Resonant waveguide grating based assays for colloidal aggregate detection and promiscuity characterization in natural products

Resonant waveguide grating based assays to eliminate colloidal aggregate induced false activity involving natural products.

Colloidal Aggregate Detection by Rapid Fluorescence Measurement of Liquid Surface Curvature Changes in Multiwell Plates

A simple fluorescence method is reported for the detection of colloidal aggregate formation in solution, with specific applications to determine the critical micelle concentration (CMC) of surfactants and detect small-molecule promiscuous inhibitors. The method exploits the meniscus curvature changes in high-density multiwell plates associated with colloidal changes in solution. The shape of the meniscus has a significant effect on fluorescence intensity when detected using a top-read fluorescence plate reader because of the effect of total internal reflection on fluorescence emission through a curved liquid surface. A dynamic range of 60% is calculated and observed and is measured with a relative sensitivity of 2%. Facile determination of the CMC of a variety of surfactants is demonstrated, as well as a screening assay for aggregate forming properties of small drug-like compounds, a common cause of promiscuous inhibition in high-throughput screening (HTS) enzyme inhibitor assays. Our preliminary results show a potential HTS assay with Z′ factor of 0.76, with good separation between aggregating and nonaggregating small molecules. The method combines the high sensitivity and universality of classic surface tension methods with simplicity and high-throughput determination, enabling facile detection of molecular interactions involving a change in liquid or solid surface character. ( Journal of Biomolecular Screening 2007:966-971)

Tailoring of the self-organized structure of sulfonated polyaniline from a fibrillar network to a colloidal aggregate

Self-organized structures of the sodium salt of sulfonated polyaniline (prepared from the leucoemeraldine base of polyaniline) in the presence of a mixture of cationic and nonionic surfactants were studied. It was used in the latex form, which has been prepared using a conventional method with sodium dodecyl sulfate. The cationic surfactant used was didodecyl dimethyl ammonium bromide, and the nonionic surfactant used was Triton-X-100. The supramolecular organization was made in aqueous medium by varying the concentrations of the components. A three-dimensional fibrillar network and colloidal aggregate were produced due to the supramolecular organization. The thermal study indicated reversible first-order phase transition in the former cases fulfilling the criteria of thermoreversible gels. A probable explanation of the different morphology from the variation of charge density on the vesicle surface has been offered. The conductivity of fibrillar network is two orders higher than that of the colloidal aggregate.