Opto Field-Effect Transistors for Detecting Quercetin-Cu2+ Complex.

In this study, we explored the potential of applying biosensors based on silicon nanowire field-effect transistors (bio-NWFETs) as molecular absorption sensors. Using quercetin and Copper (Cu2+) ion as an example, we demonstrated the use of an opto-FET approach for the detection of molecular interactions. We found that photons with wavelengths of 450 nm were absorbed by the molecular complex, with the absorbance level depending on the Cu2+ concentration. Quantitative detection of the molecular absorption of metal complexes was performed for Cu2+ concentrations ranging between 0.1 µM and 100 µM, in which the photon response increased linearly with the copper concentration under optimized bias parameters. Our opto-FET approach showed an improved absorbance compared with that of a commercial ultraviolet-visible spectrophotometry.

Luminescent MoS2 Quantum Dots with Tunable Operating Potential for Energy-Enhanced Aqueous Supercapacitors.

Wide band gap luminescent MoS2 quantum dots (QDs) and MoS2 nanocrystals (NCs) have been synthesized by using laser-assisted chemical vapour deposition and used as an electrode material in supercapacitors. Size-dependent properties of the MoS2 QDs and NCs were examined by UV-vis absorption, photoluminescence, and Raman spectroscopy. The morphological evolution of the NCs and QDs were characterized by using field emission scanning electron microscopy, high-resolution transmission electron microscopy, and atomic force microscopy. The as-synthesized uniform QDs with a size of ∼2 nm exhibited an extended electrochemical potential window of 0.9 V with a specific capacitance value of 255 F/g, while the NCs values were 205 F/g and 0.8 V and the pristine MoS2 with values of 105 F/g and 0.6 V at a scan rate of 1 mV s-1. A shorter conductive pathway and 3D quantum confinement of MoS2 QDs that exhibited a higher number of active sites ensure that the efficient charge storage kinetics along with the intercalation processes at the available edge sites enable significant widening of operating potential window and enhance the capacitance. The symmetric device constructed with the QDs showed a remarkable device capacitance of 50 F/g at a scan rate of 1 mV s-1 with an energy density of ∼5.7 W h kg-1 and achieved an excellent cycle stability of 10,000 consecutive cycles with ∼95% capacitance retention.

Laser assisted synthesis of inorganic fullerene like MoS2-Au nanohybrid and their cytotoxicity against human monocytic (THP-1) cells.

Here in, we report the investigation of the immunotoxicity of gold nanoparticles decorated on inorganic fullerene like MoS2 nanostructure (IFMoS2- AuNPs) on the THP-1 immune cell line. The MoS2 nanoparticle with fullerene like nanostructure (IFMoS2) was synthesized by double pulsed laser-assisted chemical vapour deposition (LCVD) method from bulk MoS2 at the temperature of 700 °C. The MoS2 inorganic fullerene-like nanoparticles grown by vapour-solid process (VS). The surface of the IFMoS2 was decorated with gold nanoparticles (AuNPs) to develop the semiconductor biocompatibility interface. The IFMoS2 are typically with diameters 20-50 nm as observed from the electron microscopy analysis. The stability of IFMoS2-AuNPs were examined by dynamic light scattering (DLS) and zeta potential measurements. The decoration of AuNPs on IFMoS2 surface was analyzed by UV-Vis, FTIR, PXRD, FESEM, EDX with elemental mapping and HRTEM measurement. The in vitro cytotoxicity evaluation of the FMoS2-AuNPs was determined on acute monocytic leukemic cells (THP-1) in which cell viability, caspase activity (CASP -3&7/CASP -8/CASP -9) and cell- structural changes were assessed. From FESEM revealed that IFMoS2-AuNPs induced apoptosis in THP-1 cells. Further, THP-1 cell viability markedly decreased at higher IFMoS2-AuNPs concentrations (65-100 µg/ml), indicating its potential as a chemotherapeutic agent in the treatment of human monocytic leukemia.

Detection of electrically neutral and nonpolar molecules in ionic solutions using silicon nanowires.

We report on a technique that can extend the use of nanowire sensors to the detection of interactions involving nonpolar and neutral molecules in an ionic solution environment. This technique makes use of the fact that molecular interactions result in a change in the permittivity of the molecules involved. For the interactions taking place at the surface of nanowires, this permittivity change can be determined from the analysis of the measured complex impedance of the nanowire. To demonstrate this technique, histidine was detected using different charge polarities controlled by the pH value of the solution. This included the detection of electrically neutral histidine at a sensitivity of 1 pM. Furthermore, it is shown that nonpolar molecules, such as hexane, can also be detected. The technique is applicable to the use of nanowires with and without a surface-insulating oxide. We show that information about the changes in amplitude and the phase of the complex impedance reveals the fundamental characteristics of the molecular interactions, including the molecular field and the permittivity.

Shape manipulation of ion irradiated Ag nanoparticles embedded in lithium niobate.

Spherical silver nanoparticles were prepared by means of ion beam synthesis in lithium niobate. The embedded nanoparticles were then irradiated with energetic (84)Kr and (197)Au ions, resulting in different electronic energy losses between 8.1 and 27.5 keV nm(-1) in the top layer of the samples. Due to the high electronic energy losses of the irradiating ions, molten ion tracks are formed inside the lithium niobate in which the elongated Ag nanoparticles are formed. This process is strongly dependent on the initial particle size and leads to a broad aspect ratio distribution. Extinction spectra of the samples feature the extinction maximum with shoulders on either side. While the maximum is caused by numerous remaining spherical nanoparticles, the shoulders can be attributed to elongated particles. The latter could be verified by COMSOL simulations. The extinction spectra are thus a superposition of the spectra of all individual particles.

A comparison of purification procedures for multi-walled carbon nanotubes produced by chemical vapour deposition.

A comparison of three different purification procedures for multi-walled carbon nanotubes (MWCNTs) produced by chemical vapour deposition (CVD) has been presented. The methods involved gas-phase oxidation by calcination, liquid-phase oxidation by H2O2, hydrothermal treatment and acid refluxing in HCl. Sample purity was documented with the Raman spectroscopy, Transmission electron microscopy (TEM), Scanning electron microscopy (SEM) and thermo gravimetric analysis (TGA). The Raman spectroscopy, SEM and TEM results showed that the liquid phase oxidation-acid refluxing route successfully eliminated most of the impurities without damaging the nanotube structure. TGA analysis showed in increase in density of MWCNTs with better oxidation resistance after purification and the metal content was reduced from 23.8 wt% to 5.4 wt%.

Purification of multi-walled carbon nanotubes.

The discovery of carbon nanotubes (CNTs) has stimulated intensive research to characterize their structure and to determine their physical properties, both by direct measurement and through predictive methods. Many of the fundamental and remarkable properties of CNTs are now well-known, and their exploitation in a wide range of applications forms a large part of research currently in progress. However, the absence of a reliable, large-volume production capacity, simple and efficient purification methods, the high cost of carbon nanotubes and the fact that there is little selectivity in controlling the properties of the product are factors that have principally inhibited the commercialization of CNT technologies. Ever since CNTs were detected, considerable efforts have been directed at their synthesis, characterization and functionalization. Nevertheless, the CNT sample obtained by different techniques has the disadvantage of containing non-CNT impurities, such as graphitic particles, fullerenes, residual catalyst particles and amorphous carbon, which degrade the intrinsic properties of these materials. If the carbon nanotube is ever to accomplish its promise as an industrial material, large and high-quality aliquots, will be required. A number of purification methods involving elimination processes, such as physical separation, gas-phase and liquid-phase oxidation, in combination with chemical treatments, have been developed for nanotube materials. Though the quantitative determination of purity remains controversial, reported yields are best regarded with an appropriate level of scepticism on the method of assay. This review highlights the past and recent developments in the purification of multi-walled carbon nanotubes.

Purification of laser synthesized SWCNTs by different methods: a comparative study.

A comparison of different purification procedures for single walled carbon nanotubes (SWCNTs) synthesized by laser-vapourization has been presented. The methods involved gas-phase oxidation by calcination, liquid-phase oxidation by H2O2, hydrothermal treatment and acid refluxing in HCI. Sample purity is documented with Raman spectroscopy, Transmission electron microscopy, Scanning electron microscopy and thermogravimetric analysis. Multi-spot analyses were done to check the homogeneity of the purified samples. Different purification processes produced SWCNT material with purity in the range of 48-78%. Raman and TEM results suggested that prolonged calcination results in selective etching of larger diameter nanotubes. SEM and TGA analyses showed increase in density of SWCNTs with better oxidation resistance after purification.

Purification of single-walled carbon nanotubes.

The discovery of carbon nanotubes (CNTs) created much excitement and stimulated extensive research into the properties of nanometer-scale cylindrical networks. From then on, various methods for the synthesis and characterization of aligned CNTs-both single-walled (SWCNTs) and multi-walled (MWCNTs) by different methods have been hotly pursued. Unfortunately, most methods currently in use produce raw multi component solid products, only a small fraction of which contains carbon nanotubes. The balance of the material is composed of residual catalyst particles (some of which are encased in concentric graphitic shells), fullerenes, other graphitic materials and amorphous carbon. These impurities cause a serious impediment for their detailed characterization and applications. If the carbon nanotube is ever to fulfill its promise as an engineering material, large, high quality aliquots will be required. A number of purification methods involving elimination processes such as physical separation, gas phase and liquid phase oxidation in combination with chemical treatments have been developed for nanotube materials. Though the quantitative determination of purity remains controversial, reported yields are best regarded with an appropriate level of skepticism on the method of assay. In this article, a review is given on the past and recent advances in purification of SWCNTs.