Fluorometric and electrochemical dual-mode nanoprobe for tetracycline by using a nanocomposite prepared from carbon nitride quantum dots and silver nanoparticles

A fluorometric and electrochemical dual-mode method is described for sensitive and specific detection of tetracycline (Tc). A novel nanoprobe was designed that is making use of a Tc-specific aptamer (apta), carbon nitride quantum dots (CNQDs) and silver nanoparticles (AgNPs). The aptamer was linked to the CNQDs which then were used as templates to synthesize the apta-CNQD@AgNP nanocomposites. The blue fluorescence of the nanocomposites (with excitation/emission maxima at 365/440 nm) is quenched. The addition of Tc leads to fluorescence recovery and a decrease in the electroconductivity of a gold electrode modified with apta-CNQD@AgNPs. The fluorometric method has a linear response in the 0.1 μM - 10 mM Tc concentration range and a 15 nM detection limit. The amperometric method (best performed at a working voltage of 0.21 V vs. Ag/AgCl) has a linear response in the 1 nM to 0.1 mM Tc concentration range and a 0.26 nM detection limit. Recoveries of Tc from spiked milk samples were comparable to data obtained by HPLC.