Characterization Facilities

Analytical Ultra Centrifuge

FOCUS OF RESEARCH

An ultracentrifuge is a centrifuge with a very high rotor speed. In an analytical ultracentrifuge, the sample under study can be monitored by an optical detection system. The equipment produces information on shape, conformation changes and size distribution of macromolecules. The two widely used experiment type under AUC are the sedimentation velocity and sedimentation equilibrium. Sedimentation velocity experiments are used to determine the molecular weight and degree of aggregation of macromolecules. High rotor speed are used for these measurements to completely sediment all the particles in solution. Monomers and the corresponding aggregated species having different degree of sedimentation rate can be identified clearly. Sedimentation equilibrium experiments use lower rotor speed and measures the equilibrium binding constant.

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Ultraviolet (UV)-Visible (Vis)-Near Infrared (NIR) Spectrophotometer

FOCUS OF RESEARCH

UV-Vis-NIR spectroscopy oftentimes refers to absorption spectroscopy. The technique can be used for the quantitative determination of various analytes that are capable to produce signal in the spectral range of interest. System under interest absorbs light at characteristic wavelengths in the electromagnetic spectrum. The behavior is governed by the Lambert-Beer law. The absorption process results in the promotion of electrons from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO) (in molecules) and from the valence band to the conduction band (in bulk semiconductors and quantum dots). The lowest excitonic band in the absorption spectrum corresponds to the band gap of the material. Monitoring the absorption properties of a system is of extreme importance in the field of luminescence because the absorption spectrum guides in deciding the excitation wavelength for acquiring the luminescence spectrum.

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Spectroscopic Ellipsometer

FOCUS OF RESEARCH

The layer thickness and dielectric properties of a material can be investigated by ellipsometry. The technique is based on the measurement of the change of the polarization of a linearly localized light that is reflected from a surface. The instrument consists of a light source, a polarizer, sample, an analyzer and a detector.

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Fourier Transform Infrared Spectroscopy (FTIR) with Photo Imaging Device

FOCUS OF RESEARCH

An infrared spectrum of a solid, liquid or gas can be obtained by FTIR technique. This is primarily used for determining the chemical structure of materials by revealing the characteristics frequencies of a chemical functional group. FTIR has unique advantages over the dispersive spectrometer (collection of signal over the entire spectral range simultaneously resulting in a faster data acquisition, better signal to noise ratio owing to lesser loss from optics, use of laser as an internal standard for precise measurements by wavelength calibration). The collection of signal in an FTIR instrument relies on an interferometer. The interferometer design consists of a light source, a beam splitter, one stationary mirror, one moving mirror, sample and a detector. The beam in the direction of the moving mirror travels a different distance compared to the optical path in the direction of the stationary mirror. Upon combination of these two beams, some of them interfere constructively and some destructively. This creates the interference pattern (interferogram) at the beam splitter. Sample under interest absorbs at some portions of the spectral range, the transmitted part reaches the detector. The detector collects the signal from the entire spectral range simultaneously. The detector signal is Fourier transformed to obtain the corresponding transmittance and hence the absorption spectrum. The FTIR equipment is combined with the photo imaging device.

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Particle Size Analyzer (DLS)

FOCUS OF RESEARCH

Dynamic light scattering (also known as photon correlation spectroscopy) is an analytical technique to determine the size distribution of macromolecular solutions. The technique relies on determination of rate of fluctuations of laser light intensity that is scattered by particles. This is performed by measuring the second order autocorrelation function of the intensity trace. At longer times, the autocorrelation function decays exponentially. The exponential function is related to the translational diffusion co-efficient and hence to the motion of the particles. The instrument is equipped with zeta potential experiments.

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