Bacterial patterns hide messages until triggered with correct biochemical

Researchers have developed a novel photodynamic nanoparticle-based platform that creates high-resolution, biochemically responsive bacterial patterns capable of securely encoding information. By coating bacteria with specially designed nanoparticles that generate reactive oxygen species (ROS) under white light, the system selectively kills exposed bacteria while leaving unexposed ones alive to form precise patterns on membranes. This approach overcomes previous limitations by enabling spatial control of bacterial survival without relying on genetically engineered strains, achieving pattern resolutions of approximately 16 micrometers and allowing biofilm transfer between culture media without pattern degradation. The platform leverages differences in bacterial metabolism to reveal hidden messages only when triggered by specific biochemical substrates. For example, MRSA converts tellurite into black colonies, while E. coli processes X-Gal to produce cyan deposits, enabling the creation of complex living codes such as Morse patterns and QR codes. Some codes can display false information under one substrate but reveal the true message under another, enhancing security. This system represents the first photodynamic bacterial encoding method