Biodetection Based on Resonance Light Scattering of Noble Metal Nanoparticles - From Bioimaging to Biosensors: Noble Metal Nanoparticles in Biodetection - page 171

Aptamer-conjugated Au NPs are selective and sensitive for
detection of proteins and small analytes. 40-43 Through speciic
binding of the aptamers with the platelet-derived growth factor,
MDA-MB-231 and Hs578T cancerous cells that over-express the
platelet-derived growth factor, interact with aptamer-Au-NPs to
greater extents than do H184B5F5/M10 normal cells. 49 Aggregation
of the aptamer-Au NPs in the cytoplasm of the cancerous cells leads
to the generation of a strong yellow scattered light upon photo-
illumination; this phenomenon allows one to readily differentiate
between the tested cancerous cells and normal cells using a
laboratory-made dark ield microscope.
8.3.1.3 DNA
Like proteins, DNA can induce aggregation of Au NPs bioconjugated
with recognition molecules such as DNA and proteins. Aggregates of
DNA functionalized Au NPs can be formed through cross-linking and
non-cross-linking reactions. The latter refers to aggregation through
van der Waal's forces. Factors that control the surface properties
(e.g., charge density) of DNA-Au NPs, such as ionic strength and pH,
are important. By carefully controlling ionic strength, colorimetric
and luorescence detections of Hg 2+ and adenosine triphosphate
using DNA-Au-NPs have been realized. 50-52 Cross-linking reactions
through complimentary DNA hybridization are more common in the
aggregation of DNA-Au NPs. Colorimetric sensors of DNA using DNA-
Au NPs are useful for single-nucleotide polymorphisms study and
disease diagnosis. 53-56 These successful colorimetric approaches
indicate that RLS techniques using DNA-Au-NPs have potential for
detection of DNA.
Figure 8.10 displays an application of 80 nm diameter Au NPs,
bioconjugated with anti-biotin antibodies, for the detection of DNA
hybridization on cDNA microarrays. 57 The arrays are composed
of ~2000 human genes that were hybridized with colabeled (Cy3
and biotin) human lung cDNA probes at concentrations ranging
from 8.3 ng/μL to 16.7 pg/μL. After hybridization, the arrays were
treated with 80 nm diameter Au NPs, bioconjugated with anti-biotin
antibodies and imaged in a white light CCD-based imaging system.
For hybridizations with a probe concentration of 83.3 pg/μL,
RLS detected ~1150 positive genes, while luorescence detection
only detected ~110 positive genes. RLS using DNA-Au-NPs is also
practical for the detection of DNA in homogeneous solutions. 58 The