Current Nanoscience - Volume 6, Issue 4, 2010

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Sensors play a significant role in everyday life. Nowadays, there has been a strong demand for highly selective, sensitive, responsive, stable and cost effective sensors. As a result, research emphasis is on developing new sensing materials and technologies. Carbon nanotubes (CNTs) have many distinct properties that may be exploited to develop next generation of sensors. They exhibit extraordinary strength and unique combination of excellent mechanical, electrical, thermal, optical and electrochemical properties even in its small dimension nature, which has generated increasing interest in the application of CNTs as sensors. The main thrust of this review is to highlight the present and future research and development work in the area of CNT based sensors. Different types of sensors such as biosensors, chemical sensors, mass sensors, temperature sensors, strain sensors and pressure sensors based on CNTs are also discussed in detail. This manuscript concludes with an outline of the advantages of these CNT based sensors for real-world applications. This review aims to act as a reference source for researchers to help them in developing new applications of sensors based on CNTs.

Nanoparticles have long been sought as promising drug delivery system for cancer therapy, including liposomes, polymeric micelles, polymer-drug conjugates, dendrimers and polymeric nanoparticles. However, conventional nanoparticles would be specifically entrapped by the monocyte phagocytic system (MPS), and then quickly eliminated following intravenous administration, so the applications of nanoparticles are limited due to short circulation lifetime. Since long-circulation property is the prerequisite for nanoparticles reaching the target site of interest, the nanoparticle surface is usually modified by hydrophilic polymer materials such as PEG, to reduce plasma opsonization and MPS uptake. Furthermore, increased tumor specificity and cell internalization will improve the treatment efficacy and decrease the serious side effects for many cytotoxic antineoplastic drugs. Introducing the targeting ligands for interaction with specific tumor cells or tissues will offer major enhancement in cancer therapeutics via site specificity, reduction of multidrug resistance and improved delivery efficiency. This article will give an overview on the current state of long-circulating nanoparticles and describe their major advantages and potential pitfalls. Special emphasis is placed on the superiority of long-circulating nanoparticles used for tumor targeting.

We focus on most commonly used epitaxial growth techniques of quantum wells (QWs) and study the single electron transitions within the QW laser structures made with II-VI's (e.g. CdSe/ZnSe) and III-V's (e.g. GaN/AlN), considering only emission of longitudinal optical (LO) phonons. Two different approaches have been employed in order to describe the initial electron wavefunctions in the continuum energy spectrum: the width of the barrier region is a) small b) large, relative to the electron mean free path. For the LO phonons, we have used the bulk phonon approximation and the dielectric continuum (DC) model to study the lattice dynamics in the crystal. Our theoretical models show that the scattering times for II-VI's are very short comparing to the III-V's semiconductor (except the V-III nitrides) laser structures and highlight that the size of the well is of special importance for the laser operation.

In this paper, we report a facile biological method for extracellular synthesis of copper oxide nanoparticles (CONPs) using Escherichia coli (E. coli). We report that trichloroacetic acid (TCA) precipitated protein fraction of E. coli has synthesized copper oxide nanoparticles (CONPs), under simple experimental conditions like aerobic environment, neutral pH and room temperature. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) results have shown that proteins of molecular weight ranging from 22 KDa, 52 KDa, and 25 KDa are not only involved in reduction of Cu (II) into CONPs, but also play a significant role in stabilization of formed nanoparticles at room temperature. Further, transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction measurements (XRD) and fourier transform infrared (FTIR) analysis have confirmed the synthesis of nanoparticles through microbial route. CONPs formed were of variable size and shapes.

We report Opuntia ficus-indica mediated synthesis of colloidal silver nanoparticles. Detection and characterization of nanoparticles were carried out by UV-Vis- and Fourier Transform Infra Red Spectroscopy, Scanning Electron Microscopy and X-ray Diffraction analysis respectively. The aim of the present study was synthesis of silver nanoparticles, assessment of their antibacterial activity, and study of possible mechanism involved. The silver nanoparticles in combination with commercially available antibiotics showed a remarkable antibacterial activity. Some of the commercially available antibiotics in combination with silver nanoparticles showed remarkable activity. However, the maximum activity was demonstrated by Ampicillin followed by Streptomycin and Vancomycin. On the basis of the information obtained in this work, two-step mechanism has been proposed as bioreduction and formation of an intermediate complex leading to formation of capped nanoparticles.

Plant pathogenic fungus Fusarium culmorum (MTCC-2090) assists in the mycosynthesis of silver nanoparticles. Formation of spherical silver nanoparticles was confirmed from TEM analysis and found in the range of 5-25 nm with an average diameter of 11 nm. Different temperature and pH affects the synthesis of silver nanoparticles indicating that synthesis depends significantly on temperature and pH. Formation of silver nanoparticles at room temperature and pH-7 was found to be optimum for synthesis process. The combined effects of mycosynthesized silver nanoparticles with different antibiotics like kanamycin, erythromycin, oxacillin, tetracycline, vancomycin and gentamycin against Klebsiella pneumoniae (MTCC-7407) and Enterobacter aerogenes (MTCC-6804) were carried out. Oxacillin showed the maximum increase in fold area as compared to other antibiotics tested against both the test organisms. Fungal proteins are responsible for the synthesis of silver nanoparticles. This process is easy, eco-friendly and scalable for the large scale synthesis of silver nanoparticles. The synthesis of silver nanoparticles by F. culmorum has not been reported in the past, and thus, it is being reported for the first time.

Metal oxide nanoparticles are known to possess strong antimicrobial properties. Titanium dioxide (titania) nanoparticles have wide range antimicrobial as well biomedical applications. In the present work the antimicrobial properties of Titanium dioxide- anatase nanoparticles were investigated in the concentration range 10-100 ppm using Escherichia coli, Bacillus subtilis and Pseudomonas aeruginosa. The average size of the nanoparticles used was measured to be below 25 nm. The concentration dependent growth inhibitory effect of titania nanoparticles on the three bacterial strains were compared based on batch growth kinetic data (by dynamic growth rate). Bacterial sensitivity to nanoparticles was found to vary depending on the microbial species. The mode of antibacterial action was investigated by assaying extracellular proteins, the integrity of the cell membranes and the permeability of the inner membrane (IM) of the microbial strains. The results suggested that titania caused the antibacterial effect through membrane damage mechanisms. FT-IR studies revealed that most of amide-I, amide -II groups were absent in the nanoparticles treated cells when compared with that of control, corroborating the cell damage mode of action. The antimicrobial effects of the nanoparticles essentially differed between the microbial strains due to structural differences in the cell membranes.

Sentinel lymph node (SLN) biopsy is a reliable predictor of lymph node status in staging solid cancers and it is generating a great deal of enthusiasm among clinicians. Herein, methylene blue (MB) was encapsulated within a microemulsion nanosystem. Its near-infrared (NIR) fluorescence was used for mouse SLN imaging and mapping. The results show an obvious improvement in the NIR fluorescence of the MB aqueous solution after the MB was encapsulated into the microemulsion. When a mouse was intradermally injected with the microemulsion-encapsulated MB (ME-MB) into the paw, its axillary SLN rapidly emitted brighter fluorescence than that of the SLN of a mouse intradermally injected with the MB aqueous solution only. Furthermore, the retention time of the fluorescent signal emitted from the SLN mapped with the ME-MB was longer than that of the fluorescent signal emitted from the SLN mapped with the MB aqueous solution only. This was due to the microemulsion being a lymphatic targeting nanosystem, and the ME-MB having brighter fluorescence, thereby giving the operator enough time to identify and ensure complete resection of the SLN. SLN mapping with the NIR fluorescence of ME-MB nanosystem is a simple, intuitive and highly efficient technique compared to traditional methods.

This study examines the optoelectronic characteristics and carrier transport model of a nanostructure p-ZnO/SiO2 ultrathin interlayer/n-Si photodiode in various magnetic fields. The magneto-induced current in photodiode increases exponentially as the reverse bias and illumination flux increases. This is primarily the result of the magneto-optical multiplication effects. The absorption edges of photodiodes with applied magnetic fields of 0.1, 0.5, and 0.7 Tesla shifted from 370.5 nm to 370, 369, and 368.5 nm, respectively, while the photon energy shifts were approximately 4.52, 13.60, and 18.16 meV, respectively. These shifts are attributed to the interband magneto- optical absorption caused by Landau splitting of the band structure of nanostructure ZnO film in the presence of a magnetic field.

Lanthanide ions are visible to near-infrared ultra-narrowband emitters with long lifetime thus have potential applications in lasing, up-conversion and in bioimaging. Present work report a general, single step and easy solvothermal method to synthesize well crystalline, pure and Eu3+ doped ZnSe nanocrystals in a unified system. The products were well characterized by powder X-ray diffraction (XRD), UV-visible (UV-vis) spectroscopy, photoluminescence spectroscopy (PL), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), energy dispersive X-ray diffraction (EDAX) and by Raman spectroscopy. Semiconducting NPs exhibiting cubic phases were obtained at low temperature under mild conditions. The products were found to show significant finite size effect as characterized by broadened XRD peaks, blue shift of the interband optical absorption edge and by Raman scatterings. The structure and properties were correlated and detailed growth mechanism has also been discussed.

This study is related to the preparation of boron supported YBa2Cu3O7 (YBCO) superconducting material. The first step was the preparation of a composite formed by mixing yttrium, barium, and copper acetates with polyvinyl alcohol (PVA) at a suitable temperature. The resulting composite polymer was electrospun to produce nanofibers. Finally, the obtained nanofibers were subjected to thermal treatments at 500°C, 600°C and 1000°C to elucidate their morphological properties. The conductivity of the nanofibers was measured by the four probe techniques, and the boron supported polymer was found that it had a higher conductivity. Differential Scanning Calorimetry (DSC) data for the boron doped material revealed that the addition of boron increased the thermal resistance of the fibers. Scanning electron microscopy (SEM) images of the fibers showed that they were homogeneously electrospun, and there was no beading or heaping on them.

Macrophage targeting therapies are a promising approach to treat various intracellular infections like AIDS, tuberculosis and leprosy. The present paper demonstrates the design and development of mannosylated nanoparticles of biopolymeric origin. Spherical and smooth gelatin nanoparticles in the size range of 100-200 nm with a narrow polydispersity index (<0.1) were synthesized and characterized by TEM, AFM and XPS for their morphology and mannosylation. Cell uptake studies by spectrofluorimetry in J774 macrophage cell-line demonstrate two-fold greater internalisation of mannosylated gelatin nanoparticles (MGNP) through macrophage mannose-receptor, than unconjugated nanoparticles (GNP); enhanced uptake of MGNP in J774 macrophages was confirmed by laser confocal microscopy. Evaluation of cellular toxicity by MTT assay reveals close to 100% cell viability confirming biocompatibility. In addition, neither MGNP nor GNP caused ROS (reactive oxidative species) generation in J774 cells. Biodistribution studies in murine model showed significant uptake of MGNP by reticuloendothelial system as early as 15 min after intravenous administration (spleen 0.99±0.14 percent injected dose/100 mg tissue; liver, 1.04±0.11 percent dose/100 mg). The anti-HIV drug stavudine was loaded to 38.2% entrapment efficiency in MGNP and showed 77.5% release in 96 h. Thus, these mannosylated nanoparticles appear to be a very useful carrier system for receptor-specific drug delivery in treatment of macrophage-mediated intracellular infections.

Present study reports optimal conditions for the preparation of cyclosporin A loaded PLGA nanoparticles with a diameter <200nm. In a systematic approach, various process variables such as homogenization/sonication, choice of suitable stabilizer and its concentration, drug loading etc. were optimized to achieve maximum drug loading and desired particle size (<200nm) and the optimized formulation was further characterized for shape and morphology by atomic forced microscopy (AFM), nature of drug inside the nanoparticles by X-ray diffraction pattern (XRD) analysis and in-vitro drug release. A step wise freeze drying cycle was developed and suitable lyoprotectants were screened for long term shelf storage of the formulation in dried form. Accelerated stability testing was also carried out to determine the change in physicochemical characteristics of the nanoparticles during storage. Nanoparticles were successfully prepared with high encapsulation efficiency (>85%w/w) and low particle size (163 nm) using 2% w/v PVA as surfactant with probe sonication technique. AFM images confirmed the spherical shape and smooth surface of the particles and drug was found to be molecularly dispersed in the polymer matrix of nanoparticles as revealed by XRD analysis. Developed formulation showed a zero order in vitro release pattern up to 20 days with no initial burst release when carried out using a cellulose dialysis bags with a molecular mass cut-off of 12000 Da. Step wise freeze drying was successfully carried out using relatively low concentration (2.5%w/v) of dextrose and mannitol as lyoprotectants with insignificant changes in particle size and entrapment efficiency. No significant changes in characteristics of nanoparticles were observed after 3 months of storage in accelerated stability conditions. The developed formulation can be successfully used as potential delivery vehicle for delivery of cyclosporin A through oral/topical routes for possible systemic or dermatological applications. The nanoparticles would be loaded into a gel for possible topical application and such studies are underway in our laboratory.

A novel, cost effective, environment-friendly and energetically beneficial alternative method for the synthesis of giant dielectric pseudo-perovskite material CaCu3Ti4O12 (CCTO) is presented. The method involved auto-combustion of an aqueous precursor solution in oxygen atmosphere with the help of external fuels and is capable of producing high amount of CCTO at ultra-low temperature, in the combustion residue itself. The amount of phase generated was observed to be highly dependent on the combustion process i.e. on the nature and amount of external-fuels added for combustion. Two successful fuel combinations capable of producing reasonably higher amount of the desired compound were investigated. On a structural characterization grain size was observed to decrease drastically to nano-dimension compared to submicron-size that was obtained in a traditional sol-gel combustion and subsequent cacination method. Therefore, the method reported can produce nano-crystalline CaCu3Ti4O12 ceramic matrix at an ultra-low temperature and is expected to be applicable for other multifunctional perovskite oxide materials.