Application of Biosensors for the Detection of Mycotoxins for the Improvement of Food Safety.

Mycotoxins, secondary metabolites synthesized by various filamentous fungi genera such as Aspergillus, Penicillium, Fusarium, Claviceps, and Alternaria, are potent toxic compounds. Their production is contingent upon specific environmental conditions during fungal growth. Arising as byproducts of fungal metabolic processes, mycotoxins exhibit significant toxicity, posing risks of acute or chronic health complications. Recognized as highly hazardous food contaminants, mycotoxins present a pervasive threat throughout the agricultural and food processing continuum, from plant cultivation to post-harvest stages. The imperative to adhere to principles of good agricultural and industrial practice is underscored to mitigate the risk of mycotoxin contamination in food production. In the domain of food safety, the rapid and efficient detection of mycotoxins holds paramount significance. This paper delineates conventional and commercial methodologies for mycotoxin detection in ensuring food safety, encompassing techniques like liquid chromatography, immunoassays, and test strips, with a significant emphasis on the role of electrochemiluminescence (ECL) biosensors, which are known for their high sensitivity and specificity. These are categorized into antibody-, and aptamer-based, as well as molecular imprinting methods. This paper examines the latest advancements in biosensors for mycotoxin testing, with a particular focus on their amplification strategies and operating mechanisms.

Solution-processed transparent ferroelectric nylon thin films.

Ferroelectricity, a bistable ordering of electrical dipoles in a material, is widely used in sensors, actuators, nonlinear optics, and data storage. Traditional ferroelectrics are ceramic based. Ferroelectric polymers are inexpensive lead-free materials that offer unique features such as the freedom of design enabled by chemistry, the facile solution-based low-temperature processing, and mechanical flexibility. Among engineering polymers, odd nylons are ferroelectric. Since the discovery of ferroelectricity in polymers, nearly half a century ago, a solution-processed ferroelectric nylon thin film has not been demonstrated because of the strong tendency of nylon chains to form hydrogen bonds. We show the solution processing of transparent ferroelectric thin film capacitors of odd nylons. The demonstration of ferroelectricity, as well as the way to obtain thin films, makes odd nylons attractive for applications in flexible devices, soft robotics, biomedical devices, and electronic textiles.

Oligoprolines guide the self-assembly of quaterthiophenes.

Control over the molecular organization of π-conjugated oligothiophenes into different types of supramolecular assemblies is key to their use in organic electronics but difficult to achieve as these chromophores have a pronounced tendency to aggregate. Herein we show that oligoprolines, which do not self-assemble on their own, control the self-assembly of quaterthiophenes. Spectroscopic, microscopic, and diffraction studies with quaterthiophene-oligoproline conjugates revealed the formation of mono- or double-layered sheets or, alternatively, helically twisted ribbons - depending on the length of the oligoproline. The dimensions of the nanoscopic objects, which extend into the micrometer regime, correlate with the molecular dimensions of the quaterthiophene-oligoproline building blocks.

Self-Organization and Charge Transport Properties of Selenium and Tellurium Analogues of Polythiophene.

A series of conjugated polymers comprising polythiophene, polyselenophene, and polytellurophene with branched 3,7-dimethyloctyl side chains, well-matched molecular weight, dispersity, and regioregularity is synthesized. The ionization potential is found to vary from 5.14 to 5.32 eV, with polytellurophene having the lowest potential. Field-effect transistors based on these materials exhibit distinct hole transport mobility that varies by nearly three orders of magnitude, with polytellurophene having the highest mobility (2.5 × 10-2 cm² V-1 s-1 ). The large difference in mobility demonstrates the significant impact of heteroatom substitution. Although the series of polymers are very similar in structure, their solid-state properties are different. While the thin film microstructure of polythiophene and polyselenophene is identical, polytellurophene reveals globular features in the film topography. Polytellurophenes also appear to be the least crystalline, even though their charge transport properties are superior to other samples. The torsional barrier and degree of planarity between repeat units increase as one moves down group-16 elements. These studies show how a single atom in a polymer chain can have a substantial influence on the bulk properties of a material, and that heavy group-16 atoms have a positive influence on charge transport properties when all other variables are kept unchanged.

Positional Isomers of Chromophore-Peptide Conjugates Self-Assemble into Different Morphologies.

Ordering π-systems into defined supramolecular structures is important for the development of organic functional materials. In recent years, peptides with defined secondary structures and/or self-assembly properties were introduced as powerful tools to order peptide-chromophore conjugates into different morphologies. This work explores whether or not the directionality of peptides can be used to control the self-assembly. The position of the π-system in conjugates between oligoprolines and perylene monoimide (PMI) chromophores was varied by attaching the PMI moiety to the second-to-last residue from the C- and N-termini, respectively. Microscopic and diffraction analysis revealed that the positional isomers form distinctly different supramolecular architectures that extend into the micrometer regime. NMR spectroscopic studies in solution phase allowed correlation of the self-assembly properties with markedly different conformational preferences of the isomeric building blocks. These insights enabled the design of building blocks with predictable self-assembly properties. Thus, the directionality of peptides offers exciting opportunities for controlling the self-assembly and electronic properties of π-systems.

A triaxial supramolecular weave.

Despite recent advances in the synthesis of increasingly complex topologies at the molecular level, nano- and microscopic weaves have remained difficult to achieve. Only a few diaxial molecular weaves exist-these were achieved by templation with metals. Here, we present an extended triaxial supramolecular weave that consists of self-assembled organic threads. Each thread is formed by the self-assembly of a building block comprising a rigid oligoproline segment with two perylene-monoimide chromophores spaced at 18 Å. Upon π stacking of the chromophores, threads form that feature alternating up- and down-facing voids at regular distances. These voids accommodate incoming building blocks and establish crossing points through CH-π interactions on further assembly of the threads into a triaxial woven superstructure. The resulting micrometre-scale supramolecular weave proved to be more robust than non-woven self-assemblies of the same building block. The uniform hexagonal pores of the interwoven network were able to host iridium nanoparticles, which may be of interest for practical applications.

Morphology Control in Films of Isoindigo Polymers by Side-Chain and Molecular Weight Effects.

The performance of devices relying on organic electronic materials, such as organic field-effect transistors (OFET) and organic photovoltaics (OPV), is strongly correlated to the morphology of the conjugated material in thin films. For instance, several factors such as polymer solubility, weak intermolecular forces between polymers and fullerene derivatives, and film drying time impact phase separation in the active layer of a bulk heterojunction OPV device. In an effort to probe the influence of polymer assembly on morphology of polymer thin films and phase separation with fullerene derivatives, five terthiophene-alt-isoindigo copolymers were synthesized with alkyl side-chains of varying lengths and branching on the terthiophene unit. These P[T3(R)-iI] polymers were designed to have similar optoelectronic properties but different solubilities in o-dichlorobenzene and were predicted to have different tendencies for crystallization. All polymers with linear alkyl chains exhibit similar thin film morphologies as investigated by grazing-incidence wide-angle X-ray scattering (GIWAXS) and atomic force microscopy (AFM). The main differences in electronic and morphological properties arise when P[T3(R)-iI] is substituted with branched 2-ethylhexyl (2EH) side-chains. The bulky 2EH substituents lead to a blue-shifted absorption, a lower ionization potential, and reduced ordering in polymer thin films. The five P[T3-iI] derivatives span hole mobilities from 1.5 × 10-3 to 2.8 × 10-2 cm2 V-1 s-1 in OFET devices. In OPV devices, the 2EH-substituted polymers yield open-circuit voltages of 0.88 V in BHJ devices yet low short-circuit currents of 0.8 mA cm-2, which is explained by the large phase separation observed by AFM in blends of P[T3(2EH)-iI] with PC71BM. In these P[T3(R)-iI] systems, the propensity for the polymers to self-assemble prior to aggregation of PC71BM molecules was key to achieving fine phase separation and increased short-circuit currents, eventually resulting in power conversion efficiencies of 5% in devices processed using a single solvent.

Microstructure-Dependent Charge Carrier Transport of Poly(3-hexylthiophene) Ultrathin Films with Different Thicknesses.

Since the interfacial order of conjugated polymers plays an essential role for the performance of field-effect transistors, comprehensive understanding on the charge carrier transport in ultrathin semiconducting films below thicknesses of 10 nm is required for the development of transparent and flexible organic electronics. In this study, ultrathin films based on poly(3-hexylthiophene) as conjugated polymer model system with a thickness range from single monolayer up to several multilayers are investigated in terms of microstructure evolution and electrical properties of different molecular weights. Interestingly, a characteristic leap in field-effect mobility is observed for films with thickness greater than four layers. This threshold mobility regarding film thickness is attributed to the transition from 2D to 3D charge carrier transport along with an increased size of the P3HT aggregates in the upper layers of the film. These results disclose key aspects on the role of the film interlayer on the charge carrier transport through conjugated polymers in transistors.

Controlling the volatility of the written optical state in electrochromic DNA liquid crystals.

Liquid crystals are widely used in displays for portable electronic information display. To broaden their scope for other applications like smart windows and tags, new material properties such as polarizer-free operation and tunable memory of a written state become important. Here, we describe an anhydrous nanoDNA-surfactant thermotropic liquid crystal system, which exhibits distinctive electrically controlled optical absorption, and temperature-dependent memory. In the liquid crystal isotropic phase, electric field-induced colouration and bleaching have a switching time of seconds. Upon transition to the smectic liquid crystal phase, optical memory of the written state is observed for many hours without applied voltage. The reorientation of the DNA-surfactant lamellar layers plays an important role in preventing colour decay. Thereby, the volatility of optoelectronic state can be controlled simply by changing the phase of the material. This research may pave the way for developing a new generation of DNA-based, phase-modulated, photoelectronic devices.

Effect of Structural Modifications on the Self-Assembly of Oligoprolines Conjugated with Sterically Demanding Chromophores.

Conjugates between oligoprolines and sterically demanding perylene monoimides (PMIs) form hierarchical supramolecular self-assemblies. The influence of the length and stereochemistry at the attachment site between the peptide backbone and the chromophore on the self-assembly properties of the conjugates was explored. Comparison between oligoprolines bearing 4R- or 4S-configured azidoprolines (Azp) for the conjugation with the PMIs revealed that diastereoisomers with 4R configuration guide the self-assembly consistently better than conjugates with 4S configuration. Elongating the peptide chain beyond nine proline residues or introducing structural "errors", by altering the absolute configuration of one stereogenic center at the outside of the functionalizable oligoproline helix, lowered the efficacy of self-assembly significantly, both in solution phase and in the solid state. The results showed how subtle structural modifications allow for tuning the self-assembly of chromophores and provided further design principles for the development of peptide-chromophore conjugates into nanostructured materials.

Free-Standing Monolayer Two-Dimensional Supramolecular Organic Framework with Good Internal Order.

Utilizing dynamic self-assembly and self-sorting to obtain large-area, molecularly precise monolayered structures represents a promising approach toward two-dimensional supramolecular organic frameworks (2D SOF) or 2D supramolecular polymers. So far, related approaches suffer from small domain sizes, fragility and weak long-range internal order. Here we report on the self-assembly of a host-guest enhanced donor-acceptor interaction, consisting of a tris(methoxynaphthyl)-substituted truxene spacer, and a naphthalene diimide substituted with N-methyl viologenyl moieties as donor and acceptor monomers, respectively, in combination with cucurbit[8]uril as host monomer toward monolayers of an unprecedented 2D SOF. Featuring orthogonal solubility, the participating molecules self-assemble at a liquid-liquid interface, yielding exceptionally large-area, insoluble films, which were analyzed by transmission electron microscopy, atomic force microscopy and optical microscopy to be monolayers with a thickness of 1.8 nm, homogeneously covering areas up to 0.25 cm(2), and featuring the ability to be free-standing over holes of 10 µm(2). Characterization with ultraviolet-visible absorption spectroscopy, solid-state nuclear magnetic resonance spectroscopy, infrared spectroscopy, and grazing incidence wide-angle X-ray scattering allowed for confirmation of a successful complexation of all three monomers toward an internal long-range order and gave indications to an expected hexagonal superstructure. Our results extend the existing variety of two-dimensional soft nanomaterials by a versatile supramolecular approach, whereas the possibility of varying the functional monomers is supposed to open adaptability to different applications like membranes, sensors, molecular sieves, and optoelectronics.

Thermal Evaporation versus Spin-Coating: Electrical Performance in Columnar Liquid Crystal OLEDs.

The electrical responses of a columnar liquid crystal (a diimidodiester derivative of benzo[ghi]perylene) deposited either by spin-coating or by thermal evaporation into a typical OLED device are compared. For the spin-coated film, homeotropic alignment was induced by thermal annealing, which enhanced the charge carrier mobility significantly. For the evaporated films, homeotropic alignment could not be obtained by annealing. However, a degree of rectification higher than 3 orders of magnitude was achieved, even without annealing, with an electrical response similar to the response of the aligned spin-coated film. A trap-limited space-charge-limited current model was used to extract the charge carrier mobility directly from the current-voltage curves. Grazing incidence wide-angle X-ray scattering confirmed the homeotropic alignment of the annealed spin-coated film, whereas the columns are mostly oriented parallel to the surface in the evaporated case. In a field-effect transistor with bottom-gate bottom-contact geometry, the evaporated film exhibited a typical behavior of an n-type transistor. The degree of intermolecular order is thereby strongly dependent on the deposition method where vacuum deposition leads to a higher order. This higher order, however, impedes reorientation by annealing of the evaporated film but leads to improved charge transport between the electrodes even without homeotropic alignment of columnar liquid crystal.

Solvent-free liquid crystals and liquids based on genetically engineered supercharged polypeptides with high elasticity.

A series of solvent-free elastin-like polypeptide liquid crystals and liquids are developed by electrostatic complexation of supercharged elastin-like polypeptides with surfactants. The smectic mesophases exhibit a high elasticity and the values can be easily tuned by varying the alkyl chain lengths of the surfactants or the lengths of the elastin-like polypeptides.

Solvent-free Liquid Crystals and Liquids from DNA.

As DNA exhibits persistent structures with dimensions that exceed the range of their intermolecular forces, solid-state DNA undergoes thermal degradation at elevated temperatures. Therefore, the realization of solvent-free DNA fluids, including liquid crystals and liquids, still remains a significant challenge. To address this intriguing issue, we demonstrate that combining DNA with suitable cationic surfactants, followed by dehydration, can be a simple generic scheme for producing these solvent-free DNA fluid systems. In the anhydrous smectic liquid crystalline phase, DNA sublayers are intercalated between aliphatic hydrocarbon sublayers. The lengths of the DNA and surfactant are found to be extremely important in tuning the physical properties of the fluids. Stable liquid-crystalline and liquid phases are obtained in the -20 °C to 200 °C temperature range without thermal degradation of the DNA. Thus, a new type of DNA-based soft biomaterial has been achieved, which will promote the study and application of DNA in a much broader context.

A molecular nematic liquid crystalline material for high-performance organic photovoltaics.

Solution-processed organic photovoltaic cells (OPVs) hold great promise to enable roll-to-roll printing of environmentally friendly, mechanically flexible and cost-effective photovoltaic devices. Nevertheless, many high-performing systems show best power conversion efficiencies (PCEs) with a thin active layer (thickness is ~100 nm) that is difficult to translate to roll-to-roll processing with high reproducibility. Here we report a new molecular donor, benzodithiophene terthiophene rhodanine (BTR), which exhibits good processability, nematic liquid crystalline behaviour and excellent optoelectronic properties. A maximum PCE of 9.3% is achieved under AM 1.5G solar irradiation, with fill factor reaching 77%, rarely achieved in solution-processed OPVs. Particularly promising is the fact that BTR-based devices with active layer thicknesses up to 400 nm can still afford high fill factor of ~70% and high PCE of ~8%. Together, the results suggest, with better device architectures for longer device lifetime, BTR is an ideal candidate for mass production of OPVs.

Thermotropic liquid crystals from biomacromolecules.

Complexation of biomacromolecules (e.g., nucleic acids, proteins, or viruses) with surfactants containing flexible alkyl tails, followed by dehydration, is shown to be a simple generic method for the production of thermotropic liquid crystals. The anhydrous smectic phases that result exhibit biomacromolecular sublayers intercalated between aliphatic hydrocarbon sublayers at or near room temperature. Both this and low transition temperatures to other phases enable the study and application of thermotropic liquid crystal phase behavior without thermal degradation of the biomolecular components.

Transition between band and hopping transport in polymer field-effect transistors.

Hall effect and slightly negative temperature dependence of the mobility in polymeric transistors are demonstrated. The semiconductor channel is based on a polycyclopentadithiophene-benzothiadiazole (CDT-BTZ) donor-acceptor copolymer film whose chain direction is oriented by mechanical compression at the surface of an ionic liquid. The mobility is 5.6 cm(2) V(-1) s(-1) at room temperature, and is further improved to 6.7 cm(2) V(-1) s(-1) at 260 K.

Hierarchical supramolecular assembly of sterically demanding π-systems by conjugation with oligoprolines.

Self-assembly from flexible worm-like threads via bundles of rigid fibers to nanosheets and nanotubes was achieved by covalent conjugation of perylene monoimide (PMI) chromophores with oligoprolines of increasing length. Whereas the chromophoric π-system and the peptidic building block do not self-aggregate, the covalent conjugates furnish well-ordered supramolecular structures with a common wall/fiber thickness. Their morphology is controlled by the number of repeat units and can be tuned by seemingly subtle structural modifications.

Tailored donor-acceptor polymers with an A-D1-A-D2 structure: controlling intermolecular interactions to enable enhanced polymer photovoltaic devices.

Extensive efforts have been made to develop novel conjugated polymers that give improved performance in organic photovoltaic devices. The use of polymers based on alternating electron-donating and electron-accepting units not only allows the frontier molecular orbitals to be tuned to maximize the open-circuit voltage of the devices but also controls the optical band gap to increase the number of photons absorbed and thus modifies the other critical device parameter-the short circuit current. In fact, varying the nonchromophoric components of a polymer is often secondary to the efforts to adjust the intermolecular aggregates and improve the charge-carrier mobility. Here, we introduce an approach to polymer synthesis that facilitates simultaneous control over both the structural and electronic properties of the polymers. Through the use of a tailored multicomponent acceptor-donor-acceptor (A-D-A) intermediate, polymers with the unique structure A-D1-A-D2 can be prepared. This approach enables variations in the donor fragment substituents such that control over both the polymer regiochemistry and solubility is possible. This control results in improved intermolecular π-stacking interactions and therefore enhanced charge-carrier mobility. Solar cells using the A-D1-A-D2 structural polymer show short-circuit current densities that are twice that of the simple, random analogue while still maintaining an identical open-circuit voltage. The key finding of this work is that polymers with an A-D1-A-D2 structure offer significant performance benefits over both regioregular and random A-D polymers. The chemical synthesis approach that enables the preparation of A-D1-A-D2 polymers therefore represents a promising new route to materials for high-efficiency organic photovoltaic devices.

Stability analysis of phonon transport equations derived via the Chapman-Enskog method and transformation of variables.

Under the assumption of Callaway's model of the Boltzmann-Peierls equation, the Chapman-Enskog method for a phonon gas forms the basis to derive various hydrodynamic equations for the energy density and the drift velocity of interest when normal processes dominate over resistive ones. The first three levels of the expansion (i.e., the zeroth-, first-, and second-order approximations) are satisfactory in that they are entropy consistent and ensure linear stability of the rest state. However, the entropy density contains a weakly nonlocal term, the entropy production is a degenerate function of variables, and the next order in the Chapman-Enskog expansion gives the equations with linearly unstable rest solutions. In the context of Burnett and super-Burnett equations, a similar type of problem was recognized by several authors who proposed different ways to deal with it. Here we report on yet another possible device for obtaining more satisfactory equations. Namely, inspired by the fact that there exists no unique way to truncate the Chapman-Enskog expansion, we combine the Chapman-Enskog procedure with the method of variable transformation and subsequently find a class of epsilon -dependent transformations through which it is possible to derive the second-order equations possessing a local entropy density and nondegenerate expression for the entropy production. Regardless of this result, we also show that although the method cannot be used to construct linearly stable third-order equations, it can be used to make the originally stable first-order equations asymptotically stable.