Single-particle spectroscopy allows far-field investigation of nanoscale structures or nanoprobes one at a time. It provides detailed information on the manner in which a nanoprobe's physical and chemical characteristics, including its interaction with the environment, evolve with time. Until recently, this powerful approach can only be applied to nanostructures that have been immobilized on a substrate. This report describes a new approach that lifts this limitation. The 3D single-particle tracking spectroscopy affords realtime correlation of the nanoprobe's spectroscopic characteristics with its three-dimensional spatial location. The design principles and its applications will be discussed.