IMMUNO-MAGNETIC BEAD MASS TRANSPORT AND CAPTURE EFFICIENCY AT HIGH TARGET CELL DENSITIES IN PHOSPHATE-BUFFERED SALINE

In this manuscript we present a modified kinetic model for pathogen capture efficiency (E) variation with mixing time (tau(mix)) which is applicable for most combinations of immuno-magnetic bead (IMB)-target organism concentrations (e.g., [IMB] similar to 8 x 10(6) IMB mL(-1); Salmonella enterica. serovar Enteritidis, [SE] similar to 10(2)-10(8) CFU mL(-1)). We found that as the ratio of [IMB] to [SE] was decreased from more than 10(5) to ca. 10(-1), the average number of cells captured per IMB (.) SE complex increased from ca. 1 to 4 +/- 1. Concurrently, using a modified kinetic model for fitting E variation with tau(mix), the maximum possible level of capture (xi) was observed to decline from similar to 100% (xi similar to 1; [IMB] > > [SE]) to 23 % (xi similar to 0.23; [IMB]:[SE] similar to 0.1). Using a purely kinetic approach we also found that an empirical mass transport term (gamma(obs) = {3.1 +/- 1.2} x 10(-9) mL IMB-1 min(1); averaged across all [SE] tested: [IMB]:[SE] similar to 200000, 200, 3, and 0.1) did not differ much from gamma(obs) reported in earlier work ({3.35 +/- 0.2} x 10(-9) mL min(-1) IMB-1) at extremely low [SE] (e.g., less than or equal to 100 CFU mL(-1)). Upon inserting the classically-derived equation for gamma into the kinetic model and solving for the effective IMB radius (r(IMB)), we found that the r(IMB) was 2.3 +/- 0.16 mum ((x) over bar +/- s; averaged across all [IMB]:[SE]) which was only 0.5-0.9 mum greater than the r(IMB) reported by the manufacturer (1.4 +/- 0.2 mum). These results support previous work which showed a similar small r(IMB) deviation possibly due to the hydro-dynamic behavior of the IMBs in relatively dilute buffer suspensions ([IMB similar to 8 x 10(6) IMB mL(-1)) and argues that IMB-based cell capture is almost exclusively a function of mass transport.