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SPIO Nanoparticles for Drug Delivery and Imaging of Microbes In Vivo via Biomarker Interactions
Super-Paramagnetic Iron Oxide Nanoparticles are probes that are able to accumulate within or on target cellular structures in vivo, and are able to be imaged with a high degree of contrast and spatiotemporal specificity. SPIO’s can attach to the surface of cells, or with minor modifications they can also find themselves within the cytoplasm of the cell. This allows for further scientific inquiry, especially in the field of microbiology due to the theranostic properties of these nanoparticles: they provide the possibility of not only imaging the microbe or target cell, but it also allows for the delivery of therapeutic reagents to promote or suppress the growth of the target. Depending on the strain and nanoparticle concentration, microbes can either use the heat for hyperthermia and growth or inhibition. The high free energy content of the nanoparticle is useful in microbial energetics as well. For targeting, the nanoparticles have peptides complementary to a target sequence within the microbes genetic sequence (i.e. rRNA) and therefore functions much like FISH (fluorescent in situ hybridization). The peptides allow for the docking of the nanoparticles, and subsequent reactions that create a cascade effect and allow for signals that can promote signal transduction within the target cell. The high degree of biocompatibility between microbes and nanoparticles underscores this powerful theranostic technique.

Currently, a theranostic approach to epithelial cancers has proven the basis for such a capability of nanoparticles to image and deliver medicine by reducing uMUC1 antigen expression in a majority of adenocarcinomas, including breast, ovarian, and colon cancer tumors. This implicates SPIO ability to prevent transformation of non-tumorous cells to cancer tumor cells by not only docking and imaging the correct tumor area within the body, but by delivering and promoting metabolic activity within the cell that can result in a change in gene expression. Nanoparticle technology aims to stand at the forefront of  modern medicinal microbiology as it is a multimodal form of imaging and drug delivery.

Magnetic Particle Imaging
In order to utilize the potential of SPIO nanoparticle technology, imaging the nanoparticles with minimal background is needed. Cell tracking of microbes can be performed with SPIO’s using a Magnetic Particle Imaging (MPI) machine. Michigan State University, Stanford University, amongst a few other large research institutions are home to such machines as it provides for high spatiotemporal specificity as well as a platform for theranostics (diagnostics mingled with therapy). MPI machines allow magnetic nanoparticles to align with the applied magnetic field by permitting passage through a Field Free Region (FFR). With low radioactivity, MPI still allows for imaging of deep sub-cellular structures with high specificity by attaching sugar branches that are complementary to the protein/other denoted biomarker on the microbe or cell of interest. This allows for more in vivo methods Previous methods using MPI to track stem cells have yielded success in imaging the development of the cells and response to therapy (theranostic imaging).

Tumor cell response to chemotherapy has been successful in utilizing nanoparticle imaging techniques to measure changes in antigen expression following delivery of a therapeutic. These methods were studied both in vitro and in vivo. Furthermore, stem cells and their growth are able to be tracked using nanoparticles. This is important in stem cell tracking and therapy following transplantation of cells in vivo. This will allow scientists to measure differentiation of cells within their respective biome, and the same can be done for microbes. Conventional approaches using nanoparticles for cell targeting and tracking rely on Magnetic Resonance Imaging (MRI) which results in negative contrast images when introduced to dense layers of the human body. MPI is able to filter out background by only picking up signals from the nanoparticles and assigning them to their respective location on the coordinate grid mapping of the subject.

Theranostic Imaging & Radioomics
Theranostic Imaging is considered a subset of a paradigm within imaging known as radioomics. Advanced imaging techniques have allowed for imaging of individual cellular structures within the human body with a high degree of resolution and sensitivity. Using nanoparticles to conjugate around specific cellular/sub-cellular targets can provide a fruitful mechanism of targeting diseases causing agents within the human microbiome. Realizing the growth pattern of a tumor and applying chemotherapy as needed based off of tumor density can allow for treatment that is not only personalized to the target microbe/cell but is also time sensitive and quick enough to prevent transformation/other changes in the target. The fact that these nanoparticles are uptaken by various strains of bacteria further enforce their capability of being used as agents of identifying and measuring changes in the human microbiome and microbes within their respective, natural environments. The goal of theranostics and radiomics is to utilize imaging modalities to identify, diagnose, and treat target structures within the human body. By combining conventional methods of synthesizing complementary molecules to our target cell and and performing in vivo imaging and cell tracking, scientists are able to manipulate nanoparticle technology to further expand former "-omics" techniques.

The ability of nanoparticles not only to provide a mechanism for imaging the target cell, but there are also ways for the nanoparticle to deliver any conjugated gene, therapeutic, or medicine with timed-release once in the cytoplasm of the intended target. The capability of nanoparticles to deliver such agents has widespread implications for genetic engineering and preventative measures in approaching disease treatment and evaluation. The nanoparticles release these conjugated agents upon a specific trigger mechanism. The reducing environment of cellular cytoplasm provides a fruitful mechanism of delivery/release of molecules from the nanoparticle's dextran-coated surface.