Polymeric Micelles Based on Light-Responsive Block Copolymers for the Phototunable Detection of Mercury(II) Ions Modulated by Morphological Changes

Polymeric micelles based on light-responsive block copolymers were prepared and used for the phototunable detection of mercury(II) ions. 2-Nitrobenzyl acrylate (NBA) and (E)-2-((4-(4-formylphenyl)diazenyl)phenyl) (methyl)-amino) ethyl acrylate (FPDEA) were copolymerized from a poly(ethylene oxide) (PEO) macroinitiator via atom transfer radical polymerization (ATRP), leading to a well-defined block copolymer of PEO113-b-[p(NBA(10)-co-FPDEA(3))] with a low polydispersity index (PDI = 1.16). After polymerization, the aldehyde groups of PEO-b-[p(NBA-co-FPDEA)] were converted to aldoxime groups by reacting with hydroxylamine, leading to the formation of a final oxime-containing polymeric probe, PEOb-[p(NBA-co-HPDEA)], P1. The resulting block copolymer, P1, was self-assembled in water to yield spherical micelles that consist of a PEO block forming a hydrophilic shell and a copolymer of light-responsive NBA and a mercury(II) ion-detecting HPDEA block forming a hydrophobic core. Upon the addition of mercury(II) ions to this micellar solution, no detection was observed since water-soluble mercury(II) ions have limited accessability to the oxime units of P1, which are located in the hydrophobic core. After UV light irradiation, however, the photolabile 2-nitrobenzyl moieties were cleaved, and hydrophobic PNBA was transformed to hydrophilic poly(acrylic acid) (PAA), leading to the photoinduced dissociation of micelles to unimers. As a result, the oxime units of P1 were exposed to a hydrophilic environment and could react with mercury(II) ions to form nitrile groups, resulting in the turn-on detection of mercury(II) ions by UV light irradiation.