Ultrathin NiS/Ni(OH)2 Nanosheets Filled within Ammonium Polyacrylate-Functionalized Polypyrrole Nanotubes as an Unique Nanoconfined System for Nonenzymatic Glucose Sensors

Advances in nanostructured material-based non-enzymatic electrochemical glucose sensors

Non-enzymatic electrochemical sensors that use functional materials to directly catalyze glucose have shown great promise in diabetes management, food control, and bioprocess inspection owing to the advantages of high sensitivity, long-term stability, and low cost. Recently, in order to produce enhanced electrochemical behavior, significant efforts have been devoted to the preparation of functional materials with regular nanostructure, as it provides high specific surface area and well-defined strong active sites for electrochemical sensing. However, the structure-performance correlation in this field has not been reviewed thoroughly in the literature. This review aims to present a comprehensive report on advanced zero- to three-dimensional nanostructures based on the geometric feature and to discuss in depth their structural effects on enzyme-free electrochemical detection of glucose. It starts by illustrating the sensing principles of nanostructured materials, followed by a detailed discussion on the structural effects related to the features of each dimension. The structure-performance correlation is explored by comparing the performance derived from diverse dimensional architectures, which is beneficial for the better design of regular nanostructure to achieve efficient enzyme-free sensing of glucose. Finally, future directions of non-enzymatic electrochemical glucose sensors to solve emerging challenges and further improve the sensing performance are also proposed.

Synthesis of a Ni(OH)2@Cu2Se hetero-nanocage by ion exchange for advanced glucose sensing in serum and beverages

Cu₂Se nanosheets were coated on the surface of Ni(OH)₂ nanocages (NCs) by ion exchange driven by selenium incorporation. The resulting Ni(OH)₂@Cu₂Se hollow heterostructures (Ni(OH)₂@Cu₂Se HHSs) showed high electrical conductivity and electrocatalytic activities derived from the synergistic effects of Ni/Cu phases. These structures enhanced glucose adsorption abilities, confirmed by density function theory (DFT) calculations, and the robustness of the integrated nano-electrocatalyst. Remarkably, Ni(OH)₂@Cu₂Se HHSs modified electrodes excited excellent glucose sensing behavior with a wide linear range (0.001-7.5 mM), a sensitivity up to 2420.4 Μa mM^-1 cm², a low limit of detection (LOD, 0.15 μM), and fast response (less 2 s). Furthermore, Ni(OH)₂@Cu₂Se HHSs competently analyzed glucose in serum and beverages with good recoveries ranging from 94.4 to 103.6%. Integrating copper selenide and Ni-based materials as 3D hollow heterostructures expands the selection of electrocatalysts for sensitive glucose detection in food and biological samples.

One-step potentiostatic electrodeposition of NiS-NiS2 on sludge-based biochar and its application for a non-enzymatic glucose sensor

Conventional nanomaterials are available in electrochemical glucose nonenzymatic sensing, but their broad applications are limited due to their high cost and complicated preparation procedures. In this study, NiS-NiS₂/sludge-based biochar/GCE was fabricated by one-step potentiostatic electrodeposition on biochar and used as an interface material for non-enzymatic sensing of glucose in 0.1 M NaOH. With an electrodeposition time of 300 s, the as-prepared sensors delivered the best electrochemical performance toward glucose due to the synergistic effects of NiS-NiS₂ and sludge-based biochar. The as prepared NiS-NiS₂/sludge-based biochar surface morphology, surface composition, and electrochemical properties were characterized by SEM elemental mapping, XPS and cyclic voltammetry. Under optimized conditions, the linearity between the current response and the glucose concentration has been obtained in the range of 5-1500 μM with a detection limit of 1.5 μM. More importantly, the fabricated sensor was successfully utilized to measure glucose in serum of sweetened beverages and human blood. Accordingly, NiS-NiS₂/sludge-based biochar/GCE can hopefully be applied as a normal enzyme-free glucose sensor with excellent properties of sensitivity, reproducibility, stability, as well as sustainability.

In situ growth of Prussian blue analogue-derived Fe-doped NiS on Ni(OH)2 for efficient hydrogen evolution reaction

The energy industry is placing more and more emphasis on the need for effective and affordable electrocatalysts for hydrogen evolution reactions (HER). In this work, an iron-doped NiS/Ni(OH)₂/CC composite material was synthesized by simple hydrothermal sulfurization processes of bimetallic Prussian blue analogue (PBAs) precursors grown in situ on three-dimensional (3D) Ni(OH)₂ nanosheets. The overpotential can be 103 mV to attain current densities of 10 mA cm^-2. The excellent catalytic activity of Fe-NiS/Ni(OH)₂/CC is because of the unique 3D structure and the uniform doping of iron caused by the in situ growth of PBA, as well as the high conductivity of the self-supported electrode carbon cloth.

Unexpected spontaneous dynamic oxygen migration on carbon nanotubes

Combining density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD) simulations, we show that oxygen functional groups exhibit unexpected spontaneous dynamic behaviors on the interior surface of single-walled carbon nanotubes (SWCNTs). The hydroxyl and epoxy migrations are achieved by the C-O bond breaking/reforming reactions or the proton transfer reaction between the neighboring epoxy and hydroxyl groups. It is demonstrated that the spontaneous dynamic characteristic is attributed to the sharply reduced energy barrier less than or comparable to thermal fluctuations. We also observe a stable intermediate state with a dangling C-O bond, which permits the successive migration of the oxygen functional groups. However, on the exterior surface of SWCNTs, it is difficult for the oxygen groups to migrate spontaneously because there are relatively high energy barriers, and the dangling C-O bond prefers to transform into the more stable epoxy configuration. The spontaneous oxygen migration is further confirmed by the oxygen migration process using DFT calculations and AIMD simulations at room temperature. Our work provides a new understanding of the behavior of oxygen functional groups at interfaces and gives a potential route to design new carbon-based dynamic materials.

A hierarchical hollow Ni/Co-functionalized MoS2 architecture with highly sensitive non-enzymatic glucose sensing activity

A hierarchical hollow Ni/Co-codoped MoS2 architecture was successfully prepared using a Ni/Co Prussian Blue analogue as the precursor followed by the solvothermal-assisted insertion of MoS42- and extraction of [Co(CN)6]3- at 200 °C for 32 h. The obtained Ni/Co-codoped MoS2 composite exhibited a hollow microcubic structural characteristic, and the morphology, structure, and chemical compositions were carefully characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS), respectively. The Ni/Co-codoped MoS2 composite used as an electrode material featured excellent glucose sensing activity and a high sensitivity of 2546 μA mM-1 cm-2 with a relatively low detection limit of 0.69 μM (S/N = 3). In addition, the Ni/Co-codoped MoS2 composite showed good anti-interference sensing performance in the presence of ascorbic acid (AA), lysine (Lys), cysteine (Cys), urea, H2O2, KCl, and other interferents. These experimental results revealed that the composite is a promising electrode material for enzyme-free glucose sensing, and the feasible synthetic strategy may provide an effective and controlled route to prepare other multi-metal substituted sulfide-based hierarchical structures with high electrochemical sensing performance.

Incorporating MoO3 Patches into a Ni Oxyhydroxide Nanosheet Boosts the Electrocatalytic Oxygen Evolution Reaction

The electrocatalytic oxygen evolution reaction from H₂O (OER) is essential in a number of areas like electrocatalytic hydrogen production from H₂O. A Ni oxyhydroxide nanosheet (NiNS) is among the most widely studied OER catalysts but still suffers from low activity, sluggish kinetics, and poor stability. Herein, we incorporate MoO₃ patches into NiNS to form a nanosheet with an intimate Ni-Mo interface (NiMoNS) for the OER. The overpotential at 10 mA cm^-2 and Tafel slope on NiMoNS (260 mV, 54.7 mV dec^-1) are lower than those on NiNS (296 mV, 89.3 mV dec^-1), implying that higher activity and faster kinetics are achieved on NiMoNS. There is no change in electrocatalytic efficiency of NiMoNS after 18 h of OER, but the electrocatalytic efficiency of NiNS decreases by 56% after only 8 h of OER. Thus, NiMoNS has better stability. The intimate Ni-Mo interface promotes two-dimensional lateral growth of NiMoNS to form a surface area 1.5 times larger than that of NiNS, and facilitates electron transfer from Ni to Mo. This makes the Ni³⁺/Ni²⁺ ratio on the NiMoNS surface (1.32) higher than that on the NiNS surface (0.68). Moreover, the Ni³⁺/Ni²⁺ ratio on NiMoNS surface increases to 1.81 after 18 h of OER but the Ni³⁺/Ni²⁺ ratio on the NiNS surface decreases to 0.51 after 8 h of OER. Therefore, the NiMoNS surface has more abundant and stable Ni³⁺ sites which are catalytically active toward OER. This could be the reason for the enhanced activity, kinetics, and stability of NiMoNS. The results are very valuable for fabricating more efficient catalysts for electrocatalysis.

Nickel sulfide nanoworm network architecture as a binder-free high-performance non-enzymatic glucose sensor

Nickel sulfide nanoworm (Ni₃S₂ NW) network architecture was directly grown on the poly (3,4-ethylenedioxythiophene)-reduced graphene oxide hybrid films (PEDOT-rGO HFs) modified on glassy carbon electrode (GCE), acting as a binder-free sensor for high-performance non-enzymatic glucose monitoring. The sensor exhibited the satisfactory sensitivity (2123 μA mM^-1 cm^-2), wide linear range (15~9105 μM), low detection limit (0.48 μM), and rapid response time (< 1.5 s) at a potential of 0.5 V (vs. SCE) in 0.1 M NaOH and possessed good selectivity, reproducibility, and stability. The enhanced electrocatalytic activity of the sensor towards glucose oxidation was attributed to the particular morphology, satisfying hydrophilic nature, strong combination between Ni₃S₂ NWs, PEDOT-rGO, and bare GCE. Moreover, it can be used for assaying glucose in human serum samples without dilution, indicating potential for clinical diagnostic applications. Graphical abstract Nickel sulfide nanoworms (Ni₃S₂ NWs)/poly (3,4-ethylenedioxythiophene)-reduced graphene oxide hybrid films (PEDOT-rGO HFs) were used to construct a binder-free high-performance non-enzymatic glucose sensor with satisfactory sensitivity, wide linear range, low detection limit, good selectivity, amazing reproducibility, and stability.

Frozen-State Polymerization as a Tool in Conductivity Enhancement of Polypyrrole

Polypyrrole (PPy) is oxidatively polymerized in the frozen state at -24 °C in the presence of various organic dyes as morphology guiding agents in order to form homogeneous 1D PPy nanoforms. The freezing polymerization of pyrrole has a significant influence on the electrical conductivity and thermal stability but negligible influence on the yield compared to widely used room temperature polymerization.

Ultrathin 1T-MoS2 Nanoplates Induced by Quaternary Ammonium-Type Ionic Liquids on Polypyrrole/Graphene Oxide Nanosheets and Its Irreversible Crystal Phase Transition During Electrocatalytic Nitrogen Reduction

Ultrathin nanoplates of metastable 1T-MoS₂ have been successfully stabilized and uniformly distributed on the surface of n-butyl triethyl ammonium bromide functionalized polypyrrole/graphene oxide (BTAB/PPy/GO) by a very simple hydrothermal method. BTAB as a typical kind of quaternary ammonium-type ionic liquids (ILs) played a crucial role in the formation of the obtained 1T-MoS₂/BTAB/PPy/GO. It was covalently linked with PPy/GO and arranged in a highly ordered order at the solid-liquid interface of PPy/GO and H₂O due to Coulombic interactions and other intermolecular interactions, which would induce and stabilize ultrathin 1T-MoS₂ nanoplates by morphosynthesis. The good electrocatalytic activity toward nitrogen reduction reaction (NRR) with strong durability and good stability can be achieved by 1T-MoS₂/BTAB/PPy/GO due to their excellent inorganic/organic hierarchical lamellar micro-/nanostructures. Especially, after the long-term electrocatalysis for NRR at a negative potential, metastable 1T-MoS₂ as the catalytic center undergoes two types of irreversible crystal phase transition, which was converted to 1T'-MoS₂ and Mo₂N, caused by the competitive hydrogen evolution reaction (HER) process and the electrochemical reaction between the electroactive 1T-MoS₂ and N₂, respectively. The new N-Mo bonding prevents Mo atoms from binding to other N atoms in N₂, resulting in the deactivation of the electrocatalysts to NRR after being used for 18 h. Even so, quaternary ammonium-type ILs would induce the crystal structures of transition-metal dichalcogenides (TMDCs), which might provide a new thought for the reasonable design of electrocatalysts based on TMDCs for electrocatalysis.

Laser-induced graphene hybrid photoelectrode for enhanced photoelectrochemical detection of glucose

The combination of an electrocatalyst with a semiconductor light absorber is of great importance to increase the efficiency of photoelectrochemical (PEC) glucose detection. Here, in situ and synchronous fabrication of a Ni-based electrocatalyst (NiEC) and CdS semiconductor in laser-induced graphene (LIG) on indium-tin oxide glass is demonstrated via a one-step laser-induced solid phase transition. A series of component and structural characterization experiments suggest that the laser-induced NiEC uniformly disperses in the hybrid nanocomposite and exists mainly in the Ni⁰ and NiO states. Moreover, both electrochemical and PEC investigations confirm that the as-prepared hybrid photoelectrode exhibits excellent photoelectrocatalytic ability towards glucose, which is not only attributed to the strong synergistic interaction between CdS and NiEC, but also benefited from the high conductivity as well as 3D macroporous configuration of the simultaneously formed LIG, providing the key factor to achieve sensitive non-enzymatic PEC glucose sensors. Therefore, the laser-induced hybrid photoelectrode is then applied to the PEC detection of glucose, and a low detection limit of 0.4 μM is obtained with good stability, reproducibility, and selectivity. This study provides a promising paradigm for the facile and binder-free fabrication of an electrocatalyst-semiconductor-graphene hybrid photoelectrode, which will find potential applications in sensitive PEC biosensing for a broad range of analytes.

Universal laser-assisted growth of transition metal nanoparticles on a flexible graphene electrode for a nonenzymatic glucose sensor

A universal laser-assisted method was used for the construction of transition metal nanoparticles on graphene as a glucose sensor.