Biogenic Silver Nanoparticles Capped with Proteins: Timed Knowledge and Perspectives

Biogenic silver nanoparticles are synthesized through silver(I) reduction, which is promoted by biomolecules available in the biological world and mostly obtained from plant extracts, fungal bioproduction, and some bacteria. The exact mechanisms accounting for such oxidoreduction processes are not fully known. However, some studies have already mentioned oxidoreductases, cofactors (nicotinamide adenine dinucelotide hydrogen (NADH), dihydroflavine-adenine dinucleotid (FADH2)), and phenolic compounds, as the main reductive species engaged in the formation of silver(0) and silver nanoparticles (silver NPs) synthesis. Biosynthesis is a one-pot process that leads to stable silver NP colloids that, regarding their size, shape, and uniformity, can be successfully controlled; and show great stability when one takes into account their surface capping by some biomolecules that as well take part in their synthesis. Although great efforts have been made to feature capping biomolecules and their interactions with silver NP surfaces, knowledge of the quantity (exact number per cm2) and type of biomolecules that cap or surround silver NPs remains limited. The literature provides detailed information on protein capping, but it still shows gaps regarding many aspects of fine biophysical protein featuring. The reason why certain proteins prefer to interact with silver NP surface and form chemical bonds, whereas others rather have intermolecular interaction with the first layer of proteins remains unknown. Assessing capping proteins’ involvement in the bioactivity of biogenic silver NPs is another relevant research field. Certain proteins enhance bioactivity of silver NPs and lower toxicity; however, the way antimicrobial processes benefit from protein capping is yet to be discovered. Finally, biogenic silver NPs can be found both in the environment and in water; moreover, their additional activity and behavior must be known or, at least, hypothesized.

生物源银纳米颗粒（Biogenic Silver Nanoparticles）通过银(I)还原反应合成，该反应由生物界中存在的生物分子所促进，其制备原料大多提取自植物提取物、真菌生物制备产物以及部分细菌。阐明这类氧化还原反应的具体机制目前尚未完全明晰。不过已有多项研究指出，氧化还原酶、辅酶（烟酰胺腺嘌呤二核苷酸氢（NADH）、二氢黄素腺嘌呤二核苷酸（FADH2））以及酚类化合物，是参与零价银形成与银纳米颗粒（Silver NPs）合成的主要还原物质。生物合成是一种一锅法工艺，可制备得到稳定的银纳米颗粒胶体；其粒径、形貌与均匀性均可得到有效调控，且由于部分参与合成过程的生物分子对其表面进行了包覆，该胶体展现出优异的稳定性。尽管学界已针对包覆型生物分子及其与银纳米颗粒表面的相互作用开展了大量研究，但关于包覆或附着于银纳米颗粒表面的生物分子的数量（每平方厘米的精确数目）与种类，目前的认知仍较为有限。现有文献虽对蛋白质包覆情况已有详细记载，但在蛋白质精细生物物理表征的诸多方面仍存在研究空白。为何部分蛋白质倾向于与银纳米颗粒表面结合并形成化学键，而其余蛋白质仅与第一层包覆蛋白发生分子间相互作用，其背后的原因目前仍不明确。评估包覆蛋白在生物源银纳米颗粒生物活性中的作用，是另一个重要的研究方向。部分蛋白质可提升银纳米颗粒的生物活性并降低其毒性，但蛋白质包覆如何助力抗菌过程的机制仍有待阐明。最后，生物源银纳米颗粒广泛存在于环境与水体之中；此外，其额外的活性与行为模式，要么需要被明确认知，要么至少需要得到合理的假说阐释。