Peter A. Lieberzeit

Molecular imprints as artificial antibodies — a new generation of chemical sensors

Abstract Highly cross-linked polymers containing molecular hollows generated by the method of molecular imprinting are chemically and mechanically stable sensitive materials that are highly suitable for being used in rough environments. We prepared layers also for detection of PAHs in drinking water as to follow engine oil degradation. Different polycyclic aromatic hydrocarbons can be monitored in drinking water down to concentrations of several ng/l by fluorimetric or mass sensitive methods. Even analysis of lubricant degradation processes is possible despite their high complexity: layers imprinted with fresh oil and its used counterpart show selective incorporation of the lubricant they were synthesized with.

Chemical Sensors Based on Molecularly Imprinted Sol-Gel Materials †

The sol-gel technique is earning the worldwide attention of researchers in the field of material science, due to its versatility in synthesizing inorganic ceramic materials at mild conditions. High purity, homogeneity, controlled porosity, stable temperature and nanoscale structuring are the most remarkable features offered by this method for generating highly sensitive and selective matrices to incorporate analyte molecules. The crafting of sol-gel sensors through molecular imprinting has put great influence on the development of innovative chemical sensors, which can be seen from the growing number of publications in this field. The review provides a brief overview of sol-gel sensor applications, and discusses the contribution of molecular imprinting in exploring the new world of sensors.

Detection of viruses with molecularly imprinted polymers integrated on a microfluidic biochip using contact-less dielectric microsensors

Rapid detection of viral contamination remains a pressing issue in various fields related to human health including clinical diagnostics, the monitoring of food-borne pathogens, the detection of biological warfare agents as well as in viral clearance studies for biopharmaceutical products. The majority of currently available assays for virus detection are expensive, time-consuming, and labor-intensive. In the present work we report the creation of a novel micro total analysis system (microTAS) capable of continuously monitoring viral contamination with high sensitivity and selectivity. The specific interaction between shape and surface chemistry between molecular imprinted polymer (MIP) and virus resulted in the elimination of non-specific interaction in the present sensor configuration. The additional integration of the blank (non-imprinted) polymer further allowed for the identification of non-specific adsorption events. The novel combination of microfluidics containing integrated native polymer and MIP with contact-less dielectric microsensors is evaluated using the Tobacco Mosaic Virus (TMV) and the Human Rhinovirus serotype 2 (HRV2). Results show that viral binding and dissociation events can be readily detected using contact-less bioimpedance spectroscopy optimized for specific frequencies. In the present study optimum sensor performance was achieved at 203 kHz within the applied frequency range of 5-500 kHz. Complete removal of the virus from the MIP and device reusability is successfully demonstrated following a 50-fold increase in fluid velocity. Evaluation of the microfluidic biochip revealed that microchip technology is ideally suited to detect a broader range of viral contaminations with high sensitivity by selectively adjusting microfluidic conditions, sensor geometries and choice of MIP polymeric material.

Chemosensors for Viruses Based on Artificial Immunoglobulin Copies

2010 WILEY-VCH Verlag Gmb The increasing importance of biological analytes in chemistry has triggered the development of a vast number of techniques for rapid assessment that require materials with highly selective recognition properties. Being derived from nature, selforganization has proven a very powerful tool for actually achieving artificial receptors. Molecularly imprinted polymers (MIP) are one way to implement this into material design. They can, for example, be used as stationary phases for chromatography or in sensitive-materials’ incorporation, thereby selectively detecting a wide variety of analytes, including an early approach to target bacteria withMIP particles. Furthermore, the rugged polymeric matrix also makes it possible to determine analytes in complexmatrices, such as blood or crude plant sap, which is especially relevant for bioanalytical tasks. More recently, this has included artificial receptors for cells or plant viruses. Furthermore, Mosbach and co-workers reported on molecularly imprinted polymers to favor the formation of enzyme inhibitors. Generally speaking, the goals and strategies of molecular imprinting are quite similar to those that the human body applies for selecting specific antibodies, for example, against viruses: natural immunoglobulins (IgG) have highly variable recognition areas on the end of the shorter two arms of the Y-shaped structure. Then, the molecule optimally targeting a specific pathogen is amplified and thus ready for the respective immune response; thus, high selectivity towards a specified antigen is generated. In imprinting, on the other hand, the crucial point is to precisely mimic the chemical structure of the template on the molecular range by self-organizing the polymer chains around it. Native immunoglobulins can also be applied as selective sensor materials in analysis. However, the substantial advantages of their artificial counterparts are their mechanical and chemical robustness and their production by self-assembling processes without time-consuming, complex synthesis. Additionally, the monomeric building blocks used are often readily available by mass production. In contrast to such artificial antibodies, natural ones have to be produced and extracted from living organisms, which makes them quite expensive and tedious to obtain. Being inanimate materials, the polymeric antibodies are also resistant to chemical changes within their environment. This is not the case for biological systems, where mutation or denaturing can alter the composition of important binding sites. Within the present work, we chose to further extend the concept of molecular imprinting by not only templating a polymer with immunoglobulins (i.e., natural antibodies), but also using these MIP as stencils for designing actual plastic replicas of the initial antibody. Figure 1 sketches the concept underlying the synthesis: after first generating the MIP nanoparticle template with the respective antibody, we applied it as template in a surface imprinting process and thus generated a structured polymer surface directly on a 10MHz quartz crystal microbalance (QCM). We chose these transducers, because their mass sensitivity allows for direct, label-free detection of the respective recognition phenomena. The imprinted nanoparticles were produced by pre-polymerizing a suitable monomer solution in the presence of the antibody and precipitating them. For this purpose, we transferred the monomer solution into vigorously stirred acetonitrile, which is a poor solvent for the polymer and thus leads to particle formation. Reference particles were generated by the same synthetic pathway, but without adding the template immunoglobulin. All particles consisted of poly(vinylpyrrolidoneco-methacrylic acid) crosslinked with N,N’-(1,2-dihydroxyethylene)bisacrylamide (DHEBA). Systematic assessment of the polymerization reaction revealed that higher amounts of crosslinker favor precipitation of the respective particles. Furthermore, the size of the particles can be varied by pre-polymerizing for different amounts of time or modifying the amount of pre-polymer injected into the acetonitrile. After precipitation, we coated microscope slides with the particles and thus generated adhered layers that are then suitable templates for further imprinting.

Nano- and micro-structuring of sensor materials—from molecule to cell detection

Abstract Self organisation is a key technique for the spontaneous and efficient structuring of materials for chemical sensing. For example, polymer materials are patterned by surface molecular imprinting via stamping techniques. Mass-sensitive measurements with quartz crystal microbalances (QCMs) prove that by this way “fingerprints” of enzymes, viruses and cells are generated which are capable of reversibly absorbing the imprint species. These coatings are highly selective, so that, e.g. yeast cells can be detected in the presence of other cells. Sensitive layers reacting towards viruses can also be generated leading to an easy-to-use detection method. Another major advantage of imprinting is the fact that templates are not restricted to well-known defined substances but can be complex mixtures. Monitoring the degradation of oils is an example for such a complex analytical problem. Chemically sensitive layers for both edible oils and automotive lubricants based on a bulk-imprinting process are introduced, which are capable of selectively extracting oxidation products from the oil matrix.

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.

Dual and tetraelectrode QCMs using imprinted polymers as receptors for ions and neutral analytes

Polymers as coating materials were combined with quartz crystal microbalances (QCMs) to design sensor devices for the detection of both ionic and neutral analytes in liquid phase. The design and geometry of dual and tetraelectrode QCMs have been optimized to reduce electric field interferences. An unusual Sauerbrey effect was observed while exposing potassium salt solution to 10- and 20-MHz QCMs, i.e. increase in the frequency shifts by a factor of seven, which is attributed to electro-acoustic phenomena. Non-functionalized sol-gel materials were synthesized by templating with hydrophobic salt such as tetraethyl ammonium picrate. Imprinting with these ions of low charge density leads to sensitive layers, and UV–Vis spectroscopy was used to check re-inclusion of this analyte. In the next strategy, functionalized polyurethane for potassium ions and sol-gel materials with aminopropyl group as ligand were generated to tune selectivity and sensitivity towards Ni2+ and Cu2+. Methacrylic acid polymers were optimized for the detection of atrazine by hydrogen bonding; double molecular imprinted polyurethane approach was followed for pyrene recognition. Finally, these imprinted polymers were combined with tetraelectrode QCM to develop sensor platform.

QCM-arrays for sensing terpenes in fresh and dried herbs via bio-mimetic MIP layers.

A piezoelectric 10 MHz multichannel quartz crystal microbalance (MQCM), coated with six molecularly imprinted polystyrene artificial recognition membranes have been developed for selective quantification of terpenes emanated from fresh and dried Lamiaceae family species, i.e., rosemary (Rosmarinus Officinalis L.), basil (Ocimum Basilicum) and sage (Salvia Officinalis). Optimal e-nose parameters, such as layer heights (1–6 KHz), sensitivity <20 ppm of analytes, selectivity at 50 ppm of terpenes, repeatability and reproducibility were thoroughly adjusted prior to online monitoring. Linearity in reversible responses over a wide concentration range <20–250 ppm has been achieved. Discrimination between molecules of similar molar masses, even for isomers, e.g. α-pinene and β-pinene is possible. The array has proven its sensitive and selective properties of sensor responses (20–1,200 Hz) for the difference of fresh and dried herbs. The sensor data attained was validated by GC-MS, to analyze the profiles of sensor emanation patterns. The shelf-life of herbs was monitored via emanation of organic volatiles during a few days. Such an array in association with data analysis tools can be utilized for characterizing complex mixtures.

Rapid bioanalysis with chemical sensors: novel strategies for devices and artificial recognition membranes

AbstractThe increasing importance of biological analytes in chemistry has triggered the development of a vast number of techniques for rapidly assessing them. Aside from microbiological test methods, a wide range of analytical sensor and detection methods are being developed. Within this article, we review the literature on this topic from the last five years, stressing two main aspects of method development. The first aspect is the design of novel analytical strategies and transducers to generate signals more sensitively, more rapidly and more efficiently. Most of the progress in this field has focused on electrochemical detection, although novel approaches to optical and mass-sensitive measurements have been reported. Second, we provide an overview of two main approaches to creating artificial interaction layers for sensors based on tailored interaction sites in polymeric or biomimetic systems. The most prominent of these approaches is (molecular) imprinting, where selectivity is achieved by directly templating a polymer material with the target analyte or a model compound, thus achieving biomimetic interaction sites within both thin films and particles. FigureSensors as means for rapid analysis gain increasing interest and importance in bioanalyte sensing. This article reviews recent developments in the design of transducers and artificial recognition membranes for assessing different biological species.

QCM array for on-line-monitoring of composting procedures

Six QCM resonators forming a sensor array were coated with different molecularly imprinted polymers for the on-line monitoring of composting procedures. Four key analytes are traced, namely water, 1-propanol, ethyl acetate and limonene. Trendlines obtained on-line by the sensor during measurements in a commercial composter give a distinct pattern: the signal for the alcohols first decreases according to an increase in ethyl acetate concentration, and increases again, when obviously no more acetic acid is formed. Limonene is detected in later stages of composting. Similar trends could also be observed by GC-MS. Additionally, chromatographic and sensor data for limonene could be correlated with each other.