**6. Conclusion**

*Materials at the Nanoscale*

occurred in pHs from 9 to 11, respectively [94].

However, of the five magnetite-interacting peptides identified in that study, three had arginine as half the residues in the sequence. The cationic poly-arginine was used as an additive to the iron precipitation. The resulting nanoparticles possessed a fine size distribution (30-40 nm), reproducible – despite irregular – morphologies and colloidal stability. These characteristics were not achieved in the control of conventional precipitation. Poly-arginine also improves the tuneability of the biomimetic synthesis. In the presence of the additive, the average diameters of the magnetite precipitates could be adjusted from 10 to 40 nm when the reaction

As polyaminoacids, single aminoacids can promote control over magnetic nanoparticle syntheses [85]. When arginine and lysine were tested for that purpose, the latter was able to control the particle size according to its concentration (**Table 2**) [85]. The side-chain amino group in lysine can perform a steadier stabilization of the anionic oxyhydroxide precursor of magnetite. Then, further growth of lysine-stabilized nuclei enables a larger crystal size with a better-defined hexahedral shape. The control over size and shape also reflects in the magnetic properties of the nanomaterial. The obtained nanoparticles displayed a superparamagnetic behavior,

with a large magnetic moment and magnetization saturation (67 emu/g).

synthesis, but the colloidal stability of bioinspired nanomagnets is generally

stability obtained in biomimetic nanoparticles is a fundamental property.

The knowledge gained from biomimetic approaches was used to construct a double-stimuli-responsive nanoformulation consisting of a nanomagnet bound to the antiproliferative drug oxaliplatin [95]. The nanocrystal was synthesized by co-precipitation of iron ions in the presence of recombinant MamC. The magnetiteoxaliplatin bond was stable at pH 7.2. In acidic pH, the release of oxaliplatin was triggered. This release was further boosted by the application of an alternating magnetic field and the cytotoxicity against colorectal cancer cells was improved [95]. The responsive to alternating magnetic fields also enables MamC-derived magnetic nanoparticles to be used in hyperthermia treatments [96]. A 25 mg/mL suspension of the biomimetic nanoparticles exposed to an alternating field of 226 Oe at a 280 kHz frequency can cause a temperature increase of 16.7 °C (specific

Another functional magnetic nanoparticle was coprecipitated in the presence of a bifunctional polypeptide and ginger extract [87]. The fourteen-residue-long polypeptide was designed from two heptapeptides: a magnetite binding domain and a cell-targeting domain with specificity to ovarian carcinoma cells. The metalreducing and chelating activity of the ginger extract leads to nanoparticles averaging 10 nm in length and 48.9 emu/g of magnetization saturation. When different cell lines – A2780 (ovarian carcinoma) and L929 (mouse fibroblast) – were treated with the functional nanoparticle, the first group exhibited a particle uptake almost

Not only is the size dispersity and morphology better controlled in biomimetic

improved. The magnetic core of bare nanomagnets exerts an attractive force, possibly leading to instability to the colloidal suspension [78, 85]. When peptides are added to the precipitation media, functional groups of the same charge become exposed on the nanoparticle surface and counterbalance the attractive force with electrostatic repulsion [78, 85]. Due to the interaction of cationic amino groups with magnetite, carboxyl groups become exposed during coprecipitation with lysine [85]. Thus, the zeta-potential of those nanoparticles was -31 mV at physiological pH, while the control nanoparticles showed a 0 value. The synthesis of magnetite supplemented with poly-aspartate led to nanoparticles with surface-exposed carboxyl groups [78]. Therefore, the measured zeta potential was approximately -30 mV. Because suspension stability in aqueous media is crucial for biomedical applications, the colloidal

**30**

absorption rate = 47 W/g).

5 times more intense.

In this chapter, we have summarized how the basic-science knowledge gained through molecular biology, phylogenetics, and metagenomics of MTB can be translated into tools of technological interest. Although the authors had not the pretentiousness of gathering extensive information available on the topic, the chapter evidences how cross-disciplinary research is crucial for understanding and applying such a complex biological phenomenon. This is especially true in a field in which intriguing discoveries are made at a fast pace.
