Forced Agglutination as a Tool to Improve the Sensory Response of a Carboxylated Poly(p-phenyleneethynylene)

A water-soluble biotinylated poly( p -phenyleneethynylene) (PPE, 3 ) was synthesized by postfunctionalization of an amine−PPE precursor 2a and investigated for sensory responses in aqueous buffer at physiological pH. Polymer 3 shows similar sensitivity ( K SV = 1.1 × 10 4 M -1 ) to Hg 2+ ions when compared to PPE 1 ( K SV = 1.3 × 10 4 M -1 ); 3 was exposed to streptavidin-coated microspheres (SCM) to form a self-assembled complex, which exhibits an enhanced sensitivity toward Hg 2+ ions. If 3 was exposed to either avidin, a streptavidin−rhodamine conjugate, or a streptavidin−Texas Red conjugate, fluorescence of 3 was quenched with K SV values of 33 × 10 6, 28 × 10 6, and 9 × 10 6 M -1, respectively. When lightly cross-linked polymer arrays 3 −avidin were exposed to Hg 2+ ions, they were more sensitive than 3 alone. The complex was quenched by Hg 2+ ions with a K SV of 1.1 × 10 5 M -1 . The negatively charged PPE 1 was incubated with the positively charged avidin to form an electrostatic 1 −avidin complex. The 3 −avidin complex was about 10 times as sensitive to Hg 2+ ions as 1 and 25 times as sensitive to Hg 2+ as 1 −avidin.