Distance Dependent Resonance Energy Transfer Between Molecular Machine and Plasmonic Nanostructure

poster abstractPhotoswitchable molecules (molecular machines) have attracted a great deal of attention over the past few years for the design of molecular sensors. Among photoswitchable molecules, azobenzene is widely studied due to its trans-cis photoisomerization, which produces a simple structure and optical and Raman spectra, and is photo and electrochemically active, and can be utilized for optical storage and other applications. Localized surface plasmon resonance (LSPR) properties of the metal nanostructures in conjunction with the photoswitching properties of the azobenzene molecules allow the nanoscale environment to be more controlled and to ultimately improve the sensing abilities of the metallic nanostructure. Herein, we develop an ultrasensitive molecular sensor by functionalizing the gold nanoprism with a selfassembled monolayer of alkanethiols containing azobenzenes. This is the first study where light-induced reversible switching of azobenzenes to cis and trans conformations was detected by monitoring the LSPR of gold nanoprisms-based sensing platforms. It was found that the LSPR red shift was observed as the light exposure was switched from UV to blue light due to the cis to trans isomerization of the azobenzene. This shift is consistent with the increase in thickness of the local dielectric environment (0.6 nm) surrounding the nanoprisms with perhaps a contribution from electronic interaction between the nanoprisms and azobenzene. We hypothesize that this electronic interaction is the nearfield resonance energy transfer (NF-RET). Changing the alkanethiol chain length altered the distance between the nanoprisms’ surface to the azobenzene. The LSPR red shift decreases as the distance between azobenzenes and nanoprisms increases due to the decrease in NF-RET. The LSPR shift was found to be reversible as the light source was switched back and forth several times from UV to blue light. The effects of the azobenzene conformational change and its photoreversibility were also probed through surface enhanced Raman spectroscopy (SERS) demonstrating that the NF-RET between the nanoprisms and bound azobenzenes in their cis conformation significantly enhances the intensity of the Raman bands of the azobenzenes and is highly dependent on the distance of azobenzene from the surface of the nanoprisms. The SERS data suggested that the isomerization was controlled by first-order kinetics with a rate constant of 1.0 x 10−4 s−1. Our demonstration of light-induced photoreversibility of this type of molecular machine is the first step toward eliminating current limitations on detection of molecular motion in solid-state devices using LSPR spectroscopy with nanoprisms. Modulating the LSPR position and controlling energy transfer across the nanostructure organic molecule interface are very important for the fabrication of plasmonic-based nanoscale devices

Change in the room temperature magnetic property of ZnO upon Mn doping

We present in this paper the changes in the room temperature magnetic property of ZnO on Mn doping prepared using solvo-thermal process. The zero field cooled (ZFC) and field cooled (FC) magnetisation of undoped ZnO showed bifurcation and magnetic hysteresis at room temperature. Upon Mn doping the magnetic hysteresis at room temperature and the bifurcation in ZFC-FC magnetization vanishes. The results seem to indicate that undoped ZnO is ferromagnetic while on the other hand the Mn doped ZnO is not a ferromagnetic system. We observe that on addition of Mn atoms the system shows antiferromagnetism with very giant magnetic moments.Comment: 5 figure

Effect of different sources of organic matter on the yield of rice and soil health in red and lateritic zone of West Bengal, India

Field experiment was conducted to study effect of different sources of organic matter on the yield of rice and soil at Rice Research Station, Bankura, West Bengal, India during kharif season of 2009, 2010 and 2011. Average of three years data revealed that inclusion of vermi-compost in the fertilizers schedule of rice cultivation [variety: Swarna (MTU 7029)] increased the grain yield (30.26%) as well as straw yield (32.70%). However higher pH was observed in treatments receiving paddy straw application and organic carbon (%) was also higher in the respective plots where vermi-compost and paddy straw was applied. Regarding available P2O5, there was an increasing trend up to 13-20 kg ha-1 in vermi-compost and green manure applied plots. In case of available K2O, there was a decrease value in all treatments were observed. So there was a positive balance of P and negative balance of K