Bacterial Inactivation by a Singlet Oxygen Bubbler: Identifying Factors Controlling the Toxicity of ~1O_2 Bubbles

摘要

A microphotoreactor device was developed to generate bubbles (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 byproducts other than O_2. From a comparative study in deaerated, air saturated, and oxygenated solutions, it was reasoned that the singlet oxygen bubbles inactivate Escherkhia 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 ~1O_2 far into the solution; by comparison the diffusion distance of ~1O_2 fully solvated in H_2O is much shorter (～150 nm). Bubbles that reached the outer air-water interface contained no ~1O_2. The mechanism by which ~1O_2 deactivated organisms was explored through the addition of detergent molecules and Ca~(2+) ions. Results indicate mat the preferential accumulation of E. coli at the air-water interface of the bubble leads to enhanced toxicity of bubbles containing ~1O_2. The singlet oxygen device offers intriguing possibilities for creating new types of disinfection strategies based on photodynamic (~1O_2) bubble carriers.