Holographic Optical Tweezers for the study of colloidal interactions

Colloids or particles in suspension in a medium are omnipresent in our everyday life, such as in food, paints or drugs. Consequently, colloidal interactions have interesting applications in domains like biology, fabrication or industrial processes. Among the different techniques that can measure colloidal interactions, optical tweezers is the most versatile. This technique permits to trap particles with a force that can be precisely tuned, while also allowing to measure the particle position with nanometer precision, as well as the force applied on that particle down to femtonewton resolution. In addition to this, the inclusion of a spatial light modulator in an optical tweezers setup gives the opportunity to create multiple steerable traps in space, making the measurements between multiple particles in suspension possible. Such a setup is referred to as holographic optical tweezers. In this project, we demonstrate the use of a custom-built holographic optical tweezers setup for the measurement of interaction forces between microspheres coated with compounds relevant to oral drug delivery applications. More specifically, we tested the interaction between porcine gastric mucin and selected permeation enhancers, the first being representative of the mucus layer inside our small intestine and the second in the place of potential compounds that could help with increasing the efficiency of some oral drugs.