Immuno-magnetic bead mass transport and capture efficiency at low target cell densities in phosphate-buffered saline

摘要

Anti-salmonella immuno-magnetic bead (IMB) capture efficiency (E) was determined by varying both IMB levels (IMB) and mixing time (tau(MIX)) and enumerating captured Salmonella enteritidis cells. We observed that E varied with tau(MIX) as a Pseudo-first order process with a rate constant (kappa) of 0.028 +/- 0.001 min(-1) and an infinite tau(MIX) asymptote of 0.97 (97 capture). Thus, even at low target cell densities (S. E. less than or equal to 70 CFU mL(-1)), nearly 100 of the bacteria were captured as tau(MIX) approached 2 h. We hypothesize that kappa is the product of both IMB mass transport (gamma) and IMB concentration (IMB) terms. Thus, gamma represents the total volume which each IMB samples per unit time of mixing. This idea appears reasonable as gamma({3.2 +/- 0.2} x 10(-9) mL min(-1) IMB-1), determined from E-based observations at various IMB levels (similar to10(6) -10(8) IMB mL(-1)) and fixed tau(MIX) (30 min), was nearly identical to gamma ((3.5 +/- 0.1) x 10(-9) mL min(-1) IMB-1) derived kinetically (tau(MIX) = 0-120 min; IMB 8 X 10(6) IMBs mL(-1)). Estimating a mass transport term (gamma(CALC)) founded on classical dynamics we obtained a value 5.3 X 10(-10) mL min(-1) IMB-1 whereupon gamma(CALC) and gamma would have completely agreed were the IMB radius (r(IMB) = 1.4 mum) 0.8 PM larger. The apparent discrepancy in r(IMB) might be explained by a greater effective (hydrodynamic) r(IMB) which could result from some combination of IMB swelling and brownian motion. These results argue that IMB-based target cell capture is modulated by IMB mass transport and collision probability.