Effective seed-assisted synthesis of gold nanoparticles anchored nitrogen-doped graphene for electrochemical detection of glucose and dopamine

Facile synthesis of tantalum decorated on iron selenide with nitrogen-doped graphene hybrid for the sensitive detection of trolox in berries: Density functional theory interpretation

This work presents a hydrothermal method followed by a sonochemical treatment for synthesizing tantalum decorated on iron selenide (Ta/FeSe2) integrated with nitrogen-doped graphene (NGR) as a susceptible electrode material for detecting trolox (TRX) in berries samples. The surface morphology, structural characterizations, and electrochemical performances of the synthesized Ta/FeSe2/NGR composite were analyzed via spectrophotometric and voltammetry techniques. The GCE modified with Ta/FeSe2/NGR demonstrated an impressive linear range of 0.1 to 580.3 μM for TRX detection. Additionally, it achieved a remarkable limit of detection (LOD) of 0.059 μM, and it shows a high sensitivity of 2.266 μA μМ-1 cm-2. Here, we used density functional theory (DFT) to investigate the structures of TRX and TRX quinone and the locations of energy levels and electron transfer sites. The developed sensor exhibits significant selectivity, satisfactory cyclic and storage stability, and notable reproducibility. Moreover, the practicality of TRX was assessed in different types of berries, yielding satisfactory recoveries.

Magnetic MOF composites for the electrocatalysis and biosensing of dopamine released from living cells

Metal-organic frameworks (MOFs) with fit ligands and metals can be integrated into electrochemical biosensors for the detection of various biomolecules. In this study, we have synthesized novel magnetic MOF composites as electrocatalysts and constructed a novel biosensor for electrochemical detection of dopamine. The composites named Fe3O4@ZIF-8@AuNPs-COOH are synthesized through layer-by-layer assembly. They exhibit excellent stability and cooperative catalytic activity. In addition, green recycling is readily achieved through magnetizing/demagnetizing the electrode. The large specific surface area and ordered porous structures of the magnetic MOFs ensure good dispersion of gold nanoparticles, while the carboxyl group efficiently shields other redox-active interfering substances. The proposed electrochemical biosensor accomplishes the sensitive detection of dopamine in human serums and living cells. This study broadens the application of MOFs in electrochemical biosensing, validates the feasibility of biosensors for in vivo analysis, and provides new insights into green sensing.

Dual single atomic Ni sites constructing Janus hollow graphene for boosting electrochemical sensing of glucose

Single atom catalysts (SACs) have attracted attention due to their excellent catalysis activity under specific reactions and conditions. However, the low density of SACs greatly limits catalytic performance. The three-dimensional graphene hollow nanospheres (GHSs) with very thin shell structure can be used as excellent carrier materials. Not only can its outer surface be used to anchor metal single atoms, but its inner surface can also provide rich sites. Here, a novel step-by-step assembly strategy is reported to anchor nickel single atoms (Ni SAs) on the inner and outer surfaces of GHSs (Ni SAs/GHSs/Ni SAs), which significantly increases the loading capacity of Ni SAs (4.8 wt%). Compared to conventional materials that only anchor Ni SAs to the outer surface of the carrier (Ni SAs/GHSs), Ni SAs/GHSs/Ni SAs exhibits significantly higher electrocatalytic activity toward glucose oxidation in alkaline media. The sensitivity of Ni SAs/GHSs/Ni SAs/GCE is nearly five times higher than that of Ni SAs/GHSs/GCE. Moreover, the sensor based on Ni SAs/GHSs/Ni SAs can detect glucose in a wide concentration range of 0.8 µM-1.1244 mM with a low detection limit of 0.19 µM (S/N = 3). This study not only provides an effective sensing material for glucose detection, but also opens a new avenue to construct high-density metal SACs.

Advances of Transition Metal-Based Electrochemical Non-enzymatic Glucose Sensors for Glucose Analysis: A Review

Glucose concentration is a crucial parameter for assessing human health. Over recent years, non-enzymatic electrochemical glucose sensors have drawn considerable attention due to their substantial progress. This review explores the common mechanism behind the transition metal-based electrocatalytic oxidation of glucose molecules through classical electrocatalytic frameworks like the Pletcher model and the Hydrous Oxide-Adatom Mediator model (IHOAM), as well as the redox reactions at the transition metal centers. It further compiles the electrochemical characterization techniques, associated formulas, and their ensuing conclusions pertinent to transition metal-based non-enzymatic electrochemical glucose sensors. Subsequently, the review covers the latest advancements in the field of transition metal-based active materials and support materials used in non-enzymatic electrochemical glucose sensors in the last decade (2014-2023). Additionally, it presents a comprehensive classification of representative studies according to the active metal catalysts components involved.

A sensitive sandwich-type electrochemical immunosensor using nitrogen-doped graphene/metal-organic framework-derived CuMnCoOx and Au/MXene for the detection of breast cancer biomarker

In terms of cancer-related deaths among women, breast cancer (BC) is the most common. Clinically, human epidermal growth receptor 2 (HER2) is one of the most commonly used diagnostic biomarkers for facilitating BC cell proliferation and malignant growth. In this study, a disposable gold electrode (DGE) modified with gold nanoparticle-decorated Ti3C2Tx (Au/MXene) was utilized as a sensing platform to immobilize the capturing antibody (Ab1/Au/MXene). Subsequently, nitrogen-doped graphene (NG) with a metal-organic framework (MOF)-derived copper-manganese-cobalt oxide, tagged as NG/CuMnCoOx, was used as a probe to label the detection antibody (Ab2). A sandwich-type immunosensor (NG/CuMnCoOx/Ab2/HER2-ECD /Ab1/Au/MXene/DGE) was developed to quantify HER2-ECD. NG/CuMnCoOx enhances the conductivity, electrocatalytic active sites, and surface area to immobilize Ab2. In addition, Au/MXene facilitates electron transport and captures more Ab1 on its surface. Under optimal conditions, the resultant immunosensor displayed an excellent linear range of 0.0001 to 50.0 ng. mL-1. The detection limit was 0.757 pg·mL-1 with excellent selectivity, appreciable reproducibility, and high stability. Moreover, the applicability for determining HER2-ECD in human serum samples indicates its ability to monitor tumor markers clinically.

Current advancements and prospects of enzymatic and non-enzymatic electrochemical glucose sensors

This review discusses the most current developments and future perspectives in enzymatic and non-enzymatic glucose sensors, which have notably evolved over the preceding quadrennial period. Furthermore, a thorough exploration encompassed the sensor's intricate fabrication processes, the diverse range of materials employed, the underlying principles of detection, and an in-depth assessment of the sensors' efficacy in detecting glucose levels within essential bodily fluids such as human blood serums, urine, saliva, and interstitial fluids. It is worth noting that the accurate quantification of glucose concentrations within human blood has been effectively achieved by utilizing classical enzymatic sensors harmoniously integrated with optical and electrochemical transduction mechanisms. Monitoring glucose levels in various mediums has attracted exceptional attention from industrial to academic researchers for diabetes management, food quality control, clinical medicine, and bioprocess inspection. There has been an enormous demand for the creation of novel glucose sensors over the past ten years. Research has primarily concentrated on succeeding biocompatible and enhanced sensing abilities related to the present technologies, offering innovative avenues for more effective glucose sensors. Recent developments in wearable optical and electrochemical sensors with low cost, high stability, point-of-care testing, and online tracking of glucose concentration levels in biological fluids can aid in managing and controlling diabetes globally. New nanomaterials and biomolecules that can be used in electrochemical sensor systems to identify glucose concentration levels are developed thanks to advances in nanoscience and nanotechnology. Both enzymatic and non-enzymatic glucose electrochemical sensors have garnered much interest recently and have made significant strides in detecting glucose levels. In this review, we summarise several categories of non-enzymatic glucose sensor materials, including composites, non-precious transition metals and their metal oxides, hydroxides, precious metals and their alloys, carbon-based materials, conducting polymers, metal-organic framework (MOF)-based electrocatalysts, and wearable device-based glucose sensors deeply.

Graphene electrochemical transistor incorporated with gel electrolyte for wearable and non-invasive glucose monitoring

With the rapid development of wearable electronic devices, health monitoring is undergoing a fundamental shift from hospital-centered treatment to patient-centered diagnosis. Solution-gated graphene transistors provide an effective platform for developing high-sensitivity wearable devices due to their unique signal amplification, low energy consumption, and compatibility for miniaturization. However, it is still a major challenge to perform real-time sweat composition monitoring directly on the dry skin surface. In this work, a skin-based flexible gel electrolyte graphene transistor (GEGT) was successfully designed and fabricated for glucose detection, consisting of a gate electrode decorated with Au nanoparticles modified reduced graphene oxide (AuNPs/RGO) nanocomposites and a monolayer graphene channel. Glycerin gel was used to replace the traditional liquid electrolyte, not only could better fit the human skin, but also play the role of fluid collection, providing stable testing conditions for the sensor. Based on the high electron mobility of graphene channel and the excellent electrocatalytic performance of AuNPs/RGO nanocomposites, the constructed GEGT sensor exhibits excellent sensing performance for glucose with good selectivity, low operating voltage (0.5 V), wide detection range (10 nM - 25 mM), and low detection limit (10 nM). The device maintains stable performance after up to 1000 bending cycles with a bending radius of 4 mm. In addition, the GEGT sensor displays good accuracy in sweat detection and sensitive dynamic response during actual wearing, which provides a guarantee for the construction of wearable transistor devices and real-time health tracking.

Highly Sensitive and Selective Graphene Nanoribbon Based Enzymatic Glucose Screen-Printed Electrochemical Sensor

A simple, sensitive, cost effective, and reliable enzymatic glucose biosensor was developed and tested. Nitrogen-doped heat-treated graphene oxide nanoribbons (N-htGONR) were used for modification of commercially available screen-printed carbon electrodes (SPCEs), together with MnO₂ and glucose oxidase. The resulting sensors were optimized and used to detect glucose in a wide linear range (0.05-5.0 mM) by a simple amperometric method, where the limit of detection was determined to be 0.008 mM. (lifetime), and reproducibility studies were also carried out and yielded favorable results. The sensor was then tested against potential interfering species present in food and beverage samples before its application to real matrix. Spiked beer samples were analyzed (with glucose recovery between 93.5 and 103.5%) to demonstrate the suitability of the developed sensor towards real food and beverage sample applications.

Surface charge modulation enhanced high stability of gold oxidation intermediates for electrochemical glucose sensors

Rapid and accurate blood glucose detection is significant for diagnosing and treating diabetes. Herein, ultra-low-content gold nanoparticles were loaded on different metal foams and applied to electrochemical enzyme-free glucose sensors via simple displacement reactions. The structures and properties of the produced catalysts were determined by various characterization methods. The performance of the glucose sensor was examined in relation to the interactions between three different metal substrates and gold. The one with the best performance is the sample of gold nanoparticles grown on copper foam (Au300 Cu Foam). It has the advantage of a porous three-dimensional network, a large electroactive surface area, and the high catalytic activity of gold. The combination of Cu and Au increased the valence state of Au, thus favoring the catalytic activity for glucose oxidation. Cyclic voltammetry and chronoamperometry measurements revealed that Au is responsible for the electrocatalytic oxidation of glucose. The sensitivity of Au300 Cu Foam was found to be 10 839 μA mM^-1 cm^-2 in the linear range of 0.00596-0.0566 mM, with a detection limit (LOD) of 0.223 μM, and 2-3 s response time at 0.4 V vs. Ag/AgCl. The Au300 Cu Foam glucose sensor also offered outstanding stability and anti-interference performance. The prepared Au300 Cu Foam electrode was also successfully applied to detect different levels of glucose in human body fluids, such as saliva. These characteristics make Au300 Cu Foam promising for non-invasive glucose detection.

Melamine-derived N-rich C-entrapped Au nanoparticles for sensitive and selective monitoring of dopamine in blood samples

Several neurological disorders, including Parkinson's disease, schizophrenia, human immunodeficiency virus infection, and restless leg syndrome, majorly result from disruption in the dopamine (DA) level. Thus, useful information about the treatment and prevention of various genetic majorly mental health problems can be obtained through precise and real-time monitoring of DA. Herein, we report the fabrication of novel N-rich carbon-coated Au nanoparticles (NC@Au-NPs) by deriving from melamine-crosslinked citrate-stabilized Au NPs. NC@Au-NPs offer fast electro-oxidation efficacy towards DA, because of strong electrostatic attraction between negatively charged NC@Au-NPs and positively charged DA. The catalytic efficacy and shelf life of the designed system were further boosted by applying a mixture of polydopamine (PDA) and benzimidazolium-1-acetate ionic liquid (IL) as a sandwich between the working electrode surface (graphitic pencil electrode: GPE) and the designed nanohybrid NC@Au-NPs as a redox mediator. The results indicate that the designed novel NC@Au/PDA-IL/GPE exhibits excellent sensitivity, selectivity, and reproducibility over a wide linear range (50-1000 nm) and a low detection limit of 0.002 μM ± 0.001 as well. The developed sensor was successfully applied to monitor DA in the blood of COVID-19 quarantined patients and pharmaceutical samples with high accuracy, thus suggesting a powerful tool for the diagnosis of mental problems.

Facile electrooxidation of ethanol on reduced graphene oxide supported Pt-Pd bimetallic nanocomposite surfaces in acidic media

Development of electrocatalysts with extended homogeneity and improved metal-support interactions is of urgent scientific need in the context of electrochemical energy applications. Herein, bimetallic Pt-Pd nanoparticles with good homogeneity are fabricated using a convenient solution phase chemical reduction method onto a reduced graphene oxide (rGO) support. X-ray diffraction studies revealed that Pt-Pd/rGO possesses the crystallite size of 3.1 nm. The efficacies of Pt-Pd/rGO catalyst (20 wt% Pt + 10 wt% Pd on rGO support, Pt:Pd atomic ratio = 1:1) towards ethanol electrooxidation reaction (EOR) are evaluated in acidic conditions by cyclic voltammetry using catalyst-coated glassy carbon electrode as a working electrode. With the better dispersion on rGO support the Pt-Pd/rGO nancomposite catalyst exhibit highest mass specific activity (0.358 mA/µg-Pt) which is observed to be 1.9 times of similarly synthesized 20 wt% Pt/rGO (0.189 mA/µg-Pt) and 2.5 times of commercial 20 wt% Pt/C (0.142 mA/µg-Pt), respectively. Apart from the observed improved EOR activity, the Pt-Pd/rGO catalyst exhibited better stability than Pt/rGO and Pt/C catalysts. Strong synergy offered by Pt, Pd and rGO support could contribute to the observed higher EOR activity of Pt-Pd/rGO.

Electrochemical Biosensor Using Nitrogen-Doped Graphene/Au Nanoparticles/DNAzyme for Ca2+ Determination

An electrochemical biosensor for detecting Ca²⁺ concentration was proposed using glass carbon electrodes (GCEs) modified with nitrogen-doped graphene (NGR), gold nanoparticles (AuNPs) and DNAzyme. The resistance signal was amplified through two methods: electrochemical reduction of AuNPs on the NGR surface to increase the specific surface area of the electrode and strengthen the adsorption of DNAzyme; and increasement of the DNAzyme base sequence. The process of electrode modification was characterized by scanning electron microscopy, Raman spectroscopy, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). Experimental parameters’ influence, such as the deposition time of gold nanoparticles and the detection time, were assessed by electrochemical methods. The linear ranges of the electrochemical biosensor were in the range from 5 × 10⁻⁶ to 5 × 10⁻⁵ and 5 × 10⁻⁵ to 4 × 10⁻⁴ M, with a detection limit of 3.8 × 10⁻⁶ M. The concentration of Ca²⁺ in the serum of dairy cows was determined by the biosensor with satisfactory results, which could be potentially used to diagnose subclinical hypocalcemia.

A novel electrochemical sensor for glucose detection based on a Ti3C2Tx/ZIF-67 nanocomposite

A Ti₃C₂T_x/ZIF-67 nanocomposite with outstanding conductivity has been prepared by loading ZIF-67 onto a two-dimensional Ti₃C₂T_x nanosheet. Ti₃C₂T_x sheets were synthesized by etching Ti₃AlC₂, and then ZIF-67 was grown in situ on the Ti₃C₂T_x nanosheet. The Ti₃C₂T_x/ZIF-67 nanocomposite exhibits excellent detection performance for glucose, with a low LOD of 3.81 μM and wide linear detection range of 5–7500 μM. This terrific result is contributed by the synergistic effect of the high electrically conductive ability of Ti₃C₂T_x and active catalytic performance of ZIF-67. Moreover, the electrochemical sensor prepared using the Ti₃C₂T_x/ZIF-67 nanocomposite also shows excellent selectivity, stability and repeatability for glucose detection. The Ti₃C₂T_x/ZIF-67 nanocomposite with outstanding performance has potential applications for electrochemical sensors.

A Ti₃C₂T_x/ZIF-67 nanocomposite with outstanding conductivity has been prepared. The electrochemical sensor based on this nanocomposite exhibits excellent selectivity, stability and repeatability for glucose detection.

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.

β-Cyclodextrin functionalized 3D reduced graphene oxide composite-based electrochemical sensor for the sensitive detection of dopamine

A three-dimensional reduced graphene oxide nanomaterial with β-cyclodextrin modified glassy carbon electrode (3D-rGO/β-CD/GCE) was constructed and used to detect the electrochemical behavior of dopamine (DA). The nanocomposite materials were characterized by scanning electron microscopy (SEM), infrared spectrometry (FT-IR), Raman spectrogram and thermogravimetric analysis (TGA), which showed that β-CD was well modified on 3D graphene with a porous structure. The electrochemical properties of different modified electrodes were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), proving the highest electron transfer rate of the 3D-rGO/β-CD modified electrode. The experimental conditions such as scan rate, pH, enrichment time and layer thickness were optimized. Under the best experimental conditions, DA was detected by differential pulse voltammetry (DPV) by 3D-rGO/β-CD/GCE with excellent electrocatalytic ability and satisfactory recognition ability, resulting in a wide linear range of 0.5-100 μM and a low detection limit (LOD) of 0.013 μM. The modified electrode based on 3D-rGO/β-CD nanocomposites is promising in the field of electrochemical sensors due to its high sensitivity and other excellent properties.

Detection of dopamine by a minimized electrochemical sensor using a graphene oxide molecularly imprinted polymer modified micropipette tip shaped graphite electrode

A simple and efficient electrochemical sensor based on a homemade reshaped micropipette tip carbon paste electrode is reported. Molecularly imprinted polymer membranes of graphene oxide and polypyrrole are synthesized and modified on the surface of micropipette tip carbon paste electrode. The merit of the method is evaluated under optimized conditions via differential pulse voltammetrics. The prepared sensor exhibits remarkable sensitivity toward dopamine with a linear range of 6.4 × 10−8–2 × 10−4 M, with a limit of detection as low as 1 × 10−8 M. The proposed method is applied for the determination of dopamine in urine samples by the standard addition route. A range of 1 × 10−7–1 × 10−4 M is obtained from these samples. The relative recoveries are in the range of 95.2%–104%. The proposed method has acceptable performance for the determination of dopamine in real samples with excellent sensitivity and selectivity.

Non-Enzymatic Glucose Biosensor Based on Highly Pure TiO2 Nanoparticles

This study proposes a non-enzymatic glucose sensor fabricated by synthesizing high-purity TiO₂ nanoparticles in thermal plasma and depositing it directly on a substrate and then depositing chitosan–polypyrrole (CS-PPy) conductive polymer films by electrochemical method. The structural properties of the deposited TiO₂ nanoparticles were analyzed by X-ray diffraction (XRD) and dynamic light scattering (DLS) system. The chemical composition and structural properties of the TiO₂ nanoparticle layer and the conductive polymer films were confirmed by X-ray photoelectron spectroscopy (XPS) spectra and scanning electron microscope (SEM). The glucose detection characteristics of the fabricated biosensor were determined by cyclic voltammetry (CV). CS-PPy/TiO₂ biosensor showed high sensitivity of 302.0 µA mM⁻¹ cm⁻² (R² = 0.9957) and low detection limit of 6.7 μM. The easily manufactured CS-PPy/TiO₂ biosensor showed excellent selectivity and reactivity.

Green synthesis of nonprecious metal-doped copper hydroxide nanoparticles for construction of a dopamine sensor

Background: Copper oxide nanoparticles doped with nonprecious metal species (Ni and Mn) were synthesized. Method: A glassy carbon electrode (GCE) was modified by drop-casting of nanostructure suspensions, constructing Ni:Cu(OH)₂/GCE, Mn:Cu(OH)₂/GCE and Cu(OH)₂/GCE. Results: The voltammetric oxidation of dopamine (DA) by the constructed electrodes confirmed that the electrocatalytic oxidation of DA is a reversible, pH-dependent, diffusion-controlled process; the best response was obtained by Mn:Cu(OH)₂/GCE. A sensitive calibration graph (0.664 μA/μM) was produced for DA in the concentration range of 0.3-10.0 μM, with a detection limit of 79 nM using Mn:Cu(OH)₂/GCE. Conclusion: The Mn:Cu(OH)₂/GCE possessed an accurate response toward DA with an acceptable selectivity, stability and antifouling effect, revealing the applicability of the Mn:Cu(OH)₂/GCE for DA analysis in biological samples.

DNA-Gated Graphene Field-Effect Transistors for Specific Detection of Arsenic(III) in Rice

As one of the most toxic forms of arsenic, inorganic As(III) is easy to accumulate in rice, leading to severe public health problems. Effective control of As(III) requires the development of fast analytical methods for its detection with high sensitivity and specificity. Toward this end, in this work, we report the fabrication of an As(III) electrochemical sensor based on a solution-gated graphene transistor (SGGT) platform with a novel sensing mechanism. The gold gate electrode of the SGGT was modified with DNA probes and then blocked with bovine serum albumin (BSA). The specific interaction between As(III) and gold disrupted the adsorption states of DNA probes, redistributing surface charges on the gate electrode, further leading to potential drop changes at the interfaces of the gate electrode and graphene active layer. This new mechanism based on DNA-charge-redistribution-induced SGGT current responses (denoted as "DNA-SGGT") was found to greatly improve the selectivity of the sensor: the response of DNA-SGGT to As(III) was effectively enhanced fourfold, while to other interfering cations, it was significantly reduced. The optimized sensor showed a detection limit as low as 5 nM with superior selectivity to As(III). The as-prepared DNA-SGGT-based sensor has also been successfully applied to the detection of As(III) in practical rice samples with a high recovery rate, showing great potential for heavy metal detection in many types of food samples.

A highly sensitive poly(chrysoidine G)-gold nanoparticle composite based nitrite sensor for food safety applications

This work demonstrated the development of conducting poly(chrysoidine G) (PCG)-gold nanoparticle (AuNP)-modified fluorine-doped tin oxide (F : SnO₂, FTO) film-coated glass electrodes for the sensitive electrochemical detection of nitrite (NO₂^-). The homogeneously distributed PCG nanoparticle layer was deposited onto the FTO electrode by cyclic voltammetry sweeping. AuNPs were then anchored onto the PCG/FTO electrode by the chemical reduction of pre-adsorbed Au³⁺ ions. The as-prepared AuNP/PCG/FTO electrode exhibited excellent electrocatalytic activity for the oxidation of NO₂^- with high sensitivity (approximately 0.63 μA cm^-2μM^-1) and a low limit of detection (0.095 μM), which is relevant within the normal concentration range of NO₂^- in human bodily fluids. The AuNP/PCG/FTO sensor showed sufficient reproducibility, repeatability, low interference, and strong recovery for NO₂^- detection in food samples. These results indicate that the AuNP/PCG nanocomposites have immense potential for the electrochemical detection of other biologically important compounds.

A Screen-Printed Electrode Modified With Graphene/Co3O4 Nanocomposite for Electrochemical Detection of Tramadol

In this paper, graphene (Gr)/Co₃O₄ nanocomposite was synthesized and utilized for the development of a novel electrochemical sensor to detect tramadol. Tramadol determination was examined by linear sweep voltammetry, differential pulse voltammetry, cyclic voltammetry, and chronoamperometry on Gr/Co₃O₄ nanocomposite-modified screen-printed electrode (Gr/Co₃O₄/SPE) in phosphate-buffered saline (PBS). Under the optimized condition, the detection limit of tramadol is 0.03 μM (S/N = 3) in the linear ranges of 0.1–500.0 μM. Furthermore, Gr/Co₃O₄/SPE was satisfactorily utilized to detect tramadol in tramadol tablet and urine specimens.

Au-Nitrogen-Doped Graphene Quantum Dot Composites as "On-Off" Nanosensors for Sensitive Photo-Electrochemical Detection of Caffeic Acid

Herein, gold–nitrogen-doped graphene quantum dot (Au/NGQD) composite modified electrodes were fabricated and applied as “on–off” nanosensors for the photo-electrochemical (PEC) detection of caffeic acid under visible-light irradiation. An effective and simple strategy was established for the preparation of Au/NGQD composites by hydrothermal and calcination methods. Owing to the quantum confinement effect of NGQDs, the local surface plasmon resonance (LSPR) effect of Au nanoparticles (NPs), and the synergistic effect between Au and NGQDs NPs, the Au/NGQDs showed excellent PEC performance, with wide linear concentration ranges (0.11 to 30.25 μM and 30.25 to 280.25 μM), a low detection limit (0.03 μM), excellent sensitivity, and high stability. The present study may provide an advanced strategy for the simple design of Au/NGQD composites to allow their effective application for selective and sensitive sensing of small biological molecules.

Carbon Nanomaterials as Versatile Platforms for Biosensing Applications

A biosensor is defined as a measuring system that includes a biological receptor unit with distinctive specificities toward target analytes. Such analytes include a wide range of biological origins such as DNAs of bacteria or viruses, or proteins generated from an immune system of infected or contaminated living organisms. They further include simple molecules such as glucose, ions, and vitamins. One of the major challenges in biosensor development is achieving efficient signal capture of biological recognition-transduction events. Carbon nanomaterials (CNs) are promising candidates to improve the sensitivity of biosensors while attaining low detection limits owing to their capability of immobilizing large quantities of bioreceptor units at a reduced volume, and they can also act as a transduction element. In addition, CNs can be adapted to functionalization and conjugation with organic compounds or metallic nanoparticles; the creation of surface functional groups offers new properties (e.g., physical, chemical, mechanical, electrical, and optical properties) to the nanomaterials. Because of these intriguing features, CNs have been extensively employed in biosensor applications. In particular, carbon nanotubes (CNTs), nanodiamonds, graphene, and fullerenes serve as scaffolds for the immobilization of biomolecules at their surface and are also used as transducers for the conversion of signals associated with the recognition of biological analytes. Herein, we provide a comprehensive review on the synthesis of CNs and their potential application to biosensors. In addition, we discuss the efforts to improve the mechanical and electrical properties of biosensors by combining different CNs.

N-Doped Reduced Graphene Oxide/Gold Nanoparticles Composite as an Improved Sensing Platform for Simultaneous Detection of Dopamine, Ascorbic Acid, and Uric Acid

Gold nanoparticles (AuNPs) were homogeneously electrodeposited on nitrogen-doped reduced graphene oxide (N-rGO) to modify a glassy carbon electrode (GCE/N-rGO-Au) in order to improve the simultaneous detection of dopamine (DA), ascorbic acid (AA), and uric acid (UA). N-rGO was prepared by the hydrothermal treatment of graphene oxide (GO) and urea at 180 °C for 12 h. AuNPs were subsequently electrodeposited onto the surface of GCE/N-rGO using 1 mM HAuCl₄ solution. The morphology and chemical composition of the synthesized materials were characterized by field-emission scanning electron microscopy and X-ray photoelectron spectroscopy. The electrochemical performance of the modified electrodes was investigated through cyclic voltammetry and differential pulse voltammetry measurements. Compared to GCE/rGO-Au, GCE/N-rGO-Au exhibited better electrochemical performance towards the simultaneous detection of the three analytes due to the more homogeneous distribution of the metallic nanoparticles as a result of more efficient anchoring on the N-doped areas of the graphene structure. The GCE/N-rGO-Au-based sensor operated in a wide linear range of DA (3–100 µM), AA (550–1500 µM), and UA (20–1000 µM) concentrations with a detection limit of 2.4, 58, and 8.7 µM, respectively, and exhibited satisfactory peak potential separation values of 0.34 V (AA-DA), 0.20 V, (DA-UA) and 0.54 V (AA-UA). Remarkably, GCE/N-rGO-Au showed a very low detection limit of 385 nM towards DA, not being susceptible to interference, and maintained 90% of its initial electrochemical signal after one month, indicating an excellent long-term stability.

A novel electrochemical sensing platform for detection of dopamine based on gold nanobipyramid/multi-walled carbon nanotube hybrids

Dopamine homeostasis is an important clinical diagnostic index, because an abnormal level in the human body is closely related to certain serious diseases. Herein, a novel electrochemical sensing platform based on gold nanobipyramid/multi-walled carbon nanotube hybrids (AuNBP/MWCNTs) is developed to detect dopamine in human fluids. Using field emission scanning electron microscopy, it is observed that AuNBPs of about 60 nm with two pyramids are well dispersed on the surface of MWCNTs. Energy-dispersive X-ray spectrometry, X-ray diffraction and X-ray photoelectron spectroscopy confirm that AuNBPs are self-assembled onto the surface of MWCNTs to form the hybrids. Cyclic voltammetry reveals that the AuNBP/MWCNTs exhibit good electrocatalytic activity toward dopamine oxidation owing to the synergistic effects of AuNBPs and MWCNTs. In addition, both cyclic voltammetry and differential pulse voltammetry display three well-resolved and distinct oxidation peaks on the AuNBP/MWCNT-modified glassy carbon electrode. Based on AuNBP/MWCNTs, the newly developed electrochemical sensor is used to detect dopamine in the presence of ascorbic acid and uric acid over a wide linear range from 50 nM to 2.7 mM and a low detection limit of 15 nM (at S/N = 3). The electrochemical sensor can also be applied for the quantitative analysis of dopamine in real samples. Graphical abstract A novel electrochemical sensing platform based on gold nanobipyramid/multi-walled carbon nanotube hybrids (AuNBP/MWCNTs) was proposed to detect dopamine in the presence of ascorbic acid and uric acid.

A novel dual-tasking hollow cube NiFe2O4-NiCo-LDH@rGO hierarchical material for high preformance supercapacitor and glucose sensor

Binary transition metal oxides as electroactive materials have continuously aroused grumous attention due to their high theoretical specific capacitance, high valtage window, and multiple oxidation states. However, the tiny specific surface area, poor conductivity and unsatisfactory cycle stability limit their practical application. Hence, a synthetic strategy is designed to fabricate a dual-tasking hollow cube nickel ferrite (NiFe₂O₄) - based composite (NiFe₂O₄-NiCo-LDH@rGO) with hierarchical structure. The composite is constructed by firstly preparing hollow NiFe₂O₄ from cube-like Ni - Fe bimetallic organic framework (NiFe-MOF), and then integrating nickel cobalt layered double hydroxide (NiCo-LDH) nanowires, together with reduced graphene oxide (rGO) via pyrolysis in conjuction with hydrothermal method. The NiFe₂O₄ possessing cubic hollow structure contributes to a huge accessible surface area, meanwhile alleviates large volume expansion/contraction effect, which facilitates suffcient permeation of the electrolyte and rapid ion/charge transport, and results in high cycling stability. The introduction of layered NiCo-LDH results in hierarchical structure and thus offers maximum contact areas with electrolyte, which heightens the specific capacitance of obtained composite and enhances the electro-catlytic activity towards oxidation of glucose. Furthermore, rGO layer greatly improves the electrical conductivity and ion diffusion/transport capability of composite. Benefiting from the unique structure and individual components of NiFe₂O₄-NiCo-LDH@rGO composite, the electrode delivers a high specific capacitance (750 C g^-1) and superb durability. Simultaneously, the asymmetrical device based on NiFe₂O₄-NiCo-LDH@rGO as positive electrode delivers remarkable energy density (50 Wh kg^-1). Moreover, NiFe₂O₄-NiCo-LDH@rGO exhibits good sensing performance with a sensitivity of 111.86 µA/µM cm^-2, the wide linear range of 3.500 × 10^-5 - 4.525 × 10^-3 M, and the detection limit of 12.94 × 10^-6 M with a signal to noise ratio of 3. Consequently, the NiFe₂O₄-NiCo-LDH@rGO could provide a prospective notion constructing bifunctional materials with hollow-cube hierarchical structure in the field of supercapacitors and electrochemical sensors.

A novel solution-gated graphene transistor biosensor for ultrasensitive detection of trinucleotide repeats

A novel SGGT biosensor is constructed to achieve highly sensitive and selective sensing of GAA TNRs by integrating G-quadruplex enzymes.

Nonenzymatic Glucose Sensing and Magnetic Property Based On the Composite Formed by Encapsulating Ag Nanoparticles in Cluster-Based Co-MOF

Utilizing the oxygen-bridged 5,5'-oxidiisophthalic acid (H₄L) linker, one Co(II)-based 3D porous MOF {[Co₅(L)₂(OH)₂(OH₂)₂(H₂O)₄]·2DMF·H₂O}_n (1) with pentanuclear [Co₅(μ₃-OH)₂(μ₂-OH₂)₂]⁸⁺ cluster was prepared. The glassy carbon electrode was modified by 1, and the obtained electrode revealed electrocatalytic performance for glucose oxidation. The porous MOF matrix is beneficial for dispersing Ag nanoparticles evenly in the interior cages or channels, so Ag@1 composite composed of both Ag nanoparticles and MOF was further prepared through deposition-reduction method to enhance electrocatalytic activity. The result demonstrates that the glucose oxidation by Ag@1 was greatly increased with low detection limit (1.32 μM) and good selectivity and sensitivity (0.135 μA μM^-1), which promote the application of MOF-template porous composites as advanced electrochemical sensor materials. Furthermore, 1 shows an interesting magnetic spin-glass slow dynamics for the existing of peculiar pentanuclear Co(II) clusters.

Functionalization of Carbon Nanomaterials for Biomedical Applications

Over the past decade, carbon nanostructures (CNSs) have been widely used in a variety of biomedical applications. Examples are the use of CNSs for drug and protein delivery or in tools to locally dispense nucleic acids to fight tumor affections. CNSs were successfully utilized in diagnostics and in noninvasive and highly sensitive imaging devices thanks to their optical properties in the near infrared region. However, biomedical applications require a complete biocompatibility to avoid adverse reactions of the immune system and CNSs potentials for biodegradability. Water is one of the main constituents of the living matter. Unfortunately, one of the disadvantages of CNSs is their poor solubility. Surface functionalization of CNSs is commonly utilized as an efficient solution to both tune the surface wettability of CNSs and impart biocompatible properties. Grafting functional groups onto the CNSs surface consists in bonding the desired chemical species on the carbon nanoparticles via wet or dry processes leading to the formation of a stable interaction. This latter may be of different nature as the van Der Waals, the electrostatic or the covalent, the π-π interaction, the hydrogen bond etc. depending on the process and on the functional molecule at play. Grafting is utilized for multiple purposes including bonding mimetic agents such as polyethylene glycol, drug/protein adsorption, attaching nanostructures to increase the CNSs opacity to selected wavelengths or provide magnetic properties. This makes the CNSs a very versatile tool for a broad selection of applications as medicinal biochips, new high-performance platforms for magnetic resonance (MR), photothermal therapy, molecular imaging, tissue engineering, and neuroscience. The scope of this work is to highlight up-to-date using of the functionalized carbon materials such as graphene, carbon fibers, carbon nanotubes, fullerene and nanodiamonds in biomedical applications.