Size-dependent antimicrobial properties of CuO nanoparticles against Gram-positive and -negative bacterial strains

Figures & data

Table 1 Variation of crystallite size and lattice parameters with annealing temperature

Temperature (°C)	a (Å)	b (Å)	c (Å)	Crystallite size (nm)
400	4.688	3.427	5.132	20
500	4.711	3.429	5.133	21
600	4.715	3.430	5.135	25
700	4.719	3.432	5.136	27

Figure 1 XRD spectra of CuO nanoparticles annealed at 400°C.

Abbreviations: XRD, X-ray diffraction; CuO, copper oxide; AU, units of intensity.

Figure 2 XRD spectra of CuO nanoparticles annealed at different temperatures.

Abbreviations: XRD, X-ray diffraction; CuO, copper oxide; AU, units of intensity.

Figure 3 TEM image of CuO nanoparticles.

Notes: TEM image of CuO nanoparticles annealed at (a) 400°C (b) 700°C.

Abbreviations: TEM, transmission electron microscopy; CuO, copper oxide; n, number.

Figure 4 FTIR spectra of CuO nanoparticles annealed at different temperatures.

Note: Inset shows Raman spectrum of CuO nanoparticles annealed at 400°C.

Abbreviations: FTIR, Fourier-transform infrared spectroscopy; CuO, copper oxide.

Table 2 Antimicrobial activity of copper oxide (CuO) nanoparticles against two Gram-positive and two Gram-negative bacteria

Treatment (100 μL)	Zone of inhibition (mm)
	Escherichia coli	Pseudomonas aeruginosa	Bacillus subtilis	Staphylococcus aureus
CuO (400°C)a	20	21	24	22
CuO (500°C)b	17	20	22	20
CuO (600°C)c	15	12	20	18
CuO (700°C)d	14	10	15	12
Tetracyclinee	20	18	20	22

Note:

a–e indicate the copper oxide nanoparticles synthesized at different temperatures was used in an antimicrobial experiment on nutrient agar plates in Figure 5.

Table 3 MIC of copper oxide nanoparticles (annealed at different temperatures) against different laboratory bacterial strains

Microorganisms	MIC of copper nanoparticles (μg/mL)
	400°C	500°C	600°C	700°C
E. coli	20 ± 3	35 ± 5	45 ± 4	65 ± 6
P. aeruginosa	28 ± 4	40 ± 3	50 ± 5	55 ± 5
B. subtilis	30 ± 5	50 ± 4	65 ± 4	70 ± 5
S. aureus	25 ± 4	42 ± 2	70 ± 5	75 ± 4

Note: Each value in mean ± standard deviation.

Abbreviation: MIC, minimum inhibitory concentration.

Table 4 MBC of copper oxide nanoparticles (annealed at different temperatures) against different laboratory bacterial strains

Microorganisms	MBC of copper nanoparticles (μg/mL)
	400°C	500°C	600°C	700°C
E. coli	30 ± 2	45 ± 5	60 ± 3	95 ± 4
P. aeruginosa	35 ± 2	50 ± 3	75 ± 5	85 ± 5
B. subtilis	45 ± 3	62 ± 4	85 ± 4	95 ± 5
S. aureus	32 ± 5	75 ± 2	90 ± 5	100 ± 4

Note: Each value in mean ± standard deviation.

Abbreviation: MBC, minimum bactericidal concentration.

Figure 5 Zone of inhibition of copper oxide nanoparticles.

Notes: Zone of inhibition of copper oxide nanoparticles synthesized at different temperatures (a–d) and positive control, a known antibiotic tetracycline (e) against two Gram-negative bacteria (A) Escherichia coli and (B) Pseudomonas aeruginosa, and two Gram-positive bacteria (C) Bacillus subtilis and (D) Staphylococcus aureus.

Figure 6 Bar graph representing the zone of inhibition for CuO nanoparticles and tetracycline against Gram-positive and -negative bacteria.

Abbreviation: CuO, copper oxide.