Invited Speaker: Haw YangTime-Resolved and Time-Dependent Spectroscopy of Single Nano Objects Moving in Solution*

An interesting challenge in experimental physical chemistry is how to interrogate chemical dynamics in complex environments. Here, a complex environment could be the solid-liquid interface of a functioning fuel cell, the interior of a living mammalian cell, or the juncture between an invading viral particle and a cell membrane, for example. These environments share the same characteristics: that they are anisotropic and highly heterogeneous both in space and in dynamics. Therefore, if quantitative experimental studies could be carried out in them, it would be possible to start addressing the fundamental question: To what extent are the current chemical dynamics concepts applicable in these environments? After all, the current chemical physics paradigm has been established under idealized conditions, isotropic, homogeneous, and primarily resting on a two-body interaction framework.

 

In this presentation, we will discuss one promising approach meeting this challenge, the real-time 3D single-particle tracking spectroscopy [1]. It allows doing time-dependent spectroscopy on a single nano object such as a quantum dot or a gold nanoparticle while the object is freely moving in room-temperature solution. This is achieved by photon-counting sensing of the nano object’s 3D position and a fast feedback mechanism to counter the object’s displacement from the microscope objective focal point. The end result is that the nano object appears as if stationary in the laboratory frame even though it is freely moving in 3D in solution. In essence, the instrument allows real-time hardware-based mechanical coordinate transformation between the nanoobject-based coordinate frame and the laboratory-based coordinate frame. This experimental concept routinely delivers a time resolution of ~10 μs and a spatial localization precision of 10 nm in all X-Y-Z dimensions [2]. In terms of application, if time permits, we will touch upon time-dependent single-particle spectroscopy on freely moving single particles [3-6], 3D multi-resolution imaging [7, 8], and the recently developed time-resolved capabilities [9].