  Multivalent particles bind to targets via many independent ligand-receptor
bonding interactions. This microscopic design spans length scales in both
synthetic and biological systems. Classic examples include interactions between
cells, virus binding, synthetic ligand-coated micrometer-scale vesicles or
smaller nano-particles, functionalised polymers, and toxins. Equilibrium
multivalent binding is a continuous yet super-selective transition with respect
to the number of ligands and receptors involved in the interaction. Increasing
the ligand or receptor density on the two particles leads to sharp growth in
the number of bound particles at equilibrium.
  Here we present a theory and Monte Carlo simulations to show that applying
mechanical force to multivalent particles causes their adsorption/desorption
isotherm on a surface to become sharper and more selective, with respect to
variation in the number of ligands and receptors on the two objects. When the
force is only applied to particles bound to the surface by one or more ligands,
then the transition can become infinitely sharp and first-order---a new binding
regime which we term "hyper-selective". Force may be imposed by, e.g. flow of
solvent around the particles, a magnetic field, chemical gradients, or
triggered uncoiling of inert oligomers/polymers tethered to the particles to
provide a steric repulsion to the surface. This physical principle is a step
towards "all or nothing" binding selectivity in the design of multivalent
constructs.
