title: Second harmonic generation correlation spectroscopy for characterizing translationally diffusing protein nanocrystals.
abstract: Second harmonic generation correlation spectroscopy (SHG-CS) is demonstrated as a new approach to protein nanocrystal characterization. A novel line-scanning approach was performed to enable autocorrelation analysis without sample damage from the intense incident beam. An analytical model for autocorrelation was developed, which includes a correction for the optical scattering forces arising when focusing intense, infrared beams. SHG-CS was applied to the analysis of BaTiO3 nanoparticles ranging from 200 to ∼500 nm and of photosystem I nanocrystals. A size distribution was recovered for each sample and compared with the size histogram measured by scanning electron microscopy (SEM). Good agreement was observed between the two independent measurements. The intrinsic selectivity of the second-order nonlinear optical process provides SHG-CS with the ability to distinguish well ordered nanocrystals from conglomerates and amorphous aggregates. Combining the recovered distribution of particle diameters with the histogram of measured SHG intensities provides the inherent hyperpolarizability per unit volume of the SHG-active nanoparticles. Simulations suggest that the SHG activity per unit volume is likely to exhibit relatively low sensitivity to the subtle distortions within the lattice that contribute to resolution loss in X-ray diffraction, but high sensitivity to the presence of multi-domain crystals.
authors.affiliation: Chemistry Department, Purdue University, West Lafayette, IN 47907, USA.
authors.forename: Ximeng Y
authors.initials: XY
authors.lastname: Dow
authors.affiliation: Chemistry Department, Purdue University, West Lafayette, IN 47907, USA.
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Dettmar
authors.affiliation: Chemistry Department, Purdue University, West Lafayette, IN 47907, USA.
authors.forename: Emma L
authors.initials: EL
authors.lastname: DeWalt
authors.affiliation: Chemistry Department, Purdue University, West Lafayette, IN 47907, USA.
authors.forename: Justin A
authors.initials: JA
authors.lastname: Newman
authors.affiliation: Chemistry Department, Purdue University, West Lafayette, IN 47907, USA.
authors.forename: Alexander R
authors.initials: AR
authors.lastname: Dow
authors.affiliation: School of Molecular Sciences, Arizona State University, Tempe, AZ 85287-1604, USA.
authors.forename: Shatabdi
authors.initials: S
authors.lastname: Roy-Chowdhury
authors.affiliation: School of Molecular Sciences, Arizona State University, Tempe, AZ 85287-1604, USA.
authors.forename: Jesse D
authors.initials: JD
authors.lastname: Coe
authors.affiliation: School of Molecular Sciences, Arizona State University, Tempe, AZ 85287-1604, USA.
authors.forename: Christopher
authors.initials: C
authors.lastname: Kupitz
authors.affiliation: School of Molecular Sciences, Arizona State University, Tempe, AZ 85287-1604, USA.
authors.forename: Petra
authors.initials: P
authors.lastname: Fromme
authors.affiliation: Chemistry Department, Purdue University, West Lafayette, IN 47907, USA.
authors.forename: Garth J
authors.initials: GJ
authors.lastname: Simpson
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry*; D017609:Barium Compounds / Q000737:chemistry*; D003460:Crystallization / Q000379:methods*; D004058:Diffusion; D007259:Infrared Rays; D008855:Microscopy, Electron, Scanning; D053758:Nanoparticles / Q000737:chemistry*; D055620:Optical Phenomena; D045331:Photosystem I Protein Complex / Q000737:chemistry*; D013057:Spectrum Analysis / Q000379:methods*; D046940:Synechococcus / Q000737:chemistry*; D014025:Titanium / Q000737:chemistry*
chemical_list: D001426:Bacterial Proteins; D017609:Barium Compounds; D045331:Photosystem I Protein Complex; C024547:barium titanate(IV); D014025:Titanium
keywords: XFEL; correlation spectroscopy; protein nanocrystals; second harmonic generation; size distribution