Ordering and motion of anisotropic nanomaterials

Multi-scale ordering of the components is of utmost importance for the preparation of any functional system. This is particularly interesting for the assembly of plamonic nanoparticles which show drastic differences in their optical properties compared to the individual counterparts, giving rise to the unique opportunity to perform enhanced spectroscopies, sensing, and transporting optical information below the diffraction limitation of light. The control over ordering of nanoscale materials is therefore of paramount importance. Template based bottom up approaches such as using nematic liquid crystals promise a long range, reversible ordering of nanomaterials. It also promises active control over plasmonic properties of metal nanoparticles due to the electric field induced reorientation of liquid crystals, resulting in a change of the local refractive index. This thesis discusses the possibility of ordering anisotropic metal nanoparticles and performing active modulaton of the plasmonics response using a nematic liquid crystals. While long polymer chains can be solvated and aligned in liquid crystal solvents, anisotropic metal nanoparticles could not be dissolved in the nematic liquid crystal phase because of their poor solubility. Here, I show that appropriate surface functionalization can increase the otherwise low solubility of plasmonic nanoparticles in a nematic liquid crystal matrix. I also show that it is possible to reversibly modulate the polarized scattering of individual gold nanorods through an electric field induced phase transition of the liquid crystal. In this thesis, I also studied the motion of a molecular machine, commonly known as nanocars, over different solid surface. I show that individual nanocars, which consist of four carborane wheels attached to an aromatic backbone chassis, can move up to several micrometers over a glass surface at ambient temperature. Their movement is consistent with the rolling of the carborane wheels and can be controlled by tuning the interaction between the surface and the wheels

Fumed alumina-in-nematic liquid crystal suspensions under shear and electric field

Al2O3 nanoparticles causes a significant depression in the nematic-isotropic phase transition temperature (TNI). The gel-like suspensions are less sensitive to pre-shear and show a large structural recovery after shear when compared to Al2O3/silicone oil suspensions. At and above a critical nanoparticle ϕ = 0.005, the suspensions exhibit a reversible nematic-isotropic phase transition under the application of E.by Saket Kumar, Saumyakanti Khatua and Prachi Tharej

A "turn off" red-emitting fluorophore for nanomolar detection of heparin

by Palash Jana, Mithun Radhakrishna, Saumyakanti Khatua and Sriram Kanva

Light-controlled in situ bidirectional tuning and monitoring of gold nanorod plasmon via oxidative etching with FeCl3

We report on light-controlled in situ bidirectional tuning of longitudinal surface plasmon resonance (LSPR) of single gold nanorods via oxidative etching with ferric chloride. By removing the surfactant layer from the surface of a gold nanorod, we demonstrate that the etching happens only in the presence of an excitation laser, and the etching rate and directionality can be controlled by the intensity of excitation light. At a low excitation power, a blue shift of a nanorod’s LSPR of up to 50 nm was observed, which indicates preferential etching from its tips. Whereas at a high power, we see a red shift of the nanorod’s LSPR of up to 140 nm indicating etching from sides. These results present a new approach for in situ finer adjustments of a selected nanorod’s plasmon resonance.by Varsha Thambi, Ashish Kar, Piue Ghosh and Saumyakanti Khatu

A “Turn-Off” Red-emitting fluorophore for nanomolar detection of Heparin

A simple fluorophore bearing a diethylaminocoumarin donor and a pyridinium acceptor was synthesized and utilized for the ultra-sensitive detection of heparin. The synthesized dicationic push–pull coumarin derivative emits strongly in the red-region (665 nm) and detects nanomolar concentrations (14.8 nM to 148 nM) of heparin in HEPES buffer and FBS serum solutions. The dication exhibits excellent fluorescence selectivity and sensitivity towards heparin over its analogues such as chondroitin 4-sulfate (CS), hyaluronic acid (HA) and dextran. This fluorescence assay is a convenient, sensitive method for monitoring heparin levels in biological samples. These findings were confirmed using coarse-grained Monte Carlo simulations, which provide us with a rationale for the selective binding of heparin.by Palash Jana, Mithun Radhakrishna, Saumyakanti Khatuaa and Sriram Kanva

Synthesis of gold nanorods with tunable surface plasmon resonance for near-infrared biosensing applications

by Piue Ghosh, Varsha Thambi, Saumyakanti Khatua, and Arup Lal Chakrabort

Synthesis of complex nanoparticle geometries via pH-Controlled overgrowth of gold nanorods

by Varsha Thambi, Ashish Kar, Piue Ghosh, Diptiranjan Paital, Abhay Raj Singh Gautam and Saumyakanti Khatu

Influence of the Substrate on the Mobility of Individual Nanocars

We monitored the mobility of individual fluorescent nanocars on three surfaces: plasma cleaned, reactive ion etched, and amine-functionalized glass. Using single-molecule fluorescence imaging, the percentage of moving nanocars and their diffusion constants were determined for each substrate. We found that the nanocar mobility decreased with increasing surface roughness and increasing surface interaction strength