Biological materials are often based on simple constituents and grown by the principle of self-assembly under ambient conditions. In particular, biomineralization approaches exploit efficient pathways of inorganic material synthesis. There is still a large gap between the complexity of natural systems and the practical utilization of bioinspired formation mechanisms. Here we describe a simple self-assembly route leading to a CaCO₃ microlens array, somewhat reminiscent of the brittlestars' microlenses, with uniform size and focal length, by using a minimum number of components and equipment at ambient conditions. The formation mechanism of the amorphous CaCO₃ microlens arrays was elucidated by confocal Raman spectroscopic imaging to be a two-step growth process mediated by the organic surfactant. CaCO₃ microlens arrays are easy to fabricate, biocompatible and functional in amorphous or more stable crystalline forms. This shows that advanced optical materials can be generated by a simple mineral precipitation.

Haematococcus pluvialis, in the dormant aplanospore (cyst) status after 30 d of cultivation, accumulates high levels of a superpotent antioxidant, astaxanthin, which has been demonstrated to have enormous therapeutic benefits. However, owing to the robust structure of its trilayered cell wall, the recovery of astaxanthin from the cyst cells remains an energy-intensive process. In the present study, a novel strategy utilizing a short-period germination based on the natural life cycle of H. pluvialis was developed as an energy-efficient pretreatment for the extraction of astaxanthin using ionic liquids (ILs) as green solvents. The germination resulted in damage and deconstruction of the cyst cell wall, and thereby facilitated the extraction of astaxanthin by ILs at room temperature. By this natural pretreatment with 1-ethyl-3-methylimidazolium ethylsulfate for a very short reaction time of 1 min, a high astaxanthin yield of 19.5 pg per cell was obtained, which was about 82% of a conventional volatile organic solvent extraction by strong, 30 000 psi French-pressure-cell homogenization. The maximal astaxanthin-extraction yield from H. pluvialis cells was observed for 12–18 h germination. The germination rate furthermore could be improved by manipulating the nutritional composition (especially the nitrate concentration) of the culture medium. In light of these results, it can be posited that natural germination following the principles of green chemistry can be a uniquely simple method of robust microalgal cyst cell pretreatment and extraction of astaxanthin with room-temperature ILs.

The functionalization of cationic surfactants on Fe ₃ O ₄ nanoparticles serves two roles at the same time: microalgae harvesting and cell disruption for lipid extraction.