Biology Reference
In-Depth Information
8.4.3.3 Potentiometric stripping analysis
InadditiontoLSVandDPV,chronopotentiometryhasalsobeenused
to detect metal nanoparticle labels ([31], [36]). In PSA, the metal
ions from the labels are reduced onto the electrode as described
previously andthen theelectrode isprogrammed topassaconstant
current, often in the order of microamps. To satisfy this current the
electrode potential moves to a value where M
0
will be reoxidized.
Once M
0
is depleted from the electrode the potential must shift
positively until a new redox reaction (possibly solvent electrolysis)
canprovidethecurrent.Thetime
τ
forthispotentialtransitionisthe
analyticalsignalcorrespondingtocurrentheightinvoltammetry.To
the best of our knowledge the expression of
τ
foranMFEusedin
ASVhasnotbeenderived.ForASVusingaHMDEofradius
r
passing
acurrent
I
,
τ
isrelated to
c
M
by [49]
r
2
15
D
nFArc
M
3
I
τ
=
−
(8.9)
assumingthatall(oraconsiderablepart)ofM
0
inthemercurydrop
is oxidized and that the inequality
r
2
<
7
Dt
is fulfilled. When the
dropradiusissmallandthecurrentislow,thesecondtermbecomes
negligible. Some of the chronopotentiometric stripping responses
for metal nanoparticle detection [31, 36] have been reported in the
form of peaks with heights measured in units of s V
−
1
, which means
presumably some differential of thecurrent was measured.
8.5 Latex as a Label Support
8.5.1
Introduction
The term “latex” originally referred to the milky sap of rubber
trees and certain plants. This sap was found to be an aqueous
mediumcontainingcolloidsofnaturalrubber,stabilizedbyproteins.
Laboratory-synthesized polymer colloids were hence described as
“synthetic latexes,” and finally just “latexes.” That term will be used
here. Billions of pounds of latexes are synthesized worldwide each
year, for a large variety of applications. The reasons for interest in
their use in constructing electrochemical labelsare
