Molecularly imprinted core-shell Au nanoparticles for 2,4-dichlorophenoxyacetic acid detection in milk using surface-enhanced Raman spectroscopy

The growing concern about chemical contaminants in food has increased the need for a rapid, selective, and cost-efficient sensing technology. Molecularly imprinted polymers (MIPs) have emerged as potential artificial sensing elements owing to their high sensitivity, stability, selectivity, and reproducibility. Recent advances further highlight the growing role of computational tools, including molecular docking, molecular dynamics (MD), quantum chemical calculations (QC), and molecular mechanics (MM), in rational MIP design. These methods guide the rational selection of monomers, solvents, and cross-linkers by predicting their effects on template interactions, solvent polarity, and cavity stability, thereby minimizing trial and error in MIP design. This review presents a comprehensive overview of recent progress in MIP-based sensors for the detection of chemical contaminants in food, emphasizing experimental and computational perspectives. In addition, this review covers chromatography-integrated MIP systems, where imprinted polymers are used as selective recognition elements within separation-based methods for food contaminant analysis. The reviewed platforms enable not only sensitive detection but also reliable quantification of food contaminants across diverse matrices. Special focus is given to case studies that demonstrate the applications of MIPs in food analysis and the role of in silico strategies in optimizing sensor performance. By bridging experimental innovation with a computational design, this review aims to provide researchers with an integrated framework for developing next-generation sensing platforms that are selective, sensitive, and practical for real-world food safety monitoring.

A Biosensor Combining Molecularly Imprinted Polymers (M-MIPs) and Surface Enhanced Raman Spectroscopy (SERS) to Detect Antibiotics in Food Samples   Yi Sun,1*, Jon Ashley1, Kaiyu Wu1, and Anja Bosen1. 1 Department of Micro- and Nanotechnology, Technical University of Denmark, Ørsteds Plads, DK-2800 Kgs. Lyngby, Denmark   * Email: sun.yi@nanotech.dtu.dk; Tel.: +45 45256319   In this study, temperature-responsive magnetic molecularly imprinted polymers (M-MIP) nanoparticles were synthesized for the first time for the extraction of cloxacillin in pork products. By combining the M-MIPs with surface enhanced Raman spectroscopy (SERS), a sensitive biosensor was demonstrated to detect cloxacillian with pico-mole sensitivity. MIPs are synthetic ligands which can be tailored to bind any analyte of choice1.  They are of great interest due to their thermal stability, robustness, low cost and comparable binding affinity. They have been used in sample preparation and biosensing as an attractive alternative to natural antibodies to capture targets ranging from small molecules to big proteins.   In this work, the magnetic nanoparticles with MIP-based receptors were synthesized for efficient and rapid extraction of antibiotic residues in pork samples.  Fe3O4 nanoparticles were obtained using the solvothermal synthesis.  The resultant nanoparticles were treated with Tetraethyl orthosilicate (TEOS) to form a SiO2 layer.  Finally a thin MIP layer was polymerized round the nanoparticles using azobisisobutyronitrile (AIBN) as the initiator, ethylene glycol dimethacrylate (EDGMA) as the cross-linker, N-isopropylmethacryamide (NIPAm), methacrylic acid (MAA) as the monomers and the antibiotic as the template.  By adding the monomer NIPAm, the MIPs become temperature responsive, and can swell at low temperature to release the target. The corresponding magnetic non-imprinted polymer nanoparticles (M-NIP) was prepared using the same method in the absence of the template. An Overview of the synthesis strategy is shown in Fig. 1. The resultant M-MIP nanoparticles were characterized using IR, XRD scanning electron microscopy (SEM) and transmission electron microscopy (TEM) (Fig. 2).  Both binding affinities of the resultant M-MIPs and M-NIPs were tested using UV absorbance (Fig. 3). M-MIPs with 300-400 nm in size and good binding capacities were obtained. To demonstrate the feasibility of using M-MIPs for sample preparation, the synthesized M-MIPs were mixed with pork blood samples spiked with Chloxacillian. After incubation at room temperature, the M-MIPs were collected using a magnet and washed by acetonitrile. Owing to the thermos-responsive properties of MIPs, Chloxacillian was easily released by cooling the MIPs to 4 degree. The collected Chloxacillian was dropped on a SERS substrate which contained an array of silicon micropillars coated with silver. The corresponding calibration plots showed a detection limit (LOD) of about 50 pmol (Fig. 4). The biosensor combining M-MIPs and SERS would be widely used on site or in the field for rapidly screening food contaminants to ensure food safety. Fig. 1: Overview of the synthesis of M-MIPs     Fig.2 IR characterization of Fe3O4, Fe3O4@SiO2, Fe3O4@ SiO2-MPA and, Fe3O4@SiO2-MIP; XRD of Fe3O4. Fig.3 (A) Binding kinetics and (B) Binding capacity of Cloxacillian MIPs and NIPs.                         Fig.4 SERS spectra of cloxacillin in MeOH:acetic acid (9:1) and corresponding calibration plots.   REFERENCES:   J. Ashley, M-A. Shahbazi, K. Kant, V. A. Chidambara, A.Wolff, D. D. Bang, Y. Sun, “Molecularly Imprinted Polymers for Sample Preparation and Biosensing in Food analysis: Progress and Perspectives, Biosens. Bioelectron. 2017, 91, 606-615.    

With the globalization of food and its complicated networking system, a wide range of food contaminants is introduced into the food system which may happen accidentally, intentionally, or naturally. This situation has made food safety a critical global concern nowadays and urged the need for effective technologies capable of dealing with the detection of food contaminants as efficiently as possible. Hence, Surface-enhanced Raman spectroscopy (SERS) has been taken as one of the primary choices for this case, due to its extremely high sensitivity, rapidity, and fingerprinting interpretation capabilities which account for its competency to detect a molecule up to a single level. Here in this paper, we present a comprehensive review of various SERS-based novel approaches applied for direct and indirect detection of single and multiple chemical and microbial contaminants in food, food products as well as water. The aim of this paper is to arouse the interest of researchers by addressing recent SERS-based, novel achievements and developments related to the investigation of hazardous chemical and microbial contaminants in edible foods and water. The target chemical and microbial contaminants are antibiotics, pesticides, food adulterants, Toxins, bacteria, and viruses. In this paper, different aspects of SERS-based reports have been addressed including synthesis and use of various forms of SERS nanostructures for the detection of a specific analyte, the coupling of SERS with other analytical tools such as chromatographic methods, combining analyte capture and recognition strategies such as molecularly imprinted polymers and aptasensor as well as using multivariate statistical analyses such as principal component analysis (PCA)to distinguish between results. In addition, we also report some strengths and limitations of SERS as well as future viewpoints concerning its application in food safety.

The quinolone antibiotics represented by enrofloxacin (ENRO) are harmful to the ecological environment and human health due to illegal excessive use, resulting in increasing food residues and ENRO levels in the environment. To this end, we developed a MIPs–SERS method using surface-enhanced Raman spectroscopy (SERS) and molecularly imprinted polymers (MIPs) to detect ENRO in food matrices. Firstly, a layer of silver nanoparticles (Ag NPs) with the best SERS effect was synthesized on the surface of copper rods as the enhancing material by in situ reductions, and then MIPs targeting ENRO were prepared by the native polymerization reaction, and the MIPs containing template molecules wrapped on the surface of silver nanoparticle films (Ag NPs–MIPs) were obtained. Our results showed that the Ag NPs–MIPs could specifically identify ENRO from the complex environment. The minimum detection limit for ENRO was 0.25 ng/mL, and the characteristic peak intensity of ENRO was linearly correlated to the concentration with a linear range of 0.001~0.1 μg/mL. The experimental results showed that in comparison to other detection methods, the rapid detection of ENRO in food matrices using Ag NPs–MIPs as the substrate is reliable and offers a cost-effective, time-saving, highly selective, and sensitive method for detecting ENRO residues in real food samples.

There is growing concern in recent years for consumers about contamination of pesticides in fruits due to increasing use of pesticides in fruits. The objective of this study was to use surface-enhanced Raman spectroscopy (SERS) to detect and characterize pesticides extracted from fruit surfaces. Gold-coated SERS-active nanosubstrates were used for SERS measurement. Three types of pesticides (carbaryl, phosmet, and azinphos-methyl) widely used in apples and tomatoes were selected. Significantly enhanced Raman signals of pesticides were acquired by SERS from the extract of fruit samples and exhibited characteristic patterns of the analytes. Multivariate statistical methods such as partial least squares and principal component analysis were used to develop quantitative and qualitative models. SERS was able to detect all three types of pesticides extracted from fruit samples at the parts per million level. The study of detection limit demonstrated that at 99.86% confidence interval, SERS can detect carbaryl at 4.51 ppm, phosmet at 6.51 ppm, and azinphos-methyl at 6.66 ppm spiked on apples; and carbaryl at 5.35 ppm, phosmet at 2.91 ppm, and azinphos-methyl at 2.94 ppm on tomatoes. Most of these detection limits meet the maximum residue limits established by Food and Agriculture Organization of the United Nations and World Health Organization. Satisfactory recoveries (78–124%) were achieved for samples with concentrations at and larger than the detection limit. These results demonstrate that SERS coupled with novel SERS-active nanosubstrates is a rapid, sensitive, and reliable method for detection and characterization of chemical contaminants in foods.

Shrinking gap between nanoparticles in gold nanofilms to enhance Surface-Enhanced Raman Spectroscopy performance investigated by both experimental and theoretical methods

The chemical contaminants in food and the environment are quite harmful to food safety and human health. Rapid, accurate, and cheap detection can effectively control the potential risks derived from these chemical contaminants. Among all detection methods, the immunoassay based on the specific interaction of antibody-analyte is one of the most widely used techniques in the field. However, biological antibodies employed in the immunoassay usually cannot tolerate extreme conditions, resulting in an unstable state in both physical and chemical profiles. Molecularly imprinted polymers (MIPs) are a class of polymers with specific molecular recognition abilities, which are highly robust, showing excellent operational stability under a wide variety of conditions. Recently, MIPs have been used in biomimetic immunoassays for chemical contaminants as an antibody substitute in food and the environment. Here, we reviewed these applications of MIPs incorporated in different analytical platforms, such as enzyme-linked immunosorbent assay, fluorescent immunoassay, chemiluminescent immunoassay, electrochemical immunoassay, microfluidic paper-based immunoassay, and homogeneous immunoassay, and discussed current challenges and future trends in the use of MIPs in biomimetic immunoassays.

Surface-enhanced Raman spectroscopy (SERS) is a spectroscopic technique that simultaneously combines fingerprint recognition capabilities, typical of vibrational spectroscopies, and very high sensitivity (down to single molecule), owing to the enhancement provided by plasmonic effects. SERS inherits the rich chemical fingerprint information on Raman spectroscopy and gains sensitivity by Plasmon-enhanced excitation and scattering. In particular, most Raman peaks have a narrow width suitable for multiplex analysis, and the measurements can be conveniently made under ambient and aqueous conditions. SERS applications in bio analysis involve the complex interactions of plasmonicnanomaterials with biological systems and their environments. We then introduce the current understanding of the interaction of nanomaterials with biological systems, mainly living cells, to guide the design of functionalized SERS nanoparticles for target detection. In the end, we give an outlook of the key challenges in bio analytical SERS, including reproducibility, sensitivity, spatial and time resolution. The last section illustrates the applications of SERS in several fields of sensing, like the detection of chemical warfare agents, environmental pollutants, food contaminants, and illicit drugs; the use of SERS in art preservation, forensic science, and medical diagnosis. Keywords: SERS, Plasmon’s, Enhancement, Nanoparticles, Resonance, Finger printing

In recent years, concerns have been raised regarding the contamination of grapes with pesticide residues. As consumer demand for safer food products grows, regular monitoring of pesticide residues in food has become essential. This study sought to develop a rapid and sensitive technique for detecting two specific pesticides (phosmet and paraquat) present on the grape surface using the surface-enhanced Raman spectroscopy (SERS) method. Gold nanostars (AuNS) particles were synthesized, featuring spiky tips that act as hot spots for localized surface plasmon resonance, thereby enhancing Raman signals. Additionally, the roughened surface of AuNS increases the surface area, resulting in improved interactions between the substrate and analyte molecules. Prominent Raman peaks of mixed contaminants were acquired and used to characterize and quantify the pesticides. It was observed that the SERS intensity of the Raman peaks changed in proportion to the concentration ratio of phosmet and paraquat. Moreover, AuNS exhibited superior SERS enhancement compared to gold nanoparticles. The results demonstrate that the lowest detectable concentration for both pesticides on grape surfaces is 0.5mg/kg. These findings suggest that SERS coupled with AuNS constitutes a practical and promising approach for detecting and quantifying trace contaminants in food. PRACTICAL APPLICATION: This research established a novel surface-enhanced Raman spectroscopy (SERS) method coupled with a simplified extraction protocol and gold nanostar substrates to detect trace levels of pesticides in fresh produce. The detection limits meet the maximum residue limits set by the EPA. This substrate has great potential for rapid measurements of chemical contaminants in foods.

Practical implementation of surfaced enhanced Raman spectroscopy (SERS) sensing is hindered by complexity of real-life samples, which often requires long and costly pretreatment and purification. Here, we present a novel nanopillar-assisted SERS chromatography (NPC-SERS) method for simultaneous quantitation of target molecules and analysis of complex, multicomponent fluids, e.g., human urine spiked with a model drug paracetamol (PAR). Gold-coated silicon nanopillar (AuNP) SERS substrates and a centrifugal microfluidic platform are tactfully combined, which allows (i) a precise and fully automated sample manipulation and (ii) spatial separation of different molecular species on the AuNP substrate. The NPC-SERS technique provides a novel approach for wetting the stationary phase (AuNP) using the "wicking effect", and thus minimizes dilution of analytes. Separation of PAR and the main human urine components (urea, uric acid, and creatinine) has been demonstrated. Quantitative detection of PAR with ultrawide linear dynamic range (0-500 ppm) is achieved by analyzing the spreading profiles of PAR on the AuNP surface. NPC-SERS transforms SERS into a sensing technique with general applicability, facilitating rapid and quantitative detection of analytes in complex biofluids, such as saliva, blood, and urine.

Molecularly Imprinted Polymers for Detection of Chemical and Microbial Contaminants in Foods

Recent advance in SERS techniques for food safety and quality analysis: a brief review

Determination of trace levels of compounds in agri‐foods are challenging due to the complexity of the agricultural and food matrices. A specific and complete separation and enrichment of the target compound is sometimes more important than the development of detection tools. Raman spectroscopy and its derivative, surface enhanced Raman spectroscopy (SERS), have been widely used for the detection of specific food components due to their unique ability to record “fingerprinting” features of each molecule. However, Raman spectroscopy/SERS records the spectral signatures of all the food components, demonstrating that a pre‐separation of the target compound is critical. Molecularly imprinted polymers (MIPs), defined as “artificial antibodies”, have been constructed and integrated with Raman spectroscopy/SERS for an accurate and reliable separation and detection of target compounds in agri‐foods with minimum interference from food matrices. Compared to other separation elements (e.g., antibody, aptamer etc.) that can be integrated with Raman spectroscopy/SERS for sensing, MIPs do not contribute to spectral signature, can be reused multiple times and are more resistant to environmental factors, demonstrating the potential to be used for in‐field and on‐line screening of food safety and quality.

Surface-enhanced Raman spectroscopy (SERS) is a spectroscopic technique that simultaneously combines fingerprint recognition capabilities, typical of vibrational spectroscopies, and very high sensitivity (down to single molecule), owing to the enhancement provided by plasmonic effects. Its discovery dates back to the 1970s, and since then, SERS has gained a lot of interest in the scientific community, as witnessed by the quick raise in the percentage of publications involving SERS, especially in the last two decades. In this book chapter, we would like to provide the reader with an overview of SERS, going from the illustration of its basic principles to the description of a wide selection of its applications. At first, the physical phenomena responsible for the electromagnetic and chemical SERS enhancements are described; thereafter, two key features of SERS, namely, its distance dependence and the concept of hot spot, are discussed, as well as the near- vs. far-field properties in plasmonic systems. Two sections are then dedicated to the materials that are more often used in SERS and to the strategies adopted to fabricate efficient SERS substrates. The last section illustrates the applications of SERS in several fields of sensing, like the detection of chemical warfare agents, environmental pollutants, food contaminants, and illicit drugs; the use of SERS in art preservation, forensic science, and medical diagnosis is also described, with specific and relevant examples from the most recent literature.

Selective recognition and determination of malachite green in fish muscles via surface-enhanced Raman scattering coupled with molecularly imprinted polymers