Label-free protein detection based on the heat-transfer method-a case study with the peanut allergen Ara h 1 and aptamer-based synthetic receptors

© 2015 American Chemical Society. Aptamers are an emerging class of molecules that, because of the development of the systematic evolution of ligands by exponential enrichment (SELEX) process, can recognize virtually every target ranging from ions, to proteins, and even whole cells. Although there are many techniques capable of detecting template molecules with aptamer-based systems with high specificity and selectivity, they lack the possibility of integrating them into a compact and portable biosensor setup. Therefore, we will present the heat-transfer method (HTM) as an interesting alternative because this offers detection in a fast and low-cost manner and has the possibility of performing experiments with a fully integrated device. This concept has been demonstrated for a variety of applications including DNA mutation analysis and screening of cancer cells. To the best our knowledge, this is the first report on HTM-based detection of proteins, in this case specifically with aptamer-type receptors. For proof-of-principle purposes, measurements will be performed with the peanut allergen Ara h 1 and results indicate detection limits in the lower nanomolar regime in buffer liquid. As a first proof-of-application, spiked Ara h 1 solutions will be studied in a food matrix of dissolved peanut butter. Reference experiments with the quartz-crystal microbalance will allow for an estimate of the areal density of aptamer molecules on the sensor-chip surface

Array Formatting of the Heat-Transfer Method (HTM) for the Detection of Small Organic Molecules by Molecularly Imprinted Polymers

In this work we present the first steps towards a molecularly imprinted polymer (MIP)-based biomimetic sensor array for the detection of small organic molecules via the heat-transfer method (HTM). HTM relies on the change in thermal resistance upon binding of the target molecule to the MIP-type receptor. A flow-through sensor cell was developed, which is segmented into four quadrants with a volume of 2.5 μL each, allowing four measurements to be done simultaneously on a single substrate. Verification measurements were conducted, in which all quadrants received a uniform treatment and all four channels exhibited a similar response. Subsequently, measurements were performed in quadrants, which were functionalized with different MIP particles. Each of these quadrants was exposed to the same buffer solution, spiked with different molecules, according to the MIP under analysis. With the flow cell design we could discriminate between similar small organic molecules and observed no significant cross-selectivity. Therefore, the MIP array sensor platform with HTM as a readout technique, has the potential to become a low-cost analysis tool for bioanalytical applications

From colossal magnetoresistance to solar cells: An overview on 66 years of research into perovskites

© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Perovskites are a huge family of compounds to which the natural titanium mineral CaTiO3 is the common ancestor. The cubic structure looks apparently simple, but the variety of metal ions and mixtures thereof that fit into a perovskite lattice is tremendous. Even in the case that the ionic radii do not allow for a perfect cubic ordering, there are various superstructures and orbital-ordering effects to cope elegantly with distortions. The compositional and structural flexibility offers a large toolbox to design and synthesize perovskites with tailored properties searched for by physicists, chemists, materials scientists and device engineers. These materials are equally of interest for fundamental studies and for applied research while both viewpoints cross-fertilize each other regularly. Our overview starts with the discovery of ferromagnetism in manganites in 1950 and ranges until 2016: Today, halide perovskites are fully in focus for their potential in photovoltaic applications. This is certainly not an endpoint, but another milestone in a long series of often-unexpected discoveries on an ‘evergreen material’. Ball-and-stick model of the ideal cubic perovskite structure. The cation at the central position or ‘B site’ (small black dot) defines the group name (e.g., titanates) and plays a key role for the physical properties of the material.status: publishe

Laser-Grafted Molecularly Imprinted Polymers for the Detection of Histamine from Organocatalyzed Atom Transfer Radical Polymerization

© 2019 American Chemical Society. To be applicable to in vivo measuring, molecularly imprinted polymer (MIP) based sensors need to have high reproducibility, require miniaturization, and must be free of toxic materials (such as heavy metals). To address these requirements, a metal-free photo atom transfer radical polymerization (ATRP) grafting procedure is described using a pulsed UV laser as light source to create thin molecularly imprinted polymer (MIP) films (∼10 nm thickness) on a sensor surface. Analysis via X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) revealed the composition of the polymer film and the necessity for an excess of functional monomer to ensure its incorporation are demonstrated. MIP films were templated toward the target molecule histamine, for which in vivo studies can reveal unknown pathological pathways of inflammatory bowel diseases. By use of impedance spectroscopy, the biosensor surface is characterized in comparison to nonimprinted film grafts, and a high selectivity and sensitivity toward the target molecule are identified, revealing a histamine concentration limit of detection of 3.4 nM.status: publishe

Real-time monitoring of interactions between Ebola fusion peptide and solid-supported phospholipid membranes: Effect of peptide concentration and layer geometry

The pathogenesis of the Ebola virus which leads to a severe hemorrhagic fever in hosts is a very complex process which is not completely understood. Glycoproteins of the viral envelope are believed to play a crucial role in receptor binding and subsequently in fusion of the virus with the target cells of the host. As a result, the virus enters the cells and replicates. This process causes further cytopathic, and pathological reactions in the host's body. To gain further insights into the fusogenic interactions of the virus with cell membranes, we used well-controlled simple biomimetic systems, consisting of solid-supported phospholipid layers together with a small sequence of the viral glycoprotein (EBO17), which is believed to be the most important part responsible for viral pathogenesis. We monitor the real-time interaction of a EBO17 peptide sequence from the Ebola virus with dipalmitoylphosphatidylcholine (DMPC) phospholipid membranes using quartz crystal microbalance with dissipation monitoring (QCM-D) as a label-free method. In particular, we focus on the influence of the concentration of the peptide and the lipid layer geometry on the disrupting mechanism of the EBO17 peptide. Results indicate that for 2D supported lipid bilayers, low peptide concentrations induce a small, but detectable change in layer stability due to the presence of an α-helix configuration of the peptide. With large peptide concentrations, the peptide acquires a β-sheet configuration and no significant layer changes can be observed. A different mechanism is responsible for the interaction of the EBO17 peptides with the more complex 3D supported vesicle layers, for which a concentration-dependent trend can be observed leading to thicker lipid layers. Complementary analysis of the lipids' main phase transition evidences the differences induced in layer organization on the two layer geometries. These results confirm the importance of the interplay between lipid layer geometry and related peptide organization as an essential marker in peptide activity.info:eu-repo/semantics/publishe

A spectroscopic study on the curing of polymers used for synthetic whole-cell receptors for bacterial detection

Surface imprinted polymers (SIPs) are versatile receptors in bioanalytical applications for the selective detection of cells and microorganisms such as bacteria. One of the synthesis routes is the so-called stamping method in which template bacteria are pressed mechanically into a thin, gel-like polyurethane layer, which is then cured in the presence of the templates to create cell-specific binding pockets on the polymer. The present work focusses on two specific steps of the imprinting protocol: First, we evaluate the sedimentation of two different groups of bacteria, Escherichia coli and Escherichia blattae, on silicone stamps with respect to the resulting surface coverage, which is a key factor for the efficiency of the imprinting process. Second, we analyse the temperature dependence of the thermal- and dielectric properties of polyurethane during curing by dielectric- and pyroelectric spectroscopy. This provides information for improved curing protocols and on the stability of SIP materials at elevated temperatures.status: accepte

Low cost, sensitive impedance detection of E. Coli bacteria in food-matrix samples using surface-imprinted polymers as whole-cell receptors

Herein, a biomimetic sensor platform that allows sensitive, onsite detection of Escherichia coli (E. coli) with a limit of detection of 30 cells mL(-1) in both buffer suspension and rinsing water from an industrial food-preparation machine is reported. Ultrathin surface-imprinted polymers are combined with non-Faradaic impedance spectroscopy to measure the increase in resistance at the solid-to-liquid interface due to the binding of target cells by the receptor layer. The detection limit reached with this sensing principle is determined using an established, commercial impedance spectrometer and a low-cost, home-built impedance unit. Cross-selectivity tests, with both an unrelated bacterial species and four species belonging to the same Enterobacteriales order, show that the response is strongest for the target bacterium while only a small cross-selectivity signal (approximate to 10-25%) is visible for all other types of bacteria. Therefore, this sensor is not only fast and low cost, but also sensitive and selective. Sample preparation is minimal, which is an asset for onsite bacterial detection in a food industry context

Selective Campylobacter detection and quantification in poultry : a sensor tool for detecting the cause of a common zoonosis at its source

Thermotolerant Campylobacter bacteria, most notably Campylobacter jejuni and Campylobacter coli, are a major cause of human foodborne gastroenteritis, which is usually related to consumption of contaminated poultry. In this work, we present a sensor and the associated assay for the on-site detection of the prevalent species C. jejuni and C. coli. The sensor uses surface-imprinted polymer (SIP) layers as selective, biomimetic recognition elements in combination with a modified heat-transfer method (M-HTM) as a label-free, quantitative readout principle. The selectivity for C. coli and C. jejuni was evaluated against six other morphologically similar Campylobacterales species, confirming that the sensor is selective at species level while responding uniformly to different strains within the same species. For the relevant matrix, that is chicken cecal droppings suspended in PBS buffer, the detection limits are 1.1 x 10(3) CFU/mL for C. coli and 2.7 x 10(4) CFU/mL for C. jejuni, which is both low enough for a meaningful diagnostic test. The sensor concept requires only a minimum of sample preparation and a given concentration can be measured within less than one hour: Both are important assets for on-site detection such as on a poultry farm or in a slaughterhouse, keeping in mind that Campylobacter detection with established methods in analytical laboratories takes 2-4 days for obtaining the result