Antimicrobial activity of copper chalcogenides nanoparticles was investigated by synthesizing copper selenide, copper sulfide, and copper oxide via the hot-injection method. Since reaction time has a profound effect on the nanocrystals size and shapes, the effect of reaction time was also investigated during the synthesis of the copper chalcogenides to obtain nanocrystals with desired properties. The reaction time showed no effect on the phase composition of the synthesized copper sulfide, copper oxide, and copper selenide nanoparticles. However, the size variation of nanoparticles with different reaction time was observed. Reaction time of 30 minutes gave the best optical (the shape of the absorption band edge and emission maxima values) and structural (size distribution of particles) properties for CuSe and CuS compared to other reaction times (15, 45, and 60 min). Their band edges were located at 506 (2.45 eV) and 538 nm (2.30 eV), respectively. For this reaction time, copper selenide produced nanoparticles with a size range of 1–27 nm and copper sulfide nanoparticles ranged 1–18 nm. The morphologies of both chalcogenides at 30 min reaction time were spherical. Reaction time of 15 minutes gave the best optical and structural properties for copper oxide nanoparticles with a band edge of 454 nm (2.73 eV) and particle size ranging 0.8–3.2 nm, but nonetheless, 30 min was used as the optimum reaction time for all three chalcogenides. The optimum parameter (220°C, 30 min, and 1 : 1 ratio) was used to synthesize the three copper chalcogenides which were then tested against Gram-negative (
Copper chalcogenide nanoparticles are being sought in both fundamental science and technological applications [
Numerous therapeutic approaches are being used to control different diseases. A current approach is the development of new compounds such as nanoparticles. These nanoparticles will need to be in the right size range and adequate cell biocompatibility [
These nano-sized semiconductors have been synthesized by a variety of methods for tuning the properties for specific applications. As mentioned in the previous work reported by Mbewana-Ntshanka et al. [
The biological and medical research communities have exploited the unique properties of nanomaterials for various applications [
Oleylamine (OLA), copper (I) chloride, selenium powder, sulfur powder, urea solid, methanol (99.5%), and acetone (99.8%) were purchased from Sigma Aldrich. In this study, synthesis of copper oxide, copper sulfide, and copper selenide nanoparticles was approached by the colloidal hot-injection method. About 5 ml of OLA was placed in a three-neck flask, equipped with a reflux condenser (waterless condenser) and a thermometer under a nitrogen atmosphere for both reactions. The content was heated to 120°C under nitrogen environment with a magnetic stirrer on it. About 330 mg (0.0033 mol) of copper chloride was dispersed into 3 ml of OLA and injected into OLA that is in the three-neck flask via a syringe. The content was heated up to 220°C, at which a solution of about 26.06 mg (0.0033 mol) of selenium (sulfur or urea) in 3 ml of OLA was added via syringe. The content was heated at 220°C for about 30 minutes, followed by cooling to 80°C, and then cleaning twice with ethanol and once with acetone via centrifugation at 5000 rev/min for 10 min. The precipitate was left to dry for 24 hours at room temperature. The sample was dispersed into toluene, sonicated for 30 minutes, and then characterized using ultraviolet visible spectroscopy (UV-Vis), photoluminescence (PL), and transmission electron microscopy (TEM). The solid sample was further characterized with XRD.
The antimicrobial study of the synthesized nanoparticles was carried out by testing them against Gram-positive bacteria strains (
Stock cultures were maintained at 4°C on slopes of nutrient agar. Active cultures (
Disk diffusion plates for the bacterial test were prepared by weighing 10 g of malt-extraction agar (MEA) into a 200 ml flask, and 200 ml of distilled water was added. The solute was dissolved using a microwave, autoclaved for 1 hour, and then cooled to room temperature. The plates were prepared by transferring about 15 ml of a molten media into a sterile disk plates under sterilized fume hood. Disk diffusion plates for the fungal test were prepared the same way but 7.6 g of Muller–Hinton agar (MHA) was used instead of malt-extraction agar. The disk plates were left for 10 minutes to solidify. Inoculum suspension was swabbed uniformly and allowed to dry for 5 minutes. A well of 6 mm was created on a disk, and 50
Minimum inhibitory concentration (MIC) of the plant extracts’ copper chalcogenides nanoparticles (copper selenide, copper sulfide, and copper oxide) was determined using the microdilution bioassay as described by Gupta [
The optical properties of the synthesized material were determined by dissolving the synthesized nanoparticles in a toluene and placing the content in a quartz cuvette (1 cm path length). The absorbance measurements were recorded using a double beam Perkin Elmer lambda 25 UV/Vis spectroscopy with a wavelength range of 0–900 nm. The emissions were measured using a single beam Jasco spectrofluorometer FP-8600 with XE lamp at 150 W operated at 200–1010 nm. The morphology of the particles was determined by drop casting the particles that were dissolved in toluene to copper grids; then, images were taken using transmission electron microscopy (Technai G2 TEM spirit) operated at 200 kV. The X-ray diffraction patterns were determined using the Bruker D2 phase analyzer, XRD Beam knife 3 mm (5 mm is all the way up), and diffracted beam antiscatter slit 6.6 mm. Fourier transform infrared analysis were recorded on a FTIR Perkin Elmer 400 spectrometer using a diamond detector.
Semiconductor crystalline are characterized by their band gap energy (Eg) that falls within the range 0 < Eg < 4 eV and can be thought of as the minimum energy required to excite an electron from the valence band to the conduction band [
(a) Absorption and (b) emission spectra of copper selenide, copper sulfide, and copper oxide nanoparticles synthesized for 15, 30, 45, and 60 min in OLA at 220°C using 1 : 1 mole ratio.
Optical parameters of copper selenide, copper sulfide, and copper oxide nanoparticles synthesized for 15, 30, 45, and 60 min.
Time (min) | Nanoparticles | ||||||||
---|---|---|---|---|---|---|---|---|---|
CuSe | CuS | CuO | |||||||
Band edge (nm: eV) | Emission max (nm) | FWHM (nm) | Band edge (nm: eV) | Emission max (nm) | FWHM (nm) | Band edge (nm: eV) | Emission max (nm) | FWHM (nm) | |
15 | 766 (1.62) | 505 | 61 | 678 (1.80) | 482 | 68 | 454 (2.73) | 445 | 90 |
30 | 506 (2.45) | 365 | 55 | 538 (2.30) | 468 | 72 | 457 (2.71) | 502 | 69 |
45 | 587 (2.11) | 417 | 102 | 585 (2.12) | 471 | 91 | 460 (2.70) | 503 | 81 |
60 | 674 (1.84) | 457 | 53 | 598 (2.07) | 482 | 95 | 574 (2.16) | 622 | 116 |
The absorption band edges of all copper selenide, copper sulfide, and copper oxide nanoparticles that were prepared at 15, 30, 45, and 60 minutes were blue shifted from that of the bulk material band gap (1180, 1022, and 1033 nm) respectively. This blue shift results from quantum confinement effects [
The absorption curves of these two materials are also different from the rest of the three materials, suggesting that the optical properties of this material would differ from the rest of the materials. Copper sulfide nanoparticles produced two different types of absorption curves predicting different optical properties. The materials prepared at times of 30 and 60 minutes resembled a chalcocite phase characteristic while 15 min and 45 min resembled covellite phase characteristics as predicted by Ravi et al. [
Optical and physical properties of copper selenide, copper sulfide, and copper oxide nanoparticles synthesized for 30 min in comparison with previously reported data.
Nanoparticles | ||||||
---|---|---|---|---|---|---|
CuSe | CuS | CuO | ||||
Results obtained | Literature [ | Results obtained | Literature [ | Results obtained | Literature [ | |
Optimum conditions | 30 min and 220°C | 30 min and 220°C | 30 min and 220°C | 25 min and 0°C | 30 min and 220°C | 180 min and 400°C |
Band edge/band gap | 506 nm (2.45 eV) | 400 nm (3.1 eV) | 538 nm (2.3 eV) | 593 nm (2.09 eV) | 457 nm (2.71 eV) | _ |
Particle size | 1–27 nm | 2–9 nm | 1–18 nm | 3–5 nm | 0.1–8 nm | 26–30 nm |
Particle shape | Spherical | Hexagonal | Spherical | Undefined clusters | Spherical | Spherical |
The emission spectra of the three different materials are shown in Figure
Narrow emission peaks for copper selenide were observed at 30 and 60 minutes with full width at half maximum of 55 nm and 53 nm, respectively. Particles prepared at 15 and 45 minutes gave emission peaks with a full width at height maximum of 61 and 102 nm predicting less monodispersity. Copper sulfide nanoparticles showed similar trends to copper selenide, although copper selenide gave the largest FWHM value at 45 minutes. In contrast to the other materials, copper oxide gave the largest dispersity at 60 minutes with a FWHM of 116 nm.
The morphology of the synthesized copper selenide, copper sulfide, and copper oxide nanoparticles was studied by TEM, and their images are given in Figure
TEM images and size histograms of copper selenide, copper sulfide, and copper oxide nanoparticles synthesized for 15, 30, 45, and 60 min with their corresponding histogram in OLA at 220°C using 1 : 1 mole ratio of CuO.
Unlike copper selenide, 15 minutes reaction in copper sulfide produced bigger particles that are mixed morphology. The mixed morphologies’ included truncated triangles, cube-like structures, and spheres that are overlapping resulting in high agglomeration. When the reaction time was increased to 30, 45, and 60 minutes, a trend of size increase with reaction time was observed just like in copper selenide. This trend corroborates what was predicted by UV/Vis absorption spectroscopy. In both chalcogenides, the material synthesized at 30 minutes produced the smallest particle size than other three materials with shapes that are almost spherical. Copper sulfide nanoparticles synthesized at 45 minutes also produced small particles but with some smaller clusters indicating that these particles were starting to dissolve in one another and forming big particles as Sibokoza et al. [
The particle size of the four materials increased with the reaction time, and this is consistent with literature reports that suggest larger particle size when the nucleation time is prolonged [
The XRD patterns of copper selenide nanocrystals synthesized for 30 and 45 min are shown in Figure
XRD patterns of copper selenide nanoparticles synthesized for 30 min (a) and 45 min (b) in OLA at 220°C using 1 : 1 mole ratio of CuSe.
Figure
XRD patterns of copper sulfide nanoparticles synthesized for 30 min (a) and 45 min (b) in OLA at 220°C using 1 : 1 mole ratio of CuS.
The synthesized copper oxide nanoparticles were confirmed by XRD analysis, and their diffraction patters are shown in Figure
XRD patterns of copper oxide nanoparticles synthesized for 15 min (a), 30 min (b), 45 min (c), and 60 min (d) in OLA at 220°C using 1 : 1 mole ratio of CuO.
Figure
FTIR spectra of oleylamine (a), copper selenide (b), copper sulfide (c), and copper oxide nanoparticles (d).
Copper chalcogenide nanoparticles have been suggested for various potential applications, and antimicrobial has been listed among those applications [
Antibacterial study of the synthesized copper chalcogenides on
Antifungal study of the synthesized copper chalcogenides,
A disk diffusion method was used to determine the sensitivity of the abovementioned microorganisms that were used for antibacterial and antifungal studies with respect to the antimicrobial agents (copper selenide, copper sulfide, and copper oxide). The same procedure that was reported in the previous work conducted by Ntshanka et al. [
Agar disk diffusion test for screening the activity of the antimicrobial agents.
Antimicrobial agent | Solvent of plant extract | |||||
---|---|---|---|---|---|---|
CuSe | Ethanol | 12 | 5 | 12 | 14 | 6 |
CuS | Ethanol | 8 | 9 | 24 | 25 | 5 |
CuO | Ethanol | 12 | 13 | 26 | 28 | 12 |
Determination of minimum inhibitory concentrations (MICs) of antimicrobial agents by broth dilution.
Antimicrobial agent | Solvent of plant extract | |||||
---|---|---|---|---|---|---|
CuSe | Ethanol | 78.13 | 78.13 | 39.06 | 5000 | 78.13 |
CuS | Ethanol | 156.25 | 78.13 | 39.06 | 312.5 | 78.13 |
CuO | Ethanol | 78.12 | 78.13 | 39.06 | 312.5 | 78.13 |
After the screening of the antimicrobial activity, a more accurate and quantitative method (MIC) was used to determine the lowest concentration of the antimicrobial agent to inhibit bacterial activity, and the results are given in Table
Antimicrobial activity of the synthesized copper chalcogenides in comparison with previously published data.
Zone of inhibition (mm) and/MIC (mg/mL) | |||||||||
---|---|---|---|---|---|---|---|---|---|
Bacterial strains | References | ||||||||
Synthesized NPs | Results obtained | Literature | Results obtained | Literature | Results obtained | Literature | Results obtained | Literature | |
CuSe | 12 mm | _ | 5 mm | _ | 12 mm | _ | 14 mm | _ | _ |
CuS | 8 nm and 0.16 mg/mL | 0.39 mg/mL | 9 nm and 0.08 mg/mL | <0.05 mg/mL | 24 nm and 0.04 mg/mL | 3.125 mg/mL | 25 nm and 0.31 mg/mL | _ | Mofokeng [ |
CuO | 12 mm | _ | 13 mm | 22 mm | 26 mm | 21 mm | 28 mm | 20 mm | Azam [ |
The investigation of reaction time revealed that the particle size increases with longer reaction time and there is evolution of particle shapes. The shapes of the particles become more defined and well passivized at prolonged times. Amongst the three chalcogenides that were synthesized, copper oxide nanoparticles behaved differently from the selenide and sulfide nanoparticles, and this is attributed to its high reactivity in relation to the atomic size. With regards to physical and chemical properties of copper selenide and copper sulfide nanoparticles, 30 minutes reaction time gave the best optimal time as compared to 15 minutes for copper oxide nanoparticles. The antibacterial study revealed that all the microorganisms tested were susceptible to all three copper chalcogenide nanoparticles. Copper oxide showed a higher sensitivity towards both Gram-negative and Gram-positive bacteria and fungi compared to the two chalcogenides (CuSe/CuS), and copper selenide showed the least sensitivity against all bacteria and fungi tested. This confirms its less reactivity compared to copper sulfide and copper oxide nanoparticles. Over all the information about the antimicrobial activity of copper selenide nanoparticles is very limited, and this could be due to its low sensitivity towards microorganisms.
The data used to support the findings of this study are included within the article.
The authors declare that they have no conflicts of interest.
The authors would like to thank Vaal University of Technology department of chemistry for funding, laboratory support, and research infrastructure used for carrying out the research work.