A powerful combination of copper-cysteamine nanoparticles with potassium iodide for bacterial destruction

Abstract

Herein, for the first time, we demonstrate that the combination of copper-cysteamine (Cu-Cy) nanoparticles (NPs) and potassium iodide (KI) can significantly inactivate both Gram-positive MRSA and Gram-negative E. coli. To uncover the mystery of the killing, the interaction of KI with Cu-Cy NPs was investigated systematically and the products from their interaction were identified. No copper ions were released after adding KI to Cu-Cy NPs in cell-free medium and, therefore, it is reasonable to conclude that the Fenton reaction induced by copper ions is not responsible for the bacterial killing. Based on the observations, we propose that the major killing mechanism involves the generation of toxic species, such as hydrogen peroxide, triiodide ions, iodide ions, singlet oxygen, and iodine molecules. Overall, the powerful combination of Cu-Cy NPs and KI has good potential as an independent treatment or a complementary antibiotic treatment to infectious diseases.

Keywords: Bacterial killing; Copper; Copper-cysteamine; Nanoparticles; Photodynamic therapy; Photosensitizer; Potassium iodide; Reactive iodine species.

Fig. 1.

(a) Photos of Cu-Cy NPs dispersed in DI water under room light (left) and UV light (right); (b) Photoluminescence emission spectrum (right) of Cu-Cy following 360 nm excitation. Excitation spectrum is shown by monitoring emission at 607 nm (left); (c and d) Representative TEM image of Cu-Cy NPs used in this study; (e) Particle size distribution of Cu-Cy NPs used in the present study; (f) SAED of Cu-Cy crystal.

Fig. 2.

(a) Optical absorption spectrum of Cu-Cy NPs in aqueous solution. (b) RNO absorption curves of DI water (control) and Cu-Cy NPs upon UV light irradiation.

Fig. 3.

(a) Survival fraction of Cu-Cy on MRSA with or without UV light. (b) Survival fraction of Cu-Cy on E. coli with or without UV light.

Fig. 4.

PDT effect study of Cu-Cy + KI. (a) Killing effect of Cu-Cy NPs (10 μM) and (50 μM) with or without KI on PDT against MRSA. *versus control, P < 0.01, ^#versus in group, P < 0.05. (b) Killing effect of Cu-Cy NPs (50 μM) with or without KI (50 mM) against MRSA and E. coli. *versus MRSA and E. coli in group, P < 0.01, ^#versus in different group, P < 0.01.

Fig. 5.

(a) ESR spectra of Cu-Cy NPs (black) and Cu-Cy NPs + KI (red). (b) RNO absorption curves of DI water (control), Cu-Cy NPs (100 μM) + KI (100 mM), and Cu-Cy NPs (100 μM) under UV irradiation. (c) Cu-Cy NPs, Cu-Cy NPs + KI, and Cu-Cy + NaN₃ irradiated with UV light and aliquots were withdrawn and added to Amplex Red reagent. (d) Cu-Cy NPs (100 μM) and Cu-Cy NPs (100 μM) + KI (100 mM) were illuminated with increasing fluence of UV light and aliquots were withdrawn and added to starch solution. (e) Absorption spectra of Cu-Cy NPs + KI after different incubation time. (f) The photoluminecence spectra of Cu-Cy NPs after adding different concentration of KI to Cu-Cy NPs after 2 h. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 6.

A schematic illustration for photodynamic killing on bacteria from the combination of Cu-Cy NPs with KI under UV light activation.