Biosensors for the Detection of Waterborne Pathogens - Waterborne Pathogens: Detection Methods and Applications - page 199

the sensor surface leads to bending of the cantilever, which can be read out
either via piezoelectric or by optical means. 43,44 While the dimensions of
these cantilevers are on the orders of micrometers, typical deflections are in
the nanometer range. Microcantilever sensors were developed from atomic
force microscopy (AFM); are typically made from silicon, silicon nitrate,
or silicon oxide; and have been applied in a wide range of sensing applica-
tions 43,44 ( Fig. 7.10 ).
7.4. BIOSENSORS FOR WATERBORNE VIRUSES
Very few biosensors have been reported for viruses in general and for
waterborne viruses in particular. 45 Sen suggested that the reason for this is
that the epitopes on the capsid of enteroviruses are very small, rendering
immunological methods not sufficiently successful or sensitive for direct
detection in water. 46 However, it seems that recent developments in bio-
sensor transduction are beginning to address this challenge. Novel optical
methods of detection, described below, appear to dominate.
In 2012, Pineda et al. reported direct detection of rotavirus using anti-
body-based photonic crystal biosensors. Light incident to a photonic crystal
from a 90° angle is strongly reflected at a single wavelength at which an opti-
cal resonant reflection occurs. This resonant wavelength is altered upon bind-
ing of materials to the photonic crystal surface, measured in this research using
optical fibers. The authors claim this system is cheap enough for disposable
sensors. A 30 min assay of a partially processed water sample yielded a detec-
tion sensitivity of 36 virus focus forming units without the use of any external
reagents. 47 An alternative antibody-based sensor for rotavirus by Jung et al. uti-
lized a graphene oxide (GO) surface and a secondary gold nanoparticle label,
which binds to captured rotavirus and quenches the GO surface fluorescence
through fluorescence resonance energy transfer (FRET). 48 However, the limit
of detection (LOD) in this approach was much higher at 10 5 pfu mL −1 .
Silicon microring resonators have also been employed as virus bio-
sensors ( Fig. 7.11 ). In this setup, binding of biomolecules to the function-
alized microring sensor causes small changes in the effective refractive
index, resulting in a detectable shift in resonance wavelength. Shang et al.
detected norovirus using carbohydrate functionalized silicon microrings
with an LOD of 250 ng mL −1 . 50 However, the authors stress that the
focus was on examining carbohydrate-mediated host-virus interactions,
and that antibodies would offer an improved LOD. Work by McClellan