surface of SPIO NPs. The PEG coating on SPIO provides an additional advantage to

extend the blood half-life time of SPIO NPs. The tracer exhibited superior colloidal

stability and persistent intravascular MPI signal for the generation of blood pool

tracers for MPI (Khandhar et al. 2017). Moreover, Orendorff et al. presented the first

three-dimensional imaging of the initial stage of traumatic brain injury and

corresponding hematoma in the closed skull via utilization of SPIO in MPI modality.

This study demonstrated the potential of MPI modality reinforced with MNPs in

noninvasive diagnosis of internal bleeding for patients suffering from trauma in the

emergency setting and thereby, assist in differentiating between mild and moderate

injuries. Thus, MPI-based device can be harnessed for the determination of location,

severity, and depth of the bleeding from the closed skull (Orendorff et al. 2017).

Additionally, Arami et al. presented a strategy for targeting the cancerous cells

using IONPs coated by biocompatible PMAO-PEG copolymer molecules, which

were further conjugated to lactoferrin to enhance the tumor-targeting activity of

IONPs. Afterwards, external magnetic field was applied and MPI generated three-

dimensional images from only nanoparticles that were embedded in tissues, based on

their intrinsic magnetic responses. This first preclinical study of cancer-targeted NPs

using a MPI system paves the way to explore new strategies for the diagnosis of

cancer (Arami et al. 2017).

24.4

Magnetic Nanoparticles for Biosensing Applications

A biosensor is a potential device capable of converting biological event into an easily

detectable signal. Biosensors comprise three parts: a biorecognition element

(antibodies, nucleic acids, cell receptors, enzymes, etc.), transducer (physicochemi-

cal, optical, piezoelectric, and chemical), and signal processor. Firstly, biosensing of

analyte entails the attachment of biorecognition element onto the surface of the

signal transducer, accompanied by robust interaction of biorecognition element with

the target analyte, and, finally, generation of an optical or electric signal by the

transducer. Moreover, the biomolecule immobilization is the defining parameter for

controlling the performance of biosensor.

In this regard, MNPs provide a suitable platform for the immobilization of

enzymes/biomolecules owing to their high surface area, biocompatibility, and easy

amenability of surface functional groups. The efficacy of MNP towards in vivo

studies can be epitomized basically by three strategies. The first strategy involves

magnetic preconcentration of an analyte where one can preconcentrate the analyte

via interaction between MNPs and analyte. In this manner, analyte bonded to MNPs

can be attracted onto the surface of the sensor with the application of gradient

magnetic field, and thus, analyte can be detected with minimal interferences from

the sample matrix. Another method emphasizes the involvement of functionalized

MNPs as tags for the visualization and selective detection of immunocomplexes with

a target analyte. The third approach involves the integration of MNPs into the

transducer material or the surface functionalization of the sensor for the amplifica-

tion of the output signal (Farka et al. 2017).

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