A fiber optic probe for monitoring protein aggregation, nucleation and crystallization

Protein crystals are often experimentally grown in hanging drops in microgravity experiments on-board the Space Shuttle orbiter. The technique of dynamic light scattering (DLS) can be used to monitor crystal growth processes in hanging droplets (similar to 30 mu L) in microgravity experiments, but elaborate instrumentation and optical alignment problems have made in-situ applications difficult. In this paper we demonstrate that such experiments are now feasible. We apply a newly developed fiber optic probe to various earth and space (microgravity) protein crystallization system configurations to test its capabilities. These include conventional batch (cuvette or capillary) systems, a hanging drop method in a six-pack hanging drop vapor diffusion apparatus (HDVDA), a modified HDVDA for temperature induced nucleation and aggregation studies, and a newly envisioned dynamically controlled vapor diffusion system (DCVDS) configuration. Our compact system exploits the principles of DLS and offers a fast (within a few seconds) means of quantitatively and non-invasively monitoring the various growth stages of protein crystallization. In addition to DLS capability, the probe can also be used for performing single-angle static light scattering measurements. It utilizes extremely low levels of laser power (a few mu W) and essentially eliminates the usual problems associated with optical alignment and vibration isolation. The compact probe is also equipped with a miniaturized microscope for visualization of macroscopic protein crystals. This new optical diagnostic system makes possible the exploration of new ways to grow good quality crystals suitable for X-ray crystallographic analysis and may contribute to a concrete scientific basis for understanding the process of crystallization.