MNPs either individually or in integration with other signal mediators can also be

exploited as magnetic tags for the amplification of an analytical signal; for example,

Zhang et al. proposed the simultaneous detection of two tumor markers; squamous

cell carcinoma-associated antigen (SCC-Ag) and carcinoembryonic antigen (CEA)

were achieved by the electrochemical determination of two MNP-based probes on

the electrode surface as shown in Fig. 24.4. For the accomplishment of this strategy,

the

primary

antibody

was

immobilized

on

poly(1-methyl-3-(1-methyl-4-

piperidinylmethylene)thiophene-2,5-diyl chloride)-modified GCE electrode, and

the differently surface-functionalized Fe3O4 NPs (thionine and ferrocenecarboxylic

acid) were associated with secondary antibody to fabricate labels. During the

electrochemical analysis, two distinct peaks were obtained, thereby providing simul-

taneous determination of analytes (Zhang et al. 2014).

24.5

Magnetic Nanoparticles for Magnetic Resonance Imaging

With the increase in tumor morbidity rates, it has become imperative to detect these

at an early stage so that a timely treatment can be provided. Magnetic resonance

imaging (MRI) is a very important noninvasive imaging technique extensively used

in diagnostics based on high soft tissue contrast with ultrahigh spatial resolution for

the detection of proton relaxation in an externally applied magnetic field. The

protons present in water and lipid molecules majorly contribute to the MRI signals

where MNPs act as contrast agents to provide strength to the signals. For practical

Fig. 24.4 Schematic representation of preparation of immunosensor. (Reproduced with permis-

sion from Zhang et al. (2014))

24

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