Nonlinear optical techniques, such as vibrationally-resonant sum frequency spectroscopy (VR-SFS), are being increasingly applied to the study of biologically important problems. We have developed a novel approach to VR-SFS using ultrafast (< 50 femtosecond) lasers to generate infrared pulses that are spectrally very broad, enabling us to obtain the entire vibrational spectrum of a sample in a single laser pulse, and with ultrafast time resolution. Forbidden in isotropic bulk media (e.g., liquids, gases, and solids such as silicon), second-order nonlinear spectroscopies are uniquely sensitive to interfaces. We are currently studying (1) the structure and kinetics of small molecules interacting with solid supported biomimetic membranes and vesicles in solution, (2) the molecular orientation and kinetic incorporation of membrane-bound enzymes, drugs and proteins, (3) the structure and hybridization kinetics of DNA immobilized on surfaces, and (4) the dependence of peptide signaling sequence structure in cell adhesion studies, important for tissue engineering.
In a new class of experiments, we are developing ultraviolet-infrared doubly-resonant SFS to enhance sensitivity to measure the secondary structure and amino acid orientation of immobilized proteins at interfaces, important for drug design, biomaterials and biosensors. This interdisciplinary research uses many different techniques of interface preparation and characterization, and involves scientists from several NIST divisions.
Resources: Several femtosecond and picosecond laser systems for generating ultrafast pulses in the IR through UV; instrumentation for multichannel spectral, spatial, and polarization analyses of generated optical signals; sample characterization with fluorescence, FTIR, Raman and UV/VIS spectroscopies, AFM, and spectroscopic ellipsometry.
Biophotonics; Photonics; Biophysics; Molecular structure at interfaces; Nonlinear optics; Multiphoton Spectroscopy; Sum frequency spectroscopy; Surfaces and interfaces; Ultrafast dynamics;