We use the label-free microsphere-assisted microscopy to image low-contrast hexagonally close-packed polystyrene nanoparticle arrays with diameters of 300 and 250 nm.When a nanoparticle array is directly placed on a glass slide,it cannot be distinguished.If a 30-nm-thick Ag film is deposited on the surface of a nanoparticle array,the nanoparticle array with nanoparticle diameters of 300 and 250 nm can be distinguished.In addition,the Talbot effect of the 300-nm-diameter nanoparticle array is also observed.If a nanoparticle sample is assembled on a glass slide deposited with a 30-nm-thick Ag film,an array of 300-nm-diameter nanoparticles can be discerned.We propose that in microsphere-assisted microscopy imaging,the resolution can be improved by the excitation of surface plasmon polaritons(SPPs)on the sample surface or at the sample/substrate interface,and a higher near-field intensity due to the excited SPPs would benefit the resolution improvement.Our study of label-free super-resolution imaging of low-contrast objects will promote the applications of microsphere-assisted microscopy in life sciences.