Biomedical Engineering Reference
In-Depth Information
7.1
Introduction
Clinical diagnostics have tremendous potential to revolutionize the practice of
medicine. The worldwide research community has made great strides toward
developing faster, more sensitive, and more cost-effective diagnostic technologies.
Despite extensive progress, however, worldwide access to many revolutionary tech-
nologies remains limited to large centralized laboratories in the developed world.
Some of the most promising technological advances have combined engineering,
material science, chemistry, and physics in the development of devices on the
nanoscale, 1-100 nm. The size scale of these devices has been demonstrated to
have unique physical and/or chemical properties that can be exploited for biolog-
ical applications. In addition, the exceptionally small scale enables the detection
platform to be highly portable, require relatively low power, and compile numerous
sensors into one high-density array for multiplex detection. Accordingly, nanotech-
nology has been leveraged broadly in both diagnostic medicine and therapeutics.
The diagnosis of a disease requires the identification of a disease marker. The
earlier that marker is detected, the earlier the disease can be treated. Typically
these disease markers are quantified because ascertaining the concentration aids
in determining the prognosis, ideal treatment, or the progression of the disease.
Proteins and oligonucleotides, for example, serve as the most common biomolecular
markers, termed “biomarkers.” Abnormalities in the structure, function, or amount
of a biomarker present are what predispose a patient to disease or may be
indicative of a particular disease. Because nanosensors are of the same scale as
these naturally occurring biomarkers, with nanoscale detection, one can readily
interface a highly sensitive sensor with the biological molecule of interest. The
use of magnetic nanotechnology for detecting the disease biomarkers holds great
promise because magnetically responsive nanosensors often allow for improvement
in the lower limit of detection and have the additional advantage of portability
of the detection apparatus and ease of use for point-of-care (POC) application.
The magnetoresistive biosensors described in this chapter involve three distinct
components: the magnetically responsive biosensor itself, the magnetic nanoparticle
(MNP) tags, and the protein detection assay. Each aspect will be discussed in detail
in this chapter.
7.2
Magnetic Biosensing Modalities
Magnetic biosensing offers several significant advantages over conventional optical
techniques and other sensing modalities. The samples (blood, urine, serum, etc.)
naturally lack any detectable magnetic content, providing a sensing platform with
a very low background. Additionally, MNP tags are not subject to problems that
have plagued fluorescent labels such as label bleaching and autofluorescence.
Furthermore, the sensors can be arrayed and multiplexed to perform quantitative
