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Pinhole Optical Tweezers: Extending the Photobleaching Lifetime in the Presence of an Optical Trap by Wavefront Engineering

We present a new method for combining optical tweezers with single-molecule fluorescence in an engineered geometry we have coined a ‘pinhole’ optical trap. By utilizing an appropriately constructed Laguerre-Gaussian (LG) or ‘donut’ beam, and applying force along the axis of the trapping laser, one can maintain a low-intensity region of near-infrared (IR) light directly below the optical trap in which a biomolecule may be probed by both force spectroscopy and fluorescence. We show that within this region of low IR light intensity, the photobleaching lifetime of Alexa-647, an organic dye that is particularly sensitive to the high intensity trap light, can be significantly extended. This approach enables us to spatially separate the trap light from the fluorescence illumination without the need to physically separate, by many micrometers, the optical trap from the biological sample.