To test this hypothesis, SWCNTs were suspended with phospholipid-polyethylene glycol (PEG-PL) and different nucleic acids (Figure , Table ). Subsequently, we tested whether the fluorescence changes of these hybrid nanomaterials would be selective for molecules of interest. For the enzyme HRP, we selected o-and p-phenylenediamine (OPD and PPD), as well as their respective reaction products 2,3-diaminophenanzine and Bandrowski's base (BB). The selection of these substrate/product pairs was based on the premise that the substrate and the product differ significantly in their size and molecular structure which could lead to different affinities for the SWCNT surface. We expected that these molecules change the DNA conformation, which would cause a change in fluorescence. Additionally, we tested the response of three different benzidine derivatives, which form colored radicals when oxidized by HRP and H2O2. Among them, we included 3,3'-5,5'-tetramethylbenzidine (TMB), the most commonly used HRP substrate. Apart from the popularity of these substrates, it is well established that these molecules are oxidized over different radical species while the product is typically a charged complex with increased rigidity. For SWCNTs, it is well known that radical species modulate the SWCNT response. Furthermore, we expect that the enzymatic product affects the SWCNT conformation thereby leading to a fluorescent response. For the enzyme β-galactosidase, we tested the response to ortho-nitrophenyl-β-galactoside (OPNG) and chlorophenol red-β-ᴅ-galactopyranoside (CPRG), as well as their respective reaction products.