## 3 Results and Discussion
### Adrenaline Transfer Across Aqueous/DCE Interface in Simple Matrices
This similarity in shape suggests that the Adr transfer process may not be the sole contributor to the CVs, with the observed signal potentially affected by additional factors within the KCl matrix. Small fluctuations in the steady-state current across the different Adr concentrations (shown in Figure 1) are likely due to minor variations in pipet size between experimental setups. To determine if the observed peak shift (the difference in the E\({}_{1/2}\) values of background and Adv CVs) was linked to KCl or the ionophore DB24C8, we conducted further tests using an alternative ionophore, DB18C6 (Figure S1). Interestingly, similar to our initial experiments with KCl and DB24C8, we observed no increase in steady-state current with increasing Adv concentrations. Instead, the CVs demonstrated a similar E\({}_{1/2}\) shift, indicating that the potential shift may be influenced by intrinsic factors rather than the matrix or ionophore composition alone. Given the potential for multiple factors to influence the observed peak shift, we next examined the role of pH as initial experiments suggested that Adv addition altered the pH of the solution, likely due to the amine groups in Adv. To isolate the pH effect, Adv was tested in deionized (DI) water, eliminating additional positive ions from the matrix. As shown in Figure 2b, the presence of Adv in DI water resulted in a pH of approximately 7.8, accompanied by a potential shift of around 0.3 V. This solution was taken to represent a basic condition. When the pH was reduced to \(\sim\)4 by adding hydrochloric acid, the potential shift decreased to \(\sim\)0.1 V, as seen in Figure 2a. This decrease in potential shift at lower pH values is likely due to a lower concentration of the Adv cation, which is less prevalent in acidic conditions. This observation confirms that the potential shift may indeed be due to Adv cation presence and its interaction with the interface, which varies with pH. Having established that pH influences the potential shift, we next investigated whether ions in the DI water could contribute to the observed CVs and affect the potential shift. To explore this, we prepared Adv solutions using high-purity Millipore water (18.2 M\(\Omega\)) and initially analyzed them with DB24C8. As shown in Figure 3a, the CVs obtained for Millipore DI water and Adv display distinct shapes and E\({}_{1/2}\) values, in contrast to the similar CV profiles observed for background and Adv in regular DI water. This difference suggests that the CVs obtained with regular DI water (Figure 2) are likely influenced by one or more ions in the matrix, or by combined transfer processes involving both Adv and an interference ion. Figure 1: Representative CVs illustrating the transfer of Adv across the interface between a 3 mM KCl aqueous solution and DCE using a glass nanopipet sensor. CVs were recorded for Adv solutions at concentrations of 100 \(\upmu\)M, 300 \(\upmu\)M, and 1 mM, prepared in 3 mM KCl (orange), and in the presence of DB24C8 as the facilitating ionophore at a scan rate of 10 mV/s. The CV shown in blue represents the background signal obtained for 3 mM KCl without Adv. Interestingly, when Adr solutions prepared in Millipore DI water were tested with DB18C6 as the ionophore, no significant current response was detected. This lack of response can be attributed to two primary factors. First, the stability of the Adr complex when paired with DB18C6 is likely lower than that formed with the larger ring structure of DB24C8. The smaller cavity of DB18C6 may not provide sufficient coordination to stabilize the Adr complex as effectively as DB24C8, which could hinder the transfer of Adr in the presence of DB18C6. This is further supported by Figure 3b, which shows a more stable complex between Adr and DB24C8, likely facilitated by the secondary amine groups proposed by [PERSON] and [PERSON] [36]. These groups, present in Adr, appear to form a more stable interaction with the larger 24C8 crown ether, enabling better ion transfer and current response.