M.U. Anu Prathap

Hydrothermal synthesis of CuO micro-/nanostructures and their applications in the oxidative degradation of methylene blue and non-enzymatic sensing of glucose/H2O2.

In this paper, we report on the amino acids-/citric acid-/tartaric acid-assisted morphologically controlled hydrothermal synthesis of micro-/nanostructured crystalline copper oxides (CuO). These oxides were characterized by means of X-ray diffraction, nitrogen sorption, scanning electron microscopy, Fourier transform infrared, and UV-visible spectroscopy. The surface area of metal oxides depends on the amino acid used in the synthesis. The formation mechanisms were proposed based on the experimental results, which show that amino acid/citric acid/tartaric acid and hydrothermal time play an important role in tuning the morphology and structure of CuO. The catalytic activity of as-synthesized CuO was demonstrated by catalytic oxidation of methylene blue in the presence of hydrogen peroxide (H(2)O(2)). CuO synthesized using tyrosine was found to be the best catalyst compared to a variety of CuO synthesized in this study. CuO (synthesized in this study)-modified electrodes were used for the construction of non-enzymatic sensors, which displayed excellent electrocatalytic response for the detection of H(2)O(2) and glucose compared to conventional CuO. The high electrocatalytic response observed for the CuO synthesized using tyrosine can be correlated with the large surface area, which enhances the accessibility of H(2)O(2)/glucose molecule to the active site that results in high observed current. The methodology adopted in the present study provides a new platform for the fabrication of CuO-based high-performance glucose and other biosensors.

Direct synthesis of metal oxide incorporated mesoporous SBA-15, and their applications in non-enzymatic sensing of glucose.

One-step direct synthetic route is reported for the preparation of M-SBA-15 materials (M=Cu, Ni, Co, Fe, and Mn) with nSi/nM ratios ranging from 100 to 10 under mild acidic condition than conventionally employed for the synthesis of Si-SBA-15. Materials were characterized by a complementary combination of X-ray diffraction, nitrogen sorption, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared, and UV-visible spectroscopy. Experimental evidences show that metal oxides are incorporated in the pore wall of SBA-15 matrices. A non-enzymatic electrochemical sensor device was fabricated for glucose detection based on M-SBA-15 materials. Cyclic voltammetry and linear sweep voltammetry were used to evaluate the catalytic activity of the M-SBA-15 modified electrode toward glucose. It was found that the Cu-SBA-15 (Si/Cu=20) modified electrode showed enhanced electrocatalytic activity toward the oxidation of glucose in alkaline solution compared to that of the conventional CuO and other M-SBA-15 materials investigated in this study. Under the optimal detection conditions, the Cu-SBA-15 (Si/Cu=20) exhibited linear behavior in the concentration range from 10 μM to 20 mM for the quantification of glucose with a limit of detection of 10 μM. Moreover, the Cu-SBA-15 modified electrode was also relatively insensitive to commonly interfering species such as ascorbic acid, uric acid, and dopamine.

Polyaniline-Based Highly Sensitive Microbial Biosensor for Selective Detection of Lindane

A highly sensitive, selective, and rapid, whole-cell-based electrochemical biosensor was developed for detection of the persistent organochlorine pesticide γ-hexachlorocyclohexane (γ-HCH), commonly known as lindane. The gene linA2 encoding the enzyme γ-hexachlorocyclohexane (HCH) dehydrochlorinase (LinA2), involved in the initial steps of lindane (γ-HCH) biotransformation, was cloned and overexpressed in Escherichia coli . The lindane-biodegrading E. coli cells were immobilized on polyaniline film. The rapid and selective degradation of lindane and concomitant generation of hydrochloric acid by the recombinant E. coli cells in the microenvironment of polyaniline led to a change in its conductivity, which was monitored by pulsed amperometry. The biosensor could detect lindane in the part-per-trillion concentration range with a linear response from 2 to 45 ppt. The sensor was found to be selective to all the isomers of hexachlorocyclohexane (HCH) and to pentachlorocyclohexane (PCCH) but did not respond to other aliphatic and aromatic chlorides or to the end product of lindane degradation, i.e., trichlorobenzene (TCB). The sensor also did not respond to other commonly used organochlorine pesticides like DDT and DDE. On the basis of experimental results, a rationale has been proposed for the excellent sensitivity of polyaniline as a pH sensor for detection of H(+) ions released in its microenvironment.

Synthesis of mesostructured polyaniline using mixed surfactants, anionic sodium dodecylsulfate and non-ionic polymers and their applications in H2O2 and glucose sensing

Mesostructured polyaniline was prepared by the self-assembly of a mixture of an anionic surfactant, sodium dodecylsulfate and a non-ionic polymeric surfactant (polyethylene glycol, and block-co-polymers such as Pluronic P123 and Brij-35). Materials were characterized by a complementary combination of X-ray diffraction, Scanning electron microscopy, Fourier-transform infrared spectrometer and UV-visible spectrophotometer. Mesostructured polyaniline was used for construction of biosensor, which displayed excellent electrocatalytic response for the detection of H(2)O(2) and glucose compared to conventional polyaniline. The electrocatalytic response observed in the case of mesostructured polyaniline can be correlated with the large surface area and nanopores which enhances the accessibility of H(2)O(2)/glucose molecule to the active site that result in high observed current. The methodology adopted in the present study provides a new platform for the fabrication of polyaniline based high-performance glucose and other biosensors.

Facile preparation of Ni(OH)2-MnO2 hybrid material and its application in the electrocatalytic oxidation of hydrazine.

A surfactant-free synthetic methodology is reported for the preparation of Ni(OH)2-MnO2 hybrid nanostructures. For comparative study, MnO2 and Ni(OH)2 were also synthesized. Materials were characterized by X-ray diffraction, nitrogen sorption, scanning electron microscopy, and transmission electron microscopy. Ni(OH)2-MnO2 modified electrode is fabricated for the determination of hydrazine. The electrochemical oxidation of hydrazine was investigated using cyclic, linear sweep voltammetries, and chronoamperometry methods. The Ni(OH)2-MnO2 modified electrode showed hydrazine oxidation with decrease in the over voltage and increase in the oxidation peak current, when compared to MnO2, Ni(OH)2, and bare GCE. pH was optimized to obtain the best peak potential and current sensitivity. Chronoamperometry was used to estimate the diffusion coefficient of hydrazine. The kinetic parameters such as overall number of electrons involved in the catalytic oxidation of hydrazine and the rate constant (k) for the oxidation of hydrazine at Ni(OH)2-MnO2 modified electrode were determined. The Ni(OH)2-MnO2 modified electrode exhibited good sensitivity, stability, and reproducibility in hydrazine sensing.

Synthesis of nanoporous metal oxides through the self-assembly of phloroglucinol–formaldehyde resol and tri-block copolymer

A versatile route to synthesize nanoporous crystalline metal oxides has been developed through the self-assembly of phloroglucinol-formaldehyde resol and tri-block copolymer templates. Materials were characterized by a complementary combination of X-ray diffraction, nitrogen sorption, and transmission electron microscopy. Metal oxides synthesized using this route have remarkably high surface area when compared with the commercial samples. The surface area of metal oxides decreased upon calcination at higher temperatures. However, the surface area was still much higher when compared with the commercial samples. TEM investigation reveals that upon calcination at higher temperature, the size of the crystal increased but the short range order was merely disturbed. The analyses show that the present method is suitable as a direct route to synthesize crystalline nanoporous metal oxides. Hydrogen bonding plays a key role in the preferential arrangement of porous metal-carbon structure in the domain of tri-block copolymer. The nanoporous metal oxides with ordered mesoporous structure, high surface area, and crystalline framework are expected to show significant improvement in catalysis and nano-technology.

Cu nanoparticles supported mesoporous polyaniline and its applications towards non-enzymatic sensing of glucose and electrocatalytic oxidation of methanol

Cu nanoparticles supported on mesoporous polyaniline (Cu/Meso-PANI) was synthesized by the self assembly of dual surfactants followed by the in-situ reduction of CuCl2 in aqueous solution. Materials were characterized by X-ray diffraction, Scanning electron microscopy, Transmission electron microscopy, and UV-visible spectroscopic method. Cu/Meso-PANI based non-enzymatic electrochemical sensor was fabricated for glucose detection. The Cu/Meso-PANI modified electrode showed high electrocatalytic activity towards the oxidation of glucose compared to Cu/PANI (Cu nanoparticles supported on conventional polyaniline), which is due the highly dispersed copper in the high surface area Meso-PANI matrix. The Cu/Meso-PANI modified electrode exhibited high selectivity towards glucose against several common interfering species. Cu/Meso-PANI modified electrode was also explored for the electrochemical oxidation of methanol, which finds application in direct methanol fuel cell. The electrochemical oxidation of methanol was investigated at the surface of Cu/Meso-PANI modified electrode in alkaline medium using cyclic voltammetry and chronoamperometry methods. Various reaction parameters such as effect of scan rate and concentration of methanol were investigated. Furthermore, the rate constant (k) for the electrocatalytic oxidation of methanol was also calculated. The promising electrocatalytic activity of Cu/Meso-PANI modified electrode provides a new platform for the fabrication of polyaniline based high-performance sensors.

Synthesis of imidazole-based NHC–Au(I) complexes and their application in non-enzymatic glucose sensing

In this study, imidazole-based NHC–Au(I) complexes were prepared. Geometrically optimized structures and molecular orbital energy diagrams were computed using density functional theory. Cyclic voltammetry and amperometric methods were used to evaluate the catalytic activity of the NHC–Au(I)-modified electrodes toward glucose oxidation. The mechanism of electrocatalytic oxidation at NHC–Au(I)-modified electrodes is explained on the basis of the oxidation and reduction potentials in the presence of glucose. Applicability of NHC–Au(I)-modified electrode was extended to determine the glucose level in the blood serum and the precision of the method was found to be satisfactory. The non-enzymatic sensor exhibited excellent reproducibility, repeatability, antifouling, and anti-interference characteristics.