A simple experimental method to generate partially coherent optical bottle beam

An experimental study is carried out to investigate a special kind of three-dimensional intensity distribution of a partially coherent optical beam known as optical bottle beam produced by using an annular aperture and lens combination (Lens Aperture System). In this paper, we are demonstrating the experimental results of our observations. The investigation also includes the effects of coherence modulation and central obstruction of the annular aperture (used in Lens Aperture System) on the resultant partially coherent optical bottle beam. The method discussed in this paper is simple and cost effective.     

DNA-Origami-Based Assembly of Au@Ag Nanostar Dimer Nanoantennas for Label-Free Sensing of Pyocyanin

Early-stage detection of diseases caused by pathogens is a prerequisite for expedient patient care. Due to the limited signal-to-noise ratio, molecular diagnostics needs molecular signal amplification after recognition of the target molecule. In this present study, we demonstrate the design of plasmonically coupled bimetallic Ag coated Au nanostar dimers with controlled nanogap using rectangular DNA origami. We further report the utility of the designed nanostar dimer structures as efficient SERS substrate for the ultrasensitive and label-free detection of the pyocyanin molecule, which is a biomarker of the opportunistic pathogenic bacteria, Pseudomonas aeruginosa. The experimental results showed that the detection limit of pyocyanin with such nanoantenna based biosensor was 335 pM, which is much lower than the clinical range of detection. Thus, fast, sensitive and label-free detection of pyocyanin at ultralow concentration in an infected human body can pave a facile route for early stage warning for severe bacterial infections.     

Supramolecular star polymers with compositional heterogeneity

We present the synthesis of supramolecular star polymers with heterogeneous chemical compositions through potassium cation‐templated assembly of guanosine end‐functionalized random, diblock, and Y‐shaped copolymers. The assembly and disassembly processes of the synthesized star polymers have been systematically examined on changing the concentration, the temperature, the solvent, and the amount of cation using ¹H NMR, UV/vis, and CD spectroscopy. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Oxalyl chloride as carbonyl synthon in Pd-catalyzed carbonylations of triarylbismuth and triarylindium organometallic nucleophiles

Oxalyl chloride has been demonstrated to function as C1 carbonyl synthon in the carbonylations of triarylbismuth and triarylindium nucleophiles under palladium-catalyzed conditions. All the three aryl groups from both bismuth and indium reagents participated in carbonylative couplings to afford the corresponding functionalized ketones in high yields. This study also disclosed a novel utilization of oxalyl chloride as facile alternative source of CO for carbonylations under palladium catalysis.     

Imidazolinium salts derived from amino[2.2]paracyclophane compounds: synthesis and hydrolytic ring-opening

The synthesis of a series of imidazolinium chlorides containing the [2.2]paracyclophane scaffold is described. Attempts to deprotonate the salts with strong bases resulted in hydrolytic ring-opening and yielded N-formylethylenediamine products rather than the intended free carbenes.     

Phenyl-ring-bearing cationic surfactants: effect of ring location on the micellar structure

A series of isomeric cationic surfactants (S1-S5) bearing a long alkyl chain that carries a 1,4-phenylene unit and a trimethyl ammonium headgroup was synthesized; the location of the phenyl ring within the alkyl tail was varied in an effort to understand its influence on the amphiphilic properties of the surfactants. The cmc's of the surfactants were estimated using ionic conductivity measurements and isothermal calorimetric titrations (ITC); the values obtained by the two methods were found to be in excellent agreement. The ITC measurements provided additional insight into the various thermodynamic parameters associated with the micellization process. Although all five surfactants have exactly the same molecular formula, their micellar properties were seen to vary dramatically depending on the location of the phenyl ring; the cmc was seen to decrease by almost an order of magnitude when the phenyl ring was moved from the tail end (cmc of S1 is 23 mM) to the headgroup region (cmc of S5 is 3 mM). In all cases, the enthalpy of micellization was negative but the entropy of micellization was positive, suggesting that in all of these systems the formation of micelles is both enthalpically and entropically favored. As expected, the decrease in cmc values upon moving the phenyl ring from the tail end to the headgroup region is accompanied by an increase in the thermodynamic driving force (ΔG) for micellization. To understand further the differences in the micellar structure of these surfactants, small-angle neutron scattering (SANS) measurements were carried out; these measurements reveal that the aggregation number of the micelles increases as the cmc decreases. This increase in the aggregation number is also accompanied by an increase in the asphericity of the micellar aggregate and a decrease in the fractional charge. Geometric packing arguments are presented to account for these changes in aggregation behavior as a function of phenyl ring location.     

Emission studies on ZnO-inverse photonic crystals derived from self-assembly

Photonic crystals fabricated from the colloidal spheres of polymethyl methacrylate (PMMA) using the inward-growing self-assembly technique were subsequently in-filled with zinc oxide (ZnO) prepared by the sol-gel process. The polymer template was removed by heat treatment and chemical method to get ZnO-inverse photonic crystal. The structural quality of the inverse photonic crystal obtained by the chemical method was found to be superior to that obtained by heat treatment. The ZnO-inverse photonic crystal obtained by the chemical method was further treated at an elevated temperature to ensure the crystalline nature of ZnO. Laser-induced emission studies on ZnO-inverse photonic crystals were carried out at an excitation wavelength of 325 nm. The emission spectra showing UV and visible bands at collection angle of 45° from the direction of excitation helped to establish the role of crystalline ZnO.     

Rate equation simulation of temporal characteristics of a pulsed dye laser oscillator

A time-dependent, two-dimensional (in space) rate equation model of a transversely-pumped pulsed dye laser oscillator, which incorporates transverse pump intensity variation in the presence of intracavity dye laser radiation, is proposed to understand and predict its temporal behaviour. The model yields output pulses which agree well with experimental results using rhodamine 6G and kiton red dyes. The shape, amplitude and temporal position of the simulated pulse within the pump pulse vary dramatically across the tuning range of each dye depending on the relative gain and loss values.     

Kiton red S dye: Photophysical, photostability, photothermal and narrow-band laser performances using different solvents

Many aspects of photophysical, photostability and laser properties of kiton red S dye remain unresolved, particularly for pumping with 578 nm radiation of CVL and 532 nm output of Nd:YAG lasers, and these are studied using different alcohol- and water-based binary solvents. Our results show that methanol is better suited for low and high-repetition-rate KRS dye lasers because of its superior laser efficiency, photostability as well as photothermal properties.