TY - JOUR A1 - Loewer, M. A1 - Guenther, T. A1 - Igel, J. A1 - Kruschwitz, Sabine A1 - Martin, T. A1 - Wagner, N. T1 - Ultra-broad-band electrical spctroscopy of soils and sediments - a combined permittivity and conductivity model N2 - We combined two completely different methods measuring the frequency-dependent electrical properties of moist porous materials in order to receive an extraordinary large frequency spectrum. In the low-frequency (LF) range, complex electrical resistivity between 1 mHz and 45 kHz was measured for three different soils and sandstone, using the spectral induced polarization (SIP) method with a four electrode cell. In the high-frequency (HF) radio to microwave range, complex dielectric permittivity was measured between 1MHz and 10 GHz for the same samples using dielectric spectroscopy by means of the coaxial transmission line technique. The combined data sets cover 13 orders of magnitude and were transferred into their equivalent expressions: the complex effective dielectric permittivity and the complex effective electrical conductivity.We applied the Kramers-Kronig relation in order to justify the validity of the data combination. A new phenomenological model that consists of both dielectric permittivity and electrical conductivity terms in a Debye- and Cole–Cole-type manner was fitted to the spectra. The combined permittivity and conductivity model accounts for the most common representations of the physical quantities with respect to the individual measuring method. A maximum number of four relaxation processes was identified in the analysed frequency range. Among these are the free water and different interfacial relaxation processes, the Maxwell-Wagner effect, the counterion relaxation in the electrical double layer and the direct-current electrical conductivity. There is evidence that free water relaxation does not affect the electrical response in the SIP range. Moreover, direct current conductivity contribution (bulk and interface) dominates the losses in the HF range. Interfacial relaxation processes with relaxations in the HF range are broadly distributed down to the LF range. The slowest observed process in the LF range has a minor contribution to the HF response. KW - Electrical properties KW - Permeability KW - Porosity KW - Hydrogeophysics PY - 2017 U6 - https://doi.org/10.1093/gji/ggx242 VL - 210 IS - 3 SP - 1360 EP - 1373 PB - Oxford University Press CY - Oxford AN - OPUS4-42598 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Wagner, Sabine A1 - Zapata, Carlos A1 - Wan, Wei A1 - Gawlitza, Kornelia A1 - Weber, M. A1 - Rurack, Knut T1 - Role of Counterions in Molecularly Imprinted Polymers for Anionic Species N2 - Small-molecule oxoanions are often imprinted noncovalently as carboxylates into molecularly imprinted polymers (MIPs), requiring the use of an organic counterion. Popular species are either pentamethylpiperidine (PMP) as a protonatable cation or tetraalkylammonium (TXA) ions as permanent cations. The present work explores the influence of the TXA as a function of their alkyl chain length, from methyl to octyl, using UV/vis absorption, fluorescence titrations, and HPLC as well as MD simulations. Protected phenylalanines (Z-L/D-Phe) served as templates/analytes. While the influence of the counterion on the complex stability constants and anion-induced spectral changes shows a monotonous trend with increasing alkyl chain length at the prepolymerization stage, the cross-imprinting/rebinding studies showed a unique pattern that suggested the presence of adaptive cavities in the MIP matrix, related to the concept of induced fit of enzyme−substrate interaction. Larger cavities formed in the presence of larger counterions can take up pairs of Z-X-Phe and smaller TXA, eventually escaping spectroscopic detection. Correlation of the experimental data with the MD simulations revealed that counterion mobility, the relative distances between the three partners, and the hydrogen bond lifetimes are more decisive for the response features observed than actual distances between interacting atoms in a complex or the orientation of binding moieties. TBA has been found to yield the highest imprinting factor, also showing a unique dual behavior regarding the interaction with template and fluorescent monomer. Finally, interesting differences between both enantiomers have been observed in both theory and experiment, suggesting true control of enantioselectivity. The contribution concludes with suggestions for translating the findings into actual MIP development. KW - Anion receptors KW - Fluorescence sensing KW - Molecular dynamics simulations KW - Molecularly imprinted polymers KW - Rational design PY - 2018 U6 - https://doi.org/10.1021/acs.langmuir.8b00500 SN - 0743-7463 VL - 34 IS - 23 SP - 6963 EP - 6975 PB - American Chemical Society CY - Washington, D.C. AN - OPUS4-45399 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Wagner, Sabine A1 - Wan, Wei A1 - Rurack, Knut T1 - On the Influence of Counter-ions on the Recognition Behavior of Molecularly Imprinted Polymers against Amino Acids T2 - Adlershofer Forschungsforum CY - Berlin Germany DA - 2014-11-11 PY - 2014 AN - OPUS4-33748 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Wagner, Sabine A1 - Wan, Wei A1 - Rurack, Knut A1 - Panne, Ulrich T1 - Investigation of the Recognition Behavior of Molecularly Imprinted Polymers against Amino Acids by Using different Counter-ions T2 - Anakon 2015 CY - Graz, Österreich DA - 2015-03-23 PY - 2015 AN - OPUS4-33745 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Wagner, Sabine A1 - Carrasco, S. A1 - Benito-Peña, E. A1 - Walt, D. R. A1 - Moreno-Bondi, M. C. A1 - Rurack, Knut T1 - Integration of microspheres coated with fluorescent molecularly imprinted polymers with a fiber optic array for the detection of antibiotics N2 - The widespread use of antibiotics in livestock farming leads to trace residues in food products and wastewater, potentially entailing antimicrobial resistance in food-borne pathogens. The determination of antibiotics in aqueous environments and foodstuff is thus of major concern. Analytical assays based on molecularly imprinted polymers (MIPs) have emerged as a valuable tool in this field due to the low production costs, stability, format adaptability and the possibility to imprint and thus their ability to recognize a wide variety of target analytes. With regard to optical sensing technologies, however, MIPs have only been used in considerably few applications, especially in fluorescence sensors. This limitation is basically due to the fact that the incorporation of a fluorescently responding moiety into a polymer matrix is challenging. One way to overcome this limitation is to use tailor-made fluorescent indicator monomers for direct transfer of the binding event into an optical signal. If such a monomer is integrated into a thin MIP-shell on microspheres such core/shell particles can be readily used in advanced multiplexing sensory fiber-optic microarrays. Here, we propose such a fiber-optic microarray based on fluorescent MIP microspheres for antibiotics. The binding behavior and the selectivity of a microarray using these MIP were examined and compared with a non-imprinted polymer (NIP) control, employing the target molecules and other structurally closely related antibiotics. T2 - Europt(r)ode XIII CY - Graz, Austria DA - 20.03.2016 KW - Molecularly imprinted polymers KW - Fiber-optic microarray KW - Fluorescence PY - 2016 AN - OPUS4-37294 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Wagner, Sabine A1 - Bell, Jérémy A1 - Biyikal, Mustafa A1 - Gawlitza, Kornelia A1 - Rurack, Knut T1 - Integrating fluorescent molecularly imprinted polymer (MIP) sensor particles with a modular microfluidic platform for the detection of the herbicide 2,4-D N2 - 2,4-Dichlorophenoxyacetic acid (2,4-D) is an important and well-known herbicide that is widely used in agriculture because of its advantages to regulate plant growth.1 However, the use of large quantities of the treated plants as animal feed leads to residues in meat, milk and eggs. Furthermore, the herbicide can drain off and contaminate ground and drinking water. The ingestion of 2,4-D-contaminated food and water can cause damage to the inner organs of humans and animals, e.g., the kidneys and the liver. Analytical assays based on molecularly imprinted polymers (MIPs) have emerged as a valuable tool in the field of environmental analysis due to the low production costs, high stability, format adaptability and the possibility to imprint—and thus their ability to recognize—a wide variety of target analytes. Regarding optical sensing technologies, however, MIPs have only been used in considerably few applications, especially in fluorescence sensors. This limitation is basically because the incorporation of a fluorescently responding moiety into a polymer matrix is challenging. One way to overcome this limitation is to use tailor-made fluorescent indicator monomers or cross-linkers for direct transfer of the binding event into an optical signal and to coat the MIP via reversible addition-fragmentation chain transfer (RAFT) polymerization as a thin layer onto the surface of silica nanoparticles as primary sensing element. Here, we present the response behaviour of fluorescent MIP sensor particles in terms of sensitivity for 2,4-D detection (the so-called imprinting factor), discrimination ability against structurally similar compounds (the discrimination factor) and performance in a phase-transfer assay (PTA) on chip, i.e., the implementation of the assay into a microfluidic chip environment, offering a novel simple and rapid way for the detection of herbicides in water. T2 - GSSMIP2017 CY - Porto, Portugal DA - 08.06.2017 KW - 2,4-Dichlorophenoxyacetic acid KW - Molecularly imprinted polymers KW - Microfluidic device PY - 2017 AN - OPUS4-40582 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Wagner, Sabine A1 - Bell, Jérémy A1 - Biyikal, Mustafa A1 - Gawlitza, Kornelia A1 - Rurack, Knut T1 - Integrating fluorescent molecularly imprinted polymer (MIP) sensor particles with a modular microfluidic platform for nanomolar smallmolecule detection directly in aqueous samples N2 - Fluorescent sensory MIP (molecularly imprinted polymer) particles were combined with a droplet-based 3D microfluidic system for the selective determination of a prototype small-molecule analyte of environmental concern, 2,4-dichlorophenoxyacetic acid or 2,4-D, at nanomolar concentration directly in water samples. A tailor-made fluorescent indicator cross-linker was thus designed that translates the binding event directly into an enhanced fluorescence signal. The phenoxazinone-type cross-linker was co-polymerized into a thin MIP layer grafted from the surface of silica microparticles following a RAFT (reversible addition-fragmentation chain transfer) polymerization protocol. While the indicator cross-linker outperformed its corresponding monomer twin, establishment of a phase-transfer protocol was essential to guarantee that the hydrogen bond-mediated signalling mechanism between the urea binding site on the indicator cross-linker and the carboxylate group of the analyte was still operative upon real sample analysis. The latter was achieved by integration of the fluorescent core-shell MIP sensor particles into a modular microfluidic platform that allows for an in-line phasetransfer assay, extracting the analyte from aqueous sample droplets into the organic phase that contains the sensor particles. Real-time fluorescence determination of 2,4-D down to 20 nM was realized with the system and applied for the analysis of various surface water samples collected from different parts of the world. KW - Molecular imprinting KW - Microfluidics KW - Fluorescence KW - Core-shell particles KW - Droplets PY - 2018 U6 - https://doi.org/10.1016/j.bios.2017.07.053 SN - 0956-5663 VL - 99 IS - 1 SP - 244 EP - 250 PB - Elsevier B.V. CY - Amsterdam AN - OPUS4-42258 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Wagner, Sabine A1 - Wan, Wei A1 - Biyikal, Mustafa A1 - Rurack, Knut A1 - Carrasco, Sergio A1 - Moreno-Bondi, Maria C. T1 - Fluorescent Sensor Particles based on Molecularly Imprinted Polymers for the Detection of Antibiotics and Herbicides in Water N2 - As the interest in rapid and sensitive detection methods is growing, molecularly imprinted polymers (MIPs) are increasingly considered as an alternative to bio-macromolecular recognition units such as antibodies or enzymes due to their facilely tailorable selectivity towards certain analytes or a group of structurally related species. The low production costs, stability, robustness and format adaptability of MIPs combined with the possibility to imprint and thus their ability to recognize a wide variety of target analytes can be potentially useful in chemical sensor applications.[1] With regard to optical sensing technologies, however, MIPs have only been used in considerably few applications, especially in fluorescence sensors. This limitation is basically due to the fact that the incorporation of a fluorescently responding moiety into a polymer matrix is a challenge. One way to overcome this limitation is to use tailor-made fluorescent indicator monomers and thin MIP-shells on silica particles.[2] Here, we present silica sensor particles with a thin MIP layer which was grown onto the silica surface via reversible addition-fragmentation chain transfer (RAFT) polymerization. The homogeneous MIP shell contains fluorescent phenoxazine-urea monomers as signal generation elements. The carboxylate salts of the antibiotic ampicillin (AMPI) and the herbicide 2,4 dichlorophenoxyacetic acid (2,4-D) were used as templates in those studies. In this case, hydrogen bonds are formed between the urea group of the fluorescent monomer and the carboxylate group of the template. To investigate the binding behavior of the MIPs and the control non-imprinted polymer (NIP) particles in terms of discrimination and imprinting factor, titration experiments with AMPI and 2,4-D salts were performed directly in organic solution. In order to study the detection possibilities in aqueous solution, a simple phase-transfer assay using fluorescence spectroscopy was investigated for both analytes. T2 - 11th Workshop on Biosensors & Bioanalytical Microtechniques in Enviromental, Food & Clinical Analysis CY - Regensburg, Germany DA - 2015-09-26 PY - 2015 AN - OPUS4-34658 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Wagner, Sabine A1 - Wan, Wei A1 - Biyikal, Mustafa A1 - Panne, Ulrich A1 - Rurack, Knut A1 - Carrasco, Sergio A1 - Moreno-Bondi, Maria C. T1 - Fluorescent Nanosensor based on Molecularly Imprinted Polymer for the Detection of Contaminants in Water N2 - As the interest in rapid and sensitive detection methods is growing, molecularly imprinted polymers (MIPs) are increasingly considered as an alternative to bio-macromolecular recognition units such as antibodies or enzymes due to their facilely tailorable selectivity towards certain analytes or a group of structurally related species. The low production costs, stability, robustness and format adaptability of MIPs combined with the possibility to imprint and thus their ability to recognize a wide variety of target analytes can be potentially useful in chemical sensor applications.[1] With regard to optical sensing technologies, however, MIPs have only been used in considerably few applications, especially in fluorescence sensors. This limitation is basically due to the fact that the incorporation of a fluorescently responding moiety into a polymer matrix is a challenge. One way to overcome this limitation is to use tailor-made fluorescent indicator monomers and thin MIP-shells on silica particles.[2] Here, we present silica sensor particles with a thin MIP layer which was grown onto the silica surface via reversible addition-fragmentation chain transfer (RAFT) polymerization. The homogeneous MIP shell contains fluorescent phenoxazine-urea monomers as signal generation elements. The carboxylate salts of the antibiotic ampicillin (AMPI) and the herbicide 2,4 dichlorophenoxyacetic acid (2,4-D) were used as templates in those studies. In this case, hydrogen bonds are formed between the urea group of the fluorescent monomer and the carboxylate group of the template. To investigate the binding behavior of the MIPs and the control non-imprinted polymer (NIP) particles in terms of discrimination and imprinting factor, titration experiments with AMPI and 2,4-D salts were performed directly in organic solution. In order to study the detection possibilities in aqueous solution, a simple phase-transfer assay using fluorescence spectroscopy was investigated for both analytes. T2 - Adlershofer Forschungsforum 2016 CY - Berlin, Germany DA - 2015-11-11 PY - 2015 AN - OPUS4-35238 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Wan, Wei A1 - Wagner, Sabine A1 - Rurack, Knut T1 - Fluorescent monomers: "bricks" that make a molecularly imprinted polymer "bright" N2 - Molecularly imprinted polymers (MIPs) are potent and established recognition phases in separation and enrichment applications. Because of their robustness, versatility and format adaptability, they also constitute very promising sensing phases, especially when the active sensing element is directly integrated into the MIP. Fluorescent MIPs incorporating fluorescent monomers are perhaps the best developed and most successful approach here. This article reviews the state of the art in this field, discussing the pros and cons of the use of fluorescent dye and probe derivatives as such monomers, the different molecular interaction forces for template complexation, signalling modes and a variety of related approaches that have been realized over the years, including Förster resonance energy transfer processes, covalent imprinting, postmodification attachment of fluorescent units and conjugated polymers as MIPs; other measurement schemes and sensing chemistries that use MIPs and fluorescence interrogation to solve analytical problems (fluorescent competitive assays, fluorescent analytes, etc.) are not covered here. Throughout the article, photophysical processes are discussed to facilitate understanding of the effects that can occur when one is planning for a fluorescence response to happen in a constrained polymer matrix. The article concludes with a concise assessment of the suitability of the different formats for sensor realization. KW - Chemical sensors KW - Fluorescence KW - Molecularly imprinted polymers KW - Dyes KW - Sol-gel PY - 2016 U6 - https://doi.org/10.1007/s00216-015-9174-4 SN - 1618-2642 SN - 1618-2650 VL - 408 IS - 7 SP - 1753 EP - 1771 PB - Springer CY - Berlin AN - OPUS4-35830 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -