Förster Resonance Energy Transfer Control by Means of an Optical Force

Abstract Förster resonance energy transfer (FRET) is ubiquitous in optical processes in the natural world. A methodology is proposed that uses an optical force to control its efficiency without contact in an aqueous solution of a thermo‐responsive polymer, polyvinyl methyl ether (PVME). Focusing irradiation of a near infrared laser beam into the solution results in the formation and trapping of a single polymer droplet. The polymer concentration in the droplet is controllable by changing the optical force from the laser light is shown. The polarity inside the droplet decreases with increasing the optical force. When small amounts of dye molecules, D (energy donor) and A (energy accepter), are dissolved in the polymer solution, D and A are absorbed (extracted) into the droplet. The concentrations of D and A are controllable by the optical force. Based on this mechanism, FRET between D and A is induced successfully, and can control the FRET efficiency. Finally, the modulation of fluorescence color of the droplet from blue, green, yellow, to an orange color is demosntrated simply by changing the optical force. The concept and technique are unique and will open a new channel to develop droplet chemistry and photochemistry.