Biomedical Engineering Reference
In-Depth Information
1
Nanomaterials-Based Magnetic Relaxation Switch Biosensors
Tom Lowery
1.1
Introduction
Magnetic nanoparticles or microparticles can serve as magnetic relaxation switches
(MRSws) when they react with molecular targets and undergo changes in aggre-
gation state that affect solvent magnetic resonance relaxation. Coupling this
target-mediated aggregation with an appropriate detection device yields a reagent-
instrument biosensor system for detecting target analytes. Since their introduction
in 2001 [1], MRSw biosensors have been the subject of over 40 reports demonstrat-
ing their capability of detecting virtually any analyte in a variety of dirty, opaque
samples. MRSws have been shown capable of detecting nucleic acids, proteins,
enzymes, small molecules, ions, viruses and cells in solutions such as water,
blood, cell lysate, urine, plasma, and serum. Due to the broad range of possible
target analytes, and the capability of obtaining measurements without sample
preparation, MRSw technology has remarkable potential to change the paradigm
of solution-based biosensing, and thus to impact greatly on several fi elds of appli-
cation, including medical diagnostics, environmental sensing, and homeland
security.
The MRSw technology draws on the unique combination of scientifi c fi elds of
nanotechnology, biochemistry, and nuclear magnetic resonance (NMR). To date,
only one brief review has been published, relatively early during the development
of this technology [2]. Due to the rapidly growing body of these investigations, and
the interdisciplinary nature of MRSws, there is a need for a comprehensive
description of the technology and summary of recent progress. To this end, this
chapter provides an introduction to the relevant nanomaterials, an explanation of
relevant NMR measurement techniques, a summary of the underlying theoretical
physics behind nanoparticle clustering, an overview of the published MRSw
research articles, and a description of portable and miniaturized magnetic reso-
nance instrumentation. Although a sizeable body of work exists using other types
of magnetic resonance contrast agents for molecular detection [3-12], this chapter
will focus exclusively on MRSw biosensors.
