Enzyme conjugation to the polysaccharide chitosan: smart biocatalysts and biocatalytic hydrogels

Performance of a Flow-Through Enzyme Reactor Prepared from a Silica Monolith and an α-Poly(D-Lysine)-Enzyme Conjugate

Horseradish peroxidase (HRP) is covalently bound in aqueous solution to polycationic α-poly(D-lysine) chains of ≈1000 repeating units length, PDL, via a bis-aryl hydrazone bond (BAH). Under the experimental conditions used, about 15 HRP molecules are bound along the PDL chain. The purified PDL-BAH-HRP conjugate is very stable when stored at micromolar HRP concentration in a pH 7.2 phosphate buffer solution at 4 °C. When a defined volume of such a conjugate solution of desired HRP concentration (i.e., HRP activity) is added to a macro- and mesoporous silica monolith with pore sizes of 20-30 µm as well as below 30 nm, quantitative and stable noncovalent conjugate immobilization is achieved. The HRP-containing monolith can be used as flow-through enzyme reactor for bioanalytical applications at neutral or slightly alkaline pH, as demonstrated for the determination of hydrogen peroxide in diluted honey. The conjugate can be detached from the monolith by simple enzyme reactor washing with an aqueous solution of pH 5.0, enabling reloading with fresh conjugate solution at pH 7.2. Compared to previously investigated polycationic dendronized polymer-enzyme conjugates with approximately the same average polymer chain length, the PDL-BAH-HRP conjugate appears to be equally suitable for HRP immobilization on silica surfaces.

Applications and immobilization strategies of the copper-centred laccase enzyme; a review

Laccase is a multi-copper enzyme widely expressed in fungi, higher plants, and bacteria which facilitates the direct reduction of molecular oxygen to water (without hydrogen peroxide production) accompanied by the oxidation of an electron donor. Laccase has attracted attention in biotechnological applications due to its non-specificity and use of molecular oxygen as secondary substrate. This review discusses different applications of laccase in various sectors of food, paper and pulp, waste water treatment, pharmaceuticals, sensors, and fuel cells. Despite the many advantages of laccase, challenges such as high cost due to its non-reusability, instability in harsh environmental conditions, and proteolysis are often encountered in its application. One of the approaches used to minimize these challenges is immobilization. The various methods used to immobilize laccase and the different supports used are further extensively discussed in this review.

Orthogonal Enzymatic Conjugation Reactions Create Chitin Binding Domain Grafted Chitinase Polymers with Enhanced Antifungal Activity

Enzymatic reaction offers site-specific conjugation of protein units to form protein conjugates or protein polymers with intrinsic functions. Herein, we report horseradish peroxidase (HRP)- and microbial transglutaminase (MTG)-catalyzed orthogonal conjugation reactions to create antifungal protein polymers composed of Pteris ryukyuensis chitinase-A (ChiA) and its two domains, catalytic domain, CatD, and chitin-binding domain, LysM₂. We engineered the ChiA and CatD by introducing a peptide tag containing tyrosine (Y-tag) at N-termini and a peptide tag containing lysine and tyrosine (KY-tag) at C-termini to construct Y-ChiA-KY and Y-CatD-KY. Also, LysM₂ with Y-tag and KY-tag (Y-LysM₂-KY) or with a glutamine-containing peptide tag (Q-tag) (LysM₂-Q) were constructed. The proteins with Y-tag and KY-tag were efficiently polymerized by HRP reaction through the formation of dityrosine bonds at the tyrosine residues in the peptide tags. The Y-CatD-KY polymer was further treated by MTG to orthogonally graft LysM₂-Q to the KY-tag via isopeptide formation between the side chains of the glutamine and lysine residues in the peptide tags to form LysM₂-grafted CatD polymer. The LysM₂-grafted CatD polymer exhibited significantly higher antifungal activity than the homopolymer of Y-ChiA-KY and the random copolymer of Y-CatD-KY and Y-LysM₂-KY, demonstrating that the structural differences of artificial chitinase polymers have a significant impact on the antifungal activity. This strategy of polymerization and grafting reaction of protein can contribute to the further research and development of functional protein polymers for specific applications in various fields in biotechnology.

Different strategies for the lipase immobilization on the chitosan based supports and their applications

Immobilized enzymes have received incredible interests in industry, pharmaceuticals, chemistry and biochemistry sectors due to their various advantages such as ease of separation, multiple reusability, non-toxicity, biocompatibility, high activity and resistant to environmental changes. This review in between various immobilized enzymes focuses on lipase as one of the most practical enzyme and chitosan as a preferred biosupport for lipase immobilization and provides a broad range of studies of recent decade. We highlight several aspects of lipase immobilization on the surface of chitosan support containing various types of lipase and immobilization techniques from physical adsorption to covalent bonding and cross-linking with their benefits and drawbacks. The recent advances and future perspectives that can improve the present problems with lipase and chitosan such as high-price of lipase and low mechanical resistance of chitosan are also discussed. According to the literature, optimization of immobilization methods, combination of these methods with other techniques, physical and chemical modifications of chitosan, co-immobilization and protein engineering can be useful as a solution to overcome the mentioned limitations.

A novel chitosan/tripolyphosphate/L-lysine conjugates for latent fingerprints detection and enhancement

Most chemical and physical methods employed in visualizing latent marks have shown detrimental effects on human health and, therefore, some research groups have directed their attention to the utilization of various (bio)polymers with the aforementioned purpose. Although chitosan is widely used in medicine, pharmacy, food, and drug delivery systems, there are very few studies that address this biopolymer utilization in forensic applications, such as the detection of latent fingerprints. We used chitosan crosslinked with sodium tripolyphosphate and conjugated with L-lysine to enhance the visualization of latent fingerprints, due to its ability to interact with fingerprint sweat residues. These conjugates were prepared using different (w/w) amounts of chitosan and tripolyphosphate (6/1; 4/1; 1/1; 1/4; and 1/6), and those with the most promising results (i.e., 6/1 formulation) were investigated in detail. Fourier transform infrared (FT-IR) spectroscopy confirmed interactions between components of the systems. Optical microscopy and scanning electron microscope (SEM) analysis showed that prepared powder formulations were uniform in size and confirmed that chitosan/tripolyphosphate/lysine conjugates bind easily to the sweat and lipid residues present in the latent fingerprints. The testing of prepared conjugates demonstrated the potential of these systems as bio-based powder substitution for commercially available powders.

Bacterial exopolysaccharides as a modern biotechnological tool for modification of fungal laccase properties and metal ion binding

Four bacterial EPSs extracted from Rhizobium leguminosarum bv. trifolii Rt24.2, Sinorhizobium meliloti Rm1021, Bradyrhizobium japonicum USDA110, and Bradyrhizobium elkanii USDA76 were determined towards their metal ion adsorption properties and possible modification of Cerrena unicolor laccase properties. The highest magnesium and iron ion-sorption capacity (~ 42 and ~ 14.5%, respectively) was observed for EPS isolated from B. japonicum USDA110. An evident influence of EPSs on the stability of laccase compared to the control values (without EPSs) was shown after 30-day incubation at 25 °C. The residual activity of laccases was obtained in the presence of Rh76EPS and Rh1021EPS, i.e., 49.5 and 41.5% of the initial catalytic activity, respectively. This result was confirmed by native PAGE electrophoresis. The EPS effect on laccase stability at different pH (from 3.8 to 7.0) was also estimated. The most significant changes at the optimum pH value (pH 5.8) was observed in samples of laccase stabilized by Rh76EPS and Rh1021EPS. Cyclic voltamperometry was used for analysis of electrochemical parameters of laccase stabilized by bacterial EPS and immobilized on single-walled carbon nanotubes (SWCNTs) with aryl residues. Laccases with Rh76EPS and Rh1021EPS had an evident shift of the value of the redox potential compared to the control without EPS addition. In conclusion, the results obtained in this work present a new potential use of bacterial EPSs as a metal-binding component and a modulator of laccase properties especially stability of enzyme activity, which can be a very effective tool in biotechnology and industrial applications.

Chemical Synthesis of Biomimetic Hydrogels for Tissue Engineering

Owing to the high water content, porous structure, biocompatibility and tissue-like viscoelasticity, hydrogels have become attractive and promising biomaterials for use in drug delivery, 3D cell culture and tissue engineering applications. Various chemical approaches have been developed for hydrogel synthesis using monomers or polymers carrying reactive functional groups. For in vivo tissue repair and in vitro cell culture purposes, it is desirable that the crosslinking reactions occur under mild conditions, do not interfere with biological processes and proceed at high yield with exceptional selectivity. Additionally, the cross-linking reaction should allow straightforward incorporation of bioactive motifs or signaling molecules, at the same time, providing tunability of the hydrogel microstructure, mechanical properties, and degradation rates. In this review, we discuss various chemical approaches applied to the synthesis of complex hydrogel networks, highlighting recent developments from our group. The discovery of new chemistries and novel materials fabrication methods will lead to the development of the next generation biomimetic hydrogels with complex structures and diverse functionalities. These materials will likely facilitate the construction of engineered tissue models that may bridge the gap between 2D experiments and animal studies, providing preliminary insight prior to in vivo assessments.

Laccase encapsulation in chitosan nanoparticles enhances the protein stability against microbial degradation

A novel concept with the result of enzyme stabilization against microbial degradation in real bioremediation processes was developed through the encapsulation of laccase in chitosan nanoparticles. Besides of abundant information on laccase-chitosan conjugates, we report the laccase encapsulation into nanoparticles based in chitosan. The chitosan-tripolyphosphate technique was applied for the production of morphologically homogeneous enzymatic nanoparticles, with high enzyme encapsulation efficiency, small asymmetric sizes (from 40 to 90 nm), and rough surfaces. Contrary to macroscopic immobilized enzymes, temperature and pH activity profiles of nano-sized laccase were similar to those of free enzyme. The substrate affinity constant (K M) of nano-encapsulated laccase was similar to these from free enzyme, while its activity rate constant (k cat) represented 60 % of these obtained with free enzyme. Importantly, stability of nano-encapsulated laccase against microbial degradation in soil, compost, and wastewater was significantly increased. After 24 h exposure to wastewater from a treatment plant, the laccase activity of the nanoparticles was 82.8 % of initial activity, compared with only 7.8 % retained activity for free enzyme. After 36 h incubation in compost extract, the laccase nanoparticles showed 72.4 % of the initial activity, while the free enzyme was almost completely inactivated. Finally, after 84 h incubation in soil extract, the nanoparticles and free preparations showed 57.9 and 17.3 % of the initial activity, respectively. Thus, the nanoencapsulation of enzymes able to transform pollutants is an alternative to improve the operational lifetime of enzymes in real environmental applications.

Chitosan improves stability of carbon nanotube biocathodes for glucose biofuel cells

We demonstrate a novel combined chitosan–carbon-nanotube–enzyme biocathode with a fibrous microstructure that improves the performance by creating a protective microenvironment, preventing the loss of the electrocatalytic activity of the enzyme, and providing good oxygen diffusion.

The catalytic activity enhancement and biodegradation potential of free laccase and novel sol-gel laccase in non-conventional solvents

The catalytic activity of free laccase and a novel sol-gel laccase (SOLAC) in ionic liquids and organic solvents was demonstrated by using 2,6-dimethoxyphenol (2,6-DMP) as a substrate. The enhancement of the catalytic activity of the SOLAC was observed and compared to the free laccase in both media. The oxidative biodegradation of o-chlorophenol as a model of phenolic environmental pollutants in organic media shows that the degradation was observed only when using water pre-saturated organic solvents or reverse micelle system. The SOLAC gave higher biodegradation rate in either aqueous or organic solvents, in which the optimum temperature was observed at 40 °C for the reverse micelle system as a reaction medium. All results demonstrated the potential use of the SOLAC for biodegradation of phenolic environmental pollutants in non-conventional media.

Selective Modification of Chitosan to Enable the Formation of Chitosan-DNA Condensates by Electron Donator Stabilization

Chitosan, a polyaminosaccharide, has been investigated for its use in the field of drug-delivery and biomaterial applications because of its natural biocompatibility and polycationic properties. Chemical modifications of chitosan have been attempted in an effort to increase the transfection efficiency with respect to gene delivery applications; however, it is unknown how these modifications affect the formation of the condensates. This study attempts to determine the effects of modification of the cationic center of chitosan on the ability to condense DNA. Specifically, electron-donating or -withdrawing groups were used as modifiers of the cationic charge on the chitosan backbone to stabilize the protonated form of chitosan, which is necessary to form condensates and increase the efficiency of the polymer to condense DNA by yielding condensates at a lower nitrogen to phosphorous (N : P) ratio. While an N : P ratio of 7 is needed to condense DNA with unmodified chitosan, phthalate-modified chitosan yielded condensates were obtained at an N : P ratio of 1.0.

Laccase-Based CLEAs: Chitosan as a Novel Cross-Linking Agent

Laccase from Coriolopsis Polyzona was insolubilized as cross-linked enzyme aggregates (CLEAs) for the first time with chitosan as the cross-linking agent. Concentrations between 0.01 and 1.867 g/L of chitosan were used and between 0.05 and 600 mM of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride. The laccase was precipitated using ammonium sulphate and cross-linked simultaneously. Specific activity and thermal stability of these biocatalysts were measured. Activities of up to 737 U/g were obtained when 2,2-azino-bis-(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) was used as a substrate. Moreover, the stability of these biocatalysts was improved with regards to thermal degradation compared to free laccase when exposed to denaturing conditions of high temperature and low pH. The CLEAs stability against chemical denaturants was also tested but no significant improvement was detected. The total amount of ABTS to be oxidized during thermal degradation by CLEAs and free laccase was calculated and the insolubilized enzymes were reported to oxidize more substrate than free laccase. The formation conditions were analyzed by response surface methodology in order to determine an optimal environment for the production of efficient laccase-based CLEAs using chitosan as the cross-linking agent. After 24 hours of formation at pH 3 and at 4°C without agitation, the CLEAs exhibit the best specific activity.

Semi-interpenetrating polymer networks containing polysaccharides. II. Xanthan/lignin networks: a spectral and thermal characterization

Polysaccharides are important materials in food, pharmaceutical, cosmetic and related biomedical applications. Xanthan gum is a microbial polysaccharide of great commercial significance. Lignin possesses antioxidant, antimicrobial and stabilizer properties. The aim of this study was to investigate by UV-Vis and infrared spectroscopy, wide angle X-ray scattering, differential scanning calorimetry and thermogravimetric studies, the characteristics of biodegradable superabsorbant hydrogels with high swelling rate in aqueous mediums. These were obtained by crosslinking reaction between xanthan gum and different types of lignin (aspen wood lignin, annual fibre crops lignin and lignin epoxy-modified resin) using epichlorhydrine as crosslinking agent. It is expected an increased in thermal stability, hydrophilicity, biocompatibility of hydrogel-films by lignin incorporation. Applications in the food and medical field were also found.

A nitrite biosensor based on co-immobilization of nitrite reductase and viologen-modified chitosan on a glassy carbon electrode

An electrochemical nitrite biosensor based on co-immobilization of copper-containing nitrite reductase (Cu-NiR, from Rhodopseudomonas sphaeroides forma sp. denitrificans) and viologen-modified chitosan (CHIT-V) on a glassy carbon electrode (GCE) is presented. Electron transfer (ET) between a conventional GCE and immobilized Cu-NiR was mediated by the co-immobilized CHIT-V. Redox-active viologen was covalently linked to a chitosan backbone, and the thus produced CHIT-V was co-immobilized with Cu-NiR on the GCE surface by drop-coating of hydrophilic polyurethane (HPU). The electrode responded to nitrite with a limit of detection (LOD) of 40 nM (S/N = 3). The sensitivity, linear response range, and response time (t(90%)) were 14.9 nA/μM, 0.04-11 μM (r(2) = 0.999) and 15 s, respectively. The corresponding Lineweaver-Burk plot showed that the apparent Michaelis-Menten constant (K(M) (app)) was 65 μM. Storage stability of the biosensor (retaining 80% of initial activity) was 65 days under ambient air and room temperature storage conditions. Reproducibility of the sensor showed a relative standard deviation (RSD) of 2.8% (n = 5) for detection of 1 μM of nitrite. An interference study showed that anions commonly found in water samples such as chlorate, chloride, sulfate and sulfite did not interfere with the nitrite detection. However, nitrate interfered with a relative sensitivity of 64% and this interference effect was due to the intrinsic character of the NiR employed in this study.

Mixed ceria-based metal oxides biosensor for operation in oxygen restrictive environments

The unique catalytic, electrochemical, and oxygen storage properties of ceria and mixed ceria/titania hybrid composites were used to fabricate a new type of electrochemical enzyme biosensor. These materials provided increased analytical performance and possibilities for operation in oxygen-free conditions of an oxidase enzyme biosensor using tyrosinase as a model example. The investigation of the enzymatic reaction in the presence and absence of oxygen was first carried out using cyclic voltammetry. The results were used to identify the role of each metal oxide in the immobilization matrix and fabricate a simple amperometric tyrosinase biosensor for the detection of phenol and dopamine. The biosensor was optimized and characterized with respect to response time, detection limit, linear concentration range, sensitivity, and kinetic parameters. The detection limit for phenol was in the nanomolar range, with a detection limit of 9.0 x 10(-9) M and a sensitivity of 86 mA M(-1) in the presence of oxygen and of 5.6 x 10(-9) M and a sensitivity of 65 mA M(-1) in the absence of oxygen. The optimized biosensor also showed selective determination of the neurotransmitter dopamine with a detection limit of 3.4 x 10(-8) M and a sensitivity of 14.9 mA M(-1) in the presence of oxygen and of 4.2 x 10(-8) M and 14.8 mA M(-1) in the absence of oxygen. This strategy shows promise for increasing the sensitivity of oxidase enzyme sensors and provides opportunities for operation in oxygen limited conditions. It can also be extended for the development of other enzyme biosensors.

Semi-interpenetrating Polymer Networks Containing Polysaccharides. I Xanthan/Lignin Networks

The polysaccharides are important materials in food, pharmaceutical, cosmetic and related biomedical applications. Xanthan gum is a microbial polysaccharide of great commercial significance. It is well known as one of the best thickening polymers due to its high intrinsic stiffness related to the helical conformation stabilized in the presence of excess salt. It is used in a wide variety of foods for a number of important reasons, including emulsion stabilization, temperature stability, compatibility with food ingredients, and its pseudoplastic rheological properties. Due to its properties in thickening aqueous solutions, as a dispersing agent, and stabilizer of emulsions and suspensions, xanthan gum is used in pharmaceutical formulations, cosmetics, and agricultural products, as well as in textile printing pastes, ceramic glazes, slurry explosive formulations, and rust removers. In this work the crosslinking of a mixture of xanthan and lignins in the presence of the epichlorohydrin, leading to superabsorbant hydrogels with high swelling rate in aqueous mediums, was studied. The swelling properties of these composite hydrogels were investigated. Three different types of lignin have been used namely: aspen wood lignin (L), annual fiber crop lignin (GL) and lignin epoxy-modified resin (LER). Semi-interpenetrating polymer network hydrogels in various ratios were prepared. The influence of gravimetric ratio between components of the semi-interpenetrating polymer networks, as well as the kinetics of water sorption will be discussed. The maximum swelling degree of the hydrogels and the swelling rate constant were determined as a function of the hydrogel's composition. It has been established that the nature of lignin significantly influences swelling process, the chemical modified lignin having a particular behavior.

Chitosan: a soft interconnect for hierarchical assembly of nano-scale components

Traditional microfabrication has tremendous capabilities for imparting order to hard materials (e.g., silicon wafers) over a range of length scales. However, conventional microfabrication does not provide the means to assemble pre-formed nano-scale components into higher-ordered structures. We believe the aminopolysaccharide chitosan possesses a unique set of properties that enable it to serve as a length-scale interconnect for the hierarchical assembly of nano-scale components into macro-scale systems. The primary amines (atomic length scale) of the glucosamine repeating units (molecular length scale) provide sites to connect pre-formed or self-assembled nano-scale components to the polysaccharide backbone (macromolecular length scale). Connections to the backbone can be formed by exploiting the electrostatic, nucleophilic, or metal-binding capabilities of the glucosamine residues. Chitosan's film-forming properties provide the means for assembly at micron-to-centimetre lengths (supramolecular length scales). In addition to interconnecting length scales, chitosan's capabilities may also be uniquely-suited as a soft component-hard device interconnect. In particular, chitosan's film formation can be induced under mild aqueous conditions in response to localized electrical signals that can be imposed from microfabricated surfaces. This capability allows chitosan to assemble soft nano-scale components (e.g., proteins, vesicles, and virus particles) at specific electrode addresses on chips and in microfluidic devices. Thus, we envision the potential that chitosan may emerge as an integral material for soft matter (bio)fabrication.

pH- and thermosensitive polyaniline colloidal particles prepared by enzymatic polymerization

Polyaniline colloids were prepared by enzymatic polymerization using chitosan and poly(N-isopropylacrylamide) as steric stabilizers. The resulting nanoparticles undergo flocculation by changing the pH or temperature of the aqueous dispersions. The environmentally responsive behavior of these colloids contrasts with that of polyaniline colloids synthesized using poly(vinyl alcohol) as the steric stabilizer. The colloid size was a function of the steric stabilizers and ranged from approximately 50 nm for polyaniline particles prepared in the presence of chitosan and partially hydrolyzed poly(vinyl alcohol) up to 350 nm for the particles synthesized using poly(N-isopropylacrylamide). UV-visible and Fourier transform infrared spectroscopic studies indicate that polyaniline colloids are spectroscopically similar to those obtained by traditional dispersion polymerization of aniline by chemical oxidation. These polyaniline colloids have potential applications in thermochromic windows and smart fluids.

Amperometric biosensor based on tyrosinase-conjugated polysaccharide hybrid film: selective determination of nanomolar neurotransmitters metabolite of 3,4-dihydroxyphenylacetic acid (DOPAC) in biological fluid

The amperometric detection of neurotransmitters metabolite of 3,4-dihydroxyphenylacetic acid (DOPAC) was achieved at a tyrosinase-chitosan composite film-modified glassy carbon (GC) electrode. The optimal conditions for the preparation of the biosensor were established. This bio-composite film was characterized by scanning electron microscopy (SEM) and Fourier transformed infrared (FT-IR) spectra, suggesting that chitosan covalently connected to chitosan chains. Electrochemical characterization of the bio-hybrid membrane-covered electrodes were also performed in 0.05 M phosphate buffer solution (pH 6.52) containing neurotransmitters or their derivatives by using cyclic voltammetry (CV), linear sweep voltammetry (LSV), square wave voltammetry (SWV) and amperometry. This simply-prepared protein-polysaccharide hybrid film provides a microenvironment friendly for enzyme loading. The sensor was operated at -0.15 V with a short response time. The current linearly increased with the increasing concentration of DOPAC over the concentration of 6 nM-0.2 mM. The lower detection limit for DOPAC is 3 nM (S/N=3). The sensitivity of the sensor is 40 microA mM(-1). A physiological level of neurotransmitters and their derivatives including dopamine, l-dopa, adrenaline, noradrenaline and homovanillic acid as well as ascorbic acid, uric acid and acetaminophen do not affect the determination of DOPAC.

Polyelectrolyte complex formation mediated immobilization of chitosan-invertase neoglycoconjugate on pectin-coated chitin

Saccharomyces cerevisiae invertase, chemically modified with chitosan, was immobilized on pectin-coated chitin support via polyelectrolyte complex formation. The yield of immobilized enzyme protein was determined as 85% and the immobilized biocatalyst retained 97% of the initial chitosan-invertase activity. The optimum temperature for invertase was increased by 10 degrees C and its thermostability was enhanced by about 10 degrees C after immobilization. The immobilized enzyme was stable against incubation in high ionic strength solutions and was 4-fold more resistant to thermal treatment at 65 degrees C than the native counterpart. The biocatalyst prepared retained 96 and 95% of the original catalytic activity after ten cycles of reuse and 74 h of continuous operational regime in a packed bed reactor, respectively.

Multilayer-Assembled Microchip for Enzyme Immobilization as Reactor Toward Low-Level Protein Identification

A microchip reactor has been developed on the basis of a layer-by-layer approach for fast and sensitive digestion of proteins. The resulting peptide analysis has been carried out by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS). Natural polysaccharides, positively charged chitosan (CS), and negatively charged hyaluronic acid (HA) were multilayer-assembled onto the surface of a poly(ethylene terephthalate) (PET) microfluidic chip to form a microstructured and biocompatible network for enzyme immobilization. The construction of CS/HA assembled multilayers on the PET substrate was characterized by AFM imaging, ATR-IR, and contact angle measurements. The controlled adsorption of trypsin in the multilayer membrane was monitored using a quartz crystal microbalance and an enzymatic activity assay. The maximum proteolytic velocity of the adsorbed trypsin was approximately 600 mM/min mug, thousands of times faster than that in solution. BSA, myoglobin, and cytochrome c were used as model substrates for the tryptic digestion. The standard proteins were identified at a low femtomole per analysis at a concentration of 0.5 ng/muL with the digestion time <5s. This simple technique may offer a potential solution for low-level protein analysis.

Biofabrication with Chitosan

The traditional motivation for integrating biological components into microfabricated devices has been to create biosensors that meld the molecular recognition capabilities of biology with the signal processing capabilities of electronic devices. However, a different motivation is emerging; biological components are being explored to radically change how fabrication is achieved at the micro- and nanoscales. Here we review biofabrication, the use of biological materials for fabrication, and focus on three specific biofabrication approaches: directed assembly, where localized external stimuli are employed to guide assembly; enzymatic assembly, where selective biocatalysts are enlisted to build macromolecular structure; and self-assembly, where information internal to the biological material guides its own assembly. Also reviewed are recent results with the aminopolysaccharide chitosan, a material that offers a combination of properties uniquely suited for biofabrication. In particular, chitosan can be directed to assemble in response to locally applied electrical signals, and the chitosan backbone provides sites that can be employed for the assembly of proteins, nucleic acids, and virus particles.

Chitosan-mediated and spatially selective electrodeposition of nanoscale particles

Nanoscale particles offer a variety of interesting properties, and there is growing interest in their assembly into higher ordered structures. We report that the pH-responsive aminopolysaccharide chitosan can mediate the electrodeposition of model nanoparticles. Chitosan is known to electrodeposit at the cathode surface in response to a high localized pH. To demonstrate that chitosan can mediate nanoparticle deposition, we suspended fluorescently labeled latex nanoparticles (100 nm diameter spheres) in a chitosan solution (1%) and performed electrodeposition (0.05 mA/cm2 for several minutes). Results demonstrate that chitosan is required for nanoparticle electrodeposition; chitosan confers spatial selectivity to electrodeposition; and nanoparticles distribute throughout the electrodeposited chitosan film. Additionally, we observed that the deposited films reversibly swell upon rehydration. This work indicates that chitosan provides a simple means to assemble nanoparticles at addressable locations and provides further evidence that stimuli-responsive biological materials may facilitate fabrication at the microscale.