  Understanding the structural properties of random packings of jammed colloids
requires an unprecedented high-resolution determination of the contact network
providing mechanical stability to the packing. Here, we address the
determination of the contact network by a novel strategy based on fluorophore
signal exclusion of quantum dot nanoparticles from the contact points. We use
fluorescence labeling schemes on particles inspired by biology and biointerface
science in conjunction with fluorophore exclusion at the contact region. The
method provides high-resolution contact network data that allows us to measure
structural properties of the colloidal packing near marginal stability. We
determine scaling laws of force distributions, soft modes, correlation
functions, coordination number and free volume that define the universality
class of jammed colloidal packings and can be compared with theoretical
predictions. The contact detection method opens up further experimental testing
at the interface of jamming and glass physics.
