Layer-by-layer assembly of functionalized reduced graphene oxide for direct electrochemistry and glucose detection

Recent advances in glucose-oxidase-based nanocomposites for diabetes diagnosis and treatment

Glucose oxidase (GOx) has attracted a lot of attention in the field of diabetes diagnosis and treatment in recent years owing to its inherent biocompatibility and glucose-specific catalysis. GOx can effectively catalyze the oxidation of glucose in the blood to hydrogen peroxide (H2O2) and glucuronic acid and can be used as a sensitive element in biosensors to detect blood glucose concentrations. Nanomaterials based on the immobilization of GOx can significantly improve the performance of glucose sensors through, for example, reduced electron tunneling distance. Moreover, various insulin-loaded nanomaterials (e.g., metal-organic backbones, and mesoporous silica nanoparticles) have been developed for the control of blood glucose concentrations based on GOx catalytic chemistry. These nano-delivery carriers are capable of releasing insulin in response to GOx-mediated changes in the microenvironment, allowing for a rapid return of the blood microenvironment to a normal state. Therefore, glucose biosensors and insulin delivery vehicles immobilized with GOx are important tools for the diagnosis and treatment of diabetes. This paper reviews the characteristics of various GOx-based nanomaterials developed for glucose biosensing and insulin-responsive release as well as research progress, and also highlights the current challenges and opportunities facing this field.

Graphene Oxide Thin Films with Drug Delivery Function

Graphene oxide has been used in different fields of nanomedicine as a manager of drug delivery due to its inherent physical and chemical properties that allow its use in thin films with biomedical applications. Several studies demonstrated its efficacy in the control of the amount and the timely delivery of drugs when it is incorporated in multilayer films. It has been demonstrated that oxide graphene layers are able to work as drug delivery or just to delay consecutive drug dosage, allowing the operation of time-controlled systems. This review presents the latest research developments of biomedical applications using graphene oxide as the main component of a drug delivery system, with focus on the production and characterization of films, in vitro and in vivo assays, main applications of graphene oxide biomedical devices, and its biocompatibility properties.

Adsorption and Release of Rose Bengal on Layer-by-Layer Films of Poly(Vinyl Alcohol) and Poly(Amidoamine) Dendrimers Bearing 4-Carboxyphenylboronic Acid

Phenylboronic acid-bearing polyamidoamine dendrimer (PBA-PAMAM)/poly(vinyl alcohol) (PVA) multilayer films were prepared through the layer-by-layer (LbL) deposition of PBA-PAMAM solution and PVA solution. PBA-PAMAM/PVA films were constructed successfully through the formation of boronate ester bonds between the boronic acid moiety in PBA and 1,3-diol units in PVA. When the (PBA-PAMAM/PVA)₅ films were immersed in rose bengal (RB) solution, RB was adsorbed onto the LbL films. The amount of RB adsorbed was higher in the LbL films immersed in acidic solution than in basic solution. The release of RB from the LbL films was also promoted in the basic solution, while it was suppressed in the acidic solution. The boronic acid ester is oxidized to phenol by hydrogen peroxide (H₂O₂) and the carbon-boron bond is cleaved, so that the (PBA-PAMAM/PVA)₅ films can be decomposed by immersion in H₂O₂ solution. Therefore, when RB-adsorbed (PBA-PAMAM/PVA)₅ films were immersed in H₂O₂ solution, the release of RB was moderately promoted when the solution was weakly acidic.

Determination of Phosphate in Human Serum with Zirconium/Reduced Graphene Oxide Modified Electrode

An electrochemical phosphate sensor based on zirconium and reduced graphene oxide modified pencil graphite electrode (Zr/rGO-PGE) is proposed. The XRD, CV and EIS confirmed that GO was partially reduced on the PGE. Scanning electron microscopy (SEM) exhibited the layered and wrinkled structures for the rGO-PGE and Zr/rGO-PGE, respectively. Cyclic voltammetry showed the immobilized rGO was highly stable and had high activity toward zirconium adsorption. The prepared electrode was used for the electrochemical determination of phosphate. Based on the optimum condition using differential pulse voltammetry, the limit of detection and sensitivity for phosphate was obtained as [0.011(± 0.004) μM] (S/N = 3) and [622.4(± 9.6) μA μM^-1 cm^-2], respectively. The sensor was successfully evaluated for phosphate determination in human serum samples. In practical terms, the construction of this sensor was exceptionally simple, fast, cost effective and reproducible.

A review on graphene-based nanocomposites for electrochemical and fluorescent biosensors

Biosensors with high sensitivity, selectivity and a low limit of detection, reaching nano/picomolar concentrations of biomolecules, are important to the medical sciences and healthcare industry for evaluating physiological and metabolic parameters.

Green synthesis of copper oxide nanoparticles decorated reduced graphene oxide for high sensitive detection of glucose

A non-enzymatic glucose sensor based on pencil graphite electrode (PGE) modified by copper oxide nanoparticles decorated reduced graphene oxide (CuO(NP)/rGO-PGE) was prepared. XRD patterns showed partially electrochemically reduction of GO and monoclinic structure of CuO on the PGE. The prepared CuO(NP)/rGO exhibited a nanoporous structure by scanning electron microscopy (SEM). Transmittance electron microscopy (TEM) revealed copper oxide nanoparticles were well distributed on rGO and had semispherical shapes with diameter 3-5 nm. Cyclic voltammetry at CuO(NP)/rGO-PGE showed the immobilized CuO(NP)s were highly stable in alkaline solutions and had high electrocatalytic activity toward glucose oxidation. Using amperometry, the detection limit of [0.091 (±0.003) μM] and concentration sensitivity of [4760 (±3.2) μA mM^-1 cm^-2] for glucose was obtained at optimum conditions. The applicability of the sensor was evaluated to determine the glucose concentration in human blood serum samples and the experimental results were comparable with those measured by traditional spectrophotometric methods. The preparation of CuO(NP)/rGO-PGE was reproducible, very simple, fast and inexpensive for practical application.

Preparation of Nafion/Polycation Layer-by-Layer Films for Adsorption and Release of Insulin

Thin films were prepared using layer-by-layer (LbL) deposition of Nafion (NAF) and polycations such as poly(allylamine hydrochloride) (PAH), poly(ethyleneimine) (PEI), and poly(diallydimethylammonium chloride) (PDDA). Insulin was then adsorbed on the NAF-polycation LbL films by immersion in an insulin solution. The NAF-polycation LbL films were characterized using a quartz crystal microbalance and an atomic force microscope. The release of insulin from the LbL films was characterized using UV-visible adsorption spectroscopy and fluorescence emission spectroscopy. The greatest amount of insulin was adsorbed on the NAF-PAH LbL film. The amount of insulin adsorbed on the (NAF/PAH)₅NAF LbL films by immersion in a 1 mg mL-1 insulin solution at pH 7.4 was 61.8 µg cm-2. The amount of insulin released from the LbL films was higher when immersed in insulin solutions at pH 2.0 and pH 9.0 than at pH 7.4. Therefore, NAF-polycations could be employed as insulin delivery LbL films under mild conditions and as an insulin release control system according to pH change.

Polyethylene imine/graphene oxide layer-by-layer surface functionalization for significantly improved limit of detection and binding kinetics of immunoassays on acrylate surfaces

Antibody immobilization on polymeric substrates is a key manufacturing step for microfluidic devices that implement sample-to-answer automation of immunoassays. In this work, a simple and versatile method to bio-functionalize poly(methylmethacrylate) (PMMA), a common material of such "Lab-on-a-Chip" systems, is proposed; using the Layer-by-Layer (LbL) technique, we assemble nanostructured thin films of poly(ethylene imine) (PEI) and graphene oxide (GO). The wettability of PMMA surfaces was significantly augmented by the surface treatment with (PEI/GO)₅ film, with an 81% reduction of the contact angle, while the surface roughness increased by 600%, thus clearly enhancing wettability and antibody binding capacity. When applied to enzyme-linked immunosorbent assays (ELISAs), the limit of detection of PMMA surface was notably improved from 340pgmL^-1 on commercial grade polystyrene (PS) and 230pgmL^-1 on plain PMMA surfaces to 130pgmL^-1 on (PEI/GO)₅ treated PMMA. Furthermore, the accelerated antibody adsorption kinetics on the LbL films of GO allowed to substantially shorten incubation times, e.g. for anti-rat IgG adsorption from 2h down to 15min on conventional and treated surfaces, respectively.