Surface study of the building steps of enzymatic sol–gel biosensors at the micro- and nano-scales |
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Authors: | Marta Barbadillo Elena Casero Maria Dolores Petit-Domínguez Félix Pariente Encarnación Lorenzo Luis Vázquez |
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Institution: | 1.Departamento de Química Analítica y Análisis Instrumental,Universidad Autónoma de Madrid,Madrid,Spain;2.Instituto de Ciencia de Materiales de Madrid (CSIC),Madrid,Spain |
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Abstract: | We have studied, by scanning electron and atomic force (AFM) microscopies, how each step involved in the building process
of massive carbon-based sol–gel enzymatic biosensors changes and determines the resulting surface morphology and nano-mechanical
properties. The biosensor, selected as a model, is developed by the entrapment of glucose oxidase (GOx), a redox mediator
and a material conferring conductivity (graphite powder, C) into a polymeric tridimensional network generated by sol–gel technology
using tetraethoxysilane (TEOS) as precursor. The smooth TEOS morphology is formed by an irregular nanoporous network, which
is very adequate for enzyme encapsulation. Upon addition of carbon powder to the system (TEOS/C), the surface morphology changes
but it is still rather irregular since carbon powder micro-grains are found scattered on it. This morphology results in a
rather rough surface at the micro- scale whereas at the nano- scale both atomically flat graphitic and nanoporous TEOS domains
are found. In contrast, the final biosensing device surface is quite homogeneous and composed by flat platelets separated
by deep crevices. On top of most of these platelets there is a soft, as assessed by AFM force indentation experiments, layer
of globular structures whose dimensions are compatible with GOx molecules. The final device surface architecture results to
be open and accessible both at the micro and nano scales, which turns it as adequate to enhance both the accessibility of
the analytes to entrapped proteins and the mass-transfer rates. Finally, in order to show the applicability of the studied
biosensor, its response was evaluated towards varying glucose concentrations, displaying a clear electrocatalytic activity. |
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