Preparation of gold nanoparticles/functionalized multiwalled carbon nanotube nanocomposites and its glucose biosensing application

Fabrication of Carboxylated Carbon Nanotube Buckypaper Composite Films for Bovine Serum Albumin Detection

The salient point of this study is to fabricate carbon nanotube (CNT) buckypaper composite films prepared through the methods of pumping filtration and spin coating. Firstly, carboxylated CNTs were used to make the original buckypaper specimen and further modify the buckypaper surface by incorporating different surface modifiers. Then, all of original (unmodified) and modified buckypaper composite films had different concentrations of bovine serum albumin (BSA) added, and differential pulse voltammetry (DPV) electrochemical measurement was used to measure the characteristics of the various buckypaper composite films, after adding different concentrations of BSA. The experimental results show that the contact angles for four modified specimens are smaller than that of the original unmodified S–BP specimen (62°). These results indicate that the four modifiers used in this study can improve the hydrophilic properties of the original, unmodified S–BP specimen, and benefit the subsequent bonding of a modified specimen with aqueous BSA. In addition to the improvement of the hydrophilic properties of the modified specimen, which affects the bonding with BSA, the bonding type produced by the modifier also plays an essential role in the bonding between specimen and BSA. Therefore, the S–BP–EDC/NHS and S–BP–TA specimens have better linear dependence between log (BSA concentration) and oxidation current data.

Using sonochemistry for the production of poly(vinyl alcohol)/MWCNT–vitamin B1 nanocomposites: exploration of morphology, thermal and mechanical properties

Functionalized MWCNTs with vitamin B₁ as a green material were applied for the enhancement of poly(vinyl alcohol) properties.

Recent advances in designing nanomaterial based biointerfaces for electrochemical biosensing cardiovascular biomarkers

Early diagnosis of cardiovascular disease (CVD) is critically important for successful treatment and recovery of patients. At present, detection of CVD at early stages of its progression becomes a major issue for world health. The nanoscale electrochemical biosensors exhibit diverse outstanding properties, rendering them extremely suitable for the determination of CVD biomarkers at very low concentrations in biological fluids. The unique advantages offered by electrochemical biosensors in terms of sensitivity and stability imparted by nanostructuring the electrode surface together with high affinity and selectivity of bioreceptors have led to the development of new electrochemical biosensing strategies that have introduced as interesting alternatives to conventional methodologies for clinical diagnostics of CVD. This review provides an updated overview of selected examples during the period 2005-2018 involving electrochemical biosensing approaches and signal amplification strategies based on nanomaterials, which have been applied for determination of CVD biomarkers. The studied CVD biomarkers include AXL receptor tyrosine kinase, apolipoproteins, cholesterol, C-reactive protein (CRP), D-dimer, fibrinogen (Fib), glucose, insulin, interleukins, lipoproteins, myoglobin, N-terminal pro-B-type natriuretic peptide (BNP), tumor necrosis factor alpha (TNF-α) and troponins (Tns) on electrochemical transduction format. Identification of new specific CVD biomarkers, multiplex bioassay for the simultaneous determination of biomarkers, emergence of microfluidic biosensors, real-time analysis of biomarkers and point of care validation with high sensitivity and selectivity are the major challenges for future research.

Ultrasonic-assisted biosurface modification of multi-walled carbon nanotubes with Thiamine and its influence on the properties of PVC/Tm-MWCNTs nanocomposite films

The present paper represents a simple and efficient technique via ultrasonic irradiation, which utilized for chemical treatment of carboxylated multi-walled carbon nanotubes (MWCNTs-COOH) with Thiamine (Tm). Poly(vinyl chloride) (PVC) based nanocomposites (NC)s were prepared by the incorporation of various amounts of modified MWCNTs (4, 8, and 12wt%) within the PVC matrix by blending solution and ultrasonic distribution methods. The morphological, chemical structure and thermal stability of the PVC/Tm-MWCNT NCs were identified via Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction, transmission electron microscopy, field emission scanning electron microscopy, and thermogravimetric analysis. The obtained results of thermal behavior indicated the high thermal stability of PVC/Tm-MWCNT NCs in comparison with the pure PVC via presenting diverse quantities of Tm-MWCNTs. In addition, the mechanical behavior of the PVC/Tm-MWCNT NCs films was examined and the results exhibited that mechanical properties of fabricated NCs were improved.

Chemiresistive properties regulated by nanoscale curvature in molecularly-linked nanoparticle composite assembly

Interparticle spatial properties influence the electrical and functional properties of nanoparticle-structured assemblies. This report describes the nanoscale curvature-induced change in chemiresistive properties of molecularly-linked assemblies of gold nanoparticles on multiwalled carbon nanotubes, which are exploited for sensitive detection of volatile organic compounds. In addition to using linking/capping molecules to define interparticle spatial distances, the nanoscale curvature radius of the carbon nanotubes provides intriguing tunability of the interparticle spatial properties to influence electrical properties, which contrast with those observed for nanoparticle thin films assembled directly on chemiresistor devices. The electrical characteristics of the nanoparticle-nanotube composite give positive response profiles for the vapor molecules that are distinctively different to those observed for conventional nanoparticle thin-film assemblies. The dominant effect of electron coupling on overall chemiresistive properties is shown in relation to that of nanoscale curvature radius on the nanoparticle thin-film sensing properties. Sensing data are also further assessed in correlation with the solubility parameters of the vapor molecule. These findings have significant implications for the design of sensitive interfaces with nanocomposite-structured sensing materials and microfabricated chemiresistor devices.

Fabrication of a sensitive amperometric sensor for NADH and H2O2 using palladium nanoparticles-multiwalled carbon nanotube nanohybrid

Palladium nanoparticles decorated multiwalled carbon nanotubes (PdNPs-MWCNTs) were synthesized and simply cast on the surface of a glassy carbon electrode (GCE) to prepare an amperometric sensor. The fabricated sensor (PdNPs-MWCNTs/GCE) showed excellent electrocatalytic activity towards NADH and H2O2 oxidation and H2O2 reduction. A fast, linear and highly sensitive response was observed for NADH in the concentration range between 0.1 and 200 μM with a detection limit (S/N=3) of 32 nM. Also, the sensor exhibited fast and sensitive responses (<2 s) towards H2O2. The sensitivity and detection limit for H2O2 at the operating potential of +0.35 V were 167 nA μM(-1)cm(-2) and 1.2 μM, respectively and better than those obtained at the operating potential of -0.25 V (68 nA μM(-1)cm(-2) and 14 μM). Moreover, further modification of the proposed sensor by glucose oxidase led to the fabrication of a glucose biosensor with satisfactory performance.

Construction of an Electrochemical Sensor Based on Carbon Nanotubes/Gold Nanoparticles for Trace Determination of Amoxicillin in Bovine Milk

In this work, a novel electrochemical sensor was fabricated for determination of amoxicillin in bovine milk samples by decoration of carboxylated multi-walled carbon nanotubes (MWCNTs) with gold nanoparticles (AuNPs) using ethylenediamine (en) as a cross linker (AuNPs/en-MWCNTs). The constructed nanocomposite was homogenized in dimethylformamide and drop casted on screen printed electrode. Field emission scanning electron microscopy (FESEM), energy dispersive X-Ray (EDX), X-Ray diffraction (XRD) and cyclic voltammetry were used to characterize the synthesized nanocomposites. The results show that the synthesized nanocomposites induced a remarkable synergetic effect for the oxidation of amoxicillin. Effect of some parameters, including pH, buffer, scan rate, accumulation potential, accumulation time and amount of casted nanocomposites, on the sensitivity of fabricated sensor were optimized. Under the optimum conditions, there was two linear calibration ranges from 0.2-10 µM and 10-30 µM with equations of Ipa (µA) = 2.88C (µM) + 1.2017; r = 0.9939 and Ipa (µA) = 0.88C (µM) + 22.97; r = 0.9973, respectively. The limit of detection (LOD) and limit of quantitation (LOQ) were calculated as 0.015 µM and 0.149 µM, respectively. The fabricated electrochemical sensor was successfully applied for determination of Amoxicillin in bovine milk samples and all results compared with high performance liquid chromatography (HPLC) standard method.

Electrochemical Detection Using Ionic Liquids

Ionic liquids are relatively new additions to the field of electrochemical sensing. Despite that, they have had a significant impact, and several major areas are covered herein. This includes the application of ionic liquids in the quantification of heavy metals, explosives, and chemical warfare agents, and in biosensors and bioanalysis. Also highlighted are the significant advantages ionic liquids inherently have with regards to gas sensors and carbon paste electrodes, by virtue of their non-volatility, inherent conductivity, and diversity of structure and function. Finally, their incorporation with carbon nanomaterials to form various gels, pastes, films, and printed electrodes is also highlighted.

Growth kinetics of gold nanoparticles on silica/graphene surfaces for multiplex biological immunoassays

Gold nanoparticles were seed-mediated grown on graphene coated substrates and the resulting composites were employed in light-scattering imaging biosensor immunoassay application.

Neuron-like polyelectrolyte–carbon nanotube composites for ultra-high loading of metal nanoparticles

We report a simple protocol for the fabrication of multiwalled carbon nanotubes (MWCNTs) with a neuron-like structure for loading ultra-high densities of metal nanoparticles (NPs).

Chitosan-functionalized carbon nanotubes as support for the high dispersion of PtRu nanoparticles and their electrocatalytic oxidation of methanol

Carbon nanotubes (CNTs) were non-covalently functionalized with chitosan (Chit) and then employed as the support for PtRu nanoparticles. The functionalization was carried out at room temperature without the use of corrosive acids, thereby preserving the integrity and the electronic conductivity of the CNTs. Transmission electron microscopy reveals that PtRu nanoparticles were highly dispersed on the surface of Chit-functionalized CNTs (CNT-Chit) with small particle-size. Cyclic voltammetry studies indicated that the PtRu nanoparticle/CNT-Chit nanohybrids have a higher electrochemical surface area, electrocatalytic performance, and stability towards methanol oxidation compared to PtRu nanoparticles supported on the pristine CNTs.

A Biocompatible Nanocomposite for Glucose Sensing

A nanocomposite containing amine functionalized multiwalled carbon nanotubes and a room temperature ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate) was prepared and applied for glucose oxidase (GOx) immobilization on glassy carbon electrode. The proposed nanocomposite provided a favorable microenvironment to preserve the bioactivity of GOx. It could also effectively facilitate the enzyme direct electron transfer to the electrode. This brought about a remarkable improvement in the sensitivity of the glucose biosensor. Under the optimum experimental conditions, the formal potential of GOx was about −467.5 mV. Moreover, the sensitivity and response time of the biosensor toward glucose were 1277 μA mM-1 cm-2and 6 s, respectively. The biosensor provided a linear dynamic response between 0.1 and 43 μM with a very low detection limit of 63 nM. Also, the values for apparent Michaelis-Menten constant and maximum current were obtained as 18 μM and 2.7 μA, respectively.

Purification, functionalization, and bioconjugation of carbon nanotubes

Bioconjugation of carbon nanotubes (CNTs) with biomolecules promises exciting applications such as biosensing, nanobiocomposite formulation, design of drug vector systems, and probing protein interactions. Pristine CNTs, however, are virtually water-insoluble and difficult to evenly disperse in a liquid matrix. Therefore, it is necessary to attach molecules or functional groups to their sidewalls to enable bioconjugation. Both noncovalent and covalent procedures can be used to conjugate CNTs with a target biomolecule for a specific bioapplication. This chapter presents a few selected protocols that can be performed at any wet chemistry laboratory to purify and biofunctionalize CNTs. The preparation of CNTs modified with metallic nanoparticles, especially gold, is also described since biomolecules can bind and self-organize on the surfaces of such metal-decorated CNTs.

A silicon nanowire-based electrochemical glucose biosensor with high electrocatalytic activity and sensitivity

An electrochemical glucose biosensor was developed by immobilizing glucose oxidase (GOx) on an electrode decorated with a novel nanostructure, silicon nanowires (SiNWs) with in situ grown gold nanoparticles (AuNPs). The immobilized GOx displayed a pair of well-defined and quasi-reversible redox peaks with a formal potential (E(o ')) of -0.376 V in a phosphate buffer solution. The fabricated glucose biosensor has good electrocatalytic activity toward oxidation of glucose. In addition, such resultant SiNWs-based glucose biosensor possesses high biological affinity. Particularly, the apparent Michaelis-Mentan constant was estimated to be 0.902 mM, which is much smaller than the reported values for GOx at a range of nanomaterials-incorporated electrodes. Consequently, this novel SiNWs-based biosensor is expected to be a promising tool for biological assays (e.g., monitoring blood glucose).

Synthesis and application of widely soluble graphene sheets

A widely soluble graphene sheet/Congo red (GSCR) composite was synthesized and applied to prepare GSCR/Au hybrid materials. UV-vis absorption, Fourier transform infrared, Raman, and X-ray photoelectron spectra revealed that Congo red (CR) is successfully coupled on graphene sheets. The morphology of GSCR was studied by transmission electron microscopy, scanning electron microscopy, and atomic force microscopy. The dispersion behavior of the GSCR composite was also studied in 18 different solvents, and the digital images indicate that it is soluble both in water and in a variety of organic solvents. The GSCR nanosheets are still single layers or bilayers in water and individual from one to another after 100 days of storage. Furthermore, the mechanism of GSCR's good solubility was successfully explained by the Hansen solubility parameters. The four standard probe result shows that the GSCR films have a bulk conductivity of approximately 6850 S m(-1). The wide solubility and long lifetime of GSCR solutions are absolutely necessary for further treatment. As an example, Au nanoparticles densely decorated CR-functionalized graphene sheets through electrostatic interaction.