During the last couple of decades, the rapidly advancing field of nanotechnology has produced a wide palette of nanomaterials, most of which are considered as “synthetic” and, among the wider public, are often met with a certain suspicion. Despite the technological sophistication behind many of these materials, “nano” does not always equate with “artificial”. Indeed, nature itself is an excellent nanotechnologist. It provides us with a range of fine particles, from inorganic ash, soot, sulfur and mineral particles found in the air or in wells, to sulfur and selenium nanoparticles produced by many bacteria and yeasts. These nanomaterials are entirely natural, and, not surprisingly, there is a growing interest in the development of natural nanoproducts, for instance in the emerging fields of phyto- and phyco-nanotechnology. This review will highlight some of the most recent—and sometimes unexpected—advances in this exciting and diverse field of research and development. Naturally occurring nanomaterials, artificially produced nanomaterials of natural products as well as naturally occurring or produced nanomaterials of natural products all show their own, particular chemical and physical properties, biological activities and promise for applications, especially in the fields of medicine, nutrition, cosmetics and agriculture. In the future, such natural nanoparticles will not only stimulate research and add a greener outlook to a traditionally high-tech field, they will also provide solutions—pardon—suspensions for a range of problems. Here, we may anticipate specific biogenic factories, valuable new materials based on waste, the effective removal of contaminants as part of nano-bioremediation, and the conversion of poorly soluble substances and materials to biologically available forms for practical uses.

Allicin (diallylthiosulfinate) is the principal organosulfur compound present in freshly damaged garlic tissue which exhibits a wide range of biological actions including antibacterial, antifungal, antiviral and anticancer properties. The antifungal activities of allicin were investigated against plant pathogenic fungi of agriculture importance. Furthermore, a yeast genome haploinsufficiency screening was also employed to decipher the antifungal mode of action of allicin. Wildtype and 1152 yeast mutant strains (each deprived of one specific allele of an essential gene in a diploid strain) were screened against allicin. Allicin exhibited promising antifungal properties against all the tested plant pathogens. Haploinsufficiency screening revealed three hypersensitive yeast mutants with gene deletions coding for proteins involved in DNA replication, mitochondrial translation and chromatids cohesion. These processes play a vital role in the cell cycle, growth and viability of yeast cells. Taken together, the results of the present study unravel the excellent antifungal activities and mechanisms and modes of action of allicin. These findings also indicate the potential use of allicin as an alternative “green” fungicide (fumigant) in agriculture.

Many organic sulfur, selenium and tellurium compounds show considerable activity against microorganisms, including bacteria and fungi. This pronounced activity is often due to the specific, oxidizing redox behavior of the chalcogen-chalcogen bond present in such molecules. Interestingly, similar chalcogen-chalcogen motifs are also found in the elemental forms of these elements, and while those materials are insoluble in aqueous media, it has recently been possible to unlock their biological activities using naturally produced or homogenized suspensions of respective chalcogen nanoparticles. Those suspensions can be employed readily and often effectively against common pathogenic microorganisms, still their practical uses are limited as such suspensions are difficult to transport, store and apply. Using mannitol as stabilizer, it is now possible to lyophilize such suspensions to produce solid forms of the nanoparticles, which upon resuspension in water essentially retain their initial size and exhibit considerable biological activity. The sequence of Nanosizing, Lyophilization and Resuspension (NaLyRe) eventually provides access to a range of lyophilized materials which may be considered as easy-to-handle, ready-to-use and at the same time as bioavailable, active forms of otherwise insoluble or sparingly substances. In the case of elemental sulfur, selenium and tellurium, this approach promises wider practical applications, for instance in the medical or agricultural arena.

Multidrug resistance of cancer cells to cytotoxic drugs still remains a major obstacle to the success of chemotherapy in cancer treatment. The development of new drug candidates which may serve as P-glycoprotein (P-gp) efflux pump inhibitors is a promising strategy. Selenium analogues of natural products, such as flavonoids, offer an interesting motif from the perspective of drug design. Herein, we report the biological evaluation of novel hybrid compounds, bearing both the flavone core (compounds 1–3) or a bioisosteric analogue core (compounds 4–6) and the triflyl functional group against Gram-positive and Gram-negative bacteria, yeasts, nematodes, and human colonic adenocarcinoma cells. Results show that these flavones and analogues of flavones inhibited the activity of multidrug resistance (MDR) efflux pump ABCB1 (P-glycoprotein, P-gp). Moreover, the results of the rhodamine 123 accumulation assay demonstrated a dose-dependent inhibition of the abovementioned efflux pump. Three compounds (4, 5, and 6) exhibited potent inhibitory activity, much stronger than the positive control, verapamil. Thus, these chalcogen bioisosteric analogues of flavones become an interesting class of compounds which could be considered as P-gp efflux pump inhibitors in the therapy of MDR cancer. Moreover, all the compounds served as promising adjuvants in the cancer treatment, since they exhibited the P-gp efflux pump modulating activity.

Cynomorium coccineum L., the desert thumb, is a rather exotic, parasitic plant unable to engage in photosynthesis, yet rich in a variety of unique compounds with a wide spectrum of biological applications. Whilst extraction, separation and isolation of such compounds is time consuming, the particular properties of the plant, such as dryness, hardness and lack of chlorophyll, render it a prime target for possible nanosizing. The entire plant, the external layer (coat) as well as its peel, are readily milled and high pressure homogenized to yield small, mostly uniform spherical particles with diameters in the range of 300 to 600 nm. The best quality of particles is obtained for the processed entire plant. Based on initial screens for biological activity, it seems that these particles are particularly active against the pathogenic fungus Candida albicans, whilst no activity could be observed against the model nematode Steinernema feltiae. This activity is particularly pronounced in the case of the external layer, whilst the peeled part does not seem to inhibit growth of C. albicans. Thanks to the ease of sample preparation, the good quality of the nanosuspension obtained, and the interesting activity of this natural product, nanosized coats of Cynomorium may well provide a lead for future development and applications as “green” materials in the field of medicine, but also environmentally, for instance in agriculture.

Nanosizing represents a straight forward technique to unlock the biological activity of complex plant materials. The aim of this study was to develop herbal nanoparticles with medicinal value from dried leaves and stems of Loranthus micranthus with the aid of ball-milling, high speed stirring, and high-pressure homogenization techniques. The milled nanoparticles were characterized using laser diffraction analysis, photon correlation spectroscopy analysis, and light microscopy. The average size of leaf nanoparticles was around 245 nm and that of stem nanoparticles was around 180 nm. The nanoparticles were tested for their antimicrobial and nematicidal properties against a Gram-negative bacterium Escherichia coli, a Gram-positive bacterium Staphylococcus carnosus, fungi Candida albicans and Saccharomyces cerevisiae, and a nematode Steinernemafeltiae. The results show significant activities for both leaf and (particularly) stem nanoparticles of Loranthus micranthus on all organisms tested, even at a particle concentration as low as 0.01% (w/w). The results observed indicate that nanoparticles (especially of the stem) of Loranthus micranthus could serve as novel antimicrobial agents with wide-ranging biomedical applications.