Hemoglobin Adsorption to Silica Monitored with Polarization-Dependent Evanescent-Wave Cavity Ring-Down Spectroscopy

Abstract

Evanescent-wave cavity ring-down spectroscopy was used to monitor the adsorption of human hemoglobin to a fused-silica surface from aqueous solution. An uncoated dove prism was situated in a ring-down cavity such that the beam entered and exited with a normal-incidence geometry. This afforded ring-down times as high as 5 mus and values of sigma(tau)/tau as low as 0.3%. Normal-incidence geometry permits the detection of both S- and P-polarized light, yielding some information of the orientation of adsorbates. The orientation of the adsorbed hemoglobin molecules is found to change as adsorption progresses, but with a different time profile than adsorption itself. The adsorption kinetics from a quiescent solution is consistent with a reaction-diffusion model that includes both reversible and irreversible adsorption operating in parallel. Systems behaving according to this model also seem to display adsorption isotherms, although the increased adsorption from more concentrated solutions is only a consequence of the system being under kinetic control. In some cases, this may be sufficient to explain the paradox of protein adsorption systems which seem to be both irreversible and consistent with isotherm models as well.

Liquid-Phase and Evanescent-Wave Cavity Ring-Down Spectroscopy in Analytical Chemistry

“…• during the course of the experiment (14). The initial value is close to the apparent orientation of 54.7…”

“…Baseline noise levels on the order of 0.3 × 10 −4 (17), 0.5 × 10 −4 (89), and 3 × 10 −4 (14) A.U. (all determined with pulsed multimode CRDS) can be achieved, and both polarizations can be used, enabling molecular orientation studies (14,17,89).…”

“…For low coverageup to one-fiftieth of a monolayer-the molecules lie almost flat on the surface, whereas they become more vertically oriented for higher surface coverages. For hemoglobin, investigators have studied both the adsorption from a static solution and the orientation of the adsorbed molecules (14). The orientation of the hemoglobin molecules changes during prolonged adsorption.…”

“…As with liquid-phase CRDS, the development of EW-CRDS has only recently begun. EW-CRDS has shown its potential in various studies of interactions of analytes with bare silica surfaces (8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18). Modification of the TIR surface (19) may become a useful tool for studying (bio)molecular interactions and in label-free biosensing, analogous to, for example, surface plasmon resonance spectroscopy.…”

Cavity ring-down ellipsometry

“…2 More recently, various modification on the cavity ring-down technique have been used for the sensitive measurement of absorption of samples in various media and at interfaces. [3][4][5][6][7][8][9][10][11] In particular, Pipino, 12,13 Li and Zare, 14 and Everest et al 15 used polarized light and evanescent-wave cavity ring-down spectroscopy for absorption measurements of s and p polarized light for various samples, for the determination of tan ⌿. Jacob et al 16 used the cavity ring-down technique to determine ellipsometric properties of dielectric mirrors, but did not apply their method to the ellipsometric measurement of samples.…”