Synthesis and characterization of molecularly imprinted polymers and their application in preconcentrators for gas phase sensors

Various of molecularly imprinted polymers were synthesized by different protocols. Piezoelectric quartz crystals coated with molecularly imprinted polymers were prepared to detect small organic vapors. Hydroquinone (HQ) and Phenol (P) have been used as non-covalent bound templates in order to generate shape-selectivity cavities in the polymer matrix. The recognition film was immobilized on the crystal surface via a pre-coated Poly(isobutylene) layer. The selective behaviors of the imprinted polymer films were studied by their steady-state response to various kinds of small organic vapors. The partition coefficients of polymers toward vapors were evaluated. The imprinted polymers exhibit high sensitivity and selectivity toward organic vapors as toluene and benzene, which are structurally related to the templates. Imprinted polymers prepared by different synthesis schemes were compared. The influence of template concentration and the polymer components was also investigated. The adsorption capacity of molecularly imprinted polymers was characterized and compared by breakthrough studies. From our results, molecularly imprinted polymer is promising for the development of selective piezoelectric sensor for organic vapor detection.;Different types of preconcentrator devices capable of pre-concentrating organic vapors at low ppm levels were fabricated and described. The target organic vapors were enriched onto a small bed of adsorbents and subsequently released by thermal desorption scheme. Solid adsorbents (Tenax GR, TA and molecularly imprinted polymers) were evaluated for possible use in a preconcentrator. Approximate preconcentration factor in the range of several thousand can be achieved by using the block polymer imprinted with hydroquinone

Mimicking the human olfactory system: a portable e-­mucosa

The study of electronic noses has been an active area of research for over 25 years. Commercial instruments have been successfully deployed within niche application areas, for example, the food, beverage and pharmaceutical industries. However, these instruments are still inferior to their human counterparts and have not achieved mainstream success. Humans can distinguish and identify many thousands of different aromas, even at very low concentration levels, with relative ease. The human olfactory system is extremely sophisticated, which allows it to out-­perform artificial instruments. Though limited, artificial instruments can provide a lower cost option to specific problems and can be an alternative to the use of organoleptic panels. Most existing commercial electronic nose (e-­nose) instruments are expensive, bulky, desktop units, requiring a PC to operate. In addition, these instruments usually require a trained operator to gather and analyse the data. Motivated to improve the performance, size and cost of e-­nose instruments, this research aims to extract biological principles from the mammalian olfactory system to aid the implementation of a portable e-­nose instrument. This study has focused on several features of the biological system that may provide the key to its superior performance. Specifically, the large number of different olfactory receptors and the diversity of these receptors; the nasal chromatograph effect; stereo olfaction; sniff rate and odour conditioning. Based on these features, a novel, portable, cost effective instrument, called the Portable e-­Mucosa (PeM), has been designed, implemented and tested. The main components of the PeM are three sensor arrays each containing 200 carbon black composite chemoresistive sensors (totalling 600 sensors with 24 different tunings) mimicking the large number of olfactory receptors and two gas chromatographic columns (coated with non-­polar and polar compounds to maximise the discrimination) emulating the “nasal chromatograph” effect of the human mucus. A preconcentrator based on thermal desorption is also included as an odour collection system to further improve the instrument. The PeM provides USB and Multimedia Memory Card support for easy communication with a PC. The instrument weighs 700g and, with dimensions of 110 x 210 x 110 mm, is slightly larger than the commercial Cyranose 320 (produced by Smiths Detection). This novel instrument generates ‘spatio-­temporal’ data and when coupled with an appropriate pattern recognition algorithm, has shown an enhanced ability to discriminate between odours. The instrument successfully discriminates between simple odours (ethanol, ethyl acetate and acetone) and more complex odours (lavender, ylang ylang, cinnamon and lemon grass essential oils). This system can perhaps be seen as a foundation for a new generation of e-noses

Advances in Electronic-Nose Technologies Developed for Biomedical Applications

The research and development of new electronic-nose applications in the biomedical field has accelerated at a phenomenal rate over the past 25 years. Many innovative e-nose technologies have provided solutions and applications to a wide variety of complex biomedical and healthcare problems. The purposes of this review are to present a comprehensive analysis of past and recent biomedical research findings and developments of electronic-nose sensor technologies, and to identify current and future potential e-nose applications that will continue to advance the effectiveness and efficiency of biomedical treatments and healthcare services for many years. An abundance of electronic-nose applications has been developed for a variety of healthcare sectors including diagnostics, immunology, pathology, patient recovery, pharmacology, physical therapy, physiology, preventative medicine, remote healthcare, and wound and graft healing. Specific biomedical e-nose applications range from uses in biochemical testing, blood-compatibility evaluations, disease diagnoses, and drug delivery to monitoring of metabolic levels, organ dysfunctions, and patient conditions through telemedicine. This paper summarizes the major electronic-nose technologies developed for healthcare and biomedical applications since the late 1980s when electronic aroma detection technologies were first recognized to be potentially useful in providing effective solutions to problems in the healthcare industry

Advancements in microfabricated gas sensors and microanalytical tools for the sensitive and selective detection of odors

In recent years, advancements in micromachining techniques and nanomaterials have enabled the fabrication of highly sensitive devices for the detection of odorous species. Recent efforts done in the miniaturization of gas sensors have contributed to obtain increasingly compact and portable devices. Besides, the implementation of new nanomaterials in the active layer of these devices is helping to optimize their performance and increase their sensitivity close to humans’ olfactory system. Nonetheless, a common concern of general-purpose gas sensors is their lack of selectivity towards multiple analytes. In recent years, advancements in microfabrication techniques and microfluidics have contributed to create new microanalytical tools, which represent a very good alternative to conventional analytical devices and sensor-array systems for the selective detection of odors. Hence, this paper presents a general overview of the recent advancements in microfabricated gas sensors and microanalytical devices for the sensitive and selective detection of volatile organic compounds (VOCs). The working principle of these devices, design requirements, implementation techniques, and the key parameters to optimize their performance are evaluated in this paper. The authors of this work intend to show the potential of combining both solutions in the creation of highly compact, low-cost, and easy-to-deploy platforms for odor monitoringPostprint (published version

Advanced quartz crystal microbalance techniques applied to calixarene sensing membranes.

Several Quartz Crystal Microbalance (QCM) measurement techniques in conjunction with a series of calix[4]resorcinarene sensing membranes have been successfully exploited for the detection of volatile organic solvents at vapour concentrations below their lower explosive level.The impedance analysis technique involves the measurement of the electrical properties of the QCM around the resonant frequencies of crystal. Subsequent fitting of the measured spectra to an equivalent circuit allows parameters directly related to mass loading and the mechanical properties (viscosity) of the film to be obtained. An experimental setup which allows the real time in situ extraction of these parameters has been developed.It has been shown that unique changes in mass loading and the films viscoelastic properties caused by the adsorption of target vapours into a calix[4]resorcinarene C15H31 sensing membrane can be detected. In some cases this facilitates both the detection and discrimination of target vapours using a single QCM sensing element. The changes in the films mechanical properties are believed to be caused by capillary condensation of vapours at values below saturated vapour pressure inside the nano-porous calix[4]resorcinarene film matrix.The work is extended by the use of the sensor array technique. In the first instance frequency only measurements are used. Four QCM have been coated with calix[4]resorcinarene compounds with different hydrocarbon chain lengths and exposed to range of organic vapours. The variation in chain length produces selectivity between the sensing membranes, and leads to the classification of all the tested organic vapours using a feed forward multilayer Artificial Neural Network. The trained network successfully classified over 98% of the test data.The additional measurement of film dissipation using impedance analysis/QCMD shows interesting phenomena. An unexpected increase in mechanical stiffness of the film is observed for small chain length C[4]RA compounds (CH3) on vapour sorption. A speculative model has been proposed relating the chain length and effective cavity size to the observed phenomena.An alternative low cost multi parameter measurement set up has also been developed using the QCMD principle. The crystal is driven from an external oscillatory source and subsequently disconnected. The resonant frequency and dissipation factor can be extracted from the decaying sinusoid signal. This approach eliminates the need for expensive network analysers. An additional multiplexing circuit has been combined with the QCMD technique and allows both the frequency and dissipation factor of several crystals to be measured in pseudo real time. This makes the system ideally suited for multi parameter array measurements.The basis for a discriminative explosive vapour sensor based on calix[4]resorcinarene membranes has been investigated and promising results for future development have been obtained. The exact adsorption mechanisms are however complex and althoughspeculative models have been proposed, further research is suggested to fully characterize the complete adsorption process and the mechanical changes taking place within the film

Peptides, DNA and MIPs in gas sensing. From the realization of the sensors to sample analysis

Detection and monitoring of volatiles is a challenging and fascinating issue in environmental analysis, agriculture and food quality, process control in industry, as well as in ‘point of care’ diagnostics. Gas chromatographic approaches remain the reference method for the analysis of volatile organic compounds (VOCs); however, gas sensors (GSs), with their advantages of low cost and no or very little sample preparation, have become a reality. Gas sensors can be used singularly or in array format (e.g., e-noses); coupling data output with multivariate statical treatment allows un-target analysis of samples headspace. Within this frame, the use of new binding elements as recognition/interaction elements in gas sensing is a challenging hot-topic that allowed unexpected advancement. In this review, the latest development of gas sensors and gas sensor arrays, realized using peptides, molecularly imprinted polymers and DNA is reported. This work is focused on the description of the strategies used for the GSs development, the sensing elements function, the sensors array set-up, and the application in real cases

Development of analytical systems and monitoring of VOCs emissions during polymer processing

A method using direct flame ionization detector (FID) measurement was developed to study total volatile organic compounds (VOCs) emissions during thermal degradation of polymers. This was used to estimate organic emissions from both virgin polymer resins and commingled plastics. The effects of process parameters, i. e., temperature, heating rate and residence time, were also studied. Significant VOCs emissions were observed at normal processing temperatures, particularly from recycled polymers. Each polymer showed a distinct evolution pattern during its thermal degradation. Kinetics of VOCs emissions were also studied using a non-isothermal technique. The kinetic parameters were in agreement with data from the literature. Polypropylene, as a commodity recyclable thermoplastic, was studied in this research to evaluate the potential environmental impact resulting from VOCs emitted during multiple melt reprocessing. Unstabilized and stabilized PP homopolymers, referred to as U-PP and S-PP, were used to simulate recycled materials prone to degradation. They were evaluated for total VOCs emissions generated during multiple melt reprocessing by injection molding and extrusion respectively. Results show that the maximum amount of total VOCs from each cycle (up to six cycles for extrusion and up to ten for injection molding) did not significantly change, while the cumulative VOCs increased with increasing processing cycle for both materials. A good correlation was obtained between the cumulative VOCs increase and the Melt Flow Index increase for the U-PP, and the MW decrease for the S-PP. Reprocessing in all cases was accompanied by decreases in molecular weight and melt viscosity as a result of thermo-oxidative degradation. Corresponding structural changes were investigated using FTIR, and the data showed increases in carbonyl content and degree of unsaturation with the increase of processing cycle number. At equivalent cycle numbers, degradation appeared to be more severe for the extruded material in spite of the longer oxidative induction time of the as received pellets used in extrusion. The onset and type of structural changes was shown to depend on cycle number and reprocessing method. A simulation study was also performed by multiple heating and cooling of a single U-PP sample under static conditions, and under different gaseous atmospheres. The results indicate that the actual reprocessing conditions generated emissions whose levels, and rate of generation were closer to a mild thermo-oxidative degradation rather than a pure thermal one. Continuous nonmethane organic carbon (C-NMOC) analysis was considered to be a more accurate and on-line method for monitoring emissions during polymer processing. An improved version of the C-NMOC system was developed in this research. A multibed microtrap was developed to prevent the breakthrough of small molecules such as propane and methanol. Two novel sampling configurations were also developed, and were referred to as sequential valve with backflushed microtrap (SV-BM) and multiinjection sequential valve with backflushed microtrap (MSV-BM). By combining the multi-bed microtrap with the SV-BM and MSV-BM configurations, ideal performances were obtained in terms of linearity, reproducibility of multiple injections and separation of background gases. Both small molecules and large molecules could be effectively collected and desorbed with the optimized microtrap