Synthesis and characterization of gold–chitosan nanocomposite and application of resultant nanocomposite in sensors

Investigation on optical, structural and electrical properties of solid-state polymer nanocomposites electrolyte incorporated with Ag nanoparticles

A solid polymer electrolyte based on polyvinyl alcohol (PVA)/carboxymethyl cellulose (CMC)/polyethylene 3,4-dioxythiophene: sodium polystyrene sulfonate (PEDOT:PSS) has been prepared with various concentrations of incorporated silver (Ag) nanoparticles (NPs) by using solution cast approach. The FTIR spectroscopic study revealed the complexation between the polymeric nanocomposite (PNC) and the Ag NPs. The X-ray diffraction (XRD) results infer that the semicrystalline phase of PNC decreases as the amount of incorporated Ag NPs increases. The transmission electron microscope (TEM) image revealed that Ag NPs have diameters ranging from 22 to 43 nm. Complex dielectric permittivity and alternating current (AC) electrical conductivity of nanocomposite films have been investigated in the frequency range from 0.1 Hz to 20 MHz at 30 °C. Dc conductivity ([Formula: see text]) values for the nanocomposite films are estimated from AC conductivity plots. The [Formula: see text] value was observed to increase from 1.98 × 10^-9 to 2.29 × 10^-7 S.cm^-1 for the PNC system incorporated with optimal Ag NPs. From complex impedance (Z*) analysis, it has been found that the bulk electrical resistance (R_b) of the PNC films decreases with increasing the Ag NPs content. Therefore, these obtained PNC films have promising applications in energy storage devices.

Gold-Carbon Nanocomposites for Environmental Contaminant Sensing

The environmental crisis, due to the rapid growth of the world population and globalisation, is a serious concern of this century. Nanoscience and nanotechnology play an important role in addressing a wide range of environmental issues with innovative and successful solutions. Identification and control of emerging chemical contaminants have received substantial interest in recent years. As a result, there is a need for reliable and rapid analytical tools capable of performing sample analysis with high sensitivity, broad selectivity, desired stability, and minimal sample handling for the detection, degradation, and removal of hazardous contaminants. In this review, various gold–carbon nanocomposites-based sensors/biosensors that have been developed thus far are explored. The electrochemical platforms, synthesis, diverse applications, and effective monitoring of environmental pollutants are investigated comparatively.

Layer-by-Layer Assembly of Polycations and Polyanions for the Sensitive Detection of Endotoxin

Bacterial endotoxin detection is an essential safety requisite in biomedical, food, and pharmaceutical industries. Endotoxin in a sufficient concentration on entering the human bloodstream causes detrimental effects such as septic shock, which can lead to death. Hence, the sensitive and selective detection of endotoxin also known as lipopolysaccharide (LPS) is of paramount importance. Herein, a layer-by-layer (LBL) assembly of gold-chitosan nanocomposite (CGNC)-poly(acrylic acid) (PAA)-polymyxin B (PmB) on gold (Au) electrode is employed for the sensitive and selective detection of endotoxin. The surface electric charge studies using dynamic contact mode electrostatic force microscopy (DC-EFM) revealed the successful formation of each layer on the Au electrode. The polycationic PmB is a specific bioreceptor of LPS, which binds with high affinity to the anionic groups of the carbohydrate portions of LPS molecules and facilitates the selective electrochemical detection. This surface modification method presented a sensitive and selective detection of endotoxin down to the attogram level.

Synthesis of Ag@PANI nanocomposites by complexation method and their application as label-free chemo-probe for detection of mercury ions

A novel optical probe consistinsg of Ag@PANI (silver-polyaniline) nanocomposites was developed for detection of mercury ions (Hg2+). The poly-dispersed Ag@PANI nanocomposites were synthesized by complexation reaction method. We studied structural and functional properties of polymer nanocomposites thoroughly. Ag@PANI nanocomposites consist of fibrous morphology with a mean particle size of 31.39 nm. Ag@PANI nanocomposites consist of face-centered cubic crystal structure with an average crystallite size of 19.41 nm. Raman spectroscopy was used in sensitive and selective detection of Hg2+ ions in dynamic range of 0.01–0.1 ppm with limit of detection of 0.019 ppm. Ag@PANI nanocomposite sensor for Hg (II) ions has shown some sublime results in pH range 3–5. Ag@PANI-based sensing probe can be beneficial for Hg2+ ions detection in highly sensitive biological, chemical and environmental analysis. Our sensing probe has shown good reproducibility, and all recorded observations revealed that sensing probe consisting of Ag@PANI nanocomposites is well suited for detection of Hg2+ ions.

A simple sonochemical assisted synthesis of NiMoO4/chitosan nanocomposite for electrochemical sensing of amlodipine in pharmaceutical and serum samples

In this investigation, a facile sonochemical route has been developed for the preparation of porous nickel molybdate nanosheets/chitosan nanocomposite (NiMoO₄/CHIT) by using ammonium molybdate and nickel(II) acetate tetrahydrate and as nickel and molybdate precursor, respectively (ultrasonic power 60 W/cm² and frequency 20 kHz). The ultrasonic based materials preparation as a fast, convenient and economical approach has been widely used to generate novel nanomaterials. Herein, we report an efficient voltammetric sensor for amlodipine drug by using porous nickel molybdate nanosheets/chitosan nanocomposite (NiMoO₄/CHIT). Its structure and properties were characterized by x-ray diffraction pattern, scanning electron microscope, transmission electron microscope, elemental analysis and mapping. The electrochemical studies are indicated the NiMoO₄/CHIT modified glassy carbon electrode (GCE) exhibited the good performance towards electrocatalytic sensing of amlodipine drug. Consequently, a linear correlation between the anodic peak current with sensor concentration 0.025-373.6 µM with a detection limit and sensitivity of 4.62 nM and 4.753 µA·µM^-1·cm^-2, respectively. A voltammetry based drug analysis was found to be high sensitive and reproducible, which able to detect nanomolar concentration. Furthermore, the fabricated electrochemical sensor was applied in drug and biological samples.

Facile Synthesis of Nitrogen-Doped Carbon Quantum Dots with Chitosan for Fluorescent Detection of Fe3

A facile, economical, and one-step hydrothermal method was used to prepare highly luminescent nitrogen-doped carbon quantum dots (N-CQDs) with chitosan as both carbon and nitrogen sources. The as-prepared N-CQDs have an average size of 2 nm and exhibit excitation wavelength-dependent fluorescence with a maximum excitation and emission at 330 and 410 nm, respectively. Furthermore, due to the effective quenching effect of Fe³⁺ ions, the prepared N-CQDs can be used as a fluorescent sensor for Fe³⁺ ion-sensitive detection with a detection limit of 0.15 μM. The selectivity experiments revealed that the fluorescent sensor is specific to Fe³⁺ even with interference by high concentrations of other metal ions. Most importantly, the N-CQD-based Fe³⁺ ion sensor can be successfully applied to the determination of Fe³⁺ in real water samples. With excellent sensitivity and selectivity, such stable and cheap carbon materials are potentially suitable for the monitoring of Fe³⁺ in environmental application.

Label-free immunosensor based on one-step electrodeposition of chitosan-gold nanoparticles biocompatible film on Au microelectrode for determination of aflatoxin B1 in maize

Gold nanoparticles (AuNPs) embedded in chitosan (CHI) film, well-dispersed and smaller in size (about 10 nm), were fabricated by one-step electrodeposion on Au microelectrode in solution containing chitosan and chloride trihydrate. The nano-structure CHI-AuNPs composite film offers abundant amine groups, good conductivity, excellent biocompatibility and stability for antibody immobilization. The combination of aflatoxin B1 (AFB1) with immobilized antibody introduces a barrier to electron transfer, resulting in current decreasement. The morphologies and characterizations of modified microelectrodes were investigated by scanning electron microscope (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and Fourier transform infrared spectroscopy (FT-IR). The proposed non-enzyme and label-free immunosensor exhibited high sensitive amperometric response to AFB1 concentration in two linear ranges of 0.1 to 1 ng mL(-1) and 1 to 30 ng mL(-1), with the detection limit of 0.06 ng mL(-1) (S/N=3). The immunoassay was also applied for analysis of maize samples spiked with AFB1. Considering the sample extraction procedure, the linear range and limit of detection were assessed to be 1.6-16 ng mL(-1) and 0.19 ng mL(-1) respectively. The simple method showed good fabrication controllability and reproducibility for immunosensor design.

Antioxidant capacity index based on gold nanoparticles formation. Application to extra virgin olive oil samples

A simple gold nanoparticles (AuNPs) based colorimetric assay for the antioxidant activity determination has been developed. The AuNP formation is mediated by extra virgin olive oil (EVOO's) endogenous polyphenols; the reaction is described by a sigmoidal curve. The ratio KAuNPs/Xc(50) (slope of the linear part of the sigmoid/concentration at half value of the absorbance) was found to be the optimal parameter to report the antioxidant capacity with respect to the single KAuNPs or Xc(50) values. The obtained data demonstrated that the compounds with ortho-diphenols functionality are most active in reducing gold (III) to gold (0). Thus, intermediate activity was found for gallic acid, while tyrosol (mono-phenols) had a significant lower activity than the others antioxidant compounds (at least one order of magnitude). In the analysis of olive oil samples, a significant correlation among classical methods used to determine antioxidant activity and the proposed parameter was found with R values in the 0.96-0.97 range.

Construction of an electrochemical sensor based on amino-functionalized metal-organic frameworks for differential pulse anodic stripping voltammetric determination of lead

Metal-organic frameworks composite materials have received tremendous attention because of their versatile structures and tunable porosity for various applications. Herein, amino-functionalized metal-organic frameworks (NH2-Cu3(BTC)2; BTC=benzene-1,3,5-tricarboxylate) was prepared and used as a novel electrode modifier for the determination of trace levels of lead. NH2-Cu3(BTC)2 shows quite a good capability for the efficient adsorption of lead from aqueous solutions. The parameters affecting the electrochemical process, such as electrolyte solution pH, the amount of NH2-Cu3(BTC)2 suspension, accumulation potential and accumulation time, were investigated in detail. Under the optimal conditions, the electrochemical sensor exhibited a linear response to the concentration of lead in the range of 1.0×10(-8)-5.0×10(-7) mol L(-1) (R(2)=0.9951) with a detection limit of 5.0×10(-9) mol L(-1). The relative standard deviation of 11 successive scans was 3.10% for 1.0×10(-8) mol L(-1) lead. The method was validated with certified reference material (stream sediment and milk powder) and the analytical results coincided well with the certified values. Furthermore, the method was successfully applied to the determination of target analytes in tap and lake water samples and good recoveries were obtained from different spiked values.

Sorption of metal ions by poly(ethylene glycol)/β-CD hydrogels leads to gel-embedded metal nanoparticles

Inorganic nanoparticles can be embedded within gels by selectively preloading them with suitable molecular precursors followed by reduction or another suitable reaction. Here, we exploit the selective sorption properties of cross-linked β-cyclodextrin/poly(ethylene glycol) hydrogels, in analogy with polyurethane foams, to preconcentrate metal salts (HAuCl4 and K2[Co(SCN)4]) and subsequently generate gel-embedded metal nanoparticles (10-50 nm). The nanoparticles are shown to be immobilized within the gel network as a consequence of their large dimensions in comparison to the gel network pore size. We suggest this is a useful approach for the generalized synthesis of hybrid soft-hard nanomaterials.

Electrochemical sensor using neomycin-imprinted film as recognition element based on chitosan-silver nanoparticles/graphene-multiwalled carbon nanotubes composites modified electrode

A novel imprinted electrochemical sensor for neomycin recognition was developed based on chitosan-silver nanoparticles (CS-SNP)/graphene-multiwalled carbon nanotubes (GR-MWCNTs) composites decorated gold electrode. Molecularly imprinted polymers (MIPs) were synthesized by electropolymerization using neomycin as the template, and pyrrole as the monomer. The mechanism of the fabrication process and a number of factors affecting the activity of the imprinted sensor have been discussed and optimized. The characterization of imprinted sensor has been carried out by scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FTIR). The performance of the proposed imprinted sensor has been investigated using cyclic voltammetry (CV) and amperometry. Under the optimized conditions, the linear range of the sensor was from 9×10(-9)mol/L to 7×10(-6)mol/L, with the limit of detection (LOD) of 7.63×10(-9)mol/L (S/N=3). The film exhibited high binding affinity and selectivity towards the template neomycin, as well as good reproducibility and stability. Furthermore, the proposed sensor was applied to determine the neomycin in milk and honey samples based on its good reproducibility and stability, and the acceptable recovery implied its feasibility for practical application.

Synthesis and characterization of novel nano-chitosan Schiff base and use of lead (II) sensor

A new kind of nano-chitosan Schiff base ligand (CHNS) with particle size of 34 nm was formed by the reaction between the 2-amino groups of glucosamine residue of nano-chitosan and a 2,5-dihydroxybenzaldehyde. The chemical structures of the nano-chitosan and nano-chitosan Schiff base were characterized by FT-IR spectra, particle sizer, zeta potential, and elemental analysis. A new, simple and effective chemically modified carbon paste electrode with CHNS was prepared and used as a lead (II) sensor. The prepared electrode was characterized using scanning electronic microscopy (SEM-EDX) and cyclic voltammetry (CV). The modified electrode showed only one oxidation peak in the anodic scan at -0.34 V (vs. Ag/AgCl) for the oxidation of lead (II). The dedection limit (LOD) was calculated as 1.36×10(-7) for a 10-min preconcentration time at pH 6.0.