## 2 Results
### Selectivity Studies
#### 2.3.2 Binary Competitive Assays  
The selectivity of the MIPs was further tested using binary mixtures of **1** and competing analytes **17**, **18** and **19**. Analyte **20** was not pursued in this assay due to HPLC separation issues with **1**. The uptake of all analytes was observed to be higher for MIPs than in their corresponding NIPs (Supplementary Figure S24), thus suggesting that they have access to and an affinity for the imprinted cavities. To facilitate binding selectivity analysis, we introduced the quantitative values summarized in Table 3. First, the uptake of **1** as the sole analyte, a measure of the MIP binding capacity, is taken as a reference; the binding of binary analytes is then normalised against this reference. Thus, if the normalised binding of an analyte is greater than 1, i.e., greater than 100%, then this means that its uptake is higher than the expected binding capacity. The selectivity index (SI) of an analyte is defined here as the ratio of normalised analyte binding to normalised **1** binding. Although selectivity assessment is more essential for MIPs than NIPs, and despite the fact that NIP binding could be variable due to its superficial nature, the results of this study showed analyte **19** to be competitive with **1** in all NIP systems, giving normalised binding values as high as 3.15. The binding of **17** and **18**, however, was always lower or equivalent to that of **1**. Uptake of **1** by the semi-covalent NIPs is lower than the reference in all cases, while self-assembly NIPs registered **1** binding higher than the reference in some binary mixtures. In the case of MIPs, **19** was also observed to be highly competitive, reducing the uptake of **1** to a low of 0.42, i.e., 42% (**T16**MIPCHCl3), with respect to the reference and displayed normalised binding and SIs higher than **1** (as high as 1.73 and 1.85, respectively, with **E7**-MIPCHCl3) in all cases. Analyte **18** displayed low levels of competition with **1** in the self-assembly MIPs (SI = 0.16 to 0.37), slightly reducing the binding of **1** in some cases. However, the presence of **18** brought about a significant reduction in **1** binding (below 50%), resulting in a moderate SI of 0.46 (**E16**MIPCHCl3) and 0.61 (**T16**MIPCHCl3) in the case of the semi-covalent MIPs. Analyte **17** did not have a significant impact on the binding of **1**, except in **T16**MIPCHCl3, and displayed low-to-minimal competition tendency against **1**, with normalized binding and SI values all being <0.2. In some instances (also observed with the NIPs), the presence of **17** and **18** enhanced the uptake of **1**, which could be attributed to its interaction with these analytes by hydrogen bonding and/or pi-pi stacking. On the other hand, in the presence of **19**, the uptake of **1** in all polymers tested was reduced, thus confirming its observed competitive tendency against **1**. Consistent with the results of the non-competitive cross-reactivity assays, the results of the competitive (binary mixtures) binding studies showed all MIPs to be highly selective towards **1** in the presence of **17** (SI < 0.2), moderately selective in the presence of **18** (SI > 0.2 to ~0.6) and non-selective in the presence of **19** (SI > 1).