Rapid ultrasensitive detection of methamphetamine based on the FRET mechanism between apta-nanobiosensor based on CdTe/ZnS quantum dots and DNA-conjugated Cy3 fluorophore: Forensic biological fluids

A novel Apta- nano biosensor (ANB) based on CdTe/ZnS QDs were designed and applied for ultrasensitive determination of methamphetamine (MA) as one most addictive psychoactive substance at 1 min. Different steps of ANB formation and MA detection were reported by fluorescence spectra. In short, in the first step, the water-soluble ANB was prepared by the ligand-exchange method using the replacement of thioglycolic acid (TGA) and glutathione (GSH) molecules at the surface of QDs with thiolated MA aptamer. This phenomenon increases QDs' fluorescence intensity. In the second step, the optimal amount of DNA-conjugated Cy3 fluorophore was gradually added to obtain the mixture. Based on the fluorescence resonance energy transfer (FRET) mechanism, energy transfer from QDs to Cy3 fluorophore led to the quenching of QDs and turning on the fluorophore. Finally, by titrating different amounts of MA into this system, the thiolated labeled aptamer tends to attach to the target (MA). The Cy3 fluorophore is separated from the QD surface, which leads to the quenching of QDs and fluorophore. This quenching of the ANB could be performed based on a kind of photo-induced electron transfer (PET) mechanism. The detection limit of MA is 4.15 ± 1.08 × 10−12 mol L−1 with a dynamic range from 1.38 ± 0.75 × 10−11 to 99.98 ± 1.03 × 10−8 mol L−1. ANB was applied to determining MA in forensic biological fluids and the obtained results were evaluated with LC-MS-MS with satisfactory results.