nanomaterials Review Plasma and Nanomaterials: Fabrication and Biomedical Applications Nagendra Kumar Kaushik 1,* , Neha Kaushik 2, Nguyen Nhat Linh 1 , Bhagirath Ghimire 1 , Anchalee Pengkit 1, Jirapong Sornsakdanuphap 1, Su-Jae Lee 2,* and Eun Ha Choi 1,* 1 Plasma Bioscience Research Center, Applied Plasma Medicine Center, Department of Electrical and Biological Physics, Kwangwoon University, Seoul 01897, Korea; [email protected] (N.N.L.); [email protected] (B.G.); [email protected] (A.P.); [email protected] (J.S.) 2 Department of Life Science, Hanyang University, Seoul 04763, Korea; [email protected] * Correspondence: [email protected] (N.K.K.); [email protected] (S.-J.L.); [email protected] (E.H.C.) Received: 17 December 2018; Accepted: 8 January 2019; Published: 14 January 2019 Abstract: Application of plasma medicine has been actively explored during last several years. Treating every type of cancer remains a difficult task for medical personnel due to the wide variety of cancer cell selectivity. Research in advanced plasma physics has led to the development of different types of non-thermal plasma devices, such as plasma jets, and dielectric barrier discharges. Non-thermal plasma generates many charged particles and reactive species when brought into contact with biological samples. The main constituents include reactive nitrogen species, reactive oxygen species, and plasma ultra-violets. These species can be applied to synthesize biologically important nanomaterials or can be used with nanomaterials for various kinds of biomedical applications to improve human health. This review reports recent updates on plasma-based synthesis of biologically important nanomaterials and synergy of plasma with nanomaterials for various kind of biological applications. Keywords: plasma; nanomaterials; nanomaterial synthesis; plasma liquid Interactions; non-thermal plasma; biomedical applications 1. Introduction In recent years, nanomaterials have received great attention due to their exclusive characteristics compared to their bulk counterparts. With extremely small size and high surface area, nanomaterials demonstrate great biological activities in the human body. Nanomaterials play crucial roles in biomedicine, with a wide range of applications such as drug delivery, cancer therapy or bioimaging. Nevertheless, our current understanding of nanomaterials’ behaviors in human health is still inadequate. Previous reports have claimed that nanomaterials could induce dangerous effects in living organisms. A reasonable explanation for this concern is that conventional chemical approaches for nanomaterial synthesis require toxic oxidants or reductants, which are essential for nanoparticle formation and stabilization. Therefore, an alternative toxic-chemical-free synthesis is important for nanotechnology development for biomedical applications. Currently, plasma technology is gaining great attention as a prominent “green” synthesis method for nanomaterials, due to its distinguishing properties when compared to solid, liquid and gas phase synthesis approaches. Furthermore, the combination of nanomaterials and plasma in biomedical applications demonstrates several synergistic effects and better treatment efficiency. A schematic diagram showing the synergistic relationship among plasmas, nanomaterials and their biomedical applications is shown in Figure1. The use of plasmas for biomedical applications has been explored in various ways in the last few Nanomaterials 2019, 9, 98; doi:10.3390/nano9010098 www.mdpi.com/journal/nanomaterials NanomaterialsNanomaterials2019 2019, 9, ,9 98, x FOR PEER REVIEW 22 of of 19 20 in various ways in the last few decades and have shown promising effects. The uses of decadesnanomaterials and have in shownbiomedical promising applications effects. are The also uses well of nanomaterials known. Recently, in biomedical synergistic applications effects of arenanomaterials also well known. and cold Recently, plasmas synergistic in biomedical effects applications of nanomaterials have been and colddiscovered. plasmas In in this biomedical article, a applicationsreview on the have relationship been discovered. between In plasma this article, and ananomaterials review on the is relationship presented. A between brief description plasma and of nanomaterialsnon‐thermal atmospheric is presented. pressure A brief plasmas description is included of non-thermal in Section atmospheric 2. In Section pressure 3, the synthesis plasmas isof includednanomaterials in Section using2. In different Section 3types, the synthesis of plasma of is nanomaterials summarized. using Section different 4 focuses types on of plasmathe current is summarized.advances related Section to 4the focuses synergistic on the effects current of advances plasma and related nanomaterials to the synergistic in biomedical effects of applications. plasma and nanomaterials in biomedical applications. FigureFigure 1. 1.The The synergistic synergistic relationship relationship among plasmas,among plasmas, nanomaterials nanomaterials and their biomedical and their applications. biomedical applications. 2. Overview of Non-Thermal Atmospheric Pressure Plasmas and Their Characteristics 2. Overview of Non‐Thermal Atmospheric Pressure Plasmas and Their Characteristics Physical plasmas are ionized gases which generally contain electrons, ions, neutrals, excited species,Physical electric plasmas field, reactive are ionized species, gases UV photons,which generally etc. They contain exist naturally electrons, in theions, universe neutrals, or canexcited be generatedspecies, electric within field, the laboratory reactive species, environment UV photons, in the earth. etc. They Production exist naturally of plasma in within the universe the laboratories or can be cangenerated be performed within through the laboratory dissociation environment of gas molecules in the with earth. electrical Production energy confinedof plasma between within two the electrodes.laboratories This can type be performed of plasma through can be produced dissociation at low of gas pressure, molecules as well with as electrical at atmospheric energy pressure. confined Plasmasbetween at two low pressureselectrodes. (such This as type inductively of plasma coupled can plasmas,be produced plasma at torches)low pressure, are generated as well inside as at vacuumatmospheric chambers pressure. and arePlasmas much suitableat low pressures for the uniform (such treatmentas inductively of objects. coupled They plasmas, are also plasma called thermaltorches) or are quasi-equilibrium generated inside low-temperature vacuum chambers plasmas, and are as themuch temperatures suitable for of the light uniform and heavy treatment species of areobjects. almost They the same.are also At called atmospheric thermal pressures, or quasi plasmas‐equilibrium (such low as‐ atmospherictemperature pressureplasmas, plasma as the jettemperatures discharges, of dielectric light and barrier heavy discharges species are (DBD)) almost could the same. be generated At atmospheric by ionizing pressures, a gas between plasmas two(such narrow as atmospheric electrodes pressure at ambient plasma environment jet discharges, and no dielectric expensive barrier vacuum discharges equipment (DBD)) is required. could be Atmosphericgenerated by pressure ionizing plasmas a gas are between also called two non-thermal narrow electrodes or non-equilibrium at ambient plasmas, environment as the electronand no temperatureexpensive vacuum is much higherequipment than ionsis required. or gas species Atmospheric and the temperaturepressure plasmas of gas speciesare also remains called closenon‐thermal to room or temperature. non‐equilibrium Both plasmas, thermal and as the non-thermal electron temperature plasmas can is bemuch used higher for the than synthesis ions or ofgas nanomaterials. species and the temperature of gas species remains close to room temperature. Both thermal and non‐thermal plasmas can be used for the synthesis of nanomaterials. 2.1. Non-Thermal Atmospheric Pressure Plasma Sources 2.1. Non-thermalNon‐Thermal Atmospheric atmospheric Pressure pressure Plasma plasmas Sources generated at atmospheric conditions can be utilized for theNon synthesis‐thermal of nanomaterials.atmospheric pressure Several typesplasmas of plasma generated devices, at atmospheric such as DBD conditions plasma or plasmacan be jet,utilized can be for used the synthesis for combinational of nanomaterials. treatments Several with types nanomaterials of plasma [ 1devices,]. The discharge such as DBD generated plasma in or plasma jet, can be used for combinational treatments with nanomaterials [1]. The discharge Nanomaterials 2019, 9, 98 3 of 19 Nanomaterials 2019, 9, x FOR PEER REVIEW 3 of 20 generatedthe ambient in the environment ambient environment can be used forcan the be modificationused for the modification of the surface of properties the surface of properties the materials of thethrough materials electrons, through ions, electrons, excited ions, species, excited reactive species, species, reactive UVs, species, etc., generated UVs, etc., through generated the through plasma. theAn plasma. overview An of non-thermaloverview of atmosphericnon‐thermal pressure atmospheric plasma pressure sources plasma and the sources reactive and species the generated reactive speciesby them generated is presented by them in this is section.presented in this section. 2.1.1.2.1.1. Dielectric Dielectric Barrier Barrier Discharge Discharge