Component analysis of the fluorescence spectra of a lignin model compound

Lignin: The green powerhouse for enzyme immobilization in biocatalysis and biosensing

Enzymes play an important role in diverse industries and are critical components of many industrial products, yet, their application is limited due to their sensitivity to environmental conditions, recovery challenges, and susceptibility to inhibition. Immobilizing enzymes onto a suitable support matrix imparts higher resistance and improves operational flexibility, recyclability, and reusability. Lignin, a renewable and abundant biopolymer derived from the paper and pulp industry, has emerged as one of the prominent materials to be incorporated in support matrices. The distinctive characteristics of lignin include high mechanical strength, ease of separation, chemical stability, robust matrix for securing enzyme binding, biocompatibility, and ease of surface functionalization, making it a promising alternative to traditional synthetic materials. Research studies suggest the effectiveness of various lignin-based materials for immobilizing enzymes and significantly improving their stability, reusability, and catalytic activity. This article critically examines the unique properties of lignin and highlights significant contributions made in the development of enzyme immobilization for biocatalysis and biosensing applications. Additionally, the roles of hybrid materials, multienzyme immobilization, and innovative strategies like interfacial activation and enzyme shielding are discussed for overcoming the current challenges and developing sustainable, efficient, and robust biocatalytic and biosensing processes for industrial applications.

Biophysical characterization and design of a minimal version of the Hoechst RNA aptamer

RNA aptamers are oligonucleotides, selected through Systematic Evolution of Ligands by EXponential Enrichment (SELEX), that can bind to specific target molecules with high affinity. One such molecule is the RNA aptamer that binds to a blue-fluorescent Hoechst dye that was modified with bulky t-Bu groups to prevent non-specific binding to DNA. This aptamer has potential for biosensor applications; however, limited information is available regarding its conformation, molecular interactions with the ligand, and binding mechanism. The study presented here aims to biophysically characterize the Hoechst RNA aptamer when complexed with the t-Bu Hoechst dye and to further optimize the RNA sequence by designing and synthesizing new sequence variants. Each variant aptamer-t-Bu Hoechst complex was evaluated through a combination of fluorescence emission, native polyacrylamide gel electrophoresis, fluorescence titration, and isothermal titration calorimetry experiments. The results were used to design a minimal version of the aptamer consisting of only 21 nucleotides. The performed study also describes a more efficient method for synthesizing the t-Bu Hoechst dye derivative. Understanding the biophysical properties of the t-Bu Hoechst dye-RNA complex lays the foundation for nuclear magnetic resonance spectroscopy studies and its potential development as a building block for an aptamer-based biosensor that can be used in medical, environmental or laboratory settings.

Light-Emitting Microfibers from Lotus Root for Eco-Friendly Optical Waveguides and Biosensing

Optical biosensors based on micro/nanofibers are highly valuable for probing and monitoring liquid environments and bioactivity. Most current optical biosensors, however, are still based on glass, semiconductors, or metallic materials, which might not be fully suitable for biologically relevant environments. Here, we introduce biocompatible and flexible microfibers from lotus silk as microenvironmental monitors that exhibit waveguiding of intrinsic fluorescence as well as of coupled light. These features make single-filament monitors excellent building blocks for a variety of sensing functions, including pH probing and detection of bacterial activity. These results pave the way for the development of new and entirely eco-friendly, potentially multiplexed biosensing platforms.

A fluorescence spectroscopic study of light transmission and adaxial-abaxial distribution of emitting compounds in leaves of Christmas star (Euphorbia pulcherrima)

In situ fluorescence measurements have been used to investigate relative amounts of blue-green pigments and their distributions in plant leaves from Euphorbia pulcherrima. Advantage was taken from the fact that this species has white leaves on the top, with low pigment concentrations, and green leaves on the stem with ordinary pigment concentrations. Excitation- and emission spectra below 410 nm from white leaves, where pigment absorption is low, are not distorted by self-absorption. Absorption- and reflection spectra from white and green leaves were measured using a spectrophotometer equipped with an integrating sphere. The absorption spectra were used to correct recorded fluorescence spectra for self-absorption. Self-absorption corrected photosystem fluorescence from green leaves, modeling light transmission in leaf tissue exponentially, matches to the excitation/emission spectra from white leaves, apart from small differences due to the pigment concentrations and selective scattering. The introduced exponentially decaying transmission relation also predicts that the ratio of excitation spectra from a white and green leaf is in proportion to the absorption spectrum of the green leaf, which was validated for Photosystem II particle fluorescence. This relation was also used to find a scaled absorption spectrum responsible for blue-green emission, which was assumed to originate from lignin. Excitation/emission spectra of the blue-green fluorescence were decomposed into five components and their relative amounts from adaxial and abaxial sides of the leaves have been quantified. Fluorescence lifetime measurements of the leaves, upon 403 nm excitation, revealed three decay times corresponding to the lignin fluorophores emitting in blue and green spectral region, and indicated that emissions at 500 and 550 nm may originate from the same fluorophore residing in the two physically different environments.

Instant Detection of Synthetic Cannabinoids on Physical Matrices, Implemented on a Low-Cost, Ultraportable Device

Synthetic cannabinoids (SCs) make up a class of novel psychoactive substances (NPS), used predominantly in prisons and homeless communities in the U.K. SCs can have severe side effects, including psychosis, stroke, and seizures, with numerous reported deaths associated with their use. The chemical diversity of SCs presents the major challenge to their detection since approaches relying on specific molecular recognition become outdated almost immediately. Ideally one would have a generic approach to detecting SCs in portable settings. The problem of SC detection is more challenging still because the majority of SCs enter the prison estate adsorbed onto physical matrices such as paper, fabric, or herb materials. That is, regardless of the detection modality used, the necessary extraction step reduces the effectiveness and ability to rapidly screen materials on-site. Herein, we demonstrate a truly instant generic test for SCs, tested against real-world drug seizures. The test is based on two advances. First, we identify a spectrally silent region in the emission spectrum of most physical matrices. Second, the finding that background signals (including from autofluorescence) can be accurately predicted is based on tracking the fraction of absorbed light from the irradiation source. Finally, we demonstrate that the intrinsic fluorescence of a large range of physical substrates can be leveraged to track the presence of other drugs of interest, including the most recent iterations of benzodiazepines and opioids. We demonstrate the implementation of our presumptive test in a portable, pocket-sized device that will find immediate utility in prisons and law enforcement agencies around the world.

Intrinsic Fluorescence Markers for Food Characteristics, Shelf Life, and Safety Estimation: Advanced Analytical Approach

Food is a complex matrix of proteins, fats, minerals, vitamins, and other components. Various analytical methods are currently used for food testing. However, most of the used methods require sample preprocessing and expensive chemicals. New analytical methods are needed for quick and economic measurement of food quality and safety. Fluorescence spectroscopy is a simple and quick method to measure food quality, without sample preprocessing. This technique has been developed for food samples due to the application of a front-face measuring setup. Fluorescent compounds-fluorophores in the food samples are highly sensitive to their environment. Information about molecular structure and changes in food samples is obtained by the measurement of excitation-emission matrices of the endogenous fluorophores and by applying multivariate chemometric tools. Synchronous fluorescence spectroscopy is an advantageous screening mode used in food analysis. The fluorescent markers in food are amino acids tryptophan and tyrosine; the structural proteins collagen and elastin; the enzymes and co-enzymes NADH and FAD; vitamins; lipids; porphyrins; and mycotoxins in certain food types. The review provides information on the principles of the fluorescence measurements of food samples and the advantages of this method over the others. An analysis of the fluorescence spectroscopy applications in screening the various food types is provided.

Using Front-Face Fluorescence Spectroscopy and Biochemical Analysis of Honey to Assess a Marker for the Level of Varroa destructor Infestation of Honey Bee (Apis mellifera) Colonies

Varroa destructor is a parasitic mite responsible for the loss of honey bee (Apis mellifera) colonies. This study aimed to find a promising marker in honey for the bee colony infestation level using fluorescence spectroscopy and biochemical analyses. We examined whether the parameters of the honey samples' fluorescence spectra and biochemical parameters, both related to proteins and phenolics, may be connected with the level of honey bee colonies' infestation. The infestation level was highly positively correlated with the catalase activity in honey (r = 0.936). Additionally, the infestation level was positively correlated with the phenolic spectral component (r = 0.656), which was tentatively related to the phenolics in honey. No correlation was found between the diastase activity in honey and the colonies' infestation level. The results indicate that the catalase activity in honey and the PFC1 spectral component may be reliable markers for the V. destructor infestation level of the colonies. The obtained data may be related to the honey yield obtained from the apiaries.

Pickering Emulsions Stabilized by Lignin/Chitosan Nanoparticles for Biphasic Enzyme Catalysis

In this study, we construct a green and high-performance platform using Pickering emulsions for biphasic catalysis. The oil-in-water Pickering emulsions stabilized by the lignin/chitosan nanoparticles (Lig/Chi NPs) have great stability and alkali resistance, showing pH-responsive reversible emulsification and demulsification which can be recycled at least three times. The Pickering emulsion also has fluorescence and wide availability to different oil-to-water volume ratios, types of oil, storage times, temperatures, and ion concentrations. When this system is applied to the lipase-catalyzed reaction for the hydrolysis of p-nitrophenol palmitate, it will provide stable and large oil-water reaction interface areas, and the negatively charged lipase will enrich at the emulsion interface by electrostatic adsorption of the positively charged Lig/Chi NPs to achieve immobilization (lipase-Lig/Chi NPs). The reaction conversion rate can reach nearly 100% in 30 min, which is nearly three times higher than that of the conventional two-phase system. Moreover, the lipases in Pickering emulsion stabilized by Lig/Chi NPs exhibit great recyclability because of the protection of Lig/Chi NPs.

Lignin and organic free radicals in maize (Zea mays L.) seeds in response to aflatoxin B1 contamination: an optical and EPR spectroscopic study

BACKGROUND

Aflatoxin B₁ (AFB₁ ) is the most dangerous of the mycotoxins that contaminate cereal seeds naturally. A stress lignin formation is linked with the accumulation of reactive oxygen species causing a change in the redox status and formation of stable organic radicals, constituting the first layer of defense. The relationship between AFB₁ and changes in lignin organic free radicals in seeds is not known, nor is the part of the seed that is more targeted. Using optical and electron paramagnetic resonance spectroscopy, we investigated AFB₁ -induced changes in lignin and organic free radicals in seeds, and whether the inner and outer seed fractions differ in response to increasing AFB₁ .

RESULTS

Different changes in the content of lignin and free radicals with increasing AFB₁ concentrations were observed in the two seed fractions. There was a significant positive linear correlation (R = 0.9923, P = 0.00005) between lignin content and AFB₁ concentration in the outer fraction, and no correlation between the lignin content and the AFB₁ concentration in the inner fraction. We found a positive correlation between the area of the green spectral emission component (C4) and the AFB₁ concentration in the outer fraction.

CONCLUSIONS

To the best of our knowledge, the results showed, for the first time, that maize seed fractions respond differently to aflatoxin with regard to their lignin and organic free radical content. Lignin content and (C4) area may be reliable indicators for the screening of lignin changes against AFB₁ content in the seeds, and thus for seed protection capacity. © 2021 Society of Chemical Industry.

Characterization of the hierarchical architecture and micromechanical properties of walnut shell (Juglans regia L.)

In the present work a comprehensive characterization of the hierarchical architecture of the walnut shell (Juglans regia L.) was carried out using scanning electron microscopy (SEM), atomic force microscopy (AFM) and confocal laser scanning microscopy (CLSM). Furthermore, micromechanical properties (hardness, H_IT and elastic modulus, E_IT) of plant tissues were evaluated at cell wall level by applying the instrumented indentation technique (IIT). The complex architecture of the material was described in terms of four hierarchical levels (HL): endocarp (H1), plant tissues (H2), plant cells (H3) and cell wall (H4). Our findings revealed that the walnut shell consists of a multilayer structure (sclerenchyma tissue, ST; interface tissue, IT; porous tissue, PT; and flattened parenchyma tissue, FPT), where differences in the microstructure and composition of plant tissues generate parallel gradients along the cross-section. The indentation tests showed a functional gradient with a sandwich-like configuration, i.e., a lightweight and soft layer (PT, H_IT = 0.04 GPa) is located between two dense and hard layers (ST, H_IT = 0.33 GPa; FPT, H_IT = 0.28 GPa); where additionally there is an interface between ST and PT (IT, H_IT = 0.16 GPa). This configuration is a successful strategy designed by nature to improve the protection of the kernel by increasing the strength of the shell. Therefore, the walnut shell can be considered as a functionally graded material (FGM), which can be used as bioinspiration for the design of new functional synthetic materials. In addition, we proposed some structure-property-function relationships in the whole walnut shell and in each of the plant tissues.

Fluorescence Microscopy Methods for the Analysis and Characterization of Lignin

Lignin is one of the most studied and analyzed materials due to its importance in cell structure and in lignocellulosic biomass. Because lignin exhibits autofluorescence, methods have been developed that allow it to be analyzed and characterized directly in plant tissue and in samples of lignocellulose fibers. Compared to destructive and costly analytical techniques, fluorescence microscopy presents suitable alternatives for the analysis of lignin autofluorescence. Therefore, this review article analyzes the different methods that exist and that have focused specifically on the study of lignin because with the revised methods, lignin is characterized efficiently and in a short time. The existing qualitative methods are Epifluorescence and Confocal Laser Scanning Microscopy; however, other semi-qualitative methods have been developed that allow fluorescence measurements and to quantify the differences in the structural composition of lignin. The methods are fluorescence lifetime spectroscopy, two-photon microscopy, Föster resonance energy transfer, fluorescence recovery after photobleaching, total internal reflection fluorescence, and stimulated emission depletion. With these methods, it is possible to analyze the transport and polymerization of lignin monomers, distribution of lignin of the syringyl or guaiacyl type in the tissues of various plant species, and changes in the degradation of wood by pulping and biopulping treatments as well as identify the purity of cellulose nanofibers though lignocellulosic biomass.

Tunable Light Emission from Lignin: Various Photoluminescence Properties Controlled by the Lignocellulosic Species, Extraction Method, Solvent, and Polymer

This report describes the tunable light emission from lignin, which was achieved by carefully selecting the lignocellulosic species, extraction method, solvent, and polymer. Lignins comprising various taxonomic species with distinct primary structures exhibited diverse photoluminescence (PL) intensities and spectral patterns. Investigations probing how the solvent affects the PL properties revealed that the PL quenching phenomenon originated from the decreasing distance between aromatic moieties (luminophores). Therefore, polymers can play key roles as media to modulate the distance between luminophores, and the PL intensity can be enhanced by employing a relatively stiff polymer. In terms of the emission color, the PL spectral pattern can be tuned by changing the lignin primary structures or by deprotonating the phenolic hydroxyl groups. By modulating these influencing factors, various light emissions were obtained from lignins in solutions and transparent solid materials.

Nonlinear imaging and vibrational spectroscopic analysis of cellulosic fibres treated with COEX® flame-retardant for tapestry preservation

This innovative approach, based on SHG/TPEF imaging and vibrational spectroscopic techniques, investigates the effect of flame-retardant COEX® treatment on flax and cotton fibres by relating micrometric structural properties to the chemical changes.

Lignosulfonate/diblock copolymer polyion complexes with aggregation-enhanced and pH-switchable fluorescence for information storage and encryption

Employing natural polymers as building blocks is favorable to construct sustainable functional materials and realize biomass utilization. Here we developed a series of supramolecular polyion complexes (PICs) composed of lignosulfonate and double-hydrophilic diblock copolymer poly(ethylene oxide-b-N, N-dimethylaminoethyl methacrylate) (PEO₁₁₄-b-PDMAEMA₂₄), which performed a blue emission with quenching-enhancing tendency and copolymer distribution inversion-involved assembling transformation at pH 5.6 and monotonic greenish-blue fluorescence promotion at pH 9.5 by increasing PEO₁₁₄-b-PDMAEMA₂₄ contents. Electrostatic interactions and multiple hydrogen bonds were revealed controlled the assembling behavior and affected the emission via altering the restriction of molecular motion, through-space conjunction, and non-luminous complexation. The multiple interacting sites and special topology of diblock copolymer contributed to the efficient fluorescence regulation. Information writing-erasing and encryption-decryption systems were established by utilizing emission intensity regulation and pH-responsive emission chromism. This work paved a new way to enhance lignin fluorescence and broadened potential applications of lignin composites in realms of sensing, imaging, monitoring, and anticounterfeiting.

Laser Induced Method to Produce Curcuminoid-Silanol Thin Films for Transdermal Patches Using Irradiation of Turmeric Target

A new possible method to produce a transdermal patch is proposed in this paper. The study refers to the pulsed laser deposition method (PLD) applied on turmeric target in order to obtain thin layers. Under high power laser irradiation of 532 nm wavelength, thin films containing curcuminoids were obtained on different substrates such as glass and quartz (laboratory investigation) and hemp fabric (practical application). Compared FTIR, SEM-EDS and LIF analyses proved that the obtained thin film chemical composition is mainly demethoxycurcumin and bisdemethoxycurcumin which is evidence that most of the curcumin from turmeric has been demethixylated during laser ablation. Silanol groups with known role into dermal reconstruction are evidenced in both turmeric target and curcuminoid thin films. UV–VIS reflection spectra show the same characteristics for all the curcuminoid thin films, indicating that the method is reproducible. The method proves to be successful for producing a composite material, namely curcuminoid transdermal patch with silanol groups, using directly turmeric as target in the thin film deposited by pulsed laser technique. Double layered patch curcuminoid—silver was produced under this study, proving compatibility between the two deposited layers. The silver layer added on curcuminoid-silanol layer aimed to increase antiseptic properties to the transdermal patch.

Two-photon fluorescence and second harmonic generation hyperspectral imaging of old and modern spruce woods

Spruce is the commonly-used tonewood for the top plate of violin-family instruments, such as violins and cellos. The wood properties can critically determine the acoustic quality. It's been shown the wood of famous old instruments differ from modern ones due to chemical treatment and aging. To reveal the differences microscopically in both spatial and spectral domains, a two-photon hyperspectral system has been applied to investigate the autofluorescence and second harmonic generation within wood samples. Not only the cellular structures were observed through optical sectioning, but the spectral variations were revealed among different age wood samples and different cellular structures.

Morphological and Wettability Properties of Thin Coating Films Produced from Technical Lignins

Technical lignins are widely available as side streams from pulping and biorefining processes. The aromatic structure of such lignins could be exploited in coating formulations to provide antioxidant or UV-blocking functionalities to packaging films. In this study, six technical lignins sourced from different plant species by given isolation/modification methods were compared for their composition, molar mass, and functional groups. The lignins were then used to prepare thin spin-coated films from aqueous ammonia media. All the lignins formed ultrathin (<12 nm), smooth (roughness < 2 nm), and continuous films that fully covered the solid support. Most of the films contained nanometer-sized particles, while those from water-insoluble lignins also presented larger particulate features, which likely originated from macromolecular association during solvent evaporation. These latter films had water contact angles (WCAs) between 40 and 60°, corresponding to a surface energy of 42-48 mJ/m² (determined by Zisman plots). For comparison, the water wettability measured on lignin pellets obtained by mechanical compression tracked closely with the WCA obtained from the respective thin films. Considering the widely diverse chemical, molecular, and structural properties of the tested lignins, comprehensively documented here by using a battery of techniques, the solubility in water was found to be the most important and generic parameter to characterize the thin films. This points to the possibility of developing lignin coatings with predictable wetting behavior.

Autofluorescence in Plants

Plants contain abundant autofluorescent molecules that can be used for biochemical, physiological, or imaging studies. The two most studied molecules are chlorophyll (orange/red fluorescence) and lignin (blue/green fluorescence). Chlorophyll fluorescence is used to measure the physiological state of plants using handheld devices that can measure photosynthesis, linear electron flux, and CO2 assimilation by directly scanning leaves, or by using reconnaissance imaging from a drone, an aircraft or a satellite. Lignin fluorescence can be used in imaging studies of wood for phenotyping of genetic variants in order to evaluate reaction wood formation, assess chemical modification of wood, and study fundamental cell wall properties using Förster Resonant Energy Transfer (FRET) and other methods. Many other fluorescent molecules have been characterized both within the protoplast and as components of cell walls. Such molecules have fluorescence emissions across the visible spectrum and can potentially be differentiated by spectral imaging or by evaluating their response to change in pH (ferulates) or chemicals such as Naturstoff reagent (flavonoids). Induced autofluorescence using glutaraldehyde fixation has been used to enable imaging of proteins/organelles in the cell protoplast and to allow fluorescence imaging of fungal mycelium.

Differences in the Structural Chemical Composition of the Primary Xylem of Cactaceae: A Topochemical Perspective

The xylem of Cactaceae is a complex system with different types of cells whose main function is to conduct and store water, mostly during the development of primary xylem, which has vessel elements and wide-band tracheids. The anatomy of primary xylem of Cactaceae has been widely studied, but little is known about its chemical composition. The aim of this study was to determine the structural chemical composition of the primary xylem of Cactaceae and to compare it with the anatomy in the group. Seeds from eight cacti species were used, representing the Pereskioideae, Opuntioideae, and Cactoideae subfamilies. Seeds were germinated and grown for 8 months. Subsequently, only the stem of the seedling was selected, dried, milled, and processed following the TAPPI T-222 om-02 norm; lignin was quantified using the Klason method and cellulose with the Kurshner-Höffer method. Using Fourier transform infrared spectroscopy, the percentage of syringyl and guaiacyl in lignin was calculated. Seedlings of each species were fixed, sectioned, and stained for their anatomical description and fluorescence microscopy analysis for the topochemistry of the primary xylem. The results showed that there were significant differences between species (p < 0.05), except in the hemicelluloses. Through a principal component analysis, it was found that the amount of extractive-free stem and hot water-soluble extractives were the variables that separated the species, followed by cellulose and hemicelluloses since the seedlings developed mainly parenchyma cells and the conductive tissue showed vessel elements and wide-band tracheids, both with annular and helical thickenings in secondary walls. The type of lignin with the highest percentage was guaiacyl-type, which is accumulated mainly in the vessels, providing rigidity. Whereas in the wide-band tracheids from metaxylem, syringyl lignin accumulated in the secondary walls S2 and S3, which permits an efficient flow of water and gives the plant the ability to endure difficult conditions during seedling development. Only one species can be considered to have paedomorphosis since the conductive elements had a similar chemistry in primary and secondary xylem.

Rapid Determination of the Distribution of Cellulose Nanomaterial Aggregates in Composites Enabled by Multi-Channel Spectral Confocal Microscopy

There is increased interest in the use of cellulose nanomaterials for the mechanical reinforcement of composites due to their high stiffness and strength. However, challenges remain in accurately determining their distribution within composite microstructures. We report the use of a range of techniques used to image aggregates of cellulose nanocrystals (CNCs) greater than 10 µm2 within a model thermoplastic polymer. While Raman imaging accurately determines CNC aggregate size, it requires extended periods of analysis and the limited observable area results in poor reproducibility. In contrast, staining the CNCs with a fluorophore enables rapid acquisition with high reproducibility, but overestimates the aggregate size as CNC content increases. Multi-channel spectral confocal laser scanning microscopy is presented as an alternative technique that combines the accuracy of Raman imaging with the speed and reproducibility of conventional confocal laser scanning microscopy, enabling the rapid determination of CNC aggregate distribution within composites.

Lignosulfonate: A Convenient Fluorescence Resonance Energy Transfer Platform for the Construction of a Ratiometric Fluorescence pH-Sensing Probe

Lignin is a kind of natural fluorescent polymer material. However, the application based on the fluorescent property of lignin was rarely reported. Herein, a noncovalent lignin-based fluorescence resonance energy transfer (FRET) system was readily constructed by physical blending method with spirolactam rhodamine B (SRhB) and lignosulfonate (LS) as the acceptor and donor groups, respectively. The FRET behavior, self-assembly, and energy transfer mechanism of SRhB/LS composite were systematically studied. It was demonstrated that LS could be used as a convenient aptamer as energy donor to construct water-soluble ratiometric sensors because of its inherent property of intramicelle energy transfer cascades. Our results not only present a facile and general strategy for producing lignin-based functional material but also provide a fundamental understanding about lignin fluorescence to promote the functional and high-valued applications of lignin fluorescence characteristic.

Oxygen Sensing Based on the Yellowing of Newspaper

Newspaper is known to turn yellow over time. We show here that this yellowing process is sensitive to oxygen when exposed to UV light, leading to oxygen sensing. Oxygen sensing is critical to many applications, including industrial process control and breath analysis, but the existing oxygen sensors have limitations, especially for breath analysis that operates at 100% humidity. The UV irradiation also triggers fluorescence emission from newspaper, and the fluorescence intensity depends on oxygen concentration, providing an additional oxygen sensing method. Newspaper is stable in ambient air, and reactive to oxygen only with UV activation, which overcomes the instability issue of a typical colorimetric sensor in ambient air. The newspaper oxygen sensor works in 100% relative humidity air, containing various interferents. These unique properties of newspaper promise low cost and reliable oxygen sensing applications.

Seeing biomass recalcitrance through fluorescence

Lignocellulosic biomass is the only renewable carbon resource available in sufficient amount on Earth to go beyond the fossil-based carbon economy. Its transformation requires controlled breakdown of polymers into a set of molecules to make fuels, chemicals and materials. But biomass is a network of various inter-connected polymers which are very difficult to deconstruct optimally. In particular, saccharification potential of lignocellulosic biomass depends on several complex chemical and physical factors. For the first time, an easily measurable fluorescence properties of steam-exploded biomass samples from miscanthus, poplar and wheat straw was shown to be directly correlated to their saccharification potential. Fluorescence can thus be advantageously used as a predictive method of biomass saccharification. The loss in fluorescence occurring after the steam explosion pretreatment and increasing with pretreatment severity does not originate from the loss in lignin content, but rather from a decrease of the lignin β-aryl-ether linkage content. Fluorescence lifetime analysis demonstrates that monolignols making lignin become highly conjugated after steam explosion pretreatment. These results reveal that lignin chemical composition is a more important feature to consider than its content to understand and to predict biomass saccharification.

Analysis of Lignin Composition and Distribution Using Fluorescence Laser Confocal Microspectroscopy

Lignin is a polyphenolic polymer specifically accumulating in the cell walls of xylem cells in higher vascular plants. Far from being homogeneous, the lignification of xylem cell walls varies in deposition site, quantity, composition and macromolecular conformation depending on the cell wall compartment, cell type, cell developmental stage and plant species. Here, we describe how confocal microspectroscopy methods using lignin autofluorescence can be used to evaluate the relative lignin amounts, its spatial distribution and composition at the cellular and sub-cellular levels in both isolated cells and histological cross-sections of plant tissues.

Fluorescent pH-Sensing Probe Based on Biorefinery Wood Lignosulfonate and Its Application in Human Cancer Cell Bioimaging

A water-soluble, ratiometric fluorescent pH probe, L-SRhB, was synthesized via grafting spirolactam Rhodamine B (SRhB) to lignosulfonate (LS). As the ring-opening product of L-SRhB, FL-SRhB was also prepared. The pH-response experiment indicated that L-SRhB showed a rapid response to pH changes from 4.60 to 6.20 with a pK_a of 5.35, which indicated that L-SRhB has the potential for pH detection of acidic organelle. In addition, the two probes were internalized successfully by living cells through the endocytosis pathway and could distinguish normal cells from cancer cells by different cell staining rates. In addition, L-SRhB showed obvious cytotoxicity to cancer cells, whereas it was nontoxic to normal cells in the same condition. L-SRhB might have potential in cancer therapy. L-SRhB might be a promising ratiometric fluorescent pH sensor and bioimaging dye for the recognition of cancer cells. The results also provided a new perspective to the high-value utilization of lignin.

Specific tracking of xylan using fluorescent-tagged carbohydrate-binding module 15 as molecular probe

BACKGROUND

Xylan has been identified as a physical barrier which limits cellulose accessibility by covering the outer surface of fibers and interfibrillar space. Therefore, tracking xylan is a prerequisite for understanding and optimizing lignocellulosic biomass processes.

RESULTS

In this study, we developed a novel xylan tracking approach using a two-domain probe called OC15 which consists of a fusion of Cellvibrio japonicus carbohydrate-binding domain 15 with the fluorescent protein mOrange2. The new probe specifically binds to xylan with an affinity similar to that of CBM15. The sensitivity of the OC15-xylan detection approach was compared to that of standard methods such as X-ray photoelectron spectroscopy (XPS) and chemical composition analysis (NREL/TP-510-42618). All three approaches were used to analyze the variations of xylan content of kraft pulp fibers. XPS, which allows for surface analysis of fibers, did not clearly indicate changes in xylan content. Chemical composition analysis responded to the changes in xylan content, but did not give any specific information related to the fibers surface. Interestingly, only the OC15 probe enabled the highly sensitive detection of xylan variations at the surface of kraft pulp fibers. At variance with the other methods, the OC15 probe can be used in a high throughput format.

CONCLUSIONS

We developed a rapid and high throughput approach for the detection of changes in xylan exposure at the surface of paper fibers. The introduction of this method into the lignocellulosic biomass-based industries should revolutionize the understanding and optimization of most wood biomass processes.

Aggregation-induced emission: the origin of lignin fluorescence

Aggregation-induced emission plays a role in the origin of lignin fluorescence owing to the agglomeration of carbonyl groups and restriction of intramolecular rotation.

Evidence of the late lignification of the G-layer in Simarouba tension wood, to assist understanding how non-G-layer species produce tensile stress

To recover verticality after disturbance, angiosperm trees produce 'tension wood' allowing them to bend actively. The driving force of the tension has been shown to take place in the G-layer, a specific unlignified layer of the cell wall observed in most temperate species. However, in tropical rain forests, the G-layer is often absent and the mechanism generating the forces to reorient trees remains unclear. A study was carried out on tilted seedlings, saplings and adult Simarouba amara Aubl. trees-a species known to not produce a G-layer. Microscopic observations were done on sections of normal and tension wood after staining or observed under UV light to assess the presence/absence of lignin. We showed that S. amara produces a cell-wall layer with all of the characteristics typical of G-layers, but that this G-layer can be observed only as a temporary stage of the cell-wall development because it is masked by a late lignification. Being thin and lignified, tension wood fibres cannot be distinguished from normal wood fibres in the mature wood of adult trees. These observations indicate that the mechanism generating the high tensile stress in tension wood is likely to be the same as that in species with a typical G-layer and also in species where the G-layer cannot be observed in mature cells.

Xylem parenchyma cell walls lack a gravitropic response in conifer compression wood

Cell wall fluorescence and immunocytochemistry demonstrate that xylem parenchyma cell walls do not show changes in structure and composition related to gravitropic response comparable to those of tracheids, even when they have lignified secondary cell walls. Tracheid cell walls in compression wood have altered composition and structure which generates the strain responsible for correction of stem lean as part of the gravitropic response of woody plants. Xylem parenchyma cell walls vary among conifer species and can be lignified secondary walls (spruce) or unlignified primary walls (pine). It can be expected that xylem parenchyma with lignified secondary cell walls might show features of compression wood comparable to those of tracheids that have a similar type of cell wall. A comparison of xylem parenchyma cell walls in normal and compression wood in species with lignified and non-lignified parenchyma cell walls provides a unique opportunity to understand the process of reaction wood formation in conifers. Using both UV/visible fluorescence microscopy of cell wall fluorophores and immunocytochemistry of galactan and mannan epitopes, we demonstrate that xylem parenchyma cell walls do not show the changes in composition and structure typical of compression wood tracheids. Adjacent cells of different types but with similar cell wall structure can undergo cell wall developmental changes related to support or defence functions independent of their neighbours. Tracheids are sensitive to gravitropic signals while xylem parenchyma cells are not.

Comparative transcriptome analysis of developmental stages of the Limonium bicolor leaf generates insights into salt gland differentiation

With the expansion of saline land worldwide, it is essential to establish a model halophyte to study the salt-tolerance mechanism. The salt glands in the epidermis of Limonium bicolor (a recretohalophyte) play a pivotal role in salt tolerance by secreting excess salts from tissues. Despite the importance of salt secretion, nothing is known about the molecular mechanisms of salt gland development. In this study, we applied RNA sequencing to profile early leaf development using five distinct developmental stages, which were quantified by successive collections of the first true leaves of L. bicolor with precise spatial and temporal resolution. Specific gene expression patterns were identified for each developmental stage. In particular, we found that genes controlling salt gland differentiation in L. bicolor may evolve in a trichome formation, which was also confirmed by mutants with increased salt gland densities. Genes involved in the special ultrastructure of salt glands were also elucidated. Twenty-six genes were proposed to participate in salt gland differentiation. Our dataset sheds light on the molecular processes underpinning salt gland development and thus represents a first step towards the bioengineering of active salt-secretion capacity in crops.

Optimized Monitoring of Production of Cellulose Nanowhiskers fromOpuntia ficus-indica(Nopal Cactus)

Preparation of cellulose nanowhiskers (CNWs) has grown significantly because they are useful for a wide range of applications. Additional advantage in their design requires that they meet the following characteristics: nontoxicity, abundance, sustainability, renewability, and low cost. To address these requirements, nanowhiskers were prepared fromOpuntia ficus-indica(nopal) cellulose by acid hydrolysis. Monitoring the process of CNWs preparation is necessary to ensure maximum yield and purity of the end product. In this study, the cellulose preparation was monitored by analyzing microscopic morphology by SEM; the purity degree was determined by fluorescence microscopy as a novel and rapid technique, and FTIR spectroscopy was used for confirmation. The additional parameters that monitored the process were the crystallinity index by X-ray diffraction and the size of the particle by dynamic light scattering (DLS). Nopal cellulose was found to be comparable to commercial microcrystalline cellulose. The use ofOpuntia ficus-indicais a viable alternative for the production of highly pure CNWs and the strategy to supervise the preparation process was rapid.

Biotemplating plasmonic nanoparticles using intact microfluidic vasculature of leaves

Leaves are an abundant natural resource, and consist of a sophisticated microfluidic network of veins that transport nutrients and water, thereby enabling photosynthesis. Here, we simultaneously exploit the microfluidics as well as chemistry of processed leaf vasculature (venation) in order to template the in situ generation of plasmonic metal (gold and silver) nanoparticles under ambient conditions. This biotemplating approach involves capillary flow of metal salts through skeleton leaf vasculature, and does not require additional reducing agents for plasmonic nanoparticle formation. Gold nanoparticles, 30-40 nm in diameter, and silver nanoparticles, approximately 9 nm in diameter, were formed within the intact leaf vasculature using this method. Absorption spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electron diffraction analyses were employed to ascertain the formation of nanoparticles in the leaf veins. Fourier transform infrared (FT-IR) spectroscopy was employed in order to obtain insights into functional groups responsible for formation of the plasmonic nanoparticles within the leaves. Gold nanoparticles, templated within leaves, demonstrated excellent catalytic properties, thereby imparting catalytic and plasmonic properties to the leaf itself. Furthermore, nanoparticles can be recovered from the leaves as soluble dispersions by simply combusting the organic leaf matter. Taken together, this is a simple yet powerful biotemplating approach for the generation of plasmonic nanoparticles and formation of biotic-abiotic structures for diverse, low-cost applications in sensing, catalysis, and medicine.

Monitoring lignocellulosic bioethanol production processes using Raman spectroscopy

Process control automation in the emerging biorefinery industry may be achieved by applying effective methods for monitoring compound concentrations during the production processes. This study examines the application of Raman spectroscopy with an excitation wavelength of 785nm and an immersion probe for in situ monitoring the progression of pretreatment, hydrolysis and fermentation processes in the production of lignocellulosic ethanol. Raman signals were attenuated by light scattering cells and lignocellulosic particulates, which the quantification method to some degree could correct for by using an internal standard in the spectra. Allowing particulates to settle by using a slow stirring speed further improved results, suggesting that Raman spectroscopy should be used in combination with continuous separation when used to monitor process mixtures with large amounts of particulates. The root mean square error of prediction (RMSE) of ethanol and glucose measured in real-time was determined to be 0.98g/L and 1.91g/L respectively.

High-throughput enzymatic hydrolysis of lignocellulosic biomass via in-situ regeneration

The high cost of lignocellulolytic enzymes is one of the main barriers towards the development of economically competitive biorefineries. Enzyme engineering can be used to significantly increase the production rate as well as specific activity of enzymes. However, the success of enzyme optimization efforts is currently limited by a lack of robust high-throughput (HTP) cellulase screening platforms for insoluble pretreated lignocellulosic substrates. We have developed a cost-effective microplate based HTP enzyme-screening platform for ionic liquid (IL) pretreated lignocellulose. By performing in-situ biomass regeneration in micro-volumes, we can volumetrically meter biomass (sub-mg loading) and also precisely control the amount of residual IL for engineering novel IL-tolerant cellulases. Our platform only requires straightforward liquid-handling steps and allows the integration of biomass regeneration, washing, saccharification, and imaging steps in a single microtiter plate. The proposed method can be used to screen individual cellulases as well as to develop novel cellulase cocktails.

Hitherto unrecognized fluorescence properties of coniferyl alcohol

We instituted a quasi-quality assurance program for demonstrating coniferyl alcohol’s fluorescence and fluorescence diminishment following enzymatic oxidation. The magnitude of diminishment was a measure of catalysis. High throughput screening was performed in pseudo-kinetic and endpoint modes by measuring the fluorescence at 416 nm following excitation at 290, 310 or 340 nm. Dose-response tracings were linear between two and three orders of magnitude with average limits of detection and quantitation of 1.8 and 6.9 μM coniferyl alcohol, respectively. Oxidation was evident with 0.025 μg/mL laccase or 0.003 μg/mL peroxidase or inside 5 min using 0.5 μg/mL laccase or 5 μM substrate. Sodium chloride inhibited (IC₅₀, 25 mM) laccase oxidation of coniferyl alcohol. Fluorescence from 10 concentrations (1 to 1000 μM) of coniferyl alcohol was stable for 24 hours over 14 excitation/emission cycles at 3 different combinations of excitation and emission wavelengths. In conclusion, coniferyl alcohol absorption and fluorescence assays should facilitate biomass lignin analyses and improve delignification.

Application of Asymmetric Model in Analysis of Fluorescence Spectra of Biologically Important Molecules

Having a valid mathematical model for structureless emission band shapes is important when deconvoluting fluorescence spectra of complex molecules. We propose a new asymmetric model for emission spectra of five organic molecules containing aromatic ring: catechol, coniferyl alcohol, hydroquinone, phenylalanine and tryptophan. For each molecule, a series of emission spectra, varying in excitation wavelength, were fitted with the new model as well as with two other analytical expressions: log-normal, described previously in the literature, and sigmoid-exponential. Their deconvolution into two, three and four Gaussian components was also performed, in order to estimate the number of symmetric components needed to obtain a better fitting quality than that of the asymmetric models. Four subtypes of the new model, as well as the log-normal one, did not differ significantly in their fitting errors, while the sigmoid-exponential model showed a significantly worse fit. Spectra of two mixtures: hydroquinone-coniferyl alcohol and hydroquinone-tryptophan were deconvoluted into two asymmetric and four Gaussian components. Positions of asymmetric components of mixtures matched those of separate molecules, while Gaussian did not. Component analysis of a polymer molecule, lignin, was also performed. In this more complex case asymmetric and Gaussian components also grouped in alternating positions.