Selective and colorimetric detection of pyruvic acid using conformational switch of i-motif DNA and unmodified gold nanoparticles

A novel, highly selective and colorimetric strategy for pyruvic acid (PA) detection is proposed based on the conformational change of i-motif DNA and the salt-induced aggregation effects of unmodified gold nanoparticles. The addition of PA can induce the C-rich DNA to fold into a rigid close-packed i-motif DNA, which accordingly loses its ability to effectively protect and stabilize AuNPs from salt-induced aggregation. In the presence of pyruvate decarboxylase (PDC), PA can be efficiently converted to acetaldehyde and CO2 through nonoxidative decarboxylation, causing the solution pH to change from acidic to neutral. Thus, the C-rich DNA can still maintain its extended single strand status and can effectively stabilize the AuNPs from salt-induced aggregation. The absorbance difference before and after the addition of PDC depends on the concentration of PA and can be used for the quantitative determination of PA. The developed colorimetric sensor can achieve PA detection with a linear range from 5.6 x 10 (-6) M 1.68 x 10(-4) M and a detection limit of 3.0 mu M. The as-established colorimetric strategy opens a new avenue for the specific detection of DNA conformation-responsive small biomolecules.