We describe the development of a label-less ellipsometric imaging microarray reader. The ability of the ellipsometric microarray reader to measure binding of sample to microarray surface is verified using oligonucleotide complementary DNA (cDNA) microarrays. Polarized light illuminates the microarray surface through a glass substrate at an angle beyond the critical angle and changes in the polarization of totally internally reflected light resulting from binding events on the microarray surface are measured. This polarization change is used to measure the thickness of biomolecules bound to the microarray. A prototype ellipsometric imaging microarray reader is constructed and calibrated, and the performance is evaluated with cDNA microarrays. The microarray reader measures changes in refractive index changes as small as 0.0024 and thickness changes as small as 0.28 nm. The optimization of angle of incidence and substrate refractive index necessary to achieve high sensitivity is also described. This ellipsometric technique offers an attractive alternative to fluorescence-microarray readers in some genomic, proteomic, diagnostic, and sensing applications.
A new technique for simultaneous multi-angle ellipsometric measurements of anisotropic optical structures such as films used in the display industry is introduced. A very small area on the sample is illuminated with a focused beam which after it interacts with the sample and is polarization analyzed is spread across a CCD. Each pixed collects light from a different angle incident on the sample allowing data collection at numerous incident angles simultaneously. The small but significant polarization aberrations of the microscope objectives provide a significant challenge to accurate measurement A mathematical description of the ellipsometric technique is presented. The optical properties of two biaxial samples, a stretched plastic retarder element used for correcting angle of incident effects in LC displays, and a thin layer of E-type polarizing dried liquid crystal material are measured and maps of the ellipsometric parameters Ψ and ▵ as a function incident and azimuthal angles are presented. Data from both samples are reduced using an iterative algorithm with a biaxial thin film modeling software package to compute all three principle components of the dielectric tensor as well as it's orientation.
Commercial Raman confocal microscopy can acquire images with a resolution down to 200 nm. Much effort has recently been devoted to improve upon this resolution and obtain chemical characterization of ultimately a single organic molecule. As an effort in this direction, we have developed an experimental configuration by combining the analytical power of Raman spectroscopy with the nanometer resolution of atomic force microscopy (AFM). Here, an AFM silicon nitride probe, coated with a 40 nm silver layer, was used to significantly enhance the Raman signal by laser excitation of surface plasmons in the tip coating. Experimental results indicate a local surface enhanced Raman scattering (SERS) increase of 105. Lateral scanning of the sample and collecting the SERS signal allows for a 2D image of the chemical identity of the probed sample simultaneous with its topography as measured by the AFM. Also, the ratio of Stokes to anti-Stokes can be used to obtain an instantaneous and absolute map of the local temperature across the sample.