Strategies, advances, and challenges associated with the use of graphene-based nanocomposites for electrochemical biosensors

Recent developments and challenges in resistance-based hydrogen gas sensors based on metal oxide semiconductors

In recent years, the energy crisis has made the world realize the importance and need for green energy. Hydrogen safety has always been a primary issue that needs to be addressed for the application and large-scale commercialization of hydrogen energy, and precise and rapid hydrogen gas sensing technology and equipment are important prerequisites for ensuring hydrogen safety. Based on metal oxide semiconductors (MOS), resistive hydrogen gas sensors (HGS) offer advantages, such as low cost, low power consumption, and high sensitivity. They are also easy to test, integrate, and suitable for detecting low concentrations of hydrogen gas in ambient air. Therefore, they are considered one of the most promising HGS. This article provides a comprehensive review of the surface reaction mechanisms and recent research progress in optimizing the gas sensing performance of MOS-based resistive hydrogen gas sensors (MOS-R-HGS). Particularly, the advancements in metal-assisted or doped MOS, mixed metal oxide (MO)-MOS composites, MOS-carbon composites, and metal-organic framework-derived (MOF)-MOS composites are extensively summarized. Finally, the future research directions and possibilities in this field are discussed.

Development of isoniazid electrochemical sensor using nickel ferrite - nitrogen and sulfur co-doped graphene quantum dot nanocomposite as a new electrode modifier

This work reports the synthesis of nickel ferrite decorated nitrogen and sulfur co-doped graphene quantum dot (NF@N, S:GQD) and its use as an electrode modifier. The developed NF@N, S:GQD modified glassy carbon electrode (NF@N, S:GQD/GCE) was applied to assess isoniazid (INZ) concentration based on its oxidation at the surface of the proposed electrode. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were used as appropriate electrochemical techniques to study the electrochemical behavior of INZ and determine it. Based on combined evidence from surveys, research, and personal results, it is thought that the combination of nickel ferrite and doped graphene quantum dots can synergistically affect results, leading to increased sensitivity and reduced detection limits. This is probably mainly due to the high electrical conductivity of N, S-GQD structure, the electrocatalytic effect of nickel ferrite, and increased surface area resulting from the nano size of the modifier. The optimum conditions for preparing of the modified electrode and determination of INZ are selected by performing electrochemical experiments. The voltammetric response of the sensor is linear from 0.3 to 40 nM INZ under optimal conditions and the detection limit of the sensor is 0.1 nM. The validity and performance of the prepared sensor were confirmed by determining the amount of INZ in the drug and urine as real samples. The composite of doped nanoparticles and nickel ferrite is an innovative modification material to create electrochemical sensors with high sensitivity and selectivity that can be used in pharmaceutical applications.

Biomedical applications of graphene-based nanomaterials: recent progress, challenges, and prospects in highly sensitive biosensors

Graphene-based nanomaterials (graphene, graphene oxide, reduced graphene oxide, graphene quantum dots, graphene-based nanocomposites, etc.) are emerging as an extremely important class of nanomaterials primarily because of their unique and advantageous physical, chemical, biological, and optoelectronic aspects. These features have resulted in uses across diverse areas of scientific research. Among all other applications, they are found to be particularly useful in designing highly sensitive biosensors. Numerous studies have established their efficacy in sensing pathogens and other biomolecules allowing for the rapid diagnosis of various diseases. Considering the growing importance and popularity of graphene-based materials for biosensing applications, this review aims to provide the readers with a summary of the recent progress in the concerned domain and highlights the challenges associated with the synthesis and application of these multifunctional materials.

Adsorptive removal of heavy metals from aqueous solutions: Progress of adsorbents development and their effectiveness

Increased levels of heavy metals (HMs) in aquatic environments poses serious health and ecological concerns. Hence, several approaches have been proposed to eliminate/reduce the levels of HMs before the discharge/reuse of HMs-contaminated waters. Adsorption is one of the most attractive processes for water decontamination; however, the efficiency of this process greatly depends on the choice of adsorbent. Therefore, the key aim of this article is to review the progress in the development and application of different classes of conventional and emerging adsorbents for the abatement of HMs from contaminated waters. Adsorbents that are based on activated carbon, natural materials, microbial, clay minerals, layered double hydroxides (LDHs), nano-zerovalent iron (nZVI), graphene, carbon nanotubes (CNTs), metal organic frameworks (MOFs), and zeolitic imidazolate frameworks (ZIFs) are critically reviewed, with more emphasis on the last four adsorbents and their nanocomposites since they have the potential to significantly boost the HMs removal efficiency from contaminated waters. Furthermore, the optimal process conditions to achieve efficient performance are discussed. Additionally, adsorption isotherm, kinetics, thermodynamics, mechanisms, and effects of varying adsorption process parameters have been introduced. Moreover, heavy metal removal driven by other processes such as oxidation, reduction, and precipitation that might concurrently occur in parallel with adsorption have been reviewed. The application of adsorption for the treatment of real wastewater has been also reviewed. Finally, challenges, limitations and potential areas for improvements in the adsorptive removal of HMs from contaminated waters are identified and discussed. Thus, this article serves as a comprehensive reference for the recent developments in the field of adsorptive removal of heavy metals from wastewater. The proposed future research work at the end of this review could help in addressing some of the key limitations facing this technology, and create a platform for boosting the efficiency of the adsorptive removal of heavy metals.

Recent advancements and prospects in carbon-based nanomaterials derived from biomass for environmental remediation applications

The conversion of waste biomass into a value-added carbonaceous nanomaterial highlights the appealing power of biomass valorization. The advantages of using sustainable and cheap biomass precursors exhibit the tremendous opportunity for boosting energy production and their application in environmental remediation processes. This review emphasis the development and production of carbon-based nanomaterials derived from biomass, which possess favourable characteristics such as biocompatibility and photoluminescence. The advantages and limitations of various nanomaterials synthesised from different precursors were also discussed with insights into their physicochemical properties. The surface morphology of the porous nanomaterials is also explored along with their characteristic properties like regenerative nature, non-toxicity, ecofriendly nature, unique surface area, etc. The incorporation of various functional groups confers superiority of these materials, resulting in unique and advanced functional properties. Further, the use of these biomass derived nanomaterials was also explored in different applications like adsorption, photocatalysis and sensing of hazardous pollutants, etc. The challenges and outcomes obtained from different carbon-based nanomaterials are briefly outlined and discussed in this review.

One pot fabrication of diamino naphthalene -AuNPs decorated graphene nanoplatform for the MRSA detection in the biological sample

Early monitoring of MRSA can effectively mitigate the disease risk by using Penicillin-binding protein 2a (PbP2a) biomarker. Diamino naphthalene-AuNPs decorated graphene (AuNPsGO-DN) nanocomposite was synthesized for a rapid and sensitive immunosensor detecting PbP2a. The synthesized AuNPsGO-DN nanocomposites were characterized by field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (SEM-EDX), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, and X-ray diffraction spectroscopy (XRD). Electrochemical characterization done with cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrical impedance spectroscopy (EIS) techniques. Anti-PbP2a monoclonal antibodies immobilized at AuNPsGO-DN/GCE via covalent bonding. AuNPs enhanced the electrode surface area and the antibodies' loading. Mercaptopropionic acid (MPA) was a linker between the AuNPs and antibodies, orientated the antibodies as opposite to the PbP2a antigen, and improved the sensitivity and specificity. The antiPbP2a/MPA/AuNPsGO-DN/GCE electrode displayed sensitive and selective detection towards the PbP2a antigen in phosphate buffer saline (PBS pH 7.4). The broad linear range from 0.01 to 8000 pg/mL was obtained with LOD of 0.154 pg/mL and 0.0239 pg/mL, respectively. A label-free, simple, and sensitive immunosensor was developed with a 98-106 % recovery rate in spiked biological samples. It shows the potential applicability of the developed immunoelectrode.

Nanomaterials promote the fast development of electrochemical MiRNA biosensors

Cancer has become the leading cause of death worldwide. In recent years, molecular diagnosis has demonstrated great potential in the prediction and diagnosis of cancer. MicroRNAs (miRNAs) are short oligonucleotides that regulate gene expression and cell function and are considered ideal biomarkers for cancer detection, diagnosis, and patient prognosis. Therefore, the specific and sensitive detection of ultra-low quantities of miRNA is of great significance. MiRNA biosensors based on electrochemical technology have advantages of high sensitivity, low cost and fast response. Nanomaterials show great potential in miRNA electrochemical detection and promote the rapid development of electrochemical miRNA biosensors. Some methods and signal amplification strategies for miRNA detection in recent years are reviewed herein, followed by a discussion of the latest progress in electrochemical miRNA detection based on different types of nanomaterial. Future perspectives and challenges are also proposed for further exploration of nanomaterials to bring breakthroughs in electrochemical miRNA detection.

Recent advances in smart wearable sensors for continuous human health monitoring

In recent years, the biochemical and biological research areas have shown great interest in a smart wearable sensor because of its increasing prevalence and high potential to monitor human health in a non-invasive manner by continuous screening of biomarkers dispersed throughout the biological analytes, as well as real-time diagnostic tools and time-sensitive information compared to conventional hospital-centered system. These smart wearable sensors offer an innovative option for evaluating and investigating human health by incorporating a portion of recent advances in technology and engineering that can enhance real-time point-of-care-testing capabilities. Smart wearable sensors have emerged progressively with a mixture of multiplexed biosensing, microfluidic sampling, and data acquisition systems incorporated with flexible substrate and bodily attachments for enhanced wearability, portability, and reliability. There is a good chance that smart wearable sensors will be relevant to the early detection and diagnosis of disease management and control. Therefore, pioneering smart wearable sensors into reality seems extremely promising despite possible challenges in this cutting-edge technology for a better future in the healthcare domain. This review presents critical viewpoints on recent developments in wearable sensors in the upcoming smart digital health monitoring in real-time scenarios. In addition, there have been proactive discussions in recent years on materials selection, design optimization, efficient fabrication tools, and data processing units, as well as their continuous monitoring and tracking strategy with system-level integration such as internet-of-things, cyber-physical systems, and machine learning algorithms.

Sandwich-type electrochemical aptasensor based on hemin-graphite oxide as a signal label and rGO/MWCNTs/chitosan/carbon quantum dot modified electrode for sensitive detection of Acinetobacter baumannii bacteria

Acinetobacter baumannii (A. baumannii) is a pathogenic bacterium that causes severe infections and its rapid and reliable diagnosis is essential for effective control and treatment. In this study, we present an electrochemical aptasensor based on a signal amplification strategy for the detection of A. baumannii, the high specificity and affinity of the aptamer for the target make it favorable for signal amplification. This allows for a highly sensitive and selective detection of the target. The aptasensor is based on a carbon screen-printed electrode (CSPE) that has been modified with a nanocomposite consisting of multi-walled carbon nanotubes (MWCNTs), reduced graphene oxide (rGO), chitosan (CS), and a synthesized carbon quantum dot (CQD) from CS. Additionally, the self-assembled aptamers were immobilized on hemin-graphite oxide (H-GO) as a signal probe. The composition of the nanocomposite (rGO-MWCNT/CS/CQD) provides high conductivity and stability, facilitating the efficient capture of A. baumannii onto the surface of the aptasensor. Also, aptamer immobilized on Hemin-graphite oxide (H-GO/Aptamer) was utilized as an electrochemical signal reporter probe by H reduction. This approach improved the detection sensitivity and the aptamer surface density for detecting A. baumannii. Furthermore, under optimized experimental conditions, the aptasensor was demonstrated to be capable of detecting A. baumannii with a linear range of (10 - 1 × 107 Colony-forming unit (CFU)/mL) and a limit of detection (LOD) of 1 CFU/mL (σ = 3). One of the key features of this aptasensor is its ability to distinguish between live and dead bacteria cells, which is very important and critical for clinical applications. In addition, we have successfully detected A. baumannii bacteria in healthy human serum and skim milk powder samples provided using the prepared electrochemical aptasensor. The functional groups present in the synthetic CQD, rGO-MWCNT, and chitosan facilitate biomolecule immobilization and enhance stability and activity. The fast electron-transfer kinetics and high conductivity of these materials contribute to improved sensitivity and selectivity. Furthermore, The H-GO/Aptamer composite's large surface area increases the number of immobilized secondary aptamers and enables a more stable structure. This large surface area also facilitates more H loading, leading to signal amplification.

Innovative Graphene-Based Nanocomposites for Improvement of Electrochemical Sensors: Synthesis, Characterization, and Applications

Graphene, renowned for its exceptional physicochemical attributes, has emerged as a favored substrate for integrating a wide array of inorganic and organic materials in scientific endeavors and innovations. Electrochemical graphene-based nanocomposite sensors have been developed by incorporating diverse nanoparticles into graphene, effectively immobilized onto electrodes through various techniques. These graphene-based nanocomposite sensors have effectively detected and quantified various electroactive species in samples. This review delves into using graphene nanocomposites to fabricate electrochemical sensors, leveraging the exceptional electrical, mechanical, and thermal properties inherent to graphene derivatives. These nanocomposites showcase electrocatalytic activity, substantial surface area, superior electrical conductivity, adsorption capabilities, and notable porosity, which are highly advantageous for sensing applications. A myriad of characterization techniques, including Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), BET surface area analysis, and X-ray diffraction (XRD), have proven effective in exploring the properties of graphene nanocomposites and validating the adjustable formation of these nanomaterials with graphene. The applicability of these sensors across various matrices, encompassing environmental, food, and biological domains, has been evaluated through electrochemical measurements, such as cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and differential pulse voltammetry (DPV). This review provides a comprehensive overview of synthesis methods, characterization techniques, and sensor applications pertinent to graphene-based nanocomposites. Furthermore, it deliberates on the challenges and future prospects within this burgeoning field.

Heparin-stabilized gold nanoparticles embedded in graphene for the electrochemical determination of esculetin

A conductive nanocomposite consisting of heparin-stabilized gold nanoparticles embedded in graphene was prepared and characterized to develop an electrochemical sensor for the determination of esculetin in tea and jam samples. The gold nanoparticles were characterized by spectroscopic and microscopic techniques. The different proportions of graphene in the nanocomposite were evaluated and characterized by electrochemical practices. The heterostructure material on the glassy carbon electrode with esculetin showed π-π stacking interactions with an adsorption-controlled process. The voltammetric profile of esculetin using the proposed nanomaterial presented oxidation and reduction peaks at +0.61 and +0.58 V vs. Ag/AgCl, respectively, facilitating the electron transfer with esculetin through the transfer of two moles of protons and two moles of electrons per mole of esculetin. Using optimized conditions and square wave voltammetry, the calibration curve was obtained with two linear ranges, from 0.1 to 20.5 μmol L-1, with a detection limit of 43.0 nmol L-1. The electrochemical sensor showed satisfactory results for repeatability and stability, although interferences were observed in the presence of high concentrations of ascorbic acid or quercetin. The sensor was successfully applied in the determination of esculetin in samples of mulberry jam, white mulberry leaf tea, and white mulberry powder tea, presenting adequate recovery ranges. This directive provides valuable insights for the development of novel electrochemical sensors using heparin-based conductive nanomaterials with improved sensitivity and sensibility.

Electrochemical immunosensing of tumor markers

The rising incidence and mortality rates of cancer have led to a growing need for precise and prompt early diagnostic approaches to effectively combat this disease. However, traditional methods employed for detecting tumor cells, such as histopathological and immunological techniques, are often associated with complex procedures, high analytical expenses, elevated false positive rates, and a dependence on experienced personnel. Tracking tumor markers is recognized as one of the most effective approaches for early detection and prognosis of cancer. While onco-biomarkers can also be produced in normal circumstances, their concentration is significantly elevated when tumors are present. By monitoring the levels of these markers, healthcare professionals can obtain valuable insights into the presence, progression, and response to treatment of cancer, aiding in timely diagnosis and effective management. This review aims to provide researchers with a comprehensive overview of the recent advancements in tumor markers using electrochemical immunosensors. By highlighting the latest developments in this field, researchers can gain a general understanding of the progress made in the utilization of electrochemical immunosensors for detecting tumor markers. Furthermore, this review also discusses the current limitations associated with electrochemical immunosensors and offers insights into paving the way for further improvements and advancements in this area of research.

Potential Application Prospects of Biomolecule-Modified Two-Dimensional Chiral Nanomaterials in Biomedicine

Chirality, one of the most fundamental properties of natural molecules, plays a significant role in biochemical reactions. Nanomaterials with chiral characteristics have superior properties, such as catalytic properties, optoelectronic properties, and photothermal properties, which have significant potential for specific applications in nanomedicine. Biomolecular modifications such as nucleic acids, peptides, proteins, and polysaccharides are sources of chirality for nanomaterials with great potential for application in addition to intrinsic chirality, artificial macromolecules, and metals. Two-dimensional (2D) nanomaterials, as opposed to other dimensions, due to proper surface area, extensive modification sites, drug loading potential, and simplicity of preparation, are prepared and utilized in diagnostic applications, drug delivery research, and tumor therapy. Current advanced studies on 2D chiral nanomaterials for biomedicine are focused on novel chiral development, structural control, and materials sustainability applications. However, despite the advances in biomedical research, chiral 2D nanomaterials still confront challenges such as the difficulty of synthesis, quality control, batch preparation, chiral stability, and chiral recognition and selectivity. This review aims to provide a comprehensive overview of the origins, synthesis, applications, and challenges of 2D chiral nanomaterials with biomolecules as cargo and chiral modifications and highlight their potential roles in biomedicine.

An Electrochemical Immunosensor Based on Chitosan-Graphene Nanosheets for Aflatoxin B1 Detection in Corn

We reported a highly efficient electrochemical immunosensor utilizing chitosan-graphene nanosheets (CS-GNs) nanocomposites for the detection of aflatoxin B1 (AFB1) in corn samples. The CS-GNs nanocomposites, serving as a modifying layer, provide a significant specific surface area and biocompatibility, thereby enhancing both the electron transfer rate and the efficiency of antibody immobilization. The electrochemical characterization was conducted utilizing both differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS). Moreover, the antibody concentration, pH, antibody immobilization time, and immunoreaction time, were optimized. The results showed that the current change (ΔI) before and after the immunoreaction demonstrated a strong linear relationship (R2=0.990) with the AFB1 concentration, as well as good specificity and stability. The linear range extended from 0.05 to 25 ng/mL, with a detection limit of 0.021 ng/mL (S/N=3). The immunosensor exhibited a recovery rate ranging from 97.3% to 101.4% in corn samples, showing a promising performance using an efficient method, and indicating a remarkable prospect for the detection of fungal toxins in grains.

Geminal Dicationic Ionic Liquids (GDILs) and Their Adsorption on Graphene Nanoflakes

In this work, the configuration and stability of 15 geminal dicationic ionic liquids (GDILs) and their adsorption mechanism on the graphene nanoflake (GNF) are investigated using the density functional theory (DFT) method. We find that the interactions of dications ([DAm]+, [DIm]+, [DImDm]+, [DPy]+, and [DPyrr]+)) are stabilized near the anions ([BF4]-, [PF6]-, and [Tf2N]-) in the most stable configurations of GDILs through electrostatic interactions, van der Waals (vdW) interactions, and hydrogen bonding (H-bonding). Our calculations show that the adsorption of the GDILs on the GNF is consistent with the charge transfer and occurs via X···π (X = N, O, F), C-H···π, and π···π noncovalent interactions, leading to a decrease in the strength of the intermolecular interactions between the dications and anions in the GDILs. The thermochemistry calculations reveal that the formation of GDIL@GNF complexes is an exothermic and favorable reaction. The adsorption energy (Eads) calculations show that the highest Eads values for the interaction of GDILs containing [BF4]-, [PF6]-, and [Tf2N]- anions with the GNF are observed for the [DPy][BF4]@GNF (-23.56 kcal/mol), [DPy][PF6]@GNF (-29.29 kcal/mol), and [DPyrr][Tf2N]@GNF (-24.74 kcal/mol) complexes, respectively. Our results show that the adsorption of the GDILs on the GNF leads to the decrease of the chemical potential (μ), chemical hardness (η), and HOMO-LUMO energy gap (Eg) values and an increase in the electrophilicity index (ω) value of the GNF. In addition, the effect of GDIL adsorption on the UV-vis absorption spectrum was studied at the TD-M06-2X/cc-pVDZ level of theory. We find that the adsorption of GDILs results in minimal change in the shape of the main absorption peak (at λ = 363 nm) in the GNF spectrum and only shifts it to higher wavelengths. On the other hand, a new peak appears in the GNF spectrum upon adsorption of [DPy][Y] (Y = [BF4]-, [PF6]-, and [Tf2N]-) due to the relatively strong π···π interactions between the [DPy]+ dication and GNF. Finally, the transition density matrix (TDM) heat maps show that electron transfers related to the excitation states in the GDIL@GNF complexes occur mainly through π(C=C) → π*(C=C) transitions in the GNF and the transitions from [DPy]+ dication to the GNF.

Carbon Nanomaterials for Biomedical Applications: Progress and Outlook

Recent developments in nanoscale materials have found extensive use in various fields, especially in the biomedical industry. Several substantial obstacles must be overcome, particularly those related to nanostructured materials in biomedicine, before they can be used in therapeutic applications. Significant concerns in biomedicine include biological processes, adaptability, toxic effects, and nano-biointerfacial properties. Biomedical researchers have difficulty choosing suitable materials for drug carriers, cancer treatment, and antiviral uses. Carbon nanomaterials are among the various nanoparticle forms that are continually receiving interest for biomedical applications. They are suitable materials owing to their distinctive physical and chemical properties, such as electrical, high-temperature, mechanical, and optical diversification. An individualized, controlled, dependable, low-carcinogenic, target-specific drug delivery system can diagnose and treat infections in biomedical applications. The variety of carbon materials at the nanoscale is remarkable. Allotropes and other forms of the same element, carbon, are represented in nanoscale dimensions. These show promise for a wide range of applications. Carbon nanostructured materials with exceptional mechanical, electrical, and thermal properties include graphene and carbon nanotubes. They can potentially revolutionize industries, including electronics, energy, and medicine. Ongoing investigation and expansion efforts continue to unlock possibilities for these materials, making them a key player in shaping the future of advanced technology. Carbon nanostructured materials explore the potential positive effects of reducing the greenhouse effect. The current state of nanostructured materials in the biomedical sector is covered in this review, along with their synthesis techniques and potential uses.

A Multienzyme Reaction-Mediated Electrochemical Biosensor for Sensitive Detection of Organophosphorus Pesticides

Ethephon (ETH), a commonly employed growth regulator, poses potential health risks due to its residue in fruits and vegetables, leading to both acute and subchronic toxicity. However, the detection accuracy of ETH is compromised by the color effects of the samples during the detection process. In this work, a multienzyme reaction-mediated electrochemical biosensor (MRMEC) was developed for the sensitive, rapid, and color-interference-resistant determination of ETH. Nanozymes Fe3O4@Au-Pt and graphene nanocomplexes (GN-Au NPs) were prepared as catalysts and signal amplifiers for MRMEC. Acetylcholinesterase (AChE), acetylcholine (ACh), and choline oxidase (CHOx) form a cascade enzyme reaction to produce H2O2 in an electrolytic cell. Fe3O4@Au-Pt has excellent peroxidase-like activity and can catalyze the oxidation of 3,3',5,5'-tetramethvlbenzidine (TMB) in the presence of H2O2, resulting in a decrease in the characteristic peak current of TMB. Based on the inhibitory effect of ETH on AChE, the differential pulse voltammetry (DPV) current signal of TMB was used to detect ETH, offering the limit of detection (LOD) of 2.01 nmol L-1. The MRMEC method effectively analyzed ETH levels in mangoes, showing satisfactory precision (coefficient of variations, 2.88-15.97%) and recovery rate (92.18-110.72%). This biosensor holds promise for detecting various organophosphorus pesticides in food samples.

Recent Trends in Chemical Sensors for Detecting Toxic Materials

Industrial development has led to the widespread production of toxic materials, including carcinogenic, mutagenic, and toxic chemicals. Even with strict management and control measures, such materials still pose threats to human health. Therefore, convenient chemical sensors are required for toxic chemical monitoring, such as optical, electrochemical, nanomaterial-based, and biological-system-based sensors. Many existing and new chemical sensors have been developed, as well as new methods based on novel technologies for detecting toxic materials. The emergence of material sciences and advanced technologies for fabrication and signal-transducing processes has led to substantial improvements in the sensing elements for target recognition and signal-transducing elements for reporting interactions between targets and sensing elements. Many excellent reviews have effectively summarized the general principles and applications of different types of chemical sensors. Therefore, this review focuses on chemical sensor advancements in terms of the sensing and signal-transducing elements, as well as more recent achievements in chemical sensors for toxic material detection. We also discuss recent trends in biosensors for the detection of toxic materials.

Label-free genosensing of dengue serotypes with an electrodeposited reduced graphene oxide-tris(bipyridine)ruthenium(II)

Constructing a label-free electrochemical transducer platform without compromising inherent biocompatibility against specific bioreceptor remains challenging, particularly probing nucleic acid hybridization at electrode interface without external redox-mediator. Here, we show that electrochemically reduced graphene oxide-tris(bipyridine)ruthenium(II) (ErGO-TBR) nanosheets electrodeposited on carbon screen printed electrode can quantify hybridization of clinically important target sequences specific to serotypes of dengue virus (DENV) non-structural 1 (NS1) protein. Different variables including deposition potential, time, and electrolytic composition were optimized for fabrication of label-free transducer platform. Structural and electrochemical properties of ErGO-TBR/SPE were comprehensively elucidated using microscopic and spectroscopic techniques. Electrochemical quartz crystal microbalance (EQCM) analysis reveals the growth of electrodeposited redox-active species on the electrode interface. Surface functional group investigations suggested that TBR deposited on the basal and edges of ErGO substrate via electrostatic and π-π interactions. Functionalization of bio-affinity layer (B) on ErGO-TBR/SPE enables better loading of probe DNA (PDNA) toward specific detection of DENV target DNA (TDNA) with an ultralow detection limit promising for clinical diagnosis. Scalable chronoamperometry-based redox-active surface growth, customizable bioactivation strategy and external mediator-less probing of nucleic acid hybridization make the present system suitable for other translational application in healthcare diagnosis.

Biomass-derived 2D carbon materials: structure, fabrication, and application in electrochemical sensors

Biomass, a renewable hydrocarbon, is one of the favorable sources of advanced carbon materials owing to its abundant resources and diverse molecular structures. Biomass-based two-dimensional carbon nanomaterials (2D-BC) have attracted extensive attention due to their tunable structures and properties, and have been widely used in the design and fabrication of electrochemical sensing platforms. This review embarks on the thermal conversion process of biomass from different sources and the synthesis strategy of 2D-BC materials. The affinity between 2D-BC structure and properties is emphasized. The recent progress in 2D-BC-based electrochemical sensors for health and environmental monitoring is also presented. Finally, the challenges and future development directions related to such materials are proposed in order to promote their further application in the field of electrochemical sensing.

Development of a Novel H-Shaped Electrochemical Aptasensor for Detection of Hg2+ Based on Graphene Aerogels-Au Nanoparticles Composite

Hg2+, a highly toxic heavy metal, poses significant environmental and health risks, necessitating rapid detection methods. In this study, we employed an electrochemical aptasensor for rapid and sensitive detection of Hg2+ based on DNA strands (H2 and H3) immobilized graphene aerogels-Au nanoparticles (GAs-AuNPs) hybrid recognition interface and exonuclease III (Exo III)-mediated cyclic amplification. Firstly, Gas-AuNPs were modified on the surface of the ITO electrode to form a sensing interface to increase DNA loading and accelerate electron transfer. Then, DNA helper was generated with the addition of Hg2+ via Exo III-mediated cycling. Finally, the hairpin structures of H2 and H3 were opened with the DNA helper, and then the methylene blue (MB) functionalized DNA (A1 and A2) combined with the H2 and H3 to form an H-shaped structure. The current response of MB as an electrochemical probe was proportional to the concentration of Hg2+. Under optimal conditions, the aptasensor showed excellent performance for Hg2+, achieving a linear range from 1 fM to 10 nM and a detection limit of 0.16 fM. Furthermore, the aptasensor was used to detect Hg2+ in spiked milk samples, achieving a high recovery rate and demonstrating promising application prospects.

Ionic liquids revolutionizing biomedicine: recent advances and emerging opportunities

Ionic liquids (ILs), due to their inherent structural tunability, outstanding miscibility behavior, and excellent electrochemical properties, have attracted significant research attention in the biomedical field. As the application of ILs in biomedicine is a rapidly emerging field, there is still a need for systematic analyses and summaries to further advance their development. This review presents a comprehensive survey on the utilization of ILs in the biomedical field. It specifically emphasizes the diverse structures and properties of ILs with their relevance in various biomedical applications. Subsequently, we summarize the mechanisms of ILs as potential drug candidates, exploring their effects on various organisms ranging from cell membranes to organelles, proteins, and nucleic acids. Furthermore, the application of ILs as extractants and catalysts in pharmaceutical engineering is introduced. In addition, we thoroughly review and analyze the applications of ILs in disease diagnosis and delivery systems. By offering an extensive analysis of recent research, our objective is to inspire new ideas and pathways for the design of innovative biomedical technologies based on ILs.

Strategies and Applications of Graphene and Its Derivatives-Based Electrochemical Sensors in Cancer Diagnosis

Graphene is an emerging nanomaterial increasingly being used in electrochemical biosensing applications owing to its high surface area, excellent conductivity, ease of functionalization, and superior electrocatalytic properties compared to other carbon-based electrodes and nanomaterials, enabling faster electron transfer kinetics and higher sensitivity. Graphene electrochemical biosensors may have the potential to enable the rapid, sensitive, and low-cost detection of cancer biomarkers. This paper reviews early-stage research and proof-of-concept studies on the development of graphene electrochemical biosensors for potential future cancer diagnostic applications. Various graphene synthesis methods are outlined along with common functionalization approaches using polymers, biomolecules, nanomaterials, and synthetic chemistry to facilitate the immobilization of recognition elements and improve performance. Major sensor configurations including graphene field-effect transistors, graphene modified electrodes and nanocomposites, and 3D graphene networks are highlighted along with their principles of operation, advantages, and biosensing capabilities. Strategies for the immobilization of biorecognition elements like antibodies, aptamers, peptides, and DNA/RNA probes onto graphene platforms to impart target specificity are summarized. The use of nanomaterial labels, hybrid nanocomposites with graphene, and chemical modification for signal enhancement are also discussed. Examples are provided to illustrate applications for the sensitive electrochemical detection of a broad range of cancer biomarkers including proteins, circulating tumor cells, DNA mutations, non-coding RNAs like miRNA, metabolites, and glycoproteins. Current challenges and future opportunities are elucidated to guide ongoing efforts towards transitioning graphene biosensors from promising research lab tools into mainstream clinical practice. Continued research addressing issues with reproducibility, stability, selectivity, integration, clinical validation, and regulatory approval could enable wider adoption. Overall, graphene electrochemical biosensors present powerful and versatile platforms for cancer diagnosis at the point of care.

Immobilization of Enzyme Electrochemical Biosensors and Their Application to Food Bioprocess Monitoring

Electrochemical biosensors based on immobilized enzymes are among the most popular and commercially successful biosensors. The literature in this field suggests that modification of electrodes with nanomaterials is an excellent method for enzyme immobilization, which can greatly improve the stability and sensitivity of the sensor. However, the poor stability, weak reproducibility, and limited lifetime of the enzyme itself still limit the requirements for the development of enzyme electrochemical biosensors for food production process monitoring. Therefore, constructing sensing technologies based on enzyme electrochemical biosensors remains a great challenge. This article outlines the construction principles of four generations of enzyme electrochemical biosensors and discusses the applications of single-enzyme systems, multi-enzyme systems, and nano-enzyme systems developed based on these principles. The article further describes methods to improve enzyme immobilization by combining different types of nanomaterials such as metals and their oxides, graphene-related materials, metal-organic frameworks, carbon nanotubes, and conducting polymers. In addition, the article highlights the challenges and future trends of enzyme electrochemical biosensors, providing theoretical support and future perspectives for further research and development of high-performance enzyme chemical biosensors.

Modification of electrodes with polymer nanocomposites: Application to the simultaneous determination of Zn(II), Cd(II), and Cu(II) in water samples

Currently, there is a need for fast and sensitive analytical methods for monitoring metals in water due to the progressive increase in the presence of metal ions in the environment. These metals reach the environment mainly from industrial activity and heavy metals are non-biodegradable. The present work evaluates different polymeric nanocomposites to carry out the simultaneous electrochemical determination of Cu, Cd, and Zn in water samples. Screen-printed carbon electrodes (SPCE) were modified with the nanocomposites, which were obtained by a mixture of graphene, graphite oxide, and polymers, such as polyethyleneimide, gelatin, and chitosan. These polymers have amino groups in their matrix, giving the nanocomposite the ability to retain divalent cations. However, the availability of these groups plays a fundamental role in the retention of these metals. The modified SPCEs were characterized by scanning electron microscopy, Fourier-transform infrared spectroscopy, electrochemical impedance spectroscopy, and cyclic voltammetry. The electrode that presented the best performance was selected to determine the concentration of metal ions in water samples by square-wave anodic stripping voltammetry. The obtained detection limits were 0.23 μg L^-1, 0.53 μg L^-1, and 1.52 μg L^-1 for Zn(II), Cd(II), and Cu(II), respectively, with a lineal range of 0.1-50 μg L^-1. The obtained results made it possible to conclude that the method developed using the SPCE modified with the polymeric nanocomposite presented adequate LODs, reasonable sensitivity, selectivity, and reproducibility. Besides, this platform is an excellent tool for developing devices to simultaneously determine heavy metals in environmental samples.

Carbon-Based Electrochemical (Bio)sensors for the Detection of Carbendazim: A Review

Carbendazim, a fungicide widely used in agriculture, has been classified as a hazardous chemical by the World Health Organization due to its environmental persistence. It is prohibited in several countries; therefore, detecting it in food and environmental samples is highly necessary. A reliable, rapid, and low-cost method uses electrochemical sensors and biosensors, especially those modified with carbon-based materials with good analytical performance. In this review, we summarize the use of carbon-based electrochemical (bio)sensors for detecting carbendazim in environmental and food matrixes, with a particular interest in the role of carbon materials. Focus on publications between 2018 and 2023 that have been describing the use of carbon nanotubes, carbon nitride, graphene, and its derivatives, and carbon-based materials as modifiers, emphasizing the analytical performance obtained, such as linear range, detection limit, selectivity, and the matrix where the detection was applied.

Synthesis and characterization of cylindrical electrode with sucrose binder as advanced electrode materials for copper 3D-electro-oxidation

This study produced a biomass-based cylindrical electrode containing sucrose (an organic binder). The Cu2+ removal performance of the synthesized sucrose-bonded cylindrical electrode was evaluated in a 3-phase 3-dimensional electro-oxidation reactor (3D-EO) and the classical electro-oxidation method (2D-EO). Sodium Dodecyl Sulfate (SDs) was grafted onto activated carbon and used as microelectrode in 3D-EO reactors. SDs grafting resulted in a 57% reduction in the micropores of activated carbon. Therefore, the surface area of carbon after grafting decreased from 1328 m2/g to 580 m2/g. The sucrose-bonded cylindrical electrode has a rich carbon structure and consists of 84.04 wt% C, 12.10 wt% O and 3.20 wt%Si. According to CV measurement, the sucrose-bonded cylindrical electrode gives a surface reaction against Cu2+ at voltages lower than -0.62 V. Increasing the potential difference from 1V to 3V in 2D-EO and 3D-EO processes led to the removal of Cu2+ from the solution. The 3D-EO reactor achieved a removal rate of 87.12% at 3V. The 100 ppm solution was treated with a 3D-EO reactor containing 6 g/L of PC/SDs400Ws for 60 min, successfully removing 91.22% of Cu2+.

Electrochemical Determination of Epinephrine in Pharmaceutical Preparation Using Laponite Clay-Modified Graphene Inkjet-Printed Electrode

Epinephrine (EP, also called adrenaline) is a compound belonging to the catecholamine neurotransmitter family. It can cause neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, Huntington's disease and amyotrophic lateral sclerosis. This work describes an amperometric sensor for the electroanalytical detection of EP by using an inkjet-printed graphene electrode (IPGE) that has been chemically modified by a thin layer of a laponite (La) clay mineral. The ion exchange properties and permeability of the chemically modified electrode (denoted La/IPGE) were evaluated using multi-sweep cyclic voltammetry, while its charge transfer resistance was determined by electrochemical impedance spectroscopy. The results showed that La/IPGE exhibited higher sensitivity to EP compared to the bare IPGE. The developed sensor was directly applied for the determination of EP in aqueous solution using differential pulse voltammetry. Under optimized conditions, a linear calibration graph was obtained in the concentration range between 0.8 µM and 10 μM. The anodic peak current of EP was directly proportional to its concentration, leading to detection limits of 0.34 μM and 0.26 μM with bare IPGE and La/IPGE, respectively. The sensor was successfully applied for the determination of EP in pharmaceutical preparations. Recovery rates and the effects of interfering species on the detection of EP were evaluated to highlight the selectivity of the elaborated sensor.

Graphene and gold nanoparticle-based bionanocomposite for the voltammetric determination of bisphenol A in (micro)plastics

The monitoring of endocrine disruptors in the environment is one of the main strategies in the investigation of potential risks associated with exposure to these chemicals. Bisphenol A is one of the most prevalent endocrine-disrupting compounds and is prone to leaching out from polycarbonate plastic in both freshwater and marine environments. Additionally, microplastics also can leach out bisphenol A during their fragmentation in the water environment. In the quest for a highly sensitive sensor to determine bisphenol A in different matrices, an innovative bionanocomposite material has been achieved. This material is composed of gold nanoparticles and graphene, and was synthesized using a green approach that utilized guava (Psidium guajava) extract for reduction, stabilization, and dispersion purposes. Transmission electron microscopy images revealed well-spread gold nanoparticles with an average diameter of 31 nm on laminated graphene sheets in the composite material. An electrochemical sensor was developed by depositing the bionanocomposite onto a glassy carbon surface, which displayed remarkable responsiveness towards bisphenol A. Experimental conditions such as the amount of graphene, extract: water ratio of bionanocomposite and pH of the supporting electrolyte were optimized to improve the electrochemical performance. The modified electrode displayed a marked improvement in current responses for the oxidation of bisphenol A as compared to the uncovered glassy carbon electrode. A calibration plot was established for bisphenol A in 0.1 mol L^-1 Britton-Robinson buffer (pH 4.0), and the detection limit was determined to equal to 15.0 nmol L^-1. Recovery data from 92 to 109% were obtained in (micro)plastics samples using the electrochemical sensor and were compared with UV-vis spectrometry, demonstrating its successful application with accurate responses.

Calf thymus ds-DNA intercalation with pendimethalin herbicide at the surface of ZIF-8/Co/rGO/C3N4/ds-DNA/SPCE; A bio-sensing approach for pendimethalin quantification confirmed by molecular docking study

Pendimethalin (PND) is a herbicide that is regarded to be possibly carcinogenic to humans and toxic to the environment. Herein, we fabricated a highly sensitive DNA biosensor based on ZIF-8/Co/rGO/C₃N₄ nanohybrid modification of a screen-printed carbon electrode (SPCE) to monitor PND in real samples. The layer-by-layer fabrication pathway was conducted to construct ZIF-8/Co/rGO/C₃N₄/ds-DNA/SPCE biosensor. The physicochemical characterization techniques confirmed the successful synthesis of ZIF-8/Co/rGO/C₃N₄ hybrid nanocomposite, as well as the appropriate modification of the SPCE surface. The utilization of ZIF-8/Co/rGO/C₃N₄ nanohybrid as a modifier was analyzed using. The electrochemical impedance spectroscopy results showed that the modified SPCE exhibited significantly lowered charge transfer resistance due to the enhancement of its electrical conductivity and facilitation of the transfer of charged particles. The proposed biosensor successfully quantified PND in a wide concentration range of 0.01-35 μM, with a limit of detection (LOD) value of 8.0 nM. The PND monitoring capability of the fabricated biosensor in real samples including rice, wheat, tap, and river water samples was verified with a recovery range of 98.2-105.6%. Moreover, to predict the interaction sites of PND herbicide with DNA, the molecular docking study was performed between the PND molecule and two sequence DNA fragments and confirmed the experimental findings. This research sets the stage for developing highly sensitive DNA biosensors that will be used to monitor and quantify toxic herbicides in real samples by fusing the advantages of nanohybrid structures with crucial knowledge from a molecular docking investigation.

Functional Nanomaterials Enhancing Electrochemical Biosensors as Smart Tools for Detecting Infectious Viral Diseases

Electrochemical biosensors are known as analytical tools, guaranteeing rapid and on-site results in medical diagnostics, food safety, environmental protection, and life sciences research. Current research focuses on developing sensors for specific targets and addresses challenges to be solved before their commercialization. These challenges typically include the lowering of the limit of detection, the widening of the linear concentration range, the analysis of real samples in a real environment and the comparison with a standard validation method. Nowadays, functional nanomaterials are designed and applied in electrochemical biosensing to support all these challenges. This review will address the integration of functional nanomaterials in the development of electrochemical biosensors for the rapid diagnosis of viral infections, such as COVID-19, middle east respiratory syndrome (MERS), influenza, hepatitis, human immunodeficiency virus (HIV), and dengue, among others. The role and relevance of the nanomaterial, the type of biosensor, and the electrochemical technique adopted will be discussed. Finally, the critical issues in applying laboratory research to the analysis of real samples, future perspectives, and commercialization aspects of electrochemical biosensors for virus detection will be analyzed.

Electrochemical Sensing of H2O2 by Employing a Flexible Fe3O4/Graphene/Carbon Cloth as Working Electrode

We report the synthesis of Fe₃O₄/graphene (Fe₃O₄/Gr) nanocomposite for highly selective and highly sensitive peroxide sensor application. The nanocomposites were produced by a modified co-precipitation method. Further, structural, chemical, and morphological characterization of the Fe₃O₄/Gr was investigated by standard characterization techniques, such as X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM) and high-resolution TEM (HRTEM), Fourier transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS). The average crystal size of Fe₃O₄ nanoparticles was calculated as 14.5 nm. Moreover, nanocomposite (Fe₃O₄/Gr) was employed to fabricate the flexible electrode using polymeric carbon fiber cloth or carbon cloth (pCFC or CC) as support. The electrochemical performance of as-fabricated Fe₃O₄/Gr/CC was evaluated toward H₂O₂ with excellent electrocatalytic activity. It was found that Fe₃O₄/Gr/CC-based electrodes show a good linear range, high sensitivity, and a low detection limit for H₂O₂ detection. The linear range for the optimized sensor was found to be in the range of 10-110 μM and limit of detection was calculated as 4.79 μM with a sensitivity of 0.037 µA μM^-1 cm^-2. The cost-effective materials used in this work as compared to noble metals provide satisfactory results. As well as showing high stability, the proposed biosensor is also highly reproducible.

Non-enzymatic electrochemical detection of creatinine based on a glassy carbon electrode modified with a Pd/Cu2O decorated polypyrrole (PPy) nanocomposite: an analytical approach

The major constraints of standard enzymatic biosensors are poor long-term storage stability and high cost. Hence, there is extensive research towards fabrication of reliable enzymeless biosensors based on nanomaterials. In this paper, we present the development of an enzymeless electrochemical biosensor for highly precise detection of creatinine. This involves the use of a simple yet effective alternative to the commonly utilized Pd/Cu₂O/PPy nanocomposite, which was characterized by different analytical methods. The present electrochemical sensor provides a wide detection range (0.1 to 150 μM), low detection limit (0.05 μM) and high sensitivity (0.207 μA), and is capable of detecting the creatinine level in human urine samples, which are inexpensive. The results are reproducible, and the sensor is stable. The sensor demonstrates good electrocatalytic activity and selectivity towards the detection of creatinine in the presence of various other similar biological entities. When compared to other existing counterparts, the electrocatalytic behaviour of the present sensor is comparable, if not better. So, the present electrochemical sensor for creatinine might be employed as a long-term diagnostic alternative.

Carbon-based biosensors from graphene family to carbon dots: A viewpoint in cancer detection

According to the latest report by International Agency for Research on Cancer, 19.3 million new cancer cases and 10 million cancer deaths were globally reported in 2020. Early diagnosis can reduce these numbers significantly, and biosensors have appeared to be a solution to this problem as, unlike the traditional methods, they have low cost, rapid process, and do not need experts present on site for use. These devices have been incorporated to detect many cancer biomarkers and measure cancer drug delivery. To design these biosensors, a researcher must know about their different types, properties of nanomaterials, and cancer biomarkers. Among all types of biosensors, electrochemical and optical biosensors are the most sensitive and promising sensors for detecting complicated diseases like cancer. The carbon-based nanomaterial family has attracted lots of attention due to their low cost, easy preparation, biocompatibility, and significant electrochemical and optical properties. In this review, we have discussed the application of graphene and its derivatives, carbon nanotubes (CNTs), carbon dots (CDs), and fullerene (C60), for designing different electrochemical and optical cancer-detecting biosensors. Furthermore, the application of these carbon-based biosensors for detecting seven widely studied cancer biomarkers (HER2, CEA, CA125, VEGF, PSA, Alpha-fetoprotein, and miRNA21) is reviewed. Finally, various fabricated carbon-based biosensors for detecting cancer biomarkers and anticancer drugs are comprehensively summarized as well.

A label-free electrochemical immunosensor based on Au-BSN-rGO for highly-sensitive detection of β-amyloid 1-42

A label-free electrochemical immunosensor for high-sensitive detection of β-amyloid 1-42 (Aβ 1-42) was constructed based on Au-modified B, S, and N co-doped reduced graphene oxide (Au-BSN-rGO). The electronic structure of Au-BSN-rGO was investigated by first-principles calculations, which showed that the band gap of graphene was opened, thus improving its electrical conductivity. Moreover, Au-BSN-rGO was successfully prepared and characterized, and the obtained results discovered that it could be used as a signal amplifier for immunosensors due to the advantages of the good electrochemical characteristics and enormous surface area of BSN-rGO and the accelerated electron transfer ability of Au NPs. Furthermore, the label-free electrochemical immunosensor had a linear detection range of 0.1 pg mL^-1-10 ng mL^-1 and a detection limit of 0.072 pg mL^-1, and it had good specificity, stability, and reproducibility. Also, this immunosensor showed recoveries of 89%-109% with an RSD of 2.61%-4.19% for detecting Aβ 1-42 in actual sample analysis. Therefore, the label-free electrochemical immunosensor based on Au-BSN-rGO should have a promising clinical application prospect for detecting Aβ 1-42.

Carbon Electrode-Based Biosensing Enabled by Biocompatible Surface Modification with DNA and Proteins

Modification of electrodes with biomolecules is an essential first step for the development of bioelectrochemical systems, which are used in a variety of applications ranging from sensors to fuel cells. Gold is often used because of its ease of modification with thiolated biomolecules, but carbon screen-printed electrodes (SPEs) are gaining popularity due to their low cost and fabrication from abundant resources. However, their effective modification with biomolecules remains a challenge; the majority of work to-date relies on nonspecific adhesion or broad amide bond formation to chemical handles on the electrode surface. By combining facile electrochemical modification to add an aniline handle to electrodes with a specific and biocompatible oxidative coupling reaction, we can readily modify carbon electrodes with a variety of biomolecules. Importantly, both proteins and DNA maintain bioactive conformations following coupling. We have then used biomolecule-modified electrodes to generate microbial monolayers through DNA-directed immobilization. This work provides an easy, general strategy to modify inexpensive carbon electrodes, significantly expanding their potential as bioelectrochemical systems.

Recent Advances in Microfluidics-Based Electrochemical Sensors for Foodborne Pathogen Detection

Using pathogen-infected food that can be unhygienic can result in severe diseases and an increase in mortality rate among humans. This may arise as a serious emergency problem if not appropriately restricted at this point of time. Thus, food science researchers are concerned with precaution, prevention, perception, and immunity to pathogenic bacteria. Expensive, elongated assessment time and the need for skilled personnel are some of the shortcomings of the existing conventional methods. Developing and investigating a rapid, low-cost, handy, miniature, and effective detection technology for pathogens is indispensable. In recent times, there has been a significant scope of interest for microfluidics-based three-electrode potentiostat sensing platforms, which have been extensively used for sustainable food safety exploration because of their progressively high selectivity and sensitivity. Meticulously, scholars have made noteworthy revolutions in signal enrichment tactics, measurable devices, and portable tools, which can be used as an allusion to food safety investigation. Additionally, a device for this purpose must incorporate simplistic working conditions, automation, and miniaturization. In order to meet the critical needs of food safety for on-site detection of pathogens, point-of-care testing (POCT) has to be introduced and integrated with microfluidic technology and electrochemical biosensors. This review critically discusses the recent literature, classification, difficulties, applications, and future directions of microfluidics-based electrochemical sensors for screening and detecting foodborne pathogens.

Microporous carbon for fast and simple electrochemical detection of imidacloprid insecticide in fruit and water samples

Herein, a fast and sensitive electrochemical sensor was developed for imidacloprid detection using low-cost disposable microporous carbon screen-printed electrodes. The electrochemical behaviour of imidacloprid at the microporous material was investigated in detail. The developed sensor allowed imidacloprid detection in the linear range of 0.00-1.00 mM with a sensitivity of 14.43 ± 0.42 μA mM^-1 and a detection limit of 2.54 μM (3s _B/m). The sensor showed excellent selectivity and high tolerance to possible interference from other tested insecticides and ions. Excellent repeatability (3.42%, n = 3) and reproducibility (2.23%, n = 3) were demonstrated. Application of the sensor in various fruit and water samples without any treatment showed 96.2-103.0% recoveries. The developed sensor further revealed that the most effective method for removing imidacloprid residue from fruit samples was via washing with a mixture of 5% w/v NaCl and 5% w/v bicarbonate at 40 °C.

Electrochemical Sensor Based on a Composite of Reduced Graphene Oxide and Molecularly Imprinted Copolymer of Polyaniline-Poly(o-phenylenediamine) for Ciprofloxacin Determination: Fabrication, Characterization, and Performance Evaluation

Contamination of antibiotics in water is a major cause of antibiotic resistance (ABR) in pathogens that endangers human health and food security worldwide. Ciprofloxacin (CIP) is a synthetic fluoroquinolone (FQ) antibiotic and is reportedly present in surface water at a concentration exceeding the ecotoxicological predicted no-effect concentration in some areas. This study fabricated a CIP sensor using an electropolymerized molecularly imprinted polymer (MIP) of polyaniline (PANI) and poly(o-phenylenediamine) (o-PDA) with CIP recognition sites. The MIP was coated on a reduced graphene oxide (rGO)-modified glassy carbon electrode (rGO/GCE) and operated under a differential pulse voltammetry (DPV) mode for CIP detection. The sensor exhibited an excellent response from 1.0 × 10^-9 to 5.0 × 10^-7 mol L^-1 CIP, showing a sensor detection limit and sensitivity of 5.28 × 10^-11 mol L^-1 and 5.78 μA mol^-1 L, respectively. The sensor's sensitivity for CIP was 1.5 times higher than that of the other tested antibiotics, including enrofloxacin (ENR), ofloxacin (OFX), sulfamethoxazole (SMZ), and piperacillin sodium salt (PIP). The reproducibility and reusability of the sensor devices were also studied.

Sensitive detection of 4-nitrophenol based on pyridine diketopyrrolopyrrole-functionalized graphene oxide direct electrochemical sensor

For highly sensitive detection of 4-nitrophenol (4-NP) in the environment, a novel pyridine diketopyrrolopyrrole-functionalized graphene oxide (PDPP-GO) composite was constructed for the first time by an improved Hummers' method. Herein, PDPP was completely dissolved in sulfuric acid (6 mol L^-1) and reacted with GO, promoting PDPP evenly adhering to the GO surface. Moreover, the specific surface area increased from 15.51 to 22.033 m² g^-1. Infrared spectroscopy and X-ray photoelectron spectroscopy simultaneously demonstrated that PDPP was bound to GO by the strong intermolecular hydrogen bonding and π-π stacking conjugation. During the cyclic voltammetry test, the PDPP-GO coated glassy carbon electrode (PDPP-GO/GCE) direct electrochemical sensor gave expression to the best electrocatalytic activity for 4-nitrophenol detection than GO/GCE and bare GCE. Under optimization conditions, the as-prepared PDPP-GO/GCE sensor brought out remarkable sensitivities of 18.54 (0.5-50 μM) and 6.61 μA μM^-1 cm^-2 (50-163 μM) in the linear detection of 4-NP. Besides, a low detection limit of 0.10 μM, reliable long-term stability, excellent selectivity, and reproducibility were obtained. In the real sample test, the PDPP-GO/GCE demonstrated sensitive and reliable determination.

Recent advances in determination applications of emerging films based on nanomaterials

Sensitive and facile detection of analytes is crucial in various fields such as agriculture production, food safety, clinical diagnosis and therapy, and environmental monitoring. However, the synergy of complicated sample pretreatment and detection is an urgent challenge. By integrating the inherent porosity, processability and flexibility of films and the diversified merits of nanomaterials, nanomaterial-based films have evolved as preferred candidates to meet the above challenge. Recent years have witnessed the flourishment of films-based detection technologies due to their unique porous structures and integrated physical/chemical merits, which favors the separation/collection and detection of analytes in a rapid, efficient and facile way. In particular, films based on nanomaterials consisting of 0D metal-organic framework particles, 1D nanofibers and carbon nanotubes, and 2D graphene and analogs have drawn increasing attention due to incorporating new properties from nanomaterials. This paper summarizes the progress of the fabrication of emerging films based on nanomaterials and their detection applications in recent five years, focusing on typical electrochemical and optical methods. Some new interesting applications, such as point-of-care testing, wearable devices and detection chips, are proposed and emphasized. This review will provide insights into the integration and processability of films based on nanomaterials, thus stimulate further contributions towards films based on nanomaterials for high-performance analytical-chemistry-related applications.

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.

The SHERLOCK Platform: An Insight into Advances in Viral Disease Diagnosis

Persistence and prevalence of microbial diseases (pandemics, epidemics) is the most alarming threats to the human resulting in huge health and economic losses. Rapid detection and understanding of the disease dynamics by molecular biotechnology tools allow for robust reporting, treatment and control of diseases. As per WHO, the optimal diagnostic approach should be quick, specific, sensitive, without a stringed instrument, and low cost. The drawbacks of traditional detection techniques promote the use of CRISPR-mediated nucleic acid detection methods such as SHERLOCK as detection method. It takes advantage of the unexpected in vitro features of CRISPR-Cas system to develop field-deployable sensitive detection tools. Previously, CRISPR-mediated diagnostic methods have extensively been reviewed particularly for SARS-COV-2 detection, but it fails to provide the insight into advances of this technique. This study is the first attempt to review the advances of SHERLOCK approach as diagnostic tool for viral diseases detection. Variations of SHERLOCK mechanism for improved efficiency are discussed. Particularly integrated SHERLOCK approaches in terms of extraction-free assay and Bluetooth-enabled detection are reviewed to access their feasibility for the development of simpler and cost-effective diagnostic toolkits. Insight in to perks and limitations of diagnostic methods indicates its potential as ultimate diagnostic instrument for disease management.

Mechanically Enhanced Nanocrystalline Cellulose/Reduced Graphene Oxide/Polyethylene Glycol Electrically Conductive Composite Film

Traditional conductive materials do not meet the increasing requirements of electronic products because of such materials' high rigidity, poor flexibility, and slow biodegradation after disposal. Preparing flexible conductive materials with excellent mechanical properties is an active area of research. The key to flexible conductive materials lies in the combination of the polymer matrix and conductive components. This combination can be achieved by making a film of renewable nano-microcrystalline cellulose (NCC) and reduced graphene oxide (rGO) with excellent electrical conductivity-by simple filtration and introducing polyethylene glycol (PEG) to enhance the functionality of the composite film. Graphene imparted conductivity to the composite film, which reached 5.67 S·m^-1. A reinforced NCC/rGO/PEG-4 composite film with a thickness of only 21 μm exhibited a tensile strength of 30.56 MPa, which was 83% higher than that of the sample without PEG (16.71 MPa), and toughness of 727.18 kJ·m^-3, which was about 132% higher than that of the control sample (NCC/rGO, 313.86 kJ·m^-3). This ultra-thin conductive composite film-which can be prepared simply, consists of environmentally sustainable and biodegradable raw materials, and exhibits excellent mechanical properties-has substantial potential for applications in e.g., flexible electronic wearable devices, electrodes, and capacitors.

Nanomaterials-Based Ion-Imprinted Electrochemical Sensors for Heavy Metal Ions Detection: A Review

Heavy metal ions (HMIs) pose a serious threat to the environment and human body because they are toxic and non-biodegradable and widely exist in environmental ecosystems. It is necessary to develop a rapid, sensitive and convenient method for HMIs detection to provide a strong guarantee for ecology and human health. Ion-imprinted electrochemical sensors (IIECSs) based on nanomaterials have been regarded as an excellent technology because of the good selectivity, the advantages of fast detection speed, low cost, and portability. Electrode surfaces modified with nanomaterials can obtain excellent nano-effects, such as size effect, macroscopic quantum tunneling effect and surface effect, which greatly improve its surface area and conductivity, so as to improve the detection sensitivity and reduce the detection limit of the sensor. Hence, the present review focused on the fundamentals and the synthetic strategies of ion-imprinted polymers (IIPs) and IIECSs for HMIs detection, as well as the applications of various nanomaterials as modifiers and sensitizers in the construction of HMIIECSs and the influence on the sensing performance of the fabricated sensors. Finally, the potential challenges and outlook on the future development of the HMIIECSs technology were also highlighted. By means of the points presented in this review, we hope to provide some help in further developing the preparation methods of high-performance HMIIECSs and expanding their potential applications.

Metal-organic framework-derived porous ternary ZnCo2O4 nanoplate arrays grown on carbon cloth for simultaneous electrochemical determination of ascorbic acid, dopamine, and uric acid

Metal-organic frameworks derived from ternary metal oxide directly grown on the conductive substrate have attracted great interest in electrochemical sensing. In this work, metal-organic framework-derived ternary ZnCo₂O₄ nanoplate arrays that were grown on carbon cloth (ZnCo₂O₄ NA/CC) are fabricated and applied for the electrochemical determination of ascorbic acid (AA), dopamine (DA), and uric acid (UA). Field emission scanning electron microscope (FESEM) reveals that a network-like CC substrate is covered with considerable nanoplate arrays, presenting a large specific area. X-ray photoelectron spectroscopy (XPS) demonstrates the nanoplate arrays to be composed of ZnCo₂O₄. Benefiting from the unique array morphology and ternary element composition, the ZnCo₂O₄ NA/CC shows desirable performances for simultaneous detection of AA, DA, and UA. The individual detection limits are 7.14 μM for AA, 0.25 μM for DA, and 0.33 μM for UA. Additionally, the ZnCo₂O₄ NA/CC is successfully applied for the quantitative determination of AA, DA, and UA in spiked serum samples, showing its great application potential.

Sodium Dodecyl Sulfate-Mediated Graphene Sensor for Electrochemical Detection of the Antibiotic Drug: Ciprofloxacin

The present study involves detecting and determining CIP by a new electrochemical sensor based on graphene (Gr) in the presence of sodium dodecyl sulfate (SDS) employing voltammetric techniques. Surface morphology studies of the sensing material were analyzed using a scanning electron microscope (SEM) and atomic force microscope (AFM). In the electroanalysis of CIP at the developed electrode, an enhanced anodic peak response was recorded, suggesting the electro-oxidation of CIP at the electrode surface. Furthermore, we evaluated the impact of the electrolytic solution, scan rate, accumulation time, and concentration variation on the electrochemical behavior of CIP. The possible electrode mechanism was proposed based on the acquired experimental information. A concentration variation study was performed using differential pulse voltammetry (DPV) in the lower concentration range, and the fabricated electrode achieved a detection limit of 2.9 × 10^-8 M. The proposed sensor detected CIP in pharmaceutical and biological samples. The findings displayed good recovery, with 93.8% for tablet analysis and 93.3% to 98.7% for urine analysis. The stability of a developed electrode was tested by inter- and intraday analysis.

Electrochemical DNA sensors for drug determination

In this review, recent achievements in the development of the DNA biosensors developed for the drug determination have been presented with particular emphasis to the main principles of their assembling and signal measurement approaches. The design of the DNA sensors is considered with characterization of auxiliary components and their necessity for the biosensor operation. Carbon nanomaterials, metals and their complexes as well as electropolymerized polymers are briefly described in the assembly of DNA sensors. The performance of the DNA sensors is summarized within 2017-2022 for various drugs and factors influencing the sensitivity and selectivity of the response are discussed. Special attention is paid to the mechanism of the signal generation and possible drawbacks in the analysis of real samples.