A novel optofluidic chip avoids the bulk of traditional optical manipu-lation devices and enables unique applications. The laser-based optical trap has been instrumental in a broad range of investigations of small particles in liquids, gases, and vacuum. 1, 2 The field has enabled, for example, manipulation of bacteria and viruses, cooling and trapping of atoms, and pre-cise measurements of bioparticle properties. 2 However, optical trapping instruments have traditionally been bulky, involving many optical elements (e.g., microscopes). Recently, waveguide-based, on-chip optical manipulation has emerged as an inex-pensive and compact alternative. 3–10 We have conducted unique optical manipulation, trapping, and sensing applications using an optofluidic chip based on liquid-core antiresonant-reflecting optical waveguide (ARROW) technology. 10 The low refractive index core is surrounded by specific high-index dielectric layers that enable light and liquid to be confined in the same volume: see Figure 1(a). This key feature allows fluorescence detection with single-molecule-level sensitivity. 10 We developed an integrated optofluidic platform to interface liquid-and solid-core ARROWs (see Figure 1) to detect single bioparticles on a chip. 10 In addition, due to the small waveguide cross sections (typically 12 55m 2), the quasi-single-mode op-tical fields have high intensities and can manipulate small particles (100–2000nm in diameter). The response of a particle under irradiance of a given color is determined not only by its physical properties but also the beam's optical power and spa-tial area. We can exploit this sensitive particle behavior to extract information about an optical system. For example, a particle's optically induced trajectory within a liquid-core ARROW can be used to characterize the waveguide loss (the loss of light from the core). 5 The main advantages of this technique are its sim-plicity and nondestructive nature. Introducing a counter-propagating beam (see Figure 1, trap-ping beam) makes it possible to optically trap particles by Figure 1. Scanning electron microscope images of (a) hollow-and (b) solid-core waveguides with a guided-light output overlaid (bar (c) An optofluidic platform with integrated hollow-and solid-core waveguides. Figure 2. (a) Particles trapped in loss-based (LB) and divergence-based (DB) traps on an optofluidic chip. (b) A trapped E. coli bacterium attached to a latex bead. Continued on next page 10.1117/2.1201101.003508 Page 2/2 balancing the optical forces—called gradient or scattering forces—exerted on them. 1 Traditionally, the setup involves asymmetric beam divergence with single-or dual-beam configurations. 1, 2 However, we can also manipulate particles using optical-power variations, such as waveguide loss, 5, 6 to determine how the optical trap behaves. We demonstrated this loss-based trap by capturing latex beads and E. coli bacteria in a liquid-core ARROW 6 (see Figure 2). The advantages of this new type of optical trap are its ability to confine particles at any point in a liquid core and to use the chip's waveguide loss to design the trapping regions. For example, we have shown a method to locally increase the concentration of fluorescent nanoparticles by optically confining many particles. 9 The ability to manipulate and trap particles on a chip can also be exploited for optical sensing. The efficiency of a liquid-core waveguide to collect light is determined by the location of the light source. Thus, a control or guiding beam can be used to effectively draw particles to the liquid-core center, where the coupling efficiency for emitted light is highest. We proved this principle using a guiding beam to confine fluorescent mi-crobeads to the center of a liquid-core ARROW and conse-quently doubled the number of detected particles. 7 In summary, different combinations of radiation pressure in a liquid-core waveguide can be applied to move particles in a fluidic channel, trap them at desired points, and even analyze the waveguides themselves. In future work, we intend to ap-ply this platform to optically control particle sorting or tailor the trapping position using waveguide loss. As these techniques continue to mature and more innovative applications are dis-covered, on-chip optical-particle manipulation will reach its full potential.