A method for processing a substrate by using fluid flowing through a particle detector is provided. The particle detector is utilized to detect nano-particles contained in fluid. The particle detector includes a substrate and a pair of sensing electrodes disposed on the substrate. The substrate includes nano-pores, wherein the pore size of the nano-pores is greater than the particle size of the nano-particles, allowing the nano-particles contained in the fluid passing through the nano-pores. The pair of sensing electrodes are positioned adjacent to at least one of the nano-pores.