Optical tweezers: a non-destructive tool for soft and biomaterial investigations

Optical tweezers are a key technique for trapping and contactless manipulation of particles at the micro- and nanoscale that can exert and sense forces from hundreds of piconewton down to few femtonewton. In their simplest implementation, they are based on a single laser beam tightly focused to a high-intensity diffraction-limited spot. Here, after reviewing the general theoretical background on optical forces, we focus on their calibration and show a comparison between frequency and time domain methods. Then, we show novel measurements and calculations of optical forces on gold nanoparticles discussing their size scaling behavior. Finally, we describe recent applications of chiral optical trapping to soft materials, and integration of optical tweezers with Raman spectroscopy for ultra-sensitive spectroscopy of biomolecules in liquids.