Functionalization techniques for improving SERS substrates and their applications in food safety evaluation: A review of recent research trends
TL;DR: In this article, surface-enhanced Raman scattering (SERS) with the advantages of excellent sensitivity, high selectivity, non-destructive nature and significant enhancement to identify the target has demonstrated a great potential for quick detection of chemical contaminants, chemical constitutes, and pathogens in food samples.
Abstract: Background Food safety and quality have gained much attention in recent years and the capability to evaluate food quality and safety in a sensitive, rapid, and reliable manner is of great importance in the food industry. Therefore, surface-enhanced Raman scattering (SERS) with the advantages of excellent sensitivity, high selectivity, non-destructive nature and significant enhancement to identify the target has demonstrated a great potential for quick detection of chemical contaminants, chemical constitutes, and pathogens in food samples. Scope and approach The enhancement of Raman signals for SERS is not only related to the interactions between substrates and samples but also the functionalization of substrates to gain SERS active substrates. In the present review, different types of substrates are briefly discussed, functionalization techniques for SERS active substrates are discussed, and applications of functionalized SERS substrate in food samples are presented. Conclusions and key findings It is evident that functionalization techniques for improving SERS substrates have given encouraging outcomes, which provides possibility for identifying multiple target analytes within a complex matrix, and thus could be used as a powerful analytical tool in real-world applications in food safety analysis as well as for enhancing food quality surveillance.
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TL;DR: The Au@Ag/PMMA/qPCR-PET film chip showed high sensitivity with an enhancement factor of 3.14x106, long-term storage stability without changing SERS signals for more than 2 months at room temperatures, and low limit of detection for sensing TBZ in pear juice, orange juice, and grape juice.
Abstract: The high sensitivity and long-term storage stability of a plasmonic substrate are vital for practical applications of the surface-enhanced Raman scattering (SERS) technique in real-world analysis. In this study, a rationally designed, ternary film-packaged, silver-coated gold-nanoparticle (Au@Ag NP) plasmonic array was fabricated and applied as a stable and high-performance SERS chip for highly sensitive sensing of thiabendazole (TBZ) residues in fruit juices. The ternary films played different roles in the plasmonic chip: a newborn poly(methyl methacrylate) (PMMA) film serving as a template for fixing the self-assembled closely packed monolayer Au@Ag NP array that provided an intensive hot spot, a fluorescent quantitative polymerase chain reaction adhesive film (qPCR film) acting as a carrier to retrieve the Au@Ag/PMMA film that was used to improve the robustness of the plasmonic array, and a polyethylene terephthalate (PET) film covered over the Au@Ag/PMMA/qPCR film performing as a barrier to improve the stability of the chip. The Au@Ag/PMMA/qPCR-PET film chip showed high sensitivity with an enhancement factor of 3.14 × 106, long-term storage stability without changing SERS signals for more than 2 months at room temperatures, and a low limit of detection for sensing TBZ in pear juice (21 ppb), orange juice (43 ppb), and grape juice (69 ppb). In addition, the procedure for fabricating the Au@Ag/PMMA/qPCR-PET film SERS chip was easy to handle, offering a new strategy to develop flexible and wearable sensors for on-site monitoring of chemical contaminants with a portable Raman spectrometer in the future.
142 citations
TL;DR: In this article, the characteristics of different flexible materials such as cellulose, polymer film, cotton fabric, adhesive tape and bio-materials for constructing flexible SERS substrates are introduced, detection strategies including infiltration scheme, swab-sampling and in-situ detection are discussed.
Abstract: Background Food safety has attracted considerable attention in recent years. As a rapid, fingerprint-type recognition and nondestructive detection technique, surface-enhanced Raman scattering (SERS) has been among the promising techniques to meet the increasing needs for food safety analysis. Currently, emerging flexible SERS substrates as an alternative for colloidal and rigid SERS substrates have received great interest. Flexible SERS substrates possess the advantages of easy sampling by wrapping or swabbing on nonplanar surfaces, which facilitate the detection of contaminants from food surfaces and shed new lights on the nondestructive and sensitive detection of food analytes. Scope and approach In this review, the characteristics of different flexible materials such as cellulose, polymer film, cotton fabric, adhesive tape and bio-materials for constructing flexible SERS substrates are introduced, detection strategies including infiltration scheme, swab-sampling and in-situ detection are discussed, and recent applications of flexible SERS substrates in detecting trace pesticides in fruits and vegetables, chemical residues in animal farming including fungicides and antibiotics, illegal food additives and food-borne pathogens are highlighted. Key findings and conclusions Flexible SERS substrates have been increasingly studied for detecting food contaminants. In preparing SERS substrates, different properties of the materials should be considered. For the detection strategies, compared with conventional infiltration scheme, swab-sampling is unique for flexible substrates and can collect target molecules directly from the surface, while in-situ detection is the most convenient, facile and nondestructive. Encouraging application results available show that flexible SERS substrates possess enormous potentials for food safety analysis and surveillance.
133 citations
TL;DR: In order to establish SERS as a routine tool for the monitoring of food safety and quality, future research should focus on minimizing technical costs, standardizing experimental protocols, developing new SERS substrates, and integrating SERS with other methods to overcome its shortcomings.
Abstract: Background Food quality and safety are very important from health as well as fiscal point of view. Surface-enhanced Raman spectroscopy (SERS) techniques have unique advantages in the field of food detection , with characteristics of fast analysis speed, high detection sensitivity, and without interference from the water phase. Scope and approach In this review, recent and potential advances in the application of SERS in food safety and quality from the perspective of SERS substrate and SERS composite systems are addressed. SERS systems such as molecular labeling, immunochromatographic assay, microfluidics, molecularly imprinted polymers, colorimetry and imaging are discussed, and their main advantages and limitations are highlighted. The applications of SERS in food safety are reviewed critically, with focus on the detection of microorganisms, pesticides, metal ions and antibiotics. Furthermore, applications of SERS in food quality regarding food freshness and ingredients are discussed. Key findings and conclusions SERS technology has been widely used in food testing, but it still has shortcomings. In order to establish SERS as a routine tool for the monitoring of food safety and quality, future research should focus on minimizing technical costs, standardizing experimental protocols, developing new SERS substrates, and integrating SERS with other methods to overcome its shortcomings.
123 citations
TL;DR: It is demonstrated that the Au@AgNAs-based SERS method can be used as a simple, rapid and sensitive approach for sensing trace contaminants in food.
118 citations
TL;DR: The emerging bio-recognition based methods bridge the gap between culture-dependent enumeration and molecular methods, and they could be employed in the industry to ensure food safety, but the development of a validation protocol for all the emerging methods is necessary to assess their efficiency in real samples.
Abstract: Background Microbial contamination is an increasing concern in the food industry. In order to understand the effect of microorganisms, the study of their characteristics and behavior in various platforms is of prime importance. Over the years, time-consuming and labor-intensive, culture-based enumeration techniques have become obsolete for real-time applications, and increasing concerns on foodborne outbreaks necessitate rapid, on-site and sensitive methods for the detection of microorganisms in food matrices. Scope and approach In the current review, a brief discussion about biomarkers in microorganisms and bio-recognition ligands commonly used for detection assay are presented. The molecular interaction between biomarkers and ligands is critically evaluated and recent developments in bio-recognition based detection techniques for analyzing microorganism activity in complex food matrices are reviewed. Key findings and conclusions The microbial activity in food can be detected by analyzing the specific biomarkers of microorganisms such as nucleic acids, proteins, antigens, and metabolic products. Recent bio-recognition ligands in detection techniques such as biosensors, lateral flow assay, and microfluidic devices can improve the selectivity in detecting cells from complex food matrices. The emerging bio-recognition based methods bridge the gap between culture-dependent enumeration and molecular methods, and they could be employed in the industry to ensure food safety. However, the development of a validation protocol for all the emerging methods is necessary to assess their efficiency in real samples.
118 citations
References
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TL;DR: This paper introduces the localized surface plasmon resonance (LSPR) sensor and describes how its exquisite sensitivity to size, shape and environment can be harnessed to detect molecular binding events and changes in molecular conformation.
Abstract: Recent developments have greatly improved the sensitivity of optical sensors based on metal nanoparticle arrays and single nanoparticles. We introduce the localized surface plasmon resonance (LSPR) sensor and describe how its exquisite sensitivity to size, shape and environment can be harnessed to detect molecular binding events and changes in molecular conformation. We then describe recent progress in three areas representing the most significant challenges: pushing sensitivity towards the single-molecule detection limit, combining LSPR with complementary molecular identification techniques such as surface-enhanced Raman spectroscopy, and practical development of sensors and instrumentation for routine use and high-throughput detection. This review highlights several exceptionally promising research directions and discusses how diverse applications of plasmonic nanoparticles can be integrated in the near future.
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TL;DR: This review describes recent fundamental spectroscopic studies that reveal key relationships governing the LSPR spectral location and its sensitivity to the local environment, including nanoparticle shape and size and introduces a new form of L SPR spectroscopy, involving the coupling between nanoparticle plasmon resonances and adsorbate molecular resonances.
Abstract: Localized surface plasmon resonance (LSPR) spectroscopy of metallic nanoparticles is a powerful technique for chemical and biological sensing experiments. Moreover, the LSPR is responsible for the electromagnetic-field enhancement that leads to surface-enhanced Raman scattering (SERS) and other surface-enhanced spectroscopic processes. This review describes recent fundamental spectroscopic studies that reveal key relationships governing the LSPR spectral location and its sensitivity to the local environment, including nanoparticle shape and size. We also describe studies on the distance dependence of the enhanced electromagnetic field and the relationship between the plasmon resonance and the Raman excitation energy. Lastly, we introduce a new form of LSPR spectroscopy, involving the coupling between nanoparticle plasmon resonances and adsorbate molecular resonances. The results from these fundamental studies guide the design of new sensing experiments, illustrated through applications in which researchers use both LSPR wavelength-shift sensing and SERS to detect molecules of chemical and biological relevance.
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TL;DR: As SERS substrates, the as-fabricated Au nanoparticle arrays exhibit high SERS sensitivity, long-term stability, and consistent reproducibility.
Abstract: We demonstrate a convenient and cost-effective chemical approach for fabricating highly ordered Au nanoparticle arrays with sub-10-nm interparticle gaps. Near-field enhancements inside the interparticle gaps create uniform periodic arrays of well-defined “hot spots” exploitable for large surface-enhanced Raman spectroscopy (SERS) enhancements. A cetyltrimethylammonium bromide (CTAB) bilayer surrounding each individual nanoparticle upon array crystallization is responsible for this periodic gap structure; displacement of the CTAB by smaller thiolated molecules does not affect the structural integrity of the arrays. As SERS substrates, the as-fabricated Au nanoparticle arrays exhibit high SERS sensitivity, long-term stability, and consistent reproducibility.
625 citations
TL;DR: This perspective gives an overview of recent developments in surface-enhanced Raman scattering (SERS) for biosensing and shows great promise for widespread adoption of SERS biosensing.
Abstract: This perspective gives an overview of recent developments in surface-enhanced Raman scattering (SERS) for biosensing. We focus this review on SERS papers published in the last 10 years and to specific applications of detecting biological analytes. Both intrinsic and extrinsic SERS biosensing schemes have been employed to detect and identify small molecules, nucleic acids, lipids, peptides, and proteins, as well as for in vivo and cellular sensing. Current SERS substrate technologies along with a series of advancements in surface chemistry, sample preparation, intrinsic/extrinsic signal transduction schemes, and tip-enhanced Raman spectroscopy are discussed. The progress covered herein shows great promise for widespread adoption of SERS biosensing.
544 citations
TL;DR: It is evident that hyperspectral imaging can automate a variety of routine inspection tasks and is anticipated that real-time food monitoring systems with this technique can be expected to meet the requirements of the modern industrial control and sorting systems in the near future.
Abstract: In recent years, hyperspectral imaging has gained a wide recognition as a non-destructive and fast quality and safety analysis and assessment method for a wide range of food products. As the second part of this review, applications in quality and safety determination for food products are presented to illustrate the capability of this technique in the food industry for classification and grading, defect and disease detection, distribution visualization of chemical attributes, and evaluations of overall quality of meat, fish, fruits, vegetables, and other food products. The state of the art of hyperspectral imaging for each of the categories was summarized in the aspects of the investigated quality and safety attributes, the used systems (wavelength range, acquisition mode), the data analysis methods (feature extraction, multivariate calibration, variables selection), and the performance (correlation, error, visualization). With its success in different applications of food quality and safety analysis and assessment, it is evident that hyperspectral imaging can automate a variety of routine inspection tasks. Industrial relevance It is anticipated that real-time food monitoring systems with this technique can be expected to meet the requirements of the modern industrial control and sorting systems in the near future.
461 citations