Bacterial cadmium sulfide semiconductor particles: An assessment of their photoactivity by EPR spectroscopy

The bacterium Klebsiella aerogenes produces extracellular particles of cadmium sulfide in the presence of cadmium ions. The photoactivity of these particles has been studied using electron paramagnetic resonance (EPR) spectroscopy. Bacterial samples containing these semiconductor particles were irradiated with visible light in the presence of a spin trap, either phenyl-tert-butylnitrone (PBN) or 5,5-dimethyl-1-pyrroline-N-oxide (DMPO). The results obtained reveal that a number of radicals, both oxygen and carbon based, are generated. Bacterial samples grown in the absence of cadmium ions exhibit weak, irradiation-independent EPR signals. These bacterially produced radicals are quenched when CdS particles are present. The observation of light-induced radicals provides evidence that the bacterial CdS particles are photoactive, behaving in a similar manner to inorganic CdS particles, and therefore could be used to mediate photocatalytic reactions.