Catalytic hairpin activated gold-magnetic/gold-core-silver-shell rapid self-assembly for ultrasensitive Staphylococcus aureus sensing via PDMS-based SERS platform

CRISPR/Cas12a dual-mode biosensor for Staphylococcus aureus detection via enzyme-free isothermal amplification

Accurate and reliable detection of Staphylococcus aureus (S. aureus) is essential for preventing infections, particularly in healthcare and food safety contexts. This work presents a novel dual-mode biosensor that integrates the CRISPR/Cas12a system with an enzyme-free isothermal amplification method for detecting S. aureus. Hybridization chain reaction (HCR) and catalytic hairpin assembly (CHA) amplify the aptamer-triggered response, significantly enhancing sensitivity. CRISPR/Cas12a's nuclease activity is utilized in two modes: cis cleavage generates a fluorescence signal, while trans cleavage produces an electrochemical signal, enabling dual-mode detection. The biosensor demonstrates outstanding performance, with a limit of detection (LOD) as low as 5.7 CFU mL-1 in electrochemical mode and 133.7 CFU mL-1 in fluorescence mode, showcasing excellent accuracy, stability, and sensitivity. It has been successfully applied to detecting actual samples, confirming its practical applicability. This innovative approach offers a powerful tool for the swift and precise identification of S. aureus and paves the way for developing next-generation dual-mode biosensors for various analytes. Future research will aim to simplify the detection process further, making it more accessible for use in resource-limited settings.

Trace detection of S. aureus cells in food samples via RCA-assisted SERS signal amplification with core-shell nanoprobe

Staphylococcus aureus (S. aureus) has been identified as a indicator of food contamination. In this study, a sensitive and accurate biosensor strategy for S. aureus through rolling circle amplification-assisted surface-enhanced Raman scattering (RCA-assisted-SERS), has been established. The work relies on the interaction between the aptamer and its partial complementary DNA strands fabricated on the surface of gold and silver-assisted magnetic microspheres and the subsequent detachment to trigger the activation of the RCA process. In RCA, template DNA, T4 DNA ligase, and Phi29 DNA polymerase were assembled to form long single-stranded DNA containing repetitive sequences. The gold core encapsulated with a layer of 4-nitrothiophenol and further covered with a silica shell was employed as the SERS nanoprobe (Au@NTP@SiO2). Subsequently, the output and amplification of SERS signal were performed by hybridizing ssDNA functionalized Au@NTP@SiO2 to realize the quantitative detection of S. aureus. Under the optimal conditions, S. aureus sensing was monitored (36.0-3.6 × 108 cfu/mL) with a limit of detection of 2.0 cfu/mL. This strategy was further validated for S. aureus recognition in spiked real samples with favorable recoveries (94.0-103.4 %) at p > 0.05. The suggested RCA-assisted SERS approach exhibits potential for multiple foodborne pathogens in both food safety and biomedical investigations.

A three-channel biosensor based on stimuli-responsive catalytic activity of the Fe3O4@Cu for on-site detection of tetrodotoxin in fish

Tetrodotoxin (TTX), a lethal neurotoxin, poses a grave threat to human health. The available spectroscopic methods suffer from limitations such as complex procedures and inadequate on-site capabilities. In this study, we proposed a method using Fe3O4@Cu as a catalytic biosensor combined with SERS, colorimetry and image processing for TTX detection. Integrating the aptamer amplifies the specificity of the system and masks the catalytic activity of Fe3O4@Cu. The catalytic efficiency of Fe3O4@Cu in the H2O2-TMB reaction can quantify the concentration of TTX in the system. Consequently, oxidation of TMB (oxTMB) led to the generation and change of signals for SERS, colorimetry and image processing, enabling a three-channel quantitative detection of TTX. Under the optimal conditions, the detection limit of established SERS, colorimetry and image processing were 0.055, 2.127 and 0.243 ng/mL, respectively. This three-channel biosensor was applied to real samples, providing an accurate, stable and adaptable alternative for on-site TTX detection.

Microcavity Array-Based Digital SERS Chip for Rapid and Accurate Label-free Quantitative Detection of Live Bacteria

In this study, we developed a novel digital surface-enhanced Raman spectroscopy (SERS) chip that integrates an inverted pyramid microcavity array, a microchannel cover plate, and a multilayer gold nanoparticle (AuNP) SERS substrate. This innovative design exploits the synergistic effects of the microcavity array and the microchannel to enable rapid and large-scale digital discretization of bacterial suspensions. The concentration effect of the picoliter cavities, combined with the superior Raman enhancement effect of the multilayer AuNP SERS substrate, allows for the precise identification of live bacteria within the microcavities through in situ and label-free SERS testing after a short incubation period. By counting the resulting positive or negative signals, the concentration of the target analyte can be directly determined via Poisson statistics. Experimental results demonstrate that this method enables the accurate quantification of Escherichia coli (E. coli) BL21 within a 4-h incubation period. Compared with traditional analog SERS detection methods, our proposed digital SERS detection strategy reduces the impact of signal intensity fluctuations, thereby significantly improving detection efficiency and accuracy. We believe that this digital SERS chip has great application prospects in the fields of bacterial detection, antibiotic resistance analysis, and cellular dynamics monitoring.

Surface-enhanced Raman scattering based on noble metal nanoassemblies for detecting harmful substances in food

Residues of harmful substances in food can severely damage human health. The content of these substances in food is generally low, making detection difficult. Surface-enhanced Raman scattering (SERS), based on noble metal nanomaterials, mainly gold (Au) and silver (Ag), has exhibited excellent capabilities for trace detection of various substances. Noble metal nanoassemblies, in particular, have extraordinary flexibility and tunable optical properties, which cannot be offered by single nanoparticles (NPs). These nanoassemblies, with their various morphologies synthesized using NPs through artificially induced self-assembly or template-driven preparation, can significantly enhance the local electric field and create "hot spots" due to the gaps between adjacent NPs. Consequently, the SERS properties of NPs become more prominent, leading to improved performance in the trace detection of various substances and detection limits that are considerably lower than the current relevant standards. Noble metal nanoassemblies show promising potential in ensuring food safety. This review discusses the synthesis methods and SERS properties of noble metal nanoassemblies and then concentrates on their application in detecting biotoxins, drug residues, illegal additives, and heavy metals. The study provides valuable references for further research into the application of nanoassemblies in food safety detection.

Portable SERS biosensor based on aptamer-assisted catalytic hairpin assembly signal amplification for ultrasensitive detection of Staphylococcus aureus

Bacteria infections pose a serious threat to public health, and it is urgent to develop facile and accurate detection methods. To meet the important need, a potable and high-sensitive surface enhanced Raman scattering (SERS) biosensor based on aptamer recognition and catalytic hairpin assembly (CHA) signal amplification was proposed for point-of-care detection of Staphylococcus aureus (S. aureus). The SERS biosensor contains three parts: recognition probes, SERS sensing chip, and SERS tags. The feasibility of the strategy was verified by gel electrophoresis, and the one-step test route was optimized. The bacteria SERS biosensor has a good linear relationship ranging from 10 to 107 CFU mL-1 with high sensitivity low to 5 CFU mL-1, and shows excellent specificity, uniformity, and repeatability on S. aureus identification and enumeration, which can distinguish S. aureus from other bacteria. The SERS biosensor shows a good recovery rate (95.73 %-109.65 %) for testing S. aureus spiked in milk, and has good practicability for detecting S. aureus infected mouse wound, which provides a facile and reliable approach for detection of trace bacteria in the real samples.

Controllable Construction of Aptamer-Modified Fe3O4@SiO2-Au Core-Shell-Satellite Nanocomposites with Surface-Enhanced Raman Scattering and Photothermal Properties and Their Effective Capture, Detection, and Elimination of Staphylococcus aureus

The early monitoring and inactivation of bacteria are of crucial importance in preventing the further spread of foodborne pathogens. Staphylococcus aureus (S. aureus), a prototypical foodborne pathogen, is widely present in the natural environment and has the capability to trigger a range of diseases at low concentrations. In this work, we designed Fe3O4@SiO2-Au core-shell-satellite nanocomposites (NCs) modified with aptamer for efficient capture, high-sensitivity surface-enhanced Raman scattering (SERS) detection, and photothermal therapy (PTT) against S. aureus. Fe3O4@SiO2-Au NCs with tunable Au nanocrystal nanogaps were prepared. By combining the finite-difference time-domain (FDTD) method and experimental results, we studied the electric field distribution of Fe3O4@SiO2-Au under different Au nanogaps and ultimately obtained the optimal SERS substrate FSA-60. The modification of aptamer on the surfaces of FSA-60 could be used for the specific capture and selective detection of S. aureus, achieving a detection limit of as low as 50 cfu/mL. Furthermore, Apt-FSA-60 possessed excellent photothermal properties, demonstrating the strong photothermal killing ability against S. aureus. Therefore, Apt-FSA-60 is a promising high-sensitivity SERS substrate and efficient photothermal agent and is expected to be widely applied and promoted in future disease prevention and treatment.

A ratiometric SERS aptasensor based on catalytic hairpin self-assembly mediated cyclic signal amplification strategy for the reliable determination of E. coli O157:H7

A ratiometric SERS aptasensor based on catalytic hairpin self-assembly (CHA) mediated cyclic signal amplification strategy was developed for the rapid and reliable determination of Escherichia coli O157:H7. The recognition probe was synthesized by modifying magnetic beads with blocked aptamers, and the SERS probe was constructed by functionalizing gold nanoparticles (Au NPs) with hairpin structured DNA and 4-mercaptobenzonitrile (4-MBN). The recognition probe captured E. coli O157:H7 specifically and released the blocker DNA, which activated the CHA reaction on the SERS probe and turned on the SERS signal of 6-carboxyl-x-rhodamine (ROX). Meanwhile, 4-MBN was used as an internal reference to calibrate the matrix interference. Thus, sensitive and reliable determination and quantification of E. coli O157:H7 was established using the ratio of the SERS signal intensities of ROX to 4-MBN. This aptasensor enabled detection of 2.44 × 102 CFU/mL of E. coli O157:H7 in approximately 3 h without pre-culture and DNA extraction. In addition, good reliability and excellent reproducibility were observed for the determination of E. coli O157:H7 in spiked water and milk samples. This study offered a new solution for the design of rapid, sensitive, and reliable SERS aptasensors.

Bonding states of gold/silver plasmonic nanostructures and sulfur-containing active biological ingredients in biomedical applications: a review

As one of the most instrumental components in the architecture of advanced nanomedicines, plasmonic nanostructures (mainly gold and silver nanomaterials) have been paid a lot of attention. This type of nanomaterial can absorb light photons with a specific wavelength and generate heat or excited electrons through surface resonance, which is a unique physical property. In innovative biomaterials, a significant number of theranostic (therapeutic and diagnostic) materials are produced through the conjugation of thiol-containing ingredients with gold and silver nanoparticles (Au and Ag NPs). Hence, it is essential to investigate Au/Ag-S interfaces precisely and determine the exact bonding states in the active nanobiomaterials. This study intends to provide useful insights into the interactions between Au/Ag NPs and thiol groups that exist in the structure of biomaterials. In this regard, the modeling of Au/Ag-S bonding in active biological ingredients is precisely reviewed. Then, the physiological stability of Au/Ag-based plasmonic nanobioconjugates in real physiological environments (pharmacokinetics) is discussed. Recent experimental validation and achievements of plasmonic theranostics and radiolabelled nanomaterials based on Au/Ag-S conjugation are also profoundly reviewed. This study will also help researchers working on biosensors in which plasmonic devices deal with the thiol-containing biomaterials (e.g., antibodies) inside blood serum and living cells.

Rapid and sensitive detection of Staphylococcus aureus using a THz metamaterial biosensor based on aptamer-functionalized Fe3O4@Au nanocomposites

Staphylococcus aureus (S. aureus) poses a serious threat to global public health, necessitating the establishment of rapid and simple tools for its accurate identification. Herein, we developed a terahertz (THz) metamaterial biosensor based on aptamer-functionalized Fe3O4@Au nanocomposites for quantitative S. aureus assays in different clinical samples. Fe3O4@Au@Cys@Apt has the dual advantages of magnetism and a high refractive index in the THz range and was used to rapidly separate and enrich target bacteria in a complex environmental solution. Furthermore, conjugation to the nanocomposites significantly increased the resonance frequency shift of the THz metamaterial after target loading. Our results showed that the shifts in the metamaterial resonance frequency were linearly related to S. aureus concentrations ranging from 1.0 × 103 to 1.0 × 107 CFU/mL, with a detection limit of 4.78 × 102 CFU/mL. The biosensor was further applied to S. aureus detection in spiked human urine and blood with satisfactory recoveries (82.4-109.6%). Our approach also demonstrated strong concordance with traditional plate counting (R2 = 0.99306) while significantly lowering the analysis time from 24 h to <1 h. In conclusion, the proposed biosensor can not only perform culture-free and extraction-free detection of target bacteria but can also be easily extended to the determination of other pathogenic bacteria, rendering it suitable for various bacteria-related disease diagnoses.

Signal amplification strategy of DNA self-assembled biosensor and typical applications in pathogenic microorganism detection

Biosensors have emerged as ideal analytical devices for various bio-applications owing to their low cost, convenience, and portability, which offer great potential for improving global healthcare. DNA self-assembly techniques have been enriched with the development of innovative amplification strategies, such as dispersion-to-localization of catalytic hairpin assembly, and dumbbell hybridization chain reaction, which hold great significance for building biosensors capable of realizing sensitive, rapid and multiplexed detection of pathogenic microorganisms. Here, focusing primarily on the signal amplification strategies based on DNA self-assembly, we concisely summarized the strengths and weaknesses of diverse isothermal nucleic acid amplification techniques. Subsequently, both single-layer and cascade amplification strategies based on traditional catalytic hairpin assembly and hybridization chain reaction were critically explored. Furthermore, a comprehensive overview of the recent advances in DNA self-assembled biosensors for the detection of pathogenic microorganisms is presented to summarize methods for biorecognition and signal amplification. Finally, a brief discussion is provided about the current challenges and future directions of DNA self-assembled biosensors.

Research progress on the detection of foodborne pathogens based on aptamer recognition

Foodborne diseases caused by bacterial contamination are a serious threat to food safety and human health. The classical plate culture method has the problems of long detection cycle, low sensitivity and specificity, and complicated operation, which cannot meet the growing demand for rapid quantitative detection of pathogenic bacteria. The frequent outbreak of foodborne diseases has put forward higher requirements for rapid and simple detection technology of foodborne pathogens. Aptamer is a kind of oligonucleotide fragment that can recognize targets with the advantages of high affinity and good specificity. The target can be range from proteins, small molecules, cells bacteria, and even viruses. Herein, the latest advances in sensitive and rapid detection of foodborne pathogens based on aptamer recognition was reviewed. Special attention has been paid to the obtained sequences of aptamers to various foodborne pathogens, the optimization of sequences, and the mechanism of aptamer recognition. Then, the research progress of biosensors for the detection of pathogenic bacteria based on aptamer recognition were summarized. Some challenges and prospects for the detection of foodborne pathogens based on aptamer recognition were prospected. In summary, with the further deepening of aptamer research and improvement of detection technology, aptamer-based recognition can meet the needs of rapid, sensitive, and accurate detection in practical applications.

Enzyme-free sensitive SERS biosensor for the detection of thalassemia-associated microRNA-210 using a cascade dual-signal amplification strategy

BACKGROUND

β-thalassemia is a blood disorder caused by autosomal mutations. Gene modulation therapy to activate the γ-globin gene to induce fetal hemoglobin (HbF) synthesis has become a new option for the treatment of β-thalassemia. MicroRNA-210 (miR-210) contributes to studying the mechanism regulating γ-globin gene expression and is a potential biomarker for rapid β-thalassemia screening. Traditional miRNA detection methods perform well but necessitate complex and time-consuming miRNA sample processing. Therefore, the development of a sensitive, accurate, and simple miRNA level monitoring method is essential.

RESULTS

We have developed a non-enzymatic surface-enhanced Raman scattering (SERS) biosensor utilizing a signal cascade amplification of catalytic hairpin assembly reaction (CHA) and proximity hybridization-induced hybridization chain reaction (HCR). Au@Ag NPs were used as the SERS substrate, and methylene blue (MB)- modified DNA hairpins were used as the SERS tags. The SERS assay involved two stages: implementing the CHA-HCR cascade signal amplification strategy and conducting SERS measurements on the resulting product. The HCR was started by the products of target-triggered CHA, which formed lengthy nicked double-stranded DNA (dsDNA) on the Au@Ag NPs surface to which numerous SERS tags were attached, leading to a significant increase in the SERS signal intensity. High specificity and sensitivity for miR-210 detection was achieved by monitoring MB SERS intensity changes. The suggested SERS biosensor has a low detection limit of 5.13 fM and is capable of detecting miR-210 at concentration between 10 fM and 1.0 nM.

SIGNIFICANCE

The biosensor can detect miR-210 levels in the erythrocytes of β-thalassemia patients, enabling rapid screening for β-thalassemia and suggesting a novel approach for investigating the regulation mechanism of miR-210 on γ-globin gene expression. In the meantime, this innovative technique has the potential to detect additional miRNAs and to become an important tool for the early diagnosis of diseases and for biomedical research.

Detection of organic dyes using Ag NPAs/SMP SERS substrate produced via sandpaper template-assisted lithography and liquid-liquid interface self-assembly

Surface-enhanced Raman spectroscopy (SERS) is a highly sensitive and reliable fingerprinting technique. However, its analytical capability is closely related to the quality of a SERS substrate used for the analysis. In particular, conventional colloidal substrates possess disadvantages in terms of controllability, stability, and reproducibility, which limit their application. In order to address these issues, a simple, cost-effective, and efficient SERS substrate based on silver nanoparticle arrays (Ag NPAs) and sandpaper-molded polydimethylsiloxane (SMP) was proposed in this work. Successfully prepared via template lithography and liquid-liquid interface self-assembly (LLISA), the substrate can be applied to the specific detection of organic dyes in the environment. The substrate exhibited good SERS performance, and the limit of detection (LOD) of rhodamine 6G (R6G) was shown to be 10-7 M under the optimal conditions (1000 grit sandpaper) with a relative standard deviation (RSD) of 7.76%. Moreover, the SERS signal intensity was maintained at 60% of the initial intensity after the substrate was stored for 30 days. In addition, the Ag NPAs/SMP SERS substrate was also employed to detect crystal violet (CV) and methylene blue (MB) with the LODs of 10-6 M and 10-7 M, respectively. In summary, the Ag NPAs/SMP SERS substrate prepared in this study has great potential for the detection of organic dyes in ecological environments.

Development of a Magnetically-Assisted SERS Biosensor for Rapid Bacterial Detection

Introduction

Ultrasensitive bacterial detection methods are crucial to ensuring accurate diagnosis and effective clinical monitoring, given the significant threat bacterial infections pose to human health. The aim of this study is to develop a biosensor with capabilities for broad-spectrum bacterial detection, rapid processing, and cost-effectiveness.

Methods

A magnetically-assisted SERS biosensor was designed, employing wheat germ agglutinin (WGA) for broad-spectrum recognition and antibodies for specific capture. Gold nanostars (AuNSs) were sequentially modified with the Raman reporter molecules and WGA, creating a versatile SERS tag with high affinity for a diverse range of bacteria. Staphylococcus aureus (S. aureus) and Pseudomonas aeruginosa (P. aeruginosa) antibody-modified Fe3O4 magnetic gold nanoparticles (MGNPs) served as the capture probes. Target bacteria were captured by MGNPs and combined with SERS tags, forming a "sandwich" composite structure for bacterial detection.

Results

AuNSs, with a core size of 65 nm, exhibited excellent storage stability (RSD=5.6%) and demonstrated superior SERS enhancement compared to colloidal gold nanoparticles. Efficient binding of S. aureus and P. aeruginosa to MGNPs resulted in capture efficiencies of 89.13% and 85.31%, respectively. Under optimized conditions, the developed assay achieved a limit of detection (LOD) of 7 CFU/mL for S. aureus and 5 CFU/mL for P. aeruginosa. The bacterial concentration (10-106 CFU/mL) showed a strong linear correlation with the SERS intensity at 1331 cm-1. Additionally, high recoveries (84.8% - 118.0%) and low RSD (6.21% - 11.42%) were observed in spiked human urine samples.

Conclusion

This study introduces a simple and innovative magnetically-assisted SERS biosensor for the sensitive and quantitative detection of S. aureus or P. aeruginosa, utilizing WGA and antibodies. The developed biosensor enhances the capabilities of the "sandwich" type SERS biosensor, offering a novel and effective platform for accurate and timely clinical diagnosis of bacterial infections.

Target-triggered enzyme-free amplification for highly efficient AND-gated bioimaging in living cells

Rapid, simultaneous, and sensitive detection of biomolecules has important application prospects in disease diagnosis and biomedical research. However, because the content of intracellular endogenous target biomolecules is usually very low, traditional detection methods can't be used for effective detection and imaging, and to enhance the detection sensitivity, signal amplification strategies are frequently required. The hybridization chain reaction (HCR) has been used to detect many disease biomarkers because of its simple operation, good reproducibility, and no enzyme involvement. Although HCR signal amplification methods have been employed to detect and image intracellular biomolecules, there are still false positive signals. Therefore, a target-triggered enzyme-free amplification system (GHCR system) was developed, as a fluorescent AND-gated sensing platform for intracellular target probing. The false positive signals can be well avoided and the accuracy of detection and imaging can be improved by using the design of the AND gate. Two cancer markers, GSH and miR-1246, were used as two orthogonal inputs for the AND gated probe. The AND-gated probe only works when GSH and miR-1246 are the inputs at the same time, and FRET signals can be the output. In addition to the use of AND-gated imaging, FRET-based high-precision ratiometric fluorescence imaging was employed. FRET-based ratiometric fluorescent probes have a higher ability to resist interference from the intracellular environment, they can avoid false positive signals well, and they are expected to have good specificity. Due to the advantages of HCR, AND-gated, and FRET fluorescent probes, the GHCR system exhibited highly efficient AND-gated FRET bioimaging for intracellular endogenous miRNAs with a lower detection limit of 18 pM, which benefits the applications of ratiometric intracellular biosensing and bioimaging and offers a novel concept for advancing the diagnosis and therapeutic strategies in the field of cancer.

The Application of Hybridization Chain Reaction in the Detection of Foodborne Pathogens

Today, with the globalization of the food trade progressing, food safety continues to warrant widespread attention. Foodborne diseases caused by contaminated food, including foodborne pathogens, seriously threaten public health and the economy. This has led to the development of more sensitive and accurate methods for detecting pathogenic bacteria. Many signal amplification techniques have been used to improve the sensitivity of foodborne pathogen detection. Among them, hybridization chain reaction (HCR), an isothermal nucleic acid hybridization signal amplification technique, has received increasing attention due to its enzyme-free and isothermal characteristics, and pathogenic bacteria detection methods using HCR for signal amplification have experienced rapid development in the last five years. In this review, we first describe the development of detection technologies for food contaminants represented by pathogens and introduce the fundamental principles, classifications, and characteristics of HCR. Furthermore, we highlight the application of various biosensors based on HCR nucleic acid amplification technology in detecting foodborne pathogens. Lastly, we summarize and offer insights into the prospects of HCR technology and its application in pathogen detection.

Strategy of functional nucleic acids-mediated isothermal amplification for detection of foodborne microbial contaminants: A review

Foodborne microbial contamination (FMC) is the leading cause of food poisoning and foodborne illness. The foodborne microbial detection methods based on isothermal amplification have high sensitivity and short detection time, and functional nucleic acids (FNAs) could extend the detectable object of isothermal amplification to mycotoxins. Therefore, the strategy of FNAs-mediated isothermal amplification has been emergingly applied in biosensors for foodborne microbial contaminants detection, making biosensors more sensitive with lower cost and less dependent on nanomaterials for signal output. Here, the mechanism of six isothermal amplification technologies and their application in detecting FMC is firstly introduced. Then the strategy of FNAs-mediated isothermal amplification is systematically discussed from perspectives of FNAs' versatility including recognition elements (Aptamer, DNAzyme), programming tools (DNA tweezer, DNA walker and CRISPR-Cas) and signal units (G-quadruplex, FNAs-based nanomaterials). Finally, challenges and prospects are presented in terms of addressing the issue of nonspecific amplification reaction, developing better FNAs-based sensing elements and eliminating food matrix effects.

Design, Fabrication, and Applications of SERS Substrates for Food Safety Detection: Review

Sustainable and safe food is an important issue worldwide, and it depends on cost-effective analysis tools with good sensitivity and reality. However, traditional standard chemical methods of food safety detection, such as high-performance liquid chromatography (HPLC), gas chromatography (GC), and tandem mass spectrometry (MS), have the disadvantages of high cost and long testing time. Those disadvantages have prevented people from obtaining sufficient risk information to confirm the safety of their products. In addition, food safety testing, such as the bioassay method, often results in false positives or false negatives due to little rigor preprocessing of samples. So far, food safety analysis currently relies on the enzyme-linked immunosorbent assay (ELISA), polymerase chain reaction (PCR), HPLC, GC, UV-visible spectrophotometry, and MS, all of which require significant time to train qualified food safety testing laboratory operators. These factors have hindered the development of rapid food safety monitoring systems, especially in remote areas or areas with a relative lack of testing resources. Surface-enhanced Raman spectroscopy (SERS) has emerged as one of the tools of choice for food safety testing that can overcome these dilemmas over the past decades. SERS offers advantages over chromatographic mass spectrometry analysis due to its portability, non-destructive nature, and lower cost implications. However, as it currently stands, Raman spectroscopy is a supplemental tool in chemical analysis, reinforcing and enhancing the completeness and coverage of the food safety analysis system. SERS combines portability with non-destructive and cheaper detection costs to gain an advantage over chromatographic mass spectrometry analysis. SERS has encountered many challenges in moving toward regulatory applications in food safety, such as quantitative accuracy, poor reproducibility, and instability of large molecule detection. As a result, the reality of SERS, as a screening tool for regulatory announcements worldwide, is still uncommon. In this review article, we have compiled the current designs and fabrications of SERS substrates for food safety detection to unify all the requirements and the opportunities to overcome these challenges. This review is expected to improve the interest in the sensing field of SERS and facilitate the SERS applications in food safety detection in the future.

Ultrasensitive detection of Staphylococcus aureus using a non-fluorescent cDNA-grafted dark BBQ®-650 chromophore integrated hydrophilic upconversion nanoparticles/aptamer system

A highly structured fluorometric bioassay has been proposed for screening Staphylococcus aureus (S. aureus). The study exploits (i) the spectral attributes of the hexagonal NaYF₄:Yb,Er upconversion nanoparticle (UCNP)-coated 3-aminopropyl)triethoxysilane; (ii) the intrinsic non-fluorescent quenching features of the highly stable dark blackberry (BBQ®-650) receptor; (iii) the aptamer (Apt-) biorecognition and binding affinity, and (iv) the complementary DNA hybridizer-linkage efficacy. The principle relied on the excited state energy transfer between the donor Apt-labeled NH₂-UCNPs at the 3' end, and cDNA-grafted BBQ®-650 at the 5' end, as the effective receptors. The donor moieties in proximity (< 10.0 nm) trigger hybridization with the cDNA-grafted dark BBQ®-650, as the receptors of energy from the ²F_5/2 level of Yb³⁺ ions to initiate the Förster resonance energy transfer pathway. This was confirmed by the decline in the excited-state lifetimes from 223.52 μs (τ₁) to 179.26 μs (τ₂). The existence of the target S. aureus in the bioassay attracts the Apt- resulting in the detachment of the acceptor, and disintegration of the complex configuration via conformation reversal. The re-activated fluorescence monitored at λex/em = 980/652 nm, as a function of the logarithmic concentration of S. aureus (42 to 4.2 × 10⁸ CFU mL^-1), yielded an ultra-low detection response of 2.0 CFU mL^-1. The bioassay screening of S. aureus in real samples revealed satisfactory recoveries (92.44-107.82%) and validation results (p > 0.05). Hence, the comprehensive Apt-labeled NH₂-UCNPs-cDNA-grafted dark BBQ®-650 bioassay offered fast and precise S. aureus screening in food and environmental settings.

Recent advances of Raman spectroscopy for the analysis of bacteria

Rapid and sensitive bacteria detection and identification are becoming increasingly important for a wide range of areas including the control of food safety, the prevention of infectious diseases, and environmental monitoring. Raman spectroscopy is an emerging technology which provides comprehensive information for the analysis of bacteria in a short time and with high sensitivity. Raman spectroscopy offers many advantages including relatively simple operation, non-destructive analysis, and information on molecular differences between bacteria species and strains. A variety of biochemical properties can be measured in a single spectrum. This short review covers the recent advancements and applications of Raman spectroscopy for bacteria analysis with specific focuses on bacteria detection, bacteria identification and discrimination, as well as bacteria antibiotic susceptibility testing in 2022. The development of novel substrates, the combination with other techniques, and the utilization of advanced data processing tools for the improvement of Raman spectroscopy and future directions are discussed.

Facile Synthesis of Ag NP Films via Evaporation-Induced Self-Assembly and the BA-Sensing Properties

Herein, we design and prepare large-area silver nanoparticle (Ag NP) films based on evaporation-induced self-assembly, which offers the visual and real-time detection of chilled broiler meat freshness. The color change is based on the fact that an increase in the biogenic amine (BA) concentration causes a change in the absorption wavelength of Ag NPs caused by aggregation and etch of the Ag NPs, resulting in a yellow to brown color change, thus enabling a naked-eye readout of the BA exposure. The Ag NP films exhibit a rapid, sensitive, and linear response to BAs in a wide detection range of 2 µM to 100 µM. The Ag NP films are successfully applied as a quick-response, online, high-contrasting colorimetric sensor for visual detection of the freshness of chilled broiler meat.

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

Rapid control and prevention of diseases caused by foodborne pathogens is one of the existing food safety regulatory issues faced by various countries and has received wide attention from all sectors of society. The development of rapid and reliable detection methods for foodborne pathogens remains a hot research area for food safety and public health because of the limitations of complex steps, time-consuming, low sensitivity, or poor selectivity of commonly used methods. Surface-enhanced Raman spectroscopy (SERS), as a novel spectroscopic technique, has the advantages of high sensitivity, selectivity, rapid and nondestructive detection and has exhibited broad application prospects in the determination of pathogenic bacteria. In this study, the enhancement mechanisms of SERS are briefly introduced, then the characteristics and properties of liquid-phase, rigid solid-phase, and flexible solid-phase are categorized. Furthermore, a comprehensive review of the advances in label-free or label-based SERS strategies and SERS-compatible techniques for the detection of foodborne pathogens is provided, and the advantages and disadvantages of these methods are reviewed. Finally, the current challenges of SERS technology applied in practical applications are listed, and the possible development trends of SERS in the field of foodborne pathogens detection in the future are discussed.

Size, composition, and surface capping-dependent catalytic activity of spherical gold nanoparticles

Gold nanostructures are used as catalysts in heterogeneous catalytic processes and have intrigued chemists and materials scientists. Isotropic spherical gold nanoparticles (AuNPs) are ideal for catalysis due to their simple preparation process, controllable surface-active site, tunable size, and composition-dependent catalytic activity. In this study, spherical AuNPs with different size, composition, and surface capping agents have been prepared, and their catalytic activity in reduction of 4-nitrophenol (4-NP) is evaluated. The catalytic activity of AuNPs decreases as their size increases. Meanwhile, the catalytic activity of AuNPs with tartrate as the reducing agent show no evident changes because of containing anisotropic AuNPs. Moreover, silver not only improves monodisperse and spherical AuNPs, but also increases the catalytic activity of small AuNPs. Since the molecular structures of tartrate and citrate are similar, there is no remarkable difference in the catalytic activity of AuNPs using tartrate and citrate as capping agents. These results demonstrate the influence of size, composition, and surface capping on the catalytic activity of AuNPs. Overall, this study facilitates the applicability of gold-based catalyst and AuNPs in plasmonics, nanophotonics, biomedical photonics, and photocatalysis.