Real-Time Temperature Monitoring in an Optical Trap

This work demonstrates, for the first time to our knowledge, that it is possible to measure the temperature of an optical trap (OT) using an optical fiber sensor tip. A polymer capped fiber optic Fabry-Perot interferometer, which is structure and temperature sensing characteristics have been well studied, was used. The surface of the polymer cavity, attached to the single-mode fiber tip immersed in Phosphate Buffered Saline, was placed in the optical trap. A temperature change of 1.63 ± 0.021°C was measured when the power of the laser, emitting at 975nm, was increased by 100 mW. The proposed setup facilitates the measurement of temperature, since it does not require the use of fluorescent dyes and it even works while having a captured particle; these advantages allow it to be included in any OT system.

I. Introduction

Since their invention, optical tweezers, also known as optical traps (OT) [1], have experienced a drastic evolution, and have now become a highly essential analysis technique in several experimental areas such as physics, chemistry and biology, with the latter being probably the most benefited. In recent years, OT has been implemented as a tool in studies on individual cells and molecules, biological engines [2], and RNA/DNA mechanics [3], or in the biomechanical characterization of different cells [4], [5], and even for the measurement of viscosity in liquids [6], just to mention some of the typical applications. In all the biological applications of the OT, the heat in the sample under analysis, generated by the power of the laser that creates the OT, is a key parameter that must be continuously monitored since it could produce sample photodamage. In the case of trapped cells, heat can affect their viability, elongation rates, and stability [7].