Direct electrochemical analysis of glucose oxidase on a graphene aerogel/gold nanoparticle hybrid for glucose biosensing

An ultrasensitive electrochemical biosensor for microRNA-21 detection via AuNPs/GAs and Y-shaped DNA dual-signal amplification strategy

Herein, a gold nanoparticles/graphene aerogels (AuNPs/GAs) modified electrochemical biosensor with catalytic hairpin assembly (CHA) and Y-shaped DNA nanostructure dual-signal amplification approaches for ultrasensitive microRNA-21 (miR-21) detection was successfully constructed, which displayed an ultra-wide detection linear range from 5 fM to 50 nM, as well as a relatively low detection limit (LOD) of 14.70 aM (S/N = 3). Furthermore, the sensing strategy had excellent specificity among highly homologous miRNA family members and exhibited satisfactory analytical performance for miRNA detection.

Microelectrode glucose biosensor based on nanoporous platinum/graphene oxide nanostructure for rapid glucose detection of tomato and cucumber fruits

Microelectrode glucose biosensor based on three-dimensional hybrid nanoporous platinum/graphene oxide nanostructure was developed for rapid glucose detection of tomato and cucumber fruits. The nanostructure was fabricated by a two-step modification method on microelectrode for loading a larger amount of glucose oxidase. The nanoporous structure was prepared on the surface of the platinum microelectrode by electrochemical etching, and then graphene oxide was deposited on the prepared nanoporous electrode by electrochemical deposition. The nanoprorous platinum/graphene oxide nanostructure had the advantage of improving the effective surface area of the electrode and the loading quantity of glucose oxidase. As a result, the biosensor achieved a wide range of 0.1-20.0 mM in glucose detection, which had the ability to accurately detect the glucose content. It was found that the three-dimensional hybrid nanostructure on the electrode surface realized the rapid direct electrochemistry of glucose oxidase. Therefore, the biosensor achieved high glucose detection sensitivity (11.64 μA mM -1cm -2), low detection limit (13 μM) and rapid response time (reaching 95% steady-state response within 3 seconds), when calibrating in glucose standard solution. In agricultural application, the as-prepared biosensor was employed to detect the glucose concentration of tomato and cucumber samples. The results showed that the relative deviation of this method was less than 5% when compared with that of HPLC, implying high accuracy of the presented biosensor in glucose detection in plants.

Carbon-based aerogels for biomedical sensing: Advances toward designing the ideal sensor

Carbon based aerogels are special solid-state materials comprised of interconnected networks of 3D nanostructures with high amount of air-filled nanoporous. They expand the structural properties along with physicochemical characteristics of nanoscale construction blocks to macroscale, and incorporate distinctive attributes of aerogels, like large surface area, high porosity, and low density, with particular features of the different constituents. These features impart aerogels with rapid response signal, high selectivity, and ultra-sensitivity for sensing diverse targets in biomedical media. This has prompted researchers to develop a variety of aerogel-based sensors with encouraging achievements. Hence, this work outlines sensing applications of aerogel-based sensors with a comprehensive overview on the carbon aerogel hybrid materials and their analytical performances. Authors tried to list advantages and limitations of the developed approach and introduced more potent research for possible devices designing. We also point out some challenges and future perspectives related to the improvement of high-efficiency aerogel-based sensors.

Development of graphene-based enzymatic biofuel cells: A minireview

Enzymatic biofuel cells (EBFCs) have attracted increasing attention due to their potential to harvest energy from a wide range of fuels under mild conditions. Fabrication of effective bioelectrodes is essential for the practical application of EBFCs. Graphene possesses unique physiochemical properties making it an attractive material for the construction of EBFCs. Despite these promising properties, graphene has not been used for EBFCs as frequently as carbon nanotubes, another nanoscale carbon allotrope. This review focuses on current research progress in graphene-based electrodes, including electrodes modified with graphene derivatives and graphene composites, as well as free-standing graphene electrodes. Particular features of graphene-based electrodes such as high conductivity, mechanical flexibility and high porosity for bioelectrochemical applications are highlighted. Reports on graphene-based EBFCs from the last five years are summarized, and perspectives for graphene-based EBFCs are offered.

Bioaerogels: Synthesis approaches, cellular uptake, and the biomedical applications

Aerogels are a class of porous structures with promising physicochemical properties. Among aerogels with various origins, polysaccharide aerogels (e.g., cellulose, chitosan, alginate, starch, agar, and so on) have received more attention. This group of aerogels can be classified as bioaerogels, which are originated from natural, semi-synthetic, and synthetic sources with exceptional biomedical applications. This review focuses on bioaerogels from the viewpoints of synthesis approaches, cellular uptake, toxicity, biodegradability, and the biomedical application perspectives.

A Mediated BOD Biosensor Based on Immobilized B. Subtilis on Three-Dimensional Porous Graphene-Polypyrrole Composite

We have developed a novel mediated biochemical oxygen demand (BOD) biosensor based on immobilized Bacillus subtilis (B. subtilis) on three-dimensional (3D) porous graphene-polypyrrole (rGO-PPy) composite. The 3D porous rGO-PPy composite was prepared using hydrothermal method following with electropolymerization. Then the 3D porous rGO-PPy composite was used as a support for immobilizing negatively charged B. subtilis denoted as rGO-PPy-B through coordination and electrostatic interaction. Further, the prepared rGO-PPy-B was used as a microbial biofilm for establishing a mediated BOD biosensor with ferricyanide as an electronic acceptor. The indirect determination of BOD was performed by electrochemical measuring ferrocyanide generated from a reduced ferricyanide mediator using interdigited ultramicroelectrode array (IUDA) as the working electrode. The experimental results suggested a good linear relationship between the amperometric responses and BOD standard concentrations from 4 to 60 mg/L, with a limit detection of 1.8 mg/L (S/N ≥ 3). The electrochemical measurement of real water samples showed a good agreement with the conventional BOD₅ method, and the good anti-interference as well as the long-term stability were well demonstrated, indicating that the proposed mediated BOD biosensor in this study holds a potential practical application of real water monitoring.

A sensitive label-free electrochemical immunosensor for detection of cytokeratin 19 fragment antigen 21-1 based on 3D graphene with gold nanopaticle modified electrode

Previous studies have confirmed that cytokeratin 19 fragment antigen 21-1 (CYFRA 21-1) serves as a powerful biomarker in non-small cell lung cancer (NSCLC). Herein, we report for the first time a label-free electrochemical immunosensor for sensitive and selective detection of tumor marker CYFRA21-1. In this work, three-dimensional graphene @ gold nanoparticles (3D-G@Au) nanocomposite was modified on the glassy carbon electrode (GCE) surface to enhance the conductivity of immunosensor. The anti-CYFRA21-1 captured and fixed on the modified GCE through the cross-linking of chitosan (CS), glutaraldehyde (GA) and anti-CYFRA21-1. The differential pulse voltammetry (DPV) peak current change due to the specific interaction between anti-CYFRA21-1 and CYFRA21-1 on the modified electrode surface was utilized to detect CYFRA21-1. Under optimized conditions, the proposed electrochemical immunosensor was employed to detect CYFRA21-1 and exhibited a wide linear range of 0.25-800ngmL^-1 and low detection limit of 100pgmL^-1 (S/N = 3). Moreover, the recovery rates of serum samples were in the range from 95.2% to 108.7% and the developed immunosensor also shows a good correlation (less than 6.6%) with enzyme-linked immunosorbent assay (ELISA) in the detection of clinical serum samples. Therefore, it is expected that the proposed immunosensor based on a 3D-G@Au has great potential in clinical medical diagnosis of CYFRA21-1.

Carbon Nanomaterial Based Biosensors for Non-Invasive Detection of Cancer and Disease Biomarkers for Clinical Diagnosis

The early diagnosis of diseases, e.g., Parkinson's and Alzheimer's disease, diabetes, and various types of cancer, and monitoring the response of patients to the therapy plays a critical role in clinical treatment; therefore, there is an intensive research for the determination of many clinical analytes. In order to achieve point-of-care sensing in clinical practice, sensitive, selective, cost-effective, simple, reliable, and rapid analytical methods are required. Biosensors have become essential tools in biomarker sensing, in which electrode material and architecture play critical roles in achieving sensitive and stable detection. Carbon nanomaterials in the form of particle/dots, tube/wires, and sheets have recently become indispensable elements of biosensor platforms due to their excellent mechanical, electronic, and optical properties. This review summarizes developments in this lucrative field by presenting major biosensor types and variability of sensor platforms in biomedical applications.

One-step synthesis of nitrogen, boron co-doped fluorescent carbon nanoparticles for glucose detection

Heteroatom-doped carbon nanoparticles (CNPs) have attracted considerable attention due to an effective improvement in their intrinsic properties. Here, a facile and simple synthesis of nitrogen, boron co-doped carbon nanoparticles (NB-CNPs) from a sole precursor, 3-aminophenylboronic acid, was performed via a one-step solid-phase approach. Because of the presence of boronic acid, NB-CNPs can be used directly as a fluorescent probe for glucose. Based on a boronic acid-triggered specific reaction, we developed a simple NB-CNP probe without surface modification for the detection of glucose. When glucose was introduced, the fluorescence of NB-CNPs was suppressed through a surface-quenching states mechanism. Obvious fluorescence quenching allowed the highly sensitive determination of glucose with a limit of detection of 1.8 μM. Moreover, the proposed method has been successfully used to detect glucose in urine from people with diabetes, suggesting potential application in sensing glucose.

Ultradispersed Cobalt Ferrite Nanoparticles Assembled in Graphene Aerogel for Continuous Photo-Fenton Reaction and Enhanced Lithium Storage Performance

The Photo-Fenton reaction is an advanced technology to eliminate organic pollutants in environmental chemistry. Moreover, the conversion rate of Fe³⁺/Fe²⁺ and utilization rate of H₂O₂ are significant factors in Photo-Fenton reaction. In this work, we reported three dimensional (3D) hierarchical cobalt ferrite/graphene aerogels (CoFe₂O₄/GAs) composites by the in situ growing CoFe₂O₄ crystal seeds on the graphene oxide (GO) followed by the hydrothermal process. The resulting CoFe₂O₄/GAs composites demonstrated 3D hierarchical pore structure with mesopores (14~18 nm), macropores (50~125 nm), and a remarkable surface area (177.8 m²g⁻¹). These properties endowed this hybrid with the high and recyclable Photo-Fenton activity for methyl orange pollutant degradation. More importantly, the CoFe₂O₄/GAs composites can keep high Photo-Fenton activity in a wide pH. Besides, the CoFe₂O₄/GAs composites also exhibited excellent cyclic performance and good rate capability. The 3D framework can not only effectively prevent the volume expansion and aggregation of CoFe₂O₄ nanoparticles during the charge/discharge processes for Lithium-ion batteries (LIBs), but also shorten lithium ions and electron diffusion length in 3D pathways. These results indicated a broaden application prospect of 3D-graphene based hybrids in wastewater treatment and energy storage.

Reduced graphene oxide/gold nanoparticle aerogel for catalytic reduction of 4-nitrophenol

Fabrication of reduced graphene oxide/gold nanoparticle aerogel for catalytic reduction of 4-nitrophenol.

Graphene based enzymatic bioelectrodes and biofuel cells

The excellent electrical conductivity and ease of functionalization make graphene a promising material for use in enzymatic bioelectrodes and biofuel cells. Enzyme based biofuel cells have attracted substantial interest due to their potential to harvest energy from organic materials. This review provides an overview of the functional properties and applications of graphene in the construction of biofuel cells as alternative power sources. The review covers the current state-of-the-art research in graphene based nanomaterials (physicochemical properties and surface functionalities), the role of these parameters in enhancing electron transfer, the stability and activity of immobilized enzymes, and how enhanced power density can be achieved. Specific examples of enzyme immobilization methods, enzyme loading, stability and function on graphene, functionalized graphene and graphene based nanocomposite materials are discussed along with their advantages and limitations. Finally, a critical evaluation of the performance of graphene based enzymatic biofuel cells, the current status, challenges and future research needs are provided.