Label-free colorimetric detection of tetracycline using gold nanoparticles with different surface charge

Visual detection assay based on aptamer unmodified gold nanoparticles shows great potential in biotechnology. Here, we reported a visible, salt-free and highly sensitive tetracycline (TC) assay based on a colloidally stable mixture of AuNPs that contains poly (diallyl dimethylammonium chloride) capped AuNPs ((+)AuNPs) and tetracycline-specific aptamer capped AuNPs (Apt-capped AuNPs). This reported TC assay was visible and salt-free that did not need any salt during TC detection. With naked eyes, nanomolar tetracycline concentrations could be identified within 20 min. A detection limit of tetracycline down to a concentration of 1.0 fM with a broad detection range of 8 order of magnitudes (5 × 10^-14 M to 5 × 10^-6 M) was reached. Furthermore, the reported TC assay also exhibited good selectivity for tetracycline over other antibiotics, metal cations, proteins and amino acids. These findings clearly demonstrated the high potential of the reported TC assay for TC detection and monitoring.