transitionsFour variations, 1–4 (Table 1, Fig. S3), of a previously screenedZn2+aptamer [31], were investigated for the effects of aptamerlength and structure on the sensitivity of PDA color transitions.Aptamers 1 and 2 are hairpin aptamers composed of 65 nucleobasesand differ by 6 carbons in the 5carbon linker between the firstbase and the liposome surface