Detection Of Solvent Vapors Research Articles

Screen-Printed Microcantilevers Coated With Functionalized Mesocellular Foam Silica for Detection of Solvent Vapors

This work presents an application of mass-sensitive microcantilevers coated with a new alternative of sensitive materials that is hexamethyldisilazane functionalized mesocellular foam silica (HMDS-MCF-Si) for detection of solvent vapors. The microcantilevers (3 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times2$ </tex-math></inline-formula> mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times0.1$ </tex-math></inline-formula> mm) based on a lead zirconate titanate (PZT) beam sandwiched by thin gold (Au) electrodes were fabricated by screen-printing. Mesocellular foam silica (MCF-Si) was synthesized and used as the sensitive material due to its high specific surface area and pore volume. This material was functionalized by hexamethyldisilazane (HMDS) to enhance hydrophobicity. By a small deposition of HMDS-MCF-Si, the obtained devices demonstrated longitudinal vibration mode with the quality factor of approximately 200 at ambient temperatures. Responsiveness of the microcantilever coated with HMDS-MCF-Si to each solvent vapor at room temperature was compared. The largest response was obtained from exposure to toluene vapor with the sensitivity of 0.85 ppm/ppmV (218 mHz/ppmV) and a limit of detection (LOD) of 28 ppmV. The sensitivity dropped by almost six times when exposed to the higher polar vapor of ethanol. Very low response to water vapor (0.05 ppm/ppmV) confirmed the hydrophobic behavior of HMDS-MCF-Si. Detectable performances under different vapors of our device can be utilized as a guide for developing sensitive materials and resonant microcantilever-based vapor sensors.

Flexible IoT Gas Sensor Node for Automated Life Science Environments Using Stationary and Mobile Robots

In recent years the degree of automation in life science laboratories increased considerably by introducing stationary and mobile robots. This trend requires intensified considerations of the occupational safety for cooperating humans, since the robots operate with low volatile compounds that partially emit hazardous vapors, which especially do arise if accidents or leakages occur. For the fast detection of such or similar situations a modular IoT-sensor node was developed. The sensor node consists of four hardware layers, which can be configured individually regarding basic functionality and measured parameters for varying application focuses. In this paper the sensor node is equipped with two gas sensors (BME688, SGP30) for a continuous TVOC measurement. In investigations under controlled laboratory conditions the general sensors’ behavior regarding different VOCs and varying installation conditions are performed. In practical investigations the sensor node’s integration into simple laboratory applications using stationary and mobile robots is shown and examined. The investigation results show that the selected sensors are suitable for the early detection of solvent vapors in life science laboratories. The sensor response and thus the system’s applicability depends on the used compounds, the distance between sensor node and vapor source as well as the speed of the automation systems.

Metal complexes and time-resolved photoluminescence spectroscopy for sensing applications

This feature article will cover our efforts to sense biologically relevant molecules using photoluminescent metal complexes. Photoluminescent metal complexes possess large Stokes shifts, long lifetimes and tunable photoluminescence maxima. We have developed probes for DNA and RNA detection containing metal complexes of ruthenium and iridium as photoluminescent reporters. Iridium complexes have also been modified to serve as probes for amino acids such as cysteine, homocysteine, and histidine. In addition, probes sensible to the aggregation state of proteins such as amyloid-β and alpha-synuclein were developed, which display changes in photoluminescence (ruthenium dipyridophenazine complexes) or birefringence (ruthenium red). Finally, we will present the detection of solvent vapors using a photoluminescent rhenium complex within a zeolite matrix. The long photoluminescence lifetime of the aforementioned complexes has been synergistically combined with advanced time-resolved methods to enhance the detection scope of these probes. For example techniques such as time-gating have been used to detect oligonucleotides, amino acids and protein aggregation even in highly autofluorescent media. Time-gating allows selecting a time-window in a time-resolved emission spectrum where the long-lived photoluminescence of the probes can be preferentially detected from the short-lived autofluorescence of the medium. In addition, we have used time-resolved photoluminescence spectroscopy to extract the photoluminescence of free histidine from the photoluminescence of histidine-containing proteins. Also, a combination of photoluminescence intensity, maximum and lifetime was used to detect solvent vapors. These examples testify on the advantages of time-resolved photoluminescence spectroscopy for enhancing the detection of analytes using probes with long-lived photoluminescence.

Solvent Vapour Detection with Cholesteric Liquid Crystals—Optical and Mass-Sensitive Evaluation of the Sensor Mechanism

Cholesteric liquid crystals (CLCs) are used as sensitive coatings for the detection of organic solvent vapours for both polar and non-polar substances. The incorporation of different analyte vapours in the CLC layers disturbs the pitch length which changes the optical properties, i.e., shifting the absorption band. The engulfing of CLCs around non-polar solvent vapours such as tetrahedrofuran (THF), chloroform and tetrachloroethylene is favoured in comparison to polar ones, i.e., methanol and ethanol. Increasing solvent vapour concentrations shift the absorbance maximum to smaller wavelengths, e.g., as observed for THF. Additionally, CLCs have been coated on acoustic devices such as the quartz crystal microbalance (QCM) to measure the frequency shift of analyte samples at similar concentration levels. The mass effect for tetrachloroethylene was about six times higher than chloroform. Thus, optical response can be correlated with intercalation in accordance to mass detection. The mechanical stability was gained by combining CLCs with imprinted polymers. Therefore, pre-concentration of solvent vapours was performed leading to an additional selectivity.

Solvent vapour detection with a charge flow transistor

A novel method to detect reversibly high concentrations of organic vapours in air has been developed by combining an intrinsically low conductive membrane of the calix[4]resorcinarene [C7H15] derivative with a charge flow transistor. The modulation of the turn-on response for the transistor upon exposure to acetone, chloroform, methanol, hexane and water is presented. The increase in the membrane conductivity is partially attributed to condensation of the vapours in the highly microporous membrane even below the saturation vapour pressure and partially to the effect of the polar analyte molecules complexing inside and between the OH groups of the cavities. The observed sensitivity is in the order chloroform >> acetone >> methanol >> hexane >> water.

Modified cyclodextrines as mass-sensitive coatings for solvent vapour detection

Advances in robustness, selectivity and sensitivity in organic solvent vapour detection can be achieved by the application of β-cyclodextrines as coatings for mass sensitive chemical sensors. Linking the cyclodextrines with e.g. diiodooctane combines the molecular recognition capabilities of host-guest chemistry with the high stability of polymeric layers. Special increase in selectivity is achieved with anhydro cyclodextrines, since their flattened conus is adapted to benzene derivatives as can also be shown by computer modelling. Furthermore methylation elongates the cavity, guaranteeing an optimised engulfing of the analytes. In this way even a differentiation between p- and m-xylene vapours and a QMB detection limit of some μL/L is possible.

Chemical sensing with cavitands: influence of cavity shape and dimensions on the detection of solvent vapors

The influence of structural parameters of the receptors on the response of cavitand coated quartz-crystal-microbalance (QCM) sensors to several organic vapors is reported. Enhanced selectivity toward specific analytes is obtained through CH-π interactions, while sensitivity can be improved by introducing long alkyl chains on cavitands to generate highly dispersed layers. Application of cavitand coated QCM sensors for the detection of organic analytes in water is also reported.

Mass‐sensitive detection of solvent vapors: Predicting sensor effects

An understanding of analyte–coating interactions is needed in order to be able to predict the sensitivity and selectivity of coating materials considered for use in mass‐sensitive devices such as the quartz microbalance. Models are reviewed for the sensor response based on solubility parameters and calculated energies for functionalized coatings and supramolecular cavities (e.g., the substituted tetraazaparacyclophane shown in the Figure). magnified image

Mass-Sensitive Detection of Solvent Vapors. Mechanistic Studies on Host−Guest Sensor Principles by FT-IR Spectroscopy and BET Adsorption Analysis

Chemical sensors based on highly mass sensitive QCM or SAW devices, coated with sensitive layers, are especially suited for the trace analysis of organic solvent vapors, such as halogenated or aromatic hydrocarbons. The paracyclophanes B44TOS and CP44 were used as sensitive coatings, employing the principles of host−guest chemistry. The application of the BET model to the incorporation of chloroform in the sensitive coatings proves intracavitative complexation according to a 1:1 stoichiometry. Beyond the mass-sensitive detection, the complexation was studied by FT-IR spectroscopy. The exhibited saturation behavior of the characteristic CDCl3 bands confirms the results of the mass-sensitive measurements. The lowering of the C−D stretching frequency was compared with the shifts caused by several model compounds, such as N-butylaniline. All results described indicate the formation of host−guest complexes between chloroform and paracyclophanes.

Cholesteric liquid crystals for solvent vapour detection ? Elimination of cross sensitivity by band shape analysis and pattern recognition

Cholesteric liquid crystals are suitable as sensitive materials for the detection of solvent vapours, such as aromatic and halogenated hydrocarbons. The optical properties of these materials are determined by their molecular short range order, given by the so-called pitch which is influenced by analyte incorporation. Thus, the wavelength of the absorbance band is shifted and the sensor effects are followed in the visible range at a defined wavelength on the flank of the band. Even a variety of aromatic or halogenated solvents, e.g. tetrachloroethylene, can be detected in the ppm-range. By using the whole spectral information combined with partial least squares analysis a separation of solvent effects from that of the disturbing temperature is achieved. Furthermore, these spectral data allow the optimization of the detection of halogenated hydrocarbons whereas the cross sensitivity to other analytes can be diminished.

Mass sensitive detection of solvent vapors with calix[n]arenes—conformational adaptation to the analyte

Calixarenes have a hig molecular flexibility, facilitating an optimized adaptation to the shape of a large variety of guest molecules. Large substituents result in conformationally rigid compounds (Figure) but other calixarenes are ideal for coatings exhibiting high chemical sensitivity. magnified image

Organic Clathrate‐Forming Compounds as Highly Selective Sensor Coatings for the Gravimetric Detection of Solvent Vapors

Organic Clathrate‐Forming Compounds as Highly Selective Sensor Coatings for the Gravimetric Detection of Solvent Vapors

Sensitivity and selectivity of surface acoustic wave sensors for organic solvent vapour detection

Surface acoustic wave (SAW) devices have been coated with 20 organic polymers of different chemical nature. Their sensitivities, selectivities and response times towards gaseous organic solvents such as toluene, acetone, ethanol, methanol and dichloromethane in dry air have been determined. The best sensitivities and selectivities are obtained for toluene vapours. In order to compensate for the lack of selectivity, a pattern-recognition technique (partial least-squares regression, PLS) is applied to sensor responses obtained from ternary mixtures of analytes. The predictive properties of the model are discussed.

Polymer benzo[15]crown‐5 Complexes as Sensor Materials for Solvent Vapors–‐Aromatic Halogenated Hydrocarbons and Polar Solvents

Communication: For the first time thin layers of polymer‐metal complexes with crown ether ligands (see figure) have been applied as sensor materials for the detection of solvent vapors. The hydrophobic properties of these films enable the detection through conductivity measurements of even halogenated and aromatic hydrocarbons. magnified image