Photoresponsive MoS and WS microflakes as mobile biocide agents.

A fuel-free strategy for the eradication of and biofilms using WS and MoS photophoretic microflakes is described. The microflakes were prepared by liquid-phase exfoliation of the materials. Under electromagnetic irradiation at 480 or 535 nm, the microflakes experience a fast collective behavior at speeds of over 300 μm s due to photophoresis. Simultaneously to their motion, reactive oxygen species are generated. The fast microflake schooling into multiple moving swarms results in a highly efficient "collision" platform that disrupts the biofilm, enhancing radical oxygen species' contact with the bacteria for their inactivation. As such, removal biofilm mass rates of over 90% and 65% are achieved using the MoS and WS microflakes in the treatment of Gram-negative and Gram-positive biofilms after 20 min. Much lower removal biofilm mass rates (30%) are obtained under static conditions, revealing the crucial role of microflake movement and radical generation in the active eradication of biofilms. Much higher removal efficiencies are observed in biofilm deactivation as compared with the use of free antibiotics, which are not able to destroy the densely packed biofilms. The new moving microflakes hold considerable promise for the treatment of antibiotic-resistant bacteria.