Photothermal and photoacoustic methods for mapping surface absorbance: Adaptation for screening chemical and biomolecular libraries

Photoacoustic and photothermal methods are useful tools for the analysis of solid state samples and thin films. Both techniques may be used to study surface absorber distributions on surfaces.; In the photoacoustic experiment, light absorption at a solid/air interface launches a pressure wave which propagates through the air. The acoustic wave is detected by deflection of a probe laser beam. For non-parallel orientation of the probe beam with respect to the sample surface, acoustic waves launched from individual absorber features travel different distances before they intersect with the probe beam. This allows temporal encoding of the spatial distribution of surface absorbers. An experimental demonstration of this novel photoacoustic of detection scheme is presented.; In the photothermal experiment, detection is based on production of a temperature change at the sample surface following light absorption. Thermal diffusion generates temperature gradients in the solid sample and the adjacent fluid layer. The resulting refractive index gradient in the adjacent fluid medium is measured by deflection of a probe laser beam. Using the transverse photothermal deflection spectroscopy (t-PDS) method, two dimensional absorber distribution maps of a flat sample surface can be recorded. A number of colored thin polymer film are used to characterize the sensitivity in air and a value of 7.5 · 10-6 W is found.; Gold nanoparticles are excellent optical absorber labels for biological and biochemical binding assays. The synthesis and characterization of gold nanoparticles of different sizes and surface chemical functionalities is presented.; A novel readout method for protein microarrays based on photothermal detection of nanoparticle labeled proteins is described. Protein microarrays are developed with functionalized gold nanoparticles and analyzed using t-PDS. The observed coloration intensity performance depends on the intrinsic nature of the target protein. Neutravidin produces the most intensely colored spots. A spotting concentration study of Neutravidin is described. The current limit of detection is 50 Neutravidin molecules per square micron. An implementation of the t-PDS method for in-situ binding studies is presented. A dilute nanoparticle probing solution is added to the sample cell and the time dependent t-PDS signal recorded.