Aspects of recent development of immunosensors - Electrochemical Sensors, Biosensors and Their Biomedical Applications - page 246

of antibody-bearing suspensoids such as polymers, microbeads, and naoparticles may
induce a corresponding change in the solution parameters (i.e. density and viscosity)
and the interfacial properties of the crystal monitored by the QCM device [158-161].
In contrast to the common conventional piezoelectric assays, the QCM sensing format
offers a unique advantage in that the immobilization of antibodies or antigens on the
crystal is not necessary. The kind of QCM-sensing methods are widely recognized to
be simple, sensitive, and feasible for detecting relevant targets responsible for many
clinical diseases [158-163]. Kurosawa et al. fi rst developed an agglutination-based
piezoelectric immunoassay using antibody-bearing latex, termed as the latex piezoe-
lectric immunoassay (LPEIA), for detecting C-reactive protein [158]. Recently, it has
been demonstrated that the LPEIA could be greatly improved by using gold nanoparti-
cles as replacements for latex particles, resulting in a novel agglutination-based piezo-
electric immunoassay for directly detecting anti- T. gondii immunoglobulins in infected
rabbit sera and bloods [159].
9.3.4 Other kinds of immunosensors
In recent years, considerable efforts have been devoted to the development of canti-
lever-based immunosensors with unique enantio-selective antibodies [164-165]. These
devices are mainly used for quality and process control, and diagnostic biosensing for
medical analysis. They may have fast responses and high sensitivity and are suitable for
mass production. Lee et al. fabricated a piezoelectric nanomechanical cantilever by a
novel electrical measurement. They found that this technique might allow for the label-
free detection of a prostate-specifi c antigen (PSA) with a detection sensitivity as low
as 10pg mL 1 [164]. A microfabricated cantilever was utilized to perform the direct
(label-free) stereo-selective detection of trace amounts of an important class of chiral
analytes, the r-amino acids, based on immunomechanical responses involving nanos-
cale bending of the cantilever. The major advantages of the microcantilever sensors over
more traditional scale transducers such as the QCM reside in the superior sensitivity to
minute quantities of analytes and the ability to micro-fabricate compact arrays of canti-
levers to facilitate simultaneous and high throughput measurements [165].
Moreover, mass-sensitive magnetoelastic immunosensors are exploited to design
extraordinarily versatile and useful sensor platforms [166]. Magnetoelastic sensors are
well established and benefi t from mass sensitivity compared to that of a surface acous-
tic wave (SAW) sensor. However, they may cost much less and are much smaller in
size than SAW devices. Ruan et al. proposed a mass-sensitive magnetoelastic immu-
nosensor based on the immobilization of affi nity-purifi ed antibodies on the surface of
a micrometer-scale magnetoelastic cantilever achieving the highly sensitive detection
of Escherichia coli O157:H7 [167]. In addition, imaging ellipsometry (IE) has also
been developed as a new kind of immunosensor, i.e. for the detection of pathogens of
Yersinia enterocolitica [168]. As another example, a label-free multi-sensing immu-
nosensor based on the combination of IE and the protein chip was reported to be able
to detect multiple analytes simultaneously, and even to monitor multiple biological
interaction processes in situ and in real-time conditions [169].