Dual wavelength optical tweezers for confocal Raman spectroscopy

We describe the use of dual optical tweezers to manipulate micron-size particles in and out of the focus of a confocal Raman microscope. One of the beams excites the Raman spectrum while the second tweezers improves the sensitivity of the technique and also allows for the manipulation of the environment of the trapped objects. We concentrated on optimising the alignment of both trapping and Raman excitation beams and on the background subtraction method. Even at the low trapping/excitation powers used a single living cell could be trapped and monitored for over 2 h without incurring damage.