Highly flexible and stable aptamer-caged nanoparticles for control of thrombin activity

Abstract

In this paper, we have demonstrated that the thymine linker length number (T_n, n = 0–60) and stem pair number (P_m, m = 0–16) in the terminal of thrombin binding aptamers (TBAs) have a strong impact on the flexibility and stability of TBA-modified gold nanoparticles (TBA–Au NPs) and thus the binding strength and inhibitory potency toward thrombin. The anticoagulation of TBA–Au NPs increased with an increase in the linker length from T₀ to T₃₀ due to an increase in the flexibility of G-quadruplexes of TBAs on the Au NP surfaces (TBA-T_n–Au NPs). The inhibition of TBA-P_mT₁₅–Au NPs increased with an increase in the P_m from P₀ to P₈ as a result of the increase in the rigidity and the stability of G-quadruplexes of the TBAs on the Au NP surfaces. The best results were observed for multivalent TBA–Au NPs conjugates—TBA₁₅/TBA₂₉-P₈T₁₅–Au NPs—which exhibited ultra-high binding affinity toward thrombin (K_d = 8.86 × 10⁻¹² M) and thus extremely high anticoagulant (inhibitory) potency because of their particularly flexible and stable conformation and multivalency. Compared to the case without inhibitors, their measured thrombin clotting time (TCT) was 296 times longer, whereas for TBA₁₅ alone it was only 3.9 times longer. From the dosage dependence of the TCT delay, we further demonstrated the anticoagulation ability of our TBA₁₅/TBA₂₉-P₈T₁₅–Au NPs was much better than the commercial drugs (argatroban and hirudin). Moreover, the Au NPs modified with TBA with photocleavable (PC) units allow a reversal in the activity of TBA_PC–Au NPs via near-UV light-inducement of TBA release from Au NPs. We believe that our described techniques can be used widely to modify NPs with other anticoagulant DNA or RNA aptamers towards different proteins such as factor IX, activated protein C, and factor VIIa.