Sensing of Biomolecules - Bionanoelectronics: Bioinquiring and Bioinspired Devices - page 87

Fig. 2.28 Cantilever mass

sensor

m

Paddle

vaccinia virus has a weight of 5 fg, and the associated frequency shift, of 60 kHz,
was measured with a Si cantilever with L D 3:6m, t D 30 nm, and W D 1:7m.
A mass-sensitive cantilever acting as a biosensor is depicted in Fig. 2.28 .Very
recently, the white spot syndrome virus was detected using a piezoelectric cantilever
made of lead-magnesium niobate-lead titanate material ( Capobianco et al. 2010 ).
The cantilever and NEMS can be considered also as label-free sensors. For
example, a single nucleotide mismatch was detected by monitoring the optical
deflection assay ( Hansen et al. 2001 ), while a suspended microfluidic channel
with a cantilever shape was used to weigh biomolecules, single cells, and single
nanoparticles ( Burg et al. 2007 ). This microfluidic cantilever was so sensitive
that the mass resolution is six orders of magnitude better than in quartz crystal
microbalances. The microfluidic cantilever made on SOI weighs only 200 ng and
has a mechanical quality factor of 15,000.
Label-free detection of the carcinoembryonic antigen (CEA) biomarker using a
piezoelectric PZT cantilever was recently reported ( Lee et al. 2008 ). The critical
value of CEA, which is 30 pM or 5 ng ml 1 , is known as the threshold biomarker
for various cancers (breast, cervix, rectum, prostate, stomach, intestine, pancreas,
lung) and was detected by the binding of the antigen to antibody contained in a
silica sol-gel glass that coated the cantilever. A recent review of NEMS and their
applications in biological/chemical recognition is found in Eom et al. ( 2011 ).

2.4 Plasmonics Biodetection

There are many optical methods suitable for label-free detection of biomolecules.
One of the most sensitive is based on plasmonic sensors. Plasmonics is a new
area in nanophotonics, which covers the generation, propagation, and detection of
plasmonic waves. Plasmonic waves are collective electronic excitations produced
by an electromagnetic field, which propagates along a metal-dielectric interface,
around metallic nanoparticles or nanowires placed on a dielectric substrate, or
through an array of nanoholes in a metallic surface.
The simplest plasmonic configuration is the metal-dielectric interface. The
interaction between matter and the electromagnetic field is confined to and plasmons
propagate along this interface. These confined surface electromagnetic waves are
termed surface plasmon polaritons (SPP) ( Barnes 2006 ) and play an important role