Layer-by-layer Technology Research Articles

Layer-by-layer assembly in nanochannels: assembly mechanism and applications.

Layer-by-layer (LbL) assembly is a versatile technology to construct multifunctional nanomaterials using various supporting substrates, enabled by the large selection freedom of building materials and diversity of possible driving forces. The fine regulation over the film thickness and structure provides an elegant way to tune the physical/chemical properties by mild assembly conditions (e.g. pH, ion strength). In this review, we focus on LbL in nanochannels, which exhibit a different growth mechanism compared to "open", convex substrates. The assembly mechanism in nanochannels is discussed in detail, followed by the summary of applications of LbL assemblies liberated from nanochannel templates which can be used as nanoreactors, drug carriers and transporting channels across cell membranes. For fluidic applications, robust membrane substrates are required to keep in place nanotube arrays for membrane-based separation, purification, biosensing and energy harvesting, which are also discussed. The good compatibility of LbL with crossover technologies from other fields allows researchers to further extend this technology to a broader range of research fields, which is expected to result in an increased number of applications of LbL technology in the future.

Chitosan/tannic acid bilayers layer-by-layer deposited cellulose nanofibrous mats for antibacterial application

The research and development of environmentally friendly and nontoxic biomass products has become an important topic of worldwide concern. In this study, natural materials were used for producing a kind of antibacterial mats. Cellulose acetate (CA) mats prepared by electrospinning technology were converted to cellulose mats via alkali hydrolysis. Chitosan (CS) and tannic acid (TA) were used to fabricate the composite mats by using layer-by-layer (LBL) self-assembly technology. The cellulose mats exhibited good fibrous structure, three-dimensional network and small average fiber diameter ranging from 300 to 400 nm. Besides, the results of mechanical properties testing and water contact angle measurements of these LBL-structured mats demonstrated that the LBL technology was able to improve their surface characteristics, hydrophilicity and mechanical properties. The analysis of antibacterial activity of the mats revealed over 86% antibacterial activity against Escherichia coli and up to 99% antibacterial activity against Staphylococcus aureus. Hence, the LBL-structured cellulose mats have excellent antibacterial activity and mechanical properties. Therefore, these nano-cellulose mats can be expected to have considerable development prospects for food packaging or wound dressing.

Preparation of Well-Dispersed Chitosan/Alginate Hollow Multilayered Microcapsules for Enhanced Cellular Internalization.

Hollow multilayered capsules have shown massive potential for being used in the biomedical and biotechnology fields, in applications such as cellular internalization, intracellular trafficking, drug delivery, or tissue engineering. In particular, hollow microcapsules, developed by resorting to porous calcium carbonate sacrificial templates, natural-origin building blocks and the prominent Layer-by-Layer (LbL) technology, have attracted increasing attention owing to their key features. However, these microcapsules revealed a great tendency to aggregate, which represents a major hurdle when aiming for cellular internalization and intracellular therapeutics delivery. Herein, we report the preparation of well-dispersed polysaccharide-based hollow multilayered microcapsules by combining the LbL technique with an optimized purification process. Cationic chitosan (CHT) and anionic alginate (ALG) were chosen as the marine origin polysaccharides due to their biocompatibility and structural similarity to the extracellular matrices of living tissues. Moreover, the inexpensive and highly versatile LbL technology was used to fabricate core-shell microparticles and hollow multilayered microcapsules, with precise control over their composition and physicochemical properties, by repeating the alternate deposition of both materials. The microcapsules’ synthesis procedure was optimized to extensively reduce their natural aggregation tendency, as shown by the morphological analysis monitored by advanced microscopy techniques. The well-dispersed microcapsules showed an enhanced uptake by fibroblasts, opening new perspectives for cellular internalization.

Label-free and competitive aptamer cytosensor based on layer-by-layer assembly of DNA-platinum nanoparticles for ultrasensitive determination of tumor cells

A label-free and competitive electrochemical cytosensor based on layer-by-layer (LBL) assembly of DNA-platinum nanoparticles (DNA-PtNPs) for signal amplification was developed for the tumor cell determination. In this study, three different sizes of PtNPs were synthesized and successfully characterized. The PtNPs with the highest electrocatalytic activity were selected as nanocarriers. The thiolated TLS11a aptamer, with high affinity to human liver hepatocellular carcinoma (HepG2) cells, was covalently attached to the gold nanoparticles (AuNPs) deposited on indium tin oxide (ITO) glass. Meanwhile, nanoprobes were fabricated through ferrocene-labeled complementary DNA (cDNA-Fc) immobilized on the surfaces of the PtNPs. LBL technology could provide abundant signal tags and efficient signal amplifiers for electrochemical cytosensing. When the target cells competed with cDNA to bind with aptamer, double-stranded DNA was denatured and PtNPs-DNA bioconjugates were released from the ITO electrode, resulting in decreased current response. Thus the current change was related linearly to the logarithm of cell concentration from 50 to 1 × 106 cells mL−1 with a low detection limit of 15 cells mL−1, acceptable stability and reproducibility. Furthermore, the enzyme-free cytosensor could be regenerated through an electrochemical reductive desorption technique. The cytosensor possesses potential applications in early cancer diagnosis and treatment.

Surfactant-stable and pH-sensitive liposomes coated with N-succinyl-chitosan and chitooligosaccharide for delivery of quercetin

Layer-by-layer (LbL) self-assembly of multilayered liposomes is used to improve the stability of conventional liposomes. In this study, the LbL technology was used to prepare novel multilayered liposomes from chitooligosaccharide and N-succinyl-chitosan. We propose that this preparation can be used as a transdermal drug delivery system (TDDS) to enhance stability against surfactants and control drug release. Particle size increased with the number of layers in the multilayer and the zeta potential varied between positive and negative values with alternate deposition of polyelectrolytes. Finally, approximately 300–400nm-thick four-layered liposomes were prepared. These liposomes were more stable against surfactants and showed a relatively high release of quercetin at pH 5.5 than the uncoated liposomes as assessed via in vitro drug release and skin permeation studies. In summary, the multilayered liposomes showed potential for use as a surfactant-stable TDDS that effectively enhanced the permeation of quercetin, a poorly soluble drug, into the skin.

Nanoengineering Hybrid Supramolecular Multilayered Biomaterials Using Polysaccharides and Self‐Assembling Peptide Amphiphiles

Developing complex supramolecular biomaterials through highly dynamic and reversible noncovalent interactions has attracted great attention from the scientific community aiming key biomedical and biotechnological applications, including tissue engineering, regenerative medicine, or drug delivery. In this study, the authors report the fabrication of hybrid supramolecular multilayered biomaterials, comprising high‐molecular‐weight biopolymers and oppositely charged low‐molecular‐weight peptide amphiphiles (PAs), through combination of self‐assembly and electrostatically driven layer‐by‐layer (LbL) assembly approach. Alginate, an anionic polysaccharide, is used to trigger the self‐assembling capability of positively charged PA and formation of 1D nanofiber networks. The LbL technology is further used to fabricate supramolecular multilayered biomaterials by repeating the alternate deposition of both molecules. The fabrication process is monitored by quartz crystal microbalance, revealing that both materials can be successfully combined to conceive stable supramolecular systems. The morphological properties of the systems are studied by advanced microscopy techniques, revealing the nanostructured dimensions and 1D nanofibrous network of the assembly formed by the two molecules. Enhanced C2C12 cell adhesion, proliferation, and differentiation are observed on nanostructures having PA as outermost layer. Such supramolecular biomaterials demonstrate to be innovative matrices for cell culture and hold great potential to be used in the near future as promising biomimetic supramolecular nanoplatforms for practical applications.

A novel porous aspirin-loaded (GO/CTS-HA)n nanocomposite films: Synthesis and multifunction for bone tissue engineering

A novel porous graphene oxide (GO)/chitosan (CTS)-hydroxyapatite (HA) nanocomposite film was successfully prepared for the first time by combining layer-by-layer (LBL) assembly technology with biomimetic mineralization method. The LBL technology was used to control the thickness of film as well as induce the biomimetic mineralization of biocompatible HA. The obtained (GO/CTS-HA)n film provided ideal platform for the proliferation of mouse mesenchymal stem cells (mMSCs). The pore size in the film is about 300nm, and the porous architecture made the film have high aspirin loading efficiency. Also the accumulated loading dosage could be adjusted by the film thickness, and the sustained release of aspirin could ensure well anti-inflammatory effect. The above advantages may alleviate the pain of patients and give the better environment for bone regeneration. This multifunctional aspirin-loaded (GO/CTS-HA)n film provided an inspiration for the synthesis of novel porous inorganic/biomacromolecule nanocomposite films as the biocoatings applied in bone tissue engineering.

Arming embolic beads with anti-VEGF antibodies and controlling their release using LbL technology

Transarterial chemoembolization (TACE) is used to treat various types of hypervascular tumors such as hepatocellular carcinoma and renal cancer. However, embolization and blocking of blood vessels nourishing a tumor mass evokes an angiogenic response due to the secretion of vascular endothelial growth factor (VEGF), which results in the formation of new blood vessels and eventually limitation in therapeutic efficacy. The presented work investigates the feasibility of loading the clinically used embolic beads (DC Bead®) with Bevacizumab (BEV), an anti-VEGF antibody, and control its release kinetics via Layer-by-Layer (LbL) coating. This strategy has the aim to achieve high, localized and sustained concentrations of BEV at the tumor site and reduce drug exposure in the systemic circulation. High loading of BEV on lyophilized beads of about 76mg BEV/bead vial was achieved. LbL coating was carried out by depositing alternating layers of the biocompatible polymers alginate and poly-L-lysine. Coating was proven successful by monitoring the reversal of zeta potential after addition of each layer. Morphological changes of the bead surface before and after coating were illustrated using SEM imaging. Moreover, release profiles from different formulations were studied and results showed that optimizing the number of deposited layers effectively slows the release of BEV for three days. Activity of released BEV was studied in different 2D and 3D cell based assays. Released BEV fractions showed comparable activity to fresh BEV solution used as control after 3days. In conclusion, our results suggest the opportunity for loading anti-VEGF antibodies on commercially available embolic beads to increase the efficacy of TACE of hypervascular tumors.

Layer-by-layer nanoparticles for the targeted co-delivery of cisplatin and EZH2 siRNA in a model of high grade serous ovarian cancer

Event Abstract Back to Event Layer-by-layer nanoparticles for the targeted co-delivery of cisplatin and EZH2 siRNA in a model of high grade serous ovarian cancer Santiago Correa1, 2, Ki Young Choi2, 3, Aria Shi1 and Paula T. Hammond2, 3 1 MIT, Biological Engineering, United States 2 MIT, Koch Institute for Integrative Cancer Research, United States 3 MIT, Chemical Engineering, United States Introduction: Layer-by-layer (LbL) assembly is a powerful and established technique for creating composite, multifunctional nanoparticles through the controlled fabrication of nanoscale thin films composed of biologically relevant materials.[1][2][3] LbL particles exhibit multifunctional properties and stability in vivo, making them attractive drug carriers for the treatment of cancer.[4][5][6] This work aims to apply the multifunctional capabilities of LbL nanotechnology towards addressing the unique challenges posed by high-grade serous ovarian cancer (HGSOC). HGSOC represents roughly 70% of malignant epithelial ovarian cancers and is responsible for nearly two-thirds of ovarian cancer deaths[7][8][9]. The lethality of HGSOC is attributed to its striking capacity to develop resistance against platinum-based chemotherapy like cisplatin.[10] Here we seek to improve the therapeutic response to cisplatin by simultaneously silencing expression of the Polycomb protein enhancer of Zeste homolog 2 (EZH2), which is thought to contribute towards drug-resistance in ovarian cancer.[11][12] Leveraging LbL technology, cisplatin-loaded liposomes will be modified with a polyelectrolyte multilayer shell containing siRNA against EZH2. Co-delivery of the payload will be further facilitated by terminating the multilayer with the polysaccharide hyaluronan, which is known to target cancer cells by both pH dependent and ligand-specific mechanisms.[13] Materials and Methods: Figure 1. Drug-loaded liposomes will be sequentially exposed to polyelectrolytes of alternating charge to generate a film composed of poly(L-arginine) (PLA), siEZH2, and hyaluronan (HA). For preliminary experiments, cellular viability was determined over a range of cisplatin concentrations to calculate the IC50 value. Cells were either untreated before insult with cisplatin or transfected with siEZH2 72 hours prior. For uptake experiments, COV362 cells were treated with LbL nanoparticles at a final concentration of 20 pM and imaged live using a Nikon A1R confocal microscope at 24 hours post-treatment. The in vivo efficacy of the treatment will be evaluated in an orthotopic xenograft model in immune-compromised mice. All in vivo experiments will be conducted with the COV362 line, due to its genetic similarity with primary HGSOC.[14] Results and Discussion: Figure 2. Preliminary in vitro results reveal that silencing EZH2 using siRNA sensitizes COV362, SKOV3 and CAOV3 ovarian cancer cell lines to cisplatin (P<0.001 between cisplatin only and cisplatin plus siEZH2 groups, by ANOVA1 with the Bonferonni post-test). Figure 3. LbL nanoparticles formed from fluorescent polystyrene cores coated with PLA and HA were used to evaluate uptake by COV362 cells. Live cell imaging demonstrated high degree of nanoparticle internalization, consistent with the targeting capabilities attributed to HA coated particles. Cell membranes are in magenta, lysosomes are in red, and LbL nanoparticles are in green. Conclusion: Our preliminary data and existing literature provide a strong foundation for the success of this work. We have already demonstrated the sensitization of ovarian cancer cells to cisplatin by depleting EZH2. Furthermore, we have demonstrated that our LbL nanoparticles penetrate into ovarian cancer cells efficiently, indicating that they will be capable of delivering our proposed combination therapy. The authors thank the Koch Institute Swanson Biotechnology Center for technical support, specifically the Peterson nanotechnology, biopolymer, and flow cytometry facilities.

Highly Sensitive Electrochemical Determination of Alfatoxin B1 Using Quantum Dots-Assembled Amplification Labels.

A competitive electrochemical immunoassay for highly sensitive detection of AFB1 is demonstrated using layer-by-layer (LBL) assembled quantum dots (QDs) as labels. To investigate the effects of the higher sensitivity of square wave voltammetric stripping (SWV) and of the LBL technique on the proposed immunoassays, the proposed assay was compared to electrochemical (EC) and fluorescent immunoassays, which did not use LBL technology. Peanut samples were analyzed using the three immunoassays. The limits of detection (LODs) were 0.018, 0.046 and 0.212 ng/mL, respectively, while the sensitivities were 0.308, 1.011 and 4.594 ng/mL, respectively. The proposed electrochemical immunoassay displayed a significant improvement in sensitivity, thereby providing a simple and sensitive alternative strategy for determining AFB1 levels in peanut samples.

SYNTHESIS OF METAL OXIDE-BASED NANOCOMPOSITES AND MULTICOMPONENT COMPOUNDS USING LAYER-BY-LAYER METHOD AND PROSPECTS FOR THEIR APPLICATION

The ability of Layer-by-Layer (LbL) or Successive Ionic Layer Deposition (SILD) technology to synthesize the layers of nanocomposites, “hybrid” structures and multicomponent metal oxides on various substrates is being discussed in this report. It was shown that concentration and pH of the solutions used, the processing time, and the number of the LbL (SILD) cycles were the main parameters of this process. It was made a conclusion that coatings formed by LbL technology can be used in gas sensors and catalysis for the surface functionalization, in membranes and filters for the pore size controlling, in solar cells for the solar energy conversion, in medicine for the formation of bactericidal coatings, and so on.

Chitosan/siRNA functionalized titanium surface via a layer-by-layer approach for in vitro sustained gene silencing and osteogenic promotion.

Titanium surface modification is crucial to improving its bioactivity, mainly its bone binding ability in bone implant materials. In order to functionalize titanium with small interfering RNA (siRNA) for sustained gene silencing in nearby cells, the layer-by-layer (LbL) approach was applied using sodium hyaluronate and chitosan/siRNA (CS/siRNA) nanoparticles as polyanion and polycation, respectively, to build up the multilayered film on smooth titanium surfaces. The CS/siRNA nanoparticle characterization was analyzed first. Dynamic contact angle, atomic force microscopy, and scanning electron microscopy were used to monitor the layer accumulation. siRNA loaded in the film was quantitated and the release profile of film in phosphate-buffered saline was studied. In vitro knockdown effect and cytotoxicity evaluation of the film were investigated using H1299 human lung carcinoma cells expressing green fluorescent protein (GFP). The transfection of human osteoblast-like cell MG63 and H1299 were performed and the osteogenic differentiation of MG63 on LbL film was analyzed. The CS/siRNA nanoparticles exhibited nice size distribution. During formation of the film, the surface wettability, topography, and roughness were alternately changed, indicating successful adsorption of the individual layers. The scanning electron microscope images clearly demonstrated the hybrid structure between CS/siRNA nanoparticles and sodium hyaluronate polymer. The cumulated load of siRNA increased linearly with the bilayer number and, more importantly, a gradual release of the film allowed the siRNA to be maintained on the titanium surface over approximately 1 week. In vitro transfection revealed that the LbL film-associated siRNA could consistently suppress GFP expression in H1299 without showing significant cytotoxicity. The LbL film loading with osteogenic siRNA could dramatically increase the osteogenic differentiation in MG63. In conclusion, LbL technology can potentially modify titanium surfaces with specific gene-regulatory siRNAs to enhance biofunction.

Rapid Growing Clay Coatings to Reduce the Fire Threat of Furniture

Layer-by-layer (LbL) assembly coatings reduce the flammability of textiles and polyurethane foam but require extensive repetitive processing steps to produce the desired coating thickness and nanoparticle fire retardant content that translates into a fire retardant coating. Reported here is a new hybrid bi-layer (BL) approach to fabricate fire retardant coatings on polyurethane foam. Utilizing hydrogen bonding and electrostatic attraction along with the pH adjustment, a fast growing coating with significant fire retardant clay content was achieved. This hybrid BL coating exhibits significant fire performance improvement in both bench scale and real scale tests. Cone calorimetry bench scale tests show a 42% and 71% reduction in peak and average heat release rates, respectively. Real scale furniture mockups constructed using the hybrid LbL coating reduced the peak and average heat release rates by 53% and 63%, respectively. This is the first time that the fire safety in a real scale test has been reported for any LbL technology. This hybrid LbL coating is the fastest approach to develop an effective fire retardant coating for polyurethane foam.

Fabrication and in vitro evaluation of stable collagen/hyaluronic acid biomimetic multilayer on titanium coatings

Layer-by-layer (LBL) self-assembly technique has been proved to be a highly effective method to immobilize the main components of the extracellular matrix such as collagen and hyaluronic acid on titanium-based implants and form a polyelectrolyte multilayer (PEM) film by electrostatic interaction. However, the formed PEM film is unstable in the physiological environment and affects the long-time effectiveness of PEM film. In this study, a modified LBL technology has been developed to fabricate a stable collagen/hyaluronic acid (Col/HA) PEM film on titanium coating (TC) by introducing covalent immobilization. Scanning electron microscopy, diffuse reflectance Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy were used to characterize the PEM film. Results of Sirius red staining demonstrated that the chemical stability of PEM film was greatly improved by covalent cross-linking. Cell culture assays further illustrated that the functions of human mesenchymal stem cells, such as attachment, spreading, proliferation and differentiation, were obviously enhanced by the covalently immobilized Col/HA PEM on TCs compared with the absorbed Col/HA PEM. The improved stability and biological properties of the Col/HA PEM covalently immobilized TC may be beneficial to the early osseointegration of the implants.

Nanostructured 3D Constructs Based on Chitosan and Chondroitin Sulphate Multilayers for Cartilage Tissue Engineering

Nanostructured three-dimensional constructs combining layer-by-layer technology (LbL) and template leaching were processed and evaluated as possible support structures for cartilage tissue engineering. Multilayered constructs were formed by depositing the polyelectrolytes chitosan (CHT) and chondroitin sulphate (CS) on either bidimensional glass surfaces or 3D packet of paraffin spheres. 2D CHT/CS multi-layered constructs proved to support the attachment and proliferation of bovine chondrocytes (BCH). The technology was transposed to 3D level and CHT/CS multi-layered hierarchical scaffolds were retrieved after paraffin leaching. The obtained nanostructured 3D constructs had a high porosity and water uptake capacity of about 300%. Dynamical mechanical analysis (DMA) showed the viscoelastic nature of the scaffolds. Cellular tests were performed with the culture of BCH and multipotent bone marrow derived stromal cells (hMSCs) up to 21 days in chondrogenic differentiation media. Together with scanning electronic microscopy analysis, viability tests and DNA quantification, our results clearly showed that cells attached, proliferated and were metabolically active over the entire scaffold. Cartilaginous extracellular matrix (ECM) formation was further assessed and results showed that GAG secretion occurred indicating the maintenance of the chondrogenic phenotype and the chondrogenic differentiation of hMSCs.

Controlling polyurethane foam flammability and mechanical behaviour by tailoring the composition of clay-based multilayer nanocoatings

This study is a thorough evaluation of clay-based Layer-by-Layer (LbL) coatings intended to reduce the flammability of polymeric materials. Through a systematic variation of a baseline coating recipe, an ideal combination of the coating attributes that provides a rapidly developing coating with an optimum balance of flammability, mechanical, and physical attributes on a complex 3D porous substrate, polyurethane foam (PUF) was identified. Using a unique trilayer (TL) assembly approach, the coating growth was significantly accelerated by the polymer (poly(acrylic acid) (PAA)/branched polyethylenimine (BPEI)) concentration in the formulation. However, to significantly reduce flammability without compromising other performance attributes, the concentration of the nanoparticle fire retardant (nanoFR, clay) suspension was critical. This study has resulted in the most significant reduction in PUF flammability using LbL technology without compromising any of the mechanical or physical attributes of the PUF. More specifically, a reduction in the peak heat release rate (pHRR) and average heat release rate (aHRR) of 33% and 78%, respectively, has been achieved. This reduction in flammability is at least two times more effective than commercial fire retardants and other LbL FR coatings for PUF. The insights gained through this research are expected to accelerate the development of other LbL coatings regardless of the intended application.

Counterion Exchange to Achieve Reversibly Switchable Hydrophobicity and Oleophobicity on Fabrics

We describe a simple layer-by-layer (LbL) technology and counterion exchange procedure to tune the liquid wettability of commercially available cotton fabrics. A polyelectrolyte multilayer is deposited on the fabric surface by the LbL technology, and counterion exchange is used to control the surface composition and thereby to modulate the solid surface energy. The tunability of the solid surface energy, along with the inherent re-entrant texture of the cotton fabric, results in simultaneously switchable wettability between a nonwetting state and a fully wetted state for water and hexadecane. This switchable hydrophobicity and oleophobicity can be explained within a robustness factor, which is a quantitative criterion for the transition between the two states. The counterion exchange can be confirmed by X-ray photoelectron spectroscopy analysis.

Emerging trend in nano-engineered polyelectrolyte-based surrogate carriers for delivery of bioactives

Importance of the field: In recent decades a new colloidal drug delivery system based on layer-by-layer (LbL) technology has emerged, which offers promising means of delivering bioactive agents, specifically biological macromolecules including peptides and DNA. Nano-engineered capsules specifically fabricated from biocompatible and biodegradable polyelectrolytes (PEs) can provide a better option for encapsulation of cells thereby protecting cells from immunological molecules in the body, and their selective permeability can ensure the survival of encapsulated cells.Areas covered in this review: This review encompasses a strategic approach to fabricate nano-engineered microcapsules through meticulous selection of polyelectrolytes and core materials based on LbL technology. The content of the article provides evidence for its wide array of applications in medical therapeutics, as indicated by the quantity of research and patents in this area. Recent developments and approaches for tuning drug release, biocompatibility and cellular interaction are discussed thoroughly.What the reader will gain: This review aims to provide an overview on the development of LbL capsules with specific orientation towards drug and macromolecular delivery and its integration with other drug delivery systems, such as liposomes.Take home message: Selection of PEs for the fabrication of LbL microcapsules has a profound effect on stability, drug release, biocompatibility and encapsulation efficacy. The release can be easily modulated by varying different physicochemical as well as physiological conditions. Scale-up approaches for the fabrication of LbL microcapsules by means of automation must be considered to improve the possibility of application of LbL microcapsules on a large scale.

Carbon nanotubes/(pLys/dsDNA) n layer-by-layer multilayer films for electrochemical studies of DNA damage

Carboxylic group-functionalized carbon nanotubes (c-CNT) were modified on the surface of carbon paste electrode to obtain a conducting precursor film. Positively charged poly-l-lysine (pLys) and negatively charged double-stranded DNA (dsDNA) were alternately adsorbed on the c-CNT-modified electrode, forming (pLys/dsDNA)n layer-by-layer (LBL) films. Cyclic voltammetry and electrochemical impedance spectroscopy of the electroactive probe [Fe(CN)6]3−/4− could give the valuable dynamic information of multilayer films growth. The oxidative DNA damage induced by cadmium ion (Cd2+) in the LBL multilayer films was studied by differential pulse voltammetry (DPV) with methylene violet (MV) as the intercalation redox probe. The electrochemical signals of MV on the multilayer films were effectively amplified via LBL technology. The specific intercalation of MV into dsDNA base pairs and the amplified electrochemical response of MV, combined with the unique feature of loading reversibility of MV in the DNA layer-by-layer films, made the difference in DPV response between the intact, and damaged dsDNA films become pronounced. This biosensor exhibited that the (pLys/dsDNA)n films could be utilized for investigations of DNA damage.

Encapsulation of Synthetically Valuable Biocatalysts into Polyelectrolyte Multilayer Systems

Layer-by-Layer (LbL) technology recently turned out to be a versatile tool for the encapsulation of bioactive entities. In this study, the factual potential of this technology to encapsulate synthetically valuable biocatalysts, that is enzymes and whole cells expressing a specific catalytic activity, was investigated. The biocatalysts were embedded into a polyelectrolyte multilayer system involving poly(allylamine) hydrochloride (PAH) and poly(styrene sulfonate) sodium salt (PSS). The enzymes were adsorbed to CaCO3 or DEAE-cellulose previous to encapsulation. A slight increase (32%) of the catalytic performance was observed for lipase B from Candida antarctica when four layers of polyelectrolytes were applied. On the whole, however, the residual activity of the investigated enzymes after encapsulation was rather low. Similar results were obtained with whole-cell biocatalysts. It was found that the activity decrease can be attributed to mass transfer restrictions as well as direct interactions between polyelectrolytes and catalytically active molecules. Both effects need to be understood in more detail before LbL technology can be advanced to technically efficient biocatalysis.