VCSEL Arrays as micromanipulators in chip-based biosystems

The potential use of vertical cavity surface emitting laser (VCSEL) arrays for applications in cell analysis and tissue engineering is investigated by means of parallel optical trapping and active manipulation of biological cells on microfluidic chips. The simultaneous and independent transport of nine cells using a 3 x 3 array of VCSELs has been demonstrated experimentally; indicating that larger 2-dimensional array transport using individually addressable tweezers is achievable with VCSEL array devices. The transport properties of VCSEL tweezers have been investigated for various types of cells including 3T3 Murine fibroblasts, yeast, rat primary hepatocytes and human red blood cells. Due to the low relative index of refraction between the biological cell and surrounding medium and the relatively low optical power available with present VCSELs, the Laguerre-Gaussian laser mode output of the VCSEL is more favorable to use in an optical tweezer since the highest intensity is located at the outer ring of the optical aperture, producing stronger optical confinement at lower power levels. For larger biological cells or cells with a lower relative index of refraction, the power limitations of a single VCSEL were overcome through the binning of several VCSELs together by combining the outputs of a sub-array of VCSELs into a collective optical tweezer. A comprehensive analysis and simulation of how the VCSELs' pitch and output beam divergence influence the operation of the resultant optical tweezer array is presented along with our experimental data. Employing the methods of parallel array transport and the binning of multiple VCSEL outputs, allows for the manipulation and spatial arrangement of different types of cells in a co-culture so as to facilitate the formation of engineered tissues.