Evaluation of nanoparticle (NP) surface reactivity is critical to both developing functional performance and assessing environmental impacts of NPs. Many chemical assays have been applied to indicate NP surface reactivity. A majority of these assays are based upon initiating a chemical reaction participated by the targeting NPs. After a certain progression of the reaction, the concentration of the remaining reactant or the generated product is then used as an indicator of the NP reactivity and compared across different NPs. Despite the convenience of these assays to indicate reactive NPs, questions are raised on whether the directly obtained concentration reading is the most accurate indicator for the actually concerned NP reactivity.<br/>Herein we demonstrate that, when an assay is applied, kinetics modeling of reactions invoked by the assay leads to more accurate parameterization of NP reactivity. We substantiated this philosophy using three assays, including Methylene Blue Reduction by Borohydride (MBRB) assay, ferric reduction (FR) assay, and electron paramagnetic resonance(EPR) detection of hydroxyl radical (EPR-OH assay). The kinetics modeling of each assay takes account of both homogeneous and heterogeneous reactions in the system, and parameterizes rate constants of multiple reaction steps. Experimental data was fitted by each model and proved model validity. The rate constant directly associated with NP surface reaction was recognized and suggested to be the most accurate indicator for the concerned NP reactivity. Furthermore, this approach revealed that the “reactivity” analyzed by one assay can be derived from different reaction mechanisms for different NPs, calling the needs of discriminating the reactivity categories for NPs. According to our experiment and model findings, we suggest the importance of distinguishing catalytic and redox reactivity of NPs evaluated by an assay.<br/> <br/>

Kinetics modeling enabled parameterization and discrimination of nanoparticle surface reactivity evaluated by chemical assays

255th National Meeting (2018)

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