Biomedical Engineering Reference
In-Depth Information
health, and that may have a substantial impact on the quality of life of those who
depend on the polluted aquatic systems. Drinking water has two major classes of
contamination, namely biological and chemical [19, 20]. Biological contamination,
such as coliform bacteria (e.g.,
Escherichia coli
) and viruses, if detected before
exposure to human populations, can be remedied by a number of well-established
technologies. However, the detection of these analytes in natural environments is
a daunting challenge, and much ongoing research is being carried out to improve
the current state of the art.
The detection, remediation, and removal of chemical and heavy-metal contami-
nation (e.g., pesticides, radionuclides, and heavy metals such Hg and Pb) are,
likewise, diffi cult challenges [19] ( http://www.epa.gov/ogwdw/hfacts.html ). The
remediation of common organic contaminants such as pesticides, agricultural
chemicals, industrial solvents, and fuels can be accomplished using treatments
such as UV/ozone, activated-carbon, or plasma technologies [19]. The remediation
and/or removal of toxic heavy-metal contaminants (e.g., Hg, Pb, Cd) can be par-
tially addressed by using traditional sorbent materials such as ceramic oxides,
although these materials will bind metal ions nonspecifi cally and can easily be
saturated with ubiquitous species (e.g., Ca, Mg, Zn) [19]. Another weakness of
traditional ceramic oxide sorbent materials is that metal ion sorption to the surface
is a reversible process. Therefore, a functionalized sorbent material with a high
chemical specifi city that is capable of permanently sequestering the target analytes
from the contaminated water system is needed [19, 20]. An ideal sorbent material
candidate should have rapid kinetics for sorption of the analyte, while the interac-
tion between the sorbent and analyte should be effectively irreversible in all but
specifi c applications where analyte release is desirable. In addition, sorbent materi-
als that enable a more sensitive detection for a wide variety of analytical methods
through separation and preconcentration prior to analysis are needed [6]. These
types of materials would allow the analysis of complex samples containing small
amounts of analyte, without the high background signals typically associated with
environmental samples.
Magnetic nanoparticles have the potential to meet many of the above-mentioned
needs for the preconcentration, removal, and detection of both environmental and
biological contaminants. These materials have a unique property - namely, super-
paramagnetism - that arises from their nanoscale single magnetic domain struc-
tures [17]. Superparamagnetic behavior manifests itself in nanoparticles that are
smaller than the critical diameter, which is both material- and temperature - depen-
dent. Throughout this chapter, the predominant topic of discussion will be iron
oxide nanoparticles with diameters ranging from
∼
5 to 20 nm, which falls within
the established critical diameter for this material (
15 - 20 nm) [17] . From a practi-
cal standpoint, a superparamagnetic nanoparticle has little to no remnant magne-
tization after exposure to a magnetic fi eld, and low to no coercivity (the fi eld
required to bring the magnetization to zero); this means that such nanoparticles
will not agglomerate magnetically at room temperature [17]. This is a signifi cant
factor for sensing applications, where it is desirable for the nanoparticles to be
well dispersed in the sample matrix and easily manipulable by an applied external
∼
