A simple and sensitive aptasensor for colorimetric detection of adenosine triphosphate based on unmodified gold nanoparticles

The principle of the proposed strategy for colorimetric detection of ATP using unmodified gold nanoparticles is shown in the above graph. The aptamer-based hairpin probe (AHP) was constructed with anti-ATP aptamer (blue region) and another five nucleotides (red region) added to the 5′-end of the aptamer which were complementary to nucleotides at the 3′-end of the aptamer, forming a hairpin-shaped structure. In the absence of ATP, the hairpin probes were rigid, and their negatively charged phosphate backbones were exposed. The strong repulsion between the hairpin probes and negatively charged AuNPs made their binding negligible, which could not prevent salt-induced AuNP aggregation. Conversely, in the presence of ATP, the hairpin probes under went a conformational change, forming aptamer-ATP complexes and exposing flexible ssDNA ends (red region). The ssDNA ends had strong attractive electrostatic interactions with AuNPs and thus prevented them from salt-induced aggregation, corresponding to a blue-to-red color change and thus providing the colorimetric detection of the target ATP.169