Interplay of electrolyte concentration and molecular weight of polyDADMAC on cellulose surface adsorption

Cationic polyelectrolytes (PEs) are commonly used additives in manufacturing of cellulose based products such as regenerated fibers and paper to tailor their product properties. Here we are studying the adsorption of poly(diallyldimethylammonium chloride), PD, on cellulose, using in situ surface plasmon resonance spectroscopy (SPR) measurements. We employ model surfaces from regenerated cellulose xanthate (CX) and trimethylsilyl cellulose (TMSC), mimicking industrially relevant regenerated cellulose substrates. The effects of the PDs molecular weight were strongly depending on the ionic strength and type of electrolyte (NaCl vs CaCl₂). Without electrolytes, the adsorption was monolayer-type, i.e. independent of molecular weight. At moderate ionic strength, adsorption increased due to more pronounced PE coiling, while at high ionic strength electrostatic shielding strongly reduced adsorption of PDs. Results exhibited pronounced differences for the chosen substrates (cellulose regenerated from xanthate (CX_reg) vs. regenerated from trimethylsilyl cellulose, TMSC_reg). Consistently higher adsorbed amounts of the PD were determined on CX_reg surfaces compared TMSC. This can be attributed to a more negative zeta potential, a higher AFM roughness and a higher degree of swelling (investigated by QCM-D) of the CX_reg substrates.

Self-Assembly of Soft Cellulose Nanospheres into Colloidal Gel Layers with Enhanced Protein Adsorption Capability for Next-Generation Immunoassays

Soft cationic core/shell cellulose nanospheres can deform and interpenetrate allowing their self-assembly into densely packed colloidal nanogel layers. Taking advantage of their water-swelling capacity and molecular accessibility, the nanogels are proposed as a new and promising type of coating material to immobilize bioactive molecules on thin films and paper. The specific and nonspecific interactions between the cellulosic nanogel and human immunoglobulin G as well as bovine serum albumin (BSA) are investigated. Confocal microscopy, electroacoustic microgravimetry, and surface plasmon resonance are used to access information about the adsorption behavior and viscoelastic properties of self-assembled nanogels. A significant BSA adsorption capacity on nanogel layers (17 mg m^-2 ) is measured, 300% higher compared to typical polymer coatings. This high protein affinity further confirms the promise of the introduced colloidal gel layer, in increasing sensitivity and advancing a new generation of substrates for a variety of applications, including immunoassays, as demonstrated in this work.

Affinity of Serum Albumin and Fibrinogen to Cellulose, Its Hydrophobic Derivatives and Blends

This work describes the preparation of spin-coated thin polymer films composed of cellulose (CE), ethyl cellulose (EC), and cellulose acetate (CA) in the form of bi- or mono-component coatings on sensors of a quartz crystal microbalance with dissipation monitoring (QCM-D). Depending on the composition and derivative, hydrophilicity can be varied resulting in materials with different surface properties. The surfaces of mono- and bi-component films were also analyzed by atomic force microscopy (AFM) and large differences in the morphologies were found comprising nano- to micrometer sized pores. Extended protein adsorption studies were performed by a QCM-D with 0.1 and 10 mg mL⁻¹ bovine serum albumin (BSA) and 0.1 and 1 mg mL⁻¹ fibrinogen from bovine plasma in phosphate buffered saline. Analysis of the mass of bound proteins was conducted by applying the Voigt model and a comparison was made with the Sauerbrey wet mass of the proteins for all films. The amount of deposited proteins could be influenced by the composition of the films. It is proposed that the observed effects can be exploited in biomaterial science and that they can be used to extent the applicability of bio-based polymer thin films composed of commercial cellulose derivatives.

Cellulose Nano-Films as Bio-Interfaces

Cellulose, the most abundant polymer on earth, has enormous potential in developing bio-friendly, and sustainable technological products. In particular, cellulose films of nanoscale thickness (1-100 nm) are transparent, smooth (roughness <1 nm), and provide a large surface area interface for biomolecules immobilization and interactions. These attractive film properties create many possibilities for both fundamental studies and applications, especially in the biomedical field. The three liable-OH groups on the monomeric unit of the cellulose chain provide schemes to chemically modify the cellulose interface and engineer its properties. Here, the cellulose thin film serves as a substrate for biomolecules interactions and acts as a support for bio-diagnostics. This review focuses on the challenges and opportunities provided by engineering cellulose thin films for controlling biomolecules interactions. The first part reviews the methods for preparing cellulose thin films. These are by dispersing or dissolving pure cellulose or cellulose derivatives in a solvent to coat a substrate using the spin coating, Langmuir-Blodgett, or Langmuir-Schaefer method. It is shown how different cellulose sources, preparation, and coating methods and substrate surface pre-treatment affect the film thickness, roughness, morphology, crystallinity, swelling in water, and homogeneity. The second part analyses the bio-macromolecules interactions with the cellulose thin film interfaces. Biomolecules, such as antibodies and enzymes, are adsorbed at the cellulose-liquid interface, and analyzed dry and wet. This highlights the effect of film surface morphology, thickness, crystallinity, water intake capacity, and surface pre-treatment on biomolecule adsorption, conformation, coverage, longevity, and activity. Advance characterization of cellulose thin film interface morphology and adsorbed biomolecules interactions are next reviewed. X-ray and neutron scattering/reflectivity combined with atomic force microscopy (AFM), quartz crystal microbalance (QCM), microscopy, and ellipsometer allow visualizing, and quantifying the structural morphology of cellulose-biomolecule interphase and the respective biomolecules conformations, kinetics, and sorption mechanisms. This review provides a novel insight on the advantages and challenges of engineering cellulose thin films for biomedical applications. This is to foster the exploration at the molecular level of the interaction mechanisms between a cellulose interface and adsorbed biomolecules with respect to adsorbed molecules morphology, surface coverage, and quantity. This knowledge is to engineer a novel generation of efficient and functional biomedical devices.

Ultrathin Films of Cellulose: A Materials Perspective

A literature review on ultrathin films of cellulose is presented. The review focuses on different deposition methods of the films-all the way from simple monocomponent films to more elaborate multicomponent structures-and the use of the film structures in the vast realm of materials science. The common approach of utilizing cellulose thin films as experimental models is therefore omitted. The reader will find that modern usage of cellulose thin films constitutes an exciting emerging area within materials science and it goes far beyond the traditional usage of the films as model systems.

Design of Friction, Morphology, Wetting, and Protein Affinity by Cellulose Blend Thin Film Composition

Cellulose derivate phase separation in thin films was applied to generate patterned films with distinct surface morphology. Patterned polymer thin films are utilized in electronics, optics, and biotechnology but films based on bio-polymers are scarce. Film formation, roughness, wetting, and patterning are often investigated when it comes to characterization of the films. Frictional properties, on the other hand, have not been studied extensively. We extend the fundamental understanding of spin coated complex cellulose blend films via revealing their surface friction using Friction Force Microscopy (FFM). Two cellulose derivatives were transformed into two-phase blend films with one phase comprising trimethyl silyl cellulose (TMSC) regenerated to cellulose with hydroxyl groups exposed to the film surface. Adjusting the volume fraction of the spin coating solution resulted in variation of the surface fraction with the other, hydroxypropylcellulose stearate (HPCE) phase. The film morphology confirmed lateral and vertical separation and was translated into effective surface fraction. Phase separation as well as regeneration contributed to the surface morphology resulting in roughness variation of the blend films from 1.1 to 19.8 nm depending on the film composition. Friction analysis was successfully established, and then revealed that the friction coefficient of the films could be tuned and the blend films exhibited lowered friction force coefficient compared to the single-component films. Protein affinity of the films was investigated with bovine serum albumin (BSA) and depended mainly on the surface free energy (SFE) while no direct correlation with roughness or friction was found. BSA adsorption on film formed with 1:1 spinning solution volume ratio was an outlier and exhibited unexpected minimum in adsorption.

Lectins at Interfaces-An Atomic Force Microscopy and Multi-Parameter-Surface Plasmon Resonance Study

Lectins are a diverse class of carbohydrate binding proteins with pivotal roles in cell communication and signaling in many (patho)physiologic processes in the human body, making them promising targets in drug development, for instance, in cancer or infectious diseases. Other applications of lectins employ their ability to recognize specific glycan epitopes in biosensors and glycan microarrays. While a lot of research has focused on lectin interaction with specific carbohydrates, the interaction potential of lectins with different types of surfaces has not been addressed extensively. Here, we screen the interaction of two specific plant lectins, Concanavalin A and Ulex Europaeus Agglutinin-I with different nanoscopic thin films. As a control, the same experiments were performed with Bovine Serum Albumin, a widely used marker for non-specific protein adsorption. In order to test the preferred type of interaction during adsorption, hydrophobic, hydrophilic and charged polymer films were explored, such as polystyrene, cellulose, N,-N,-N-trimethylchitosan chloride and gold, and characterized in terms of wettability, surface free energy, zeta potential and morphology. Atomic force microscopy images of surfaces after protein adsorption correlated very well with the observed mass of adsorbed protein. Surface plasmon resonance spectroscopy studies revealed low adsorbed amounts and slow kinetics for all of the investigated proteins for hydrophilic surfaces, making those resistant to non-specific interactions. As a consequence, they may serve as favorable supports for biosensors, since the use of blocking agents is not necessary.

Surface-Modified Mesh Filter for Direct Nucleic Acid Extraction and its Application to Gene Expression Analysis

Rapid and convenient isolation of nucleic acids (NAs) from cell lysate plays a key role for onsite gene expression analysis. Here, this study achieves one-step and efficient capture of NA directly from cell lysate by developing a cationic surface-modified mesh filter (SMF). By depositing cationic polymer via vapor-phase deposition process, strong charge interaction is introduced on the surface of the SMF to capture the negatively charged NAs. The NA capturing capability of SMF is confirmed by X-ray photoelectron spectroscopy, fluorescent microscopy, and zeta potential measurement. In addition, the genomic DNAs of Escherichia Coli O157:H7 can be extracted by the SMF from artificially infected food, and fluorescent signal is observed on the surface of SMF after amplification of target gene. The proposed SMF is able to provide a more simplified, convenient, and fast extraction method and can be applied to the fields of food safety testing, clinical diagnosis, or environmental pollutant monitoring.

On the formation of Bi2S3-cellulose nanocomposite films from bismuth xanthates and trimethylsilyl-cellulose

The synthesis and characterization of bismuth sulfide-cellulose nanocomposite thin films was explored. The films were prepared using organosoluble precursors, namely bismuth xanthates for Bi₂S₃ and trimethylsilyl cellulose (TMSC) for cellulose. Solutions of these precursors were spin coated onto solid substrates yielding homogeneous precursor films. Afterwards, a heating step under inert atmosphere led to the formation of thin nanocomposite films of bismuth sulfide nanoparticles within the TMSC matrix. In a second step, the silyl groups were cleaved off by vapors of HCl yielding bismuth sulfide/cellulose nanocomposite films. The thin films were characterized by a wide range of surface sensitive techniques such as atomic force microscopy, attenuated total reflection infrared spectroscopy, transmission electron microscopy and wettability investigations. In addition, the formation of the nanoparticle directly in the TMSC matrix was investigated in situ by GI-SWAXS using a temperature controlled sample stage.

Direct-Write Fabrication of Cellulose Nano-Structures via Focused Electron Beam Induced Nanosynthesis

In many areas of science and technology, patterned films and surfaces play a key role in engineering and development of advanced materials. Here, we introduce a new generic technique for the fabrication of polysaccharide nano-structures via focused electron beam induced conversion (FEBIC). For the proof of principle, organosoluble trimethylsilyl-cellulose (TMSC) thin films have been deposited by spin coating on SiO2 / Si and exposed to a nano-sized electron beam. It turns out that in the exposed areas an electron induced desilylation reaction takes place converting soluble TMSC to rather insoluble cellulose. After removal of the unexposed TMSC areas, structured cellulose patterns remain on the surface with FWHM line widths down to 70 nm. Systematic FEBIC parameter sweeps reveal a generally electron dose dependent behavior with three working regimes: incomplete conversion, ideal doses and over exposure. Direct (FT-IR) and indirect chemical analyses (enzymatic degradation) confirmed the cellulosic character of ideally converted areas. These investigations are complemented by a theoretical model which suggests a two-step reaction process by means of TMSC → cellulose and cellulose → non-cellulose material conversion in excellent agreement with experimental data. The extracted, individual reaction rates allowed the derivation of design rules for FEBIC parameters towards highest conversion efficiencies and highest lateral resolution.

Selective immobilization and detection of DNA on biopolymer supports for the design of microarrays

DNA immobilization for the manufacturing of microarrays requires sufficient probe density, low unspecific binding and high interaction efficiency with complementary strands that are detected from solutions. Many of these important parameters are affected by the surface chemistry and the blocking steps conducted during DNA spotting and hybridization. This work describes an alternative method to selectively immobilize probes and to detect DNA on biocompatible, hydrophilic cellulose coated supports with low unspecific binding, high selectivity and appropriate sensitivity. It takes advantage of a relatively selective adsorption of water soluble polysaccharides on a solid cellulose matrix. Single strands of DNA were conjugated to this soluble polysaccharide and subsequently micro-spotted on solid cellulose thin films that were coated on glass and polymer slides. This resulted in adsorptively bound DNA-probes that were used to detect complementary, labelled DNA strands with different lengths and sequences by hybridization. The interaction of the DNA-conjugates with cellulose surfaces and the selectivity of hybridization were investigated by a quartz crystal microbalance with dissipation monitoring (QCM-D) and fluorescence scanning. The method of non-covalent immobilization of DNA probes on an uncharged, non-reactive, hydrophilic support lowers the unspecific binding and the number of handling steps required to conduct the experiments for the detection of DNA on microarrays. Simultaneously selectivity, hybridization efficiency and detection limits are maintained.

Surface immobilization of a protease through an inhibitor-derived affinity ligand: a bioactive surface with defensive properties against an inhibitor

Surface immobilization of a protease through its inhibitor-derived peptide was shown to be advantageous in retaining the enzymatic activity of the protease and protecting the protease from being inhibited by its inhibitor.

Photolithographic patterning of cellulose: a versatile dual-tone photoresist for advanced applications

In many areas of science and technology, patterned films and surfaces play a key role in engineering and development of advanced materials. Here, we present a versatile toolbox that provides an easy patterning method for cellulose thin films by means of photolithography and enzymatic digestion. A patterned UV-illumination of trimethylsilyl cellulose thin films containing small amounts of a photo acid generator leads to a desilylation reaction and thus to the formation of cellulose in the irradiated areas. Depending on the conditions of development, either negative and positive type cellulose structures can be obtained, offering lateral resolutions down to the single-digit micro meter range by means of contact photolithography. In order to highlight the potential of this material for advanced patterning techniques, cellulose structures with sub-µm resolution are fabricated by means of two-photon absorption lithography. Moreover, these photochemically structured cellulose thin films are successfully implemented as dielectric layers in prototype organic thin film transistors. Such photopatternable dielectric layers are crucial for the realization of electrical interconnects for demanding organic device architectures.

Photoregeneration of trimethylsilyl cellulose as a tool for microstructuring ultrathin cellulose supports

Microstructured thin films based on cellulose, the most abundant biopolymer on Earth, have been obtained by UV-irradiation of acid-labile trimethylsilyl cellulose thin films in the presence of N-hydroxynaphtalimide triflate as photoacid generator. We demonstrate that this photoregeneration process can be exploited for the manufacture of cellulose patterns having feature sizes down to 1 μm, with potential applications in life sciences.

Triggering protein adsorption on tailored cationic cellulose surfaces

The equipment of cellulose ultrathin films with BSA (bovine serum albumin) via cationization of the surface by tailor-made cationic celluloses is described. In this way, matrices for controlled protein deposition are created, whereas the extent of protein affinity to these surfaces is controlled by the charge density and solubility of the tailored cationic cellulose derivative. In order to understand the impact of the cationic cellulose derivatives on the protein affinity, their interaction capacity with fluorescently labeled BSA is investigated at different concentrations and pH values. The amount of deposited material is quantified using QCM-D (quartz crystal microbalance with dissipation monitoring, wet mass) and MP-SPR (multi-parameter surface plasmon resonance, dry mass), and the mass of coupled water is evaluated by combination of QCM-D and SPR data. It turns out that adsorption can be tuned over a wide range (0.6-3.9 mg dry mass m(-2)) depending on the used conditions for adsorption and the type of employed cationic cellulose. After evaluation of protein adsorption, patterned cellulose thin films have been prepared and the cationic celluloses were adsorbed in a similar fashion as in the QCM-D and SPR experiments. Onto these cationic surfaces, fluorescently labeled BSA in different concentrations is deposited by an automatized spotting apparatus and a correlation between the amount of the deposited protein and the fluorescence intensity is established.

Preparation of PDMS ultrathin films and patterned surface modification with cellulose

Patterned surface functionalization of PDMS with the biopolymer cellulose via lithographic methods.