Methods and apparatus (1100) for trapping fluid-borne object(s) (212) using one or more Fresnel zone plates (202) located in proximity to a fluid medium (208). Optical tweezers based on one or more Fresnel zone plates may be integrated with a microfluidic structure (e.g., chambers, channels) (1104) of various geometries so as to form one or more optical traps (215) within a fluid medium contained by the microfluidic structure(s). Three-dimensional trapping of objects can be obtained with stiffness comparable to that of conventional optical tweezers based on a microscope objective. In one example, a single Fresnel zone plate is particularly configured to form multiple optical traps upon irradiation, so as to trap multiple objects simultaneously. Exemplary applications of the methods and apparatus disclosed herein include determination of various fluid medium properties (e.g., velocity, refractive index, viscosity, temperature, pH) and object sorting.