Functionalized Gold Nanoparticles - Octadecylamine Hybrid Langmuir-Blodgett Film for Enzyme Sensor

Periodically-ordered one and two dimensional CdTe QD superstructures: a path forward in photovoltaics

By using the state-of-the-art theoretical method, we herein explore the potentiality of covalently linked periodically-ordered 1D chain, 2D hexagonal and square ordered superstructures of CdTe QDs in photovoltaics.

Unveiling the effect of 11-MUA coating on biocompatibility and catalytic activity of a gold-core cerium oxide-shell-based nanozyme

The biocompatibility and catalytic activity of nanomaterials exhibiting biological enzyme-like functions (nanozymes) are controlled by shape, size, composition, and surface capping molecules. Although synthesis of multifunctional nanozymes for multiple applications has shown tremendous attraction among researchers worldwide, often their biocompatibility is compromised. In this work, we report the replacement of CTAB by 11-MUA from the surface of a Au-core CeO₂-shell NP-based nanozyme studied for exhibiting multiple enzyme-like activities such as peroxidase, catalase, and superoxide dismutase. We compared the biocompatibility and enzyme-like activities of CTAB coated Au-core CeO₂-shell NPs (CSNPs) before and after 11-MUA coating. The catalytic reaction mechanism of peroxidase-like activity of CTAB coated CSNPs was found to be the “Random Bi–Bi”, which also remained unaltered after removal of surface CTAB with 11-MUA. The other kinetic parameters, K_m and V_max values, of 11-MUA coated CSNPs were found to be comparable to the CTAB coated NPs.

Replacement of CTAB and CeO₂ nanoparticle layer by 11-MUA from the surface of Au core-CeO₂ shell nanoparticle.

Synthesis and Properties of the Self-Assembly of Gold-Copper Nanoparticles into Nanoribbons

We report the efficient wet-chemical production of self-assembled gold-copper bimetallic nanoparticles (diameter of ∼2 nm) into two-dimensional flexible ribbonlike nanostructures. The direct observation of a layered arrangement of particles into nanoribbons was provided through high-resolution transmission electron microscopy and electron tomography. These nanoribbons showed photoluminesce and efficient photocatalytic activity for the conversion of 4-nitrophenol. The thermal stability of the nanoribbons was also measured by in situ heat treatment in the electron microscope, confirming that the self-assembled gold-copper nanoribbons efficiently supported up to 350 °C. The final morphology of the nanoparticles and their ability to self-assemble into flexible nanoribbons were dependent on concentration and the ratio of precursors. Therefore, these experimental factors were discussed. Remarkably, the presence of copper was found to be critical to triggering the self-assembly of nanoparticles into ordered layered structures. These results for the synthesis and stability of self-assemblies of metallic nanoparticles present a potential extension of the method to producing materials with catalytic applications.

Mediator-free total cholesterol estimation using a bi-enzyme functionalized nanostructured gold electrode

A one-step electrochemical route for the synthesis, functionalization and deposition of Au nanostructures and for the bi-enzyme functionalization of a Au electrode has been proposed.

Inducing electrocatalytic functionality in ZnO thin film by N doping to realize a third generation uric acid biosensor

A third generation uric acid biosensor has been developed by exploiting the electrocatalytic functionality of nitrogen (N) doped zinc oxide (ZnO:N) thin film matrix deposited using pulsed laser deposition technique. The electrochemistry of ZnO:N thin film based electrode is investigated by using electrochemical impedance spectroscopy and cyclic voltammetry. The obtained results demonstrate that nitrogen doping in ZnO matrix offers a striking electrocatalytic activity to the immobilized uricase towards the oxidation of analyte (uric acid) and promotes the direct transfer of electrons from active sites of enzyme onto the electrode without any mediator. In contrast to pure ZnO, ZnO:N (8% N) thin film based uric acid biosensor gives a high sensitivity of about 1.38 mA/mM in the absence of mediator. Moreover, ZnO:N derived bio-electrode exhibits excellent selectivity and outstanding analytical stability and reproducibility, which enables a reliable and sensitive determination of uric acid in the serum. The ZnO:N thin film based biosensor exhibits a linear sensing response in the range from 0 to 1.0mM of uric acid concentration and the apparent Michaelis-Menten kinetic parameter (Km) is estimated to be about 0.13 mM which indicates the high affinity of the prepared bio-electrode towards uric acid. The obtained results are encouraging and indicate that the ZnO:N thin film matrix offers a new and promising platform for the development of novel third generation biosensors without using any mediator.

Realization of an efficient cholesterol biosensor using ZnO nanostructured thin film

A zinc oxide (ZnO) nanostructured thin film synthesized by a vapour phase transport technique on a platinum coated silicon (Pt/Si) substrate has been successfully utilized for the detection of cholesterol. Amperometric and photometric studies reveal that the prepared bioelectrode ChOx/ZnO/Pt/Si is highly sensitive to the detection of cholesterol over a wide concentration range, 0.12-12.93 mM (5-500 mg dl(-1)). The higher sensitivity is attributed to the large surface area of ZnO thin film for effective loading of ChOx besides its high electron communication capability. A relatively low value of the enzyme's kinetic parameter (Michaelis-Menten constant, 1.08 mM) indicates an enhanced affinity of the enzyme (ChOx) towards the analyte (cholesterol). The prepared bioelectrode is found to exhibit a long shelf life of more than 10 weeks, having negligible interference from the presence of other biomolecules present in human serum indicating potential application of the ZnO nanostructured thin film for cholesterol sensing.

Polyaniline Langmuir-Blodgett film based aptasensor for ochratoxin A detection

Ochratoxin A (OTA) produced by Aspergillus Ochraceus and Penicillium verrucosum is a very dangerous toxin due to its toxic effects in human beings and its presence in a wide range of food products and cereals. A Langmuir-Blodgett (polyaniline (PANI)-stearic acid (SA)) film based highly sensitive and robust impedimetric aptasensor has been developed for ochratoxin A (OTA) detection. DNA Aptamer (Apt-DNA) specific to OTA has been covalently immobilized onto mixed Langmuir-Blodgett (LB) monolayer comprising of PANI-SA deposited onto indium tin-oxide (ITO) coated glass plates. This Apt-DNA/PANI-SA/ITO aptaelectrode has been characterized using scanning electron microscopy, Fourier transform-infrared spectroscopy, contact angle measurements, cyclic voltammetry and electrochemical impedance spectroscopy, respectively. The Apt-DNA/PANI-SA/ITO aptasensor shows detection of OTA by electrochemical impedance spectroscopy in the linear range of 0.0001 μg/ml (0.1 ng/ml) to 0.01 μg/ml (10 ng/ml) and 1 μg/ml-25 μg/ml with detection limit of 0.1 ng/ml in 15 min. The Apt-DNA/PANI-SA/ITO aptasensor can be reused ∼13 times. The binding or affinity constant (K(a)) of aptamer with OTA, calculated using Langmuir adsorption isotherm, is found be 1.21×10(7) M(-1).

Covalent immobilization of cholesterol oxidase on self-assembled gold nanoparticles for highly sensitive amperometric detection of cholesterol in real samples

A novel scheme for the fabrication of gold nanoparticle modified cholesterol oxidase based bioelectrode is presented and its application potential for cholesterol biosensor is investigated. The fabrication procedure is based on the deposition of gold nanoparticles on the 1,6-hexanedithiol modified gold electrode, functionalization of the surface of deposited gold nanoparticles with carboxyl groups using 11-mercaptoundecanoic acid and then covalent immobilization of cholesterol oxidase on the surface of gold nanoparticle film using the N-ethyl-N'-(3-dimethylaminopropyl carbodimide) and N-hydroxysuccinimide ligand chemistry. The assembly process of the bioelectrode is investigated using atomic force microscopy, cyclic voltammetry and electrochemical impedance spectroscopy. The gold nanoparticle film on the electrode surface provided an environment for the enhanced electrocatalytic activities and thus resulted in enhanced analytical response. The resulting bioelectrode is further applied to the amperometric detection of cholesterol and exhibited a linear response to cholesterol in the range of 0.04-0.22 mM with a detection limit of 34.6 μM, apparent Michaelis-Menten constant (K(m)(app)) of 0.062 mM and a high sensitivity of 9.02 μA mM(-1). The fabricated bioelectrode is successfully used for the selective determination of cholesterol in human serum samples.