Ratiometric SERS Sensor with Schiff-Base Reaction and Solvent Internal Standard for High-Precision Detection of Hydrazine

Abstract Hydrazine (N2H4) is a widely used industrial chemical yet poses severe toxicity risks to human health and ecological systems. It is highly urgent to develop rapid, reliable, and accurate analytical methods for trace N2H4 monitoring. Surface-enhanced Raman spectroscopy (SERS) offers distinct advantages for trace analysis owing to its fingerprint specificity and ultrahigh sensitivity. However, conventional SERS strategies for hydrazine detection often suffer from poor signal reproducibility and unsatisfactory quantitative accuracy. Herein, we rationally construct a robust ratiometric SERS sensor for precise trace N2H4 determination by using highly stable gold@silver core–shell nanocubes (Au@AgNCs) as the enhancing substrate and 4-ethynylbenzaldehyde (4-EBA) as the specific recognition probe. The aldehyde group of 4-EBA selectively reacts with N2H4 via a Schiff-base reaction, generating a hydrazone product with a characteristic C═N Raman peak at 1533 cm–1. Crucially, the intrinsic Raman band of ethanol was employed as a built-in internal standard to effectively eliminate signal fluctuations caused by laser power drift, substrate inhomogeneity, and measurement variations, thereby significantly improving quantitative reliability and reproducibility. Density functional theory (DFT) calculations were further conducted to validate the sensing mechanism. The developed sensor exhibited excellent sensitivity, high selectivity, and good stability for N2H4 detection. Notably, it achieved strong anti-interference ability and reliable quantitative performance in real river water samples. This work provides a feasible and promising strategy for the on-site, accurate monitoring of toxic environmental pollutants.