Abstract:
Background: Antimicrobial resistance (AMR) is a global health crisis. Nanoparticles with strong
biocidal activity are promising candidates in combatting AMR compared to the time and labor
intensive manufacturing of new antibiotics. Semiconductor-nanoparticles also have the potential
to degrade bio-accumulative azo-dyes that cause serious threats to water quality and public health.
Objectives: To evaluate the antibacterial activity of water extracts (WE) of Cordyline fruticosa
sp. leaves and silver nanoparticles (AgNPs) synthesized using the above extract against gram
positive and gram-negative bacteria. The study also assesses photocatalytic activity of AgNPs
against the model dye Malachite Green (MG)
Methods: Nanoparticles synthesized from three varieties of C. fruticosa; candy cane (1CC),
waihee rainbow (2WR) and pink cascade (4PC) and their water extracts were tested for
antibacterial activity against strains of Escherichia coli (ATCC 25922) and Staphylococcus aureus
(ATCC 25923), using the well-diffusion technique. Gentamycin discs were used as positive
control and 0.9% saline solution was used as negative control. Samples of 267 and 4000 ppm of
4PC-AgNPs were assessed for their photocatalytic activity using Malachite Green (MG) as a
model-dye and reassessed with the addition of NaBH4. Bandgap energy was calculated for AgNPs
and one-way ANOVA analysis was conducted using MS Excel.
Results: Zones of inhibition (ZOI) of 35 mm and 29 mm, higher than ZOI of the positive control,
against S. aureus and E. coli respectively were displayed by 4PC-AgNPs. However, AgNPs and
WE did not have a significant difference in antibacterial activity against either strain, as p>0.05
and F<F crit. Bandgap energy calculations showed that all synthesized AgNPs were
semiconductors. Although a significant reduction of the absorption peak of MG was not observed
when 4PC-AgNPs were tested alone, the absorption dropped from around 2.0 to 0.1 when both
concentrations were tested with NaBH4. Visual observations suggest that MG completely
degraded within 5 minutes.
Conclusion: WE and AgNPs both display antibacterial potential, although not significant, with a
greater activity against gram-positive bacterial strains. 4PC-AgNPs were identified as a potential
candidate for azo-dye degradation, with NaBH4 maximizing its photocatalytic efficiency.
