Fig. 6: Surface functionalization of polydiacetylene (PDA)-based colorimetric sensors using specific (bio)receptors.

a Functionalization protocol using an aptamer and corresponding sensing mechanism. PDA monomers with a molar ratio composition of TCDA, TCDA-NHS, and dimyristoylphosphatidylcholine (DMPC) of 9:1:6 were self-assembled to form PDA liposomes, followed by aptamer conjugation via a carbodiimide reaction and UV-assisted polymerization, resulting in an initial blue-colored PDA sensor. When the PDA liposome-aptamer binds specifically to the target bacteria, the binding process distorts the conjugated backbone of PDA, resulting in a visible color change from blue to red. Adapted from ref. ⁷, copyright (Royal Society of Chemistry, 2024). b FTIR spectra of PDA-(bio) receptor conjugations confirming successful aptamer conjugation on PDA through the appearance of characteristic amide (C = O and N–H) stretching peaks, indicating covalent-bond formation. c UV–Vis absorption spectra of PDA before and after aptamer attachment, illustrating the aptamer conjugation onto the surface of liposomes. d Conjugation efficiency of a PDA-(bio) receptor at different aptamer concentrations (1–12%), demonstrating an optimal attachment density for achieving maximum sensing response. e Particle-size-distribution analysis of a PDA-(bio) receptor before and after aptamer modification, demonstrating stable nanoscale structures. Reproduced from ref. ⁷, copyright (Royal Society of Chemistry, 2024). f Analytical performance of a PDA liposome-aptamer sensor for Zn²⁺ ion detection. The selectivity study of the PDA liposome-aptamer towards various cations showed a preferred response to Zn²⁺. g Red chromatic shift of PDA liposome-aptamer in response to increased Zn²⁺ concentration at different incubation times. h Representative color change from blue to red in PDA liposome-aptamer with increasing Zn²⁺ concentration from 0 to 1000 µM, compared to negative and positive controls. Reproduced from ref. ¹³⁹, copyright (Elsevier B.V., 2016).