Contents lists available at ScienceDirect Food Chemistry journal homepage: www.elsevier.com/locate/foodchem Analytical Methods Rapid detection and quantification of 2,4-dichlorophenoxyacetic acid in milk using molecularly imprinted polymers–surface-enhanced Raman spectroscopy Marti Z. Hua a , Shaolong Feng a , Shuo Wang b , Xiaonan Lu a, ⁎ a Food, Nutrition and Health Program, Faculty of Land and Food Systems, The University of British Columbia, Vancouver, BC, Canada b Tianjin Key Laboratory of Food Science and Health, School of Medicine, Nankai University, Tianjin 300071, China ARTICLE INFO Keywords: SERS Molecular imprinting Artificial antibody 2,4-D Milk Food safety ABSTRACT We report the development of a molecularly imprinted polymers–surface-enhanced Raman spectroscopy (MIPs–SERS) method for rapid detection and quantification of a herbicide residue 2,4-dichlorophenoxyacetic acid (2,4-D) in milk. MIPs were synthesized via bulk polymerization and utilized as solid phase extraction sorbent to selectively extract and enrich 2,4-D from milk. Silver nanoparticles were synthesized to facilitate the collection of SERS spectra of the extracts. Based on the characteristic band intensity of 2,4-D (391 cm -1 ), the limit of detection was 0.006 ppm and the limit of quantification was 0.008 ppm. A simple logarithmic working range (0.01–1 ppm) was established, satisfying the sensitivity requirement referring to the maximum residue level of 2,4-D in milk in both Europe and North America. The overall test of 2,4-D for each milk sample required only 20 min including sample preparation. This MIPs-SERS method has potential for practical applications in detecting 2,4-D in agri-foods. 1. Introduction Since the commercialization of 2,4-dichlorophenoxyacetic acid (2,4- D) after World War II, 2,4-D and its derivatives have been widely used to control broadleaf weeds in multiple settings, including agriculture, aquatic areas, landscape, and turf (Walters, 1999). With the extensive use, the residue of 2,4-D has been detected in the environment water (Yang, Jiao, Zhou, Chen, & Jiang, 2013), fresh produce (Ting & Kho, 1998), dairy products (Bogialli et al., 2006), and commonly in human urine (Ye, Wong, Zhou, & Calafat, 2014). The toxicity of 2,4-D has been debated for decades both in academia and government, including the frequent reviews and evaluations focusing on the carcinogenicity to humans (Health Canada, 2016; Smith, Smith, La Merrill, Liaw, & Steinmaus, 2017; von Stackelberg, 2013; World Health Organization, 2015). Regardless, maximum residue levels (MRLs) of 2,4-D in various food products are strictly regulated worldwide. In particular, the MRLs of 2,4-D in milk are set as 0.01 mg/kg (ppm) (European Commission, 2005), 0.03 ppm (Health Canada, 2013), and 0.05 ppm (2,4-D; Tolerances for Residues, 2012). Currently, liquid chromatography–mass spectrometry (LC–MS) is still the gold standard for the detection of 2,4-D in foods with the limit of quantification (LOQ) at sub-ppb level (Bogialli et al., 2006; Xiong et al., 2014). However, LC–MS is well known as high-cost, time-con- suming, and requiring expertise in operation. Moreover, complicated pre-treatment and clean-up procedures are usually required in prior to a 0.5–1 h of sample running (Bogialli et al., 2006). Besides chromato- graphic methods, immunoassays have also been reported with the working ranges at sub-ppm level in water (Vinayaka, Basheer, & Thakur, 2009) and orange peel (Vdovenko et al., 2013), but a long incubation time of 2–3 h was required. Rapid detection methods for 2,4- D include ratiometric fluorescence sensor (Wang et al., 2016), carbon nanotube liquid gated transistor (Wijaya et al., 2010), and others. Yet, their applications were limited to samples requiring no or little matrix effect, such as water and soil extracts. Therefore, a rapid and relatively cost-effective detection method that can be applied to real food samples in a high-throughput manner is highly required, especially for perish- able foods, such as milk. Molecularly imprinted polymers (MIPs) are polymers that are che- mically synthesized, forming cavities with high affinity to a selected “template” molecule. Briefly, the template (i.e., targeted analyte) and selected functional monomers assemble spontaneously when they are mixed, followed by co-polymerization with the cross-linkers. After that, the template molecules are removed from the complex, leaving the MIPs with cavities that are complementary to the template (Fig. 1). https://doi.org/10.1016/j.foodchem.2018.03.075 Received 26 May 2017; Received in revised form 15 January 2018; Accepted 17 March 2018 ⁎ Corresponding author at: Food, Nutrition, and Health Program, Faculty of Land and Food Systems, The University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada. E-mail address: xiaonan.lu@ubc.ca (X. Lu). Food Chemistry 258 (2018) 254–259 Available online 19 March 2018 0308-8146/ © 2018 Elsevier Ltd. All rights reserved. T