Composition and Purity

Biomedical nanomaterials can be comprised of a wide variety of substances, including polymers, metals and metal oxides, lipids and other organic compounds, and large biomolecules such as protein or DNA. In most cases, the nanomaterials combine two or more of these substances, such as in a core or shell of a particle, and in encapsulated or conjugated material. Analysis of chemical composition will be critical for confirming the purity and homogeneity of nanomaterial product preparations.

Elemental analysis, such as CHN analysis, is most often used to ascertain the purity of small molecules. For nanomaterials, elemental analysis can be used to determine the composition and ratios of different elements present in the sample. For example, this technique can be used to determine the amount of linker present, if a unique element (such as sulfur) has been employed in the synthesis. In the case of core-shell metal nanoparticles, the ratio of core to shell material ratios can be determined.

Atomic absorption (AA) and atomic emission (AE) spectroscopies can also be utilized to determine the composition of nanomaterials. For imaging applications using iron oxide nanopar-ticles or gadolinium (Gd)-based chelates, composition analysis is very important to quantify metals present in the preparation which influence imaging efficacy. Inductively coupled plasmon optical emission spectroscopy (ICP-OES) is very sensitive to determine the amount of Gd in such contrast agent conjugates.47 Specific T1/T2 relaxivities of magnetic resonance contrast agents can, of course, be assessed under in vitro conditions in the actual MRI instrument.

The purity of synthetic small molecules can be determined with a high degree of certainty since the analyte usually consists of a single component. With nanomaterials, purity must be determined in the context of multiple layered, conjugated, and encapsulated components. Purity analysis must account for the presence of solvents, free metals and chelates, unconjugated therapeutic or other agents, precursors, dimers, etc., that result in artifacts and side products of the preparation.48 Characterization of the inhomogeneity in ligand distribution is very important for efficacy as well as testing batch-to-batch reproducibility.49 Proper methods and techniques to detect the presence of all these entities are required to ensure the purity and quality of nanomaterial preparations and to further expand our understanding of SARs.

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