Figure 3. The Diels–Alder cycloaddition reaction to generate QD-TALEs.

(a) Schematic of fluorescence labelling of TALE N2-L with red QDs. First, trans-cyclooctene TCO2 is ligated onto the LAP-tag fused to the TALE N2-L. Second, the TCO2-decorated TALE is conjugated with the tetrazine-QDs (Tz1-QDs) via the Diels–Alder cycloaddition. Molecular formula of TCO2 and Tz1 are shown on the right side. (b) ¹H nuclear magnetic resonance spectrum of ∼5 mg of TCO2 in CDCl₃ and its species assignments. (c) Agarose gel electrophoresis of native QDs and conjugated with tetrazine.