Immunosensing with artificial antibodies in organic solvents or complex matrices

The detection of analytes in complex matrices without labour intensive sample preparation is an important goal in analytical chemistry. In this article we would like to address this issue by transferring the selectivity of natural antibody in a cheap, robust and reusable polymer, employing a double imprinting protocol. Antibodies with the desired selectivity were used as template to generate imprinted polymer particles. These antibodies were added to a prepolymer and particles were precipitated. After the antibodies were removed from the particles, cavities remained which reproduce size, shape and surface chemistry of the antibodies. In a second imprinting step the particles with cavities were pressed into a second polymer. After the second polymer has cured the particles can be removed leaving positive structures behind that react with the desired antigen. Such a sensitive coating was applied to the surface of a quartz crystal microbalance and incorporated into a microfluidic chip. An immunosensor for estradiol was fabricated having six times higher affinity to its antigen than to structurally related molecules. The measurements can also be performed after an extraction into an organic solvent which improves the detection limit greatly and would not be possible for natural antibodies. The feasibility of the method for complex matrices was shown by detecting viruses in plasma or allergenic PROTEIN in bread extract

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

Conductometric Sensors for Monitoring Degradation of Automotive Engine Oil†

Conductometric sensors have been fabricated by applying imprinted polymers as receptors for monitoring engine oil quality. Titania and silica layers are synthesized via the sol-gel technique and used as recognition materials for acidic components present in used lubricating oil. Thin-film gold electrodes forming an interdigitated structure are used as transducers to measure the conductance of polymer coatings. Optimization of layer composition is carried out by varying the precursors, e.g., dimethylaminopropyltrimethoxysilane (DMAPTMS), and aminopropyl-triethoxysilane (APTES). Characterization of these sensitive materials is performed by testing against oil oxidation products, e.g., carbonic acids. The results depict that imprinted aminopropyltriethoxysilane (APTES) polymer is a promising candidate for detecting the age of used lubricating oil. In the next strategy, polyurethane-nanotubes composite as sensitive material is synthesized, producing appreciable differentiation pattern between fresh and used oils at elevated temperature with enhanced sensitivity

Molecular Imprinting and Functional Polymers for All Transducers and Applications

The main challenge in developing a chemical sensor is the synthesis of recognition coatings, which are very sensitive and selective to analytes of interest. Molecular imprinting has proven to be the most innovative strategy for this purpose in functional polymer design in the last few decades. Moreover, the introduction of functional groups brings about new applications for all available transducers. Sensitivity and selectivity features of sensor coatings can be tuned by this approach. The strategy produces molecular cavities and interaction sites in sensor coatings. The synthesis of these tailored recognition materials is performed in an outstanding manner, saving time and the high costs of chemicals. Furthermore, intermolecular interactions between the analyte and chemical layers will generate sites that are complementary to the analyte. This procedure can easily be done, directly on a transducer surface, which entails engulfing the analyte by a prepolymer and crosslinking the polymeric material. These imprinted polymers form a robust recognition layer on the transducer surface, which cannot be peeled off and can withstand very harsh conditions, both in gaseous and liquid media. These recognition materials are very suitable, for small molecules and even large bioparticles

Blood Group Typing: From Classical Strategies to the Application of Synthetic Antibodies Generated by Molecular Imprinting

Blood transfusion requires a mandatory cross-match test to examine the compatibility between donor and recipient blood groups. Generally, in all cross-match tests, a specific chemical reaction of antibodies with erythrocyte antigens is carried out to monitor agglutination. Since the visual inspection is no longer useful for obtaining precise quantitative information, therefore there is a wide variety of different technologies reported in the literature to recognize the agglutination reactions. Despite the classical methods, modern biosensors and molecular blood typing strategies have also been considered for straightforward, accurate and precise analysis. The interfacial part of a typical sensor device could range from natural antibodies to synthetic receptor materials, as designed by molecular imprinting and which is suitably integrated with the transducer surface. Herein, we present a comprehensive overview of some selected strategies extending from traditional practices to modern procedures in blood group typing, thus to highlight the most promising approach among emerging technologies

Imprinted Oxide and MIP/Oxide Hybrid Nanomaterials for Chemical Sensors †

The oxides of transition, post-transition and rare-earth metals have a long history of robust and fast responsive recognition elements for electronic, optical, and gravimetric devices. A wide range of applications successfully utilized pristine or doped metal oxides and polymer-oxide hybrids as nanostructured recognition elements for the detection of biologically relevant molecules, harmful organic substances, and drugs as well as for the investigative process control applications. An overview of the selected recognition applications of molecularly imprinted sol-gel phases, metal oxides and hybrid nanomaterials composed of molecularly imprinted polymers (MIP) and metal oxides is presented herein. The formation and fabrication processes for imprinted sol-gel layers, metal oxides, MIP-coated oxide nanoparticles and other MIP/oxide nanohybrids are discussed along with their applications in monitoring bioorganic analytes and processes. The sensor characteristics such as dynamic detection range and limit of detection are compared as the performance criterion and the miniaturization and commercialization possibilities are critically discussed

Graphene Hybrid Materials in Gas Sensing Applications

Graphene, a two dimensional structure of carbon atoms, has been widely used as a material for gas sensing applications because of its large surface area, excellent conductivity, and ease of functionalization. This article reviews the most recent advances in graphene hybrid materials developed for gas sensing applications. In this review, synthetic approaches to fabricate graphene sensors, the nano structures of hybrid materials, and their sensing mechanism are presented. Future perspectives of this rapidly growing field are also discussed

Surface Acoustic Wave (SAW) for Chemical Sensing Applications of Recognition Layers

Surface acoustic wave (SAW) resonators represent some of the most prominent acoustic devices for chemical sensing applications. As their frequency ranges from several hundred MHz to GHz, therefore they can record remarkably diminutive frequency shifts resulting from exceptionally small mass loadings. Their miniaturized design, high thermal stability and possibility of wireless integration make these devices highly competitive. Owing to these special characteristics, they are widely accepted as smart transducers that can be combined with a variety of recognition layers based on host-guest interactions, metal oxide coatings, carbon nanotubes, graphene sheets, functional polymers and biological receptors. As a result of this, there is a broad spectrum of SAW sensors, i.e., having sensing applications ranging from small gas molecules to large bio-analytes or even whole cell structures. This review shall cover from the fundamentals to modern design developments in SAW devices with respect to interfacial receptor coatings for exemplary sensor applications. The related problems and their possible solutions shall also be covered, with a focus on emerging trends and future opportunities for making SAW as established sensing technology