Abstract
Surface enhanced Raman scattering (SERS) is a powerful technique for food inspection because of its readiness, sensitivity, and minimum sample preparation requirements.1 Milk is a vulnerable target for contamination. In this work, we demonstrate a reliable SERS method for detecting toxins in milk focusing on brodifacoum, an anticoagulant rodenticide and sodium fluoroacetate, also commonly known as 1080. Surface-enhanced Raman spectroscopy is an advanced Raman technique for ultrasensitive detection of chemical and biological species. Liquid milk presents further challenges due to the complex colloidal nature of milk itself; producing much weaker SERS. Therefore, we applied and omniphobic surface platform, which has the potential to deliver near 100% analyte concentration by constant contact angle drying (and therefore no contact line pinning). Such omniphobic SERS substrates, so-called Slippery liquid-infused porous surfaces (SLIPS) were recently reported.2 SLIPSERS method coupled with the dilution of rodenticide spiked milk samples and then extraction with a mixed solvent of methanol: water (3:1) was performed for rodenticide detection.3 All the spectra were taken on an in-house Raman set up based on a Princeton Instruments FERGIE spectrometer using 532 nm excitation wavelength (with 2-3 mW laser power) focused onto the sample using a 40 × 0.65 NA objective. A series of diluted concentrations of each rodenticide ranging from 8- fold dilution to 1600-fold dilution were used to construct a calibration curve. There is a good linear relationship (R2 =0.9897) in this concentration range. A critical challenge in detecting bioanalytes is to achieve high specificity, high throughput, and trace-level detection.4 The approach adopted in this work can be extended to detect various molecules in complex chemical and biological matrices.
