Facile Fabrication of NiO-Decorated Double-Layer Single-Walled Carbon Nanotube Buckypaper for Glucose Detection

Recent trends and prospective developments in metal oxide composites-based electrochemical nonenzymatic glucose sensors

Diabetes mellitus is among the fastest-growing chronic diseases worldwide, with its prevalence increasing at an alarming rate across various populations. Recent advancements notably impact the swift development of nonenzymatic glucose sensors within the fields of nanotechnology and materials science. This review comprehensively examines the relationship between nanostructure design and sensor performance, emphasizing the importance of controlling nanomaterial dimensions to enhance selectivity, specificity, sensitivity, and stability. We discuss various electrode materials' unique nanostructures and highlight innovative fabrication methods that improve glucose detection in alkaline media. This review briefly summarizes the direct oxidation of glucose by metallic redox centers, explaining the underlying mechanisms using the chemisorption model combined with the incipient hydrous oxide/adatom mediator (IHOAM) model. It then highlights recent advances in nonenzymatic glucose sensors based on transition metal oxides (such as CuO, NiO, Co3O4, IrO2, Rh2O3, Fe2O3, MnO2, TiO2, ZnO, and intermixed metal oxides). Additionally, we discuss the advantages and challenges associated with selectivity in nonenzymatic glucose sensing, while proposing practical strategies for optimization. Finally, this review aims to promote further progress in the design and synthesis of nanostructured materials by offering an extensive analysis of current research and future perspectives.

Fabrication of a graphene@Ni foam-supported silver nanoplates-PANI 3D architecture electrode for enzyme-free glucose sensing

Reliable and cost-effective glucose sensors are in rising demand among diabetes patients. The combination of metals and conducting polymers creates a robust electrocatalyst for glucose oxidation, offering enzyme-free, high stability, and sensitivity with outstanding electrochemical results. Herein, graphene is grown on nickel foam by chemical vapor deposition to make a graphene@nickel foam scaffold (G@NF), on which silver nanoplates-polyaniline (Ag-PANI) 3D architecture is developed by sonication-assisted co-electrodeposition. The resulting binder-free 3D Ag-PANI/G@NF electrode was highly porous, as characterized by x-ray photoelectron spectroscopy, Field emission scanning electron microscope, x-ray diffractometer, FTIR, and Raman spectroscopy. The binder-free 3D Ag-PANI/G@NF electrode exhibits remarkable electrochemical efficiency with a superior electrochemical active surface area. The amperometric analysis provides excellent anti-interference performance, a low limit of deduction (0.1 nM), robust sensitivity (1.7 × 1013µA mM-1cm-2), and a good response time. Moreover, the Ag-PANI/G@NF enzyme-free sensor is utilized to observe glucose levels in human blood serums and exhibits excellent potential to become a reliable clinical glucose sensor.

Pyridine-Regulated Lamellar Nickel-Based Metal-Organic Framework (Ni-MOF) for Nonenzymatic Electrochemical Glucose Sensor

2D metal-organic frameworks (MOFs) are considered as promising electrochemical sensing materials and have attracted a lot of attention in recent years. Compared with bulk MOFs, the construction of 2D MOFs can increase the exposure of active sites by obtaining a larger surface area ratio. Herein, a facile one-pot hydrothermal synthesis of pyridine-regulated lamellar Ni-MOFs with ultrathin and well-defined 2D morphology is described. Compared with the bulk structure, the 2D lamellar Ni-MOF has higher surface area and active site density, showing better electrochemical glucose sensing performance. The 2D lamellar Ni-MOF exhibits a fast amperometric response of less than 3 s and a high sensitivity of 907.54 µA mm-1 cm-2 toward glucose with a wide linear range of 0.5-2665.5 µm. Furthermore, the 2D lamellar Ni-MOF also possesses excellent stability and reproducibility, and can be used to detect glucose with high accuracy and reliability in different environments.

A sensitive enzyme-free electrochemical sensor based on a rod-shaped bimetallic MOF anchored on graphene oxide nanosheets for determination of glucose in huangshui

In this work, we propose a bimetallic Ni-Co based MOF attached to graphene oxide (GO) by a one-step hydrothermal approach which may be employed as an electrochemical enzyme-free glucose sensor. Due to the obvious synergistic catalysis of Ni and Co, as well as the combination of NiCo-MOF and GO, NiCo-MOF/GO not only enhances energy transfer and electrocatalytic performance but also provides a larger surface area and more active sites. Electrochemical studies show that NiCo-MOF/GO exhibits outstanding electrochemical activity, with a sensitivity of 11 177 μA mM^-1 cm^-2 and 4492 μA mM^-1 cm^-2 in the linear ranges of 1-497 μM and 597-3997 μM, a detection limit of 0.23 μM, and a response time of 2 seconds. More importantly, the newly fabricated sensor is successfully applied for glucose determination in huangshui. This method provides a novel strategy for the controlled fermentation process and product quality of Chinese baijiu.

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.

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

Conventional enzyme-based glucose biosensors have limited extensive applications in daily life because glucose oxidase is easily inactivated and is expensive. In this paper, we propose a strategy to prepare a new type of cost-effective, efficient, and robust nonenzymatic Ni-CNT-O for electrochemical glucose sensing. It is first followed by the pyrolysis of Ni-ABDC nanostrips using melamine to grow carbon nanotubes (CNTs) to give an intermediate product of Ni-CNT, which is further accompanied by partial oxidation to enable the facile formation of hierarchical carbon nanomaterials with improved hydrophilicity. A series of physicochemical characterizations have fully proved that Ni-CNT-O is a carbon-coated heterostructure of Ni and NiO nanoparticles embedded into coordination polymer-derived porous carbons. The obtained Ni-CNT-O exhibits a better electrocatalytic activity for glucose oxidation stemming from the synergistic effect of a metal element and a metal oxide than unoxidized Ni-CNT, which also shows high performance with a wide linear range from 1 to 3000 μM. It also offers a high sensitivity of 79.4 μA mM^-1 cm^-2, a low detection limit of 500 nM (S/N = 3), and a satisfactory long-term durability. Finally, this glucose sensor exhibits good reproducibility, high selectivity, as well as satisfactory results by comparing the current response of simulated serum within egg albumen.

Construction of a binder-free non-enzymatic glucose sensor based on Cu@Ni core-shell nanoparticles anchored on 3D chiral carbon nanocoils-nickel foam hierarchical scaffold

Bimetallic nanostructures composited with carbonaceous materials are the potential contenders for quantitative glucose measurement owing to their unique nanostructures, high biomimetic activity, synergistic effects, good conductivity and chemical stability. In the present work, chemical vapors deposition technique has been employed to grow 3D carbon nanocoils (CNCs) with a chiral morphology on hierarchical macroporous nickel foam (NF) to get a CNCs/NF scaffold. Following, bimetallic Cu@Ni core-shell nanoparticles (CSNPs) are effectively coupled with this scaffold through a facile solvothermal route in order to fabricate a binder-free novel Cu@Ni CSNPs/CNCs/NF hybrid nanostructure. The constructed free-standing 3D hierarchical composite electrode guarantees highly efficient glucose redox activity due to core-shell synergistic effects, enhanced electrochemical active surface area, excellent electrochemical stability, improved conductivity with better ion diffusivity and accelerated reaction kinetics. Being a non-enzymatic glucose sensor, this electrode achieves highly swift response time of 0.1 s, ultra-high sensitivity of 6905 μA mM^-1 cm^-2, low limit of detection of 0.03 μM along with potential selectivity and good storage stability. Moreover, the proposed sensor is also tested successfully for the determination of glucose concentration in human serum samples under good recovery ranging from 96.6 to 102.1 %. The 3D Cu@Ni CSNPs/CNCs/NF composite electrode with unprecedented catalytic performance can be utilized as an ideal biomimetic catalyst in the field of non-enzymatic glucose sensing.

Advancement in Nanoparticle-Based Biosensors for Point-of-Care In Vitro Diagnostics

Abstract:

Recently, there has been great progress in the field of extremely sensitive and precise detection of bioanalytes. The importance of the utilization of nanoparticles in biosensors has been recognized due to their unique properties. Specifically, nanoparticles of gold, silver, and magnetic plus graphene, quantum dots, and nanotubes of carbon are being keenly considered for utilizations within biosensors to detect nucleic acids, glucose, or pathogens (bacteria as well as a virus). Taking advantage of nanoparticles, faster and sensitive biosensors can be developed. Here we review the nanoparticles' contribution to the biosensors field and their potential applications.

An amphiprotic paper-based electrode for glucose detection based on layered carbon nanotubes with silver and polystyrene particles

In this work, a flexible amphiprotic amino-bonded carbon nanotube-Ag nanoparticle/polystyrene (CNT-NH₂-Ag/PS) paper electrode was fabricated to measure glucose in human body fluids by a combination of vacuum filtration and high temperature baking. The front side of the fabricated paper electrode was hydrophobic and conductive, whereas its back side was hydrophilic and nonconductive. In the fabrication process, the coating sequence of CNT-NH₂, Ag and PS was critical to determine the performance of the resulting CNT-NH₂-Ag/PS electrode besides other parameters (e.g., amount of soluble starch, PS and Ag nanoparticles, type and amount of CNT-NH₂, and electrode sensing area). Based on a series of experimental observations, the possible mechanism of glucose detection on the paper electrode was proposed, in which glucose was more favorable to migrate to the hydrophilic back side of the paper and interact with the active species (e.g., O₂^-) on the electrode surface. The electrochemical results showed that the CNT-NH₂-Ag/PS paper electrode maintained stable electrochemical properties even after five cycles of use and 60 days of storage in air. The amphiprotic paper electrode demonstrated excellent sensing performance for glucose with a linear range of 1 μM to 1000 μM, a low detection limit of 0.2 μM, and a sensitivity of 31 333.0 μA mM^-1 cm^-2. The fabricated paper electrode was also successfully applied to detect different levels of glucose in complex human body fluids such as saliva, urine, and serum. These features make this type of paper electrode promising for glucose measurement.

Facile fabrication of binder-free photoelectrode for sensitive glucose sensing

A novel carbon nitride particle-decorated three-dimensional porous nickel foam (CN/NF) was fabricated by a simple thermal polymerization deposition method for photoelectrochemical glucose detection. In this PEC sensing system, the synergetic effect of the photoactive CN and conductive current collector NF with multi-charge transfer channels contributed to the efficient separation of photoexcited charge carriers. The CN/NF electrode showed an excellent response for glucose detection and good anti-interference properties. A wide linear detection up to 1000μM and sensitivity of 460.2μA cm^-2mM^-1were obtained. This work provides a new strategy for designing binder-free electrodes for PEC sensing.

Applications of Carbon Nanotubes in the Internet of Things Era

The post-Moore's era has boosted the progress in carbon nanotube-based transistors. Indeed, the 5G communication and cloud computing stimulate the research in applications of carbon nanotubes in electronic devices. In this perspective, we deliver the readers with the latest trends in carbon nanotube research, including high-frequency transistors, biomedical sensors and actuators, brain-machine interfaces, and flexible logic devices and energy storages. Future opportunities are given for calling on scientists and engineers into the emerging topics.

A Conformable, Gas-Permeable, and Transparent Skin-Like Micromesh Architecture for Glucose Monitoring

Monitoring the concentration of useful biomarkers via electronic skins (e-skins) is highly important for the development of wearable health management systems. While some biosensor e-skins with high flexibility, sensitivity, and stability have been developed, little attention has been paid to their long-term comfortability and optical transparency. Here, a conformable, gas permeable, and transparent skin-like Cu₂ O@Ni micromesh structural glucose monitoring patch is reported. With its self-supporting micromesh structure, the skin-like glucose monitoring patch exhibits excellent shape conformability, high gas permeability, and high optical transmittance. The skin-like glucose biosensor achieves real-time monitoring of glucose concentrations with high sensitivity (15 420 µA cm^{- 2} mM^{- 1} ), low detection limit (50 nM), fast response time (＜2 s), high selectivity, and long-term stability. These desirable performance properties arise from the synergistic effects of the self-supporting micromesh configuration, high conductivity of the metallic Ni micromesh, and high electrocatalytic activities of the Cu₂ O toward glucose. This work presents a versatile and efficient strategy for constructing conformable, gas permeable, and transparent biosensor e-skins with excellent practicability towards wearable electronics.

A photoelectrochemical self-powered sensor for the detection of sarcosine based on NiO NSs/PbS/Au NPs as photocathodic material

In this study, lead(II) sulfide (PbS) nanocrystals were modified on nickel(II)oxide nanosheets (NiO NSs) via the chemical bath method. Afterwards, Au nanoparticles (NPs) were also modified successfully. A photoelectrochemical (PEC) self-powered platform for detecting sarcosine with high PEC activity was constructed. The capacity of NiO NSs to be loaded with other sensitizing materials was mainly attributed to its porous structure and large specific surface area. Under optimum conditions, the constructed PEC self-powered cathodic sensor for detecting sarcosine exhibited a linear range in 5.0 × 10^-8-5.0 × 10^-2 mol/L with a detection limit (LOD) of 1.7 × 10^-8 mol/L. The biosensor demonstrated good reproducibility, acceptable stability and high specificity, thus confirming its potential application in the detection of other similar substances.

Synthesis of POMOFs with 8-fold helix and its composite with carboxyl functionalized SWCNTs for the voltammetric determination of dopamine

Although many satisfactory studies have been developed for biomolecule detection, the complexity of biofluids still poses a major challenge to improve the performance of nanomaterials as electrochemical sensors. Herein, unprecedented polyoxometalate-based metal-organic frameworks (POMOFs) with 8-fold meso-helical feature, [Ag₅(trz)₄]₂[PMo₁₂O₄₀] (PAZ), were synthesized and explored as electrochemical sensors to detect dopamine (DA). To improve the conductivity of PAZ and the binding ability with single-walled carbon nanotubes (SWCNTs), the nanocomposite of carboxyl functionalized SWCNTs (SWCNTs-COOH) with nano-PAZ (NPAZ), NPAZ@SWCNTs-COOH, was fabricated, and transmission electron microscopy (TEM) shows that NPAZ can interact stably and uniformly with SWCNTs-COOH, owing to more defect sites on the surface of SWCNTs-COOH. The electrochemical result of NPAZ@SWCNTs-COOH/GCE towards detecting DA shows that the linear range was from 0.05 to 100 μM with a detection limit (LOD) of 8.6 nM (S/N = 3). A new electrochemical biosensing platform by combining 8-fold helical POMOFs with SWCNTs-COOH was developed for enhancing detection of dopamine for the first time, exhibiting the lowest detection limit to date.

Stretchable and Transparent Electrochemical Sensor Based on Nanostructured Au on Carbon Nanotube Networks for Real-Time Analysis of H2O2 Release from Cells

Various electrochemical biosensors have been developed for direct and real-time recording of biomolecules released from living cells. However, since these traditional electrodes are commonly rigid and nonflexible, in situ monitoring of biochemical signals while cell deformation occurs remains a great challenge. Herein, we report a facile approach for the development of a stretchable and transparent electrochemical cell-sensing platform based on Au nanostructures (nano-Au) and carbon nanotube (CNT) films embedded in PDMS (nano-Au/CNTs/PDMS). The sandwich-like nanostructured network of nano-Au/CNTs endows the sensor with excellent mechanical stability and electrochemical performance. The obtained nano-Au/CNTs/PDMS electrode displays desired performance for H₂O₂ detection with a wide linear range (20 nM-25.8 μM) and low detection limit (8 nM). Owing to good biocompatibility and flexibility, HeLa and human umbilical vein endothelial cells can be directly cultured on the electrode and real-time monitoring of H₂O₂ release from cells under their stretched state was realized. The proposed strategy demonstrated in this work provides an effective way for design of stretchable sensors and more opportunities for sensing biomolecules from mechanically sensitive cells.

An Overview on Recent Progress of Metal Oxide/Graphene/CNTs-Based Nanobiosensors

Nanobiosensors are convenient, practical, and sensitive analyzers that detect chemical and biological agents and convert the results into meaningful data between a biologically active molecule and a recognition element immobilized on the surface of the signal transducer by a physicochemical detector. Due to their fast, accurate and reliable operating characteristics, nanobiosensors are widely used in clinical and nonclinical applications, bedside testing, medical textile industry, environmental monitoring, food safety, etc. They play an important role in such critical applications. Therefore, the design of the biosensing interface is essential in determining the performance of the nanobiosensor. The unique chemical and physical properties of nanomaterials have paved the way for new and improved sensing devices in biosensors. The growing demand for devices with improved sensing and selectivity capability, short response time, lower limit of detection, and low cost causes novel investigations on nanobiomaterials to be used as biosensor scaffolds. Among all other nanomaterials, studies on developing nanobiosensors based on metal oxide nanostructures, graphene and its derivatives, carbon nanotubes, and the widespread use of these nanomaterials as a hybrid structure have recently attracted attention. Nanohybrid structures created by combining these nanostructures will directly meet the future biosensors' needs with their high electrocatalytic activities. This review addressed the recent developments on these nanomaterials and their derivatives, and their use as biosensor scaffolds. We reviewed these popular nanomaterials by evaluating them with comparative studies, tables, and charts.

3D NiCo-Layered double Hydroxide@Ni nanotube networks as integrated free-standing electrodes for nonenzymatic glucose sensing

Nickel cobalt layered double hydroxide (NiCo-LDH)-based materials have recently emerged as catalysts for important electrochemical applications. However, they frequently suffer from low electrical conductivity and agglomeration, which in turn impairs their performance. Herein, we present a catalyst design based on integrated, self-supported nickel nanotube networks (Ni-NTNWs) loaded with NiCo-LDH nanosheets, which represents a binder-free, hierarchically nanostructured electrode architecture combining continuous conduction paths and openly accessible macropores of low tortuosity with an ultrahigh density of active sites. Similar to macroscale metallic foams, the NTNWs serve as three-dimensionally interconnected, robust frameworks for the deposition of active material, but are structured in the submicron range. Our synthesis is solely based on scalable approaches, namely templating with commercial track-etched membranes, electroless plating, and electrodeposition. Morphological and compositional characterization proved the successful decoration of the inner and outer nanotube surfaces with a conformal NiCo-LDH layer. Ni-NTNW electrodes and hydroxide-decorated variants showed excellent performance in glucose sensing. The highest activity was achieved for the catalyst augmented with NiCo-LDH nanosheets, which surpassed the modification with pure Ni(OH)₂. Despite its low thickness of 20 µm, the optimized catalyst layer provided an outstanding sensitivity of 4.6 mA mM^-1 cm^-2, a low detection limit of 0.2 µM, a fast response time of 5.3 s, high selectivity and stability, and two linear ranges covering four orders of magnitude, up to 2.5 mM analyte. As such, derivatized interconnected metal nano-networks represent a promising design paradigm for highly miniaturized yet effective catalyst electrodes and electrochemical sensors.

Green fabrication of Cu/rGO decorated SWCNT buckypaper as a flexible electrode for glucose detection

As a paper-like membrane composed of single-walled carbon nanotube (SWCNT), buckypaper possesses high conductivity, ideal flexibility, large surface area, great thermal/chemical stability and biocompatibility, which has manifested its potential as an alternative support material. However, due to the lack of defects, high quality SWCNT synthesized by arc-discharge method is difficult to be modified with metal nanoparticles for electro-catalysis. In this paper, a novel green strategy has been developed to fabricate SWCNT buckypaper decorated with Cu/reduced graphene oxide (Cu/rGO-BP) for the first time, in which graphene oxide functions as the intermediate between SWCNT and Cu nanoparticles. The fabricated Cu/rGO-BP was applied as a flexible electrode for electrochemical glucose detection. The electrode exhibited excellent electro-catalytic activity for glucose oxidation. The sensor based on Cu/rGO-BP performed a high upper limit of linear range (25 mM), which is close to commercial glucose sensors. The proposed strategy for Cu/rGO-BP fabrication can be extended to modify buckypaper with other metal or metal oxide nanoparticles, and thus opens an innovative route to potential practical applications of flexible buckypaper in wearable bioelectronics.

Hetero-structured MnO-Mn3O4@rGO composites: Synthesis and nonenzymatic detection of H2O2

The construction of metal-oxide heterojunction architecture has greatly widened applications in the fields of optoelectronics, energy conversions and electrochemical sensors. In this study, olive-like hetero-structured MnO-Mn₃O₄ microparticles wrapped by reduced graphene oxide (MnO-Mn₃O₄@rGO) were synthesized through a facile solvothermal-calcination treatment. The morphology and structure of MnO-Mn₃O₄@rGO were characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and X-ray diffraction. The as-synthesized MnO-Mn₃O₄@rGO exhibited prominent catalyzing effect on the electroreduction of H₂O₂, due to the combination of good electrical conductivity of rGO and the synergistic effect of MnO and Mn₃O₄. The MnO-Mn₃O₄@rGO modified glassy carbon electrode provided a wide linear response from 0.004 to 17 mM, a low detection limit of 0.1 μM, and high sensitivity of 274.15 μA mM^-1 cm^-2. The proposed sensor displayed noticeable selectivity and long-term stability. In addition, the biosensor has been successfully applied for detecting H₂O₂ in tomato sauce with good recovery, revealing its promising potential applications for practical electrochemical sensors.

Facile one-step targeted immobilization of an enzyme based on silane emulsion self-assembled molecularly imprinted polymers for visual sensors

Immobilized enzymes play significant roles in many practical applications. However, the enzymes need to be purified before immobilization by conventional immobilizing methods, and the purification process is expensive, laborious, complicated and results in a decrease of the enzymatic activity. So, we present a novel method by a facile one-step targeted immobilization of an enzyme without a purification process from complex samples. For this purpose, a novel molecularly imprinted polymer was prepared via a silane emulsion self-assembly method using boric acid-modified Fe3O4 nanoparticles as magnetic nuclei, horseradish peroxidase as a template, 3-aminopropyltriethoxysilane as a functional monomer and tetraethyl orthosilicate as a crosslinking agent. The molecularly imprinted polymers were characterized using a scanning electron microscope, X-ray photoelectron spectroscope, vibrating sample magnetometer and X-ray diffractometer. The as-prepared and characterized materials were employed to immobilize horseradish peroxidase from a crude extract of horseradish. Moreover, the immobilized horseradish peroxidase was employed to develop visual sensors for the detection of glucose and sarcosine. This study demonstrated that the molecularly imprinted polymers prepared via the silane emulsion self-assembly method can facilely immobilize horseradish peroxidase from a crude extract of horseradish without any purification process. The developed visual method based on the immobilized horseradish peroxidase shows great potential applications for the visual detection of glucose and sarcosine.

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.

A buckypaper decorated with CoP/Co for nonenzymatic amperometric sensing of glucose

A freestanding and flexible buckypaper modfied with CoP/Co (CoP/Co-BP) is described. It has a sponge-like nanostructure and is shown to enable improved nonenzymatic sensing of glucose. The CoP/Co-BP was prepared by first depositing a uniform layer of ZIF- 67 crystals on BP, followed by two steps of pyrolysis treatment and phosphidation under an argon atmosphere. The morphology and structure of the material were characterized by scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The electrochemical properties were investigated by cyclic voltammetry and amperometric response. The amperometric sensor, best operated at 0.45 V (vs. SCE) at pH 13 has a linear range that extends from 0.5 μM to 1.8 mM of glucose, a 0.2 μM detection limit (at S/N = 3), and a sensitivity of 6427 μA mM^-1 cm^-2 in alkaline solution. This is mainly attributed to the synergistic effect between the highly active CoP nanostructure and BP which results in excellent conductivity. The uniformly distributed CoP nanoparticles in the network of BP prevent the formation of close-packed structure and facilitate electron transfer. The sensor has good selectivity and excellent long-term stability. It was applied to the determination of glucose in spiked human serum, and satisfactory results were obtained. Graphical abstractSchematic presentation of a freestanding and flexible buckypaper modfied with CoP/Co. It has a sponge-like nanostructure and exhibits improved catalytic activity toward glucose oxidation. This material was used for high-performance electrochemical glucose sensing.

Engineering the valence state of ZIF-67 by Cu2O for efficient nonenzymatic glucose detection

The valence state regulation of Co-based electrocatalysts is extremely important and greatly challenging to enhance the electrochemical performance toward glucose oxidation.

A comparative study of electrocatalytic oxidation of glucose on conductive Ni-MOF nanosheet arrays with different ligands

A glucose sensor based on conductive Ni-MOF nanosheet arrays/CC exhibits a fast response time, a low detection limit, a high sensitivity, and it can also be applied for the detection of glucose in human serum samples.

Electrochemical non-enzymatic glucose sensors: recent progress and perspectives

This review summarizes recent advances in the development of electrocatalysts for non-enzymatic glucose detection. The sensing mechanism and influencing factors are discussed, and the perspectives and challenges are also addressed.

Fluorescent biosensor based on magnetic cross-linking enzyme aggregates/CdTe quantum dots for the detection of H2O2-bioprecursors

A fluorescent sensing system for H₂O₂-bioprecursors based on CdTe quantum dots and magnetic cross-linking enzyme aggregates was designed.

Self-assembled multilayer surfaces of highly fluorescent spirobifluorene-based dye for label-free protein recognition

The preparation of smart surfaces for protein detection is a challenging field of research. With the aim to achieve label-free detection in the solid state, we report on the organic surface functionalization for protein recognition without the need of previous chemical modification of the fluorophore. Layer-by-layer deposition of polyelectrolyte poly(vinyl benzyl tetramethylammonium) chloride (p(VBTMA)Cl) and a tetrasulfonate water-soluble low molecular weight fluorophore (1) based on spirobifluorene leads to modified glass and quartz substrates with outstanding photophysical properties in response to bovine serum albumin (BSA). The absorbance, photoluminescence as well as the fluorescence lifetimes were recorded for all surfaces. The surface structure and height of the different number of bilayers polymer/fluorophore were characterized by atomic force microscopy and ellipsometry. The results show linear trends in the absorption, fluorescence and height of the multilayer with increasing number of functionalization steps. Upon incubation with BSA the multilayer shows an increase in fluorescence up to 3-fold, which is also detectable with the naked eye. In conclusion, we report an easy, fast and biocompatible approach for the construction of protein sensors by self-assembly.

Tailoring the dimensionality of carbon nanostructures as highly electrochemical supports for detection of carcinoembryonic antigens

Partially- and fully-unzipped nitrogen-doped carbon nanotubes (NCNTs) were prepared by unzipping pristine NCNTs and three carbon nanostructures were applied to support Au nanoparticles (AuNPs) to form nanocomposites (Au/NCNTs, Au/PU-NCNTs, and Au/FU-NCNTs). The electrochemical behavior and the electrocatalytic activities of the nanocomposite-modified electrodes were examined. The oxygen functional groups, doped N content, and AuNP loaded concentrations are dependent on the unzipping-degree and then affect the electrochemical response and electrocatalytic performance of the electrodes. Besides, the three nanocomposites were also used for the immobilization of carcinoembryonic antigen (CEA) aptamer strands and applied for the detection of CEA. The Au/FU-NCNTs possess the optimal electrocatalytic activity and biosensing performance for the biomolecules and CEA, which is attributed to the maximum loaded AuNPs, the largest specific surface areas and the most active sites. The Au/FU-NCNT-based electrochemical aptasensor exhibits high sensitivity with a low detection limit of 6.84 pg mL-1 within a broad linear range of CEA concentration from 0.01 to 10 ng mL-1. All of these results indicate that the Au/FU-NCNTs may be a potential support for construction of aptasensors with high electrochemical effect and can be employed in the fields of biosensing or biomedical diagnosis.