 10 to 300 nM with a detection limit of 6.9 nM. This detection system showed high specificity for Cu²⁺. Moreover, the system has been efficaciously implemented for Cu²⁺ detection in actual tap water samples. The layered-nanostructures of MnO₂ nanosheets make it possess high chemical and thermal stability. TMB can be quickly oxidized within 10 min by the catalyzing of MnO₂ nanosheets with high oxidase-like activity. There is no need of expensive reagents, additional H₂O₂ and complicated modification processes during the colorimetric assay. Therefore, the strategy primarily based on MnO₂ nanosheets is promising for real-time, rapid and highly sensitive detection of Cu²⁺ under practical conditions.

Sandwich-type microRNA biosensor based on graphene oxide incorporated 3D-flower-like MoS2 and AuNPs coupling with HRP enzyme signal amplification

A sandwich electrochemical biosensing strategy for ultrasensitive detection of miRNA-21 was developed by using graphene oxide incorporated 3D-flower-like MoS₂ (3D MoS₂-rGO) nanocomposites as the substrate and horseradish peroxidase (HRP)-functionalized DNA strand 1 (S1)-gold nanoparticles (S1-AuNPs-HRP) as signal amplification probes. Herein, 3D MoS₂-rGO nanocomposites not only had a large specific surface area and excellent conductivity, but also provided more attachment sites for electrodepositing AuNPs. In the presence of target miRNA, a sandwich structure was formed, and the determination of the miRNA-21 was carried out by measuring the DPV response of H₂O₂ mediated by hydroquinone (HQ) at a potential of + 0.052 V (vs AgCl reference electrode). Under the optimal experimental conditions, the as-prepared biosensor enabled the ultrasensitive detection of miRNA-21 from 5 fM to 0.5 μM with the low detection limit of 0.54 fM (S/N = 3), comparable or lower than previous reported methods for miRNA-21 detection, which benefited from the synergistic amplification of 3D MoS₂-rGO and AuNPs-HRP. The prepared biosensor showed satisfactory selectivity, reproducibility, and stability towards miRNA-21 detection. The biosensor was feasible for accurate and quantitative detection of miRNA-21 in normal human serum samples with RSD below 5.86%, which showed a great potential in clinical analysis and disease diagnosis.

Recent Trends in Synthesis and Applications of porous MXene Assemblies: A Topical Review

MXene possesses high conductivity, excellent hydrophilicity, rich surface chemistry, hence holds great potential in various applications. However, MXene materials have low surface area utilization due to the agglomeration of ultrathin nanosheets. Assembling 2D MXene nanosheets into 3D multi-level architectures is an effective way to circumvent this issue. Incorporation of MXene with other nanomaterials during the assembly process could rationally tune and tailor the specific surface area, porosity and surface chemistry of the MXene assemblies. The complementary and synergistic effect between MXene and nanomaterials could expand their advantages and make up for their disadvantages, thus boost the performance of 3D porous MXene composites. Herein, we summarize the recent progress in fabrication of porous MXene architectures from 2D to 3D, and also discuss the potential applications of MXene nanostructures in energy harvesting systems, sensing, electromagnetic interference shielding, water purification and photocatalysis.

Triple-enzyme mimetic activity of Fe3O4@C@MnO2 composites derived from metal-organic frameworks and their application to colorimetric biosensing of dopamine

Novel Fe₃O₄@C@MnO₂ composites were successfully synthesized for the first time via an interfacial reaction between magnetic porous carbon and KMnO₄, in which the magnetic porous carbon was derived from the pyrolysis of Fe-MIL-88A under N₂ atmosphere. Interestingly, the obtained Fe₃O₄@C@MnO₂ composites were found to have triple-enzyme mimetic activity including peroxidase-like, catalase-like, and oxidase-like activity. As a peroxidase mimic, Fe₃O₄@C@MnO₂ composites could catalyze the oxidation of TMB into a blue oxidized product by H₂O₂. As a catalase mimic, Fe₃O₄@C@MnO₂ could catalyze the decomposition of H₂O₂ to generate O₂ and H₂O. As an oxidase mimic, Fe₃O₄@C@MnO₂ could catalyze the direct oxidation of TMB to produce a blue oxidized product without H₂O₂. Reactive oxygen species measurements revealed that the oxidase-like activity originated from ¹O₂ and O₂^-∙and little∙OH generated by the dissolved oxygen, which was catalyzed by the Fe₃O₄@C@MnO₂ in the TMB oxidation reaction. The oxidase-like activity of Fe₃O₄@C@MnO₂ was investigated in detail. Under the optimized conditions, a rapid, sensitive, visual colorimetric method for dopamine detection was developed based on the inhibitory effect of dopamine on the oxidase-like activity. The proposed method allows for dopamine detection with a limit of detection of 0.034 μM and a linear range of 0.125-10 μM. This new colorimetric method was successfully used for the determination of dopamine in human blood samples.

Diagnosis of COVID-19, vitality of emerging technologies and preventive measures

Coronavirus diseases-2019 (COVID-19) is becoming increasing serious and major threat to public health concerns. As a matter of fact, timely testing enhances the life-saving judgments on treatment and isolation of COVID-19 infected individuals at possible earliest stage which ultimately suppresses spread of infectious diseases. Many government and private research institutes and manufacturing companies are striving to develop reliable tests for prompt quantification of SARS-CoV-2. In this review, we summarize existing diagnostic methods as manual laboratory-based nucleic acid assays for COVID-19 and their limitations. Moreover, vitality of rapid and point of care serological tests together with emerging biosensing technologies has been discussed in details. Point of care tests with characteristics of rapidity, accurateness, portability, low cost and requiring non-specific devices possess great suitability in COVID-19 diagnosis and detection. Besides, this review also sheds light on several preventive measures to track and manage disease spread in current and future outbreaks of diseases.

Using Graphene-Based Biosensors to Detect Dopamine for Efficient Parkinson's Disease Diagnostics

Parkinson's disease (PD) is a neurodegenerative disease in which the neurotransmitter dopamine (DA) depletes due to the progressive loss of nigrostriatal neurons. Therefore, DA measurement might be a useful diagnostic tool for targeting the early stages of PD, as well as helping to optimize DA replacement therapy. Moreover, DA sensing appears to be a useful analytical tool in complex biological systems in PD studies. To support the feasibility of this concept, this mini-review explores the currently developed graphene-based biosensors dedicated to DA detection. We discuss various graphene modifications designed for high-performance DA sensing electrodes alongside their analytical performances and interference studies, which we listed based on their limit of detection in biological samples. Moreover, graphene-based biosensors for optical DA detection are also presented herein. Regarding clinical relevance, we explored the development trends of graphene-based electrochemical sensing of DA as they relate to point-of-care testing suitable for the site-of-location diagnostics needed for personalized PD management. In this field, the biosensors are developed into smartphone-connected systems for intelligent disease management. However, we highlighted that the focus should be on the clinical utility rather than analytical and technical performance.

Recent Advances in Layered Double Hydroxide-Based Electrochemical and Optical Sensors

Layered double hydroxides (LDHs) have attracted considerable attention as promising materials for electrochemical and optical sensors owing to their excellent catalytic properties, facile synthesis strategies, highly tunable morphology, and versatile hosting ability. LDH-based electrochemical sensors are affordable alternatives to traditional precious-metal-based sensors, as LDHs can be synthesized from abundant inorganic precursors. LDH-modified probes can directly catalyze or host catalytic compounds that facilitate analyte redox reactions, detected as changes in the probe's current, voltage, or resistance. The porous and lamellar structure of LDHs allows rapid analyte diffusion and abundant active sites for enhanced sensor sensitivity. LDHs can be composed of conductive materials such as reduced graphene oxide (rGO) or metal nanoparticles for improved catalytic activity and analyte selectivity. As optical sensors, LDHs provide a spacious, stable structure for synergistic guest-host interactions. LDHs can immobilize fluorophores, chemiluminescence reactants, and other spectroscopically active materials to reduce the aggregation and dissolution of the embedded sensor molecules, yielding enhanced optical responses and increased probe reusability. This review discusses standard LDH synthesis methods and overviews the different electrochemical and optical analysis techniques. Furthermore, the designs and modifications of exemplary LDHs and LDH composite materials are analyzed, focusing on the analytical performance of LDH-based sensors for key biomarkers and pollutants, including glucose, dopamine (DA), H2O2, metal ions, nitrogen-based toxins, and other organic compounds.

Graphene and Carbon Nanotube-based Electrochemical Sensing Platforms for Dopamine

Dopamine (DA) is an important neurotransmitter, which is created and released from the central nervous system. It plays a crucial role in human activities, like cognition, emotions, and response to anything. Maladjustment of DA in human blood serum results in different neural diseases, like Parkinson's and Schizophrenia. Consequently, researchers have started working on DA detection in blood serum, which is undoubtedly a hot research area. Electrochemical sensing techniques are more promising to detect DA in real samples. However, utilizing conventional electrodes for selective determination of DA encounters numerous problems due to the coexistence of other materials, such as uric acid and ascorbic acid, which have an oxidation potential close to DA. To overcome such problems, researchers have put their focus on the modification of bare electrodes. The aim of this review is to present recent advances in modifications of most used bare electrodes with carbonaceous materials, especially graphene, its derivatives, and carbon nanotubes, for electrochemical detection of DA. A brief discussion about the mechanistic phenomena at the electrode interface has also been included in this review.

Well-Designed Construction of Yttrium Orthovanadate Confined on Graphitic Carbon Nitride Sheets: Electrochemical Investigation of Dimetridazole

Antibiotics are the most important drugs for people and animals to fight bacterial illnesses. Overuse of antibiotics has had unintended consequences, such as antibiotic resistance and ecosystem eradication owing to toxic chemical discharge, which have a negative influence on the biome. Herein, we report the synthesis of a hollow ellipsoid-shaped yttrium vanadate/graphitic carbon nitride (YVO₄@CN) nanocomposite by a hydrothermal approach followed by a sonochemical method for the effective detection of dimetridazole (DMZ). The synergic and coupling effect between both the phases offer non-linear cumulative ramifications which can positively enhance the individual properties of the materials under consideration. This positive hybrid effect increases the conductivity, shortens the ion-diffusion pathway, enhances the electron/ion transportation, and provides more active sites and electron-conducting channels. The accurate optimization of the experimental conditions proposes good electrocatalytic activity for the YVO₄@CN catalyst, exhibiting a good response toward DMZ detection. It reveals an extensive linear concentration range (0.001-153.3 and 176.64-351.6 μM), a low detection limit (0.8 nM), higher sensitivity (4.98 μA μM^-1 cm^-2), appreciable selectivity, increased operational stability (2200 s), and good cycle stability (60 cycles). The electrochemical performance of YVO₄@CN indicates its practical application in real-time sample analysis of several families of nitroimidazole drugs.

Selective Voltammetric Detection of Ascorbic Acid from Rosa Canina on a Modified Graphene Oxide Paste Electrode by a Manganese(II) Complex

Voltammetric techniques have been considered as an important analytical tool applied to the determination of trace concentrations of many biological molecules including ascorbic acid. In this paper, ascorbic acid was detected by square wave voltammetry, using graphene oxide paste as a working electrode, modified by a film of a manganese(II) complex compound. Various factors, such as the effect of pH, affecting the response characteristics of the modified electrode were investigated. The relationship between the peak height and ascorbic acid concentration within the modified working electrode was investigated, using the calibration graph. The equation of the calibration graph was found to be: I = 0.0550γac + 0.155 with R2 = 0.9998, where I is the SWV current and γac is the mass concentration of ascorbic acid. The LOD and LOQ of the proposed method were determined to be 1.288 μg/L and 3.903 μg/L, respectively. Several compounds, such as riboflavin, biotin, and ions, such as Fe and Cu, were tested and it seemed that they did not interfere with the analytic signal. The proposed procedure was successfully applied in the determination of ascorbic acid in Rosa canina hips.