The theory and design principles for electrochemical sensors have been primarily developed for threeelectrode configurations and thus were not entirely applicable to our proposed system, Thus, before focusing on our target analytes, we aimed to gain some insight into two-electrode electrochemical detection, including its working range and limitations. To this end, we first evaluated the optimal voltage for the detection of ferrocyanide by measuring sampled-current voltammograms in the presence or absence of the redox probes (Fig. ). This allowed us to extract the faradic current-overpotential response by subtracting non-faradic contributions (Fig. ). The response resembles that of a characteristic Nernstian system, revealing fast and reversible electron transfer kinetics and diffusion control. In subsequent measurements, we chose an applied voltage of 0.35 V corresponding to approximately 90% of the maximum faradic current attainable, with a small degree of non-faradic contribution (~25%). Compared to a typical three-electrode format, the applied voltage in the twoelectrode system is larger because it represents the voltage difference between the WE and CE, rather than that between the WE and the reference electrode (Fig. ). It can be seen that when the ferrocyanide ([Fe II (CN)6] 4-) concentration varies relative to ferricyanide ([Fe III (CN)6] 3-), whilst maintaining a total concentration of 250 mM, two distinct regimes in the current responses exist (Fig. ). Up to a ferrocyanide concentration of 125 mM, the oxidation signal is linearly proportional to its concentration and consistent with the Cottrell equation for a conventional cell (𝑖 = 𝑛𝐹𝐴𝐶 0 𝐷 0.5 𝑡 -0.5 𝜋 -0.5 , where i and t are current and time, respectively, n the number of electrons transferred, A the surface area of the WE and C0 the analyte concentration with diffusion coefficient D). Beyond 125 mM, a sudden current drop is observed, owing to the deficiency of ferricyanide available at the CE for reduction, and thus unable to absorb the electrons generated at the anode. That said, if we consider the complete chronoamperometric curves (Figs. 3d, S2 and S3), responses appear to deviate from the classical Cottrell equation, namely i ∝ t -0.5 . Indeed, there exists a noticeable delay in response at high ferrocyanide concentrations. Further modelling efforts are required to fully explain this observation. These results demonstrate the importance of considering the linear regime of twoelectrode detectors, as it will ultimately determine the upper detection limit for a given application.