Functionality

Analysis of the functional components of nanomaterials, such as targeting, imaging, and therapeutic agents, is critical to understand the in vivo efficacy of the preparation. Characteristic features of functional components include their quantity, distribution, orientation, and activity. For targeting agents, a key advantage of their use in nanoparticles is their ability to provide increased avidity to the target due to polyvalency. The level of polyvalency and activity of targeting agents can be monitored using surface plasmon resonance (SPR) to measure the rate constants for nano-particle association and dissociation. During preclinical development, the affinity of nanomaterial preparations for their target molecule/receptor can be analyzed using SPR and compared to data obtained for binding to cellular receptors in culture.45

The average number of targeting agents per nanoparticle has to be optimized for both solubility and binding affinity. Affinity chromatography or SEC can be employed with some nanoparticles to separate nanoparticles with targeting agents from those without targeting agents. In nanoparticles containing antibodies19,46 or proteins, quantification can be achieved using an enzyme-linked immunosorbent assay (ELISA) or bicinchoninic acid assay (BCA) if the inherent property of the nanoparticle itself does not interfere with the assay. In the case of dendrimers, NMR has been successfully applied to analyze the average number of targeting agents by comparing the integration values of the signals associated with the targeting agents to those belonging to the dendrimer. This is still an averaged technique that cannot distinguish the distribution of targeting agent density on a population of nanoparticles.

For targeted drug delivery applications, it is obviously important for both the targeting and therapeutic agents to be on the same particle. If the therapeutic has UV-vis absorption, it can be quantified using UV-vis spectroscopy with the extinction coefficient of the drug. HPLC analysis is possible in some cases to evaluate the amount of the drug present in a known amount of material, after isolating the drug from the sample.

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