7. Conclusions

It is observed that E. coli bacteria in the samples treated using metamaterials consisting of quartz unordered granules were completely inactivated. On the other hand, for the samples treated without metamaterials, the bacteria were not completely inhibited (Figure 14C). In this case, some E. coli colonies are still present in the decontaminated liquid. This convincingly demonstrates the key role of quartz metamaterials in liquid decontamination under UV-C irradiation.

Figure 14. Specially prepared E. coli contaminated samples. (M) control sample; (B) sample after static treatment using

quartz unordered granules in the core tube; (C) sample after static treatment without metamaterials.

Static decontamination regime was applied to examine samples of Kombucha tea, Medusomyces gisevii [46]—symbiotic culture of acetic acid—producing bacteria and yeast (Symbiotic Community Of Bacteria and Yeast—SCOBY). They contain one or several species of bacteria and yeast, which form a zoogloeal mat [47], known as "mother" [46]. After a storage period at a temperature higher than 20C for about 3 weeks, a microbial biofilm is appearing onto the surface of the fermented Kombucha tea. It usually has the aspect of a giant oily pellicle. This dense microbial mat is fused together by cellulose produced by bacteria primarily responsible for the glued community. Yeast living in biofilm uses tea sugars to produce alcohol, which is then consumed by neighboring bacteria to produce acetic acid. The yeasts that can form a Kombucha culture are Saccharomyces cerevisiae, Brettanomyces bruxellensis, Candida stellata, Schizosaccharomyces pombe, and Zygosaccharomyces bailli [48]. The bacterial component of Kombucha consists of several species but always includes Gluconacetobacter xylinus (G. xylinus, formerly Acetobacter xylinus). Kombuchafermented tea samples were prepared as follows: sugar (10%) is added to the fresh black tea and then a 1:1 quantity to 1-month-fermented Kombucha tea, which presents already a dense microbial biofilm on the surface. The UV-C irradiation time was set at 5, 7, 9, or 11 min. The core tube of the decontamination equipment was filled out with (1) granular unordered quartz of 1– 5 mm transparent to 254 nm or (2) glass spheres nontransmitting at 254 nm. In the third case, the core tube was kept empty, without metamaterials—the case that models the traditional decontamination method (see Section 3). In Kombucha black tea at room temperature, colonies of bacteria (15 103 CFU/mL) and yeast (7 103 CFU/mL) have been observed [49]. It was also

6.2. Inactivation of Kombucha tea under static treatment regime

192 Advanced Surface Engineering Research

A method of annihilation of pathogens using optical metamaterials consisting of microspheres and fiber optical structures having various geometries is suggested. It is proved that using optical metamaterials, like photonic crystal, we get a substantial gain in the decontamination contact surface during the propagation of the contaminated translucent liquid (by viruses and bacteria) through the space between the microspheres (or optical fibers) of metamaterials. The increase of the surface contact of the UV radiation with contaminated liquid strongly depends on the refractive index of metamaterial, liquid volume, and optical properties of viruses and bacteria. We investigated the possibility to trap the viruses and bacteria using an efficient UV decontamination method.

The advancement of nonlinear models based on UV-C interaction with microorganisms opens novel possibilities for the decontamination and diagnosis of different collective processes, which can occur in viruses, bacteria, or other cellular structures under the action of external UV pulses. The possibility to select the UV radiation, which acts on microorganisms with minimal effects, was studied and presented herewith.

Acknowledgements

projects.

Author details

, Sergiu Bizgan<sup>1</sup>

, Elena Starodub<sup>1</sup>

\*Address all correspondence to: ion.mihailescu@inflpr.ro

Sciences of Moldova, Chisinau, Republic of Moldova

Pharmacy "Nicolae Testemitanu", Chisinau, Moldova

Radiation Physics (INFLPR), Magurele, Ilfov, Romania

applications. COMPEL. 2013;32(5):1596-1608

nian Reports in Physics. 2015;67(4):1602-1607

Nicolae Enaki<sup>1</sup>

Tatiana Pislari<sup>1</sup>

References

917-924

158

This paper was supported by the NATO EAP SFPP 984890, STCU 6140, and 43 NATO/2017

Efficient Microbial Decontamination of Translucent Liquids and Gases Using Optical Metamaterials

, Viorica Tonu1,2, Marina Turcan1

\*

http://dx.doi.org/10.5772/intechopen.80639

, Gianina-Florentina Popescu-Pelin<sup>3</sup>

,

195

,

, Andrei Nistreanu<sup>1</sup>

, Aurelia Profir<sup>1</sup>

1 Quantum Optics and Kinetic Processes Lab, Institute of Applied Physics, Academy of

2 Department of Human Physiology and Biophysics, State University of Medicine and

3 "Laser-Surface-Plasma Interactions" Laboratory, National Institute for Lasers, Plasma and

[1] Zheludev NI, Kivshar YS. From metamaterials to metadevices. Nature Materials. 2012;11:

[2] Iovine R, La Spada L, Vegni L. Nanoparticle device for biomedical and optoelectronics

[3] Liberal I, Engheta N. Near-zero refractive index photonics. Nature Photonics. 2017;11:149-

[4] Bazgan S, Ristoscu C, Negut I, Hapenciuc C, Turcan M, Ciobanu N, et al. Propagation of UV radiation through meta-materials and its application in bio decontamination. Roma-

[5] Enaki N, Profir A, Bazgan S, Paslari T, Ristoscu C, Mihailescu CN, et al. Metamaterials for antimicrobial biofilm applications: Photon-crystals of microspheres and fiber optics for decontamination of liquids and gases. In: Tiwari A, editor. Handbook of Anti-Microbial Coatings. Amsterdam NL, Oxford UK, Cambridge MA USA: Elsevier Inc; 2018. pp. 257-282

Maria Badiceanu3,4, Carmen-Georgeta Ristoscu3 and Ion N. Mihailescu<sup>3</sup>

4 Physics Department, University of Bucharest, Magurele, Ilfov, Romania

The efficient antimicrobial action of the evanescent wave acting around quartz granules in a circulating contaminated translucent liquid when submitted to UV-C irradiation was demonstrated. The treated liquids were polluted water from a natural source, yeast solution, or Kombucha fermented tea, while the radiation was generated by 6 UV-C 30 W lamps. Glass microspheres of 1–3 mm diameter were used in experiments, in comparison with quartz unordered granules.

1. Dynamic treatment regime: The complete annihilation of E. coli and Enterococcus bacteria was observed after 5 min of irradiation; the total elimination of Coliform bacteria was achieved after 10 min of irradiation.

The fermentation of the liquid containing yeast fungi was completely stopped after 15 min UV-C irradiation in the presence of quartz granules. To the contrary, normal fermentation continues after 20 min of irradiation in the absence of optical metamaterials—the case that corresponds to the traditional decontamination method.

2. Static treatment regime: E. coli bacteria were completely inactivated in the presence of quartz granules after 1 min irradiation, while in the absence of the quartz metamaterials, some colonies were still present inside the analyzed liquid. This convincingly demonstrates the key role of the quartz metamaterial in fluid decontamination under UV-C irradiation.

Kombucha-fermented tea microorganisms were completely inactivated after 7 min of treatment using quartz unordered metamaterials. After 7 min of treatment in the presence of glass metamaterials, a thin biofilm may still be observed on the sample surface. Therefore, when using quartz granules, the microorganism inactivation is considerably augmented than in the case of using glass spheres. The biofilm formation on the surface of the liquid after 7 min of treatment becomes visible when using glass spheres, or without metamaterials in the core tube. Mat formation contracted in direct relation with irradiation dose.

One expects a large increase of the observed effects when passing from simple lamps to laser irradiation, that is, from incoherent to coherent light sources. Also, a significant improvement is expected when using optical fibers for evanescent wave generation instead, or in tandem with, quartz granules.

Our results prove that the energy emerging via evanescent waves from multistructures submitted to dynamic irradiation is not in any case lost but efficiently used for antimicrobial action. This can contribute to a positive balance of light propagation through PC and PCF metamaterials in view of using light sources with maximum efficiency.
