Biomedical Engineering Reference
In-Depth Information
2
Multiplexed Detection with Magnetic Nanoparticles
Robert Wilson
2.1
Introduction
Although, during the early stages of their evolution, detection methods were
designed to detect a single analyte in a large volume of sample, two trends have
subsequently emerged. In one trend, the sample volume has been decreased with
the aid of improved sample processing techniques and more sensitive detection
methods, whilst in the other trend the number of analytes that are detected in the
same sample has been increased. These trends of increasing numbers and smaller
size are analogous to what has occurred in the semiconductor industry, where an
increasing number of electronic components have been compressed into a shrink-
ing volume of hardware. Thus, today, multiple tests can be carried out on the same
small volume of sample by techniques that are collectively known as multiplexed
detection. Over time, however, this term has acquired several different meanings.
In this chapter, it is defi ned as the detection of multiple analyte (target) molecules
in the same undivided volume (aliquot) of sample, at the same time. For biomo-
lecular assays, two main platforms are used for multiplexed detection; in one
platform the sample is interrogated with a two - dimensional ( 2 - D ) array of probe
molecules (Figure 2.1a) [1-3], while in the other platform the probe molecules are
attached (conjugated) to encoded particles and added to the sample (Figure 2.1b).
The latter will henceforth be referred to as suspension arrays [4 - 6] . Each of these
alternatives has its own advantages: in general, 2-D arrays allow many more ana-
lytes to be interrogated in the same sample, but suspension arrays are less expen-
sive and have shorter sample to answer times. Magnetic nanoparticles - either on
their own or as constituents of magnetic microspheres - are
used
in
both
procedures.
