title: Nanophotonic force microscopy: characterizing particle-surface interactions using near-field photonics.
abstract: Direct measurements of particle-surface interactions are important for characterizing the stability and behavior of colloidal and nanoparticle suspensions. Current techniques are limited in their ability to measure pico-Newton scale interaction forces on submicrometer particles due to signal detection limits and thermal noise. Here we present a new technique for making measurements in this regime, which we refer to as nanophotonic force microscopy. Using a photonic crystal resonator, we generate a strongly localized region of exponentially decaying, near-field light that allows us to confine small particles close to a surface. From the statistical distribution of the light intensity scattered by the particle we are able to map out the potential well of the trap and directly quantify the repulsive force between the nanoparticle and the surface. As shown in this Letter, our technique is not limited by thermal noise, and therefore, we are able to resolve interaction forces smaller than 1 pN on dielectric particles as small as 100 nm in diameter.
authors.affiliation: Sibley School of Mechanical and Aerospace Engineering, Cornell University , Ithaca, New York 14853, United States.
authors.forename: Perry
authors.initials: P
authors.lastname: Schein
authors.forename: Pilgyu
authors.initials: P
authors.lastname: Kang
authors.forename: Dakota
authors.initials: D
authors.lastname: O'Dell
authors.forename: David
authors.initials: D
authors.lastname: Erickson
mesh_terms: D008853:Microscopy / Q000379:methods*; D053758:Nanoparticles; D013499:Surface Properties
keywords: Force measurement; colloidal stability; nanoparticle characterization; optical tweezers; photonic crystals; surface interactions