A novel hierarchical 3D N-Co-CNT@NG nanocomposite electrode for non-enzymatic glucose and hydrogen peroxide sensing applications

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.

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.

Enhancing electrochemical sensing through the use of functionalized graphene composites as nanozymes

Graphene-based nanozymes possess inherent nanomaterial properties that offer not only a simple substitute for enzymes but also a versatile platform capable of bonding with complex biochemical environments. The current review discusses the replacement of enzymes in developing biosensors with nanozymes. Functionalization of graphene-based materials with various nanoparticles can enhance their nanozymatic properties. Graphene oxide functionalization has been shown to yield graphene-based nanozymes that closely mimic several natural enzymes. This review provides an overview of the classification, current state-of-the-art development, synthesis routes, and types of functionalized graphene-based nanozymes for the design of electrochemical sensors. Furthermore, it includes a summary of the application of functionalized graphene-based nanozymes for constructing electrochemical sensors for pollutants, drugs, and various water and food samples. Challenges related to nanozymes as electrocatalytic materials are discussed, along with potential solutions and approaches for addressing these shortcomings.

Electrochemical Sensor Made with 3D Micro-/Mesoporous Structures of CoNi-N/GaN for Noninvasive Detection of Glucose

Noninvasive detection of glucose (NGD) is important because ∼10% of the global population is suffering from diabetes. Herein, a three-dimensional (3D) micro-/mesoporous structure, i.e., a CoNi-N nanosheet-coated GaN 3D scaffold (CoNi-N@GaN-3S), was proposed for detecting saliva glucose, where the GaN scaffold can provide a large open surface for nanosheet decoration, while the catalytic nanosheets can increase the surface area and prevent the GaN-3S from anodic corrosion. Moreover, it was found that high-temperature ammoniation of CoNi can lead to dense atomic holes and an N-terminated surface (CoNi-N), which promoted the ionization of CoNi with a higher catalytic activity. It is the first time that dense atomic holes have been observed in CoNi to our knowledge. The designed CoNi-N@GaN-3S sensor was applied to the electrochemical detection of glucose with a low limit of detection (LOD) of 60 nM and a high sensitivity, selectivity, and stability. In addition, detection of human-saliva glucose was realized with an LOD of 5 μM, which was more than 4-fold lower than reported reliable LODs. An integrated sensor with a low consumption of saliva sample was demonstrated for NGD.

Electrochemical Sensors for the Detection of Reactive Oxygen Species in Biological Systems: A Critical Review

Reactive oxygen species (ROS) involving superoxide anion, hydrogen peroxide and hydroxyl radical play important role in human health. ROS are known to be the markers of oxidative stress associated with different pathologies including neurodegenerative and cardiovascular diseases, as well as cancer. Accordingly, ROS level detection in biological systems is an essential problem for biomedical and analytical research. Electrochemical methods seem to have promising prospects in ROS determination due to their high sensitivity, rapidity, and simple equipment. This review demonstrates application of modern electrochemical sensors for ROS detection in biological objects (e.g., cell lines and body fluids) over a decade between 2011 and 2021. Particular attention is paid to sensors materials and various types of modifiers for ROS selective detection. Moreover, the sensors comparative characteristics, their main advantages, disadvantages and their possibilities and limitations are discussed.

Water Quality Carbon Nanotube-Based Sensors Technological Barriers and Late Research Trends: A Bibliometric Analysis

Water is the key element that defines and individualizes our planet. Relative to body weight, water represents 70% or more for the majority of all species on Earth. Taking care of water as a whole is equivalent with taking care of the entire biodiversity or the whole of humanity itself. Water quality is becoming an increasingly important component of terrestrial life, hence intensive work is being conducted to develop sensors for detecting contaminants and assessing water quality and characteristics. Our bibliometric analysis is focused on water quality sensors based on carbon nanotubes and highlights the most important objectives and achievements of researchers in recent years. Due to important measurement characteristics such as sensitivity and selectivity, or low detection limit and linearity, up to the ability to measure water properties, including detection of heavy metal content or the presence of persistent organic compounds, carbon nanotube (CNT) sensors, taking advantage of available nanotechnologies, are becoming increasingly attractive. The conducted bibliometric analysis creates a visual, more efficient keystones mapping. CNT sensors can be integrated into an inexpensive real-time monitoring data acquisition system as an alternative for classical expensive and time-consuming offline water quality monitoring. The conducted bibliometric analysis reveals all connections and maps all the results in this water quality CNT sensors research field and gives a perspective on the approached methods on this specific type of sensor. Finally, challenges related to integration of other trends that have been used and proven to be valuable in the field of other sensor types and capable to contribute to the development (and outlook) for future new configurations that will undoubtedly emerge are presented.

3D Modeling of Silver Doped ZrO2 Coupled Graphene-Based Mesoporous Silica Quaternary Nanocomposite for a Nonenzymatic Glucose Sensing Effects

We described the novel nanocomposite of silver doped ZrO2 combined graphene-based mesoporous silica (ZrO2-Ag-G-SiO2,) in bases of low-cost and self-assembly strategy. Synthesized ZrO2-Ag-G-SiO2 were characterized through X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDX), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy, Nitrogen adsorption-desorption isotherms, X-ray photoelectron spectroscopy (XPS), and Diffuse Reflectance Spectroscopy (DRS). The ZrO2-Ag-G-SiO2 as an enzyme-free glucose sensor active material toward coordinate electro-oxidation of glucose was considered through cyclic voltammetry in significant electrolytes, such as phosphate buffer (PBS) at pH 7.4 and commercial urine. Utilizing ZrO2-Ag-G-SiO2, glucose detecting may well be finished with effective electrocatalytic performance toward organically important concentrations with the current reaction of 9.0 × 10-3 mAcm-2 and 0.05 mmol/L at the lowest potential of +0.2 V, thus fulfilling the elemental prerequisites for glucose detecting within the urine. Likewise, the ZrO2-Ag-G-SiO2 electrode can be worked for glucose detecting within the interferometer substances (e.g., ascorbic corrosive, lactose, fructose, and starch) in urine at proper pH conditions. Our results highlight the potential usages for qualitative and quantitative electrochemical investigation of glucose through the ZrO2-Ag-G-SiO2 sensor for glucose detecting within the urine concentration.

A web of poly(bisbenzimidazolatocopper(ii)) around multiwalled carbon nanotubes for the electrochemical detection of hydrogen peroxide

The present work focuses on the electrochemical determination of hydrogen peroxide (H2O2), using a poly(bisbenzimidazolatocopper(ii)) coordinated multiwalled carbon nanotube modified glassy carbon electrode (MWCNT/(BIM–Cu2+)n@GCE).

Electrical and Electrochemical Sensors Based on Carbon Nanotubes for the Monitoring of Chemicals in Water-A Review

Carbon nanotubes (CNTs) combine high electrical conductivity with high surface area and chemical stability, which makes them very promising for chemical sensing. While water quality monitoring has particularly strong societal and environmental impacts, a lot of critical sensing needs remain unmet by commercial technologies. In the present review, we show across 20 water monitoring analytes and 90 references that carbon nanotube-based electrochemical sensors, chemistors and field-effect transistors (chemFET) can meet these needs. A set of 126 additional references provide context and supporting information. After introducing water quality monitoring challenges, the general operation and fabrication principles of CNT water quality sensors are summarized. They are sorted by target analytes (pH, micronutrients and metal ions, nitrogen, hardness, dissolved oxygen, disinfectants, sulfur and miscellaneous) and compared in terms of performances (limit of detection, sensitivity and detection range) and functionalization strategies. For each analyte, the references with best performances are discussed. Overall, the most frequently investigated analytes are H+ (pH) and lead (with 18% of references each), then cadmium (14%) and nitrite (11%). Micronutrients and toxic metals cover 40% of all references. Electrochemical sensors (73%) have been more investigated than chemistors (14%) or FETs (12%). Limits of detection in the ppt range have been reached, for instance Cu(II) detection with a liquid-gated chemFET using SWCNT functionalized with peptide-enhanced polyaniline or Pb(II) detection with stripping voltammetry using MWCNT functionalized with ionic liquid-dithizone based bucky-gel. The large majority of reports address functionalized CNTs (82%) instead of pristine or carboxyl-functionalized CNTs. For analytes where comparison is possible, FET-based and electrochemical transduction yield better performances than chemistors (Cu(II), Hg(II), Ca(II), H2O2); non-functionalized CNTs may yield better performances than functionalized ones (Zn(II), pH and chlorine).

Bi-Functional Fe3 O4 /Au/CoFe-LDH Sandwich-Structured Electrocatalyst for Asymmetrical Electrolyzer with Low Operation Voltage

The reduction of the overall electrolysis potential to produce hydrogen is a critical target for fabricating applicable hydrogen evolution cells. Sandwich-structured Fe₃ O₄ /Au/CoFe-LDH is synthesized via a spontaneous galvanic displacement reaction. A series of structural characterizations indicate the successful synthesis of sandwich-structured Fe₃ O₄ /Au/CoFe-LDH electrocatalyst. The trace amount of Au laying between Fe₃ O₄ and CoFe-LDH significantly improves the intrinsic conductivity and catalytic activity of the composite catalyst. In-depth investigations indicate that Fe₃ O₄ and CoFe-LDH are responsible for the electrocatalytic hydrogen evolution reaction (HER) whereas Au is responsible for the electrocatalytic glucose oxidation (GOR). The electrocatalytic tests indicate Fe₃ O₄ /Au/CoFe-LDH offers excellent electrocatalytic activity and stability for both HER and GOR, even at high current density (i.e., 1000 mA cm^-2 ). Further electrochemistry examinations in a two-compartment cell with a two-electrode configuration show that Fe₃ O₄ /Au/CoFe-LDH can significantly reduce the overall potential for this asymmetrical cell, with only 0.48 and 0.89 V required to achieve 10 mA cm^-2 current density with and without iR-compensation, which is the lowest overall potential requirement ever reported. The design and synthesis of Fe₃ O₄ /Au/CoFe-LDH pave a new way to electrochemically produce hydrogen and gluconate under extremely low cell voltage, which can readily match with a variety of solar cells.

Tamarindus indica seed-shell nanoparticles‑silver nanoparticles-Ceratonia silique bean gum composite for copper-micro mesh grid electrode fabrication and its application for glucose detection in artificial salivary samples

This study used a new approach to fabricate a glucose detection system based on nano-engineered biomaterials. The fabrication steps included strategic synthesis, integration and stabilization of biological and metal nanoparticles in superabsorbent hydrogel gum matrix. The design of the high-performance electrochemical biosensor platform includes copper-micro mesh grid electrode modified with polymer phase comprising of silver nanoparticles surface coroneted with Ceratonia silique locust bean gum (LBG), Tamarindus indica seed-shell nanoparticles and glucose oxidase (GOx). Fundamental assessment of catalytic properties of the nanobiocomposite films on copper grid probe were performed by cyclic voltammetry, amperometry, differential pulse voltammetry. Probes showed good repeatability, reproducibility, selectivity, and long-term stability. The GOx was well-immobilized and stabilized by C. siliqua nano-matrix, with 85% and 98% activity retention when stored at different condiions for 6 month and 3 months, respectively. The fabricated grid-platform exhibited linear response in a wide range of glucose concentration, with detection limit of 1.0 nM (S/N = 3) and sensitivity 38.7 mA nM^-1 cm^-2. The bionanomaterial-based sensor was successfully applied for ultra-low glucose detection in artificial salivary samples. The designed sensor, perhaps with further modifications, has potential for the next generation of sensing platform in various biological fluids especially for non-invasive glucose detection for diabetic patients.

Cobalt and nitrogen co-doped mesoporous carbon for electrochemical hydrogen peroxide sensing: the effect of graphitization

In this study, a facile strategy for the scalable synthesis of cobalt and nitrogen co-doped mesoporous carbon (Co-N/C) is reported. Structural characterization demonstrated that Co and N were successfully co-doped in the highly porous carbon. Graphitization of porous carbon was achieved by the introduction of cobalt species. The degree of graphitization of Co-N/C could be further promoted by increasing the calcination temperature. By taking advantage of the excellent mass and electron transfer kinetics attributed to the high specific surface area, high porosity and high graphitization, the obtained Co-N/C exhibited good electrochemical activity towards H₂O₂ reduction and excellent sensing performance for the electrochemical detection of H₂O₂. The Co-N/C-950 catalyst obtained at 950 °C showed good electrochemical sensing performance with a detection limit of 2 μM and a wide linear response over the concentration range from 0.03 mM to 13 mM. Meanwhile, Co-N/C exhibited high selectivity toward the detection of H₂O₂ in the presence of possible interferences during the applications such as NaCl, glucose, ascorbic acid and so on. The results confirm that Co-N/C could be used as an efficient electrocatalyst to fabricate electrochemical sensing devices.

Fe3C-Assisted Single Atomic Fe Sites for Sensitive Electrochemical Biosensing

The rational construction of advanced sensing platforms to sensitively detect H₂O₂ produced by living cells is one of the challenges in both physiological and pathological fields. Owing to the extraordinary catalytic performances and similar metal coordination to natural metalloenzymes, single atomic site catalysts (SASCs) with intrinsic peroxidase (POD)-like activity have shown great promise for H₂O₂ detection. However, there still exists an obvious gap between them and natural enzymes because of the great challenge in rationally modulating the electronic and geometrical structures of central atoms. Note that the deliberate modulation of the metal-support interaction may give rise to the promising catalytic activity. In this work, an extremely sensitive electrochemical H₂O₂ biosensor based on single atomic Fe sites coupled with carbon-encapsulated Fe₃C crystals (Fe₃C@C/Fe-N-C) is proposed. Compared with the conventional Fe SASCs (Fe-N-C), Fe₃C@C/Fe-N-C exhibits superior POD-like activity and electrochemical H₂O₂ sensing performance with a high sensitivity of 1225 μA/mM·cm², fast response within 2 s, and a low detection limit of 0.26 μM. Significantly, sensitive monitoring of H₂O₂ released from living cells is also achieved. Moreover, the density functional theory calculations reveal that the incorporated Fe₃C nanocrystals donate electrons to single atomic Fe sites, endowing them with improved activation ability of H₂O₂ and further enhancing the overall activity. This work provides a new design of synergistically enhanced single atomic sites for electrochemical sensing applications.

Enhanced non-enzymatic glucose sensing based on porous ZIF-67 hollow nanoprisms

Porous ZIF-67 hollow nanoprisms based non-enzymatic glucose sensor was successfully prepared using Co₅(OH)₂(OAc)₈·2H₂O as a precursor by a diffusion-controlled strategy, which exhibited wide linear range and high sensitivity.

Nano-spinel cobalt decorated sulphur doped graphene: an efficient and durable electrocatalyst for oxygen evolution reaction and non-enzymatic sensing of H2O2

We report the synthesis of a nano-spinel cobalt decorated sulphur doped reduced graphene oxide (Co@S–rGO) composite exhibiting excellent electrocatalytic performance and electrochemical stability toward oxygen evolution reaction in an alkaline medium.

Direct Growth of Polycrystalline GaN Porous Layer with Rich Nitrogen Vacancies: Application to Catalyst-Free Electrochemical Detection

It has been demonstrated that defect engineering is an effective strategy to enhance the activity of materials. Herein, a polycrystalline GaN porous layer (PGP) with high catalytic activity was grown by self-assembly on GaN-coated sapphire substrate by using low-temperature (LT) MOCVD growth. Without doping, LT growth can significantly improve the activity and electrical conductivity of PGP, owing to the presence of rich N-vacancies (∼10²⁰ cm^-3). Identification of rich N-vacancies in the PGP material was realized by using atomically resolved STEM (AR-STEM) characterization. The optimized PGP was applied to catalyst-free electrochemical detection of H₂O₂ with a limit of detection (LOD) of 50 nM, a fast response speed of 3 s, a wide linear detection range (50 nM to 12 mM), and a high stability. The LOD is exceeding 40 fold lower than that of reported metal-catalyst decorated GaN. Moreover, a quantitative relationship between the sensing performances and N-vacancy of PGP was established. To our knowledge, it is the first time that intrinsic GaN materials can exhibit high catalytic activity.

Progress of Advanced Nanomaterials in the Non-Enzymatic Electrochemical Sensing of Glucose and H2O2

Non-enzymatic sensing has been in the research limelight, and most sensors based on nanomaterials are designed to detect single analytes. The simultaneous detection of analytes that together exist in biological organisms necessitates the development of effective and efficient non-enzymatic electrodes in sensing. In this regard, the development of sensing elements for detecting glucose and hydrogen peroxide (H₂O₂) is significant. Non-enzymatic sensing is more economical and has a longer lifetime than enzymatic electrochemical sensing, but it has several drawbacks, such as high working potential, slow electrode kinetics, poisoning from intermediate species and weak sensing parameters. We comprehensively review the recent developments in non-enzymatic glucose and H₂O₂ (NEGH) sensing by focusing mainly on the sensing performance, electro catalytic mechanism, morphology and design of electrode materials. Various types of nanomaterials with metal/metal oxides and hybrid metallic nanocomposites are discussed. A comparison of glucose and H₂O₂ sensing parameters using the same electrode materials is outlined to predict the efficient sensing performance of advanced nanomaterials. Recent innovative approaches to improve the NEGH sensitivity, selectivity and stability in real-time applications are critically discussed, which have not been sufficiently addressed in the previous reviews. Finally, the challenges, future trends, and prospects associated with advanced nanomaterials for NEGH sensing are considered. We believe this article will help to understand the selection of advanced materials for dual/multi non-enzymatic sensing issues and will also be beneficial for researchers to make breakthrough progress in the area of non-enzymatic sensing of dual/multi biomolecules.

Nanoporous Silver Submicrocubes Layer by Layer Encapsulated with Polyelectrolyte Films: Nonenzymatic Catalysis for Glucose Monitoring

This article describes the synthesis of nanoporous silver submicrocubes (Np-Ag) capped with poly(allylamine hydrochloride) PAH/poly(styrenesulfonate) PSS bilayers (Np-Ag(PAH/PSS)_n, 1 ≤ n ≤ 4) via layer-by-layer (LBL) assembly for the electrochemical glucose sensing. The consecutive LBL encapsulation of Np-Ag (average size ≈530 nm) with positively charged PAH and negatively charged PSS layers was monitored by using ζ-potential analyses, which showed that the sign of the ζ-potential became positive (+10 mV) or negative (-22 mV) depending on the charge of the encapsulating species. The thickness of two PAH/PSS bilayers on the Np-Ag was estimated to be ∼4 nm (consistent with a literature value of ∼1 nm per PAH or PSS layer) on the basis of a high-resolution transmission electron microscopy image of the Np-Ag(PAH/PSS)₂. Moreover, the high quality of the polyelectrolyte capping on Np-Ag was evidenced by the elemental mapping analysis of particles (obtained by using high-angle annular dark-field scanning transmission electron microscopy), which showed a uniform spatial distribution of C, N, and S (derived from PAH and PSS layers). Among the four different Np-Ag(PAH/PSS)n (1 ≤ n ≤ 4) electrodes, Np-Ag(PAH/PSS)₂ exhibited the highest electrocatalytic activity toward glucose because of the optimal thickness and density of its polyelectrolyte films (fabricated onto Np-Ag). The (Np-Ag(PAH/PSS)₂ electrode demonstrated a detection limit of 20 μM, a sensitivity limit of 472.15 μA mM^-1 cm^-2, and a wide range of detection for glucose at concentrations as high as 23.3 mM along with good selectivity toward glucose. The findings of this study are expected to contribute to improvements in the fabrication and stability of various particle-type catalysts on an electrode surface and to efforts to optimize the device performance using the LBL encapsulation technique.

Flexible Active-Site Engineering of Monometallic Co-Layered Double Hydroxides for Achieving High-Performance Bifunctional Electrocatalyst toward Oxygen Evolution and H2O2 Reduction

It is highly desirable but challenging to develop a facile and scalable strategy to synthesize efficient bifunctional electrocatalysts for oxygen evolution and H₂O₂ reduction by engineering the active site of monometallic-layered double hydroxides (LDHs). Herein, we developed a convenient, efficient, and scalable method for the construction of monometallic Co-LDHs with tunable Coⁿ⁺ (n = 2, 3) concentration by a one-pot solvothermal reaction in a short time (e.g., 2 and 4 h) using only cobalt nitrate and hexamine as raw materials. The catalytic performance of Co-LDHs was mainly determined by the Coⁿ⁺ (n = 2, 3) concentration, which could be simply regulated by tuning the solvothermal time. Combining the joint merits of three-dimensional flowerlike architecture (abundant accessible active sites and a fast electron/mass transport), Co-LDHs-4 with abundant Co³⁺ species exhibited an excellent electrocatalytic activity for oxygen evolution reaction in terms of a low overpotential at 10 mA cm^-2 (η₁₀ = 241 mV) and long-term durability for 70 h at 100 mA cm^-2, better than the state-of-the-art IrO₂ and most of the reported analogues. Besides, Co-LDHs-2 enriched in Co²⁺ displayed a superior electrochemical activity for H₂O₂ detection with a broad linear range (0.002-20 mM), a low detection limit (0.002 mM), and a high response sensitivity (272.02 μA mM^-1 cm^-2). Therefore, this work opens a new horizon for the rational development of a highly active electrocatalyst with tunable concentrations of active components.

In situ growth of CuS decorated graphene oxide-multiwalled carbon nanotubes for ultrasensitive H2O2 detection in alkaline solution

A novel hybrid nanomaterial composed of nanoparticles, nanotubes and nanosheets for electrochemical H₂O₂ detection.

Nitrogen-Doped Graphene-Encapsulated Nickel Cobalt Nitride as a Highly Sensitive and Selective Electrode for Glucose and Hydrogen Peroxide Sensing Applications

To explore a natural nonenzymatic electrode catalyst for highly sensitive and selective molecular detection for targeting biomolecules is a very challenging task. Metal nitrides have attracted huge interest as promising electrodes for glucose and hydrogen peroxide (H₂O₂) sensing applications due to their exceptional redox properties, superior electrical conductivity, and superb mechanical strength. However, the deprived electrochemical stability extremely limits the commercialization opportunities. Herein, novel nitrogen-doped graphene-encapsulated nickel cobalt nitride (Ni _xCo_{3- x}N/NG) core-shell nanostructures with a controllable molar ratio of Ni/Co are successfully fabricated and employed as highly sensitive and selective electrodes for glucose and H₂O₂ sensing applications. The highly sensitive and selective properties of the optimized core-shell NiCo₂N/NG electrode are because of the high synergistic effect of the NiCo₂N core and the NG shell, as evidenced by a superior glucose sensing performance with a short response time of <3 s, a wide linear range from 2.008 μM to 7.15 mM, an excellent sensitivity of 1803 μA mM^-1 cm^-2, and a low detection limit of 50 nM (S/N = 3). Furthermore, the core-shell NiCo₂N/NG electrode shows excellent H₂O₂ sensing performances with a short response time of ∼3 s, a wide detection range of 200 nM to 3.4985 mM, a high sensitivity of 2848.73 μA mM^-1 cm^-2, and ultra-low limit detection of 200 nM (S/N = 3). The NiCo₂N/NG sensor can also be employed for glucose and H₂O₂ detection in human blood serum, promising its application toward the determination of glucose and H₂O₂ in real samples.

Copper Nanoparticle and Nitrogen Doped Graphite Oxide Based Biosensor for the Sensitive Determination of Glucose

Copper nanoparticles with the diameter of 50 ± 20 nm decorated nitrogen doped graphite oxide (NGO) have been prepared through a simple single step carbonization method using copper metal-organic framework (MOF), [Cu₂(BDC)₂(DABCO)] (where BDC is 1,4-benzenedicarboxylate, and DABCO is 1,4-Diazabicyclo[2.2.2]octane) as precursor. The surface morphology, porosity, surface area and elemental composition of CuNPs/NGO were characterized by various techniques. The as-synthesized CuNPs/NGO nanomaterials were coated on commercially available disposable screen-printed carbon electrode for the sensitive determination of glucose. We find that the modified electrode can detect glucose between 1 μM and 1803 μM (linear range) with good sensitivity (2500 μA mM⁻¹ cm⁻²). Our glucose sensor also possesses low limits of detection (0.44 μM) towards glucose determination. The highly selective nature of the fabricated electrode was clearly visible from the selectivity studies. The practicability of CuNPs/NGO modified electrode has been validated in the human serum samples. The storage stability along with better repeatability and reproducibility results additionally substantiate the superior electrocatalytic activity of our constructed sensor towards glucose.

New Titanium Dioxide-Based Heterojunction Nanohybrid for Highly Selective Photoelectrochemical-Electrochemical Dual-Mode Sensors

A new titanium dioxide (TiO₂)-based heterojunction nanohybrid (HJNH) composed of TiO₂, graphene (G), poly[3-aminophenylboronic acid] (PAPBA), and gold nanoparticles (Au NPs) was synthesized and designated as TiO₂(G) NW@PAPBA-Au HJNH. The TiO₂(G) NW@PAPBA-Au HJNH possesses dual-mode signal photoelectrochemical (PEC) and electrochemical transduction capabilities to sense glucose and glycated hemoglobin (HbA1c) independently. The synthesis of the HJNH material involved two sequential stages: (i) simple electrospinning synthesis of G-embedded TiO₂ nanowires [TiO₂(G) NWs] and (ii) one-step synthesis of Au NP-dispersed PAPBA nanocomposite (NC) in the presence of TiO₂(G) NWs. The as-synthesized TiO₂(G) NW@PAPBA-Au HJNH was characterized by field emission scanning electron microscopy, field emission transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared, thermogravimetric analysis, and UV-visible diffuse reflectance spectroscopy. A PEC platform was developed with TiO₂(G) NW@PAPBA-Au HJNH for the selective detection of glucose without any enzyme auxiliary. The PEC glucose sensor presents an acceptable linear range (from 0.5 to 28 mM), good sensitivity (549.58 μA mM^-1 cm^-2), and low detection limit (0.11 mM), which are suited for diabetes glucose monitoring. Besides, the boronic acid groups in PAPBA were utilized as a host to capture HbA1c. We fabricated the electrochemical HbA1c sensor based on monitoring the electrocatalytic reduction current of hydrogen peroxide produced by HbA1c tethered to the sensor probe. The amperometric electrochemical sensor for HbA1c exhibited linear responses to HbA1c levels from 2.0 to 10% (with a detection limit of 0.17%). Notably, the performances of the fabricated glucose and HbA1c sensors are superior in the dual-signal transduction modes as compared to the literature, suggesting the significance of the newly designed bifunctional TiO₂(G) NW@PAPBA-Au HJNH.

Preparation and Characterization of Thermoresponsive Poly(N-isopropylacrylamide-co-acrylic acid)-Grafted Hollow Fe₃O₄/SiO₂ Microspheres with Surface Holes for BSA Release

Thermoresponsive P(NIPAM-AA)/Fe₃O₄/SiO₂ microspheres with surface holes serving as carriers were prepared using p-Fe₃O₄/SiO₂ microspheres with a thermoresponsive copolymer. The p-Fe₃O₄/SiO₂ microspheres was obtained using a modified Pickering method and chemical etching. The surface pore size of p-Fe₃O₄/SiO₂ microspheres was in the range of 18.3 nm~37.2 nm and the cavity size was approximately 60 nm, which are suitable for loading and transporting biological macromolecules. P(NIPAM-AA) was synthesized inside and outside of the p-Fe₃O₄/SiO₂ microspheres via atom transfer radical polymerization of NIPAM, MBA and AA. The volume phase transition temperature (VPTT) of the specifically designed P(NIPAM-AA)/Fe₃O₄/SiO₂ microspheres was 42.5 °C. The saturation magnetization of P(NIPAM-AA)/Fe₃O₄/SiO₂ microspheres was 72.7 emu/g. The P(NIPAM-AA)/Fe₃O₄/SiO₂ microspheres were used as carriers to study the loading and release behavior of BSA. This microsphere system shows potential for the loading of proteins as a drug delivery platform.