Nanoparticle-based biosensors and bioassays - Electrochemical Sensors, Biosensors and Their Biomedical Applications - page 446

Several groups, including ours, have developed powerful nanoparticle-based electro-
chemical DNA hybridization assays [31-37]. Such protocols have relied on capturing
the DNA coded nanoparticle probes to the hybridized target, followed by acid dissolu-
tion and anodic-stripping electrochemical measurement of the metal tracers (Fig. 14.3,
see Plate 15 for color version). The probe or target immobilization is accomplished in
connection with streptavidin coated magnetic beads [31], through the use of chitosan or
polypyrrole surface layers [37], or via adsorption onto the walls of polystyrene microw-
ells [32]. Picomolar and subnanomolar levels of the DNA target have thus been detected.
Further sensitivity enhancement can be obtained by catalytic enlargement of the gold
tracer in connection with nanoparticle-promoted precipitation of gold [31] or silver [39-
41] (Fig. 14.3b, see Plate 15 for color version). Combining such enlargement of the metal
particle tags, with the effective “built-in” amplifi cation of electrochemical stripping anal-
ysis, paved the way to subpicomolar detection limits. The silver-enhancement electrical
route has been applied recently for detection in “lab-on-chip” systems in connection with

MB

Biotinylated
Capture Probe

Biotinylated
Target

CdS labeled
probe

Cd
Amplification

Silver Enhancement

HBr
Au(III)

HNO 3

HNO 3

Ag(I)

Zn Cd Pb

Au(III)

MD

Me

Au(III)

Me 2
Mercury Coated Glassy
Carbon Electrode

Me 2

M

Au(I)

Disposable Screen-
Printed Electrode

MD

Au(I)

Disposable Screen-
Printed Electrode

(a) (b) (c) (d) (e)

FIGURE 14.3 Nanoparticle-based electrochemical detection of DNA. These assays involve the intro-
duction of the probe coated magnetic beads, the addition of the target/hybridization event, magnetic removal
of unwanted materials, binding of the metal, and amplifi ed electrochemical detection of the dissolved gold
(a), silver (b), and cadmium sulfi de (d) nanoparticles. Me: metal tag. Also shown are solid-state stripping (c)
and multi-target (e) detection protocols. See text for details (see Plate 15 for color version).