Sudden breakdown in linear response of a rotationally driven magnetic microparticle and application to physical and chemical microsensing.

In this work, sensing magnetic microparticles were used to probe both the local pH and the viscosity-dependent nonlinear rotational behavior of the particles. The latter resulted from a critical transition marking a driven particle's crossover from phase-locking to phase-slipping with an externally rotating magnetic field, i.e., a sudden breakdown in its linear response that can be used to measure a variety of physical quantities. The transition from simple rotation to wobbling is described both theoretically and experimentally. The ability to measure both chemical and physical properties of a system could enable simultaneous monitoring of chemical and physical interactions in biological or other complex fluid microsystems.

Synthesis of fluorescent derivatives of wortmannin and demethoxyviridin as probes for phosphatidylinositol 3-kinase.

Fluorescent analogs were synthesized of the potent PI 3-kinase inhibitors, wortmannin and demethoxyviridin. The esterification of 11-deacetylwortmannin, 17-hydroxywortmannin, and demethoxyviridin with the fluorescent carboxylic acids NBD-sarcosine and 7-dimethylaminocoumarin-4-acetic acid generated six novel fluorescent esters. Potent inhibition of PI 3-kinase-alpha was observed for the derivatives of 11-desacetylwortmannin and demethoxyviridin.