IMMUNO‐MAGNETIC BEAD MASS TRANSPORT AND CAPTURE EFFICIENCY AT HIGH TARGET CELL DENSITIES IN PHOSPHATE‐BUFFERED SALINE1

Abstract

In this manuscript we present a modified kinetic model for pathogen capture efficiency (E) variation with mixing time (Tmix) which is applicable for most combinations of immuno‐magnetic bead (IMB)‐target organism concentrations (e.g., [IMB] ˜ 8 × 106 IMB mL‐1; Salmonella enterica serovar Enteritidis, [SE] ˜ 102‐108 CFU mL‐1). We found that as the ratio of [IMB] to [SE] was decreased from more than 105 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 Tmix, the maximum possible level of capture (§) was observed to decline from ˜ 100% (§˜ 1; [IMB] > > [SE]) to 23% (§˜ 0.23; [IMB]:[SE] ˜ 0.1). Using a purely kinetic approach we also found that an empirical mass transport term (yobs= (3.1 ± 1.2) × 10‐9 mL IMB‐1 min 1; averaged across all [SE] tested: [IMB]:[SE] ˜ 200000, 200, 3, and 0.1) did not differ much from yobs reported in earlier work (3.35 ± 0.2 × 10‐9 mL min‐1 IMB‐1) at extremely low [SE] (e.g., ± 100 CFU mL‐1). Upon inserting the classically‐derived equation for γ into the kinetic model and solving for the effective IMB radius (rIMB), we found that the rIMB was 2.3 ± 0.16 μ (§ S; averaged across all [IMB]:[SE]) which was only 0.5–0.9 μ greater than the rIMB reported by the manufacturer (1.4 ± 0.2 μ). These results support previous work which showed a similar small rIMB deviation possibly due to the hydro‐dynamic behavior of the IMBs in relatively dilute buffer suspensions ([IMB ˜ 8 × 106 IMB mL‐1) and argues that IMB‐based cell capture is almost exclusively a function of mass transport.