Measurement and control of the flow of protein solutions in a micro-fluidic macro-molecular crystallizer.

摘要

X-ray crystallography provides vital information regarding a protein's 3D structure. However, in order to perform X-ray crystallography, one needs to be able to grow large, defect-free crystals.; A major drawback of currently used lab scale techniques for crystallization is that it is very difficult to control the state of the crystallization volume after start-up. However, if controlled amounts of very small volumes could be added to or removed from this volume, we should be able to grow better crystals. However, the flow-rates needed to achieve such control are as low as a few picoliters per second. So far, controlled delivery of such low volumes (flow-rates) has not, to our knowledge, been tried.; The Crystallization Micro-Array (CRYMA) is being designed do so. It shall consist of reservoirs of protein, precipitant, and buffer solution that will be connected to a large number of micro-reactors via pumps and flow meters, which will control the delivery of each solution to each micro-reactor. A major part of the effort has been directed towards the development of a flow-sensor that can be incorporated into the CRYMA---the Lag After Pulsed Separation (LAPS) meter. An upstream event (electrophoretic separation of concentration of the particles in one section of the device) is detected downstream (by change in AC resistance). The time lag between the event and the detection is inversely proportional to the velocity, providing a non-invasive, no-moving-parts flow measurement. The LAPS meter can measure the flowrate of solutions containing one or more charged biomacromolecules or particles. It could also be utilized for other purposes, such as in Micro-Total Analysis Systems (m-TAS), operating micro-bioreactors, drug delivery, and in micro-dosing systems for performing drug assays on a small number of cells.; The flow rate of each solution through each pump will be controlled to maintain a different concentration vs. time profile in each reactor of the CRYMA. We have also looked at how feed rates of protein and salt affect the likelihood of obtaining large protein crystals, and have suggested a method to calculate the optimal feed profiles to maximize the average crystal size obtained in the reactor.