Kimberly A. Briggman

Selective study of polymer/dielectric interfaces with vibrationally resonant sum frequency generation via thin-film interference

A technique for selective characterization of the structure of free and buried thin-film interfaces by vibrationally resonant sum frequency generation spectroscopy is described. Manipulation of Fresnel coefficients by choice of film thickness on a reflecting substrate allows simultaneous optimization of the signal from the desired interface and minimization of the signal from other interfacial sources. This technique is demonstrated for the free polystyrene (PS)/air and the buried PS/spin-on glass interfaces. Our spectra show that the pendant phenyl group orientation is similar at the buried and free interfaces, with the phenyls pointing away from the bulk PS at each interface.

Correlation of molecular orientation with adhesion at polystyrene/solid interfaces

Vibrationally resonant sum-frequency generation (VR-SFG) has been used to characterize the molecular orientation of the phenyl groups at the interface between polystyrene (PS) films and surface-modified glass substrates. Both the interface structure and the film adhesion are found to vary as the substrate surface is changed from hydrophobic to hydrophilic. The improved adhesion on the hydrophilic substrate is attributed to the development of attractive hydrogen bonds between surface hydroxyl (OH) groups and the p electron cloud of the phenyl ring. This interaction is manifest by changes in the orientation distribution of the phenyl rings at the interface. Published by Elsevier Science B.V.

Nonlinear Optics as a Detection Scheme for Biomimetic Sensors: SFG Spectroscopy of Hybrid Bilayer Membrane Formation

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 from the reorganization of phospholipid vesicles at akanethiol monolayers.

Imaging and autocorrelation of ultrafast infrared laser pulses in the 3–11-μm range with silicon CCD cameras and photodiodes

Standard silicon photodiodes and CCD cameras are convenient and inexpensive alternatives to cryogenically cooled diodes or arrays for autocorrelation and imaging of ultrafast IR laser pulses in the wavelength range 3-11 mum . The response of these Si devices to IR pulses of duration ~100 fs is proportional to E(n) , where E is the pulse energy and n is approximately the Si electronic bandgap divided by the photon energy.

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.

Scattering based hyperspectral imaging of plasmonic nanoplate clusters towards biomedical applications

A new optical scattering contrast-agent based on polymer-nanoparticle encapsulated silver nanoplates (PESNs) is presented. Silver nanoplates were chosen due to the flexibility of tuning their plasmon frequencies. The polymer coating preserves their physical and optical properties and confers other advantages such as controlled contrast agent delivery. Finite difference time domain (FDTD) simulations model the interaction of light with the nanoplates in different orientations in the cluster. Hyperspectral dark field microscopy (HYDFM) observes the scattering spectra of the PESNs. An unsupervised sequential maximum angle convex cone (SMACC) image analysis resolves spectral endmembers corresponding to different stacking orientations of the nanoplates. The orientation-dependent endmembers qualitatively agree with the FDTD results. For contrast enhancement, the uptake and spatial distribution of PESNs are demonstrated by an HYDFM study of single melanoma cells to result in an enhanced contrast of up to 400%. A supervised spatial mapping of the endmembers obtained by the unsupervised SMACC algorithm reveals spatial distributions of PESNs with various clustering orientations of encapsulated nanoplates. Our study demonstrates tunability in plasmonics properties in clustered metal nanoparticles and its utility for the development of scatter-based imaging contrast agents for a broad range of applications, including studies of single cells and other biomedical systems.

Fluorescence intermittency and spectral shifts of single bio-conjugated nanocrystals studied by single molecule confocal fluorescence microscopy and spectroscopy

We have fabricated a combined measurement system capable of confocal microscopy and fluorescence spectroscopy to simultaneously evaluate multiple optical characteristics of single fluorescent nanocrystals. The single particle detection sensitivity is demonstrated by simultaneously measuring the dynamic excitation-time-dependent fluorescence intermittency and the emission spectrum of single cadmium selenide/zinc sulfide (CdSe/ZnS) nanocrystals (quantum dots, QDs). Using this system, we are currently investigating the optical characteristics of single QDs, the surface of which are conjugated with different ligands, such as trioctylphosphine oxide (TOPO), mercaptoundecanoicacid (MDA), and amine modified DNA (AMDNA). In this paper, we present the progress of our measurements of the time-dependent optical characteristics (fluorescence intermittency, photostability, and spectral diffusion) of single MDA-QDs and AMDNA-MDA-QDs in air in an effort to understand the effects of surface-conjugated biomolecules on the optical characteristics at single QD sensitivities.

Effects of Surface Functionality and Humidity on the Adhesion Force And Chemical Contrast Measured with AFM

The ability to probe chemical heterogeneity with nanometer scale resolution is essential for developing a molecular–level understanding of a variety of phenomena occurring at surfaces of materials. One area that could benefit greatly from nanoscale chemical measurement is an understanding of the degradation mechanisms of polymeric materials exposed to the environment. For example, the degradation (photo and hydrolytic) of polymers and polymeric materials has been observed to occur non-uniformly in which nanometer pits form locally, which deepen and enlarge with exposure (1, 2). The pitting has been postulated to initiate in the hydrophilic degradation-susceptible regions of the films (3). However, due to the lack of spatial resolution of the most current surface analytical techniques, the chemical nature of the degradation-initiated locations has not been identified. The use of a chemically-functionalized probe in an AFM (chemical force microscopy CFM) (4) has been shown to be capable of discriminating chemically-different domains of self-assembled monolayer (SAM) surfaces at the nanoscale spatial resolution. This study provides data to demonstrate that, by using proper RH at the tip-sample environment, the contrast between the hydrophilic and hydrophobic domains in SAM and polymer samples can be discerned, and presents results on the effects of RH on tipsample adhesion forces for different substrates.

Label-free hyperspectral microscopy for scatter imaging of biological processes in cells(Conference Presentation)

We will present unique applications of a label-free, hyperspectral scatter imaging technique in different microscopy platforms including conventional wide-field, dark-field, and confocal. In different platforms, we conducted label-free imaging of cells undergoing biological processes such as nanoparticle uptake, apoptosis, and metabolic flux change in response to the variation of the osmotic pressure. Hyperspectral image analyses resolved spectral endmembers corresponding to unique scattering and absorption characteristics as a result of such processes at the single particle, single organelle, and single cell level, delineating the details of nanomaterial-cell interactions in a 2D cell culture, cell apoptotic characteristics in a 3D culture, and volumetric changes of single cells under the variation of osmotic pressure. Our label-free scatter imaging has the potential for a broad range of biological and biomedical applications such as the development of scatter-based imaging contrast agents and the measurement of scatter parameters of subcellular organelles to identify the sub-micron scale origins of scattering signals in tissue scattering measurements.

Molecular order at polymer interfaces measured by broad-bandwidth vibrationally-resolved sum frequency generation spectroscopy

Summary form only given. Measurement of the structure of polymer/dielectric interfaces is crucial to an understanding of adhesion between such materials. Vibrationally-resolved sum frequency generation (VR-SFG) spectroscopy is a non-invasive, interface specific and chemically sensitive probe of the buried interfaces of transparent media. The use of broad bandwidth femtosecond pulses enables the parallel acquisition of spectra across an entire resonant spectral range without laborious laser tuning. The coherence of SFG allows the measurement of the phase of the VR-SFG signal relative to a nonresonant reference, which reveals the absolute orientation of the resonant molecular species.