Figure 2

Raman tweezers. The figure has been adapted from Hamden et al., 2005 [67]. The figure is a schematic of a model Raman tweezers. The combined laser tweezers and Raman spectroscopy instrument possesses a laser beam at 785 nm from a wavelength-stabilized, beam shape-circulated semiconductor diode laser that is introduced into an inverted microscope through a high numerical aperture objective (100×, NA = 1.30) to form an optical trap. The same laser beam is used to excite Raman scattering of the trapped particle. The scattering light from the particle is collected by the objective and coupled into a spectrograph through a 200-μm pinhole, which enables confocal detection and rejection of off-focusing Rayleigh scattering light. A holographic notch filter is used as a dichroic beam splitter that reflects the 785-nm excitation beam and transmits the Raman shifted light. A green-filtered illumination lamp and a video camera system are used to verify trapping and observe the image of the cell. The spectrograph is equipped with a liquid-nitrogen-cooled charge-coupled detector (CCD). Abbreviations: M-mirror; L-lens; DM-dichroic mirror; PH-pinhole; HNF-holograph notch filter.