Bacterial Inactivation by a Singlet Oxygen Bubbler: Identifying Factors Controlling the Toxicity of 1O2 Bubbles

摘要

A microphotoreactor device was developed to generate bubbles (sized: 1.4 mm diameter, 90 μL) containing singlet oxygen at levels toxic to bacteria and fungus. As singlet oxygen decays rapidly to triplet oxygen, the bubbles leave behind no waste or by-products other than O2. From a comparative study in deaerated, air saturated, and oxygenated solutions, it was reasoned that the singlet oxygen bubbles inactivate Escherichia coli and Aspergillus fumigatus, mainly by an oxygen gradient inside and outside of the bubble such that singlet oxygen is solvated and diffuses through the aqueous solution until it reacts with the target organism. Thus, singlet oxygen bubble toxicity was inversely proportional to the amount of dissolved oxygen in solution. In a second mechanism, singlet oxygen interacts directly with E. coli that accumulate at the gas-liquid interface although this mechanism operates at a rate approximately 10 times slower. Due to encapsulation in the gaseous core of the bubble and a 0.98 ms lifetime, the bubbles can traverse relatively long 0.39 mm distances carrying ¹O2 far into the solution; by comparison the diffusion distance of ¹O2 fully solvated in H2O is much shorter (~150 nm). Bubbles that reached the outer air/water interface contained no ¹O2. The mechanism by which ¹O2 deactivated organisms was explored through the addition of detergent molecules and Ca²⁺ ions. Results indicate that the preferential accumulation of E. coli at the air-water interface of the bubble leads to enhanced toxicity of bubbles containing ¹O2. The singlet oxygen device offers intriguing possibilities for creating new types of disinfection strategies based on photodynamic (¹O2) bubble carriers.