Tweezing and manipulating micro- and nanoparticles by optical nonlinear endoscopy

The precise control and manipulation of micro- and nanoparticles using an optical endoscope are potentially important in biomedical studies, bedside diagnosis and treatment in an aquatic internal organ environment, but they have not yet been achieved. Here, for the first time, we demonstrate optical nonlinear endoscopic tweezers (ONETs) for directly controlling and manipulating aquatic micro- and nanobeads as well as gold nanorods. It is found that two-photon absorption can enhance the trapping force on fluorescent nanobeads by up to four orders of magnitude compared with dielectric nanobeads of the same size. More importantly, two-photon excitation leads to a plasmon-mediated optothermal attracting force on nanorods, which can extend far beyond the focal spot. This new phenomenon facilitates a snowball effect that allows the fast uploading of nanorods to a targeted cell followed by thermal treatment within 1 min. As two-photon absorption allows an operation wavelength at the center of the transmission window of human tissue, our work demonstrates that ONET is potentially an unprecedented tool for precisely specifying the location and dosage of drug particles and for rapidly uploading metallic nanoparticles to individual cancer cells for treatment. Optical tweezers: Nonlinear benefits Two-photon absorption can dramatically enhance the trapping force applied to fluorescent nanobeads and metallic nanoparticles. Min Gu and co-workers at the Swinburne University of Technology in Australia say that their fibre-based optical nonlinear endoscopic tweezers, which exploit two-photon absorption, can provide a trapping force that is three to four orders of magnitude stronger than usual. Their device could therefore be a potentially important tool for in vivo biomedical studies. In principle, the nonlinear tweezers allow large amounts of gold nanorods to be delivered rapidly to a desired location, for example to kill cancerous cells. This allows operation with a near-infrared source at the peak in transmission of biological tissue (800 nm), thus allowing greater penetration and reduced photodamage in the surrounding area.