Biomedical Engineering Reference
In-Depth Information
and optical (i.e., fl uorescent) detection schemes. Their role is to bind the target
analyte in solution and rapidly bring it to the sensor surface, or to separate it from
the background interferents upon the application of an external magnetic fi eld. In
most cases, an applied magnetic fi eld from either an electromagnet or permanent
magnet is typically employed to capture the nanoparticle/analyte complex from
solution prior to analysis [6, 13, 122, 123].
The present authors' group has demonstrated the use of both magnetic [6]
and nonmagnetic [114] high - surface - area sorbent materials to enhance the
electrochemical detection of toxic heavy metals from natural waters. The sorbent
materials, which were either functionalized magnetic nanoparticles or mesopo-
rous silica, were modifi ed with a wide range of thiol-containing organic molecules
that possesses a high affi nity towards heavy metals (e.g., Hg, Pb, Cd), and
were placed or collected at an electrode surface (Figure 9.9) [6, 114]. By using
these high-surface-area sorbent materials, it has been possible to demonstrate
the sensitive electrochemical detection of environmentally relevant heavy metals
(e.g., Pb, Hg, Cd) in complex environmental (e.g., river water) and clinical (e.g.,
urine) samples [6, 114]. Superparamagnetic Fe
3
O
4
nanoparticles functionalized
with dimercaptosuccinic acid (DMSA) (similar to those discussed above) were
used to fi rst bind the heavy-metal contaminants from complex samples, and
then subsequently to carry them to the surface of a magnetic electrode (see Figure
9.9 ) [6] .
By using an applied magnetic fi eld to remove the target analytes from solution
prior to electrochemical analysis, the analytes are effectively isolated from the huge
number of potential interferents present in complex sample matrices. In using
this system, two of the biggest problems that have prevented the widespread
(a)
(b)
to 1-5 V power
supply
to detector
to detector
copper wire
80Ni-15.5Fe-4.5Mo core
3 mm dia
×
80 mm long
PTFE housing
6 mm O.D.
×
38 mm long
0.3 mm dia, OFHC
copper windings,
800-850 turns
neodymium magnet
3 mm dia
×
25 mm long
conducting epoxy used to
bond GCE to core
CPE, 3 mm dia
×
1 mm thick
GCE, 3 mm dia
×
1.5 mm thick
Figure 9.9
Schematics of (a) the magnetic electrode and
(b) the electromagnetic electrode which preconcentrate metal
ions using superparamagnetic nanoparticles. Reprinted with
permission from Ref. [6]; © The Royal Society of
Chemistry (RSC).
