Partially Oxidized Carbon Nanomaterials with Ni/NiO Heterostructures as Durable Glucose Sensors

Electroactive Molecularly Imprinted Polymer Nanoparticles (eMIPs) for Label-free Detection of Glucose: Toward Wearable Monitoring

The diagnosis of diabetes mellitus (DM) affecting 537 million adults worldwide relies on invasive and costly enzymatic methods that have limited stability. Electroactive polypyrrole (PPy)-based molecularly imprinted polymer nanoparticles (eMIPs) have been developed that rival the affinity of enzymes whilst being low-cost, highly robust, and facile to produce. By drop-casting eMIPs onto low-cost disposable screen-printed electrodes (SPEs), sensors have been manufactured that can electrochemically detect glucose in a wide dynamic range (1 µm-10 mm) with a limit of detection (LOD) of 26 nm. The eMIPs sensors exhibit no cross reactivity to similar compounds and negligible glucose binding to non-imprinted polymeric nanoparticles (eNIPs). Measurements of serum samples of diabetic patients demonstrate excellent correlation (>0.93) between these eMIPs sensor and the current gold standard Roche blood analyzer test. Finally, the eMIPs sensors are highly durable and reproducible (storage >12 months), showcasing excellent robustness and thermal and chemical stability. Proof-of-application is provided via measuring glucose using these eMIPs sensor in a two-electrode configuration in spiked artificial interstitial fluid (AISF), highlighting its potential for non-invasive wearable monitoring. Due to the versatility of the eMIPs that can be adapted to virtually any target, this platform technology holds high promise for sustainable healthcare applications via providing rapid detection, low-cost, and inherent robustness.

Improved Urea Oxidation Performance via Interface Electron Redistributions of the NiFe(OH)x/MnO2/NF p-p Heterojunction

The development of highly efficient urea oxidation reaction (UOR) electrocatalysts is the key to simultaneously achieving green hydrogen production and the treatment of urea-containing wastewater. Ni-based electrocatalysts are expected to replace precious metal catalysts for UOR because of their high activity and low cost. However, the construction of Ni-based electrocatalysts that can synergistically enhance UOR still needs further in-depth study. In this study, highly active electrocatalysts of NiFe(OH)x/MnO2 p-p heterostructures are constructed on nickel foam (NF) by electrodeposition (NiFe(OH)x/MnO2/NF), illustrating the effect of electronic structure changes at heterogeneous interfaces on UOR and revealing the catalytic mechanism of UOR. The NiFe(OH)x/MnO2/NF only needs 1.364 V (vs Reversible Hydrogen Electrode, RHE) to reach 10 mA cm-2 for UOR. Structural characterizations and theoretical calculations indicate that energy gap leads to directed charge transfer and redistribution at the heterojunction interface, forming electron-rich (MnO2) and electron-poor (NiFe(OH)x) regions. This enhances the catalyst's adsorption of urea and reaction intermediates, reduces thermodynamic barriers during the UOR process, promotes the formation of Ni3+ phases at lower potentials, and thus improves UOR performance. This work provides a new idea for the development of Ni-based high-efficiency UOR electrocatalysts.

Iridium oxide-based non-enzymatic glucose sensor: Superior electro-catalytic performance in biological environmental media

Nanostructured inorganic materials have potential advantages as glucose-sensing elements in diabetes care, thereby circumventing the need for expensive enzymatic agents. However, many nonenzymatic sensors face challenges related to selectivity and reliability, reducing their efficacy in body fluids. In this study, we introduce an Iridium oxide (IrO2)-based non-enzymatic glucose sensor. This sensor demonstrates exceptional electro-catalytic properties in human serum, characterized by high sensitivity (638 μA μM-1cm2) and a consistent recovery rate (∼104%) across 15 cycles in saline. Furthermore, its impressive performance in human serum, as evidenced by a low relative standard deviation (RSD <1.57%), underscores its applicability in biological matrices such as interstitial fluids. Overall, the IrO2 sensor is a promising, highly reversible, economical, and simple method for detecting glucose in continuous monitoring systems.

Nanostructured Polyoxometalate-Based Heterogeneous Electrode Materials for Electrochemical Sensing of Glucose

We exploited a tactic to obtain a low-cost, high-efficiency, pollution-free, and stable nonenzymatic polyoxometalate-based heterogeneous electrode material for electrochemical sensing of glucose. It is first followed by the countercation exchange of K2Na8[Cu4(H2O)2(PW9O34)2] (CuPOM) using cesium chloride to prepare an insoluble CuPOM (Cs-CuPOM), which exhibits a uniform and perfect claviform shape with smooth surface. Further, it was mixed with graphite powder to prepare Cs-CuPOM-modified carbon paste electrode (Cs-CuPOM/CPE) with the Cs-CuPOM content between 15% and 50% in weight. This obtained electrode material Cs-CuPOM shows a better electrochemical sensor activity than Cs-MnPOM, Cs-FePOM, and other reported POM-based electrode materials for glucose oxidation on account of their quicker electron transfer kinetics, which also exhibits conspicuous characteristics with a wide linear range of 5-1500 μM. It also possesses a high sensitivity of 16.3 A M-1 cm-2 and a low limit of detection (LOD) of 0.99 × 10-6 M at the signal-to-noise ratio of 3. The conspicuous sensing feature, low cost, and liable synthetic method can make Cs-CuPOM a promising candidate for the exploitation of a preeminent glucose sensor.

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.

Electrochemical sensor based on amine- and thiol-modified multi-walled carbon nanotubes for sensitive and selective determination of uranyl ions in real water samples

Novel selective and sensitive electrochemical sensors based on the modification of a carbon paste electrode (CPE) with novel amine- and thiol-functionalized multi-walled carbon nanotubes (MWCNT) have been developed for the detection and monitoring of uranyl ions in different real water samples. Multiwalled carbon nanotubes were grafted with 2-aminothiazole (AT/MWCNT) and melamine thiourea (MT/MWCNT) via an amidation reaction in the presence of dicyclohexyl carbodiimide (DCC) as a coupling agent. This modification for multiwalled carbon nanotubes has never been reported before. The amine and thiol groups were considered to be promising functional groups due to their high affinity toward coordination with uranyl ions. The modified multi-walled carbon nanotubes were characterized using different analytical techniques including FTIR, SEM, XPS, and elemental analysis. Subsequently, 10 wt% MT/MWCNT was mixed with 60 wt% graphite powder in the presence of 30 wt% paraffin oil to obtain a modified carbon paste electrode (MT/MWCNT/CPE). The electrochemical behavior and applications of the prepared sensors were examined using cyclic voltammetry, differential pulse anodic stripping voltammetry, and electrochemical impedance spectroscopy. The MT/MWCNT/CPE sensor exhibited a good linearity for UO22+ in the concentration range of 5.0 × 10-3 to 1.0 × 10-10 mol L-1 with low limits of detection (LOD = 2.1 × 10-11 mol L-1) and quantification (LOQ = 7 × 10-11 mol L-1). In addition, high precision (RSD = 2.7%), good reproducibility (RSD = 2.1%), and high stability (six weeks) were displayed. Finally, MT-MWCNT@CPE was successfully utilized to measure the uranyl ions in an actual water sample with excellent recoveries (97.8-99.3%). These results demonstrate that MT-MWCNT@CPE possesses appropriate accuracy and is appropriate for environmental applications.

Ultrafast Response in Nonenzymatic Electrochemical Glucose Sensing with Ni(II)-MOFs by Dimensional Manipulation

Metal-organic frameworks (MOFs) are emerging as promising candidates for electrochemical glucose sensing owing to their ordered channels, tunable chemistry, and atom-precision metal sites. Herein, the efficient nonenzymatic electrochemical glucose sensing is achieved by taking advantage of Ni(II)-based metal-organic frameworks (Ni(II)-MOFs) and acquiring the ever-reported fastest response time. Three Ni(II)-MOFs ({[Ni6L2(H2O)26]4H2O}n (CTGU-33), {Ni(bib)1/2(H2L)1/2(H2O)3}n (CTGU-34), {Ni(phen)(H2L)1/2(H2O)2}n (CTGU-35)) have been synthesized for the first time, which use benzene-1,2,3,4,5,6-hexacarboxylic acid (H6L) as an organic ligand and introduce 1,4-bis(1-imidazoly)benzene (bib) or 1,10-phenanthroline (phen) as spatially auxiliary ligands. Bib and phen convert the coordination mode of CTGU-33, affording structural dimensions from 2D of CTGU-33 to 3D of CTGU-34 or 1D of CTGU-35. By tuning the dimension of the skeleton, CTGU-34 with 3D interconnected channels exhibits an ultrafast response of less than 0.4 s, which is superior to the existing nonenzymatic electrochemical sensors. Additionally, a low detection limit of 0.12 μM (S/N = 3) and a high sensitivity of 1705 μA mM-1 cm-2 are simultaneously achieved. CTGU-34 further showcases desirable anti-interference and cycling stability, which demonstrates a promising application prospect in the real-time detection of glucose.

Optimized Pore Nanospace through the Construction of a Cagelike Metal-Organic Framework for CO2/N2 Separation

The development of metal-organic framework (MOF) adsorbents with a potential molecule sieving effect for CO₂ capture and separation from flue gas is of critical importance for reducing the CO₂ emissions to the atmosphere yet challenging. Herein, a cagelike MOF with a suitable cage window size falling between CO₂ and N₂ and the cavity has been constructed to evaluate its CO₂/N₂ separation performance. It is noteworthy that the introduction of coordinated dimethylamine (DMA) and N,N'-dimethylformamide (DMF) molecules not only significantly reduces the cage window size but also enhances the framework-CO₂ interaction via C-H···O hydrogen bonds, as proven by molecular modeling, thus leading to an improved CO₂ separation performance. Moreover, transient breakthrough experiments corroborate the efficient CO₂/N₂ separation, revealing that the introduction of DMA and DMF molecules plays a vital role in the separation of a CO₂/N₂ gas mixture.