Label-free colorimetric logic gates based on free gold nanoparticles and the coordination strategy between cytosine and silver ions

Abstract

A colorimetric sensing strategy combined with logic gates was demonstrated by taking advantage of the dispersion and aggregation of gold nanoparticles (AuNPs) on a paper-based analytical platform. By employing cytosine–Ag⁺–cytosine (C–Ag⁺–C) coordination chemistry, label-free oligonucleotide sequences (S₁) could be attached to unmodified AuNPs, which on addition of S₂ (complementary to S₁) or silver ions (Ag⁺) immediately aggregated, giving rise to an OR function. Furthermore, the gate could be employed to analyze Ag⁺ rapidly. By taking advantage of the disparate adsorption properties of single-stranded or double-stranded DNA modified AuNPs, an INHIBIT logic gate was constructed with S₁ and Ag⁺ as inputs to the S₂-attached AuNP mixture. In addition, using the S₁/S₂-attached-AuNP mixture as a basic work unit and Ag⁺ and cysteine as two inputs, the IMPLICATION logic gate was also designed, which provided an approach for cysteine detection. The proposed logic gates with excellent selectivity toward Ag⁺ against other metal ions addressed concerns of low cost, simple fabrication, and easy operation, providing an attractive alternative to conventional methods, which usually involve sophisticated instruments, complicated processes, and long periods of time. More importantly, such methods exhibited high sensitivity in the detection of Ag⁺ in river water samples.