A SERS nanoswitch based on Cu(II)-mediated dual-ligand AuNPs reversible aggregation for pyrophosphate ions detection

Surface enhanced Raman spectroscopy (SERS) detection was not as accurate and reproducible as fluorometry due to some uncertainties such as operator's focus adjustment and difference between capillaries. Herein, the weak Raman signal (1640 cm−1) from water bending vibration is adopted as a benchmark to improve the practical applicability of Raman detection. Specifically, amygdalin and citrate sodium were applied as reducing and capping agent to synthesize dual-ligand gold nanoparticles (DL-AuNPs). Additionally, the cyano group of amygdalin can attach to the surface of DL-AuNPs and generate a primary SERS signal (2174 cm−1), which can be significantly enhanced by Cu(II) as DL-AuNPs aggregates. More importantly, the strong binding affinity between pyrophosphate ions (PPi) and Cu(II) redisperses DL-AuNPs and decreases the signal intensity, making the DL-AuNPs/Cu(II) SERS sensor promising for the detection of PPi. This proposed method presents a reliable SERS analysis with the stable water background calibration and broaden the application of SERS technique in aqueous solution target monitoring.