We have built and operated a device capable to monitor surfce stress
changes of two micro-fabricated cantilever beams in a liquid flow-through
set-up. Adsorption/desorption processes on the cantilever surface induce
a static bending of the whole beam which is measured with a laser beam-bounce
technique. Cantilevers can be handled and coated separately.
By coating each cantilever with speciflc receptors, it is possible
to detect the presence and to measure the concentration of analytes with
high sensititvity.
The use of more cantilevers in parallel, a coated one acting as sensor
and an uncoated one as reference, can minimise disturbances deriving from
external noise, temperature changes, turbulent liquid flow, and drifts
due, to slow physico-chemical processes [1].
Furthermore, the design with two separate laser diodes and photodetectors
allows one to monitor continuosly changes in resonant frequency,
which are caused by the change of mass load due to adsorption/desorption
processes on the cantilever surface. The principle of the technique will
be described together with preliminary results and comparisons with another
set-up based on a commercial Atomic Force Microscope [2-5].
References
1. Lang H.P., et al., Chemical sensor based on a micromechanical cantilver array for the identification of gases and vapors, Applied Physics A, 1998, 66, s61-S64.
2. Raiteri R., Butt, H.J., Measuring electrochemically induced surface strees with an atomic force microscope, The Journal of Physical Chemistry 1995, 100, 15728-15732.
3. Butt H.J., A sensitive method to measure changes in the surface stress in solids, Journal of Colloid and Interfac Science 1996, 180, 251-260.
4. Raiteri R., Butt H.J., Grattarola M., Changes in surface strees measured with an atomic force microscope, Scanning Microscopy, 1997, 11(1).
5. Raiteri R., et al., A novel transducer for direct sensing of bioaffinity interactions based on microfabricated cantilevers, Biophysical Journal, submitted.