Suspendable porous glass particles

#1. Field

#This invention relates generally to porous glass particles and specifically to an aqueous suspension of porous glass particles having a closely controlled average particle size, the suspension being especially useful in the field of solid phase radioimmunoassay.

#2. Prior Art

#FIGS. 1-2 illustrate comparisons of particle size distributions for porous glass samples prepared in accordance with the teachings herein and porous glass samples which were merely milled.

#A very critical feature of our suspension is the close control of the particle sizes of the porous glass particles and the method for preparing porous glass particles within a very critical particle size range. In using porous glass as an antibody carrier in SPRIA, it has been shown that carrier particle size is very important. See, for example, U.S. patent application Ser. No. 447,252, now U.S. Pat. No. 3,975,511 filed of even date in the names of W. Vann and S. Yaverbaum, entitled "Solid Phase Radioimmunoassay," and assigned to the present assignee. Since an accurate SPRIA requires complete separation of all complexed products prior to counting, it has been found that the carrier particle size should not exceed about 10 microns, very preferably, less than about 3.0 microns, so that the carrier-antibody composite will remain suspended in solution for a period of time to allow complexing with the labelled and unlabelled substances. Composites having carrier particle sizes above about 10 microns tend to settle relatively rapidly in solution, thus limiting the ability to draw uniform aliquots of the suspension over reasonable periods of time. Further the very size of particles beyond 10 microns can limit the diffusion of the antigen deeply into the pores thereby not fully utilizing the bonded antibodies within the pores of the porous glass. The average pore diameter of porous glass can be readily controlled, and it has been found that for most SPRIA applications the porous glass particles should have an average pore diameter within the range of about 100 A to about 1200 A. The lower pore size is dictated by antibody and/or antigen size. The higher pore size is dictated by minimum surface area requirements for maximum antibody loading per gram of carrier. For antibody loading, the surface area should be at least above 10 m.sup.2 /g, very preferably at least about 20 m.sup.2 /g. Utilizing this same consideration of surface area requirements with respect to non-porous particles, it is evident from the table shown below that such non-porous particles would have to be less than about 0.7 micron in average particle diameter to satisfy the preferred minimum surface area requirement.

#Table I ______________________________________ Avg. Particle Dia. (.mu.) Avg. External Surface Area(m.sup.2 /g) ______________________________________ 10 1.4 1.0 13.9 0.7 19.8 0.5 27.7 0.25 55.4 0.1 138.6 ______________________________________

#Thus, in the very preferred particle range of 0.7 to about 3.0.mu., it is necessary to use a porous particle to achieve maximum antibody activity (loading).