6 research outputs found
Glucose-Sensitive QCM-Sensors Via Direct Surface RAFT Polymerization
Thin, phenylboronic acid-containing polymer coatings are potentially attractive sensory layers for a range of glucose monitoring systems. This contribution presents the synthesis and properties of glucose-sensitive polymer brushes obtained via surface RAFT polymerization of 3-methacrylamido phenylboronic acid (MAPBA). This synthetic strategy is attractive since it allows the controlled growth of PMAPBA brushes with film thicknesses of up to 20 nm via direct polymerization of MAPBA without the need for additional post-polymerization modification or deprotection steps. QCM-D sensor chips modified with a PMAPBA layer respond with a linear change in the shift of the fundamental resonance frequency over a range of physiologically relevant glucose concentrations and are insensitive toward the presence of fructose, thus validating the potential of these polymer brush films as glucose sensory thin coatings
Aqueous Fabrication of pH-Gated, Polymer-Brush-Modified Alumina Hybrid Membranes
In
this Article, we studied the surface immobilization of five
organic-acid-modified atom-transfer radical polymerization (ATRP)
initiators based on salicylic acid, catechol, phthalic acid, and <i>m</i>- and <i>p</i>-benzoic acid on alumina, and we
also investigated the growth of hydrophilic poly(2-hydroxyethyl methacrylate)
(PHEMA) and poly(poly(ethylene glycol)methycrylate) (PPEGMA<sub>6</sub>) brushes from the resulting initiator-modified substrates. Whereas
the surface immobilization of phthalic acid- and benzoic acid-based
initiators results in only very thin brushes or no brush growth at
all, SI-ATRP of HEMA and PEGMA<sub>6</sub> from alumina surfaces modified
with salicylate or catechol generates brushes with thicknesses comparable
to those obtained using organosilane-based initiators. Most interestingly,
the surface immobilization of the catechol- and salicylate based-initiators
was found to be pH-dependent, which allowed facile variation of the
ATRP initiator surface concentration and, concomitantly, the polymer
brush grafting density by adjusting the pH of the aqueous solution
that was used to immobilize the initiator. This is in contrast to
organosilane-based initiators, where the variation of the grafting
density is usually accomplished using mixtures of the ATRP initiator
and an ATRP inactive “dummy”. Another difference between
the organosilane-based initiators and the organic acid analogues is
the stability of hydrophilic brushes grown from alumina. After a certain
threshold thickness was exceeded, organosilane-tethered PPEGMA<sub>6</sub> brushes were observed to detach from the substrate, in contrast
to brushes grown from catechol or salicylate initiators, which did
not show signs of degradation. Finally, as a first proof-of-concept,
the salicylate-based initiator was used to develop an all-aqueous
protocol for the modification of alumina membranes with hydrophilic
PHEMA and succinic anhydride post-modified polymer brushes. The water
permeation properties of these hybrid membranes can be controlled
by adjusting the brush thickness in the case of the neutral PHEMA
brush coating or can be pH-gated after post-polymerization modification
to introduce carboxylic acid groups
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Phenolic condensation and facilitation of fluorescent carbon dot formation: a mechanism study
Fluorescent carbon dots have received considerable attention as a result of their accessibility and potential applications. Although several prior studies have demonstrated that nearly any organic compound can be converted into carbon dots by chemical carbonization processes, mechanisms explaining the formation of carbon dots still remain unclear. Herein, we propose a seed-growth mechanism of carbon dot formation facilitated by ferulic acid, a widespread and naturally occurring phenolic compound in the seeds of Ocimum basilicum (basil). Ferulic acid triggers the local condensation of polysaccharide chains and forms catalytic core regions resulting in nanoscale carbonization. Our study indicates that carbon dots generated from natural sources might share the similar mechanism of phenolic compound mediated nanoscale condensation followed by core carbonization