Direct electrochemistry and electrocatalysis based on a film of horseradish peroxidase intercalated into Ni–Al layered double hydroxide nanosheets

Determination of the total antioxidant capacity of the Chinese tea based on a novel "peroxidase/zirconium phosphonate"composite electrochemical sensor

In this work, a novel zirconium phosphonate (ZrPR1R2) was prepared by decorating both the aminoethoxy- group (R1) and the carboxypropyl- group (R2) on the zirconium phosphate layers in order to manipulate further the immobilization of the peroxidase (POD), and an antioxidant biosensor with higher sensitivity was constructed by dropping the POD/ZrPR1R2 composite onto the glassy carbon electrode surface. The activity of the POD/ZrPR1R2 composite was detected by Uv-vis spectra. The direct electrochemical behavior, the electrocatalytic response to dissolved oxygen and hydrogen peroxide, as well as the ability to detect total antioxidant capacity in tea sample were investigated by the methods of cyclic voltammetry. The results indicated that the immobilization of POD in ZrPR1R2 nanosheets matrix enhanced the enzymatic activity, and achieved the fast and direct electron transfer between POD and glassy carbon electrode. Moreover, the POD/ZrPR1R2 composite modified electrode show the electrocatalytic response to hydrogen peroxide in the linear range of 8.8×10-8 to 8.8×10-7 mol L-1, with the detection limit of 3.3×10-8 mol L-1. Attributing to the sensitive response to dissolved oxygen, the total antioxidant capacity can be detected directly in the real tea water by this POD/ZrPR1R2 composite modified electrode.

Surface modification of two-dimensional layered double hydroxide nanoparticles with biopolymers for biomedical applications

Layered double hydroxides (LDHs) are appealing nanomaterials for (bio)medical applications and their potential is threefold. One can gain advantage of the structure of LDH frame (i.e., layered morphology), anion exchanging property towards drugs with acidic character and tendency for facile surface modification with biopolymers. This review focuses on the third aspect, as it is necessary to evaluate the advantages of polymer adsorption on LDH surfaces. Beside the short discussion on fundamental and structural features of LDHs, LDH-biopolymer interactions will be classified in terms of the effect on the colloidal stability of the dispersions. Thereafter, an overview on the biocompatibility and biomedical applications of LDH-biopolymer composite materials will be given. Finally, the advances made in the field will be summarized and future research directions will be suggested.

Carbon dot based nucleus targeted fluorescence imaging and detection of nuclear hydrogen peroxide in living cells

Investigation of the intracellular generation of H2O2, one of the most important reactive oxygen species (ROS), is crucial for preventing various diseases since it is closely linked with different physiological and complex cell signaling pathways. Despite the development of various fluorescent probes, the majority of the fluorescent probes cannot move across the nuclear membrane. However, detection of the nuclear level of H2O2 is very important since it can directly cause oxidative DNA damage which ultimately leads to various diseases. Therefore, in this study, p-phenylenediamine based carbon quantum dots (B-PPD CDs) have been synthesized and integrated with 4-formylbenzeneboronic acid as a doping agent for the detection of H2O2. The detection mechanism showed that, upon exposure to H2O2, the fluorescence of the B-PPD CDs was immediately quenched. Further investigation has been done in the in vitro RAW 264.7 cell line by both exogenous and endogenous exposure of H2O2 to demonstrate the feasibility of the method. It is shown successfully that the exogenous presence and endogenous generation of H2O2 in RAW 264.7 cells can be detected using B-PPD CDs. The limit of detection (LOD) was determined to be 0.242 μM. The development of such imaging probes using carbon quantum dots will lead to live-cell imaging as well as ROS detection.

Layer-by-Layer Assembly of Electroactive Dye/LDHs Nanoplatelet Matrix Film for Advanced Dual Electro-optical Sensing Applications

It proved that the most destructive effects of the toxic Al3+ ion on the human nervous system and disease that are involved with this system, such as Alzheimer's. The development of solid-state electrodes is still in its infancy during the sensor-based detection methods for Al3+. Hence, in this study, a novel flexible ITO/PET-based electrochemical solid-state sensor was designed and constructed. Modification of the surface of electrode bedding was done by layer-by-layer (LbL) assembly of Mg-Al LDH. nanoplatelets along with alizarin red S (ARS) in an interconnected matrix film. In the molecular design of sensing base of the electrode, the electroactive organic units (ARS molecules) present in the ITO/PET-layered (ARS/LDHs)n matrix are involved in electrochemical reactions when exposed to the target molecule (Al3+ ion), so the electrochemical changes of the new formed Al-chelated system are detectable. This type of sensor is used for sensitive and selective detection of Al3+. The minimum sheet resistance, morphology and high electrocatalytic activity of the modified matrix film are obtained in the fifth cycle of LbL assembly technique. In this electrochemical sensor, both electrochemical and optical methods were detected with high sensitivity and selectivity of Al3+, so that in a cyclic voltammetry electrochemical method, the lower detection limit of 10.1 nM with a linear range of [0.2-120 μM] was obtained compared to the fluorescence-based optical method.

Graphene blended with SnO2 and Pd-Pt nanocages for sensitive non-enzymatic electrochemical detection of H2O2 released from living cells

This paper described a novel, facile and nonenzymatic electrochemical biosensor to detect hydrogen peroxide (H₂O₂). The sensor was fabricated based on Pd-Pt nanocages and SnO₂/graphene nanosheets modified electrode (PdPt NCs@SGN/GCE). The electrochemical behavior of PdPt NCs@SGN/GCE exhibited excellent catalytic activity toward H₂O₂ with fast response, high selectivity, superior sensitivity, low detection limit of 0.3 μM and large linear range from 1 μM to 300 μM. Under these obvious advantages, the constructed biosensor provided to be reliable for determination of H₂O₂ secreted from human cervical cancer cells (Hela cells). Hence, the proposed biosensor is a promising candidate for detection of H₂O₂ in situ released from living cells in clinical diagnostics.

Size-tunable LDH–protein hybrids toward the optimization of drug nanocarriers

Stabilization of LDH nanoparticles containing chloride and dodecylsulfate with BSA points to optimization of drug nanocarriers based on these solids.

Fluorescence of Zn-Al-Eu ternary layered hydroxide response to phenylalanine

We reported the fluorescence of a Zn-Al-Eu ternary layered double hydroxide (LDH) response to an amino acid (phenylalanine) for the first time. As shown in fluorescence, the red emissions attributed to (5)D(0)-(7)F(J) transitions (J=1, 2, 3, 4) of Eu(3+) ions were quenched by the phenylalanine (Phe), and a strong blue emission at around 445 nm appeared. The fluorescent changes may be due to ligand-to-metal charges transfer, which was caused by the interaction between the Zn-Al-Eu LDH and Phe. This interaction was manifested by markedly different chemical shift positions of the Zn 3p(3/2), Al 2p, Eu 4d(3/2), O 1s, and C 1s peaks in the XPS spectra from those of the Zn-Al-Eu LDH and Zn-Al-Eu/Phe composite. Furthermore, the interaction between the LDH and Phe was supported by the results of X-ray diffraction (XRD) measurements, Fourier transform infrared (FT-IR) spectra, and thermogravimetric and differential thermogravimetric (TG-DTG) analysis. The fluorescence of Zn-Al-Eu LDH response to Phe may be potential application in biological techniques.

Facile synthesis of NiAl-layered double hydroxide/graphene hybrid with enhanced electrochemical properties for detection of dopamine

Layered double hydroxides (LDHs), also known as hydrotalcite-like anionic clays, have been investigated widely as promising electrochemical active materials. Due to the inherently weak conductivity, the electrochemical properties of LDHs were improved typically by utilization of either functional molecules intercalated between LDH interlayer galleries, or proteins confined between exfoliated LDH nanosheets. Here, we report a facile protocol to prepare NiAl-LDH/graphene (NiAl-LDH/G) nanocomposites using a conventional coprecipitation process under low-temperature conditions and subsequent reduction of the supporting graphene oxide. Electrochemical tests showed that the NiAl-LDH/G modified electrode exhibited highly enhanced electrochemical performance of dopamine electrooxidation in comparison with the pristine NiAl-LDH modified electrode. Results of high-resolution transmission electron microscopy and Raman spectra provide convincing information on the nanostructure and composition underlying the enhancement. Our results of the NiAl-LDH/G modified electrodes with the enhanced electrochemical performance may allow designing a variety of promising hybrid sensors via a simple and feasible approach.

Three-dimensional network polyamidoamine dendrimer-Au nanocomposite for the construction of a mediator-free horseradish peroxidase biosensor

A three-dimensional network PAMAM-Au nanocomposite (3D-PAMAM-Au NC) was prepared by using the first generation polyamidoamine dendrimer (G1 PAMAM) as the dispersant agent. The resultant 3D-PAMAM-Au NC was successfully used as an immobilization matrix for the construction of a reagentless mediator-free horseradish peroxidase (HRP)-based H(2)O(2) biosensor on a multi-walled carbon nanotubes (MWCNTs) modified glassy carbon electrode. With the advantages of the three-dimensional network, the organic-inorganic hybrid materials dramatically facilitate the direct electron transfer of HRP, and good bioelectrocatalytic activity towards H(2)O(2) was demonstrated. Under optimum conditions, the current response of the enzyme modified electrode at -0.30 V was detected. The current response is linearly correlated to H(2)O(2) concentration within the range of 18.00 μM to 20.80 mM with a correlation coefficient of 0.9992 and a sensitivity of 377.78 μA mM(-1) cm(-2). The detection limit was down to 6.72 μM (S/N = 3). Furthermore, the biosensor exhibits some other excellent characteristics, such as high selectivity, short response time, and long-term stability. The 3D-PAMAM-Au NC has proved to be a promising biosensing platform for the construction of mediator-free biosensors, and may find wide potential applications in biosensors, biocatalysis, bioelectronics and biofuel cells.

Prospects of Nanobiomaterials for Biosensing

Progress and development in biosensor development will inevitably focus upon the technology of the nanomaterials that offer promise to solve the biocompatibility and biofouling problems. The biosensors using smart nanomaterials have applications for rapid, specific, sensitive, inexpensive, in-field, on-line and/or real-time detection of pesticides, antibiotics, pathogens, toxins, proteins, microbes, plants, animals, foods, soil, air, and water. Thus, biosensors are excellent analytical tools for pollution monitoring, by which implementation of legislative provisions to safeguard our biosphere could be made effectively plausible. The current trends and challenges with nanomaterials for various applications will have focus biosensor development and miniaturization. All these growing areas will have a remarkable influence on the development of new ultrasensitive biosensing devices to resolve the severe pollution problems in the future that not only challenges the human health but also affects adversely other various comforts to living entities. This review paper summarizes recent progress in the development of biosensors by integrating functional biomolecules with different types of nanomaterials, including metallic nanoparticles, semiconductor nanoparticles, magnetic nanoparticles, inorganic/organic hybrid, dendrimers, and carbon nanotubes/graphene.

Characterization of hemoglobin immobilized in MgAl-layered double hydroxides by the coprecipitation method

Hemoglobin was immobilized in Mg(2)Al-Layered Double Hydroxides (LDH) by coprecipation method at pH 9.0. Interactions between Hb and LDH particles were investigated by X-ray diffraction patterns, FTIR, UV-vis, circular dichroism, and fluorescence spectroscopies. Morphology and porosity of Mg(2)Al-Hb(cop) biohybrid are analyzed from SEM and TEM images and permeability measurement. The direct electron transfer of immobilized Hb was studied by cyclic voltammetry, and the electrocatalytic activity was evaluated at glassy carbon modified with this Mg(2)Al-Hb(cop) biohybrid. Even though the percentage of electroactive Hb was less than 2%, this bioelectrode showed a low detection limit (1.5 x 10(-8) M) and a very high sensitivity (37 A/M cm(2)) for the amperometric detection of H(2)O(2).

Biosensing applications of clay-modified electrodes: a review

Two-dimensional layered inorganic solids, such as cationic clays and layered double hydroxides (LDHs), also defined as anionic clays, have open structures which are favourable for interactions with enzymes and which intercalate redox mediators. This review aims to show the interest in clays and LDHs as suitable host matrices likely to immobilize enzymes onto electrode surfaces for biosensing applications. It is meant to provide an overview of the various types of electrochemical biosensors that have been developed with these 2D layered materials, along with significant advances over the last several years. The different biosensor configurations and their specific transduction procedures are discussed.