Ultralow detection of 3,4-methylenedioxymethylamphetamine using an immunofluorescence nanoconjugate of heavy metal-free alloyed quantum dots and NiCeFe3O4 magnetic nanoparticles

The recreational use of 3,4-methylenedioxymethylamphetamine (MDMA) remains consistently high on a global level. This reinforces the importance of early, rapid and accurate detection of MDMA. This work reports on the novel development of a rapid, ultrasensitive and selective immunofluorescence nanobiosensor probe for MDMA. To develop the nanoprobe, heavy metal-free AuZnFeSeS alloyed quantum dots (QDs) were synthesized and coated with carboxy (COOH)-silica and subsequently conjugated to an anti-MDMA antibody (Ab). Secondly, spinel NiCeFe3O4 magnetic nanoparticles (MNPs) were synthesized, surface functionalized with L-cysteine and conjugated to the same anti-MDMA Ab. An immunocomplex was established where both AuZnFeSeS QDs-Ab and NiCeFe3O4-Ab each captured the target MDMA drug. The bound QDs fluorescently reported the surface bio-molecular interaction between the nanomaterials and Ab while the bound NiCeFe3O4 MNPs functioned as an adsorbent and as a signal amplifier. The Ab binding on AuZnFeSeS QDs surface switched off the fluorescence of the QDs but upon interaction of AuZnFeSeS QDs-Ab with NiCeFe3O4-Ab, the fluorescence of the bound QDs was switched on. Experimental analysis revealed the inefficiency of AuZnFeSeS QDs-Ab (without NiCeFe3O4-Ab) to detect MDMA ultrasensitively and selectively; hence, the use of NiCeFe3O4-Ab was justified in the probe system. Under optimum reaction conditions, MDMA was quantitatively detected using the AuZnFeSeS QDs-Ab-NiCe-Fe3O4-Ab nanocomplex in the concentration range of 0.05-50,000 nM and a detection limit of 0.02 nM (0.0046 ng/mL) was obtained. The developed AuZnFeSeS QDs-Ab-NiCeFe3O4-Ab nanoprobe was successfully used to detect MDMA in urine with satisfactory recoveries.