Application of atomic force microscopy and grating coupler for the characterization of biosensor surfaces

Kuhlmeier, D, Rodda, E, Kolarik, L, Furlong, N and Bilitewski, U 2003, 'Application of atomic force microscopy and grating coupler for the characterization of biosensor surfaces', Biosensors and Bioelectronics, vol. 18, no. 7, pp. 925-936.


Document type: Journal Article
Collection: Journal Articles

Title Application of atomic force microscopy and grating coupler for the characterization of biosensor surfaces
Author(s) Kuhlmeier, D
Rodda, E
Kolarik, L
Furlong, N
Bilitewski, U
Year 2003
Journal name Biosensors and Bioelectronics
Volume number 18
Issue number 7
Start page 925
End page 936
Total pages 12
Publisher Elsevier BV
Abstract Atomic force microscopy (AFM) and an optical grating coupler system were used to improve the understanding of the biosensing layer on a Ta2O5-light-guiding surface. Exemplary, we investigated the immobilization of the protein avidin, the subsequent binding of biotinylated oligonucleotides and hybridization of a complementary 12-mer. The AFM measurements revealed the height of -1.6 nm for a single avidin molecule, while the thickness of the avidin layer on the biosensor surface seemed to be 2.8-3.0 nm. This result lead to the conclusion that the protein was not forming a simple monolayer. However, the thickness of the avidin layer could not be determined directly, but only after shifting of protein by the tip of the AFM leading to grooves of 1 μm2 and -3 nm depth. As the height of oxide particles forming the waveguide surface was also in the range of 1.5 nm, the depth of these grooves could also be a result of the deposition of proteins on top of the oxide particles. This was consistent with the increased roughness of the surface after protein binding. Thus, investigations with the grating coupler were used to determine quantitatively the amount of immobilized avidin. On a biotinylated surface the amount of immobilized avidin lead to the assumption of a complete monolayer, whereas simple adsorption proved to be less efficient. A binding ratio of 1:1.3 for avidin and a biotinylated oligonucleotide was achieved. Up to 83% of the bound single strand were accessible for a subsequent hybridization reaction with a 12-mer. These results supported the model of avidin being deposited mainly on top of the oxide particles leading to the picture of a 'rough' complete protein monolayer, which was postulated from the AFM investigations.
Keyword(s) atomic force microscopy
grating coupler
hybridization
optical biosensor
surface coverage
DOI - identifier 10.1016/S0956-5663(02)00213-0
ISSN 0956-5663
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