Chemiluminescence detection with microfluidics for innovative in situ measurement of unbound cobalt ions in dynamic equilibrium with bound ions in binding study with polyethyleneimine and its functionalized nanoparticles.

This work reports a novel method for in situ measurement of binding of cobalt ions to polyethyleneimine (PEI) and polyethyleneimine-functionalized poly (methyl methacrylate) nanoparticles (PEI-NPs) using simple microfluidics with a chemiluminescence detection system. The catalytic effect of free cobalt ion in solution on the luminol-hydrogen peroxide chemiluminescence was employed for the detection of unbound cobalt in dynamic equilibrium with cobalt bound to PEI or PEI-NPs. Many binding measurements lead to incorrect estimation of free metal ions due to insufficient separation of bound and free ions. The catalytic activity of only unbound cobalt ion on the luminol reaction was demonstrated by observing that PEI and PEI-NPs alone did not give chemiluminescence. Also, both Co-PEI and Co-PEI-NPs complexes gave no chemiluminescence when cobalt ion is fully bound with excess PEI or PEI-NPs. In addition diethylenetriamine (dien) as a model ligand to completely bind the cobalt ions was also employed as further confirmation. The chemiluminescence measurement employing microfluidics was then successfully applied for the measurement of binding cobalt ion to PEI and PEI-NPs. This in situ measurement of binding does not require filtration of the two species. As there is no perturbation of equilibrium, an accurate binding measurement can therefore be successfully performed. Experimental parameters, such as concentrations of polymers and cobalt ions, and equilibration time were investigated. Analysis of the experimental data employed the binding equation derived assuming independent and equivalent binding sites of the polymer for the metal ions. Also the binding constant of cobalt ions with PEI-NPs is first reported employing chemiluminescence detection. This work provides quantitative determination of the binding constant and total binding capacity of PEI and PEI-NPs with cobalt ions using chemiluminescence detection and microfluidics as an innovative in situ measurement of the unbound cobalt ions.