Physicochemical Characterization Strategies

Successful characterization strategies will enable one to begin associating the physicochemical properties of a nanomaterial with its in vivo behavior (i.e., SARs). This is an important step in the development of any material used for medical applications. For small molecules, the basis of most traditional drugs, the characterization techniques have been well established and standardized to determine their attributes, such as melting point, boiling point, molecular weight and structure, identity, composition, solubility, purity, and stability. These characteristics are measured and adequately defined using elemental analysis, mass spectrometry (MS), nuclear magnetic resonance (NMR), ultraviolet-visible (UV-vis) spectrophotometry, infrared (IR) spectroscopy, high-performance liquid chromatography (HPLC), gas chromatography (GC), capillary electrophoresis (CE), polarimetry, and other common analytical methods. Each of these individual techniques provides unique information about the sample, while together they provide the foundation for product quality control, manufacturing, and regulatory approval.

Many of the techniques used to characterize small molecules apply to nanomaterials. However, due to the composite nature of nanomaterials, the definition and measurement of these attributes can be quite different. To fully understand the attributes of a nanomaterial, additional characterizations are needed, such as size, surface chemistry, surface area, polydispersity, and zeta potential (see Figure 7.2). A comprehensive analysis of these properties is necessary to better understand in vivo effects and to allow for greater consistency and reproducibility in their preparation. The requirements set by regulatory bodies for quality control and consistency of biomedical nanomaterials are likely to be as stringent as those for small molecule preparations, but the path to verifying quality will require a more sophisticated approach. At the core of this analysis is an array of tools and instrumentation that are particularly well suited to measuring the properties of nanomaterials.

7.2.2 Instrumentation Spectroscopy

Many traditional analytical methods can be applied to the characterization of nanomaterials. For example, NMR is extensively used to characterize dendrimers, polymers, and fullerenes derivatives, and provides unique information on the structure, purity, and functionality.12-14

Small molecules

Liposome Dendrimer Gold nanoshell w

Quantum dot Fullerene


Elemental analysis Mass spectrometry NMR spectroscopy UV-vis spectroscopy IR spectroscopy HPLC GC


Physicochemical Parameters

• Composition

• Physical properties

• Chemical properties

• Identification

• Electrophoresis (CE, PAGE)

• Zeta potential

• Fluorimetry

FIGURE 7.2 Physicochemical characterization methods and instrumentation for small molecules and nanotechnology.

In addition, the average number of terminal capping groups, number of small molecule ligands, and drugs in a multifunctional nanomaterial can be ascertained by comparing the integration values with chemical shifts unique to the ligands. UV-vis absorption spectrophotometry is also extensively used to identify and quantify the chromophore present in the preparation by using its extinction coefficient. Spectrofluorimetry is used in cases where the material has inherent fluorescence (such as quantum dots) or labeled with a fluorescence probe. Matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) MS is used extensively for macromolecules, dendrimers, and polymers to determine the molecular weight and utilize novel matrices to minimize the fragmentation of the macromolecule before reaching the detector. In the case of lower generation dendrimers, the presence of impurities, incomplete reaction, and reaction byproducts can be easily determined using MS.

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