title: Physical and chemical immobilization of choline oxidase onto different porous solid supports: Adsorption studies.
abstract: This work carries out for the first time the comparison between the physical and chemical immobilization of choline oxidase onto aminated silica-based porous supports. The influence on the immobilization efficiency of concentration, pH, temperature and contact time between the support and choline oxidase, was evaluated. The immobilization efficiency was estimated taking into consideration the choline oxidase activity, which was assessed by using cadmium telluride (CdTe) quantum dots (QDs), obtained by hydrothermal synthesis, as photoluminescent probes. Hydrogen peroxide produced by enzyme activity was capable of quenching CdTe QDs photoluminescence. The magnitude of the PL quenching process was directly related with the enzyme activity. By comparing the chemical process with the physical adsorption, it was observed that the latter provided the highest choline oxidase immobilization. The equilibrium data were analyzed using Langmuir and Freundlich isotherms and kinetic data were fitted to the pseudo-first-order and pseudo-second-order models. Thermodynamic parameters, such as Gibbs free energy and entropy were also calculated. These results will certainly contribute to the development of new sensing schemes for choline, taking into account the growing demand for its quantification in biological samples.
authors.affiliation: LAQV, REQUIMTE, Department of Chemical Sciences, Laboratory of Applied Chemistry, Faculty of Pharmacy, Porto University, Rua de Jorge Viterbo Ferreira, 228, 4050-313 Porto, Portugal. Electronic address: marietapassos@gmail.com.
authors.forename: Marieta L C
authors.initials: ML
authors.lastname: Passos
authors.affiliation: LAQV, REQUIMTE, Department of Chemical Sciences, Laboratory of Applied Chemistry, Faculty of Pharmacy, Porto University, Rua de Jorge Viterbo Ferreira, 228, 4050-313 Porto, Portugal.
authors.forename: David S M
authors.initials: DS
authors.lastname: Ribeiro
authors.affiliation: LAQV, REQUIMTE, Department of Chemical Sciences, Laboratory of Applied Chemistry, Faculty of Pharmacy, Porto University, Rua de Jorge Viterbo Ferreira, 228, 4050-313 Porto, Portugal.
authors.forename: João L M
authors.initials: JL
authors.lastname: Santos
authors.affiliation: LAQV, REQUIMTE, Department of Chemical Sciences, Laboratory of Applied Chemistry, Faculty of Pharmacy, Porto University, Rua de Jorge Viterbo Ferreira, 228, 4050-313 Porto, Portugal. Electronic address: lsaraiva@ff.up.pt.
authors.forename: M Lúcia M F S
authors.initials: ML
authors.lastname: Saraiva
mesh_terms: D000327:Adsorption; D000429:Alcohol Oxidoreductases / Q000737:chemistry* / Q000378:metabolism*; D015374:Biosensing Techniques; D019187:Cadmium Compounds / Q000737:chemistry; D002794:Choline / Q000032:analysis; D004795:Enzyme Stability; D004800:Enzymes, Immobilized / Q000737:chemistry / Q000378:metabolism; D007700:Kinetics; D016062:Porosity; D045663:Quantum Dots / Q000737:chemistry / Q000378:metabolism; D012822:Silicon Dioxide; D013691:Tellurium / Q000737:chemistry; D013816:Thermodynamics
chemical_list: D019187:Cadmium Compounds; D004800:Enzymes, Immobilized; D012822:Silicon Dioxide; D000429:Alcohol Oxidoreductases; C019888:choline oxidase; D002794:Choline; D013691:Tellurium; C028337:cadmium telluride
keywords: Adsorption; Biosensors; Choline oxidase; Enzyme activity; Immobilized enzymes; Kinetic parameters