Micro-cantilevers are small V-shaped or
rectangular cantilevers (typically made of silicon nitride (SiNx)
or silicon (Si)) which are on the order of 200 mm
long, 50 mm wide and 1-5 mm
thick (see figure 1). Although micro-cantilevers were originally designed
to be used in atomic force microscopes for surface imaging, they have
recently been employed as ultra-sensitive sensors to detect phenomena
such as changes in temperature [1], changes in mass [2] and the detection
of chemical reactions through changes in surface stress [3].
Figure 1: Scanning electron micrograph
showing (from left to right) three V-shaped micro-cantilevers and
one rectangular micro-cantilever. (SEM image compliments of John W.
Cross)
[1] Gimzewshi et al., Chem. Phys, Lett.
217, 598 (1994)
[2] Davis et al., J. Vac. Sci. Technol. B, 18, 612-616, (1996)
[3] Berger et al., Science 276, 2021 (1997)
Cantilever sensors are
a promising technology for performing molecular detection and
recognition (See figure 2). On a regular basis, scientists publish
new applications for these types of sensors. Despite the numerous
applications we are still a long way from seeing cantilever
sensors as a commercial product. Why? Because of their incredible
sensitivity, which is what makes them so attractive in the first
place, these sensors are sensitive to numerous parameters
which can influence their measurements. In short, cantilever
sensors do not, at this point in time, provide reliable and
reproducible measurements.
How
does a cantilever sensor detect alkanethiols?
Figure 2:
When alkanethiols bind to the cantilever which has been coated
on one side with a gold film, a self-assembled monolayer (SAM)
is formed. The SAM causes an increase in the lattice parameter
of the Au film which causes the cantilever to bend similarly
to the bimetallic effect. The red lines in this animation represent
the incident and reflected laser beams used to monitor the deflection
of the cantilever.
The main objective of this lab will be to identify the parameters
which influence the reliability and reproducibility of cantilever
sensors. Work in this direction has already begun.
