Aromatic Surfactant as Aggregating Agent for Aptamer-Gold Nanoparticle-Based Detection of Plasmodium Lactate Dehydrogenase.

A novel ssDNA aptamer (P38), with a 40 mer random region flanked by primer-binding sites on both sides, targeting Plasmodium falciparum lactate dehydrogenase (PfLDH) has been developed through systematic evolution of ligands by exponential enrichment (SELEX), including counter SELEX against human lactate dehydrogenase A and B (hLDH A and B). The 2D structure of P38 shows the presence of three stem loops with a δG of -9.18 kcal/mol. EMSA studies on P38 complexes with the increasing concentration of PfLDH revealed a dissociation constant of 0.35 µM. P38 has been exploited for the quantitative detection of PfLDH using cationic surfactant-mediated aggregation of gold nanoparticles (16-nm diameter) as an optical probe. Among the three different cationic surfactants, characterized by different hydrocarbon tail groups, benzalkonium chloride (BCK) was found to be most efficient with a limit of detection of 281 ± 11 pM. This BCK-based approach with the novel highly selective aptamer provides simple and sensitive detection of PfLDH in the clinically relevant range.