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Figure 2.12 When the capture/target/probe sandwich is positioned in the gap between two
electrodes, catalytic reduction of silver onto the sandwich system results in a signal that can be
detected electrically.
Source: Science http://www.aaas.org
Gold nanoparticles have been investigated for use in sensors for both chemical and
biological warfare agents. One example, ‘chemiresistors’, makes use of thin films of gold
nanoparticles encapsulated in monomolecular layers of functionalized alkanethiols that
have been deposited on interdigitated microelectrodes. These reversibly absorb vapours
leading to monolayer swelling or dielectric alteration in the thin film and production of a
small current. The system appears to have minimal water sensitivity, and can detect
harmful vapours down to the parts per billion level or lower. Selectivity of the sensors
can be tailored by changing the structure and functionality of the alkanethiol. This sensor
has been developed by STREM chemicals.
• Colorimetric
Nanoparticles have shown exceptional colorimetric properties that can easily replace
traditional fluorescent detection systems. For example, a single 80 nm gold particle has a
light-scattering power equivalent to the signal generated from about 10 6 fluorescein
molecules, and unlike molecular fluorophores, the light-scattering signal from metal
nanoparticles is quench resistant. (N.L. Rosi and C.A. Mirkin, 2005).
Researchers from Georgia Institute of Technology have used 2.5 nm gold nanoparticles
as quenchers in a molecular fluorophore nucleic acid probe, to detect the presence of
target DNA (S. Nie et al., 2002, see Figure 2.13).
Figure 2.13 Gold nanoparticles are modified with oligonucleotides functionalized on one end
with a thiol and the other end with a molecular fluorophore. The thiol binds to the surface of the
gold particle, and the fluorophore can interact non-specifically with the gold, resulting in a “loop”
structure in which the gold nanoparticle quenches the emission from the fluorophore. In the
presence of target DNA the “loop” is broken, separating the fluorophore from the nanoparticle
quencher, and resulting in measurable fluorescence.
Source: http://pubs.acs.org/spotlight/november2002/ja025814p.pdf?sessid=7922
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