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The goal of this work was to evaluate the ability of photothermal induced resonance (PTIR) to measure the local infrared absorption spectra of crystalline organic drug nanoparticles embedded within solid matrices. Herein, the first reports of the chemical characterization of sub-100 nm organic crystals are described; infrared spectra of 90 nm griseofulvin particles were obtained, confirming the chemical resolution of PTIR beyond the diffraction limit. Additionally, particle size distributions via dynamic light scattering and PTIR image analysis were found to be similar, suggesting that the PTIR measurements are not significantly affected by inhomogeneous infrared absorptivity of this system. Thus as medical applications increasingly emphasize localized drug delivery via micro/nano-engineered structures, PTIR can be used to unambiguously chemically characterize drug formulations at these length scales.

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[a] 1IntroductionAf undamentalu nderstanding of the adhesionb etween explosives residues, swabs used during detection of these residues, and surfaces to which the residues adhere is necessary to optimize the detection of these residues in airport security settings. The basic forcest hat control the behavioro f the residues are the van der Waals (vdW)f orces, whichc an be considered to be comprised of Keesom (dipole-dipole interactions), Debye (dipole-induced dipole interactions), and London dispersion forces( induced dipole-induced dipole interactions). The Hamaker constant A estimates the magnitude of vdW forcesb etweent wo dissimilar materials or within ap ure material [1].A dhesive Hamaker constants betweenm aterials i and k in medium j are denoted as A ijk while cohesive Hamaker constants for material i in a vacuum are denoteda sA ii .U sing combining rules established by Israelachvili [1],f amilies of A ii can be used to estimate A ijk amongavariety of materials in varying media. As ar esult, A ii of explosivesr esidues allow prediction of A ijk 's (and correspondingly the strengtho fa dhesion) between these residues and commonly swabbed surfaces.Methods of predicting A ii using Hamaker's pair-wise additive approach [2]

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