Chemically Grafted Polymeric Filters for Chemical Sensors:  Hyperbranched Poly(acrylic acid) Films Incorporating β-Cyclodextrin Receptors and Amine-Functionalized Filter Layers

Abstract

We report a new “molecular-filter” approach for enhancing the selectivity of chemical sensors. Specifically, we describe electrochemical sensors prepared from Au electrodes coated with β-cyclodextrin-functionalized, hyperbranched poly(acrylic acid) (PAA) films capped with a chemically grafted, ultrathin polyamine layer. The hyperbranched PAA film is a highly functionalized framework for covalently binding the β-cyclodextrin molecular receptors. The thin, grafted polyamine overlayer acts as a pH-sensitive “molecular filter” that selectively passes suitably charged analytes. Poly(amidoamine) dendrimers or poly-d-lysine is used as 10−15-nm-thick filter layers. The results show that at low pH, when the polyamines are fully protonated, positively charged redox probe molecules, such as benzyl viologen (BV), do not permeate the filter layer. However, at high pH, when the filter layer is uncharged, BV penetrates the filter layer and is reduced at the electrode. The opposite pH dependence is observed for negatively charged redox molecules such as anthraquinone-2-sulfonate (AQS). Both BV and AQS specifically interact with the β-cyclodextrin receptors underlying the polyamine filter layers.

Ultrathin polymer coatings by complexation of polyelectrolytes at interfaces: suitable materials, structure and properties

“…4). Also, dendrimers [227][228][229][230][231][232][233][234]380) are reported to deposit well, as are hyperbranched polyelectrolytes 134,135,141) (cf. Fig.…”

“…Treatment with various functionalized silanes, such as trialkoxy-3-aminopropylsilane 113,114,143,200,219,227,286,388,395) , provides an additional, "easy" access to positively charged surfaces. In a similar way, treatment of gold with functionalized thiols or disulfides, respectively, enables the tailoring of both positively (e. g. when applying cysteamine 119,211,277,296,387) ) or negatively (e. g. when applying mercaptoundecanoic acid 115,116,228,269,286,396,397) ) charged surfaces. As discussed above, film growth is characteristic for a chosen pair of polyelectrolytes and its "matching", and on the conditions for adsorption.…”

Chemical modification of hyperbranched ultrathin films on gold and polyethylene

“…Indeed, while we did successfully develop chemistry to prepare carboxamide and ester derivatives of these hyperbranched PAA grafts, the products of this chemistry were mixtures of carboxylic acids and carboxylic acid derivatives due to incomplete conversion of the PAA carboxylic acid groups. 4,9,10 This was not a problem in cases where the objective was further grafting or introduction of a spectroscopic label (e.g., a pyrene group). 4 It is a concern if quantitative conversion of functional groups is desired.…”

“…In the first scheme, the hydroxyl groups of a reduced film were converted to trichloroacetate esters. We had earlier used the Mn 2 (CO) 10 -promoted radical polymerization of such esters in surface modification. 19 This graft chemistry also works with these films.…”

Hydrogen (H2) sensing and catalysis with organic-stabilized Pd and Pd alloy nanoparticles.

“…Similarly, they have demonstrated that by controlling the pH of a solution, dendrimers can act as molecular-gates admitting molecules on the basis of overall charge. 186,187 Bruening and co-workers have examined the size-based selectivity of Pd NPs embedded in multilayered polyelectrolyte films in hydrogenation of mono-, di-, and tri-substituted alkenes. [180][181][182] These catalysts showed remarkable intramolecular selectivity in the hydrogenation of alkenes based on the degree of substitution of the double bond.…”