XPS and AFM Characterization of the Enzyme Glucose Oxidase Immobilized on SiO₂ Surfaces

Abstract

A process to immobilize the enzyme glucose oxidase on SiO2 surfaces for the realization of integrated microbiosensors was developed. The sample characterization was performed by monitoring, step by step, oxide activation, silanization, linker molecule (glutaraldehyde) deposition, and enzyme immobilization by means of XPS, AFM, and contact angle measurements. The control of the environment during the procedure, to prevent silane polymerization, and the use of oxide activation to obtain a uniform enzyme layer are issues of crucial importance. The correct protocol application gives a uniform layer of the linker molecule and the maximum sample surface coverage. This result is fundamental for maximizing the enzyme bonding sites on the sample surface and achieving the maximum surface coverage. Thin SiO2 layers thermally grown on a Si substrate were used. The XPS Si 2p signal of the substrate was monitored during immobilization. Such a signal is not completely shielded by the thin oxide layer and it is fully suppressed after the completion of the whole protocol. A power spectral density analysis on the AFM measurements showed the crucial role of both the oxide activation and the intermediate steps (silanization and linker molecule deposition) to obtain uniform immobilized enzyme coverage. Finally, enzymatic activity measurements confirmed the suitability of the optimized protocol.

Towards microstructured optical fibre sensors: surface analysis of silanised lead silicate glass

“…These CxHyNz and 15 CxHyNzO organic fragments are related to the structure of 3 and the APTES coating and most of the CxHyNz and CxHyNzO organic fragments are negatively correlated to PC1 and positively correlated to PC2. Samples with 3/EDC/NHS/base have negative PC1 scores and positive PC2 scores, which matches the pattern 20 for CxHyNz and CxHyNzO organic fragments. Furthermore, PC1 appears correlated to the quantity of 3 attached to the APTES grafted glass surface.…”

“…Cleaned APTES coated slides were placed in an individual vial and incubated in 2 mL 9:1 THF:water solution with 1, 2, or 3 (0.1 mM) for 9 hours incubation. After incubation, slides were rinsed 20 with THF (< 4 mL  2), pH 5 potassium hydrogen phthalate buffer solution (< 4 mL  2), and finally RO water (< 4 mL  2).…”

“…XPS and ToF-SIMS have been widely used for the quantification and characterization of organic films, biomolecules such as DNA and protein on silicate surfaces. [18][19][20][21][22][23] Each analysis undertaken provides complementary information for semi-quantitative 15 determination of the surface concentration, relative coating thickness, and coating coverage of an organic molecule, in this case a PET fluoroionophore, on 3-aminopropyltriethoxysilane (APTES) functionalised extruded lead silicate (F2) glass slides ( Figure 1). Importantly, the coupling procedure employed is 20 transferable to MOFs.…”

Immobilization of β-glucosidase onto silicon oxide nanoparticles and augment of phenolics in sugarcane juice

“…The silicon oxide nanoparticles were washed twice with deionized water and recovered by centrifugation. The washed silicon oxide nanoparticles were suspended in 1 M glutaraldehyde (Libertino et al 2008). Support activation was carried out at 25°C in a shaker (150 rpm) for 4 h. The activated support was removed by centrifugation at 5700g and then washed thrice with 30 ml of distilled water to remove the glutaraldehyde and subsequently washed with 100 mM sodium acetate buffer (Stober and Fink 1968).…”

Promising plasmid DNA vector based on APTES-modified silica nanoparticles

“…One common chemical used for surface functionalization is aminopropyltriethoxysilane (APTES), which has the chemical formula NH 2 (CH 2 ) 3 -Si(OC 2 H 5 ) 3 . [11][12][13][14] The silane end of the APTES molecule binds covalently to surface silicon atoms, and the amino end of the molecule increases protein adsorption on the surface by electrostatic interactions. The structural transition of a single dsDNA molecule immobilized on an APTES-treated substrate has been demonstrated.…”