Optical trapping techniques have proven to be powerful experimental tools, and in the past three decades, they have transformed many areas of biochemistry and molecular biology. Yet these techniques are typically restricted to a specialized group of individuals who spend many years constructing a single instrument, and also require repeated measurements, one molecule at a time. In order to make these techniques accessible to a broader scientific community, a new generation of optical trapping instruments is essential. A ‘plug-and-play’ instrument, capable of manipulation with both high resolution and high throughput, would potentially revolutionize the single molecule field. In the first steps towards this goal, we demonstrated dynamic optical trapping control of nanoparticles by a nanophotonic standing-wave array trap (nSWAT) (Soltani et al., 2014). This novel, electro-optofluidic platform uses photonic interference functionalities to establish an array of stable, three-dimensional on-chip optical traps at the antinodes of a standing-wave evanescent field on a nanophotonic waveguide. The nSWAT contains integrated electric microheaters that enable precision trap repositioning at high speeds, ultimately allowing for the sorting and manipulation of individual DNA molecules. This controllable trapping device has the potential to achieve high-throughput precision measurements on chip.
Schematic of device design. nSWATs were implemented with silicon waveguides on a silicon-oninsulator (SOI) platform. Laser input to the waveguide is partitioned into two nSWATs using a Mach–Zehnder interferometer (MZI). nSWATs have a 50/50 waveguide beamsplitter with output arms connected to generate counter-propagating waves. Three microheaters are located above the waveguides, one in the MZI to control partitioning of the laser into the two nSWATs and two more to control the trap positions in each nSWAT. The microheaters and waveguides are buried in oxide, except for the exposed waveguides in the fluidic pool trapping region. Inset: Array of traps with a DNA molecule suspended between two beads held by nSWATs. The coloured three-dimensional plot shows the calculated energy density of standing waves on both waveguides