Second Harmonic Generation Data Research Articles

Angle Measurement Based on Second Harmonic Generation Using Artificial Neural Network

This article proposed an angle measurement method based on second harmonic generation (SHG) using an artificial neural network (ANN). The method comprises three sequential parts: SHG spectrum collection, data preprocessing, and neural network training. First, the referenced angles and SHG spectrums are collected by the autocollimator and SHG-based angle sensor, respectively, for training. The mapping is learned by the trained ANN after completing the training process, which solves the inverse problem of obtaining the angle from the SHG spectrum. Then, the feasibility of the proposed method is verified in multiple-peak Maker fringe and single-peak phase-matching areas, with an overall angle measurement range exceeding 20,000 arcseconds. The predicted angles by ANN are compared with the autocollimator to evaluate the measurement performance in all the angular ranges. Particularly, a sub-arcsecond level of accuracy and resolution is achieved in the phase-matching area.

Abstract P5-02-13: A novel detection technique for collagen (and other macromolecules) on H&E slides without special stains for improved cancer prognostics

Abstract Background: Stromal density including the characterization of the type, abundance and alignment of collagen and other extracellular matrix (ECM) protein fibers in proximity to breast precancers and cancers has emerged as an important and evolving tool for understanding tumor progression and stratifying/classifying mortality risk. Standard methods for this evaluation including second harmonic generation (SHG) microscopy requires access to fresh or FFPE tissue samples of limited availability. In contrast, standard diagnostic H&E slides are more readily available for large retrospective and prospective studies. Methods: We developed a method for dual emission and transmission (DUET) microscopy that employs combined brightfield and fluorescence modalities, plus quantitative image analysis. The prototype instrument has whole-slide scanning capabilities for collagen detection and pixel-accurate alignment with conventional H&E-stained images. We have analyzed a retrospective cohort of 700 breast cancers with available outcome follow-up of greater than 5 years using this DUET method Results: DUET microscopy provides clear discrimination of collagen and ECM directly from standard H&E specimens, requiring only a few minutes to scan whole slides. Using the method, contrast enhancement similar to special staining techniques (e.g. trichrome, periodic acid Schiff’s, and picrosirius red stains). Image analysis from DUET directly corresponds to SHG data. DUET imaging discriminates between stroma surrounding invasive cancer and benign epithelium. DUET imaging of 700 breast cancers shows outcome correlation. Ongoing multivariate analysis comparing standard measures (grade, tumor infiltrating lymphocytes, tumor phenotype, etc.) to the DUET stromal score will be reported. Conclusions: DUET provides a straightforward, rapid and inexpensive approach for highlighting collagen distribution patterns on existing histology slides. This method should enable current research using improved quantitative tools, including AI-based, for correlation with patient outcomes, by enabling the use of standard and available H&E slides. Citation Format: Farzad Fereidouni, Alexander D. Borowsky, Richard M. Levenson. A novel detection technique for collagen (and other macromolecules) on H&E slides without special stains for improved cancer prognostics [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P5-02-13.

Crystal structure of the inversion-breaking metal Cd2Re2O7

Second harmonic generation (SHG) on the pyrochlore metal Cd2Re2O7 indicates the presence of three order parameters setting in below an inversion breaking transition. Here, we explore a possible structural explanation and relate it not only to the SHG data, but also to neutron and x-ray diffraction, where we find that such a structural scenario can explain certain reflection extinctions observed in single crystal x-ray data. From this analysis, we suggest future experiments that could be done to resolve this matter. Finally, we comment on the Landau-violating nature of the inversion breaking transition and its relation to similar phenomena observed in improper ferroelectrics.

Induction strategies of the noncentrosymmetricity in centrosymmetric nonlinear optical nanocrystal processes

The second harmonic generation (SHG) is one of the measures of the optical nonlinearity. However, the SHG is prevented by symmetry in a centrosymmetric material. Therefore, in order to observe the SHG it is necessary to form a noncentrosymmetric process in a centrosymmetric material. Noncentrosymmetric nanosize-material processes CdI2 are formed by doping it with the impurity copper, controlling the size of the crystal and crystal temperature, and by pumping with an IR laser beam. The noncentrosymmetricity in the processes are probed by the observation of SHG and the second-order optical susceptibility (χijk(2)) is calculated from the SHG data. The value of χijk(2) is found to depend fashionably on the impurity content of the nanomaterials: χijk(2) = C1 exp[-1∕2{(Si-C2)∕C3}2], where Si is the concentration of impurity of the type i (here Si is SCu), and C1, C2 and C3 are parameters whose values depend on the crystal temperature and thickness of the nanomaterials. A photoluminescence measurement supports the third-order nonlinearity (χijkl(3)) of the centrosymmetric CdI2 system and hence SHG in the induced processes. The results also show that a significant enhancement (from 0.37 pm/V to 0.83 pm/V) in the noncentrosymmetric response χijk(2) is achieved in nanomaterials with reduced sizes and at low temperatures. A recipe of the induction strategies of the noncentrosymmetricity in centrosymmetric nonlinear optical processes CdI2 is explored and the results are discussed. However, the findings resulting from this investigation show that cadmium iodide nanocrystals might have potential in applications as optoelectronic nanodevices.

Characterization of Pancreatic Cancer Tissue Using Multiphoton Excitation Fluorescence and Polarization-Sensitive Harmonic Generation Microscopy.

Thin tissue sections of normal and tumorous pancreatic tissues stained with hematoxylin and eosin were investigated using multiphoton excitation fluorescence (MPF), second harmonic generation (SHG), and third harmonic generation (THG) microscopies. The cytoplasm, connective tissue, collagen and extracellular structures are visualized with MPF due to the eosin stain, whereas collagen is imaged with endogenous SHG contrast that does not require staining. Cellular structures, including membranous interfaces and nuclear components, are seen with THG due to the aggregation of hematoxylin dye. Changes in the collagen ultrastructure in pancreatic cancer were investigated by a polarization-sensitive SHG microscopy technique, polarization-in, polarization-out (PIPO) SHG. This involves measuring the orientation of the linear polarization of the SHG signal as a function of the linear polarization orientation of the incident laser radiation. From the PIPO SHG data, the second-order non-linear optical susceptibility ratio, χ(2)zzz'/χ(2)zxx', was obtained that serves as a structural parameter for characterizing the tissue. Furthermore, by assuming C6 symmetry, an additional second-order non-linear optical susceptibility ratio, χ(2)xyz'/χ(2)zxx', was obtained, which is a measure of the chirality of the collagen fibers. Statistically-significant differences in the χ(2)zzz'/χ(2)zxx' values were found between tumor and normal pancreatic tissues in periductal, lobular, and parenchymal regions, whereas statistically-significant differences in the full width at half maximum (FWHM) of χ(2)xyz'/χ(2)zxx' occurrence histograms were found between tumor and normal pancreatic tissues in periductal and parenchymal regions. Additionally, the PIPO SHG data were used to determine the degree of linear polarization (DOLP) of the SHG signal, which indicates the relative linear depolarization of the signal. Statistically-significant differences in DOLP values were found between tumor and normal pancreatic tissues in periductal and parenchymal regions. Hence, the differences observed in the χ(2)zzz'/χ(2)zxx' values, the FWHM of χ(2)xyz'/χ(2)zxx' values and the DOLP values could potentially be used to aid pathologists in diagnosing pancreatic cancer.

Combining (Non)linear Optical and Fluorescence Analysis of DiD To Enhance Lipid Phase Recognition

The widespread interest in phase recognition of lipid membranes has led to the use of different optical techniques to enable differentiation of healthy and not fully functional cells. In this work, we show how the combination of different (non)linear optical methods such as one-photon absorption (OPA), two-photon absorption (TPA), and second harmonic generation (SHG) as well as the study of the fluorescence decay time leads to an enhanced screening of membrane phases using a fluorescent 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine (DiD) probe. In the current study we consider the pure liquid disordered phases of DOPC (dioleoyl- sn-glycero-3-phosphocholine, room temperature) and DPPC (1,2-dipalmitoyl- sn-glycero-3-phosphocholine, 323 K), the solid gel phase of DPPC (298 K), and the liquid ordered phase of a 2:1 binary mixture of sphingomyelin and cholesterol. By means of extensive hybrid quantum mechanics-molecular mechanics calculations and based upon the (non)linear absorption of the embedded probes, it is found that DiD can be used to identify the lipid bilayer phase. The joint TPA and SHG as well as fluorescence analyses qualifies DiD as a versatile probe for phase recognition. In particular, the SHG data obtained by means of hyper-Rayleigh scattering and by electric field induced second harmonic generation reveal differences in polarization of the probe in the different environments. The TPA results finally confirm the particular location of the probe in between the polar headgroup region of the 2:1 SM:Chol mixture in the liquid ordered phase.

A set-up for simultaneous measurement of second harmonic generation and streaming potential and some test applications

We present a measurement cell that allows simultaneous measurement of second harmonic generation (SHG) and streaming potential (SP) at mineral-water interfaces with flat specimen that are suitable for non-linear optical (NLO) studies. The set-up directly yields SHG data for the interface of interest and can also be used to obtain information concerning the influence of flow on NLO signals from that interface. The streaming potential is at present measured against a reference substrate (PTFE). The properties of this inert reference can be independently determined for the same conditions. With the new cell, for the first time the SHG signal and the SP for flat surfaces have been simultaneously measured on the same surface. This can in turn be used to unambiguously relate the two observations for identical solution composition. The SHG test of the cell with a fluorite sample confirmed previously observed differences in NLO signal under flow vs. no flow conditions in sum frequency generation (SFG) investigations. As a second test surface, an inert (“hydrophobic”) OTS covered sapphire-c electrolyte interface was studied to verify the zeta-potential measurements with the new cell. For this system we obtained combined zeta-potential/SHG data in the vicinity of the point of zero charge, which were found to be proportional to each other as expected. Furthermore, on the accessible time scales of the SHG measurements no effects of flow, flow velocity and stopped flow occurred on the interfacial water structure. This insensitivity to flow for the inert surface was corroborated by concomitant molecular dynamics simulations. Finally, the set-up was used for simultaneous measurements of the two properties as a function of pH in automated titrations with an oxidic surface. Different polarization combinations obtained in two separate titrations, yielded clearly different SHG data, while under identical conditions zeta-potentials were exactly reproduced. The polarization combination that is characteristic for dipoles perpendicular to the surface scaled with the zeta-potentials over the pH-range studied, while the other did not. The work provides an advanced approach for investigating liquid/surface interactions which play a major role in our environment. The set-up can be upgraded for SFG studies, which will allow more detailed studies on the chemistry and the water structure at a given interface, but also the combined study of specific adsorption including kinetics in combination with electrokinetics. Such investigations are crucial for the basic understanding of many environmental processes from aquatic to atmospheric systems.

A polarizable embedding approach to second harmonic generation (SHG) of molecular systems in aqueous solutions

We present the extension to second harmonic generation (SHG) of the atomistic fully polarizable QM/FQ method that treats the solvent atomistically and embeds each atom in the solvent with a fluctuating charge (FQ) which responds to the solute quantum mechanical (QM) electrostatic potential in a self-consistent manner. The proposed approach is able to achieve an adequate modeling of solvent effects both in the quantum mechanical response equations and on the conformational properties of the system, which is sampled by resorting to molecular dynamics simulations. The application of the model to selected organic acids in aqueous solution, for which the interaction with the surrounding environment is dominated by HB interactions, shows a good agreement in both the modeling of solvent effects and in the reproduction of experimental SHG data extracted from hyper-Raman scattering experiments.

Pressure-induced transformations of multiferroic relaxor PbFe0.5Nb0.5O3

The effects of hydrostatic pressure at ambient temperature on the structural and dielectric properties of PbFe0.5Nb0.5O3 (PFN) were investigated using second harmonic generation (SHG) and powder x-ray diffraction measurements to 31 GPa. The results demonstrate that PFN undergoes a pressure-induced structural transition from the R3m ferroelectric to the R3¯m paraelectric phase. SHG measurements showed a continuous decrease in the signal with pressure and complete disappearance at 7.1 GPa. Effective nonlinear optical coefficients were determined from the SHG data, and their pressure behavior was used to infer the nature of the transition. The loss of the SHG signal is accompanied by drastic changes in line widths of Bragg reflections, but no discontinuous change in volume was observed. The pressure-volume data were fit to various equations of state, and a bulk modulus K0 = 136 (±2) GPa, bulk modulus pressure derivative K0′ = 4.0 (±0.2), and initial volume V0 = 64.5 (±0.1) Å3 were obtained.

Interfacial electrostatics of poly(vinylamine hydrochloride), poly(diallyldimethylammonium chloride), poly-l-lysine, and poly-l-arginine interacting with lipid bilayers.

Charge densities of cationic polymers adsorbed to lipid bilayers are estimated from second harmonic generation (SHG) spectroscopy and quartz crystal microbalance with dissipation monitoring (QCM-D) measurements. The systems surveyed included poly(vinylamine hydrochloride) (PVAm), poly(diallyldimethylammonium chloride) (PDADMAC), poly-l-lysine (PLL), and poly-l-arginine (PLR), as well as polyalcohol controls. Upon accounting for the number of positive charges associated with each polyelectrolyte, the binding constants and apparent free energies of adsorption as estimated from SHG data are comparable despite differences in molecular masses and molecular structure, with ΔGads values of -61 ± 2, -58 ± 2, -57 ± 1, -52 ± 2, -52 ± 1 kJ mol-1 for PDADMAC400, PDADMAC100, PVAm, PLL, and PLR, respectively. Moreover, we find charge densities for polymer adlayers of approximately 0.3 C m-2 for poly(diallyldimethylammonium chloride) while those of poly(vinylamine) hydrochloride, poly-l-lysine, and poly-l-arginine are approximately 0.2 C m-2. Time-dependent studies indicate that polycation adsorption to supported lipid bilayers is only partially reversible for most of the polymers explored. Poly(diallyldimethylammonium chloride) does not demonstrate reversible binding even over long timescales (>8 hours).

Label-free fluorescence lifetime and second harmonic generation imaging microscopy improves quantification of experimental renal fibrosis

All forms of progressive renal diseases develop a final pathway of tubulointerstitial fibrosis and glomerulosclerosis. Renal fibrosis is usually quantified using histological staining, a process that is time-consuming and pathologist dependent. Here we develop a fast and operator-independent method to measure fibrosis utilizing the murine unilateral ureteral obstruction model which manifests a time-dependent fibrotic increase in obstructed kidneys while the contralateral kidneys are used as controls. After ureteral obstruction, kidneys were analyzed at 7, 14, and 21 days. Fibrosis was quantified using fluorescence lifetime imaging (FLIM) and second harmonic generation (SHG) in a Deep Imaging via Enhanced photon Recovery deep tissue imaging microscope. This microscope was developed for deep tissue along with second and third harmonic generation imaging and has extraordinary sensitivity toward harmonic generation. SHG data suggest the presence of more fibrillar collagen in the obstructed kidneys. The combination of short-wavelength FLIM and SHG analysis results in a robust assessment procedure independent ofobserver interpretation and let us create criteria to quantify the extent of fibrosis directly from the image. Thus, the FLIM-SHG technique shows remarkable improvement in quantification of renal fibrosis compared to standard histological techniques.

Adsorption and Aggregation at Silica/Methanol Interfaces: The Role of Solute Structure

Second harmonic generation (SHG) and time-resolved, total internal reflection fluorescence (TR-TIRF) spectroscopy were used to examine the adsorption, solvation, and aggregation of a coumarin solute, Coumarin 152 (C152), at the silica/methanol interface. Experiments were performed as a function of bulk C152 concentration with SHG data providing information about relative surface coverage and ground state solvation environment. TR-TIRF data measured emission lifetimes of C152 adsorbed to the silica/methanol interface. SHG spectra show strong resonance enhancement at 365 nm, a result that is blue-shifted considerably from C152’s electronic excitation of ∼400 nm in bulk methanol. Given C152’s solvatochromic behavior, this observation implies that C152 adsorbed to the silica/methanol interface experiences a local dielectric environment that is significantly less polar than in bulk methanol. TR-TIRF decays at sub-micromolar bulk concentrations were fit to two lifetimes: one assigned to C152 emission in bulk methanol (0.9 ns) and a longer lifetime assigned to contributions from adsorbed C152 (∼4 ns). The longer lifetime is similar to C152 in alkanes, a result that is consistent with SHG data. Isothermal data from SHG experiments show unusual behavior as bulk C152 concentration increases. Instead of approaching an asymptotic limit signifying monolayer coverage, the SHG response rises at the lowest C152 concentrations and then decreases dramatically, suggesting the onset of aggregate formation. Changes in the TR-TIRF emission behavior of C152 at higher C152 bulk concentrations support this hypothesis. These findings are interpreted in terms of C152’s ability to self-associate, and the energetics of dimer formation are explored using ab initio calculations and polarizable continuum models.

ChemInform Abstract: Ion Specific Effects: Decoupling Ion‐Ion and Ion‐Water Interactions

AbstractReview: 110 refs.

Precipitates of Al(III), Sc(III), and La(III) at the muscovite-water interface.

The interaction of Al(III), Sc(III), and La(III) with muscovite-water interfaces was studied at pH 4 and 10 mM NaCl using second harmonic generation (SHG) and X-ray photoelectron spectroscopy (XPS). SHG data for Sc(III) and La(III) suggest complete and/or partial irreversible adsorption that is attributed by XPS to the growth of Sc(III) and La(III) hydroxides/oxides on the muscovite surface. Al(III) adsorption appears to coincide with the growth of gibbsite (Al(OH)3) deposits on the muscovite surface, as indicated by the magnitude of the interfacial potential computed from the SHG data. This interpretation of the data is consistent with previous studies reporting the epitaxial growth of gibbsite on the muscovite surface under similar conditions. The implication of our findings is that the surface charge density of mica may change (and in the case of Al(III), even flip sign from negative (mica) to positive (gibbsite)) when Al(III), Sc(III), or La(III) is present in aqueous phases in contact with heterogeneous geochemical media rich in mica-class minerals, even at subsaturation conditions.

Adsorption of dissolved aluminum on sapphire-c and kaolinite: implications for points of zero charge of clay minerals.

We have studied the impact of dissolved aluminum on interfacial properties of two aluminum bearing minerals, corundum and kaolinite. The effect of intentionally adding dissolved aluminum on electrokinetic potential of basal plane surfaces of sapphire was studied by streaming potential measurements as a function of pH and was complemented by a second harmonic generation (SHG) study at pH 6. The electrokinetic data show a similar trend as the SHG data, suggesting that the SHG electric field correlates to zeta-potential. A comparable study was carried out on kaolinite particles. In this case electrophoretic mobility was measured as a function of pH. In both systems the addition of dissolved aluminum caused significant changes in the charging behavior. The isoelectric point consistently shifted to higher pH values, the extent of the shift depending on the amount of aluminum present or added. The experimental results imply that published isoelectric points of clay minerals may have been affected by this phenomenon. The presence of dissolved aluminum in experimental studies may be caused by particular pre-treatment methods (such as washing in acids and subsequent adsorption of dissolved aluminum) or even simply by starting a series of measurements from extreme pH (causing dissolution), and subsequently varying the pH in the very same batch. This results in interactions of dissolved aluminum with the target surface.A possible interpretation of the experimental results could be that at low aluminum concentrations adatoms of aluminum (we will refer to adsorbed mineral constituents as adatoms) can form at the sapphire basal plane, which can be rather easily removed. Simultaneously, once the surface has been exposed to sufficiently high aluminum concentration, a visible change of the surface is seen by AFM which is attributed to a surface precipitate that cannot be removed under the conditions employed in the current study.In conclusion, whenever pre-treatment or the starting point of an experiment favor the dissolution of aluminum, dissolved Al may remain in the experimental system and interact with the target surfaces. The systems are then no longer pristine and points of zero charge or sorption data are those of aluminum-bearing systems.

Measurement of electric-field induced second harmonic generation in hydrogenated amorphous silicon

We quantitatively separate interface optical second harmonic generation (SHG) and electric-field induced second harmonic generation (EFISH) from hydrogenated amorphous silicon (a-Si:H) interfaces and bulk. Using a 1.51 eV probe laser, we measure SHG signals from indium tin oxide (ITO) ITO/a-Si:H/ITO sandwich structures and vary the electric fields in the a-Si:H layer using an applied voltage bias. The a-Si:H/ITO interfaces form back-to-back diodes. Because of finite optical penetration depth, SHG probes only the front diode. When the front diode is reverse biased, the EFISH contribution dominates the SHG signal and probes the electric field in the ∼30 nm adjacent to the interface. Through fitting of the SHG data, we find that in this near-interface region, the electric field is proportional to the square root of the applied bias. The fitting measures the interfacial ITO/a-Si:H built-in voltage to be ∼0.2 V.

In situ Imaging of Collagen Synthesis by Osteoprogenitor Cells in Microporous Bacterial Cellulose Scaffolds

Microscopy techniques based on laser-induced nonlinear optical processes allow for chemically specific imaging of unmodified samples at high spatial resolution in three dimensions and provide powerful tools for characterization of tissue-engineering constructs. This is highlighted by the simultaneous imaging of scaffold material, cells, and produced extracellular matrix collagen in samples consisting of osteoprogenitor MC3T3-E1 cells seeded on microporous bacterial cellulose (BC), a potential scaffold material for synthesis of osseous tissue. BC and collagen have been visualized by second harmonic generation (SHG) microscopy, and verification of collagen identification on cellulose scaffolds has been carried out on sectioned samples by comparison with the conventional histological staining technique. Both methods showed similar collagen distributions and a clear increase in the amount of collagen when comparing measurements from two time points during growth. For investigations of intact cellulose scaffolds seeded with cells, SHG was combined with simultaneous coherent anti-Stokes Raman scattering (CARS) microscopy for visualization of cell arrangement in three dimensions and to be correlated with the SHG data. Results showed that the osteoprogenitor cells were able to produce collagen already during the first days of growth. Further on, developed collagen fiber networks could be imaged inside compact regions of cells located in the cellulose micropores. Collagen production, the initial step of tissue mineralization, demonstrates the potential of BC as a scaffold material for bone tissue engineering. Furthermore, the noninvasive in situ monitoring of collagen inside compact tissue clearly manifests the benefits of nonlinear microscopy techniques, such as SHG and CARS, for use in tissue engineering.

Automated Multiscale Morphometry of Muscle Disease From Second Harmonic Generation Microscopy Using Tensor-Based Image Processing

Practically, all chronic diseases are characterized by tissue remodeling that alters organ and cellular function through changes to normal organ architecture. Some morphometric alterations become irreversible and account for disease progression even on cellular levels. Early diagnostics to categorize tissue alterations, as well as monitoring progression or remission of disturbed cytoarchitecture upon treatment in the same individual, are a new emerging field. They strongly challenge spatial resolution and require advanced imaging techniques and strategies for detecting morphological changes. We use a combined second harmonic generation (SHG) microscopy and automated image processing approach to quantify morphology in an animal model of inherited Duchenne muscular dystrophy (mdx mouse) with age. Multiphoton XYZ image stacks from tissue slices reveal vast morphological deviation in muscles from old mdx mice at different scales of cytoskeleton architecture: cell calibers are irregular, myofibrils within cells are twisted, and sarcomere lattice disruptions (detected as "verniers") are larger in number compared to samples from healthy mice. In young mdx mice, such alterations are only minor. The boundary-tensor approach, adapted and optimized for SHG data, is a suitable approach to allow quick quantitative morphometry in whole tissue slices. The overall detection performance of the automated algorithm compares very well with manual "by eye" detection, the latter being time consuming and prone to subjective errors. Our algorithm outperfoms manual detection by time with similar reliability. This approach will be an important prerequisite for the implementation of a clinical image databases to diagnose and monitor specific morphological alterations in chronic (muscle) diseases.

U(VI) Adsorption and Speciation at the Acidic Silica/Water Interface Studied by Resonant and Nonresonant Second Harmonic Generation

Second harmonic generation (SHG) was used to study U(VI) interactions with a buried mineral oxide/water interface using pH 4 uranyl solutions that contained carbonate and environmentally relevant electrolyte concentrations. SHG resonance enhancement at 290 nm was observed at a NaCl concentration of 10 mM, whereas it was necessary to collect the adsorption isotherm using the nonresonant χ(3) technique at 1 mM NaCl concentration. Both methods resulted in the same (within one kT) adsorption free energy of −33 kJ/mol. This value is 10 kJ/mol less favorable than the free energy that was previously reported for the same system at pH 7, indicating that uranyl–surface interactions depend on pH. The charge density due to adsorbed uranyl species was also determined via the χ(3) technique to be +0.0031(5) C/m2, which is half the magnitude previously measured at pH 7. On the basis of the resonant and nonresonant SHG data, it is concluded that the surface-active uranyl species at pH 4 are neutral or univalent, cationic species, which, based on thermodynamic speciation calculations, can consist of the following aquated species present in bulk solution at pH 4: UO2(OH)2, UO2OH+, and UO2CO3. The results of this work are of value as benchmarks for geochemical transport models of uranium pollution resulting from acid mine drainage and nuclear waste storage.

Automated classification of healthy and keloidal collagen patterns based on processing of SHG images of human skin

All-optical microspectroscopic and tomographic tools have a great potential for the clinical investigation of human skin and skin diseases. However, automated optical tomography or even microscopy generate immense data sets. Therefore, in order to implement such diagnostic tools into the medical practice in both hospitals and private practice, there is a need for automated data handling and image analysis ideally implementing automized scores to judge the physiological state of a tissue section. In this contribution, the potential of an image processing algorithm for the automated classification of skin into normal or keloid based on second-harmonic generation (SHG) microscopic images is demonstrated. Such SHG data is routinely recorded within a multimodal imaging approach. The classification of the tissue implemented in the algorithm employs the geometrical features of collagen patterns that differ depending on the constitution, i.e., physiological status of the skin.