Multiscale Visualization and Quantitative Analysis of l -Cystine Crystal Dissolution

There is considerable interest in the growth and dissolution of the hexagonal form of l-cystine crystals, not in the least because l-cystine kidney stones - aggregates of single crystals of l-cystine - are a consequence of the genetic disorder cystinuria. While recent investigations have revealed the growth mechanism and kinetics of l-cystine crystals at the molecular level, the dissolution process has not yet been considered. Dissolution involves coupled surface and diffusion processes at different crystal faces exposed to solution, presenting a significant challenge for quantitative physicochemical measurements. The multimicroscopy approach herein uses a range of complementary in situ microscopy techniques - atomic force microscopy (AFM), scanning ion conductance microscopy (SICM), and optical microscopy - combined with finite element method (FEM) analysis, to reveal the mechanism of face-specific dissolution and the associated kinetics. Dissolution from the {0001} face involves the formation of funnel-shaped hexagonal pits, centered at single screw dislocation cores, but the handedness of the dissolution spirals is opposite to that found for steps in growth spirals. Significantly, step velocities measured by AFM quantitatively scale up to capture the overall dissolution kinetics of this face, and the measurements further serve as a roadmap for the quantitative analysis of single crystal dissolution and growth.