Adsorption of biomolecules on microcantilevers

Allan Glargaard Hansen^a,b, Anja Boisen^a, and Jens Ulstrup^b

a) Microelectronics Centre, Technical University of Denmark, bldg. 345e, DK-2800 Lyngby, Denmark.
b) Department of Chemistry, Technical University of Denmark, bldg. 207, DK-2800 Lyngby, Denmark.

We have used a microcantilever sensor to measure the surface stress change upon adsorption of sulphur-containing biomolecules and smaller reference molecules. The sensor contains a gold coated working cantilever and a silicon nitride reference cantilever. The molecules investigated were the electron transfer protein yeast cytochrome c, L-cysteine (amino acid), 6-mercapto-1-hexanol and the alkanethiol 1-octadecylthiol. Previous STM and XPS investigations have shown that alkanethiols, cysteine and proteins with surface sulphur groups have a strong affinity for gold and form well ordered molecular monolayers [1]. Microcantilever investigations of cytochromes have not been published to our knowledge.
The change in surface stress of the working cantilever can provide in situ, real time information about the molecular adsorption process: e.g. the rate of adsorption, which depends on the concentration, and the nature of the interaction between the adsorbing molecules and between the molecules and the surface.
The molecules investigated all exhibit tensile surface stress on the order of 0.5 N/m. As expected, the observed adsorption rates are seen to vary systematically with the concentration. The rates for alkanethiols correspond well to literature. The stress signal for cytochrome c saturates within 200-300 s for a concentration of 95 ｵM. The cysteine signal saturates within 70-100 seconds at concentrations of 0.18-2.3 mM

[1] QJ Chi, JD Zhang, JU Nielsen, EP Friis, I Chorkendorff, GW Canters, JET Andersen, J Ulstrup: Molecular monolayers and interfacial electron transfer of Pseudomonas aeruginosa azurin on Au(111), J. Am. Chem. Soc. 122 (17) 4047-4055 (2000).