Vibrational spectroscopy characterization of impregnated activated carbon adsorption of H2S.

Activated carbon filters are used for the removal of hazardous gases from the air. This research applied vibrational spectroscopy methods, including Fourier-transform infrared spectroscopy and Raman spectroscopy to characterize hydrogen sulfide adsorption on impregnated carbon materials with metals having reactivity toward hydrogen sulfide. The Fourier-transform infrared spectroscopy results demonstrated the formation of a new chemical bond between the impregnating metals and the sulfur, indicated by the appearance of a new band at 618 cm-1. The Raman spectra results showed that for the copper-impregnated activated carbon with the highest hydrogen sulfide adsorption capacity, a new vibrational band at 475 cm-1 evolved, indicating a copper-sulfur bond. In addition, upshifts in the carbon D sub-bands were observed after efficient hydrogen sulfide adsorption, along with a larger area of the approximately 1500 cm-1 band. Therefore, Fourier-transform infrared spectroscopy and Raman spectroscopy combination can potentially indicate H2S adsorption on impregnated activated carbon filters.

Placing CF2 in the Center: Major Physicochemical Changes Upon a Minor Structural Alteration in Gem-Difunctional Compounds.

Fluorine atoms play an important role in all branches of chemistry and accordingly, it is very important to study their unique and varied effects systematically, in particular, the structure-physicochemical properties relationship. The present study describes exceptional physicochemical effects resulting from a H/F exchange at the methylene bridge of gem-difunctional compounds. The Δlog P(CF2-CH2) values, that is, the change in lipophilicity, observed for the CH2 /CF2 replacement in various α,α-phenoxy- and thiophenoxy-esters/amides, diketones, benzodioxoles and more, fall in the range of 0.6-1.4 units, which for most cases, is far above the values expected for such a replacement. Moreover, for compounds holding more than one such gem-difunctional moiety, the effect is nearly additive, so one can switch from a hydrophilic compound to a lipophilic one in a limited number of H/F exchanges. DFT studies of some of these systems revealed that polarity, conformational preference as well as charge distributions are strongly affected by such hydrogen to fluorine atom substitution. The pronounced effects described, are a result of the interplay between changes in polarity, H-bond basicity and molecular volume, which were obtained with a very low 'cost' in terms of molecular weight or steric effects and may have a great potential for implementation in various fields of chemical sciences.

Non-Contact, Continuous Sampling of Porous Surfaces for the Detection of Particulate and Adsorbed Organic Contaminations by Low-Temperature Plasma Coupled to Ion Mobility Spectrometer.

Chemical analysis of hazardous surface contaminations, such as hazardous substances, explosives or illicit drugs, is an essential task in security, environmental and safety applications. This task is mostly based on the collection of particles with swabs, followed by thermal desorption into a vapor analyzer, usually a detector based on ion mobility spectrometry (IMS). While this methodology is well established for several civil applications, such as border control, it is still not efficient enough for various conditions, as in sampling rough and porous surfaces. Additionally, the process of thermal desorption is energetically inefficient, requires bulky hardware and introduces device contamination memory effects. Low-temperature plasma (LTP) has been demonstrated as an ionization and desorption source for sample preparation-free analysis, mostly at the inlet of a mass spectrometer analyzer, and in rare cases in conjunction with an ion mobility spectrometer. Herein, we demonstrate, for the first time, the operation of a simple, low cost, home-built LTP apparatus for desorbing non-volatile analytes from various porous surfaces into the inlet of a handheld IMS vapor analyzer. We show ion mobility spectra that originate from operating the LTP jet on porous surfaces such as asphalt and shoes, contaminated with model amine-containing organic compounds. The spectra are in good correlation with spectra measured for thermally desorbed species. We verify through LC-MS analysis of the collected vapors that the sampled species are not fragmented, and can thus be identified by commercial IMS detectors.

Phosphate Additives for Aging Inhibition of Impregnated Activated Carbon against Hazardous Gases.

Impregnated activated carbons (IACs) used in air filtration gradually lose their efficacy for the chemisorption of noxious gases when exposed to humidity due to impregnated metal deactivation. In order to stabilize IACs against aging, and to prolong the filters' shelf life, inorganic phosphate compounds (phosphoric acid and its three salts, NaHPO4, Na2HPO4, and Na3PO4) were used as anti-aging additives for two different chromium-free IACs impregnated with copper, zinc, molybdenum, and triethylenediamine (TEDA). Phosphoric acid, monosodium, and disodium phosphate were found to be very efficient in inhibiting the aging of IACs over long periods against cyanogen chloride (the test agent) chemisorption, with the latter being the most efficient. However, the efficiency of phosphate as an anti-aging additive was not well correlated with its ability to inhibit the migration of metal impregnants, especially copper, from the interior to the external surface of carbon granules. Unlike organic additives, the inorganic phosphate additives did not decrease the surface area of the IAC or its physical adsorption capacity for toluene. Using a phosphate additive in IAC used in collective protection and personal filters can improve the safety of the user and the environment and dramatically reduce the need to replace these filters after exposure to humid environments. This has safety, economic, logistical, and environmental advantages.

Sonic-spray introduction of liquid samples to hand-held Ion mobility spectrometry analyzers.

Sampling hazardous compounds in the form of solids and liquids is a growing need in the fields of homeland security and forensics. Chemical analysis of particles and droplets under field conditions is crucial for various tasks carried out by counter-terrorism and law enforcement units. The use of simple, small and low cost means to achieve this goal is constantly pursued. In this work, an approach for rapid, continuous generation of vapors from liquid samples using sonic spray (SS) as the sample introduction technique, followed by analysis using hand-held ion mobility spectrometry (IMS) vapor analyzers is presented. Transfer of analytes is demonstrated from liquid state to the gas phase at the inlet of an IMS detector using a sonic spray apparatus that consists of a nebulizer, spraying solution, a source of compressed gas and an unheated transfer line tube to the detector inlet nozzle. This technique does not require any electrical, radiative or thermal energy. Analysis of several narcotic substances including cocaine, methamphetamine and amphetamine, and of an explosive compound, TNT, is demonstrated, using two commercial devices as analyzers. Two sampling configurations are presented: direct sampling of liquid, either from a vial or a spill (SS-IMS) and extraction of a substance collected with a swab by dipping it in the spray solvent (ESS-IMS), being suitable for both drops and particles. Limits of detection of the presented method are comparable to those obtained with thermal desorption sample introduction of the commercial device. Time traces of the IMS signals show a continuous and stable signal with a short rise time. This sampling technique may offer competitive performance to that of common thermal desorption techniques, with the advantages of coupling to simpler, smaller and cheaper vapor detectors, optimized for field use, and of a continuous, pulseless sample or object interrogation.

Towards Understanding the Genetic Nature of Vasovagal Syncope.

Syncope, defined as a transient loss of consciousness caused by transient global cerebral hypoperfusion, affects 30-40% of humans during their lifetime. Vasovagal syncope (VVS) is the most common cause of syncope, the etiology of which is still unclear. This review summarizes data on the genetics of VVS, describing the inheritance pattern of the disorder, candidate gene association studies and genome-wide studies. According to this evidence, VVS is a complex disorder, which can be caused by the interplay between genetic factors, whose contribution varies from monogenic Mendelian inheritance to polygenic inherited predisposition, and external factors affecting the monogenic (resulting in incomplete penetrance) and polygenic syncope types.

Surface-enhanced Raman spectroscopy (SERS) for detection of VX and HD in the gas phase using a hand-held Raman spectrometer.

A sensitive surface-enhanced Raman spectroscopy (SERS) substrate was developed to enable hand-held Raman spectrometers to detect gas-phase VX and HD. The substrate comprised Au nanoparticles modified onto quartz fibres. Limits of detection (LOD) of 0.008 µg L-1 and 0.054 µg L-1 were achieved for VX and HD, respectively. Gas-phase experiments were performed using a homemade gas-phase flow system inside a climatic chamber at 25 °C and 50% relative humidity. Preliminary experiments were conducted using VX and HD in solution with Au and Ag nanoparticle colloidal suspensions. We developed and optimized several SERS methods for detection of VX and HD in solution. Gold nanoparticles were optimal for detection of VX and HD and were modified onto quartz fibres for gas-phase detection. The LODs for HD and VX detection in solution were 1.8 × 10-3 µg mL-1 (1.1 × 10-8 M) and 2.5 × 10-3 µg mL-1 (9.3 × 10-9 M), respectively. This study demonstrates that integration of SERS substrates with hand-held Raman spectrometers expands the applicability of Raman technology to homeland security, as reflected by increased sensitivity and gas-phase detection capabilities.

Super-resolution in label-free photomodulated reflectivity.

We demonstrate a new, label-free, far-field super-resolution method based on an ultrafast pump-probe scheme oriented toward nanomaterial imaging. A focused pump laser excites a diffraction-limited spatial temperature profile, and the nonlinear changes in reflectance are probed. Enhanced spatial resolution is demonstrated with nanofabricated silicon and vanadium dioxide nanostructures. Using an air objective, resolution of 105 nm was achieved, well beyond the diffraction limit for the pump and probe beams and offering a novel kind of dedicated nanoscopy for materials.

Manipulating and Monitoring On-Surface Biological Reactions by Light-Triggered Local pH Alterations.

Significant research efforts have been dedicated to the integration of biological species with electronic elements to yield smart bioelectronic devices. The integration of DNA, proteins, and whole living cells and tissues with electronic devices has been developed into numerous intriguing applications. In particular, the quantitative detection of biological species and monitoring of biological processes are both critical to numerous areas of medical and life sciences. Nevertheless, most current approaches merely focus on the "monitoring" of chemical processes taking place on the sensing surfaces, and little efforts have been invested in the conception of sensitive devices that can simultaneously "control" and "monitor" chemical and biological reactions by the application of on-surface reversible stimuli. Here, we demonstrate the light-controlled fine modulation of surface pH by the use of photoactive molecularly modified nanomaterials. Through the use of nanowire-based FET devices, we showed the capability of modulating the on-surface pH, by intensity-controlled light stimulus. This allowed us simultaneously and locally to control and monitor pH-sensitive biological reactions on the nanodevices surfaces, such as the local activation and inhibition of proteolytic enzymatic processes, as well as dissociation of antigen-antibody binding interactions. The demonstrated capability of locally modulating the on-surface effective pH, by a light stimuli, may be further applied in the local control of on-surface DNA hybridization/dehybridization processes, activation or inhibition of living cells processes, local switching of cellular function, local photoactivation of neuronal networks with single cell resolution and so forth.

Monolithic integration of a silicon nanowire field-effect transistors array on a complementary metal-oxide semiconductor chip for biochemical sensor applications.

We present a monolithic complementary metal-oxide semiconductor (CMOS)-based sensor system comprising an array of silicon nanowire field-effect transistors (FETs) and the signal-conditioning circuitry on the same chip. The silicon nanowires were fabricated by chemical vapor deposition methods and then transferred to the CMOS chip, where Ti/Pd/Ti contacts had been patterned via e-beam lithography. The on-chip circuitry measures the current flowing through each nanowire FET upon applying a constant source-drain voltage. The analog signal is digitized on chip and then transmitted to a receiving unit. The system has been successfully fabricated and tested by acquiring I-V curves of the bare nanowire-based FETs. Furthermore, the sensing capabilities of the complete system have been demonstrated by recording current changes upon nanowire exposure to solutions of different pHs, as well as by detecting different concentrations of Troponin T biomarkers (cTnT) through antibody-functionalized nanowire FETs.

Morphological and chemical stability of silicon nanostructures and their molecular overlayers under physiological conditions: towards long-term implantable nanoelectronic biosensors.

BACKGROUND: The detection of biological and chemical species is of key importance to numerous areas of medical and life sciences. Therefore, a great interest exists in developing new, rapid, miniature, biocompatible and highly sensitive sensors, capable to operate under physiological conditions and displaying long-term stabilities (e.g. in-body implantable sensors). Silicon nanostructures, nanowires and nanotubes, have been extensively explored as building blocks for the creation of improved electrical biosensing devices, by virtue of their remarkably high surface-to-volume ratios, and have shown exceptional sensitivity for the real time label-free detection of molecular species adsorbed on their surfaces, down to the sensitivity of single molecules.Yet, till this date, almost no rigorous studies have been performed on the temporal morphological stability of these nanostructures, and their resulting electrical devices, under physiological conditions (e.g. serum, blood), as well as on the chemical stability of the molecular recognition over-layers covering these structures. RESULTS: Here, we present systematic time-resolved results on the morphological stability of bare Si nanowire building blocks, as well on the chemical stability of siloxane-based molecular over-layers, under physiological conditions. Furthermore, in order to overcome the observed short-term morpho-chemical instabilities, we present on the chemical passivation of the Si nanostructures by thin metal oxide nanoshells, in the range of 3-10 nm. The thickness of the metal oxide layer influences on the resulting electrical sensitivity of the fabricated FETs (field effect transistors), with an optimum thickness of 3-4 nm. CONCLUSIONS: The core-shell structures display remarkable long-term morphological stability, preventing both, the chemical hydrolytic dissolution of the silicon under-structure and the concomitant loss of the siloxane-based chemical over-layers, for periods of at least several months. Electrical devices constructed from these nanostructures display excellent electrical characteristics and detection sensitivities, with exceptionally high morphological and functional stabilities. These results pave the road for the creation of long-term implantable biosensing devices in general, and nanodevices in particular.

Optically-gated self-calibrating nanosensors: monitoring pH and metabolic activity of living cells.

Quantitative detection of biological and chemical species is critical to numerous areas of medical and life sciences. In this context, information regarding pH is of central importance in multiple areas, from chemical analysis, through biomedical basic studies and medicine, to industry. Therefore, a continuous interest exists in developing new, rapid, miniature, biocompatible and highly sensitive pH sensors for minute fluid volumes. Here, we present a new paradigm in the development of optoelectrical sensing nanodevices with built-in self-calibrating capabilities. The proposed electrical devices, modified with a photoactive switchable molecular recognition layer, can be optically switched between two chemically different states, each having different chemical binding constants and as a consequence affecting the device surface potential at different extents, thus allowing the ratiometric internal calibration of the sensing event. At each point in time, the ratio of the electrical signals measured in the ground and excited states, respectively, allows for the absolute concentration measurement of the molecular species under interest, without the need for electrical calibration of individual devices. Furthermore, we applied these devices for the real-time monitoring of cellular metabolic activity, extra- and intracellularly, as a potential future tool for the performance of basic cell biology studies and high-throughput personalized medicine-oriented research, involving single cells and tissues. This new concept can be readily expanded to the sensing of additional chemical and biological species by the use of additional photoactive switchable receptors. Moreover, this newly demonstrated coupling between surface-confined photoactive molecular species and nanosensing devices could be utilized in the near future in the development of devices of higher complexity for both the simultaneous control and monitoring of chemical and biological processes with nanoscale resolution control.

Highly sensitive chemiluminescence sensors for the detection and differentiation of chemical warfare agents.

Highly sensitive chemiluminescence-based probes that effectively detect and differentiate between the extremely toxic real G- and V-type organophosphorus chemical warfare agents (OPCWAs) are presented. This straightforward approach does not require any instrumentation or light source; hence, it appears ideal for the future development of field colorimetric detectors.

Confinement-guided shaping of semiconductor nanowires and nanoribbons: "writing with nanowires".

To fully exploit their full potential, new semiconductor nanowire building blocks with ab initio controlled shapes are desired. However, and despite the great synthetic advances achieved, the ability to control nanowire's geometry has been significantly limited. Here, we demonstrate a simple confinement-guided nanowire growth method that enables to predesign not only the chemical and physical attributes of the synthesized nanowires but also allows a perfect and unlimited control over their geometry. Our method allows the synthesis of semiconductor nanowires in a wide variety of two-dimensional shapes such as any kinked (different turning angles), sinusoidal, linear, and spiral shapes, so that practically any desired geometry can be defined. The shape-controlled nanowires can be grown on almost any substrate such as silicon wafer, quartz and glass slides, and even on plastic substrates (e.g., Kapton HN).

Si nanowires forest-based on-chip biomolecular filtering, separation and preconcentration devices: nanowires do it all.

The development of efficient biomolecular separation and purification techniques is of critical importance in modern genomics, proteomics, and biosensing areas, primarily due to the fact that most biosamples are mixtures of high diversity and complexity. Most of existent techniques lack the capability to rapidly and selectively separate and concentrate specific target proteins from a complex biosample, and are difficult to integrate with lab-on-a-chip sensing devices. Here, we demonstrate the development of an on-chip all-SiNW filtering, selective separation, desalting, and preconcentration platform for the direct analysis of whole blood and other complex biosamples. The separation of required protein analytes from raw biosamples is first performed using a antibody-modified roughness-controlled SiNWs (silicon nanowires) forest of ultralarge binding surface area, followed by the release of target proteins in a controlled liquid media, and their subsequent detection by supersensitive SiNW-based FETs arrays fabricated on the same chip platform. Importantly, this is the first demonstration of an all-NWs device for the whole direct analysis of blood samples on a single chip, able to selectively collect and separate specific low abundant proteins, while easily removing unwanted blood components (proteins, cells) and achieving desalting effects, without the requirement of time-consuming centrifugation steps, the use of desalting or affinity columns. Futhermore, we have demonstrated the use of our nanowire forest-based separation device, integrated in a single platform with downstream SiNW-based sensors arrays, for the real-time ultrasensitive detection of protein biomarkers directly from blood samples. The whole ultrasensitive protein label-free analysis process can be practically performed in less than 10 min.

Biorecognition layer engineering: overcoming screening limitations of nanowire-based FET devices.

Detection of biological species is of great importance to numerous areas of medical and life sciences from the diagnosis of diseases to the discovery of new drugs. Essential to the detection mechanism is the transduction of a signal associated with the specific recognition of biomolecules of interest. Nanowire-based electrical devices have been demonstrated as a powerful sensing platform for the highly sensitive detection of a wide-range of biological and chemical species. Yet, detecting biomolecules in complex biosamples of high ionic strength (>100 mM) is severely hampered by ionic screening effects. As a consequence, most of existing nanowire sensors operate under low ionic strength conditions, requiring ex situ biosample manipulation steps, that is, desalting processes. Here, we demonstrate an effective approach for the direct detection of biomolecules in untreated serum, based on the fragmentation of antibody-capturing units. Size-reduced antibody fragments permit the biorecognition event to occur in closer proximity to the nanowire surface, falling within the charge-sensitive Debye screening length. Furthermore, we explored the effect of antibody surface coverage on the resulting detection sensitivity limit under the high ionic strength conditions tested and found that lower antibody surface densities, in contrary to high antibody surface coverage, leads to devices of greater sensitivities. Thus, the direct and sensitive detection of proteins in untreated serum and blood samples was effectively performed down to the sub-pM concentration range without the requirement of biosamples manipulation.

Unwrapping core-shell nanowires into nanoribbon-based superstructures.

A prize for the ribbons: High-quality crystalline semiconducting nanoribbons can be prepared by "unwrapping" core-shell nanowire precursors. For example, Ge nanowires were coated with a Si shell and the top surface was carved by etching whereas the sides were protected by a thin layer of photoresist material. Finally the Ge core was removed selectively by chemical means to give fully opened and flat nanoribbon structures.

Non-covalent monolayer-piercing anchoring of lipophilic nucleic acids: preparation, characterization, and sensing applications.

Functional interfaces of biomolecules and inorganic substrates like semiconductor materials are of utmost importance for the development of highly sensitive biosensors and microarray technology. However, there is still a lot of room for improving the techniques for immobilization of biomolecules, in particular nucleic acids and proteins. Conventional anchoring strategies rely on attaching biomacromolecules via complementary functional groups, appropriate bifunctional linker molecules, or non-covalent immobilization via electrostatic interactions. In this work, we demonstrate a facile, new, and general method for the reversible non-covalent attachment of amphiphilic DNA probes containing hydrophobic units attached to the nucleobases (lipid-DNA) onto SAM-modified gold electrodes, silicon semiconductor surfaces, and glass substrates. We show the anchoring of well-defined amounts of lipid-DNA onto the surface by insertion of their lipid tails into the hydrophobic monolayer structure. The surface coverage of DNA molecules can be conveniently controlled by modulating the initial concentration and incubation time. Further control over the DNA layer is afforded by the additional external stimulus of temperature. Heating the DNA-modified surfaces at temperatures >80 °C leads to the release of the lipid-DNA structures from the surface without harming the integrity of the hydrophobic SAMs. These supramolecular DNA layers can be further tuned by anchoring onto a mixed SAM containing hydrophobic molecules of different lengths, rather than a homogeneous SAM. Immobilization of lipid-DNA on such SAMs has revealed that the surface density of DNA probes is highly dependent on the composition of the surface layer and the structure of the lipid-DNA. The formation of the lipid-DNA sensing layers was monitored and characterized by numerous techniques including X-ray photoelectron spectroscopy, quartz crystal microbalance, ellipsometry, contact angle measurements, atomic force microscopy, and confocal fluorescence imaging. Finally, this new DNA modification strategy was applied for the sensing of target DNAs using silicon-nanowire field-effect transistor device arrays, showing a high degree of specificity toward the complementary DNA target, as well as single-base mismatch selectivity.

Studying the Physical and Chemical Properties of Polydimethylsiloxane Matrix Reinforced by Nanostructured TiO2 Supported on Mesoporous Silica.

In this study, a reactive adsorbent filler was integrated into a polymeric matrix as a novel reactive protective barrier without undermining its mechanical, thermal, and chemical properties. For this purpose, newly synthesized TiO2/MCM/polydimethylsiloxane (PDMS) composites were prepared, and their various properties were thoroughly studied. The filler, TiO2/MCM, is based on a (45 wt%) TiO2 nanoparticle catalyst inside the pores of ordered mesoporous silica, MCM-41, which combines a high adsorption capacity and catalytic capability. This study shows that the incorporation of TiO2/MCM significantly enhances the composite's Young's modulus in terms of tensile strength, as an optimal measurement of 1.6 MPa was obtained, compared with that of 0.8 MPa of pristine PDMS. The composites also showed a higher thermal stability, a reduction in the coefficient of thermal expansion (from 290 to 110 ppm/°C), a 25% reduction in the change in the normalized specific heat capacity, and an increase in the thermal degradation temperatures. The chemical stability in organic environments was improved, as toluene swelling decreased by 40% and the contact angle increased by ~15°. The enhanced properties of the novel synthesized TiO2/MCM/PDMS composite can be used in various applications where a high adsorption capacity and catalytic/photocatalytic activity are required, such as in protective equipment, microfluidic applications, and chemical sensor devices.

Vasovagal Syncope Is Associated with Variants in Genes Involved in Neurohumoral Signaling Pathways.

Vasovagal syncope (VVS) is the most common cause of sudden loss of consciousness. VVS results from cerebral hypoperfusion, due to abnormal autonomic control of blood circulation, leading to arterial hypotension. It is a complex disease, and its development is largely associated with genetic susceptibility. Since abnormal neurohumoral regulation plays an important role in VVS development, we analyzed the association of VVS with polymorphic variants of ADRA1A, ADRB1, HTR1A, ADORA2A, COMT, and NOS3 genes, the products of which are involved in neurohumoral signaling, in patients with a confirmed VVS diagnosis (157 subjects) and individuals without a history of syncope (161 subjects). We were able to identify the associations between VVS and alleles/genotypes ADRA1A rs1048101, ADRB1 rs1801253, ADORA2A rs5751876, and COMT rs4680, as well as NOS3 rs2070744 in biallelic combination with COMT rs4680. Thus, we are the first to observe, within a single study, the role of the genes that encode α- and ß-adrenergic receptors, catechol-O-methyltransferase, adenosine receptors and nitric oxide synthase in VVS development. These findings demonstrate that the genes involved in neurohumoral signaling pathways contribute to the formation of a genetic susceptibility to VVS.