Biology Reference
In-Depth Information
event by using an adsorbed biotinylated albumin layer to capture
streptavidin-gold conjugates on a pre-treated carbon paste elec-
trode.Thecolloidalgoldlabelwasdetectedfollowingitsoxidationat
ahighpotentialinanacidicmedium,andthenreducingthereleased
AuCl
4
complex using differential pulse voltammetry. A modified
version of this detection principle was applied by the groups of
Limoges and Wang to detect DNA hybridization events based on
the oxidative dissolution of the particle in acidic bromine-bromide
solution and using highly sensitive stripping voltammetry [20,
21]. In the former case the 406-base pair human cytomegalovirus
DNA sequence was detected using oligonucleotide-modified gold
nanoparticle probes at probe-modified screen-printed microband
electrodes and had a detection limit of 5 pM. In the latter case
a two-surface technique was used to detect a DNA sequence
related to the BRCA1 breast cancer gene where magnetic bead
probe DNA complexes were used to hybridize to biotinylated DNA
that was conjugated to commercially available 10 nm streptavidin
goldnanoparticles.Followingmagneticseparationandnanoparticle
dissolution, the oxidized gold ions were used to determine the
amount of hybridized target at a thick-film screen-printed carbon
electrode using potentiometric stripping analysis. In both cases
a significant amplification signal can be attributed to metal
accumulation in the pre-concentration step of the stripping analysis
which makes the technique sensitive to the detection of trace
metalsandparticularlywellsuitedformetalnanoparticledetection.
Further amplification can be performed after the hybridization
event by catalytically precipitating metals, such as gold and silver,
onto the nanoparticle label “seed”. Thus, more metal can be grown
in solution to increase the sensitivity of DNA hybridization binding
events[22].Attomolardetectionlimitswereachievedusingatriple-
amplification strategy [23]. Instead of single nanoparticles being
used for each hybridization event, streptavidin-coated polystyrene
microspheres, each containing multiple biotinylated gold nanopar-
ticles and biotinylated DNA secondary capture probes were used.
Gold precipitation, acidic dissolution, and detection after DNA
hybridization resulted in a significant lowering of detection limits.
Wang
et al.
[24]alsoreportedasolid-statedetectionmethodwhere,
after a silver-enhanced precipitation step, the enlarged gold-silver
