Using molecular dynamics simulations and scaling theory, we present a systematic study of the function of cylindrical nanopores which are decorated with polymer brushes. Our focus is on the regimes in which these systems are able to function as switchable gates for bulky nanoparticles. The process of switching is triggered through the addition of a smaller component to the solvent, which acts as a co-nonsolvent, causing a discontinuous collapse of the brush and opening a central passway through the nanopore. We quantify the conditions under which agents of different diameters are allowed to pass through the nanopore, through direct simulation of their fluxes as well as evaluations of the free energy profiles during a forceful inclusion of these particles into the pore. Our results quantitatively confirm how these nanopores serve as semipermeable gates which grant passage of small compounds, while blocking larger ones under certain conditions.