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Microcantilevers are really promising sensitive sensors despite their small surface. In order to increase this surface and consequently their sensitivity, we nanostructured them with copper oxide (CuO) nanorods. The synthesis of the nanostructure consists of the oxidation of a copper layer deposited beforehand on the surface of the sample. The oxidation is performed in an alkaline solution containing a mixture of Na(OH) and (NH4)2S2O8. The synthesis procedure was first optimized on a silicon wafer, then transferred to optical cantilever-based sensors. This transfer requires specific synthesis modifications in order to cover all the cantilever with nanorods. A masking procedure was specially developed and the copper layer deposition was also optimized. These nanostructured cantilevers were engineered in order to detect vapors of organophosphorous chemical warfare agents (CWA). The nanostructured microcantilevers were exposed to various concentration of dimethyl methylphosphonate (DMMP) which is a well-known simulant of sarin (GB). The detection measurements showed that copper oxide is able to detect DMMP via hydrogen interactions. The results showed also that the increase of the microcantilever surface with the nanostructures improves the sensors efficiency. The evolution of the detection performances of the CuO nanostructured cantilevers with the DMMP concentration was also evaluated.
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Self-controlled active oscillating microcantilevers with a piezoresistive readout are very promising sensitive sensors, despite their small surface. In order to increase this surface and consequently their sensitivity, we nanostructured them with copper hydroxide (Cu(OH)2) or with copper oxide (CuO) nanorods. The Cu(OH)2 rods were grown, on a homogeneous copper layer previously evaporated on the top of the cantilever. The CuO nanorods were further obtained by the annealing of the copper hydroxide nanostructures. Then, these copper based nanorods were used to detect several molecules vapors. The results showed no chemical affinity (no formation of a chemical bond) between the CuO cantilevers and the tested molecules. The cantilever with Cu(OH)2 nanorods is selective to nitrogen dioxide (NO2) in presence of humidity. Indeed, among all the tested analytes, copper hydroxide has only an affinity with NO2. Despite the absence of affinity, the cantilevers could even so condensate explosives (1,3,5-trinitro-1,3,5-triazinane (RDX) and pentaerythritol tetranitrate (PETN) on their surface when the cantilever temperature was lower than the explosives source, allowing their detection. We proved that in condensation conditions, the cantilever surface material has no importance and that the nanostructuration is useless because a raw silicon cantilever detects as well as the nanostructured ones.
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The specific attributes of nanodiamonds have attracted increasing interest for electronics or biomedical applications. An efficient synthetic route towards nanodiamonds is via detonation of hexolite (i.e. a mixture of TNT [2,4,6-trinitrotoluene] and RDX [1,3,5-trinitro-1,3,5-triazine]). In particular, detonation of hexolite crystallized by spray flash evaporation (SFE) yields extremely small diamonds (<4â nm). To unravel the detonation mechanism, a structural characterization of the explosives is required but is challenging due to their thermal instability. We demonstrate a combination of conventional Raman spectroscopy and tip-enhanced Raman spectroscopy (TERS) for resolving morphological and structural differences of differently prepared hexolite nanocomposites. The experiments allow for the first time a structural differentiation of individual TNT and RDX crystals and 15-20â nm sized core-shell structures, consequently providing a general approach to investigate the actual composition of mixtures on the nanometer scale.
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Nanoestruturas/química , Triazinas/química , Trinitrotolueno/química , Microscopia de Força Atômica , Estrutura Molecular , Análise Espectral RamanRESUMO
The nonlinear optical mechanisms and the optical limiting behavior of porphyrin functionalized detonation nanodiamonds are investigated and compared to the conventional detonation nanodiamonds (DNDs). The optical limiting behavior is characterized by means of nonlinear transmittance, Z-scan, and scattered intensity measurements when submitted to a nanosecond pulsed Nd:YAG laser operating at the second harmonic wavelength. We found that the largest nonlinear attenuation was observed on the 4,4',4'',4'''-(porphyrin-5, 10, 15, 20-tetrayl) tetrakis benzoic acid (PCOOH) suspension. Using Z-scan experiments, it is shown that nonlinear refraction predominates in the unfunctionalized DND suspension, while nonlinear absorption is the most relevant mechanism in the porphyrin functionalized DNDs. Furthermore, a stronger backscattered intensity signal is highlighted for the unfunctionalized DNDs through nonlinear scattering measurements.
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Smart detection systems for explosive sensors are designed both to detect explosives in the air at trace level and identify the threat for a specific response. Following this need we have succeeded in using microthermal analysis to sensitively identify and discriminate between RDX and PETN explosive vapors at trace level. Once the explosive vapor is trapped in a porous material, heating the material at a fast rate of 3000 K/s up to 350 °C will result in a thermal pattern specifically corresponding to the explosive and its interaction with the porous material. The explosive signatures obtained make it possible to simultaneously identify the presence and the nature of the explosive vapor in just a few milliseconds. Therefore, this also allows the development of multitarget devices using porous material for capturing the vapor combined with microthermal analysis for fast detection and identification. So far it is the first time that chip calorimetry has been used to characterize and identify explosives in vapor state.
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Metal sulfates (Ba, Bi, Ca, Cu, Mg, Mn, Na, Zn, Zr) were used as oxidizers in reactive compositions with Al nanopowder. These new kinds of nanothermites have outstandingly high reaction heats (4-6â kJ g(-1) ) compared to conventional Al/metal oxides (1.5-4.8â kJ g(-1) ) and also have good combustion velocities (200-840â m s(-1) vs 100-2500â m s(-1) ). These compositions are extremely insensitive to friction making their preparation and handling easy and safe. The sulfate hydration water increases the reaction heats and has a significant effect on the sensitivity to impact and to electrostatic discharge. The reaction of Al with water is easier to initiate than the one with sulfate which leads to two possible decomposition modes for samples exposed to an open flame. The pyrotechnical properties observed with sulfates have also been found for other sulfur oxygenates (SO3 (2-) , S2 O3 (2-) , S2 O8 (2-) ) which opens up new horizons in the domain of metastable interstitial composites.
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Combining photonic integrated circuits with a biologically based sensing approach has the ability to provide a new generation of portable and low-cost sensor devices with a high specificity and sensitivity for a number of applications in environmental monitoring, defense, and homeland security. We report herein on the specific biosensing under continuous air flow of DMMP, which is commonly used as a simulant and a precursor for the synthesis of Sarin. The proposed technology is based on the selective recognition of the targeted DMMP molecule by specifically modified proteins immobilized on photonic structures. The response of the biophotonic structures shows a high stability and accuracy over 3 months, allowing for the detection in diluted air of DMMP at concentration as low as 35 µg/m(3) (6.8 ppb) in less than 15 min. The performance of the developed technology satisfies most current homeland and military security requirements.
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Substâncias para a Guerra Química/química , Compostos Organofosforados/química , Sarina/síntese química , Terrorismo Químico , Monitoramento Ambiental , MicrocomputadoresRESUMO
A microelectromechanical-systems-based calorimeter designed for use on a synchrotron nano-focused X-ray beamline is described. This instrument allows quantitative DC and AC calorimetric measurements over a broad range of heating/cooling rates (≤100000â Kâ s(-1)) and temperature modulation frequencies (≤1â kHz). The calorimeter was used for high-resolution thermal imaging of nanogram-sized samples subjected to X-ray-induced heating. For a 46â ng indium particle, the measured temperature rise reaches â¼0.2â K, and is directly correlated to the X-ray absorption. Thermal imaging can be useful for studies of heterogeneous materials exhibiting physical and/or chemical transformations. Moreover, the technique can be extended to three-dimensional thermal nanotomography.
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Nitrogen-vacancy defect centers (NV) contained in nanodiamonds (NDs) are a promising candidate in quantum information processing and single photon sources due to the capability of controlling their assembly on various surfaces. However, their detection with traditional optical techniques becomes challenging when probing high NV densities at the nanometer scale. Here, we combine scanning probe techniques to characterize in a monolayer the structural and electronic properties of bucky-diamonds with sizes below 10 nm. We further observe by light-assisted Kelvin- and scanning tunneling spectroscopy a clear signature of negatively charged subsurface NV centers in NDs at the nanoscale where conventional techniques are limited.
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Nanodiamantes/química , Nitrogênio/química , Óptica e Fotônica , Luz , Fótons , Propriedades de SuperfícieRESUMO
Melamine (Mel) was used as host matrix for liquid nitroglycerin (NG), to prepare Mel/NG solid powdered compounds containing up to 45 wt% of this explosive. The two preparation processes used for this purpose consisted in evaporating a solution of both components, either in ambient conditions or under reduced pressure by the Spray Flash-Evaporation (SFE) process. In Mel/NG materials, amorphous nitroglycerin is distributed in the crystallized melamine matrix as inclusions, which were found to be smaller in size in the material prepared by the SFE process. Mel/NG materials are not stable over time: they gradually lose the nitroglycerin they contain by evaporation.
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Nanostructured microcantilevers have shown promise for sensing application of molecules in the vapor phase. Nanostructures have improved the molecule capture ability of microcantilevers by highly enhancing the surface of capture. Here, to improve the sensitivity and selectivity of a commercial microcantilever without functionalization, we developed 3D core-shell titanium dioxide@manganese dioxide (TiO2@MnO2) nanorod arrays on a microcantilever, which exhibited a high enhancement in the sensing performance beyond that of 1D nanostructures for the detection of dimethyl methylphosphonate, a simulant of sarin.
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Microgravimetric sensor platforms with physico- or chemo-selective interfaces offer promising sensing properties. They are widely used to detect chemical warfare agents (CWAs). However, a comprehensive insight into adsorption mechanisms and interactions between low concentrations of these adsorbates and low-mass adsorbents is still lacking. In this study, we report a complete and detailed analytical method to model the adsorption processes of low traces of vapor-phase DiMethyl MethylPhosphonate (DMMP), a conventional simulant of CWAs, on a double-side nanostructured microcantilever coated with vertically-aligned titanium dioxide nanotubes (TiO2-NTs). We find that the geometrical configuration of NTs plays an important role in the diffusion regimes of molecules during the adsorption. This study shines light on the adsorption and kinetic mechanisms of low-traces DMMP offering opportunities to have a better insight of the adsorption of CWAs on complex nanostructures and to improve microcantilever sensors.
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Surface enhanced Raman spectroscopy (SERS) and confocal Raman microscopy are applied to investigate the structure and the molecular arrangement of sub-micron furosemide and polyvinylpyrrolidone (furosemide/PVP) particles produced by spray flash evaporation (SFE). Morphology, size and crystallinity of furosemide/PVP particles are analyzed by scanning electron microscopy (SEM) and X-ray powder diffraction (XRPD). Far-field Raman spectra and confocal far-field Raman maps of furosemide/PVP particles are interpreted based on the far-field Raman spectra of pure furosemide and PVP precursors. Confocal far-field Raman microscopy shows that furosemide/PVP particles feature an intermixture of furosemide and PVP molecules at the sub-micron scale. SERS and surface-enhanced confocal Raman microscopy (SECoRM) are performed on furosemide, PVP and furosemide/PVP composite particles sputtered with silver (40 nm). SERS and SECoRM maps reveal that furosemide/PVP particle surfaces mainly consist of PVP molecules. The combination of surface and bulk sensitive analyses reveal that furosemide/PVP sub-micron particles are formed by the agglomeration of primary furosemide nano-crystals embedded in a thin PVP matrix. Interestingly, both far-field Raman microscopy and SECoRM provide molecular information on a statistically-relevant amount of sub-micron particles in a single microscopic map; this combination is thus an effective and time-saving tool for investigating organic sub-micron composites.
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Among various methods for landmine detection, as well as soil and water pollution monitoring, the detection of explosive compounds in air is becoming an important and inevitable challenge for homeland security applications, due to the threatening increase in terrorist explosive bombs used against civil populations. However, in the last case, there is a crucial need for the detection of vapor phase traces or subtraces (in the ppt range or even lower). A novel and innovative generator for explosive trace vapors was designed and developed. It allowed the generation of theoretical concentrations as low as 0.24 ppq for hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in air according to Clapeyron equations. The accurate generation of explosive concentrations at subppt levels was verified for RDX and 2,4,6-trinitrotoluene (TNT) using a gas chromatograph coupled to an electron capture detector (GC-ECD). First, sensing material experiments were conducted on a nanostructured tungsten oxide. The sensing efficiency of this material determined as its adsorption capacity toward 54 ppb RDX was calculated to be five times higher than the sensing efficiency of a 54 ppb TNT vapor. The material sensing efficiency showed no dependence on the mass of material used. The results showed that the device allowed the calibration and discrimination between materials for highly sensitive and accurate sensing detection in air of low vapor pressure explosives such as TNT or RDX at subppb levels. The designed device and method showed promising features for nanosensing applications in the field of ultratrace explosive detection. The current perspectives are to decrease the testing scale and the detection levels to ppt or subppt concentration of explosives in air.
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This paper reports on the first attempt to enclose diamond nanoparticles--produced by detonation--into a Kevlar matrix. A nanocomposite material (40 wt% diamond) was prepared by precipitation from an acidic solution of Kevlar containing dispersed nanodiamonds. In this material, the diamond nanoparticles (Ø = 4 nm) are entirely wrapped in a Kevlar layer about 1 nm thick. In order to understand the interactions between the nanodiamond surface and the polymer, the oxygenated surface functional groups of nanodiamond were identified and titrated by Boehm's method which revealed the exclusive presence of carboxyl groups (0.85 sites per nm2). The hydrogen interactions between these groups and the amide groups of Kevlar destroy the "rod-like" structure and the classical three-dimensional organization of this polymer. The distortion of Kevlar macromolecules allows the wrapping of nanodiamonds and leads to submicrometric assemblies, giving a cauliflower structure reminding a fractal object. Due to this structure, the macroscopic hardness of Kevlar doped by nanodiamonds (1.03 GPa) is smaller than the one of pure Kevlar (2.31 GPa). To our knowledge, this result is the first illustration of the change of the mechanical properties induced by doping the Kevlar with nanoparticles.
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The poor solubility and related low bioavailability are a major concern for a large number of small molecule drugs, both on the market and in development. Several formulation strategies exist to overcome this issue. Among them, particle engineering is of outmost importance. The aim of this work is to present the potential of Spray Flash Evaporation (SFE), a new technology for drug particle engineering. To assess the potential of SFE, we carried out a case study on the nano-crystallization of furosemide, a BCS class IV drug. A thorough characterization of the obtained nanocrystals is presented along with a study of dissolution which highlights the solubility improvement provided by nanocrystals produced via SFE technology. The obtained results show a particle size reduction when compared to the raw material, as well as an increase of the dissolution rate of 4.5-fold.
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Nanopartículas , Preparações Farmacêuticas , Furosemida , Tamanho da Partícula , Solubilidade , TecnologiaRESUMO
Atomic Force Microscopy coupled with Tip Enhanced Raman Spectroscopy (AFM-TERS) was applied to obtain information about the structure and surface composition of single nano co-crystals. For this purpose, a co-crystalline system consisting of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazatetracyclo-[5.5.0.03,11.05,9]-dodecane (CL-20) and 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX) in a molar ratio of 2 : 1 (CL-20/HMX) was chosen. CL-20/HMX nano-plates were prepared by spray flash evaporation. To ensure co-crystallinity and nanostructures, powder X-ray diffraction and AFM investigations were performed. The results demonstrate that coherence lengths and particle dimensions are on a similar level though coherence lengths appear shorter than measured particle dimensions. According to this fact, defects inside the nano co-crystals are minimized. The co-crystallinity was additionally proven by confocal Raman spectroscopy. Here, marker bands for pristine CL-20 and HMX were chosen which appear in the CL-20/HMX spectrum in an intensity ratio of â¼2.5 : 1 (CL-20 : HMX). Afterwards surface investigations of single CL-20/HMX nano-plates were performed by AFM-TERS. Due to the surface sensitivity of TERS, these experiments reveal that the ratio of the Raman intensities between CL-20 and HMX inverts at CL-20/HMX nano-plate surfaces. Therefore, it is concluded that nano co-crystal surfaces consist of molecular layers of HMX. A theoretical approximation of the normal coordinates of the investigated marker vibrations supports this conclusion since it can exclude the occurrence of the intensity ratio inversion because of the given orientation between CL-20/HMX nano-plates and the Raman scattering system. Based on this finding, an impact ignition mechanism is proposed, enabling explanation of the close impact sensitivity values of ß-HMX and CL-20/HMX.
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We reported a new strategy to enhance the sensing performances of a commercial microcantilever with optical readout in dynamic mode for the vapor detection of organophosphorus compounds (OPs). In order to increase significantly the surface area accessible to the molecules in the vapor phase, we nanostructured both sides of the microcantilever with ordered, open and vertically oriented amorphous titanium dioxide nanotubes (TiO2-NTs) in one step by an anodization method. However, due to the aggressive conditions of anodization synthesis it remains a real challenge to nanostructure both sides of the microcantilever. Consequently, we developed and optimized a protocol of synthesis to overcome these harsh conditions which can lead to the total destruction of the silicon microcantilever. Moreover, this protocol was also elaborated in order to maintain a good reflection of the laser beam on one side of the microcantilever towards the position sensitive photodiode and limit the light diffusion by the NTs film. The results related to the detection of dimethyl methylphosphonate (DMMP) showed that TiO2 and the nanostructuring on both sides of the microcantilever with NTs indeed improved the response of the sensor to vapors compared to a microcantilever nanostructured on only one side. The dimensions and morphology of NTs guaranteed the access of molecules to the surface of NTs. This approach showed promising prospects to enhance the sensing performances of microcantilevers.
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We report the fabrication of nanostructured microcantilevers employed as sensors for the detection of organophosphorus (OPs) vapors. These micromechanical sensors are prepared using a two-step procedure first optimized on a silicon wafer. TiO2 one-dimensional nanostructures are synthesized at a silicon surface by a solvothermal method and then grafted with bifunctional molecules having an oxime group known for its strong affinity with organophosphorus compounds. The loading of oxime molecules grafted on the different nanostructured surfaces was quantified by UV spectroscopy. It has been found that a wafer covered by vertically aligned rutile TiO2 nanorods (NRs), with an average length and width of 9.5 µm and 14.7 nm, respectively, provides an oxime function density of 360 nmol cm-2. The optimized TiO2 nanorod synthesis was successfully reproduced on the cantilevers, leading to a homogeneous and reproducible TiO2 NR film with the desired morphology. Thereafter, oxime molecules have been successfully grafted on the nanostructured cantilevers. Detection tests were performed in a dynamic mode by exposing the microcantilevers to dimethyl methylphosphonate (a model compound of toxic OPs agents) and following the shift of the resonant frequency. The nanostructure and the presence of the molecules on a TiO2 NR surface both improve the response of the sensors. A detection limit of 2.25 ppm can be reached with this type of sensor.
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Cantilevers are really promising sensitive sensors despite their small surface. In order to increase this surface and consequently their sensitivity, we nanostructured them with zinc oxide (ZnO) nanorods or nanotubes having a diameter of approximately 100 nm and a length of 1 µm. The nanostructure growth was first optimized on a silicon wafer and then transferred to the cantilevers. The ZnO nanorods were grown in an autoclave. The centre of the nanorods was dissolved in order to obtain nanotubes. The dissolution conditions were optimized in order to have the longest etching depth. After 1.25 h in a dissolution solution containing 0.75 wt% of NH3(aq) and 0.75 wt% of cetyltrimethyl ammonium bromide, the longest etching depth was obtained. After the transfer of the syntheses to the cantilevers, nanorods/nanotubes grew on both sides of the cantilever, which prevents the reflection of the laser allowing the resonance frequency measurement. A masking procedure was developed in order to avoid the growth on one face of the cantilever of zinc oxide nanostructures. As far as the authors are concerned, for the first time, zinc oxide nanotubes were synthesized on only one face of cantilevers with optical readout.