Layer-by-layer assembly of a magnetic nanoparticle shell on a thermoresponsive microgel core

We describe the surface modification of magnetic nanoparticles (MNPs), the coverage of poly(N-isopropylacrylamide) (PNiPAM) microgel with the MNPs and the inductive heating of these carriers. PNiPAM surface itself was modified using the layer-by-layer (LbL) assembly of polyelectrolytes to facilitate the deposition of surface-modified MNPs. One advantage of this concept is it allows the tuning of the magnetic and thermoresponsive properties of individual components (nanoparticles and microgels) separately before assembling them. Characterisations of the hybrid core–shell are discussed. In particular, it is shown that (i) each layer is successfully deposited and, more importantly, (ii) the coated microgel retains its thermoresponsive and magnetic behaviour.     

Polyaniline-iron oxide nanohybrid film as multi-functional label-free electrochemical and biomagnetic sensor for catechol

Polyaniline-iron oxide magnetic nanohybrid was synthesized and characterized using various spectroscopic, microstructural and electrochemical techniques. The smart integration of Fe₃O₄ nanoparticles within the polyaniline (PANI) matrix yielded a mesoporous nanohybrid (Fe₃O₄@PANI) with high surface area (94 m² g⁻¹) and average pore width of 12.8 nm. Catechol is quasi-reversibly oxidized to o-quinone and reduced at the Fe₃O₄@PANI modified electrodes. The amperometric current response toward catechol was evaluated using the nanohybrid and the sensitivity and detection limit were found to be 312 μA μL⁻¹ and 0.2 nM, respectively. The results from electrochemical impedance spectroscopy (EIS) indicated that the increased solution resistance (R_s) was due to elevated adsorption of catechol on the modified electrodes. Photoluminescence spectra showed ligand-to-metal charge transfer (LMCT) between p-π orbitals of the phenolate oxygen in catechol and the d-σ* metal orbital of Fe₃O₄@PANI nanohybrid. Potential dependent spectroelectrochemical behavior of Fe₃O₄@PANI nanohybrid toward catechol was studied using UV/vis/NIR spectroscopy. The binding activity of the biomagnetic particles to catechol through Brownian relaxation was evident from AC susceptibility measurements. The proposed sensor was used for successful recovery of catechol in tap water samples.     

Dihydrophenazine-based double-anchoring dye for dye-sensitized solar cells

A novel dihydrophenazine-based organic di-anchoring dye DK-11 was synthesized by utilizing a simple synthetic protocol. The dye was characterized by optical and electrochemical studies and used as a sensitizer for dye-sensitized solar cell. The proposed butterfly structure was supported by IR experiments which ensured the binding of both carboxylic acid units on the semiconductor surface. Using the dye DK-11 , the device generated an efficiency of 5.07% with J_SC, V_OC, and FF values of 10.65 mA/cm², 0.67 V, and 0.71, respectively.     

Novel pyrenoimidazole-based organic dyes for dye-sensitized solar cells

A novel class of organic dyes containing pyrenoimidazole donors, cyanoacrylic acid acceptors, and oligothiophene π-linkers has been synthesized and characterized. The electro-optical properties of these dyes can be tuned by changing the conjugation length of the π-linkers. A dye containing terthiophene in the conjugation pathway exhibited a solar energy-to-electricity conversion efficiency of 5.65%.     

Impedimetric biosensor for early detection of cervical cancer

An impedimetric biosensor based on PEGylated arginine functionalized magnetic nanoparticles for early detection of cervical cancer is reported. The cervical cancer cells could be selectively and sensitively detected down to 10 cells mL(-1) on the modified electrode, which is promising for advancement in clinical diagnosis and monitoring of tumors.     

Kinetic arrest of the first-order to R3c Pbnm phase transition in supercooled La(x)MnO(3+δ) (x = 1 and 0.9)

We report the occurrence of kinetic arrest of the first-order phase transition from R3c to Pbnm in supercooled La(x)MnO(3±δ) (x = 1 and 0.9, i.e. δ > 0.125). Structural studies have been done, employing low temperature transmission electron microscopy (LT-TEM) and low temperature x-ray diffraction (LT-XRD) techniques. No phase transformation was observed even in La(x)MnO(3±δ) aged for ~12 h at 98 K. The evidence of the occurrence of kinetic arrest was realized at low temperatures through in situ electron beam triggered nucleation and perpetual devitrification of the R3c phase into a Pbnm phase. It was clearly evidenced that the R3c structure of La(x)MnO(3±δ), below its ferromagnetic transition temperature, is metastable and prone to be transformed to a Pbnm orthorhombic structure following initiation by an electron beam trigger. The electron beam transformed Pbnm phase was found to transform back to the R3c phase through a first-order phase transition occurring close to the ferromagnetic to paramagnetic transition (T(c)) during heating. The glass-like kinetics of the arrested R3c phase has been investigated through resistance relaxation measurements, showing a decreasing logarithmic rate of decay of the arrested R3c phase towards the stable Pbnm phase with decreasing temperature, down to 5 K. On the basis of the correlations observed in the resistance-versus-temperature, magnetization-versus-temperature, magnetization-versus-field, resistance relaxation and LT-XRD measurements, the occurrence of kinetic arrest has been attributed to the suppression of Jahn-Teller distortion by double exchange across the insulator-metal transition.     

Validated RP–LC Method for Standardization of Ashokarishta: A Polyherbal Formulation

A rapid LC-photodiode array method for the separation and identification of secondary plant metabolites especially phenolic compounds belonging to different types in a run (35 min) has been developed. The method has been optimized and validated using the selectivity, precision, recovery and robustness parameters with an aim for standardization of herbal drugs. Almost all the compounds have linearity with an R ² more than 98% and an RSD of less than 5% (in terms of variation of retention time). Inter-day and intra-day variability was also found to be less than 5%. The method thus developed has been successfully applied in identification and quantification of phenolic compounds present in polyherbal ayurvedic formulation (Ashokarishta). The results indicate that the method developed is rapid, accurate and robust for the analysis of different classes of phenolic compounds and can be successfully applied in the quality control and standardization of herbal drugs as well as polyherbal formulations.     

One pot synthesis of maleimide and hydantoin by Fe(CO)5 catalyzed [2 + 2 + 1] co-cyclization of acetylene, isocyanate and CO

In the presence of a catalytic amount of Fe(CO)(5), terminal acetylenes, isocyanates and CO undergo [2 + 2 + 1] cyclization to form substituted maleimides and hydantoins; when internal alkynes are used, exclusive maleimide formation is observed. While the maleimides can be obtained as the major products, in up to 90% yield, when the reaction is carried out in CO atmosphere, in absence of CO, the hydantoins are formed in up to 87% yield. Formation of maleimides has been shown to occur via the formation of a ferrole intermediate, whereas the hydantoins are proposed to form through successive insertion of isocyanate into the iron-acetylide bond. All compounds were characterized by spectroscopic methods and molecular structures of some compounds were established by single crystal X-ray diffraction method.     

Sonochemical stabilization of ultrafine colloidal biocompatible magnetite nanoparticles using amino acid,l-arginine,for possible bio applications

Materials obtained by the synergistic combination of nanotechnology and biomedicine are an important source of drug delivery and other health care related applications. The anchoring of amino acids onto the surface of nano-sized magnetite is one such example. Herein, we report on the binding of a semi-essential amino acid, l-arginine, onto the surface of nano magnetite, creating a stable aqueous suspension by an in situ one-step method using sonochemical synthesis. An ex situ two-step process was also attempted, but was soon discarded owing to the relative short duration of the suspension attributed to increase in particle size and lower extent of binding. The initial concentration of the amino acid was found to play an important role in controlling the particle size and also the binding motif. Lower concentrations of arginine were found to favor the formation of elongated tubular structures, while at higher concentrations, the elongated structures were less prominent and arginine was found to be adsorbed onto the surface of the magnetite. This surface-functionalized nanomagnetite with amino acids could become a promising vehicle for drug delivery.