SERS-based immunosensor for E. coli contaminants detection in milk using silver-coated nanoporous silicon substrates

A novel SERS method for detecting E. coli based on an aptamer-functionalized Au-Ag@Si triangular pyramid substrate

Escherichia coli contamination in food and pharmaceutical preparations needs to be strictly controlled according to the regulations in many countries. However, rapid and sensitive E. coli detection is still a challenge. In this study, an aptamer-based surface-enhanced Raman spectroscopy (SERS) sandwich method was developed for the rapid and sensitive detection of E. coli using an aptamer-functionalized Au-Ag@Si triangular pyramid (TP) substrate. The Au-Ag@Si TP substrate was functionalized with E. coli aptamer to work as both the capture probe and SERS tag by integrating with Raman reporter (6-carboxy-X-rhodamine). The fabrication of the capture probe, SH-apt@Au-Ag@Si TP, was simple and rapid (20.5 h). This method could selectively and rapidly detect E. coli with a limit of detection of 2.8 CFU/mL within approximately 3 h. It was successfully applied to a traditional Chinese medicine preparation, Xinhuang tablets, with recoveries ranging from 90.19 % to 104.17 %. The results indicated that the developed method was simple and rapid, and it could be a promising alternative for the on-site detection of E. coli in pharmaceutical and food samples.

Porous silicon-based sensing and delivery platforms for wound management applications

Wound management remains a great challenge for clinicians due to the complex physiological process of wound healing. Porous silicon (PSi) with controlled pore morphology, abundant surface chemistry, unique photonic properties, good biocompatibility, easy biodegradation and potential bioactivity represent an exciting class of materials for various biomedical applications. In this review, we focus on the recent progress of PSi in the design of advanced sensing and delivery systems for wound management applications. Firstly, we comprehensively introduce the common type, normal healing process, delaying factors and therapeutic drugs of wound healing. Subsequently, the typical fabrication, functionalization and key characteristics of PSi have been summarized because they provide the basis for further use as biosensing and delivery materials in wound management. Depending on these properties, the rise of PSi materials is evidenced by the examples in literature in recent years, which has emphasized the robust potential of PSi for wound monitoring, treatment and theranostics. Finally, challenges and opportunities for the future development of PSi-based sensors and delivery systems for wound management applications are proposed and summarized. We hope that this review will help readers to better understand current achievements and future prospects on PSi-based sensing and delivery systems for advanced wound management.

Unveiling the Crucial Role of Chemical Enhancement in the SERS Analysis of Amphetamine-Metal Interactions on Gold and Silver Surfaces: Importance of Selective Amplification of the Narrow Interval of Vibrational Modes

The use of addictive substances, including drugs, poses significant health risks and contributes to various social problems, such as increased crime rates associated with substance-induced aggressive behavior. To address these challenges, possession of addictive substances is legally prohibited. However, detecting and analyzing these substances remain a complex task for law enforcement, primarily due to the presence of adulterants or limited sample quantities. In response to the evolving illicit market, continuous development and adaptation of analytical techniques are essential. One approach is the utilization of surface-enhanced Raman scattering (SERS) spectroscopy, which involves adsorbing the analyte onto nanostructured plasmonic surfaces. This study explores the potential of SERS in detecting amphetamine-based addictive stimulants with a specific focus on the properties of enhancing surfaces chosen. Comparative investigations were performed using silver and gold surfaces, with gold colloidal systems demonstrating a favorable performance. Moreover, to provide a comprehensive interpretation of the measured spectra, extensive density functional theory (DFT) calculations were conducted, allowing for a deeper understanding of the observed spectral features and molecular interactions with the metal surfaces. This review presents insights into the role of chemical enhancement in SERS analysis of amphetamine-metal interactions, shedding light on the selective amplification of vibrational modes. These findings, supported by DFT calculations, have implications in the fields of spectroscopy, physical chemistry, and drug analysis, providing valuable contributions to forensic applications and a deeper understanding of chemical enhancement phenomena. We present the impact of the secondary resonances of Stokes-scattered photons. This illustrates the significance of recognizing the constraints of the frequently employed "E4" approximation, even in measurements involving multiple molecules rather than single molecules.

Plasmonic substrates for biochemical applications of surface-enhanced Raman spectroscopy

Due to its great practical importance, the detection and determination of many biomolecules in body fluids and other samples is carried out in a large number of laboratories around the world. One of the most promising analytical techniques now being widely introduced into medical analysis is surface-enhanced Raman scattering (SERS) spectroscopy. SERS is one of the most sensitive analytical methods, and in some cases, a good quality SERS spectrum dominated by the contribution of even a single molecule can be obtained. Highly sensitive SERS measurements can only be carried out on substrates generating a very high SERS enhancement factor and a low Raman spectral background, and so using of right nanomaterials is a key element in the success of SERS biochemical analysis. In this review article, we present progress that has been made in the preparation of nanomaterials used in SERS spectroscopy for detecting various kinds of biomolecules. We describe four groups of nanomaterials used in such measurements: nanoparticles of plasmonic metals and deposits of plasmonic nanoparticles on macroscopic substrates, nanocomposites containing plasmonic and non-plasmonic parts, nanostructured macroscopic plasmonic metals, and nanostructured macroscopic non-plasmonic materials covered by plasmonic films. We also describe selected SERS biochemical analyses that utilize the nanomaterials presented. We hope that this review will be useful for researchers starting work in this fascinating field of ​​science and technology.

Highly sensitive SERS platform for pathogen analysis by cyclic DNA nanostructure@AuNP tags and cascade primer exchange reaction

The capacity to identify small amounts of pathogens in real samples is extremely useful. Herein, we proposed a sensitive platform for detecting pathogens using cyclic DNA nanostructure@AuNP tags (CDNA) and a cascade primer exchange reaction (cPER). This platform employs wheat germ agglutinin-modified Fe3O4@Au magnetic nanoparticles (WMRs) to bind the E. coli O157:H7, and then triggers the cPER to generate branched DNA products for CDNA tag hybridization with high stability and amplified SERS signals. It can identify target pathogens as low as 1.91 CFU/mL and discriminate E. coli O157:H7 in complex samples such as water, milk, and serum, demonstrating comparable or greater sensitivity and accuracy than traditional qPCR. Moreover, the developed platform can detect low levels of E. coli O157:H7 in mouse serum, allowing the discrimination of mice with early-stage infection. Thus, this platform holds promise for food analysis and early infection diagnosis.

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.

Gold nanoparticle-decorated covalent organic frameworks as amplified light-scattering probes for highly sensitive immunodetection of Salmonella in milk

Traditional immunoassays exhibit insufficient screening sensitivity for foodborne pathogens due to their low colorimetric signal intensities. Herein, we propose an ultrasensitive dynamic light scattering (DLS) immunosensor for Salmonella based on a "cargo release-seed growth" strategy enabled by a probe, namely gold nanoparticle-decorated covalent organic frameworks (COF@AuNP). Large amounts of AuNPs in COF@AuNP can be released by acid treatment-induced decomposition of the imine-linked COF, and then they are enlarged via gold growth to generate a dramatically enhanced light-scattering signal, leading to a vast improvement in detection sensitivity. Based on an immunomagnetic microbead carrier, the proposed DLS immunosensor is capable of detecting trace Salmonella in milk in the range of 2.0 × 102-2.0 × 105 CFU mL-1, with a limit of detection of 60 CFU mL-1. The immunosensor also demonstrated excellent selectivity, good accuracy and precision, and high reliability for detecting Salmonella in milk.

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.

A characteristic bacterial SERS marker for direct identification of Salmonella in real samples assisted by a high-performance SERS chip and a selective culture medium

Salmonella should be absent in pharmaceutical preparations and foods according to the regulations. However, up to now, rapid and convenient identification of Salmonella is still full of challenge. Herein, we reported a label-free surface-enhanced Raman scattering (SERS) method for direct identification of Salmonella spiked in drug samples based on a characteristic bacterial SERS marker assisted by a high-performance SERS chip and a selective culture medium. The SERS chip being fabricated through in situ growth of bimetallic Au-Ag nanocomposites on silicon wafer within 2 h, featured a high SERS activity (EF > 10⁷), good uniformity and batch-to-batch consistency (RSD < 10 %), and satisfactory chemical stability. The directly-visualized SERS marker at 1222 cm^-1 originated from bacterial metabolite hypoxanthine was robust and exclusive for discrimination of Salmonella with other bacterial species. Moreover, the method was successfully used for direct discrimination of Salmonella in mixed pathogens by using a selective culture medium, and could identify Salmonella contaminant at ∼1 CFU spiked level in a real sample (Wenxin granule, a botanical drug) after 12 h of enrichment. The combined results showed that developed SERS method is practical and reliable, and could be a promising alternative for rapid identification of Salmonella contamination in pharmaceutical and foods industries.