Advances in surface-enhanced Raman spectroscopy technology for detection of foodborne pathogens

Highly sensitive SERS nanoplatform based on aptamer and vancomycin for detection of S. aureus and its clinical application

Staphylococcus aureus (S. aureus) is the most common pathogen in human purulent infections, which can cause local purulent infections, as well as pneumonia, pseudomembranous enteritis, pericarditis, and even systemic infections. The conventional methods including bacteria colony counting, polymerase chain reaction and enzyme-linked immunosorbent assay can't fully meet the requirement of highly sensitive detection of S. aureus due to their own disadvantages. Therefore, it's an urgent need to develop new platform to detect S. aureus in the early infection stage. In this study, a new surface-enhanced Raman scattering (SERS)-based nanoplatform based on dual-recognition of aptamer (Apt) and vancomycin (Van) was developed for the highly sensitive detection of S. aureus. The SERS nanoplatform consisted of two functional parts: aptamer-conjugated Fe3O4 magnetic nanoparticles (Fe3O4-Apt MNPs) for bacteria enrichment and vancomycin modified-Au nanoparticles (Van-Au NPs) as the SERS probes for S. aureus quantitative detection. Upon the target bacteria enrichment, the SERS signals of the supernatant after magnetic separation could be obtained and analyzed under different concentrations of S. aureus. The limit of detection of the proposed assay was found to be 3.27 CFU/mL. We believe that the proposed SERS-based nanoplatform has great potential as a powerful tool in the early detection of specific bacteria.

An innovative homogeneous electrochemistry coupled with colorimetry dual-model sensing strategy for perfluorooctane sulfonate based on Cu@CuO aerogel nanozyme

By preparing Cu@CuO aerogel as a nanozyme which exhibits prominent peroxidase-like (POD) activity, an innovative homogeneous electrochemistry (HEC) coupled with the colorimetry dual-model sensing strategy is proposed to detect perfluorooctane sulfonate (PFOS) for the first time. Cu@CuO aerogel accelerates the oxidation process of colorless o-phenylenediamine to form yellow 2,3-diaminophenazinc (DAP), and meanwhile, DAP as an electroactive substance creates a reduction peak current upon the electrochemical measurements. Interestingly, in the presence of PFOS, the POD activity of Cu@CuO aerogel is inhibited since the specific coordination between PFOS and Cu(II) can cover the active sites, resulting in the color of the sensing system becoming light and the peak current of DAP decreasing. This innovative dual-mode detection method showed excellent electrochemical detection of PFOS in the concentration range 10.0 ~ 1125.0 nM with a limit of detection (LOD) as low as 3.3 nM and a LOD of 20.8 nM in the colorimetric detection in the range 62.3 ~ 875 nM. Furthermore, the sensor was successfully used for the analysis of real samples with an RSD value  ≤ 6.5%. The successful application of this two-mode sensing method for the determination of PFOS holds promise for the detection of other contaminants in the future.

Three in one: A multifunctional oxidase-mimicking Ag/Mn3O4 nanozyme for colorimetric determination, precise identification, and broad-spectrum inactivation of foodborne pathogenic bacteria

A multifunctional oxidase-mimicking Ag/Mn3O4 was prepared, catalyzing the 3, 3', 5, 5'-tetramethylbenzidine (TMB) chromogenic reaction. Six foodborne pathogenic bacteria species, including Escherichia coli, Staphylococcus aureus, Salmonella enterica, Listeria monocytogenes, Bacillus cereus, and Cronobacter sakazakii, were observed to differentially inhibit its oxidase-like activity, resulting in decelerating the TMB chromogenic reaction. Owing to these properties, the following achievements were achieved: colorimetric determination of these bacteria with high sensitivity can be achieved using Ag/Mn3O4 + TMB reaction system; precise identification of these bacteria at different concentrations, including individual bacterium, binary mixtures, and even multivariate mixtures, can be effectively realized by combining the Ag/Mn3O4-based colorimetric sensor array with principal component analysis (PCA); broad-spectrum inactivation of these bacteria can be remarkably realized through catalyzation of Ag/Mn3O4 to generate superoxide anion free radicals. Therefore, our proposed Ag/Mn3O4 holds significant application potential in the colorimetric determination, precise identification, and broad-spectrum inactivation of foodborne pathogenic bacteria.

AFB1-responsive mesoporous silica nanoparticles for AFB1 quantification based on aptamer-regulated release of SERS reporter

In this study, we propose a novel surface-enhanced Raman scattering (SERS) method for quantifying aflatoxin B1 (AFB1). This method relies on the target-triggered release of a SERS reporter from aptamer-sealed aminated mesoporous silica nanoparticles (MSNs). These MSNs were synthesized to accommodate 4-mercaptophenylboronic acid (4-MPBA) within their well-defined micropores, which were subsequently sealed with AFB1 aptamers. Upon specific binding of AFB1 to its aptamer, the conformational change in the aptamer is regulated by the presence of the target. Consequently, a positive linear relationship between the AFB1 concentration and the 4-MPBA SERS signal was observed. Under optimal conditions, the method exhibited a good linear relationship over the range of 0.1 to 5 ng/mL AFB1, with a limit of detection (LOD) of 0.03 ng/mL. This strategy was validated using wheat samples, yielding results comparable to high performance liquid chromatography-fluorescence detector (P > 0.05), confirming its reliability for detecting AFB1 in complex food matrices.

Programmable and ultra-efficient Argonaute protein-mediated nucleic acid tests: A review

With the attributes of high sensitivity, single-base resolution, multiplex detection capability, and programmability upon nucleic acid recognition, Argonaute (Ago)-based biosensing assays are increasingly recognized as one of the most promising tools for precise identification and quantification of target analytes. Employed as highly specific sequence recognition elements of these robust diagnostic methods, Agos are revolutionizing how nucleic acid targets are detected. A systematic and comprehensive summary of this emerging and rapid-advancing technology is necessary to give play to the potential of Ago-based biosensing assays. The structure and function of Agos were briefly overviewed at the beginning of the work, followed by a review of the recent advancements in employing Agos sensing for detecting various targets with a comprehensive analysis such as viruses, tumor biomarkers, pathogens, mycoplasma, and parasite. The significance and benefits of these platforms were then deliberated. In addition, the authors shared subjective viewpoints on the existing challenges and offered relevant guidance for the future progress of Agos assays. Finally, the future research outlook regarding Ago-based sensing in this field was also outlined. As such, this review is expected to offer valuable information and fresh perspectives for a broader group of researchers.

A CRISPR/Cas12a-powered gold/nickel foam surface-enhanced Raman spectroscopy biosensor for nucleic acid specific detection in foods

Food is a necessary source of energy, but it also serves as a pathway for transmitting infectious pathogens, making food safety a matter of great concern. Rapid, accurate, and specific detection methods for foodborne viruses are crucial. Surface-Enhanced Raman Scattering (SERS), due to its superior sensitivity and characteristic fingerprint spectra, holds enormous potential. However, due to the limitations of SERS, it requires specific conditions to achieve specificity. In order to enhance the specificity and accuracy of nucleic acid detection based on SERS, we have developed a CRISPR-Cas12a-mediated SERS technique to identify target DNA, harnessing the targeting recognition capability of CRISPR-Cas12a and ultra-sensitive SERS tags and successfully addressing SERS' lack of specific detection capability. This system includes a gold/nickel foam substrate (Au-NFs) and a reporter (ssDNA-ROX). The phenomenon of colloidal gold/silver nano-aggregation due to magnesium ions, which is commonly encountered in CRISPR-SERS, was simultaneously solved using AuNFs. The qualitative and quantitative analysis of target DNA in drinking water was performed by monitoring the intensity change of ROX Raman reporter molecules. The results showed that the sensor detected DNA within 30 min and the limit of detection (LOD) was 8.23 fM. This is expected to become one of the alternative methods for nucleic acid detection for its rapid detection and high specificity.

Illuminating the Tiny World: A Navigation Guide for Proper Raman Studies on Microorganisms

Raman spectroscopy is an emerging method for the identification of bacteria. Nevertheless, a lot of different parameters need to be considered to establish a reliable database capable of identifying real-world samples such as medical or environmental probes. In this review, the establishment of such reliable databases with the proper design in microbiological Raman studies is demonstrated, shining a light into all the parts that require attention. Aspects such as the strain selection, sample preparation and isolation requirements, the phenotypic influence, measurement strategies, as well as the statistical approaches for discrimination of bacteria, are presented. Furthermore, the influence of these aspects on spectra quality, result accuracy, and read-out are discussed. The aim of this review is to serve as a guide for the design of microbiological Raman studies that can support the establishment of this method in different fields.

SERS detection of volatile gas in spoiled pork with the Ag/MoS2 nano-flower cavity/PVDF micron-bowl cavity (FIB) substrate

Putrescine and cadaverine are significant volatile indicators used to assess the degree of food spoilage. Herein, we propose a micro-nano multi cavity structure for surface-enhanced Raman spectroscopy (SERS) to analyze the volatile gas putrescine and cadaverine in decomposing food. The MoS2 nano-flowers are inserted into a PVDF micro-cavity through in-situ growth, followed by vacuum evaporation technology of Ag nanoparticles to form an Ag/MoS2 nano-flower cavity/PVDF micron-bowl cavity (FIB) substrate. The micro-nano multi cavity structure can improve the capture capacity of both light and gas, thereby exhibiting high sensitivity (EF = 7.71 × 107) and excellent capability for gas detection of 2-naphthalenethiol. The SERS detections of the putrescine and cadaverine are achieved in the spoiled pork samples with the FIB substrate. Therefore, this substrate can provide an efficient, accurate, and feasible method for the specific and quantitative detection in the food safety field.

Key steps for improving bacterial SERS signals in complex samples: Separation, recognition, detection, and analysis

Rapid and reliable detection of pathogenic bacteria is absolutely essential for research in environmental science, food quality, and medical diagnostics. Surface-enhanced Raman spectroscopy (SERS), as an emerging spectroscopic technique, has the advantages of high sensitivity, good selectivity, rapid detection speed, and portable operation, which has been broadly used in the detection of pathogenic bacteria in different kinds of complex samples. However, the SERS detection method is also challenging in dealing with the detection difficulties of bacterial samples in complex matrices, such as interference from complex matrices, confusion of similar bacteria, and complexity of data processing. Therefore, researchers have developed some technologies to assist in SERS detection of bacteria, including both the front-end process of obtaining bacterial sample data and the back-end data processing process. The review summarizes the key steps for improving bacterial SERS signals in complex samples: separation, recognition, detection, and analysis, highlighting the principles of each step and the key roles for SERS pathogenic bacteria analysis, and the interconnectivity between each step. In addition, the current challenges in the practical application of SERS technology and the development trends are discussed. The purpose of this review is to deepen researchers' understanding of the various stages of using SERS technology to detect bacteria in complex sample matrices, and help them find new breakthroughs in different stages to facilitate the detection and control of bacteria in complex samples.

Novel Digital SERS-Microfluidic Chip for Rapid and Accurate Quantification of Microorganisms

In this work, we present a simple and novel digital surface-enhanced Raman spectroscopy (SERS)-microfluidic chip designed for the rapid and accurate quantitative detection of microorganisms. The chip employs a high-density inverted pyramid microcavity (IPM) array to separate and isolate microbial samples. The presence or absence of target microorganisms is determined by scanning the IPM array using SERS and identifying the characteristic Raman bands. This approach allows for the "digitization" of the SERS response of each IPM, enabling quantification through the application of mathematical statistical techniques. Significantly, precise quantitative detection of yeast was achieved within a concentration range of 106-109 cells/mL, with the maximum relative standard deviation from the concentration calibrated by the cultivation method being 5.6%. This innovative approach efficiently addresses the issue of irregularities in SERS quantitative detection, which arises due to fluctuations in SERS intensity and poor reproducibility. We strongly believe that this digital SERS-microfluidic chip holds immense potential for diverse applications in the rapid detection of various microorganisms, including pathogenic bacteria and viruses.

Dual-mode colorimetric and fluorescence biosensors for the detection of foodborne bacteria

Due to the growing demand for detection technologies, there has been significant interest in the development of integrated dual-modal sensing technologies, which involve combining two signal transduction channels into a single technique, particularly in the context of food safety. The integration of two detection signals not only improves diagnostic performance by reducing assumptions, but also enhances diagnostic functions with increased application flexibility, improved accuracy, and a wider detection linear range. The top two output signals for emerging dual-modal probes are fluorescent and colorimetric, due to their exceptional advantages for real-time sensitive sensing and point-of-care applications. With the rapid progress of nanotechnology and material chemistry, the integrated colorimetric/fluorimetric dual-mode systems show immense potential in sensing foodborne pathogenic bacteria. In this comprehensive review, we present a detailed summary of various colorimetric and fluorimetric dual-modal sensing methods, with a focus on their application in detecting foodborne bacteria. We thoroughly examine the sensing methodologies and the underlying principles of the signal transduction systems, and also discuss the challenges and future prospects for advancing research in this field.

ZnO@Ag-Functionalized Paper-Based Microarray Chip for SERS Detection of Bacteria and Antibacterial and Photocatalytic Inactivation

Bacterial infections caused by pathogenic microorganisms have become a serious, widespread health concern. Thus, it is essential and required to develop a multifunctional platform that can rapidly and accurately determine bacteria and effectively inhibit or inactivate pathogens. Herein, a microarray SERS chip was successfully synthesized using novel metal/semiconductor composites (ZnO@Ag)-ZnO nanoflowers (ZnO NFs) decorated with Ag nanoparticles (Ag NPs) arrayed on a paper-based chip as a supporting substrate for in situ monitoring and photocatalytic inactivation of pathogenic bacteria. Typical Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli and Vibrio parahemolyticus were selected as models. Partial least-squares discriminant analysis (PLS-DA) was performed to minimize the dimensionality of SERS spectra data sets and to develop a cost-effective identification model. The classification accuracy was 100, 97.2, and 100% for S. aureus, E. coli, and V. parahemolyticus, respectively. The antimicrobial activity of ZnO@Ag was proved by the microbroth dilution method, and the minimum inhibitory concentrations (MICs) of S. aureus, E. coli, and V. parahemolyticus were 40, 50, and 55 μg/mL, respectively. Meanwhile, it demonstrated remarkable photocatalytic performance under natural sunlight for the inactivation of pathogenic bacteria, and the inactivation rates for S. aureus, E. coli, and V. parahemolyticus were 100, 97.03 and 97.56%, respectively. As a result, the microarray chip not only detected the bacteria with high sensitivity but also confirmed the antibacterial and photocatalytic sterilization properties. Consequently, it offers highly prospective strategies for foodborne diseases caused by pathogenic bacteria.

Determination of sulfide in complex biofilm matrices using silver-coated, 4-mercaptobenzonitrile-modified gold nanoparticles, encapsulated in ZIF-8 as surface-enhanced Raman scattering nanoprobe

A surface-enhanced Raman scattering nanoprobe has been developed for sulfide detection and applied to  complex bacterial biofilms. The nanoprobe, Au@4-MBN@Ag@ZIF-8, comprised a gold core modified with 4-mercaptobenzonitrile (4-MBN) as signaling source, a layer of silver shell as the sulfide sensitization material, and a zeolitic imidazolate framework-8 (ZIF-8) as surface barrier. ZIF-8, with its high surface area and mesoporous structure, was applied to preconcentrate sulfide around the nanoprobe with its excellent adsorption capacity. Besides, the external wrapping of ZIF-8 can not only prevent the interference of biomolecules, such as proteins, with the Au@4-MBN@Ag assay but also enhance the detection specificity through the sulfide cleavage function towards ZIF-8. These properties are critical for the application of this nanoprobe to complex environmental scenarios. In the presence of sulfide, it was first enriched through adsorption by the outer ZIF-8 layer, then destroyed the barrier layer, and subsequently reacted with the Ag shell, leading to changes in the Raman signal. Through this rational design, the Au@4-MBN@Ag@ZIF-8 nanoprobe exhibited excellent detection sensitivity, with a sulfide detection limit in the nanomolar range and strong linearity in the concentration range  50 nM to 500 μM. Furthermore, the proposed Au@4-MBN@Ag@ZIF-8 nanoprobe was effectively utilized for sulfide detection in intricate biofilm matrices, demonstrating its robust selectivity and reproducibility.

Synthesis of γ-Cyclodextrin-Reduced Fe(III) Nanoparticles with Peroxidase-like Catalytic Activity for Bacteriostasis of Food

Foodborne pathogens are a primary cause of human foodborne illness, making it imperative to explore novel antibacterial strategies for their control. In this study, Fe-γ-CD was successfully synthesized as a food antibacterial agent for use in milk and orange juice. The Fe-γ-CD consists of 6/11 Fe(II) and 5/11 Fe(III), which catalyze a Fenton-like catalytic reaction with H2O2 to generate •OH. Consequently, Fe-γ-CD exhibits exceptional peroxidase-like activity and broad-spectrum antibacterial efficacy. Fe-γ-CD not only disrupts the wall structure of ESBL-E. coli but also induces protein leakage and genetic destruction, ultimately leading to its death. Furthermore, Fe-γ-CD inhibits biofilm formation by MRSA and eradicates mature biofilms, resulting in MRSA's demise. Importantly, Fe-γ-CD demonstrates negligible cytotoxicity toward normal mammalian cells, making it an ideal candidate for application as an antibacterial agent in foodstuffs. These findings highlight that Fe-γ-CD is an effective tool for combating the spread of foodborne pathogens and food safety.

Advancing Mycotoxin Detection: Multivariate Rapid Analysis on Corn Using Surface Enhanced Raman Spectroscopy (SERS)

Mycotoxin contamination on food and feed can have deleterious effect on human and animal health. Agricultural crops may contain one or more mycotoxin compounds; therefore, a good multiplex detection method is desirable to ensure food safety. In this study, we developed a rapid method using label-free surface-enhanced Raman spectroscopy (SERS) to simultaneously detect three common types of mycotoxins found on corn, namely aflatoxin B1 (AFB1), zearalenone (ZEN), and ochratoxin A (OTA). The intrinsic chemical fingerprint from each mycotoxin was characterized by their unique Raman spectra, enabling clear discrimination between them. The limit of detection (LOD) of AFB1, ZEN, and OTA on corn were 10 ppb (32 nM), 20 ppb (64 nM), and 100 ppb (248 nM), respectively. Multivariate statistical analysis was used to predict concentrations of AFB1, ZEN, and OTA up to 1.5 ppm (4.8 µM) based on the SERS spectra of known concentrations, resulting in a correlation coefficient of 0.74, 0.89, and 0.72, respectively. The sampling time was less than 30 min per sample. The application of label-free SERS and multivariate analysis is a promising method for rapid and simultaneous detection of mycotoxins in corn and may be extended to other types of mycotoxins and crops.

Research advances of SERS analysis method based on silent region molecules for food safety detection

Food safety is a critical issue that is closely related to people's health and safety. As a simple, rapid, and sensitive detection technique, surface-enhanced Raman scattering (SERS) technology has significant potential for food safety detection. Recently, researchers have shown a growing interest in utilizing silent region molecules for SERS analysis. These molecules exhibit significant Raman scattering peaks in the cellular Raman silent region between 1800 and 2800 cm-1 avoiding overlapping with the SERS spectrum of biological matrices in the range 600-1800 cm-1, which could effectively circumvent matrix effects and improve the SERS accuracy. In this review, the application of silent region molecules-based SERS analytical technique for food safety detection is introduced, detection strategies including label-free detection and labeled detection are discussed, and recent applications of SERS analysis technology based on molecules containing alkyne and nitrile groups, as well as Prussian blue (PB) in the detection of pesticides, mycotoxins, metal ions, and foodborne pathogens are highlighted. This review aims to draw the attention to the silent region molecules-based SERS analytical technique and to provide theoretical support for its further applications in food safety detection.