Optical tweezers are instruments capable of trapping small particles using the forces generated by laser radiation pressure. The concept of pressure from the propagation of light is at the core of optical tweezers technology and was hypothesized several centuries ago. Until the 1960s it was not possible to use radiation pressure generated by light in order to modify the position of matter, but in days the advent of lasers provided a light source with the appropriate properties to generate a light trap and the rise of nanotechnology gave the opportunity to synthesize, modify and control materials in the nanometric scale. These two factors opened the way for optical trapping.
Today optical tweezers can be used to manipulate and study not only dielectric spheres with dimensions in the micron range, but also metal particles and single molecules in the range of nanometers. Additionally, the shape and polarization of the trapping potential can be modified to match the needs of a specific experiment. They are extensively used to study mechanical properties of DNA and proteins, interaction forces between colloids and molecules, in biology to study cell membranes and to manipulate cell interior (e.g. organelles) and individual cells.
In our group we have developed the first combined atomic force microscopy and optical tweezers instrument (AFM/OT). The system is based on a commercial AFM and confocal microscope. The addition of three lasers along with beam shaping and steering optics, on which the optical tweezer is based upon, provide us with the ability to manipulate small dielectric objects suspended in a fluid. Additionally, this same device allows for direct displacement and force measurement with very high resolution and accuracy in the same AFM scanning zone. We have also fitted a laser and a set of filters to observe fluorescent samples appropriately excited. This remarkable improvement of a standalone AFM force resolution allows us to conduct experiments using a hybrid double probe technique, which is fundamental for the study of single molecules, cells, biological tissues and nanomaterials from a brand-new point of view.