Enzyme immobilization on anodic aluminum oxide/polyethyleneimine or polyaniline composites

Preparation of Alumina Membrane Filters with Framework Structures by Al Anodization

Alumina membrane filters consisting of a thin filter layer (200-700 nm in thickness) supported by a framework (30-100 μm in thickness) were fabricated on the basis of the anodization of an Al substrate. The solution permeability of alumina membrane filters with tubular pores of uniform size and shape varies with membrane thickness; therefore, membrane filters with a filter layer thickness of less than 1 μm showed high solution permeability. Although the filter layer is thin, it is reinforced by a thick framework, enabling the fabrication of large freestanding membrane filters (2.5 × 2 cm2 in size). The pore size of the anodic porous alumina formed by the anodization of Al can be controlled in the range from 10 nm to ca. 2 μm by varying the preparation conditions. The alumina membrane obtained by this method is therefore useful as a membrane filter that can efficiently separate particles of various sizes, including microplastics, viruses, and bacteria. This method enables the fabrication of membrane filters with uniform pore size, high solution permeability, and sufficient mechanical strength for handling as freestanding membranes, which have been difficult to achieve with the reported preparation processes for membrane filters. The obtained membrane filters with frameworks can be applied to efficient microfiltration.

Immobilization of Fructofuranosidase from Aureobasidium sp. Onto TiO2 and Its Encapsulation on Gellan Gum for FOS Production

Fructofuranosidase (EC 3.2.1.26) from Aureobasidium sp. ATCC 20524, recovered from 5 L fermented medium, purified by two simple steps with a yield of 65 % and a purification factor of 16, was immobilized by adsorption onto titanium dioxide (FTIO). The enzyme was also covalently immobilized onto TiO2 coated with polyethyleneimine (FTIOP) and encapsulated in gellan gum (FTIOPG). FTIO and FTIOP recorded an activity of 903 U g−1 and 9212 U g−1, respectively. The immobilized enzyme showed high activity and stability at pH levels ranging from 4.0 to 8.0 and there were no changes in the temperature profile for either methodology when compared with free fructofuranosidase. The immobilized biocatalysts were reused 7 times for FOS production without significant activity loss, except FTIO at pH 5.0. Gellan gum was used for FTIOP encapsulation. FOS production was performed in a batch and a continuous reactor using FTIOPG as a biocatalyst. Batch conversion (gFOS/ginitial sucrose) was around 60 % for initial sucrose concentrations of 100, 300 and 600 g L−1, at a time of maximum conversion. Fixed-bed reactor operational stability was remarkable, providing a constant FOS production in the outlet of the column during 720 h.

Nanoporous Anodic Alumina Photonic Crystals for Optical Chemo- and Biosensing: Fundamentals, Advances, and Perspectives

Optical sensors are a class of devices that enable the identification and/or quantification of analyte molecules across multiple fields and disciplines such as environmental protection, medical diagnosis, security, food technology, biotechnology, and animal welfare. Nanoporous photonic crystal (PC) structures provide excellent platforms to develop such systems for a plethora of applications since these engineered materials enable precise and versatile control of light⁻matter interactions at the nanoscale. Nanoporous PCs provide both high sensitivity to monitor in real-time molecular binding events and a nanoporous matrix for selective immobilization of molecules of interest over increased surface areas. Nanoporous anodic alumina (NAA), a nanomaterial long envisaged as a PC, is an outstanding platform material to develop optical sensing systems in combination with multiple photonic technologies. Nanoporous anodic alumina photonic crystals (NAA-PCs) provide a versatile nanoporous structure that can be engineered in a multidimensional fashion to create unique PC sensing platforms such as Fabry⁻Pérot interferometers, distributed Bragg reflectors, gradient-index filters, optical microcavities, and others. The effective medium of NAA-PCs undergoes changes upon interactions with analyte molecules. These changes modify the NAA-PCs' spectral fingerprints, which can be readily quantified to develop different sensing systems. This review introduces the fundamental development of NAA-PCs, compiling the most significant advances in the use of these optical materials for chemo- and biosensing applications, with a final prospective outlook about this exciting and dynamic field.

Surface-Engineered Biocatalytic Composite Membranes for Reduced Protein Fouling and Self-Cleaning

A new biocatalytic nanofibrous composite ultrafiltration membrane was developed to reduce protein fouling interactions and self-clean the membrane surface. The dual-layer poly(vinylidenefluoride)/nylon-6,6/chitosan composite membrane contains a hydrophobic poly(vinylidenefluoride) cast support layer and a hydrophilic functional nylon-6,6/chitosan nanofibrous surface layer where enzymes were chemically attached. The intrinsic surface chemistry and high surface area of the nanofibers allowed optimal and stable immobilization of trypsin (TR) and α-chymotrypsin enzymes via direct covalent binding. The enzyme immobilization was confirmed by X-ray photoelectron spectroscopy and visualized by confocal microscopy analysis. The prepared biocatalytic composite membranes were nanoporous with superior permeability offering stable protein antiadhesion and self-cleaning properties owing to the repulsive mechanism and digestion of proteins into peptides and amino acids, which was quantified by the gel electrophoresis technique. The TR-immobilized composite membranes exhibited 2.7-fold higher permeance and lower surface protein contamination with 3-fold greater permeance recovery, when compared to the pristine membrane after two ultrafiltration cycles with the model feed solution containing bovine serum albumin/NaCl/CaCl₂. The biocatalytic membranes retained about 50% of the enzyme activity after six reuse cycles but were regenerated to 100% activity after enzyme reloading, leading to a simple and cost-effective water remediation operation. Such surface- and pore-engineered membranes with self-cleaning properties offer a viable solution for severe surface protein contamination in food and water applications.

A flow-through nanoporous alumina trypsin bioreactor for mass spectrometry peptide fingerprinting

Mass spectrometry-based proteomics benefits from efficient digestion of protein samples. In this study, trypsin was immobilized on nanoporous anodized alumina membranes to create an enzyme reactor suitable for peptide mass fingerprinting. The membranes were derivatized with 3-aminopropyltriethoxysilane and the amino groups were activated with carbonyldiimidazole to allow coupling of porcine trypsin via ε-amino groups. The function was assessed using the artificial substrate Nα-Benzoyl-L-arginine 4-nitroanilide hydrochloride, bovine ribonuclease A and a human plasma sample. A 10-membrane flow-through reactor was used for fragmentation and MS analysis after a single pass of substrate both by collection of product and subsequent off-line analysis, and by coupling on-line to the instrument. The peptide pattern allowed correct identification of the single target protein in both cases, and of >70 plasma proteins in single pass mode followed by LC-MS analysis. The reactor retained 76% of the initial activity after 14days of storage and repeated use at room temperature.

SIGNIFICANCE

This manuscript describes the design of a stable enzyme reactor that allows efficient and fast digestion with negligible leakage of enzyme and enzyme fragments. The high stability facilitates the use in an online-setup with MS detection since it allows the processing of multiple samples within an extended period of time without replacement.

Bio-Inspired Polymer Membrane Surface Cleaning

To generate polyethersulfone membranes with a biocatalytically active surface, pancreatin was covalently immobilized. Pancreatin is a mixture of digestive enzymes such as protease, lipase, and amylase. The resulting membranes exhibit self-cleaning properties after “switching on” the respective enzyme by adjusting pH and temperature. Thus, the membrane surface can actively degrade a fouling layer on its surface and regain initial permeability. Fouling tests with solutions of protein, oil, and mixtures of both, were performed, and the membrane’s ability to self-clean the fouled surface was characterized. Membrane characterization was conducted by investigation of the immobilized enzyme concentration, enzyme activity, water permeation flux, fouling tests, porosimetry, X-ray photoelectron spectroscopy, and scanning electron microscopy.

Polyethylenimine: a very useful ionic polymer in the design of immobilized enzyme biocatalysts

This review discusses the possible roles of polyethylenimine (PEI) in the design of improved immobilized biocatalysts from diverse perspectives.

Functionalized anodic aluminum oxide membrane-electrode system for enzyme immobilization

A nanoporous membrane system with directed flow carrying reagents to sequentially attached enzymes to mimic nature’s enzyme complex system was demonstrated. Genetically modified glycosylation enzyme, OleD Loki variant, was immobilized onto nanometer-scale electrodes at the pore entrances/exits of anodic aluminum oxide membranes through His6-tag affinity binding. The enzyme activity was assessed in two reactions—a one-step “reverse” sugar nucleotide formation reaction (UDP-Glc) and a two-step sequential sugar nucleotide formation and sugar nucleotide-based glycosylation reaction. For the one-step reaction, enzyme specific activity of 6–20 min(–1) on membrane supports was seen to be comparable to solution enzyme specific activity of 10 min(–1). UDP-Glc production efficiencies as high as 98% were observed at a flow rate of 0.5 mL/min, at which the substrate residence time over the electrode length down pore entrances was matched to the enzyme activity rate. This flow geometry also prevented an unwanted secondary product hydrolysis reaction, as observed in the test homogeneous solution. Enzyme utilization increased by a factor of 280 compared to test homogeneous conditions due to the continuous flow of fresh substrate over the enzyme. To mimic enzyme complex systems, a two-step sequential reaction using OleD Loki enzyme was performed at membrane pore entrances then exits. After UDP-Glc formation at the entrance electrode, aglycon 4-methylumbelliferone was supplied at the exit face of the reactor, affording overall 80% glycosylation efficiency. The membrane platform showed the ability to be regenerated with purified enzyme as well as directly from expression crude, thus demonstrating a single-step immobilization and purification process.

Size-dependent optical properties of bio-compatible ZnS:Mn nanocrystals and their application in the immobilisation of trypsin

Chitosan capped zinc sulphide nanocrystals doped with manganese (ZnS:Mn) have been synthesised by chemical capping co-precipitation method and structurally characterised by XRD, TEM and EDXS techniques. The dependence of optical properties on the size of these bio-compatible ZnS:Mn nanocrystals was investigated by UV/Vis and photoluminescence (PL) spectroscopic techniques in aqueous solvents. A variation in molar concentration of the precursor, sodium sulphide, from 0.125 to 0.01 mol L(-1) is accompanied by a decrease in particle size. The excitonic peak in the UV/Vis spectra is found to be blue shifted with a decrease in size of the nanocrystals due to confinement effects. In the present study, trypsin was immobilised onto ZnS:Mn nanocrystals using glutaraldehyde (GA) as cross-linker, which was confirmed by photoluminescence (PL) and Fourier transform infrared (FTIR) spectroscopic studies. Results indicate that the activity of trypsin, immobilised onto chitosan modified nanocrystals, has improved upon cross-linking, which suggests that the immobilised trypsin has become more stable and active. This work highlights the prospects of potential applications of immobilised trypsin in therapeutic and diagnostic fields.

Progress in Nano-Engineered Anodic Aluminum Oxide Membrane Development

The anodization of aluminum is an electro-chemical process that changes the surface chemistry of the metal, via oxidation, to produce an anodic oxide layer. During this process a self organized, highly ordered array of cylindrical shaped pores can be produced with controllable pore diameters, periodicity and density distribution. This enables anodic aluminum oxide (AAO) membranes to be used as templates in a variety of nanotechnology applications without the need for expensive lithographical techniques. This review article is an overview of the current state of research on AAO membranes and the various applications of nanotechnology that use them in the manufacture of nano-materials and devices or incorporate them into specific applications such as biological/chemical sensors, nano-electronic devices, filter membranes and medical scaffolds for tissue engineering.