Optical and fluidic design for guaranteed trapping and detection of particles in a silicon microfluidic and photonic crystal system

In recent studies, optical forces have been exploited to guide particles along waveguides and to trap particles near refractive index sensors. But the ability of photonic devices to bind a freely flowing particle from an adjacent microfluidic channel has yet to be fully characterized. In order to determine the ability of a given device to trap an arbitrary particle, we develop a method to numerically calculate the trajectory of a particle flowing near a model system. We determine the trajectories of 50 nm radius particles in a fluid flowing at an average velocity of 1 cm/s near a photonic crystal resonator pumped at 1 W. The finite element method is used to calculate the force of the fluid on the particles and finite-difference time-domain simulations are used to calculate optical forces. The particle equation of motion is solved using the adaptive Runge-Kutta method.