Absolute Molecular Orientational Distribution of the Polystyrene Surface

this paper we report VR-SFG measurements of polystyrene (PS, [CH 2 CH(C 6 H 5 )] n ) thin films on oxidized silicon substrates. Characterization of the dependence of the VR-SFG response on film thickness allows unique identification of the origin of the signal. For films <400 nm thick, the dominant source of vibrationally resonant signal is the PS/air interface; while the dominant source of the nonresonant background is the Si/SiO 2 interface. The nonresonant sum frequency mixing at the Si/SiO 2 interface provides a convenient phase reference for the characterization of the PS surface. Calibration of the phase reference with a phenylsiloxane self-assembled layer allows the determination of the absolute orientation of the pendant phenyl groups at the PS surfac

Imaging and Autocorrelation of Ultrafast Infrared

Te diode arrays, which are harder to use, more expensive, and have less spatial resolution than standard CCD cameras. In this Letter we describe practical applications in which the nonlinear response of Si devices to IR light is used for laser beam profiling and pulse autocorrelation. The Letter is not a quantitative fundamental study of nonlinear multiphoton absorption in Si. Inasmuch as the electronic bandgap in Si is #1.12 eV (l # 1.1 mm, or n # 9034 cm ) at room temperature, it might seem surprising that a Si device would respond to light in the range l # 3 11 mm, e.g., with the energy of 3 -- 9 photons needed to create an electron -- hole pair in bulk Si. Two-photon-induced photoconductivity in a Si CCD camera was used previously 3 to image light at l # 1.41 mm. Likewise, temporal autocorrelation 4--8 and cross correlation 9 of near-IR ultrafast laser pulses by an approach similar to that described here was reported for hn 1 , hn 2 , Ega , #hn 1 1 hn 2 #. For these tw

Immobilization of proteins on carboxylic acid functionalized nanopatterns

The immobilization of proteins on nanopatterned surfaces was investigated using in situ atomic force microscopy (AFM) and ex situ infrared reflectance-absorption spectroscopy (IRAS). The AFM-based lithography technique of nanografting provided control of the size, geometry, and spatial placement of nanopatterns within self-assembled monolayers (SAMs). Square nanopatterns of carboxylate-terminated SAMs were inscribed within methyl-terminated octadecanethiolate SAMs and activated using carbodiimide/succinimide coupling chemistry. Staphylococcal protein A was immobilized on the activated nanopatterns before exposure to rabbit immunoglobulin G. In situ AFM was used to monitor changes in the topography and friction of the nanopatterns in solution upon protein immobilization. Complementary studies with ex situ IRAS confirmed the surface chemistry that occurred during the steps of SAM activation and subsequent protein immobilization on unpatterned samples. Since carbodiimide/succinimide coupling chemistry can be used for surface attachment of different biomolecules, this protocol shows promise for development of other aqueous-based studies for nanopatterned protein immobilization. © 2012 Springer-Verlag Berlin Heidelberg (outside the USA)

Nonlinear Optics as a Detection Scheme for Biomimetic Sensors:

Vibrational spectra of biomimetic membranes have been obtained using a broad-band approach to sum frequency generation (SFG). A new innovation, broad band SFG (BBSFG) allows for high quality SFG spectra with rapid collection times. With the BBSFG approach, we have followed in situ the formation of a hybrid bilayer membrane (HBM) from the reorganization of phospholipid vesicles at akanethiol monolayers