Kinetic profile of the adsorption and conformational change of lysozyme onself-assembled monolayers as revealed by quartz crystal resonator

This report studied the adsorption behavior of lysozyme to hydrophobic and hydrophilic self-assembled monolayer (SAM(I) and SAM(II)) of thiol and gold surfaces, by using a quartz crystal microbalance (QCM) technique. This tec hnique allows time-resolved simultaneous measurements of changes in frequen cy (f(s)) and energy dissipation (R-m) of the QCM during the adsorption pro cess, which makes it possible to investigate the viscoelastic properties of the protein layer during the adsorption process. In the QCM measurements, the influence of the energy dissipation of the protein adsorption layer on the adsorption densities were discussed. An adsorption kinetics model inclu ding reversible and irreversible adsorption states was proposed to analyze the rate constants. The rate constants for reversible adsorption (k(a1)), i rreversible adsorption (k(a2)), desorption (k(d)), and conformational trans formation from reversible state to irreversible one (k(f)), were estimated from the real time responses of the QCM. The rate constants for lysozyme on methyl-terminated hydrophobic SAM(I) interface are k(a1) = (23.1 +/- 4.6) M-1 s(-1), k(a2) = (3.72 +/- 0.49) M-1 s(-1), k(d) = (4.4 +/- 0.6) x 10(-3) s(-1) and k(f) = (7.3 +/- 1.9) x 10(-6) s(-1). The rate constants for lyso zyme on hydrophilic hydroxyl-terminated SAM(LI) interface are k(a1) = (1.96 +/- 3.7) M-1 s(-1), k(a2) = (0.51 +/- 0.09) M-1 s(-1), k(d) = (11.2 +/- 0. 7)10(-3) and k(f) = (4.8 +/- 1.4) x 10(-6) s(-1). The rate constants for ly sozyme on bare gold are k(a1) = (18.7 +/- 5.1) M-1 s(-1) k(a2) = (1.08 +/- 0.13) M-1 s(-1), k(d) = (8.6 +/- 0.5) x 10(-3) s(-1) and k(f) = (9.5 +/- 2. 6) x 10(-6) s. The adsorption densities are in the order of SAM(I) > (Au) > SAM(II). (C) 2001 Elsevier Science B.V. All rights reserved.