Enormous progress in nanomaterial research has been achieved to prepare nano-level material having supportive properties such as improved electrical conductivity, toughness and ductility, and the higher hardness number. It is well known that the Nano-sized particle is restricted under the law of quantum theory and lies between below 100 nm and higher than the diameter of an atom [1,2]. In this recent year, researchers are focusing on synthesizing Erbium nanoparticles among many rare metal Nano-materials, because they find one of the rare earth metals which acts as a sensing component and amplifier in the biomedical field and optical devices respectively [3,4] and therefore the popularity of rare earth metal nanoparticles has increased. Since the property (electrical and optical, etc.,) of ETO-NP (or rare earth nano-sized metal particles) differs from the distribution of Erbium particles in micro dimensions. These unique properties support ETO-NPs (or rare earth nano-sized metal particles) to gain various applications such as Nano-sized particle coating in paints which act as corrosion to an environmental factor, optical probe Scanning thermometry [5] Nano thermometers [6] cancer-targeted or tumor NIR imaging, to cure cancer cell line against breast cancer, brain cancer and ovarian cancer, antibacterial assay [7-12] and drug delivery system [13], etc. Also, studies show that ETO-NP can degrade Rhodamine Dye from the contaminated water containing Rhodamine Dye [14,15]. Further studies revealed that the incorporation of Erbium oxide doped nanoparticles on the glass or plastic resulted in an application of creating display monitors. Due to the large bandgap and dielectric constant (10-14) values, erbium oxide is used as a gate logic device in semiconductors [16]. The most unique properties of rare earth nano-sized metal particles arise due to the transition of electrons within the 4f-shell which permits them to act as luminescent materials. To synthesize ETO-NPs (or rare earth nano-sized metal particles) in the form of powder, a cluster of techniques such as co-precipitation, hydrothermal, and laser ablation, further extra care must be (maintaining sufficient temperature and careful preparation of the sample without the inclusion of dust particles) employed worldwide. Fabrication of nano-sized rare earth metal, either containing dopants or major components, opens the paths for new advancement in medicinal or biological fields. The supportive luminescent property permits that the rare earth metal nanoparticle functionalized with dyes or quantum dots, generally used for luminescent imaging of biomolecules or DNA or proteins in the medicinal field [17,18] which provides high photo-stability or more selectivity (sharp luminescence band) in the place of other than rare earth metal nanoparticles. The physicochemical properties of rare earth Nano-sized metal particles are strongly influenced by the core parameters such as uniform size distribution, shape, surface morphology, and compositions. The biological applications of rare earth Nano-sized metal particles lack, when it is prepared or fabricated by solid-state synthesis, for this reason, the wet chemical approach has been maintained by researchers or engineers. The careful synthesis process of rare earth nano-sized metal particles allows the formation of lesser and uniform sized NPs, otherwise irregular particle size or distribution may occur, as a result of the lesser application in the medicinal field. In the chemical synthesis of rare earth Nano-sized metal particles, an appropriate amount of precursors (capping and reducing agents) has been used to obtain Nano-sized particles with homogeneous distributions. Since the precursor releases anions during decomposition, they are responsible for the reduction of rare earth Nano-sized metal particles. Some complex components may occur during decomposition, which can be liberated on heating in a controlled process. The reaction kinetics has been optimized experimentally through the proper maintenance of solvent composition, supportive temperature, and reagent concentrations [19]. Therefore, to prepare rare earth Nanosized metal particles, extra care must be taken. The present research provides a simple and effective micro-oven technique to prepare ETO-NPs, further characterized and antimicrobial studies performed. In common, the metal or rare earth metal oxide or doped nanoparticles are used to cure cancer cell lines [20-22]. It seems, for the first time, the effective anticancer activity has been achieved using ETO-NPs in this research.

Synthesis of ETO-Nps Using Microwave Method

The Microwave irradiation Technique was employed to synthesize ETO-NPs. All reactants were purchased from Sigma Aldrich. The precursors used were 1g of Erbium (III) nitrate pentahydrate and 2 g Urea are added in 50 ml of distilled water along with AR grade Er₂O₃ and mixed well; these powders are converted to disk-shaped pellets with the help of a hydraulic handheld and then this pallet sample was kept at 800ºC for a half-hour in a microwave generating furnace. This heating process on the pellet sample which contains Er₂O₃ allows for the reduction of ETO-NPs. After half an hour of the heating process, the pellet sample (containing ETO-NPs) has been burnout to finish the process.

Characterization Techniques

Characterizing the synthesized ETO-NP is very important to reveal many aspects such as bandgap energy, functional groups of the sample and size, 2-dimensional shape, and crystalline nature of the sample. Characterization has been achieved using many techniques such as UV-Vis, XRD, FTIR, and TEM [23-25]. Among them SEM instrument controls the movement of a beam of an electron to strike the sample at the nano-scale level, further, it collects scattered electron and characteristic x rays spectra of the sample to reveal morphology information. Except for SEM instrument, other analytical spectroscopy instrument uses beam Electromagnetic radiation to find out the various aspects of the sample such as functional group, bandgap energy, and morphology, etc.,

Antimicrobial Studies

The toxic activities of ETO-NPs against the DNA destruction of chosen bacteria and fungus are studied using the disk diffusion technique [26,27]. The concentrations of ETO-NPs powder such as 100, 200, and 300 mg are tested against microbial pathogens, further; the observed result was tabulated to reveal the effective toxic activity of synthesized ETO-NPs.

Cytotoxicity and MTT Assays

The cytotoxic effects of ETO-NPs were quantified with colorimetric assay by using the MTT method [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide]. In this section cytotoxicity of ETO-NPs at different concentrations (5, 10, 20, 25, and 50 μg/ml) and further at different periods of incubation (24 and 48 h) were tested 1.5×10³ MDA-MB- 231 cells per well in 96 wells plates were kept and incubated at 37 μC/ with the presence of 5% CO2. After 48 hour period of incubation, 20 μl of MTT solution (5 mg ml−1 in PBS) was added to each well and maintained without light radiation for a period of 4 h and have 100 μl of DMSO mixed formazan crystals (insoluble in water). The cytotoxicity of ETO-NPs against cancer-producing cells was noted with the help of absorbance of 590 nm wavelength of radiation using an ELISA reader (Tecan, Austria). The untreated (without ETO-NPs) medium having 0.1% vehicle DMSO acted as the negative control. The ant proliferative activity of ETO-NPs was expressed in terms of IC50 values and this concentration and causes a 50% inhibition of cell growth.

XRD

With the help of XRD analytical technique, XRD spectrum has been obtained which is useful for the analysis of nano-crystalline structures, qualitative identification and particle sizes of ETO-NPs as well as inorganic catalysts, superconducting materials, bio-based molecules, ceramic glasses, and polymers, etc [28]. In a powdered sample containing ETO-NPs, the beam of x-ray radiation typically diffraction peaks agree well with the phase structure of ETO-NPs. The XRD spectrum (Figure 1) of the ETO-NPs confirmed that the crystalline nature of the ETO-NP belongs to a body-centered cubic structure which was well matched with the standard JCPDS No. 77-0777. The average crystallite size of ETO-NP is calculated as 62 nm by using Debye - Scherer’s formula.

Figure 1: The XRD pattern of ETO-NPs (This graph predicts the existence of miller indices of ETO-NP crystalline powder containing all possible lattice planes).

Transmission Electron Microscopy

The tunneling of electrons through the potential barrier of ETO-NP provides the topography (quantitative analysis of particle and size and 2-dimensional shapes [29,30].) information of the sample powder. It is evident from the TEM image (Figure 2) that the ETO-NPs are non-uniform in size and shape in the range from 60 to 66 nm, further crystalline nature of the ETO-NPs, confirmed with the help of the SAED pattern.

Figure 2: TEM images of ETO-NPs with different magnifications.

EDX

The Energy dispersive X-ray analysis (EDX) spectrum allows the quantitative analysis of major elements present in the synthesized sample. (Figure 3) shows the EDAX spectrum of samples containing ETO-NPs, in this spectrum, stoichiometric concentration of Erbium (Er) and oxygen (O) absorption was strongly observed at (1.5 and 7 KeV) and (0.5 KeV) respectively. Additionally, the Er element reveals a uniform distribution among the other elements, predicting that the Erbium element is homogeneously incorporated into ETO- NPs.

Figure 3: The EDAX pattern of ETO-NPs.

FTIR Analysis of ETO-Nps

FTIR spectrum of ETO-NP is shown in (Figure 4). The vibrational broadband at the point of 3424 cm^-1 and 2976 cm^-1 are due to OH stretching or vibrations of water molecules. The band that can be observed at 1647 cm^-1 is due to Amide (C=N stretching of open chain compound) or NH2 (helical structure) of Urea compound. 1593 cm^-1 is related to CO stretching vibration and 1459 cm^-1 is related to bending mode of CH2/ CH3 or symmetrical deformation of N=O. This peak at 1311 cm^-1 indicated the stretching of the C=O group arises due to the urea compound [31] which was added during the synthesis process. The fingerprint region of core element Erbium shows the absorption at 563 cm^-1and 471 cm^-1 with groups Er-O-Er and Er-O respectively [32]. These two major groups confirmed the occurrence of ETO-NPs in the sample.

Figure 4: FTIR spectrum of Erbium oxide (Er₂O₃).

Table 1: Band position and functional groups (with mode of vibration) of synthesized sample containing ETO-NPs.

UV-Visible Spectrum Analysis

UV-Vis spectroscopy provides the stability as well as bandgap of the ETO-NPs. The UV-Vis of ETO-NPs is presented in (Figure 5a,5b). Since ETO-NPs have been optical absorption which allows them to interact with particular wavelengths of UV-Vis radiations. It was found in the wavelength vs. absorbance plot (Figure 5a), the cut of the wavelength of the synthesized ETO-NPs lies around 360 nm, and similarly, the bandgap energy of synthesized ETO-NPs was observed at 4.4 eV in (Figure 5b).

Figure 5a: UV-Vis spectrum of ETO-NPs.

Figure 5b: Photon energy vs.  spectrum of ETO-NPs.

PL

Photoluminescence (PL) spectrum at ambient room temperature was executed to very much the optical absorption of ETO-NPs. PL spectrum (Figure 6) of ETO-NPs confirms the emission of UV radiation at 383.8 nm (3.23 eV) and the excitation band of the red region of light at 683.2 nm (1.81 eV). In general, the oxygen vacancies (defects in the synthesized sample containing ETO-NPs) cause the broader peak at larger wavelengths in the PL spectrum. Therefore PL spectrum (Figure 6) reveals the existence of defects in the sample containing ETO-NPs.

Figure 6: Photoluminescence spectrum of ETO-NPs.

Antifungal Activity of ETO-Nps

The infections due to fungi are most commonly occur for those who suffer from having lower immune power and to defeat fungi-mediated infections, the antifungal drugs [33,34] are incorporated with these funguses to destroy its structure. The antifungal drug must be biocompatible and non-toxic. In this research, the synthesized ETO-NPs acts as an antifungal drug and play a major role against various fungi uses and minimize fungi-mediated diseases. (Figure 7a,7b) reveal that the synthesized ETO-NP provides the effective antifungal activity against Aspergillus and Mucor respectively. The 2-dimensional zone inhibition of the sample vs. concentration (mg) chart predicts that adding a higher quantity of synthesized ETO-NPs provides the higher antifungal activity. The lowest antifungal activity (lowest zone inhibition) of ETO-NPs has been observed against Aspergillus and Mucor by adding each 100 mg of the synthesized sample powder containing ETO-NPs and similarly, the higher antifungal activity has been observed by adding 300 mg of synthesized ETO-NPs which was depicted in (Table 2) and 2-dimensional charts in (Figure 7a). It was observed that the synthesized ETO-NPs are more effective against Aspergillus (Zone inhibition: 22 mm) than Mucor (Zone inhibition: 17 mm).

ETO-NPs with different concentrations.

Figure 7a: Left: different concentrations of ETO-NP vs. Zone inhibition (2 dimensional graph depicting antifungal activity that the higher concentration of ETO-NP causes higher percentage of toxic activity). Right: antibacterial activity of ETO-NPs against Aspergillus and    Mucor using the well-known technique of disc diffusion.

ETO-NPs with different concentrations.

Figure 7b: Left: different concentrations of ETO-NP vs. Zone inhibition (2 dimensional graph depicting antifungal activity that the higher concentration of ETO-NP causes higher percentage of toxic activity). Right: antibacterial activity of ETO-NPs against Aspergillus and    Mucor using the well-known technique of disc diffusion.

Table 2:  Antifungal activity of ETO-NPs with different concentrations.

Antibacterial Activity of ETO-Nps

The ratio between surface area and volume is very high for the ETO-NPs and this property allows that the rare earth metal ETO-NPs seem to be a promising conventional alternative antibacterial agent in the place of antibiotics. The antibacterial activities of ETO- NPs are treated at various concentrations with 100-300 mg against Bacillus Sp. and E. coli using disk diffusion technique which is shown in (Figure 8). The minimum antibacterial activity has been observed by adding each 100 mg of ETO-NPs on the Bacillus Sp. and E. coli with observed inhibitions zone are 19 and 13 mm respectively. Similarly, the maximum activity was observed against Bacillus Sp. and E. coli with zone inhibition of 23 and 18 mm respectively by adding each 300 mg of synthesized ETO-NPs. It was observed from (Table 3) and chart in fig.8 that the ETO-NPs are more effective against BACILLUS SP than and E. coli bacteria.

Table 3: ETO-NPs are more effective against BACILLUS SP than and E.

Anti-Cancer Activity (Cytotoxicity Evaluation) Of Eto-Nps

Since the mutation of MDA-MB-231 cell line growth typically occurs in an uncontrolled way either in a small lobe or ducts pathway of the breast. Often, these cell lines can also travel to other parts of lymph nodes under arms further this causes cancer in additional parts of the body [35] to estimate the toxic activity of ETO-NPs against these human breast cancer-producing cells, MTT assay was used in vitro using human breast adenocarcinoma MDA-MB-231 cells. Various concentrations (5, 10, 20, 25, and 50 micro g/ml) of ETO-NPs have been treated on MDA-MB-231 cells up to 48 hours to study the cytotoxicity which is shown in (Figure 9). Since ETO-NPs interact with MDA-MB-231 cells causing cell shrinkage which resulted in lower viability of MDA-MB-231 cells.

Figure 9: Cytotoxic assay of ETO-NPs against MDA-MB-231 cancer cell line.

Table 4(a): The percentage of Cytotoxicity and Cell viability of sample Particulars containing ETO-NPs with different concentrations.

Table 4(b): The percentage of Cytotoxicity and Cell viability of sample Particulars with different concentrations.

Results in (Table 4a) show that the synthesized ETO NP provides higher cytotoxicity and lesser cell viability. These results are almost agreed with the Cytotoxicity of DPEA and PPA against the MDA-MB-231 cell line which was shown in (Table 4b). The maximum best result has been observed by adding the 10 µg of synthesized ETO-NPs which killed the 87% of living MDA-MB-231 breast cancer cells. The overall result shows that the synthesized ETO-NP kills a minimum of 83% of MDA-MB-231 breast cancer cells.

ETO-NPs with 60 to 66 nm have been successfully synthesized and characterized by XRD, UV–Visible, IR, PL spectrum, further the higher percentage of cytotoxicity against MDA-MB 231 and antimicrobial activity against micro bacteria and fungus has been investigated. Using UV-Vis spectrum, it was found that 4f orbital electrons cause ETO-NPs to absorb visible regions of light from 380 to 700 nm and this photoluminescence property allows ETO-NPs for designing the photoluminescence devices. XRD spectrum and TEM topography image with different magnifications confirmed the existence of ETO-NPs in the synthesized sample around the size range from 60 to 66 nm. This lesser size property of ETO-NP displayed a very good toxic activity against Bacillus SP, E.Coli, Aspergillus, and Mucor. Further, the antibacterial result concluded that the ETO-NP plays an effective (higher toxic activity) role against BACILLUS SP and Aspergillus than Mucor and E. coli Microbial pathogens. The synthesized ETO-NPs confirmed 87 % of cytotoxicity against the MDA-MB 231 cell line.

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