Optical trapping and microfluidic flow manipulation using cascaded bowtie photonic crystal cavities

In this paper, we present an innovative optofluidic system that leverages cascaded bowtie photonic crystal (BPhC) to achieve subwavelength-scale control of temperature and fluid motion. The strong electromagnetic field enhancement of the bowtie structure can generate a hotspot at the resonance of BPhC, due to the absorption of bulk water in the infrared wavelength range (around 1600 nm). With the assistance of a cationic surfactant, cetyltrimethylammonium chloride (CTAC), a thermoelectric field is established to attract particles towards the hot region. Our experiments show that suspended particles as small as 800 nanometers can be rapidly transported to bowtie region and become trapped at the bowtie cavity on the resonance of BPhC. The trapped particles can be released simply by tuning the wavelength from on to off resonant conditions. Our work paves the way for non-plasmonic nanophotonics to manipulate microfluidic dynamics and precisely control trapping by tuning the wavelength