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.