Biomedical Engineering Reference
In-Depth Information
magnetic aggregation, resulted in seven- and two-fold increases in projected sen-
sitivity when used with and without valency enhancement, respectively. Magnetic
aggregation cannot be applied to NP-based assays due to the attractive forces
between the magnetic dipoles of individual NP being much smaller than the forces
of Brownian motion [20]. Although it has not been exactly determined, the increase
in sensitivity for MP-based assays from magnetic aggregation most likely arose
from the more rapid kinetics due to the confi nement and resultant close proximity
of reactive surfaces. The method of magnetic aggregation has also been applied
to solution viscosity measurements by monitoring the rate of change in T
2
over
the course of MP aggregation and dispersion phenomena [20].
The most important lesson derived from the fi ndings of Koh
et al.
was that many
different methods can be used to increase MRSw sensitivity. For example, Koh
et al.
reported a sensitivity enhancement over the basic NP biosensor confi guration
of 10
5
due to the use of MP, valency enhancement, and magnetic aggregation. As
they showed, many sensitivity enhancement methods are multiplicative in their
effect, providing for highly sensitive, tailored results for a given assay. The ideal
combination of methods will depend on the particular requirements for a biosens-
ing application, which include reagent stability, time to results, dynamic range,
and sensitivity.
1.8
Micro - NMR of Magnetic Relaxation Switch Biosensors
A key component to enabling the successful application of magnetic relaxation
switch biosensors is to tailor, in appropriate fashion, the detection platform to the
setting in which it will be used. A variety of settings would greatly benefi t from a
universal detection technology such as MRSw biosensors. These include applica-
tions such as biowarfare fi rst responders and home testing, both of which require
highly mobile, robust, and perhaps handheld, instruments; applications such as
biomarker discovery, which require automation and high throughput; and applica-
tions such as health clinics or doctor' s offi ces, which require a compact, user-
friendly bench-top unit. Although the majority of commercial magnetic resonance
detection instruments are very large, recent progress in magnetic resonance tech-
nology engineering has demonstrated scalability and portability. In this section,
we will introduce the magnetic readers that have been used to obtain MRSw bio-
sensor measurements, summarize the recent progress in magnetic resonance
instrumentation that has enabled the development of miniaturized detectors for
biosensor applications, and also provide an update on progress towards developing
portable MRSw biosensor readers.
An alternative measurement approach has been proposed to circumvent the low
sample measurement throughput of current bench-top systems by a team at MGH,
led by D. Hogemann. This group demonstrated the use of a 1.5 T magnetic reso-
nance scanner and T
2
-weighted magnetic resonance images to provide HTS for
nanoparticle-based reagents. By using this method, up to 1920 samples could be
