Bactericidal effect of zero-valent iron nanoparticles on Escherichia coli

Abstract

Zero-valent iron nanoparticles (nano-Fe0) in aqueous solution rapidly inactivated Escherichia coli. A strong bactericidal effect of nano-Fe0 was found under deaerated conditions, with a linear correlation between log inactivation and nano-Fe0 dose (0.82 log inactivation/mg/L nano-Fe0 x h). The inactivation of E. coli under air saturation required much higher nano-Fe0 doses due to the corrosion and surface oxidation of nano-Fe0 by dissolved oxygen. Significant physical disruption of the cell membranes was observed in E. coli exposed to nano-Fe0, which may have caused the inactivation or enhanced the biocidal effects of dissolved iron. The reaction of Fe(II) with intracellular oxygen or hydrogen peroxide also may have induced oxidative stress by producing reactive oxygen species. The bactericidal effect of nano-Fe0 was a unique property of nano-Fe0, which was not observed in other types of iron-based compounds.

Figure 1

TEM images of (a) unoxidized and (b, c) oxidized nano-Fe⁰, and (d) variation in the UV-vis absorption spectrum of nano-Fe⁰ solution under air saturation (open to air) (pH₀ = 8.0, 2 mM carbonate buffer, [nano-Fe⁰]₀ = 90 mg/L).

Figure 2

Inactivation of E. coli by nano-Fe⁰ as functions of (a) contact time and (b) nano-Fe⁰ dose after 1 hr under air-saturated and deaerated conditions (pH₀ = 8.0, 2 mM carbonate buffer, The dashed line in Figure 2b indicates depletion of dissolved oxygen under air-saturated closed condition.)

Figure 3

(a) Nano-Fe⁰ exposure for 1 hr contact time as a function of [nano-Fe⁰]₀, and (b) plots of E. coli inactivation against nano-Fe⁰ exposure (pH₀ = 8.0, 2 mM carbonate buffer).

Figure 4

TEM images of (a, b) native E. coli cells, and treated cells with (c, d) FeSO₄ and (e, f) nano-Fe⁰ (> 3 log inactivation, [Fe(II)] = 0.1 mM for (c, d), [nano-Fe⁰] = 10 mg/L for (e, f), pH = 8.0, 2 mM carbonate buffer, treatment time = 30 min under deaerated condition)