The passive generation of spatial confinement of charged colloids and polyelectrolytes in solution in response to local substrate structure in a fluidic device was investigated. p-Type silicon substrates with 400-1000-nm thermally grown silicon dioxide were coated with 20 nm Cr and patterned by using laser lithography. The substrates were wet-etched in 5% HF solution and anodically bonded to 200 ± 25-μm-thick borosilicate 33 glass. Negatively charged fluorescent carboxyl-modified polystyrene colloidal spheres were introduced at a number density of 2.2 ×10¹⁸ in distilled water. Numerical simulations of the electrostatic potential in a fluidic slit was performed by solving the nonlinear Poisson-Boltzmann equation. It was observed that simulation of the total potential energy around a square SiO ₂ motif corresponds to a system with surface charge densities.