Sajan Daniel George

2013, Ang Chem Int Edition, Wiley Publishers, Vol 52, Pg 7291 – 7295,Photoswitchable molecules that undergo reversible structural change upon light irradiation have numerous applications, ranging from life science to interfacial fluid mechanics. The objective of this article is to demonstrate that photoswitchable molecules also enable the manipulation of micron-sized particles. Commonly employed particle manipulations techniques rely on the so-called gradient force that scales as the third power of the particle diameter in the Rayleigh regime. For this reason the trapping force rapidly diminishes with decreasing particle diameter. Here we present an optical method for the trapping and manipulation of micron-sized particles adsorbed at a gas–liquid interface based on optically induced Marangoni flow. The hydrodynamic nature of the trapping mechanism implies a force scaling with the particle diameter instead of its third power. The method relies on photo responsive surfactants adsorbed to the interface that can be reversibly switched between two isomeric states. It is experimentally demonstrated that,using optically induced Marangoni flow,microspheres can be manipulated using lower light intensities compared to conventional optical tweezers.

Journal of Luminescence, Elsevier, Vol 137, Pg 225-229.Manipulation of the characteristics of laser dyes using metal nanoparticles is one of the rapidly growing areas in nanotechnology due to their promising applications in diverse fields, ranging from biomedical imaging to green energy. The energy transfer behaviour of a silver nanoparticle (Ag NP) with a dye molecule, Rhodamine 6G (Rh 6G), is interrogated using static photoluminescence as well as a laser based dual beam thermal lens technique. Spherical Ag NPs of various concentrations are prepared using chemical reduction method and is mixed with a fixed concentration of Rh 6G. It is observed that the intrinsic fluorescence of Rh 6G (1 microMolar) is quenched in proximity of the Ag NPs and the quenching efficiency increases with an increase in Ag NP concentration (2.5*10exp(-4) – 10*10exp(-4) M). The dye–NP distance is evaluated by varying the concentrations of Ag NPs and it is found to decrease with an increase in the NP concentration in the mixture from 92 to 69 Angstroms. The distance dependent energy transfer efficiency showed that dye–NP mixture follows Rexp (-4) dependence, where R is the dye–NP distance.

Journal of Biomedical Optics, SPIE, 15, 067007.The present work deals with the evaluation of a high performance liquid chromatography laser-induced fluorescence (HPLCLIF) technique developed in our laboratory for early detection of oral cancer from protein profiles of body fluids. The results show that protein profiles of serum samples from a given class of samples, say, normal, premalignant, or malignant, are statistically very close to each other, while profiles of members of any class are significantly different from other classes. The performance of the technique is evaluated by the use of sensitivity and specificity pairs, receiver operating characteristic (ROC) analysis, and Youden’s Index. The technique uses protein profile differences in serum samples, registered by the HPLC-LIF technique. The study is carried out using serum samples from volunteers diagnosed as normal or premalignant clinically, and as malignant by histopathology. The specificities and sensitivities of the HPLC-LIF method at an ideal threshold (M-distance = 2) for normal, malignant, and premalignant classes are 100, 69.5, and 61.5%, and 86.5, 87.5, and 87.5%.

Physical Review B, 69, 235201,Thermal diffusivity of the composites of camphor sulphonic acid (CSA) doped polyaniline (PANI) and its composites with cobalt phthalocyanine (CoPc) have been measured using open cell photoacoustic technique. Analysis of the data shows that the effective thermal diffusivity value can be tuned by varying the relative volume fraction of the constituents. It is seen that polaron assisted heat transfer mechanism is dominant in CSA doped PANI and these composites exhibit a thermal diffusivity value which is intermediate to that of CSA doped PANI and CoPc. The results obtained are correlated with the electrical conductivity and hardness measurements carried out on the samples.

68,165319,This paper reported the in-plane and cross-plane measurements of the thermal diffusivity of double epitaxial layers of n-type GaAs doped with various concentrations of Si and a p-type Be-doped GaAs layer grown on a GaAs substrate by the molecular beam epitaxial method, using the laser-induced non-destructive photothermal deflection technique. The thermal diffusivity value is evaluated from the slope of the graph of the phase of the photothermal deflection signal as a function of pump-probe offset. Analysis of the data shows that the cross-plane thermal diffusivity is less than that of the in-plane thermal diffusivity. It is also seen that the doping concentration has a great influence on the thermal diffusivity value. Measurement of p-type Be-doped samples shows that the nature of the dopant also influences the effective thermal diffusivity value. The results are interpreted in terms of a phonon-assisted heat transfer mechanism and the various scattering process involved in the propagation of phonons.

PG (Co-Guided), Fourth.Structure based drug design is the process of determining the structure of a protein and designing the drug molecules that can bind and control its function. X-ray crystallographic studies provide unambiguous, accurate, and reliable three dimensional structural parameters. However, obtaining high quality protein crystals of sufficient size is always a challenging task. In order to circumvent to this difficulty, various approaches including photo chemically induced nucleation have been employed. In this work, we demonstrate the application of photothermal heating effects by laser on the growth of small molecule crystals. The present study clearly shows that laser induced heating effects can accelerate the crystal formation and aid in the formation of high quality crystals. The influence of light absorbing objects at the focal plane of laser beam on the crystallisation rate is also investigated.

UG (Guided), Sixth.Osteoporosis is a condition that features loss of the normal density of bone and fragile bone. Osteoporosis leads to literally abnormally porous bone that is more compressible like a sponge, than dense like a brick. We induced osteoporosis in small animals (mice) and exploited the possibility of Raman spectroscopic technique combined with multivariable analysis tool (Principal Component Analysis) for the differentiation of different stages of osteoporosis.