(510d) Biogenic Metallic Nanoparticles. from Microbiological Biofactories to Nanometric Trojan Horses

Biogenic
metallic nanoparticles. From microbiological biofactories to nanometric trojan
horses.

Antimicrobial resistance
to antibiotics (AMR) and cancer and two of the main concerns that the
healthcare system should face nowadays. Current drugs and antibiotic treatments
are becoming ineffective or have plenty of drawbacks related to misuse and
overuse. Therefore, new alternatives are needed, and nanotechnology is rising
as a powerful solution over time. How the nanomaterials are created has plenty of
influence in their features and applications. Traditional synthesis of
nanomaterials, taking knowledge from both physics and chemistry, is subjected
to several disadvantages, such as the production of toxic-by-products and harsh
conditions, as well as biocompatibility issues. Green nanotechnology is
presented as a suitable answer, allowing the generation of nanostructures in a
cost-effective and environmentally-friendly approach employing living
organisms, such as bacteria, and biomolecules.

In this research,
pathogenic bacteria (both antibiotic-resistant and standard strains of
Gram-negative -such as Escherichia coli- and Gram-positive -such as
Staphylococcus aureus-) and human cells (both cancerous -such as human melanoma
and glioblastoma cells, and healthy cell lines, such as astrocytes of
fibroblasts-) were used for the synthesis of different metallic -gold (Au),
palladium (Pd), platinum (Pt), gold-palladium (AuPd) and gold-platinum (AuPt)-
and metalloid -selenium (Se)- nanoparticles with sizes between 5 and 120 nm
surrounding by an organic-derived coating. Bacteria and human cells were
cultured in the presence of metallic salts under standard conditions, allowing
the generation of nanoparticles through natural detoxification processes in a
synthetic protocol that is followed using microscopy and spectrophotometric
techniques.

After generation, the
entities are purified and extensively characterized in terms of composition,
morphology and surface chemistry, through techniques such as Transmission
electron microscopy (TEM), Scanning electron microscopy (SEM),
Fourier-transform infrared spectroscopy (FTIR), X-Ray Photoelectron
spectroscopy (XPS), X-ray powder diffraction (XRD) and Raman spectroscopy, in
order to elucidate the complex organic-derived coating surrounding the
nanoparticles and the metallic/metalloid core. Nanoparticles were then used as
antimicrobial and anticancer agents, with effects characterized through growth
curve analysis, MTS experiments and colony counting growing assays, not showing
significant cytotoxicity towards healthy human cells. To understand the
mechanisms or action, Reactive Oxygen Species (ROS) analysis was accomplished
as well.

The extensive
characterization of the nanoparticles showed the presence of organic molecules
-such as proteins and lipids- coming from the living organisms, with selenium
nanoparticles with sized between 50 and 120 nm. Bacterial tests showed an
unusual selective behavior in the antimicrobial effect of bacteria-mediated
nanoparticles, indicating a dose-dependent inhibition when a bacterial strain X
was treated with nanoparticles made by the same bacteria, while poor inhibition
was found when different bacteria were used as a target. The nanoparticles
showed a robust anticancer effect towards human melanoma and glioblastoma cells
while remaining biocompatible towards the healthy cell lines. 

On the other hand, noble mono- and bimetallic nanoparticles synthesized by
human cells, with sized between 5 and 20 nm, were able to inhibit the growth of
cell lines in a similar way that nanoparticles made by bacteria showed, with a
certain degree of selectivity, remaining biocompatible. Besides, the production
of nanomaterials induced a transition of the cells into a named zombie stage''
or suspension toward the cells was not responding to chemical, physical or
temporal degradation.

Interestingly, we
observed that when the human cells were subjected to synthesis of
nanoparticles, they were able to show a “petrification” process that allowed
them to resist extreme environmental conditions, like starvation for several
weeks, extreme high and low pH, heat, frozen and so on. Therefore, it was
observed that the production of nanoparticles allow
the cells to become extremely resistant to the environment. Besides, a study of
how to stop the proliferation of cancerous cells was started, with the
production of nanoparticles inducing inhibition of the proliferation of the
cells in tissue models.

Therefore, we
demonstrated that microbiological agents are successfully used as a synthetic
machine for the generation of different metallic/metalloid nanoparticles of
different compositions with biomedical properties. Therefore, they are
presented as a suitable approach for the synthesis of nanomaterials in a green
fashion, overcoming the limitations of traditional nanotechnology, and opening
a new field for drug delivery and smart targeting of cancer and
antibiotic-resistant infections.

Figure 1. Selenium
nanoparticles synthesized by MDR Escherichia
coli (A, B) and cancerous cells (melanoma) syntehsized bimetallic
gold/palladium nanoparticles (C, D).