We demonstrate a fast and direct calibration method for systems using a single laser for optical tweezers and particle position detection. The method takes direct advantage of back-focal-plane interferometry measuring not an absolute but a differential position, i.e. the position of the trapped particle relative to the center of the optical tweezers. Therefore, a fast step-wise motion of the optical tweezers yields the impulse response of the trapped particle. Calibration parameters such as the detector's spatial and temporal response and the spring constant of the optical tweezers then follow readily from fitting the measured impulse response.
An optimized chemistry turns a small green dye into a useful label for single‐molecule experiments where steric hindrance is an issue. Thanks to a reducing and oxidizing system combined to oxygen depletion, a single Bodipy (boron‐dipyrromethene) FL fluorophore emits, on average, 20 times more photons around 510 nm (see picture) and its lifetime before photobleaching is increased by the same amount, reaching several seconds.
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