Bulk-heterojunction polymers in optically-induced dielectrophoretic devices for the manipulation of microparticles

This paper presents a decent polymer material for fabricating optically-induced dielectrophoretic (ODEP) devices, which can manipulate microparticles or cells by using moving light patterns. A thin film of a bulk-heterojunction (BHJ) polymer, a mixture of regioregular poly(3-hexylthiophene) and [6,6]-phenyl C61-butyric acid methyl ester, is used as a light-activated layer. When illuminated by a projected light beam, the photo-induced charge carriers created by the electron transfer of excitons at a donor/acceptor interface in the BHJ layer, disturbs the uniformly-distributed electric field applied on the ODEP devices. A negative DEP force is then generated by virtual electrodes defined by the optical images from a computer-programmable projector to manipulate microparticles, thus providing a functionalized platform for particle manipulation. The effect of the polymer thickness and composition on the magnitude of the generated DEP force has been extensively investigated. The maximum particle drag velocity and the force applied on 20.0 mu m diameter polystyrene beads are measured to be approximately 202.2 mu m/s and 38.2 pN, respectively, for a device with a 497.3-nm thick BHJ layer. The lifetime of the developed device is also explored (similar to 5 hours), which is sufficient for applications of disposable ODEP devices. Therefore, the BHJ polymer may provide a promising candidate for future ODEP devices capable of nanoparticle and cell manipulation. (C) 2009 Optical Society of America