Local pH oscillations witness autocatalytic self-organization of biomorphic nanostructures

Abstract

Bottom-up self-assembly of simple molecular compounds is a prime pathway to complex materials with interesting structures and functions. Coupled reaction systems are known to spontaneously produce highly ordered patterns, so far observed in soft matter. Here we show that similar phenomena can occur during silica-carbonate crystallization, the emerging order being preserved. The resulting materials, called silica biomorphs, exhibit non-crystallographic curved morphologies and hierarchical textures, much reminiscent of structural principles found in natural biominerals. We have used a fluorescent chemosensor to probe local conditions during the growth of such self-organized nanostructures. We demonstrate that the pH oscillates in the local microenvironment near the growth front due to chemical coupling, which becomes manifest in the final mineralized architectures as intrinsic banding patterns with the same periodicity. A better understanding of dynamic autocatalytic crystallization processes in such simple model systems is key to the rational development of advanced materials and to unravel the mechanisms of biomineralization.

Authigenesis of biomorphic apatite particles from Benguela upwelling zone sediments off Namibia: The role of organic matter in sedimentary apatite nucleation and growth

“…The outer layers of the rod‐shaped particles appear wider, possibly due to a geometric effect of the cross‐sections cutting through the ellipsoidal rod‐shaped particles at different distances with respect to their centre ( e.g ., Cosmidis et al., ). Similar nanometre scale autocatalytic self‐organization of the precipitates, due to oscillations in the local microenvironment, is known in silica‐carbonate biomorphs ( e.g ., Nakouzi, Ghoussoub, Knoll, & Steinbock, ), and can result in the formation of intrinsic mineralized banding patterns with the same periodicity (Montalti et al., ). Therefore, such layering observed in rod‐shaped apatite particles could be the result of alternating levels of phosphate input, in turn, a result of intermittent microbial phosphate pumping by polyphosphate‐accumulating bacteria (Jones, Flood, & Bailey, ; Schulz & Schulz, ).…”

Inorganic Reactions Self‐organize Life‐like Microstructures Far from Equilibrium

“…Most of the planar structures start from a globule on the reactor substrate and then grow on that surface radially outwards at speeds of a fraction of to a few micrometers per minute (Figure a) ,. These sheets can be surprisingly circular, but typically experience disruptions of the growth front.…”

“…also measured elemental maps using EDX spectroscopy which showed spatial bands in the Ba : Si ratio, although similar measurements by Nakouzi et al. revealed no compositional changes ,…”

On the biogenicity of Fe‐oxyhydroxide filaments in silicified low‐temperature hydrothermal deposits: Implications for the identification of Fe‐oxidizing bacteria in the rock record

“…Some of the bands that are located at the termination of the branching features appear to be completely devoid of Fe. Banded, self-assembled biomorphs have been generated experimentally by autocatalytic co-precipitation of silica and carbonate under locally fluctuating pH conditions (Montalti et al, 2017), and oscillating reaction chemistry is known to produce banded features in natural settings as well (e.g., Liesegang rings; Ortoleva, Chen, & Chen, 1994). Abiotic, non-equilibrium processes have previously been invoked to explain the growth of dendritic iron oxide moss agates produced by oxidizing, silica-rich fluids percolating through hydrothermal sulfide debris (Hopkinson et al, 1998), and manganese dendrites are regarded as products of diffusion-limited reaction processes (e.g., Chopard, Herrmann, & Vicsek, 1991).…”