PAMAM dendrimers on controlled pore glass: The effect of tethered dendrimer size and tethered affinity groups NTA and terpy on metal ion and indicator dye uptake

• PAMAM dendrimer monolayers on glass were analyzed for functional end group surface densities.
• Terminal dendrimer amine functional groups show generational dependence on controlled pore glass.
• Grafted metal affinity agents based on NTA or terpy show generational dependence for metal loading and indicator dye loading.
• We report an example of an immobilized indicator release assay for pyrophosphate with PAMAM generational dependence.

PAMAM dendrimer monolayers were covalently immobilized onto controlled pore glass (CPG) particles as platforms to graft the metal ion affinity groups nitrilotriacetic acid (NTA) and terpyridine (terpy). Functional end group analyses, metal ion loading capacities and indicator dye complexation to metal affinity sites were measured as a function of dendrimer size. Metal ions were efficiently extracted from 5 ppm solutions flowing through a packed column of modified CPG and loading capacities increased linearly with immobilized dendrimer size at pH 7.2 as determined by atomic absorption spectroscopy. The dendrimer tethered terpy affinity group was surprisingly effective in aqueous solution for extraction of Zn, Cu and Pb ions, but not as effective for Ni ions when compared to tethered NTA. Metal ion indicator dyes bind to the immobilized metal affinity sites showing a generational dependence. Subsequent addition of pyrophosphate releases dye back into solution as a demonstration of an immobilized indicator displacement assay.

Two metal affinity groups based on nitrilotriacetic acid (NTA) and terpyridine (terpy) are immobilized by surface reactions to dendrimer monolayers tethered to controlled pore glass. Metal ion loading capacities at pH 7.2 are compared using a flowing AAS method for Cu(II), Ni(II), Zn(II) and Pb(II) ions. Strong and weak binding sites for Cu(II) are presented. Metal ion indicator dyes are extracted from solution, then released by adding chelating substrates demonstrating immobilized indicator displacement assays(IDA) with a PAMAM dendrimer generational dependence.Figure optionsDownload as PowerPoint slide