Both micro-cantilevers as well as other three-dimensional micro-structures have
been exclusively used for sensing and diagnostics. Ghoshdastidar et al. [ 48 ] have
made micro-machined impedance bio-sensor for accurate and rapid detection of
E. coli through interdigited electrode structures. They have fabricated two sets of
interdigitated electrodes made of gold, embedded in a SU-8/PDMS micro-channels.
Using dielectrophoretic trapping the microorganism E. coli was focused on the
centre of the microchannel where a second set of electrodes were used to sense
through impedance spectroscopy the type and the concentration of the micro-
organism. Figure 2.15 shows the three dimensional schematic of biosensor
platform.
Boehm et al. [ 49 ] introduced a methodology for fast detection of bacteria
through a micro-fluidic lab-on-chip device to detect cells using antibody immobi-
lization. Composite self-excited PZT-Cantilever was fabricated and their frequency
of resonance was measured both in water and air. Resonant frequency of the second
mode was observed to decrease due to pathogen attachment by Campbell
et al. [ 50 ]. Weeks et al. [ 51 ] have reported detection of Salmonella strains using
silicon nitride based micro-cantilever. V shaped cantilevers were used which were
180 mm long and 18 mm wide. The cantilever was functionalized using antibody
S. Heidb. The cantilever deflection with respect to the Salmonella concentration
cfu/ml was obtained and it was directly observed that with the increase in concen-
tration of the sample, deflection was increased. Initially S. Typh strains were
injected at 100 cfu/mL but no deflections were noticed but as the S. Heidb strains
were injected deflections were obtained within 20 s.
Ilic et al. [ 52 ] have done virus detection using nanoelectromechanical devices
using a non-pathogenic insect baculovirus to test the ability to specifically bind and
detect small number of virus particles. Arrays of surface, antibody-coated poly-
crystalline silicon nanomechanical free standing cantilever beams were used to
detect the binding from varying amounts of concentrations of baculo viruses in a
buffer solution. Figure2.16shows the fabrication technique and SEM image of the
fabricated micro-cantilever. Because of their small mass, the 0.5 mm36 mm
Fig. 2.15 Three dimensional schematic of (a) impedance based biosensor for pathogen detection.
(b) Magnified view of the focusing region and detection region (Reproduced from Ghoshdastidar
et al. [ 48 ] with permission from the Royal Society of Chemistry)
2 Microfluidics Overview 53