Biology Reference
In-Depth Information
synthesis[66].LoadingofapoferritinwithZn,Cd,andPbphosphate
NPs followed by release and electrochemical stripping analysis has
been reported [67]. The use of the different metal phosphate NPs
allowed for simultaneous detection of the different NPs at different
potentials, or identification of compositionally encoded nanoparti-
cles whichmay prove e
cacious formultianalyte detection.
Electrochemical detection of DNA using apoferritin as a nanove-
hicle label was reported by Liu and coworkers [68]. Dissoci-
ated apoferritin subunits were reassembled in the presence of
[Fe(CN)
6
]
3
−
producing electroactive apoferritin, each loaded with
∼
150 [Fe(CN)
6
]
3
−
molecules. Free carboxyl groups on the exterior
of the apoferritin were coupled to amine-terminated DNA probes
via carbodiimide chemistry. This DNA-apoferritin conjugate served
as the detection probe in a magnetic bead based sandwich
hybridization assay. Following bioassay, [Fe(CN)
6
]
3
−
was released
with 0.1 M HCl/KCl solution and subsequently detected by square
wave voltammetry at a screen-printed carbon electrode resulting in
a detection limit of 3 ng/L (460 fM). Cadmium phosphate loaded
apoferritin modified with a monobase residue (guanine in this
work) via phosphoramidite chemistry was used for detection of
single-nucleotide polymorphisms or SNPs [69]. In this magnetic
bead based sandwich assay shown in Fig. 14.14, the guanine-
modified apoferritin bound to the complementary base at the
mutation site of the sample DNA, cytosine, as this residue did not
bind with the mismatched base on the capture probe. Following
collection, the sample was exposed to acetate buffer (pH 4.6) to
release the cadmium, which was detected by stripping analysis at
a mercury film coated screen-printed carbon electrode. This system
could detect 21.5 attomol SNP DNA, which the authors state should
enable quantitative analysis of nucleic acid without polymerase
chain reaction (PCR) preamplification.
14.3.7
Silica Nanoparticles
Silica nanoparticles (Si NPs) have been successfully used for
electrochemical DNA detection. As silica is inherently inactive
electrochemically, these particles are either loaded with elec-
troactive molecules and used as labels, or employed as scaffolds
