Stabilization of immobilized glucose oxidase against thermal inactivation by silanization for biosensor applications

The SARS-CoV-2 specific IgG antibodies biophotonic sensor

In this paper, we present the design and the principle of operation of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) specific immunoglobulin G (IgG) biophotonic sensor, which is based on the single-mode telecommunication fiber. We fabricated the sensor head at the face of the single mode fiber-28. Due to the process of bio-functionalization, our sensor has the ability to selectively detect the SARS-CoV-2 specific IgG antibodies. The results of preliminary tests allowed us to correctly determine the presence of antibodies in less than 1 min in 5 μl in a volume sample of concentration of 10 μg/ml, which according to studies, corresponds to the concentration of IgG antibodies in human serum. Additionally, the tested sample can be smaller than 5 μl in volume.

Zeolite-based nanocomposite as a smart pH-sensitive nanovehicle for release of xylanase as poultry feed supplement

Xylanase improves poultry nutrition by degrading xylan in the cell walls of feed grains and release the entrapped nutrients. However, the application of xylanase as a feed supplement is restricted to its low stability in the environment and gastrointestinal (GI) tract of poultry. To overcome these obstacles, Zeozyme NPs as a smart pH-responsive nanosystem was designed based on xylanase immobilization on zeolitic nanoporous as the major cornerstone that was modified with L-lysine. The immobilized xylanase was followed by encapsulating with a cross-linked CMC-based polymer. Zeozyme NPs was structurally characterized using TEM, SEM, AFM, DLS, TGA and nitrogen adsorption/desorption isotherms at liquid nitrogen temperature. The stability of Zeozyme NPs was evaluated at different temperatures, pH, and in the presence of proteases. Additionally, the release pattern of xylanase was investigated at a digestion model mimicking the GI tract. Xylanase was released selectively at the duodenum and ileum (pH 6-7.1) and remarkably preserved at pH ≤ 6 including proventriculus, gizzard, and crop (pH 1.6-5). The results confirmed that the zeolite equipped with the CMC matrix could enhance the xylanase thermal and pH stability and preserve its activity in the presence of proteases. Moreover, Zeozyme NPs exhibited a smart pH-dependent release of xylanase in an in vitro simulated GI tract.

Studies on enhancing operational stability of a reusable laccase-based biosensor probe for detection of ortho-substituted phenolic derivatives

An amperometric principle-based biosensor containing immobilized enzyme laccase from Trametes versicolor was developed for detection of ortho-substituted phenolic derivatives. Different immobilization methods for Trametes versicolor laccase enzyme on cellophane membrane and the enhancement of operational stability of the immobilized enzyme electrode using various protein-based stabilizing agents were studied. Among tested methods of immobilization, co-cross-linking method with bovine serum albumin was superior to the other methods in terms of sensitivity, limit of detection, response time, and operating and thermal stability. Biosensor response reached steady state within 3 min and exhibited maximum activity at 45 °C and pH 6.8. The sensitivity of the ortho-substituted phenols for the test biosensor developed with co-cross-linking method of immobilization using bovine serum albumin as the protein-based stabilizing agent was in the order: 2-aminophenol > guaiacol(2-methoxyphenol) > catechol(2-hydroxyphenol) > cresol(2-methyl phenol) > 2-chlorophenol. Validation of the newly developed biosensor by comparison with HPLC showed good agreement in the results. A newly developed biosensor was applied for quantification of ortho-substituted phenols in simulated effluent samples.

Selective growth of carbon nanotubes on boron-doped diamond for electrochemical biosensor application

Selective growth of MWCNTs on boron-doped diamond electrode was introduced and their electrochemical properties and glucose biosensing performances were reported.

Comparison of Different Oxidation Techniques for Biofunctionalization of Pyrolyzed Carbon

Pyrolyzed carbon micro/nano-structures have great potential as functional units in biosensors where biofunctionalization of the carbon surface is a requisite. In this work, we present a comparison of four different oxidation pretreatments, i.e. vacuum ultraviolet (VUV), electrochemical activation (EA), oxygen reactive ion etching (RIE), and ultraviolet/ozone (UV/O3) pretreatments on pyrolyzed carbon surface. X-ray photoelectron spectroscopy (XPS) results indicated that all the oxidation techniques except UV/O3 pretreatment yielded identical oxidation levels. The percentage of the carboxyl group which is suitable for covalent attachment of amine terminated biomolecules increased with pretreatment time, and was highest in the case of VUV pretreatment (15%) followed by oxygen RIE (12.5%) and EA pretreatments (12.5%) and UV/O3 pretreatment showed significantly lower carboxyl group percentage at 6%. This study helps to optimize the surface functionalization conditions for covalent binding of bioreceptors on the pyrolyzed carbon substrate for biosensing applications.

Immobilization of a Pleurotus ostreatus laccase mixture on perlite and its application to dye decolourisation

In the present study, a crude laccase preparation from Pleurotus ostreatus was successfully immobilized on perlite, a cheap porous silica material, and tested for Remazol Brilliant Blue R (RBBR) decolourisation in a fluidized bed recycle reactor. Results showed that RBBR decolourisation is mainly due to enzyme action despite the occurrence of dye adsorption-related enzyme inhibition. Fine tuning of immobilization conditions allowed balancing the immobilization yield and the resulting rate of decolourisation, with the adsorption capacity of the solid biocatalyst. In the continuous lab scale reactor, a maximum conversion degree of 56.1% was achieved at reactor space-time of 4.2 h. Stability and catalytic parameters of the immobilized laccases were also assessed in comparison with the soluble counterparts, revealing an increase in stability, despite a reduction of the catalytic performances. Both effects are most likely ascribable to the occurrence of multipoint attachment phenomena.

Enzyme immobilization on silane-modified surface through short linkers: fate of interfacial phases and impact on catalytic activity

We investigated the mechanism of enzyme immobilization on silanized surfaces through coupling agents (cross-linkers) in order to understand the role of these molecules on interfacial processes and their effect on catalytic activity. To this end, we used a model multimeric enzyme (G6PDH) and several cross-linking molecules with different chemical properties, including the nature of the end-group (-NCO, -NCS, -CHO), the connecting chain (aliphatic vs aromatic), and geometrical constraints (meta vs para-disubstituted aromatics). There did not seem to be radical differences in the mechanism of enzyme adsorption according to the linker used as judged from QCM-D, except that in the case of DIC (1,4-phenylene diisocyanate) the adsorption occurred more rapidly. In contrast, the nature of the cross-linker exerted a strong influence on the amount of enzyme immobilized as estimated from XPS, and more unexpectedly on the stability of the underlying silane layer. DIC, PDC (1,4-phenylene diisothiocyanate), or GA (glutaraldehyde) allowed successful enzyme immobilization. When the geometry of the linker was changed from 1,4-phenylene diisothiocyanate to 1,3-phenylene diisothiocyanate (MDC), the silane layer was subjected to degradation, upon enzyme adsorption, and the amount of immobilized molecules was significantly lowered. TE (terephtalaldehyde) and direct enzyme deposition without cross-linker were similar to MDC. The organization of immobilized enzymes also depended on the immobilization procedure, as different degrees of aggregation were observed by AFM. A correlation between the size of the aggregates and the catalytic properties of the enzyme was established, suggesting that aggregation may enhance the thermostability of the multimeric enzyme, probably through a compaction of the 3D structure.

Heated proteins are still active in a functionalized nanoporous support

Even under heated conditions, the nearly native conformation and activity of a protein can be hoarded in a functionalized nanoporous support via non-covalent interaction. Surprisingly, the protein released from the heated protein-nanoporous composite can maintain its nearly native conformation and activity, while free proteins are permanently denatured under the same treatment.

A method for regenerating gold surface for prolonged reuse of gold-coated surface plasmon resonance chip

We developed a method to completely regenerate the gold (Au) surface of 3-aminopropyltriethoxysilane (APTES)-functionalized Au-coated surface plasmon resonance (SPR) chip that had been used for human fetuin A (HFA) immunoassay. It involved treatment of the used SPR chip with freshly prepared piranha solution (concentrated H(2)SO(4)/30% H(2)O(2)=3:1, v/v) for 15 min followed by extensive rinsing with ethanol and deionized water. The developed method enabled prolonged reuse of the regenerated SPR chip that increased its cost-effectiveness without affecting the reproducibility of HFA immunoassays.

The mechanism of inactivation of glucose oxidase from Penicillium amagasakiense under ambient storage conditions

Glucose oxidase (GOx) from Penicillium amagasakiense has a higher specific activity than the more commonly studied Aspergillus niger enzyme, and may therefore be preferred in many medical and industrial applications. The enzyme rapidly inactivates on storage at pH 7.0-7.6 at temperatures between 30 and 40°C. Results of fluorimetry and circular dichroism spectroscopy indicate that GOx inactivation under these conditions is associated with release of the cofactor FAD and molten globule formation, indicated by major loss of tertiary structure but almost complete retention of secondary structure. Inactivation of GOx at pH<7 leads to precipitation, but at pH ≥ 7 it leads to non-specific formation of small soluble aggregates detectable by PAGE and size-exclusion chromatography (SEC). Inactivation of P. amagasakiense GOx differs from that of A. niger GOx in displaying complete rather than partial retention of secondary structure and in being promoted rather than prevented by NaCl. The contrasting salt effects may reflect differences in the nature of the interface between subunits in the native dimers and/or the quantity of secondary structure loss upon inactivation.

Wheat dehydrin DHN-5 exerts a heat-protective effect on beta-glucosidase and glucose oxidase activities

Group-2 late embryogenesis abundant (LEA) proteins, also known as dehydrins, are claimed to stabilize macromolecules against damage caused by freezing, dehydration, ionic or osmotic stresses. However, their precise function remains unknown. Here, we investigated the effect of wheat dehydrin (DHN-5) protein on the activity and thermostability of two distinct enzymes, beta-glucosidase (bglG) and glucose oxidase/peroxidase (GOD/POD) in vitro. The purified DHN-5 protein had the capacity to preserve and stabilize the activity of bglG subjected to heat treatment. In addition, DHN-5 stabilized oxidizing enzymes, as it improved reliability in measuring glucose concentrations with a glucose oxidase/peroxidase (GOD/POD) kit while the temperature increased from 37 to 70 degrees C. All together the data presented provide evidence that DHN-5 is a dehydrin able to preserve enzyme activities in vitro from adverse effects induced by heating.

Directed self-immobilization of alkaline phosphatase on micro-patterned substrates via genetically fused metal-binding peptide

Current biotechnological applications such as biosensors, protein arrays, and microchips require oriented immobilization of enzymes. The characteristics of recognition, self-assembly and ease of genetic manipulation make inorganic binding peptides an ideal molecular tool for site-specific enzyme immobilization. Herein, we demonstrate the utilization of gold binding peptide (GBP1) as a molecular linker genetically fused to alkaline phosphatase (AP) and immobilized on gold substrate. Multiple tandem repeats (n = 5, 6, 7, 9) of gold binding peptide were fused to N-terminus of AP (nGBP1-AP) and the enzymes were expressed in E. coli cells. The binding and enzymatic activities of the bi-functional fusion constructs were analyzed using quartz crystal microbalance spectroscopy and biochemical assays. Among the multiple-repeat constructs, 5GBP1-AP displayed the best bi-functional activity and, therefore, was chosen for self-immobilization studies. Adsorption and assembly properties of the fusion enzyme, 5GBP1-AP, were studied via surface plasmon resonance spectroscopy and atomic force microscopy. We demonstrated self-immobilization of the bi-functional enzyme on micro-patterned substrates where genetically linked 5GBP1-AP displayed higher enzymatic activity per area compared to that of AP. Our results demonstrate the promising use of inorganic binding peptides as site-specific molecular linkers for oriented enzyme immobilization with retained activity. Directed assembly of proteins on solids using genetically fused specific inorganic-binding peptides has a potential utility in a wide range of biosensing and bioconversion processes.

Immobilization of the Enzyme Glucose Oxidase on Both Bulk and Porous SiO₂ Surfaces

Silicon dioxide surfaces, both bulk and porous, were used to anchor the enzyme glucose oxidase. The immobilization protocol was optimized and the samples characterized using X-ray Photoelectron Spectroscopy, Energy Dispersive X-rays coupled to scanning electron microscopy and enzymatic activity measurements. We show that a uniform layer was obtained by activating the oxide before immobilization. X-ray Photoelectron Spectroscopy measurements carried out on bulk oxide showed that the silicon substrate signal was fully screened after the enzyme deposition showing the absence of uncovered surface regions. The enzyme presence was detected monitoring both the C 1s and N 1s signals. Finally, enzymatic activity measurements confirmed that the glucose oxidase activity was preserved after immobilization and maintained after three months of shelf life if the sample was properly stored. The importance of using porous silicon oxide to maximize the surface area was also evidenced.

Peptide tags for enhanced cellular and protein adhesion to single-crystalline sapphire

In order to facilitate a novel means for coupling proteins to metal oxides, peptides were identified from a dodecamer peptide yeast surface display library that bound a model metal oxide material, the C, A, and R crystalline faces of synthetic sapphire (alpha-Al(2)O(3)). Seven rounds of screening yielded peptides enriched in basic amino acids compared to the naive library. While the C-face had a high background of endogenous yeast cell binding, the A- and R faces displayed clear peptide-mediated cell adhesion. Cell detachment assays showed that cell adhesion strength correlated positively with increasing basicity of expressed peptides. Cell adhesion was also shown to be sensitive to buffer ionic strength as well as incubation with soluble peptide (with half maximal inhibition of cell binding at approximately 5 microM peptide). Next, dodecamer peptides cloned into yeast showed that lysine led to stronger interactions than arginine, and that charge distribution affected adhesion strength. We postulate binding to arise from peptide geometries that permit conformation alignment of the basic amino acids towards the surface so that the charged groups can undergo local electrostatic interactions with the surface oxide. Lastly, peptide K1 (-(GK)(6)) was cloned onto the c-terminus of maltose binding protein (MBP) and the resultant mutant protein showed a half-maximal binding at approximately 10(-7)-10(-6) M, which marked a approximately 500- to 1,000-fold binding improvement to sapphire's A-face as compared with wild-type MBP. Targeting proteins to metal oxide surfaces with peptide tags may provide a facile one-step alternative coupling chemistry for the formation of protein bioassays and biosensors.

Continuous blood glucose monitoring with a thin-film optical sensor

BACKGROUND

We recently described a holographic optical sensor with improved selectivity for glucose over fructose that was based on a thin-film polymer hydrogel containing phenylboronic acid receptors. The aim of the present work was to measure glucose in human blood plasma as opposed to simple buffers and track changes in concentration at a rate mimicking glucose changes in vivo.

METHODS

We used holographic sensors containing acrylamide, N,N'-methylenebisacrylamide, 3-acrylamidophenylboronic acid, and (3-acrylamidopropyl)trimethylammonium chloride to measure 7 human blood plasma samples at different glucose concentrations (3-33 mmol/L) in static mode. Separately, using a flow cell, the glucose concentration was varied at approximately 0.17-0.28 mmol(-1) x L(-1) x min(-1), and the sensor's ability to continuously monitor glucose was investigated over an extended period.

RESULTS

We subjected the results of the ex vivo static measurements to error grid analysis. Of 46 measurements, 42 (91.3%) fell in zone A of a Clarke error grid, and the remainder (8.7%) fell in zone B. The ex vivo flow experiments showed that the sensor is able to accurately track changes in concentration occurring in real time without lag or evidence of hysteresis.

CONCLUSIONS

We demonstrate the ability of a phenylboronic acid-based sensor to measure glucose in human blood plasma for the 1st time in vitro. Holographic glucose sensors can be used without recourse to recalibration. Their robust nature, coupled with their format flexibility, makes them an attractive alternative to conventional electrochemical enzyme-based methods of glucose monitoring for people with diabetes.

Cholesterol biosensor based on N-(2-aminoethyl)-3-aminopropyl-trimethoxysilane self-assembled monolayer

Cholesterol oxidase (ChOx) has been covalently immobilized onto two-dimensional self-assembled monolayer (SAM) of N-(2-aminoethyl)-3-aminopropyl-trimethoxysilane (AEAPTS) deposited on the indium-tin oxide (ITO) coated glass plates using N-ethyl-N'-(3-dimethylaminopropyl) carbodiimide and N-hydroxysuccinimide (EDC/NHS) chemistry. These ChO x/AEAPTS/ITO bioelectrodes are characterized using contact angle (CA) measurements, UV-visible spectroscopy, atomic force microscopy (AFM), electrochemical impedance technique, and Fourier transform infrared (FT-IR) technique. The covalently immobilized ChOx-modified AEAPTS bioelectrodes are used for the estimation of cholesterol in solution using UV-visible technique. These cholesterol sensing bioelectrodes show linearity as 50 to 500 mg/dl for cholesterol solution, detection limit as 25mg/dl, sensitivity as 4.499 x 10(-5) Abs (mg/dl)(-1), K(m) value as 58.137 mg/dl (1.5mM), apparent enzyme activity as 1.81 x 10(-3) U cm(-2), shelf life of approximately 10 weeks, and electrode reusability as 10 times.

The 2.1 A structure of Aerococcus viridans L-lactate oxidase (LOX)

The crystal structure of L-lactate oxidase (LOX) from Aerococcus viridans has been determined at 2.1 A resolution. LOX catalyzes the flavin mononucleotide (FMN) dependent oxidation of lactate to pyruvate and hydrogen peroxide. LOX belongs to the alpha-hydroxy-acid oxidase flavoenzyme family; members of which bind similar substrates and to some extent have conserved catalytic properties and structural motifs. LOX crystallized as two tightly packed tetramers in the asymmetric unit, each having fourfold symmetry. The present structure shows a conserved FMN coordination, but also reveals novel residues involved in substrate binding compared with other family members.

Purification and thermodynamic characterization of glucose oxidase from a newly isolated strain ofAspergillus niger

An intracellular glucose oxidase (GOD) was isolated from the mycelium extract of a locally isolated strain of Aspergillus niger NFCCP. The enzyme was partially purified to a yield of 28.43% and specific activity of 135 U mg–1through ammonium sulfate precipitation, anion-exchange chromatography, and gel filtration. The enzyme showed high specificity for D-glucose, with a Kmvalue of 25 mmol L–1. The enzyme exhibited optimum catalytic activity at pH 5.5. Optimum temperature for GOD-catalyzed D-glucose oxidation was 40 °C. The enzyme displayed a high thermostability having a half-life (t1/2) of 30 min, enthalpy of denaturation (H*) of 99.66 kJ mol–1, and free energy of denaturation (G*) of 103.63 kJ mol–1. These characteristics suggest that GOD from A. niger NFCCP can be used as an analytical reagent and in the design of biosensors for clinical, biochemical, and diagnostic assays.Key words: glucose oxidase, Aspergillus niger, kinetics, thermodynamics, thermal stability.

Glucose oxidase immobilization on a novel cellulose acetate–polymethylmethacrylate membrane

Glucose oxidase (GOD) was immobilized on cellulose acetate-polymethylmethacrylate (CA-PMMA) membrane. The immobilized GOD showed better performance as compared to the free enzyme in terms of thermal stability retaining 46% of the original activity at 70 degrees C where the original activity corresponded to that obtained at 20 degrees C. FT-IR and SEM were employed to study the membrane morphology and structure after treatment at 70 degrees C. The pH profile of the immobilized and the free enzyme was found to be similar. A 2.4-fold increase in Km value was observed after immobilization whereas Vmax value was lower for the immobilized GOD. Immobilized glucose oxidase showed improved operational stability by maintaining 33% of the initial activity after 35 cycles of repeated use and was found to retain 94% of activity after 1 month storage period. Improved resistance against urea denaturation was achieved and the immobilized glucose oxidase retained 50% of the activity without urea in the presence of 5M urea whereas free enzyme retained only 8% activity.

Enzyme stabilization by glutaraldehyde crosslinking of adsorbed proteins on aminated supports

The stabilization achieved by different immobilization protocols have been compared using three different enzymes (glutaryl acylase (GAC), D-aminoacid oxidase (DAAO), and glucose oxidase (GOX)): adsorption on aminated supports, treatment of this adsorbed enzymes with glutaraldehyde, and immobilization on glutaraldehyde pre-activated supports. In all cases, the treatment of adsorbed enzymes on amino-supports with glutaraldehyde yielded the higher stabilizations: in the case of GOX, a stabilization over 400-fold was achieved. After this treatment, the enzymes could no longer be desorbed from the supports using high ionic strength (suggesting the support-protein reaction). Modification of the enzymes immobilized on supports that did not offer the possibility of react with glutaraldehyde showed the same stability that the non modified preparations demonstrating that the mere chemical modification did not have effect on the enzyme stability. This simple strategy seems to permit very good results in terms of immobilization rate and stability, offering some advantages when compared to the immobilization on glutaraldehyde pre-activated supports.