Internal standard-based self-assembly Ag@4-MBN@Ag nanoarray SERS ratio sensor for sensitive detection of deltamethrin in foods

Herein, a precise and interference-free surface-enhanced Raman spectroscopy (SERS) ratio sensor was established for deltamethrin detection. A Ag@4-MBN@Ag nanoarray with abundant "hot-spots" was first prepared via liquid-liquid interface self-assembly (LLISA), then applied as a SERS substrate. The embedded 4-mercaptobenzonitrile (4-MBN) provided an interference-free nitrile stretching vibration (at 2226 cm-1) in "Raman biological-silent" region, which was utilized as SERS internal standard peak. The SERS intensity ratio I1147/I2226, where 1147 cm-1 corresponds to a SERS peak of deltamethrin, increased linearly with the logarithm of deltamethrin. Under optimized conditions, the developed SERS ratio sensor allowed sensitive detection of deltamethrin over the concentration range 10-5 to 103 μM, with a low limit of detection (LOD) of 3.16×10-7 μM. Recovery tests performed in deltamethrin-spiked pear and cabbage samples showed excellent recoveries (95.00% to 101.06%). Furthermore, the sensor was successfully applied to quantify deltamethrin in four kinds of food samples, with results consistent with analyses performed using gas chromatography.