Cellular uptake of aptamer by Quantum Dots (QDs)

Aptamers are short single stranded oligonucleotide sequences that exhibit high binding affinity and high specificity against their target molecule. Binding affinity and specificity are crucial features for aptamers in order to exploit their therapeutic and diagnostic potential and to make them an appealing candidate for the commercial market1,2. Aptamers contain functional moieties that can fold into different conformation such as hairpin stem and loops, G-quadruplexes, and pseudoknots. A study led by Dr Harleen Kaur involving unique stem-loop truncation strategy was employed to find the binding domain in a 66-mer long DNA aptamer sequence against the heparin binding domain of vascular endothelial growth factor (VEGF165) protein1. The results from the work demonstrated identification of a 26-mer long aptamer sequence referred as SL2-B in the paper with improvement in the binding affinity by more than 200-folds (Kd = 0.5nM) against VEGF protein. To improve the biostability of the aptamer in the biological fluids, the phosphorothioate linkages (PS-linkages) in the phosphate backbone of the DNA were introduced at the 5’-and 3’-termini of the obtained SL2-B aptamer sequence. The PS-modified SL2-B aptamer sequence demonstrated significant improvement in the stability without comprising