Stokes shift spectroscopy and machine learning for label-free human prostate cancer detection.

The Stokes shift spectra (S3) of human cancerous and normal prostate tissues were collected label free at a selected wavelength interval of 40 nm to investigate the efficacy of the approach based on three key molecules-tryptophan, collagen, and reduced nicotinamide adenine dinucleotide (NADH)-as cancer biomarkers. S3 combines both fluorescence and absorption spectra in one scan. The S3 spectra were analyzed using machine learning (ML) algorithms, including principal component analysis (PCA), nonnegative matrix factorization (NMF), and support vector machines (SVMs). The components retrieved from the S3 spectra were considered principal biomarkers. The differences in the weights of the components between the two types of tissues were found to be significant. Sensitivity, specificity, and accuracy were calculated to evaluate the performance of SVM classification. This research demonstrates that S3 spectroscopy is effective for detecting the changes in the relative concentrations of the endogenous fluorophores in tissues due to the development of cancer label free.

Structure and growth of vapor-deposited n-dotriacontane films studied by X-ray reflectivity.

We have used synchrotron X-ray reflectivity measurements to investigate the structure of n-dotriacontane (n-C(32)H(66) or C32) films deposited from the vapor phase onto a SiO(2)-coated Si(100) surface. Our primary motivation was to determine whether the structure and growth mode of these films differ from those deposited from solution on the same substrate. The vapor-deposited films had a thickness of approximately 50 A thick as monitored in situ by high-resolution ellipsometry and were stable in air. Similar to the case of solution-deposited C32 films, we find that film growth in vacuum begins with a nearly complete bilayer adjacent to the SiO(2) surface formed by C32 molecules aligned with their long axis parallel to the interface followed by one or more partial layers of perpendicular molecules. These molecular layers coexist with bulk particles at higher coverages. Furthermore, after thermally cycling our vapor-deposited samples at atmospheric pressure above the bulk C32 melting point, we find the structure of our films as a function of temperature to be consistent with a phase diagram inferred previously for similarly treated solution-deposited films. Our results resolve some of the discrepancies that Basu and Satija (Basu, S.; Satija, S. K. Langmuir 2007, 23, 8331) found between the structure of vapor-deposited and solution-deposited films of intermediate-length alkanes at room temperature.

Aggregation-governed oriented growth of inorganic crystals at an organic template.

X-ray studies performed during the growth of CdCO(3) and MnCO(3) crystals from supersaturated aqueous solutions, at fatty acid monolayer templates, reveal that the nucleates are nearly three-dimensional powders below a threshold supersaturation. However, at higher supersaturations, the crystals are preferentially oriented with the {0 1 2} direction vertical. Scanning electron microscope images of samples transferred to substrates show discrete crystals at low concentrations, while at higher concentrations the crystals self-aggregate to form linear chains and sheets. The authors speculate that preferential alignment at the organic-inorganic interface is enhanced as a consequence of oriented aggregation of crystals. The role of monolayer-ion interactions in governing the morphologies and the resulting orientation of the inorganic nucleate is discussed.

X-ray reflectivity study of ultrathin liquid films of diphenylsiloxane-dimethylsiloxane copolymers.

Using X-ray reflectivity, we observe drastic differences in the interfacial structure and molecular ordering of diphenylsiloxane-dimethylsiloxane copolymer thin films deposited on hydroxylated versus H-terminated (etched) silicon wafers. We find that substrate type and comonomer ratio determine the conformational arrangements in these liquid films. High-energy bonding between the substrate and the molecules and an increase in rigidity of the molecules due to replacement of methyl groups by phenyl groups leads to a specific molecular ordering at the liquid/solid interface and pronounced density oscillations in this region. The observed structural reorganizations are explained by the interplay and the established balance between the chain flexibility and the polymer-substrate interactions.

Observation of surface layering in a nonmetallic liquid.

Oscillatory density profiles (layers) have previously been observed at the free surfaces of liquid metals but not in other isotropic liquids. We have used x-ray reflectivity to study a molecular liquid, tetrakis(2-ethylhexoxy)silane. When cooled to T/Tc approximately 0.25 (well above the freezing point for this liquid), density oscillations appear at the surface. Lateral order within the layers is liquidlike. Our results confirm theoretical predictions that a surface-layered state will appear even in dielectric liquids at sufficiently low temperatures, if not preempted by freezing.