“…The fact that such a visible color change occurs in response to a variety of environmental perturbations including temperature, heat, mechanical stress, pH, and solvents lead to a nonspecific colorimetric response. Therefore, specifically designed ligands have been introduced as the terminal group of PDA for detecting specific types of bacterial strains with high sensitivity, such as glycine terminated PDA for colorimetric signaling of bacterial pore-forming toxin (Ma and Cheng, 2005), peptide functionalized PDA for detecting bacterial lipopolysaccharide (Wu et al, 2011), aptamer-based PDA for Escherichia coli O157:H7 detection (Wu et al, 2012), amine functionalized PDA for detecting surfactin from B. subtilis NCIB3610 (Park et al, 2016) and a Eu III -EDTA functionalized PDA for recognizing calcium dipicolinate (DPA), a major component of Bacillus anthrax endospores (Seo et al, 2017). However, the majority of the PDA-based sensors that have been reported were prepared in the form of a liposome in aqueous solution or thin film as two dimensional (2D) structures (Silbert et al, 2006;Scindia et al, 2007;Meir et al, 2008;Pires et al, 2011;Park et al, 2016;Seo et al, 2017).…”