Provided is a biosensor including a scaffold and a dye complex, the dye complex including a clay material associated with a dye material, where the dye complex is at least partially embedded in the scaffold. Also provided is a process for preparing the biosensor, an apparatus including the biosensor and methods for detecting viable microorganisms in an aqueous fluid test sample making use of the biosensor, for predicting biofouling in a fluid flowing system and for determining a concentration of disinfectant required to disinfect an aqueous fluid.