Photoluminescence of Gold Nanoparticles and Their Applications to Sensing and Cell Imaging - From Bioimaging to Biosensors: Noble Metal Nanoparticles in Biodetection - page 204

In the assay, the PDGF AA-Au NPs and Apt-Au NPs were mixed in
the absence and presence of PDGF. When mixed, the two differently
sized Au NPs in the luminescent PDGF AA-Au NPs and Apt-Au NPs
come into close contact, leading to luminescence quenching through
electron and/or energy transfer. As a result, the luminescence of
the PDGF AA-Au NPs at 520 nm decreases (Fig. 9.10A). This PDGF
AA-Au NP/Apt-Au NP-based molecular light switching system
allows the analysis of PDGFs as well as PDGF α-receptor in separate
homogeneous solutions (Fig. 9.10B,C). In the presence of PDGFs,
the interaction between the Apt-Au NPs and the PDGF AA-Au NPs
weaken as a result of competitive reactions between the PDGFs
and the Apt-Au NPs.
Similarly, the interactions between the Apt-Au NPs and the PDGF
AA-Au NPs weaken as a result of competitive reactions between
PDGF α-receptor and the PDGF AA-Au NPs. The LODs for PDGF AA
and PDGF α-receptor were 80 pM and 0.25 nM, respectively. When
using the Apt-Au NPs as selectors for (i) the enrichment of PDGF
AA and (ii) the removal of matrices possessing intense background
luorescence from cell media and urine samples, the LOD for PDGF AA
decreased to 10 pM. This Apt-Au NP-assisted PDGF-AA enrichment
process provided greater sensitivity than those obtained using other
signal aptamers.
Biofunctional Man-Au NPs are capable of sensing concanavalin
A (Con A) through multivalent interactions. 25 Con A is a member
of the lectin family; it binds selectively to α-mannopyranosyl and
α-glucopyranosyl residues. 78,79 Con A exists predominantly as a
tetramer of four identical subunits (each ca. 26,000 Da) at neutral
and alkaline pH. 78,79 Man-Au ND-Con A aggregates can be formed
through speciic interactions between the carbohydrate units and
the multivalent lectins. To minimize precipitation and collisions,
which can cause luorescence quenching, mixtures of Man-Au NPs
and various concentrations of Con A were incubated for 60 min and
then centrifuged prior to luminescence measurement. The recorded
luminescence intensity of the supernatant is inversely proportional
to the concentration of Con A. This approach provides an LOD of
75 pM for Con A, with remarkable selectivity over other proteins
(e.g., bovine serum albumin, β-lactalbumin, carbonic anhydrase,
conalbumin, myoglobin) and lectins (e.g., DBA from Dolichos
bilorus ; WGA from Triticum vulgari ; PSA from Pisum sativum ). 25
The biofunctional Man-Au NPs are also sensitive for the detection