Dynamic Light Scattering Application To Measure Biomacromolecule

Dynamic light scattering (DLS) is a new experimental technique. It can measure diffusion coefficient of macromolecule in solutions rapidly and exactly, and the size or dynamic radius of macromolecule can be obtained.The main content of the work are as follows: developing a compact dynamic light scattering instrument with low power laser. Compared with current instruments, the setup can decrease disturbance of disorder radiation by using double layer refractive index sample matching vessel, and it can increase collecting and transmitting efficiency of radiation by adopting single mode fiber with gradient refractive index lens. With a low power laser, the sample has a low scathe, and the laser and the measurement system can be integrated conveniently.The setup was calibrated with different diameter latex, and the measurable range of the setup is from several nanometers to one micron.A stochastic inverse technique based on gray-code genetic algorithm (GGA) to invert particle size distribution from dynamic light scattering (DLS) data is proposed. Numerical tests and latex experiments for inverting dynamic light scattering data showed that the algorithm could be successfully applied to inverse problem of DLS with high stability to the different type of distributions. Compared with standard genetic algorithms and inverse Monte Carlo methods, it has been shown that the GGA has high searching efficient, and it can be rapidly obtained optimum results with a few generations. GGA is a more efficient stochastic inverse method.The diffusion coefficient of HSA (human serum album) was measured at different concentrations and pH by means of the setup. Experimental and analytic results indicate that coulomb interactions between the charged proteins acted as main contribution to the diffusion coefficient; the effect of coulomb vanished at the isoelectric(5.2), and the diffusion coefficient of protein closed to minimal. At the isoelectric, the diffusion coefficient decreased linearly with the concentration increase.The main reason was that the coulomb interactions between proteins become decrease, and the attractive potential increased relatively. In the concentration range of 5mg/ml-40mg/ml, when 532nm light was used, it was found thatDm = D0[1- (0.00194 + 0.00008)C] , where D0= (6.74 0.0l) x 10-7 cm2/sextrapolated to zero concentration at 23 and C is in units of mg/ml. The measured diameter of HSA is 3.44 0.01 nm. The investigation is help to checking nephropathy early.The diffusion coefficient of bovine serum albumin (BSA) was studied by dynamic light scattering in different ionic strength solutions. The result showed that the diffusion coefficient of protein increased with increasing protein concentration, and that when the ionic strength increased gradually, the diffusion coefficient decreased with increasing protein concentration. The concentration dependence of BSA apparent diffusion coefficients was interpreted in the context of a two-body potential of mean force that includes repulsive hard-sphere and coulombic interactions and attractive dispersion: with increasing ionic strength, Debye screening decreased, and protein interaction changed from repulsion to attraction, and protein aggregations was onset. From the concentration dependence of BSA apparent diffusion coefficients, protein interaction parameters have been regressed. It bears a net effective charge of -9.0 and has a Hamaker constant of 2.8keT. This work demonstrated that DLS was an effective technique of studying protein interactions.