Showing papers in "Micro & Nano Letters in 2013"

Graphene-like nanocarbides and nanonitrides of d metals (MXenes): synthesis, properties and simulation

Abstract: Very recently (2011, Advanced Materials , 23, 4248), an elegant exfoliation approach was proposed to prepare a new family of two-dimensional (2D)-like transition metal carbides and nitrides from layered MAX phases. This discovery has provided the next stage in the design of new graphene-like inorganic materials with intriguing functionalities and applications. This overview is intended as an introduction to this newest family of graphene-like quasi-2D nanocarbides and nanonitrides of d metals, which are known today also as MXenes. Here the authors discuss the available results achieved for MXenes (2011-2012), when a group of various MXenes (2D-Ta 4 C 3 , Ti 3 (C 0.5 N 0.5 ) 2 , TiNbC and some others) have been successfully synthesised, a set of their properties (conductivity, mechanical behaviour etc.) were measured and systematical theoretical studies of structural, electronic properties, chemical bonding and the stability of MXenes were initiated. Besides, possible applications of MXenes as promising materials for Li ion batteries, sensors or 2D electronics etc. are noted.

Femtogram aerosol nanoparticle mass sensing utilising vertical silicon nanowire resonators

Abstract: Vertically aligned silicon nanowire (SiNW)-based resonators were fabricated and utilised to detect aerosol nanoparticles (NPs) by measuring their resonant frequency shifts caused by the additional mass of trapped NPs. Inductively coupled plasma cryogenic dry etching and multiple thermal oxidations are used in the fabrication of silicon nanowire (SiNW) arrays. The SiNWs were coated with gold for contacting to the homebuilt electrostatic NP sampler to collect the flowing NPs. In order to have a dynamic resonance operation in the frequency measurement system, a piezoelectric shear actuator was mounted onto the SiNWs. Examined in a TiO 2 aerosol sampling with a total concentration of ~8500 NP/cm 3 , the fabricated sensor exhibited its feasibility as a nanobalance to measure aerosol NP mass at the femtogram level with a mass sensitivity of 7.1 Hz/fg and a mass resolution of 31.6 fg. The NP sampling efficiency of the developed miniaturised NP sampler was found to be three times higher than that of the commercial nanometer aerosol sampler (NAS, TSI 3089). An ultrasonic removal method was used to detach the adhered NPs and further extend the operating life of the sensor.

Evolutionary algorithm and parameters extraction for dye-sensitised solar cells one-diode equivalent circuit model

Abstract: With the aim of improving energy conversion efficiency of dye-sensitised solar cells (DSCs), three evolutionary algorithms (EAs), namely genetic algorithm, particle swarm optimisation (PSO) and differential evolution, are investigated the first time to extract the DSCs parameters based on the single-diode photovoltaic (PV) equivalent circuit model. By comparing the accuracy, calculation speed and anti-noise ability of the three EA techniques, PSO shows the highest accuracy and the best anti-noise property. To evaluate the parameters, especially the series-internal resistance ( R s ) that is important for DSCs energy conversion efficiency, a batch of DSCs devices were made and the R s obtained by changing the series resistance value connected with the DSCs. The two methods give the R s approximately equal value, and almost same current-voltage figures based on PSO simulation with measured characteristics, which prove PSO is an efficient computational method and can be used to extract the parameters for the DSCs PV model.

Effects of vacancy defects on graphene nanoribbon field effect transistor

Abstract: The graphene nanoribbon (GNR) field effect transistor is one of the most competitive candidates for beyond-CMOS nanoelectronics because of the special electric characteristics of graphene. During graphene preparation, vacancy defects are inevitably introduced and affect transistor performances. In this Letter, four typical vacancy defects in GNR (i.e. single vacancy, divacancy, Stone-Wales and 555 777 defects) are examined. By quantum-mechanics-based simulation, the effects of these four defects on the energy band of the GNR are analysed. Moreover, their effects on the performances of the GNR field effect transistor, such as transmission coefficient and transfer characteristics, are studied and compared for various defect locations in the channel.

Fabrication of polyvinyl alcohol/multi-walled carbon nanotubes composite electrospun nanofibres and their application as microwave absorbing material

Abstract: Polyvinyl alcohol (PVA)/sodium dodecyl sulphate (SDS)/multi-walled carbon nanotubes (MWCNTs) composite nanofibres with various MWCNT contents (up to 10 wt%) were fabricated by electrospinning process and their microwave absorption properties were evaluated by a vector network analyser in the frequency range of 8–12 GHz (X-band) at room temperature. Scanning electron microscopy analysis of the nanofibre samples revealed that the deformation of the nanofibres increases with increasing MWCNT concentration. Very smooth surfaces of the composite electrospun nanofibres even for nanofibres with concentration of 10 wt% MWCNT have been successfully prepared because of the high stability dispersion of MWCNTs. It was observed that the absorption microwave properties improved by increasing the loading levels of MWCNTs. Finally, the PVA/SDS/MWCNT composite nanofibres sample with 10 wt% content of MWCNT has shown a reflection loss of 15 dB at a frequency of 8 GHz.

Electro-oxidation and simultaneous determination of amlodipine and atorvastatin in commercial tablets using carbon nanotube modified electrode

Abstract: Amlodipine besylate and atorvastatin calcium have been determined by the simultaneous voltammetric method at a multi-walled carbon nanotubes:graphite (MWCNTs:G) paste electrode. In comparison with a glassy carbon electrode, the prepared electrode showed an increase in the peak current because of the high electroactive surface area and excellent electronic conductivity of MWCNTs. The dependence of currents and potentials on pH were investigated for these components at the surface of the MWCNTs:G paste electrode. Differential pulse voltammetry was applied as a sensitive technique for simultaneous determination of the drugs in commercial tablets. By anodic differential pulse voltammetry, the calibration plot was linear in the range of 2.5-100 μg/ml with standard deviation between 2.7-7.1 and 1.8-8.3% for amlodipine and atorvastatin, respectively. The detection limit was 1 μg/ml at the prepared electrode in the buffered solution pH 6.

HKUST-1 coated piezoresistive microcantilever array for volatile organic compound sensing

Abstract: The HKUST-1 metal-organic framework (MOF) was selected because of the large internal surface area, excellent stability and known properties. Mechanical strain is generated upon the adsorption of analytes into the MOF; it is proportional to concentration and is a function of adsorbed species. Piezoresistive microcantilevers serve as a transduction mechanism to convert surface strain into electrical signals. N-doped piezoresistive cantilever arrays were fabricated with ten structures per die. Thin films of HKUST-1 were grown at room temperature using layer-by-layer techniques. Dry nitrogen was used as a carrier gas to expose devices to varying concentrations of 12 different volatile organic compounds (VOCs). Results show that stress-induced piezoresistive microcantilever array sensors with MOF coatings can provide a highly sensitive and reversible sensing mechanism for water vapour and methanol. Characteristic response features allow discrimination based on shape, response time constants and magnitude of response for other VOCs. Devices provided reliable data and proved durable over 18 months of testing. The key advantages of this type of sensor are higher sensitivity with a microporous MOFs, reversible response, α single chip sensing system and low power operation.

Photothermal excitation of microcantilevers in liquid: effect of the excitation laser position on temperature and vibrational amplitude

Abstract: Demands to improve the sensitivity and measurement speed of dynamic scanning force microscopy and cantilever sensing applications necessitate the development of smaller cantilever sensors. As a result, methods to directly drive cantilevers, such as photothermal or magnetic excitation, are gaining in importance. Presented is a report on the effect of photothermal excitation of microcantilevers on the increase in steady-state temperature and the dynamics of higher mode vibrations. First, the local temperature increase upon continuous irradiation with laser light at different positions along the cantilever was measured and compared with finite element analysis data. The temperature increase was highest when the heating laser was positioned at the free end of the cantilever. Next, the laser intensity was modulated to drive higher flexural modes to resonance. The dependence of the cantilever dynamics on the excitation laser position was assessed and was in good agreement with the analytical expressions. An optimal position to simultaneously excite all flexural modes of vibration with negligible heating was found at the clamped end of the cantilever. The reports findings are essential for optimisation of the excitation efficiency to minimise the rise in temperature and avoid damaging delicate samples or functionalisation layers.

Improvement of solid oxide fuel cell by imprinted micropatterns on electrolyte

Abstract: A study is presented of an improved interfacial structure between the electrode and electrolyte of a solid oxide fuel cell. An imprint process, which is considered as a powerful tool to transcribe nano to micropatterns on materials, was employed to imprint fine patterns onto a ceramic sheet of electrolyte. In the presented work, a sheet of ceramic compound material was prepared, and micropatterns were imprinted on its surface. After debinding and sintering, a dense ceramic sheet with fine micropatterns was obtained. To investigate the effect of micropatterns on the overall performance of a fuel cell, three kinds of electrolyte sheets with different surface patterns were employed for this technique. After applying anode and cathode layers, the three fuel cell samples were assembled to test the cell performance. The result was that the finer pattern caused better performance in the three samples by exhibiting the highest overall voltage and power density, and the effective factors of patterns on ion conductivity were discussed as well. Based on the investigation, some further improved three-dimensional microstructures were proposed and fabricated by the method of micro powder imprinting (μPI).

Investigation on bacterial adhesion and colonisation resistance over laser-machined micro patterned surfaces

Abstract: Micro-nano patterns created directly over solid surfaces to combat microbial activity help in preventing hospital-acquired infections. This Letter is focused on defining surface topologies by laser patterning over solid surfaces. Studies on designing surface topologies and bacterial culture have been carried out and the feasibility of micro scale features in restricting bacterial growth has been investigated. The effects of the engineered roughness index and contact angle are discussed. Contact angle measurement over patterned surfaces using a novel computer vision-based technique is demonstrated and the effect of contact angle on bacterial adhesion has been presented. The results obtained show that the designed micro scale geometries can effectively reduce the growth of bacteria on the said surfaces.

Surfactant-assisted hydrothermal synthesis and tribological properties of flower-like Mos 2 nanostructures

Abstract: Flower-like molybdenum disulfide (MoS 2 ) nanostructures with high purity were successfully synthesised via a facile surfactant-assisted hydrothermal route. The structure and morphology of the as-prepared products were characterised by X-ray powder diffraction, energy dispersive spectroscopy, scanning electron microscopy and transmission electron microscopy. The influence of the surfactant and the pH value of the initial mixture on the formation of the MoS 2 nanostructures was investigated. A possible evolutionary process of the flower-like MoS 2 nanostructures is proposed to explain the formation of various MoS 2 nanostructures on the basis of the experimental results. In addition, the tribological properties of the as-prepared MoS 2 powders as additives in HVI500 base oil were investigated on an UMT-2 multispecimen tribo-tester. The topography of worn scars was obtained using a common SEM. It is found that the addition of MoS 2 nanoflowers can improve the tribological properties of the base oil.

Realisation of semiconductor ternary quantum dot cellular automata

Abstract: Quantum dot cellular automata (QCA) have become a strong alternative for nanoscale computing. After a decade of exhaustive research on binary QCA, the newly introduced ternary QCA (tQCA) for implementing ternary logic needs further research to actually fabricate the tQCA cell. In this Letter, a quantum mechanical approach is presented for calculating the diverse parameters required for the fabrication of the tQCA. The effect of quantum dot size, the size of tQCA cell as well as the effect of temperature on polarisation for the tQCA cell are examined. The significant result for fabrication of the tQCA cell is tunnelling resistance, which must be greater than the quantum Hall resistance, that is, Rt ≫ 25.813 kΩ. The tQCA needs a quantum dot size which is < 6.36 nm to operate at room temperature and the distance of separation between two dots must be 5 nm. The steady-state behaviour of the tQCA cell using the Hubbard model and the Schrodinger time-independent equation is also explored.

Synthesis, microstructure and magnetic properties of Heusler Co2FeSn nanoparticles

Abstract: Heusler Co2FeSn nanoparticles in a B2-type cubic structure were synthesised for the first time using a simple solution reduction method. X-ray diffraction, a scanning electron microscope, an energy dispersive spectrometer and a vibrating sample magnetometer were used to characterise the synthesised products. The crystal structure and composition of the samples vary with the concentration of potassium hydroxide, synthesis temperature and reaction time. Magnetic measurement reveals that the obtained Co2FeSn nanoparticles are soft magnetic at room temperature. The Co2FeSn nanoparticles synthesised in this work are magnetically superior and economically feasible for spintronic applications.

In situ synthesis of silver nanoparticles onto cotton fibres modified with plasma treatment and acrylic acid grafting

Abstract: Silver nanoparticles were synthesised on the modified cotton fibres using an in situ method. Acrylic acid was grafted on the surface of cotton using plasma technology as a means to enhance the loading efficiency of nanoparticles. The loading efficiency of silver nanoparticles into the cotton fabric was examined by an atomic absorption spectrometer. The surface of the fibres was characterised by low-voltage scanning electron microscopy and attenuated total reflection-Fourier transform infrared spectrometry. The cotton fabrics loaded with Ag nanoparticles were examined by thermogravimetric analysis. In addition, the antibacterial activity of loaded samples was determined according to the AATCC test method 147-2004. Grafting of acrylic acid on cotton fibre leads to increase in the loading efficiency of silver nanoparticles and this sample showed the highest antibacterial activity.

Developing integrated piezoelectric direct current sensor with actuating and sensing elements

Abstract: A cantilever-based, oscillating type MEMS direct current sensor (abbreviated as DC sensor), integrated with both actuating and sensing piezoelectric plates, as well as a micromagnet is proposed to satisfy the increasing needs of DC power supply for monitoring electrical consumption by either a single-wire or two-wire appliance cord. A prototype MEMS DC sensor, with a measured resonant frequency of 23 Hz, was microfabricated and characterised. In the case of a two-wire electrical appliance cord, it was found that the change in the peak-to-valley value (abbreviated as P-V value) of the output voltage was approximately proportional to the applied DC, and increased from 10.4 to 43.2 mV when the DC increased from 0 to 2 A under an excitation voltage of 5 Vpp. The shift of the resonant frequency because of the applied DC is believed to account for the change in the P-V value (or the maximum value) of the output voltage. In summary, the proposed MEMS DC sensor integrated with both actuating and sensing piezoelectric plates was observed to measure the output voltage constantly and linearly over the applied DC directly in a two-wire appliance without using a cord separator.

Photocatalytic degradation of phenol using Au/Bi 2 WO 6 composite microspheres under visible-light irradiation

Abstract: Gold loaded Bi2WO6 (Au/Bi2WO6) nanosheet-based microspheres were prepared via a hydrothermal method combined with an in-situ reduction approach. The products were characterised by scanning electron microscopy, a high-resolution transmission electron microscope, X-ray diffraction, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy and UV–vis diffuse reflectance. The characterisation results revealed that it was the Au nanoparticles deposited on Bi2WO6 microspheres. A photocatalytic test for the degradation of phenol proved that Au loading was an effective means to enhance the photocatalytic activity of Bi2WO6 nanosheet-based microspheres under visible-light irradiation (λ > 420 nm). The photocatalytic mechanism over the Au/Bi2WO6 was analysed by active species trapping experiments. The main active species •OH for the photocatalytic test was produced by two pathways, that is, photogenerated holes oxidised water molecules to form •OH (oxidative pathway), and O2 captured the photogenerated electron to generate •O2 − and subsequently produce •OH (reductive pathway).

Fabrication and testing of porous Ti microneedles for drug delivery

Abstract: Porous metal microneedles were fabricated by an incorporated process of cutting and wet etching. Each microneedle is comprised of many connecting microholes that can deliver drugs into organisms conveniently and efficiently. The microneedle height is larger than 400 μm, the pitch distance is about 800 μm and the microholes in each microneedle are about 20 μm in diameter. In force testing, the microneedles could resist large shear forces and pierce into skins easily; in the in vivo experiment, the insulin was efficiently injected into rats by a patch of the microneedles. The testing and the experiment demonstrated that the microneedles could deliver drugs into organisms to treat diseases without fracture.

Ag 2 O/Ag 3 PO 4 heterostructures: highly efficient and stable visible-light-induced photocatalyst for degradation of methyl orange and phenol

Abstract: Ag2O/Ag3PO4 heterostructures photocatalysis was prepared for the first time. Photocatalytic tests displayed that the Ag2O/Ag3PO4 heterostructures possessed a much higher degradation rate of methyl orange and phenol than pure Ag3PO4 under visible light. The enhanced photocatalytic activity could be attributed to effective separation of photogenerated carriers driven by photoinduced potential difference generated at the Ag2O/Ag3PO4 heterojunction interface. Repetitive tests showed that the Ag2O/Ag3PO4 heterostructures maintained high stability over several cycles, and it had better regeneration capability under mild conditions. The good stability could be attributed to the protection of insoluble Ag2O nanoparticles on the surfaces of Ag3PO4 crystals in aqueous solution.

Fabrication and characterisation of functional gradient hydroxyapatite reinforced poly (ether ether ketone) biocomposites

Abstract: Biomaterials usually require simultaneous possession of excellent performances such as bioactivity, mechanical and bio-tribological properties to meet biomedical application requirements. In this reported work, the bioactive and mechanical properties of biocomposites were simultaneously optimised according to the functional gradient design idea. The functional gradient nano-hydroxyapatite reinforced polyetheretherketone (nano-HA/PEEK) biocomposites were fabricated through the layer-by-layer casting method and incorporation with thermal pressure moulding technology. The microstructure and morphology were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared (FTIR). The result of the XRD study verified that the crystallinity of the PEEK matrix obviously improved after heat treatment. The SEM observation revealed that the size of HA particles in the biocomposites was in the nanometre scale. Furthermore, two typical morphologies such as encapsulated- and dimple-like microstructures were observed by SEM. The FTIR study showed that the interaction between nano-HA particles and the PEEK molecule existed. Both the SEM and FTIR studies results revealed that the morphology and microstructure in the functional gradient HA/PEEK biocomposites were beneficial for the improvement of the mechanical properties of the gradient biocomposites.

Silver selenide nanoparticles: synthesis, characterisation and effect of preparation conditions under ultrasound radiation

Abstract: A convenient sonochemical process for the preparation of silver selenide (Ag 2 Se) nanoparticles by using different complexing agents [NH 3 , citric acid, potassium thiocyanate (KSCN)] and hydrazine as reductant agent is developed. It was found that pure Ag 2 Se nanoparticles were prepared in the presence of KSCN after 90 minutes of sonication. The products were characterised by X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy analysis. Photoluminescence was used to study the optical properties of Ag 2 Se samples.

Tin oxide nanoparticle-modified commercial PtRu catalyst for methanol oxidation

Abstract: The electrocatalytic performance of commercial PtRu/C is significantly enhanced by directly mixing a few SnO 2 nanoparticles. The composite catalysts show enhanced CO oxidation, higher activity and better stability than commercial PtRu/C. Among the different ratios of SnO 2 nanoparticles (10-40-), the SnO 2 -PtRu/C (20-) composite catalyst shows the best catalytic activity for methanol oxidation. The effect of temperature on methanol oxidation was also investigated and the apparent activation energy ( E a ) value of catalyst was obtained. The results here suggest a simple route to enhance the catalytic efficiency for commercial PtRu/C catalyst.

Bioreduction of chloroaurate ions using fruit extract Punica granatum (Pomegranate) for synthesis of highly stable gold nanoparticles and assessment of its antibacterial activity

Abstract: The design, synthesis and characterisation of biologically synthesised nanomaterials have become an area of significant interest. Presented is a report on the extracellular synthesis of gold nanoparticles using Punica granatum (Pomegranate) fruit extract as the reducing agent to synthesise Au nanoparticles. On treating aqueous chloroauric acid solutions with P. granatum fruit extract, rapid reduction of the chloroaurate ions is observed, leading to the formation of highly stable gold nanoparticles in solution. These nanoparticles showed an absorption peak at 536 nm in the UV–vis spectrum corresponding to the plasmon resonance of gold nanoparticles. Scanning electron microscopy analysis of the gold nanoparticles indicated that they ranged in size from 10 to 50 nm. The Fourier transform infrared spectroscopy spectrum confirmed the presence of main groups occurred in natural plant extract from P. granatum. The synthesised gold nanoparticles were active against Streptobacillus sp. and Escherichia coli.

Thermo-flow and temperature sensing behaviour of graphene based on surface heat convection

Abstract: This letter studies the surface heat convection of thin graphene sheets and the application of graphene wires as nanoscale flow and temperature sensors. Graphene wires with relatively large length-to-width ratios were designed and fabricated using bi- and few-layer graphene sheets. Prior to testing, the devices were packaged in a microfluidic chamber with capillary tubes as upstream and downstream connections to minimise environmental interference. The thermal inertia of the graphene wire was studied at 70°C and the flow sensing behaviour of the device was characterised by monitoring normalised resistance changes at different flow rates. The authors experimental results demonstrated the negative temperature coefficients of the bi- and few-layer graphene films. Moreover, the flow sensing resolutions of ~ 0.07 l/min and 0.1 l/min were achieved from the bi- and few-layer graphene hot wires, respectively. The temperature sensing behaviour of the graphene thermistor was studied in a small temperature range from room temperature to 80°C. The larger negative temperature coefficient of the bi-layer graphene resulted in a higher sensing response than the few-layer one.

Al-doped ZnS thin films for buffer layers of solar cells prepared by chemical bath deposition

Abstract: In this reported study, Al-doped ZnS (ZnS:Al) thin films were fabricated by chemical bath deposition in alkaline condition along with a stable complexing agent of sodium citrate in ammonia/ammonium chloride buffer solution. Al concentrations were varied from 0 to 10 at.%. The structure and composition of the films were confirmed by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectra and Raman spectroscopy. The XRD, FTIR and Raman spectra confirmed the existence of ZnS and Al-S bond, which had some effects on the properties of the films. The optical characteristics indicated the changes of the bandgap with the Al-doping concentrations. The resistivity of the ZnS:Al films with different Al-doping concentrations after annealing was analysed and the sample with 6 at.% Al concentration had the lowest resistivity of 9.9 × 10 4 Ω cm.

Fabrication of a substrate for Ag-nanorod metal-enhanced fluorescence using the oblique angle deposition process

Abstract: Metal-enhanced fluorescence (MEF) is a powerful technology to improve the sensitivity of fluorescence analysis by allowing fluorophores to interact with enhanced electromagnetic fields generated by the localised surface plasmon resonance effects of metallic nanostructures. To apply MEF technology to disposable DNA or protein microarray analysis, metallic nanostructures need to be fabricated on the full area of a glass slide at low cost. In this reported work an oblique angle deposition process was used to fabricate Ag nanorods on the whole area of a 25 × 75 mm2 glass slide to serve as an inexpensive and large-area MEF substrate. To examine the feasibility of the proposed substrate and maximise signal enhancement, Ag nanorods with different lengths were deposited on glass slides. Different concentrations of streptavidin-conjugated Cy5 in phosphate buffered saline were spotted onto the Ag nanorods and bare glass substrates, and the fluorescence signals were measured and compared. Longer Ag nanorods improved the fluorescence enhancement factor because of a higher surface plasmon resonance effect and the large surface area of the nanostructure with a high aspect ratio. A maximum enhancement factor of −23 was obtained from Ag nanorods that were 1000 nm long with comparable uniformity with the glass substrate.

Non-resonant electrostatic energy harvester for wideband applications

Abstract: Presented is a novel non-resonant electrostatic energy harvester targeted at the wideband frequency response for micro-system powering. To boost non-resonance power output under low frequency, the vertical gap changing method is adopted to induce variable charges, which generates approximately 17 times of charge change compared with the conventional method of laterally changing overlap area (at 1 mm gap). Further, to boost the low frequency and non-resonant power generating capability, the differential structure is adopted to achieve doubled output voltages. Testing results reveal that optimal output power occurs when the inner plate is of large effective movement range and large relative displacement with surrounding electrets. Maximally, 3.9–7.0 V voltage and 0.2–0.7 μW power are achieved over the 5–120 Hz frequency range.

Differential piezoresistive sensing in a bulk-mode micromechanical resonator

Abstract: A report is presented on a differential piezoresistive sensing approach for transducing the motional response of bulk-mode micromechanical resonators. High-frequency bulk-mode micoresonators have inherently high stiffness and demonstrate limited range of motion, which in turn presents challenges for the capacitive sensing method in the presence of large parasitic feedthrough. A differential piezoresistive sensing approach is implemented in this Letter to substantially reject the effects of parasitic capacitive feedthrough, leaving the response recovered directly from the measurement. With differential pick-up, a 33 dB drop of feedthrough has been achieved and a resonant peak magnitude of 14 dB is obtained for a drain current of 1 mA, which is shown to be approximately 20 times higher than that obtained for the conventional piezoresistive sensing scheme. This method also enables a low DC voltage for capacitively driving the bulk-mode resonator. As an example, a resonant peak magnitude of 5 dB is demonstrated using 3.55 mA drain current and 5 V DC driving voltage.

Nanoencapsulation of hypericum perforatum and doxorubicin anticancer agents in PLGA nanoparticles through double emulsion technique

Abstract: A comparative study is performed on Hypericum perforatum (H. perforatum) and doxorubicin (Dox) anticancer agents. Double emulsion and sonication techniques were used to enhance drug loading efficiency in poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs). To distinguish the efficiency of the double emulsion method, drug entrapment efficiency was measured. In vitro release studies were carried out to evaluate drug release profiles. Entrapment efficiency was estimated to be 48 and 21% for Dox-loaded and H. perforatum-loaded NPs, respectively. Surprisingly, the encapsulation process disrupted the formation of Dox crystals (Dox in NPs converted from the crystalline to the amorphous phase), whereas disordered crystalline was observed for H. perforatum. In vitro release studies suggested that the total released drug was about 71% of the whole entrapped drug after 20 days. MTT assay confirmed that Dox was more toxic than H. perforatum. This study revealed that H. perforatum is a good choice for further experiments in drug delivery systems because of low cardiotoxicity according to the herbaceous nature of this anticancer agent.

Enhanced photocatalytic activity induced by surface plasmon resonance on Ag-loaded strontium titanate nanoparticles

Abstract: Ag nanoparticles-modified cubic-like SrTiO3 (STO) are fabricated through a classical hydrothermal and photodeposition method. The prepared Ag-STO heterogeneous exhibit an efficient photocatalytic activity (approximate to 42% within 1 h reaction time) for degradation of tetracycline under visible-light irradiation, and Ag deposition with 8 mM AgNO3 exhibited excellent photocatalytic activity. It is considered that this excellent performance results from the surface plasmon resonance of Ag nanoparticles. Meanwhile, the basic principle of the photocatalytic process on the Ag-STO photocatalyst system is also discussed.

Size-dependent photoluminescence in silicon nanostructures: quantum confinement effect

Abstract: Visible photoluminescence (PL) from laser-etched silicon nanostructures has been analysed. A systematic size dependence study of PL from silicon nanostructures has been performed. The PL from these structures is attributed to the quantum confinement effect. Different quantum confinement models have been used for PL and Raman lineshape fitting to calculate the mean size and size distribution of silicon nanostructures and the results are comparatively studied. Calculated values of oscillator strength and radiative lifetime show that PL is due to radiative recombination of confined excitons.