Synthetic Thermo-Sensitive Hydrogel Microspheres as Temperature Probes in an Optical Tweezers Setup

Optical tweezers have numerous applications in biochemistry and biophysics research. Many optical tweezers experiments require the use of high laser powers, having a substantial heating side effect that can influence experimental results. The degree of heating and its spatial profile, however, depends on experimental conditions and requires direct measurement. Various methods for local temperature measurement have been proposed, each with its advantages and drawbacks. Herein, the use of the temperature-sensitive poly(N-isopropyl-acrylamide) (PNIPAAm) microspheres to measure the local heating caused by optical tweezers is demonstrated and the temperature profile around the laser focus at varying laser powers is characterized. The main advantage of this method is its applicability to virtually any setup and experiment. Using simple image analysis, the temperature within the biologically relevant range can be determined with 1°–2° accuracy. Possible applications and limitations of this method are discussed.