Figure 4.

Assessment of the binding interaction between Cu²⁺ ions and PEI-GA-PEI-functionalized NAA interferometers for different concentrations of Cu²⁺ ions (note: error bars denote standard deviation from average measurements obtained from n = 3 independent experiments). (a) Real-time Cu²⁺ binding stage for [Cu²⁺] = 75 ppm, where the arrows indicate ΔOT_eff and t_sat for the binding reaction performed under dynamic flow conditions (note: the dotted line shown at the left of the graph indicates the time point at which the Cu²⁺ analytical solution was injected into the flow cell system, OT_eff and time baselines). (b) Average values of ΔOT_eff for each surface chemistry engineering stage and real-time sensing. (c) Correlation between ΔOT_eff (left scale) and t_sat (right scale) with [Cu²⁺] for PEI-GA-PEI-functionalized NAA interferometers. (d) Kinetic rate (R_{PEI-GA-PEI-Cu}) for the binding reaction between Cu²⁺ ions and PEI-GA-PEI functional layers for the range of [Cu²⁺] (i.e., 1–100 ppm).