A nitrile-mediated SERS aptasensor coupled with magnetic separation for optical interference-free detection of atrazine

A novel aptasensor based on the combination of surface-enhanced Raman scattering (SERS) and magnetic separation is presented for sensitive and selective determination of atrazine. 4-(Mercaptomethyl) benzonitrile (MMBN), providing a prominent peak (2227 cm −1 ) in the Raman-silent spectral window (1800–2800 cm −1 ), is selected as Raman tag to eliminate optical interference from biomolecules in sensing system. The MMBN and atrazine-binding aptamer are assembled on silver nanoparticles (AgNPs) to serve as Raman probe (MMBN-AgNPs-aptamer). Meanwhile, Fe 3 O 4 @Au core/shell nanoparticles conjugated with the complementary DNA (Fe 3 O 4 @Au-cDNA) are prepared as Raman substrate to extract the Raman probe with magnetic separation. Atrazine specifically binds to aptamer, and hinders the formation of Fe 3 O 4 @Au-cDNA-aptamer-AgNPs-MMBN (expressed as “Fe 3 O 4 @Au-AgNPs”) complex. Therefore, the Raman intensity of MMBN on substrate decreases with the increment of atrazine concentration. Under optimal SERS conditions, the proposed aptasensor is used to detect atrazine in the laboratory and real samples. The as-prepared atrazine sensor demonstrates a broad dynamic range of 1–50 nM, as well as a low detection limit of 0.67 nM (S/N = 3). For real sample test, the recovery rate ranges from 98.7%–106.6%. The fabricated aptasensor shows superior interference-free performance for atrazine determination in the presence of analogs at high levels.