I present the behavior of colloidal adsorption to an oil-water interface in the presence of electrolyte in an aqueous subphase. The optical laser tweezers and the piezo controller are used to trap an individual polystyrene microsphere in water and forcibly transfer it to the interface in the vertical direction. Addition of an electrolyte (i.e., NaCl) in the aqueous subphase enables the particle to attach to the interface, whereas the particle escapes from the trap without the adsorption in the absence of the electrolyte. Based on the analytical calculations of the optical trapping force and the electrostatic disjoining pressure between the particle and the oil-water interface, it is found that a critical energy barrier between them should exist. This study will provide a fundamental understanding for applications of colloidal particles as solid surfactants that can stabilize the immiscible fluid-fluid interfaces, such as emulsions (i.e., Pickering emulsions) and foams.