SERS-based microdevices for use as in vitro diagnostic biosensors

High-efficiency detection of APE1 using a defective PAM-driven CRISPR-Cas12a self-catalytic biosensor

The trans-cleavage activity of the CRISPR-Cas system offers tremendous potential for developing highly sensitive and selective molecular diagnostic tools. However, conventional methods often face challenges such as limited catalytic efficiency of single Cas proteins and the necessity of complex multi-enzyme preamplification steps. To address these limitations, we present a novel defective PAM-mediated CRISPR-Cas12a self-catalytic signal amplification strategy, termed DEP-Cas-APE, for the rapid, sensitive, and specific detection of apurinic/apyrimidinic endonuclease 1 (APE1) activity. This approach integrates defective PAM-modified DNA probes to synergize Cas12a trans-cleavage with self-catalytic circuit, achieving efficient signal transformation and amplification under isothermal, one-step conditions. We systematically investigated the influence of defective PAM sequences containing apurinic/apyrimidinic (AP) sites on Cas12a activation and validated the feasibility of the DEP-Cas-APE strategy in detecting APE1. Under optimized conditions, DEP-Cas-APE achieved a detection limit as low as 7.66 × 10-8 U μL-1 within 30 min using a simple isothermal reaction. Additionally, we developed a point-of-care testing (POCT) platform by integrating DEP-Cas-APE with a colorimetric assay based on gold nanoparticles (AuNPs), enabling portable, equipment-free detection. This sensitive and selective strategy successfully detected APE1 in complex biological samples, including serum from lung cancer patients, and demonstrated the ability to distinguish cancerous from normal samples. DEP-Cas-APE represents a robust and versatile platform for advancing CRISPR-Cas12a biosensing technologies, offering new opportunities for molecular diagnostics and clinical research.

Wearable SERS devices in health management: Challenges and prospects

Surface-Enhanced Raman Scattering (SERS) is an advanced analytical technique renowned for its heightened sensitivity in detecting molecular vibrations. Its integration into wearable technologies facilitates the monitoring of biofluids, such as sweat and tears, enabling continuous, non-invasive, real-time analysis of human chemical and biomolecular processes. This capability underscores its significant potential for early disease detection and the advancement of personalized medicine. SERS has attracted considerable research attention in the fields of wearable flexible sensing and point-of-care testing (POCT) within medical diagnostics. Nonetheless, the integration of SERS with wearable technology presents several challenges, including device miniaturization, reliable biofluid sampling, user comfort, biocompatibility, and data interpretation. The ongoing advancements in nanotechnology and artificial intelligence are instrumental in addressing these challenges. This review provides a comprehensive analysis of design strategies for wearable SERS sensors and explores their applications within this domain. Finally, it addresses the current challenges in this area and the future prospects of combining SERS wearable sensors with other portable health monitoring systems for POCT medical diagnostics. Wearable SERS is a promising innovation in future healthcare, potentially enhancing individual health outcomes and reducing healthcare costs by fostering preventive health management approaches.

Highly sensitive and reproducible SERS substrate based on ordered multi-tipped Au nanostar arrays for the detection of myocardial infarction biomarker cardiac troponin I

Acute myocardial infarction (AMI) is a severe cardiovascular disease, for which early diagnosis is critical for reducing mortality and improving patient outcomes. Cardiac troponin I (cTnI) is widely recognized as the "gold standard" biomarker for AMI due to its high specificity and sensitivity. The concentration of cTnI correlates directly with different stages of AMI. Therefore, the accurate detection of cTnI concentration is of paramount importance. However, the low concentration of cTnI in biological fluids requires ultrasensitive detection methods. In this study, we developed a sandwiched surface enhanced Raman scattering (SERS)-based biosensor composed of SERS-immune substrate, target antigen, and SERS nanotags and realized sensitive and accurate detection of cTnI. The SERS-immune substrate features an ordered, multi-tipped monolayer of Au nanostars fabricated using a three-phase interfacial self-assembly method and 4-(2-hydroxyerhyl)piperazine-1-erhanesulfonic acid (HEPES) buffer modification. Compared to Au nanosphere SERS substrates, the Au nanostar SERS substrates exhibited about a 3-fold increase in Raman enhancement and demonstrated good uniformity and batch stability. This novel SERS detection platform, leveraging dual plasmonic enhancement from both the SERS-immune substrate and SERS nanotags, achieves detection of cTnI with a limit of detection (LOD) as low as 9.09 pg mL-1 and a relative standard deviation (RSD) as low as 11.24%. Thus, the Au nanostar SERS substrates developed in this study demonstrate significant potential for rapid and accurate detection of cTnI.

Surface-enhanced confocal Raman microscopy to characterize esophageal cancer cell-derived extracellular vesicles and maternal cells

Exosomes, a subtype of extracellular vesicles, are increasingly recognized as promising biomarkers for human cancers. Rapid detection and classification of esophageal cancer-associated exosomes could significantly improve non-invasive screening for potential patients. This study aims to establish a label-free, direct surface-enhanced Raman scattering (SERS) method to capture characteristic molecular information from both esophageal cancer cells and their corresponding exosomes using confocal Raman microscopy. The results revealed distinct Raman spectra for esophageal cancer cells and their exosomes within the range of 500-1600 cm-1, with notable signal similarities observed at 506-622, 778-832, 1079-1098, and 1572-1630 cm-1. In contrast, significant differences were identified in Raman peaks related to nucleic acids (723, 654, 1354 cm-1) and proteins (998, 1028, 1354, 1560 cm-1). An orthogonal partial least squares discriminant analysis (OPLS-DA) model was utilized to discern subtle variations among these highly similar samples, achieving an accuracy rate of 100%. By comparing the spectral correlations between esophageal cancer cells and their exosomes, this study provides valuable insights into the molecular composition and cellular origins of exosomes. The findings demonstrate the potential of integrating SERS with OPLS-DA for the precise and rapid detection and monitoring of esophageal cancer through exosomal biomarkers, offering a powerful tool for diagnostic applications.

3D Self-Assembly of a Bilayer Nanoparticle Metasurface for Surface-Enhanced Raman Scattering (SERS) Sensing

Controllable periodic nanoparticle (NP) metasurfaces exhibit unique optical responses, which are crucial for applications in plasmonic sensing, photocatalysis, and nanoscale optical manipulation. Compared with monolayer NPs, bilayer NPs generate additional electromagnetic field localization effects between the layers, exhibiting enhanced light absorption and scattering. Here, we propose a novel method that assembles the monolayer NPs at a three-dimensional liquid-liquid interface (3D-LLI) into large-area two-dimensional bilayer NPs. This method not only allows for the construction of independent bilayer structures for fundamental research on metasurfaces but also enables the formation of "sandwich"-type interlayer structures for in situ SERS detection of both microparticle analytes such as polystyrene (PS), polyethylene terephthalate (PET), and poly(methyl methacrylate) (PMMA) and small molecules such as melamine, cysteine (Cys), and iminothiourazole (AMT).

CRISPR/Cas-powered nucleic acid amplification and amplification-free biosensors for public safety detection: Principles, advances and prospects

Rapid, accurate, cost-effective, and efficient ultrasensitive detection strategies are essential for public health safety (including food safety, disease prevention and environmental governance). The CRISPR/CRISPR-associated (Cas) detection is a cutting-edge technology that has been widely used in the detection of public health safety due to its targeted cleavage properties (signal amplification), attomolar level sensitivity, high specificity (recognizing single-base mismatches), and rapid turnover time. However, the current research about CRISPR/Cas-based biosensors is not clear, such as mechanism problem and application differences of integrating CRISPR/Cas system with other technologies, and how to further innovate and develop in the future. Therefore, further detailed analysis and comparative discussion of CRISPR/Cas-based biosensors is needed. Currently, CRISPR/Cas system powered biosensors can be mainly categorized into two types: CRISPR/Cas system powered nucleic acid amplification biosensors and CRISPR/Cas system powered nucleic acid amplification-free biosensors. The two biosensors have different characteristics and advantages. This paper first provides an in-depth investigation of the enzymatic mechanism of CRISPR/Cas system at the molecular level. Then, this paper summarizes the principles and recent advances of CRISPR/Cas system powered nucleic acid amplification biosensors and CRISPR/Cas system powered nucleic acid amplification-free biosensors and discusses their integration mechanisms in depth. More, the differences and application-oriented between the two biosensors are further discussed. Finally, the application orientation and future perspectives of the two biosensors are discussed, and unique insights into the future development of CRISPR/Cas system are provided.

Bacterial identification in SERS-integrated microfluidics using CNN-driven 2D classification of 1D spectra

Bacterial sensing involves complex and variable samples that require advanced handling and analytical methods. To address these challenges, machine learning-especially deep learning-and SERS-based microfluidics have shown great promise. While previous studies have majorly focused on 1D spectral classification, the use of 2D representations of SERS spectra has not yet been explored, particularly for on-chip bacterial identification. In this work, we introduce a novel framework that combines SERS-enabled microfluidics with optimized 2D convolutional neural networks (2D-CNNs) for bacterial classification. SERS integration inside microfluidic chips was achieved through direct laser writing, enabling custom active areas and efficient on-chip measurements. We systematically evaluated nine distinct 1D-to-2D spectral transformations, with spectrogram and continuous wavelet transform yielding test accuracies of 99 % and 97 %, respectively, on controlled datasets. Using transfer learning, we achieved 100 % accuracy on the on-chip dataset, demonstrating the model's adaptability to new data. In contrast, other transformations, like pairwise distance and autocorrelation, performed below 93 %, indicating their limited ability to capture subtle spectral features. This framework offers high sample control, parallelization, and the potential for expanding the bacteria database, making it ideal for low-data-volume situations such as rare infections. Further development and testing across strains, environments, and practical challenges can further improve our approach's reliability for real-world diagnostics.

Targeted molecular rapid SERS diagnosis in clinical human serum through aptamer origami-collapsed nanofingers chip

Surface-Enhanced Raman Scattering (SERS) offers great potential for label-free molecular diagnosis, especially in detecting disease biomarkers. However, the complexity of the biological environment in clinical human serum often significantly impairs detection accuracy. In this study, we present a highly effective SERS strategy utilizing aptamer origami-collapsed nanofingers for the precise qualitative and quantitative detection of specific targeted biomarkers in clinical serum. Here, the biomarker-specific aptamers are anchored to gold nanofingers, which then collapse during liquid evaporation, forming sub-nanometric gaps that enhance near-field strength. The serum is introduced directly into these stabilized nanofingers, where targeted biomarkers are selectively captured in aptamer hotspots, yielding pure Raman spectra of the biomarkers without interference from other serum molecules. The ratio of the biomarker's characteristic Raman peak to that of the aptamer allows for accurate quantification. This approach was validated with alpha-fetoprotein (AFP) for hepatocellular carcinoma and cardiac troponin I (cTnI) for acute myocardial infarction in clinical serum, achieving detection within 3 min. This strategy represents a significant advancement in SERS-based medical diagnostics, offering exceptional sensitivity and specificity in complex biological samples.

Integrative plasmonics: optical multi-effects and acousto-electric-thermal fusion for biosensing, energy conversion, and photonic circuits

Surface plasmons, a unique optical phenomenon arising at the interface between metals and dielectrics, have garnered significant interest across fields such as biochemistry, materials science, energy, optics, and nanotechnology. Recently, plasmonics is evolving from a focus on "classical plasmonics," which emphasizes fundamental effects and applications, to "integrative plasmonics," which explores the integration of plasmonics with multidisciplinary technologies. This review explores this evolution, summarizing key developments in this technological shift and offering a timely discussion on the fusion mechanisms, strategies, and applications. First, we examine the integration mechanisms of plasmons within the realm of optics, detailing how fundamental plasmonic effects give rise to optical multi-effects, such as plasmon-phonon coupling, nonlinear optical effects, electromagnetically induced transparency, chirality, nanocavity resonance, and waveguides. Next, we highlight strategies for integrating plasmons with technologies beyond optics, analyzing the processes and benefits of combining plasmonics with acoustics, electronics, and thermonics, including comprehensive plasmonic-electric-acousto-thermal integration. We then review cutting-edge applications in biochemistry (molecular diagnostics), energy (harvesting and catalysis), and informatics (photonic integrated circuits). These applications involve surface-enhanced Raman scattering (SERS), surface-enhanced infrared absorption (SEIRA), surface-enhanced fluorescence (SEF), chirality, nanotweezers, photoacoustic imaging, perovskite solar cells, photocatalysis, photothermal therapy, and triboelectric nanogenerators (TENGs). Finally, we conclude with a forward-looking perspective on the challenges and future of integrative plasmonics, considering advances in mechanisms (quantum effects, spintronics, and topology), materials (Dirac semimetals and hydrogels), technologies (machine learning, edge computing, in-sensor computing, and neuroengineering), and emerging applications (5G, 6G, virtual reality, and point-of-care testing).

Advances in SERS detection method combined with microfluidic technology for bio-analytical applications

With the advancement of research on life systems and disease mechanisms, the precision of analysis tends to be at a single molecule or single gene level. The surface-enhanced Raman scattering (SERS) method is highly anticipated because of its sensitive detection ability down to a single molecule level. The SERS-based microfluidic platforms retain both advantages of SERS and microfluidics, working in a complementary way. The combination of microfluidics and SERS can provide rapid, non-destructive, high-sensitive, and high-throughput analysis for biological samples, which is of great significance to developing potential biomedical applications, thus occupying an outstanding position among the current research hot topics. This review briefly summarized the recent developments and applications of SERS-based microfluidic platforms in biological analysis. This paper first introduced the SERS-based microfluidic platforms and gave a classification of this method including continuous flow-based method, microarrays-based method, droplet-based method, lateral flow assay (LFA)-based method, and digital-based method. In particular, the bioanalytical applications of SERS-based microfluidic platforms in recent years, including biomolecule detection, cell analysis, and disease diagnosis, have been reviewed. It illustrated that SERS-based microfluidic platforms have great potential in bioanalysis.

Rapid point-of-care pathogen sensing in the post-pandemic era

In the post-pandemic era, interest in on-site technologies capable of rapidly and accurately diagnosing viral or bacterial pathogens has significantly increased. Advances in functional nanomaterials and bioengineering have propelled the progress of point-of-care (POC) sensors, enhancing their speed, specificity, sensitivity, affordability, ease of use, and accuracy. Notably, biosensors that utilize surface-enhanced Raman scattering (SERS) technology have revolutionized the rapid and sensitive diagnosis of biomarkers in pathogenic infections. This review of current POC diagnostics highlights the growing emphasis on immunoassays for swift pathogen analysis, augmented by the integration of deep learning for swift interpretation of complex signals through tailored algorithms.

Chiral Bimetallic Pt@Au Octapods with Spiral Four-Petal Flower-Like Symmetric Configuration as Sensitive SERS Probes

Here, we synthesized chiral bimetallic Pt@Au octapods by using l/d-cysteine-threonine (CT) dipeptide as chiral ligands. These had a distinct spiral four-petal flower-like symmetric configuration with a twisted concave morphology on each facet. The twisted concave structure of the Pt@Au octapods facilitated intraparticle coupling, resulting in highly concentrated electric fields within the concave regions, thus creating "hot spots" that produced a potent surface-enhanced Raman scattering (SERS) effect. The l-Pt@Au octapods showed a nearly twofold stronger SERS response to Aβ40 and Aβ42 monomers and fibrils than the d-Pt@Au octapods. The different association constants arose from the unique chiral recognition capabilities of the CT ligands on the surfaces of the l-Pt@Au octapods, which allowed them to form specific hydrogen bonds with Aβ40 and Aβ42 monomers and fibrils, producing significant differences in their Raman spectra. The data from clinical cerebrospinal fluid (CSF) samples showed that the quantitative analysis of the Aβ42/Aβ40 ratio with Raman spectroscopy can be used as an effective biomarker for the early diagnosis of Alzheimer's disease (AD), with a cut-off value of 0.085. Our results pave the way for the use of chiral nanomaterials with strong optical activities in the development of clinical testing instruments with biomedical applications.

Ligand-Driven Annular-Epitaxial Growth of CuS-Au Heterostructures as Trinity Plasmonic Nanozyme for Multimode Diagnosis of Pathogenic Bacteria

This study presents a novel method to control the site-selective growth of Au nanostars on CuS nanodisc substrate, it indicates that the surfactant ligands play a key role in the architecture control, only CTAC and homologous series with appropriate affinity to CuS can direct the annular-epitaxial growth of Au nanoparticles on the CuS, which demonstrates superior peroxidase (POD)-mimic and SERS activity. Mechanistic studies indicate that plasmon-enhanced catalytic and SERS activity can be attributed to the spatially separated CuS-Au heterostructure, which supports the light-triggered hot electron-hole pairs production and localized surface plasmon resonance hotspots. For practical biosensing, the CuS-Au heterostructures assembled lateral flow assay (LFA) was used for SERS/catalytic colorimetric/photothermal three-mode detection of Streptococcus pneumoniae and Klebsiella pneumoniae, with visually colorimetric mode at 103 CFU/mL and quantitative SERS/photothermal modes at 2-102 CFU/mL within 15 min, 15 clinical samples were used to validate the assay, the result was 100% concordant to the results of quantitative real-time PCR. This study provides a unique avenue to controllably produce plasmon-enhanced nanozyme, which can provide multi-mode signals for LFA application and meet the requirements of different scenarios.

Current Trends in In Vitro Diagnostics Using Surface-Enhanced Raman Scattering in Translational Biomedical Research

Immunoassays using surface-enhanced Raman scattering (SERS) are prosperous in disease diagnosis due to their excellent multiplexing ability, high sensitivity, and large dynamic range. Given the recent advancements in SERS immunoassays, this work provides a comprehensive overview, from fundamental principles to practical applications. An mRNA sensor utilizing Raman spectroscopy is a detection method that leverages the unique vibrational characteristics of mRNA molecules to identify and quantify their presence in a sample, often achieved through a technique called SERS, where specially designed nanoparticles amplify the Raman signal, allowing for the highly sensitive detection of even small amounts of mRNA. This review analyzes SERS assays used to detect RNA biomarkers, which show promise in cancer diagnostics and are being actively studied clinically. To selectively detect a specific mRNA sequence, a probe molecule (e.g., a DNA oligonucleotide complementary to the target mRNA) is attached to the SERS substrate, allowing the target mRNA to hybridize and generate a detectable Raman signal upon binding. Thus, the discussion includes proposals to enhance SERS immunoassay performance, along with future challenges and perspectives, offering concise, valid guidelines for platform selection based on application.

Dual-Function SERS Microdroplet Sensor for Rapid Differentiation of Influenza a and SARS-CoV-2

This study presents the development of a dual-function microdroplet sensor utilizing surface-enhanced Raman scattering (SERS) technology to identify and quantify Influenza A and COVID-19 viruses. The proposed microfluidic device incorporates compartments for two-phase segmented droplet generation, merging, splitting, and detection. Both viral strains were identified by isolating magnetic antibody-antigen complexes from the liquid medium using a magnetized bar embedded in the microfluidic channel. Concurrent Raman spectroscopic readings were obtained as suspended droplets containing residual SERS-active nanoparticles traversed the interrogation zone of the focused laser beam. Precise quantitative analysis was accomplished by correcting characteristic Raman peak intensities for both viruses with internal standards, while ensemble averaging Raman signals from multiple droplets ensured high reproducibility. This dual-function SERS microdroplet sensor represents a novel in vitro diagnostic approach capable of rapidly distinguishing between COVID-19 and Influenza A with high sensitivity and reproducibility. When coupled with a portable Raman spectrophotometer, the device shows significant potential as a diagnostic tool for swift and in situ detection of both viral pathogens.

A cellulose paper decorated with gold(-silver) nanoparticles for SERS-based immunoassays

Surface-enhanced Raman scattering (SERS)-based immunoassays offer an unprecedented method for the early diagnosis of biomarkers. However, challenges in reliability often hinder their broader applications. This study introduces a novel approach employing in situ-prepared cellulose paper decorated with gold and gold-silver nanoparticles (Au(-Ag) CP) to construct a highly sensitive and stable paper-based SERS substrate. Building on this, we developed robust SERS immunosubstrates and immunoprobes, enabling a versatile immunoassay platform. This platform demonstrated exceptional performance in detecting disease markers. Using gold nanoparticles probe with Au CP, a limit of detection (LOD) of 29.71 fg/mL was achieved for the COVID-19 antigen, while the Au-Ag CP coupled with the Au-core Ag-shell (Au@Ag) probes achieved an LOD of 10.79 fg/mL for cardiac troponin I (cTnI). Both detection modes featured a broad dynamic range from 10-13 to 10-8 g/mL and sustained stability, retaining comparable LOD after 5 weeks of storage. The paper-based SERS immunoassay platform presented here holds promise for rapid, ultra-sensitive biomarker detection, offering a transformative tool for advancing diagnostic technologies.

Continuously adjustable hollow beam for ultrafast laser fabrication of size-controllable nanoparticles

The focused vortex beam generates a hollow beam, which has been widely used for size-controlled nanoparticle formation on various materials. However, the size variation of the vortex beam is limited by the integral order of the 2π phase wrap, while the waste is caused by the large side lobe around the center. In this study, we propose a method for hollow beam generation by splitting a femtosecond laser and imparting opposite phases to the outer annular region and the central Gaussian region. After focusing, these two regions overlap at the focal spot, resulting in a hollow beam due to phase cancellation. By modulating the relative dimensions of these two regions, the hollow center can be continuously varied. When such a hollow beam is used for surface processing, the thermal capillary effect facilitates the convergence of the molten material toward the center, ultimately leading to the formation of nanoparticles. This ability to control size allows precise control of nanoparticle size with a diameter range from 140 nm to 940 nm. This method holds great promise for guiding research into nanoparticle properties that are influenced by size effects.

Advances in Functional Nucleic Acid SERS Sensing Strategies

Functional nucleic acids constitute a distinct category of nucleic acids that diverge from conventional nucleic acid amplification methodologies. They are capable of forming intricate hybrid structures through Hoogsteen and reverse Hoogsteen hydrogen bonding interactions between double-stranded and single-stranded DNA, thereby broadening the spectrum of DNA interactions. In recent years, functional DNA/RNA-based surface-enhanced Raman spectroscopy (SERS) has emerged as a potent platform capable of ultrasensitive and multiplexed detection of a variety of analytes of interest. This review aims to elucidate the operational principles of several functional nucleic acids in SERS detection, including DNAzymes, G-quadruplexes, aptamers, CRISPR, origami etc., alongside the design methodologies and practical applications of functional DNA/RNA-based SERS sensing. Initially, an overview is summarized encompassing the structural attributes and SERS sensing mechanisms inherent to diverse functional DNA/RNA. Following this, various innovative strategies for constructing functional nucleic acid-based SERS sensors are illustrated in detail, aimed at improving the present detection capabilities. A comprehensive summing up is then conducted on the applications of these sensors in crucial fields, such as disease diagnosis, environmental monitoring, and food safety detection, with a particular focus on SERS sensitivity, specificity, and analytical versatility. Finally, conclusive remarks are offered along with an exploration of the existing challenges and prospective avenues for future research in this developed field.

Surface encapsulation of ZIF-8 on Ag nanoparticles modified cotton swab for highly rapid and selective surface-enhanced Raman spectroscopy analysis of glucose and lactic acid in human sweat

Herein, ZIF-8 shell encapsulated Ag nanoparticles decorated cotton swab (CS@Ag@ZIF-8) was firstly designed and prepared for highly rapid and selective surface-enhanced Raman spectroscopy (SERS) analysis of glucose and lactic acid in human sweat. The CS not only act as support matrix for Ag modification and ZIF-8 encapsulation, but also provide great potential in-situ analysis of human sweat with low cost. The as-developed CS@Ag@ZIF-8 shows high SERS activity owing the good adsorption of ZIF-8 shell and electromagnetic enhancement of AgNPs. The 4-mercaptophenylboronic acid (4-MPBA) and 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB) with limits of detection (LOD) of 1.0 and 10.0 ng/L can be reached, as well as enhancement factor of 108 level. In addition, the good stability and repeatability of CS@Ag@ZIF-8 can be obtained in various conditions. The recognition probes based on 4-MPBA and DTNB modified CS@Ag@ZIF-8 were fabricated for rapid and selective detection of glucose and lactic acid in human sweat. The promising linearity in range of 0.1-100.0 μmol/L and 0.1-50.0 mmol/L with LOD of 0.04 μmol/L and 0.03 mmol/L for glucose and lactic acid were achieved, respectively. The detection errors between commercial meter and developed method was in range of -6.4 to 6.0 %. Our results provide a promising strategy in fabrication of portable SERS substrates with satisfied performance for rapid, selective and in-situ quantification of biomolecules in complex biological samples.

Surface Enhanced Raman Scattering for Biomolecular Sensing in Human Healthcare Monitoring

Since the 1980s, surface enhanced Raman scattering (SERS) has been used for the rapid and sensitive detection of biomolecules. Whether a label-free or labeled assay is adopted, SERS has demonstrated low limits of detection in a variety of biological matrices. However, SERS analysis has been confined to the laboratory due to several reasons such as reproducibility and scalability, both of which have been discussed at length in the literature. Another possible issue with the lack of widespread adoption of SERS is that its application in point of use (POU) testing is only now being fully explored due to the advent of portable Raman spectrometers. Researchers are now investigating how SERS can be used as the output on several POU platforms such as lateral flow assays, wearable sensors, and in volatile organic compound (VOC) detection for human healthcare monitoring, with favorable results that rival the gold standard approaches. Another obstacle that SERS faces is the interpretation of the wealth of information obtained from the platform. To combat this, machine learning is being explored and has been shown to provide quick and accurate analysis of the generated data, leading to sensitive detection and discrimination of many clinically relevant biomolecules. This review will discuss the advancements of SERS combined with POU testing and the strength that machine learning can bring to the analysis to produce a powerful combined platform for human healthcare monitoring.

Rapid and Sensitive Escherichia coli Detection: Integration of SERS and Acoustofluidics in a Lysis-Free Microfluidic Platform

Bacterial infections, such as sepsis, require prompt and precise identification of the causative bacteria for appropriate antibiotics treatment. Traditional methods such as culturing take 2-5 days, while newer techniques such as reverse transcription-polymerase chain reaction and mass spectrometry are hindered by blood impurities. Consequently, this study developed a surface-enhanced Raman scattering (SERS)-based acoustofluidic technique for rapid bacterial detection without culturing or lysing. Target bacteria are first tagged with SERS nanotags in a microtube. The solution with tagged bacteria and unbound SERS nanotags is passed through a silicon microfluidic channel. A piezoelectric transducer generates acoustic waves within the channel, concentrating larger tagged bacteria in the center and pushing smaller unbound nanotags toward the channel walls. A laser beam is focused at the center of the channel, and the Raman signals of bacteria passing through the focal volume are measured for quantitative analysis. As a proof of concept, this study detected various concentrations of Escherichia coli at a limit of detection of 1.75 × 105 CFU/mL within 1 h. This method offers significant clinical potential, enabling rapid and accurate bacterial identification without genetic material extraction, cultivation, or lysis.

Recent Developments in SERS Microfluidic Chips: From Fundamentals to Biosensing Applications

This paper reviews the latest research progress of surface-enhanced Raman spectroscopy (SERS) microfluidic chips in the field of biosensing. Due to its single-molecule sensitivity, selectivity, minimal or no preprocessing, and immediacy, SERS is considered a promising biosensing technology. However, the nondirectional interactions between biological samples and the substrate, as well as fluctuations in the sample environment temperature during signal acquisition, can affect the stability and reproducibility of SERS signals. Integrating SERS spectroscopy with microfluidic chips not only leverages the continuous sample flow, high reaction efficiency, high throughput, and multifunctionality of microfluidic chips to address challenges in biosensing applications but also expands the scope of microfluidic technology by providing a novel on-chip optical detection method. The combination of SERS and microfluidic chips not only enables the complementary advantages of both technologies but also offers a highly promising "combined technology" for the field of biosensing. This paper starts by introducing the enhancement mechanisms of SERS and presents both labeled and label-free SERS strategies. Based on the differences in substrate properties, we broadly categorize SERS microfluidic chips into colloidal nanoparticle-based SERS microfluidic chips and fixed substrate-based SERS microfluidic chips. Finally, we review the latest research progress on SERS microfluidic chips for biosensing biological targets such as nucleic acids, proteins, small biomolecules, and live cells. In the conclusion and outlook section, we summarize the challenges faced by SERS microfluidic chips in biosensing and propose feasible solutions. To better leverage the role of SERS microfluidic chips in biosensing, we also present an outlook on the future development of this combined technology.

Surface-enhanced Raman spectroscopy: a half-century historical perspective

Surface-enhanced Raman spectroscopy (SERS) has evolved significantly over fifty years into a powerful analytical technique. This review aims to achieve five main goals. (1) Providing a comprehensive history of SERS's discovery, its experimental and theoretical foundations, its connections to advances in nanoscience and plasmonics, and highlighting collective contributions of key pioneers. (2) Classifying four pivotal phases from the view of innovative methodologies in the fifty-year progression: initial development (mid-1970s to mid-1980s), downturn (mid-1980s to mid-1990s), nano-driven transformation (mid-1990s to mid-2010s), and recent boom (mid-2010s onwards). (3) Illuminating the entire journey and framework of SERS and its family members such as tip-enhanced Raman spectroscopy (TERS) and shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) and highlighting the trajectory. (4) Emphasizing the importance of innovative methods to overcome developmental bottlenecks, thereby expanding the material, morphology, and molecule generalities to leverage SERS as a versatile technique for broad applications. (5) Extracting the invaluable spirit of groundbreaking discovery and perseverant innovations from the pioneers and trailblazers. These key inspirations include proactively embracing and leveraging emerging scientific technologies, fostering interdisciplinary cooperation to transform the impossible into reality, and persistently searching to break bottlenecks even during low-tide periods, as luck is what happens when preparation meets opportunity.

DNA-Assisted CRISPR-Cas12a Enhanced Fluorescent Assay for Protein Detection in Complicated Matrices

Proteins are important biological macromolecules that perform a wide variety of functions in the cell and human body, and can serve as important biomarkers for early diagnosis and prognosis of human diseases as well as monitoring the effectiveness of disease treatment. Hence, sensitive and accurate detection of proteins in human biospecimens is imperative. However, at present, there is no ideal method available for the detection of proteins in clinical samples, many of which are present at ultralow (less than 1 pM) concentrations and in complicated matrices. Herein, we report an ultrasensitive and selective DNA-assisted CRISPR-Cas12a enhanced fluorescent assay (DACEA) for protein detection with detection limits reaching as low as attomolar concentrations. The high assay sensitivity was accomplished through the combined DNA barcode amplification (by using dual-functionalized AuNPs) and CRISPR analysis, while the high selectivity and high resistance to the matrix effects of our method were accomplished via the formation of protein-antibody sandwich structure and the specific recognition of Cas12a (under the guidance of crRNA) toward the designed target ssDNA. Given its ability to accurately and sensitively detect trace amounts of proteins in complicated matrices, the DACEA protein assay platform pioneered in this work has a potential application in routine protein biomarker testing.

Bioorthogonally activated probes for precise fluorescence imaging

Over the past two decades, bioorthogonal chemistry has undergone a remarkable development, challenging traditional assumptions in biology and medicine. Recent advancements in the design of probes tailored for bioorthogonal applications have met the increasing demand for precise imaging, facilitating the exploration of complex biological systems. These state-of-the-art probes enable highly sensitive, low background, in situ imaging of biological species and events within live organisms, achieving resolutions comparable to the size of the biomolecule under investigation. This review provides a comprehensive examination of various categories of bioorthogonally activated in situ fluorescent labels. It highlights the intricate design and benefits of bioorthogonal chemistry for precise in situ imaging, while also discussing future prospects in this rapidly evolving field.

Advances in Surface-Enhanced Raman Spectroscopy for Therapeutic Drug Monitoring

Therapeutic drug monitoring (TDM) is pivotal for optimizing drug dosage regimens in individual patients, particularly for drugs with a narrow therapeutic index. Surface-enhanced Raman spectroscopy (SERS) has shown great potential in TDM due to high sensitivity, non-destructive analysis, specific fingerprint spectrum, low sample consumption, simple operation, and low ongoing costs. Due to the rapid development of SERS for TDM, a review focusing on the analytical method is presented to better understand the trends. This review examines the latest advancements in SERS substrates and their applications in TDM, highlighting the innovations in substrate design that enhance detection sensitivity and selectivity. We discuss the challenges faced by SERS for TDM, such as substrate signal reproducibility and matrix interference from complex biological samples, and explore solutions like digital colloid-enhanced Raman spectroscopy, enrichment detection strategies, microfluidic SERS, tandem instrument technologies, and machine learning-enabled SERS. These advancements address the limitations of traditional SERS applications and improve analytical efficiency in TDM. Finally, conclusions and perspectives on future research directions are presented. The integration of SERS with emerging technologies presents a transformative approach to TDM, with the potential to significantly enhance personalized medicine and improve patient outcomes.

Biosensors for Seafood Safety Control-A Review

The increased demand for consuming seafood has made seafood production undergo a rapid period of growth. However, seafood has a high risk of contamination from harmful microorganisms and marine toxins which can cause health problems for humans consuming it. Concerning this issue, monitoring seafood safety has become a center of attention for researchers, and developing effective methods for detecting contamination in seafood has become a critical research field. In this context, biosensors have served as a promising approach to monitor seafood contamination. Compared to conventional methods, biosensors have some key benefits such as high sensitivity, selectivity, portability, and user-friendly operation. Along with significant advances in biosensors, processes of seafood monitoring can be simplified and performed outside the laboratory. In this review article, we describe the mechanisms of two main types of biosensors regarding electrochemical and optical biosensors. The current reports within the last five years on the application of these biosensors for seafood monitoring are also summarized.

Versatile, reusable and highly sensitive SERS-based point-of-care testing microplatform for reliable ATP detection

The advancement in miniaturized Raman spectrometers, coupled with the single-molecule-level sensitivity and unique fingerprint identification capability of surface-enhanced Raman scattering (SERS), offers great potential for point-of-care testing (POCT). Despite this, accurately quantifying analyte molecules, particularly in complex samples with limited sample volumes, remains difficult. Herein, we present a versatile and reusable SERS microplatform for highly sensitive and reliable quantitative detection of adenosine triphosphate (ATP) in biological fluids. The platform utilizes gold-Prussian blue core-shell nanoparticles modified with polyethyleneimine (Au@PB@PEI NPs), embedded within gold nanoparticle-immobilized capillary-based silica monolithic materials. PB acts as an internal standard, while PEI enhances molecular capture. The periodic, bimodal porous structure of the silica monolithic materials provides uniform and abundant sites for nanoparticle attachment, facilitating rapid liquid permeation, intense SERS enhancement, and efficient enrichment. The platform regulates ATP capture and release through magnesium ions in the liquid phase, eliminating matrix interferences and enabling platform reuse. Integrating efficient molecular enrichment, separation, an interference-free internal standard, a liquid flow channel, and a detection chamber, our platform offers simplicity in operation, exceptional sensitivity and accuracy, and rapid analysis (∼10 min). Employing PB as an internal calibration standard, ratiometric Raman signals (I732/I2123) facilitate precise ATP quantification, achieving a remarkable limit of detection down to 0.62 pM. Furthermore, this platform has been proven to be highly reproducible and validated for ATP quantification in both mouse cerebrospinal fluid and human serum, underscoring its immense potential for POCT applications.

Immuno-Rolling Circle Amplification (Immuno-RCA): Biosensing Strategies, Practical Applications, and Future Perspectives

In the rapidly evolving field of life sciences and biomedicine, detecting low-abundance biomolecules, and ultraweak biosignals presents significant challenges. This has spurred a rapid development of analytical techniques aiming for increased sensitivity and specificity. These advancements, including signal amplification strategies and the integration of biorecognition events, mark a transformative era in bioanalytical precision and accuracy. A prominent method among these innovations is immuno-rolling circle amplification (immuno-RCA) technology, which effectively combines immunoassays with signal amplification via RCA. This process starts when a targeted biomolecule, such as a protein or cell, binds to an immobilized antibody or probe on a substrate. The introduction of a circular DNA template triggers RCA, leading to exponential amplification and significantly enhanced signal intensity, thus the target molecule is detectable and quantifiable even at the single-molecule level. This review provides an overview of the biosensing strategy and extensive practical applications of immuno-RCA in detecting biomarkers. Furthermore, it scrutinizes the limitations inherent to these sensors and sets forth expectations for their future trajectory. This review serves as a valuable reference for advancing immuno-RCA in various domains, such as diagnostics, biomarker discovery, and molecular imaging.

Flexible paper-based Ag dendritic SERS chips for rapid in situ detection of thiram residues on pear skin

Surface-enhanced Raman scattering (SERS) is a powerful, highly efficient analytical technique capable of providing label-free, non-invasive, rapid, and ultrasensitive molecular detection down to the single-molecule level. Despite its advantages, SERS remains largely confined to laboratory settings due to the complexities of substrate fabrication and challenges in analyzing real-world samples. Developing flexible SERS substrates that achieve both high fabrication efficiency and high sensing performance, while being practical for field applications, is critical for advancing SERS toward broader, real-world use. In this study, we present a novel paper-based Ag dendritic SERS chip, fabricated via a simple chemical reduction process that directly forms Ag dendritic nanostructures on cellulose fibers. This chip substrate demonstrates exceptional sensitivity for the detection of thiram pesticide, with a detection limit as low as 7.76 × 10-11 M. The chip substrate also exhibits outstanding reliability, with reproducibility and repeatability both less than 5%. Furthermore, the flexible nature of the paper substrate enables it to conform to curved surfaces and be in direct contact with analytes, exemplified by its ability to adhere to and retrieve thiram from pear skin using a novel "paste-and-peel-off" technique. The substrate shows remarkable performance for thiram detection on pear skin, with sharp recovery rates ranging from 90% to 105%. With its facile fabrication, excellent sensitivity, high reliability, and practical applicability in non-invasive sampling, the paper-based Ag dendritic SERS substrate offers significant potential as an advanced substrate to bring SERS out of the laboratory and closer to real-world applications.

Dual-Fluorescent Quantum Dot Nanobead-Based Lateral Flow Immunoassay for Simultaneous Detection of C-Reactive Protein and Procalcitonin

Simultaneous detection of C-reactive protein (CRP) and procalcitonin (PCT) at the point of care is crucial for the management of infections in patients with inflammation and in critical care settings. The challenge of detecting high concentrations of CRP alongside low concentrations of PCT in plasma from inflammatory patients has limited the clinical application of multiplexed immunoassays. Herein, we developed a lateral flow immunoassay (LFIA) that employs quantum dot nanobeads (QDNBs) of varying sizes and colors to enable the simultaneous quantification of PCT and CRP in human plasma. To extend the dynamic range of CRP detection, we combined QDNBs with smaller particle sizes with the CRP detection antibodies, thereby increasing the assay's dynamic range and reducing the hook effect. At the same time, the stronger fluorescence emitted by these larger QDNBs, in conjugation with the PCT detection antibodies, allows for the detection of PCT at the nanogram level, meeting the demand for high sensitivity. The results show that this method can detect CRP concentrations from 0.1 to 3 mg/L and PCT with a detection limit of 0.09 ng/mL, which is on par with clinically used methods. By employing this dual-color and dual-size QDNB labeling strategy, we successfully achieved simultaneous detection of CRP with a broad dynamic range and PCT with high sensitivity in a one-step point-of-care rapid test.

Exploring Plasmonic Standalone Surface-Enhanced Raman Scattering Nanoprobes for Multifaceted Applications in Biomedical, Food, and Environmental Fields

Surface-enhanced Raman scattering (SERS) is an innovative spectroscopic technique that amplifies the Raman signals of molecules adsorbed on rough metal surfaces, making it pivotal for single-molecule detection in complex biological and environmental matrices. This review aims to elucidate the design strategies and recent advancements in the application of standalone SERS nanoprobes, with a special focus on quantifiable SERS tags. We conducted a comprehensive analysis of the recent literature, focusing on the development of SERS nanoprobes that employ novel nanostructuring techniques to enhance signal reliability and quantification. Standalone SERS nanoprobes exhibit significant enhancements in sensitivity and specificity due to optimized hot spot generation and improved reporter molecule interactions. Recent innovations include the development of nanogap and core-satellite structures that enhance electromagnetic fields, which are crucial for SERS applications. Standalone SERS nanoprobes, particularly those utilizing indirect detection mechanisms, represent a significant advancement in the field. They hold potential for wide-ranging applications, from disease diagnostics to environmental monitoring, owing to their enhanced sensitivity and ability to operate under complex sample conditions.

Lateral Flow Assay for Preeclampsia Screening Using DNA Hairpins and Surface-Enhanced Raman-Active Nanoprobes Targeting hsa-miR-17-5p

Preeclampsia (PE) is a serious complication that poses risks to both mothers and their children. This condition is typically asymptomatic until the second or even third trimester, which can lead to poor outcomes and can be costly. Detection is particularly challenging in low- and middle-income countries, where a lack of centralized testing facilities coincides with high rates of PE-related maternal mortality. Variations in the levels of hsa-miR-17-5p have been identified as constituting a potential early indicator for distinguishing between individuals with PE and those without PE during the first trimester. Thus, developing a screening test to measure hsa-miR-17-5p levels would not only facilitate rapid detection in the early stages of pregnancy but also help democratize testing globally. Here, we present a proof-of-principle lateral-flow assay (LFA) designed to measure hsa-miR-17-5p levels using DNA-hairpin recognition elements for enhanced specificity and nanoprobes for sensitive surface-enhanced resonance Raman scattering (SERS) signal transduction. The theoretical limit of detection for hsa-miR-17-5p was 3.84 × 10-4 pg/µL using SERS.

Integrating machine learning and biosensors in microfluidic devices: A review

Microfluidic devices are increasingly widespread in the literature, being applied to numerous exciting applications, from chemical research to Point-of-Care devices, passing through drug development and clinical scenarios. Setting up these microenvironments, however, introduces the necessity of locally controlling the variables involved in the phenomena under investigation. For this reason, the literature has deeply explored the possibility of introducing sensing elements to investigate the physical quantities and the biochemical concentration inside microfluidic devices. Biosensors, particularly, are well known for their high accuracy, selectivity, and responsiveness. However, their signals could be challenging to interpret and must be carefully analysed to carry out the correct information. In addition, proper data analysis has been demonstrated even to increase biosensors' mentioned qualities. To this regard, machine learning algorithms are undoubtedly among the most suitable approaches to undertake this job, automatically learning from data and highlighting biosensor signals' characteristics at best. Interestingly, it was also demonstrated to benefit microfluidic devices themselves, in a new paradigm that the literature is starting to name "intelligent microfluidics", ideally closing this benefic interaction among these disciplines. This review aims to demonstrate the advantages of the triad paradigm microfluidics-biosensors-machine learning, which is still little used but has a great perspective. After briefly describing the single entities, the different sections will demonstrate the benefits of the dual interactions, highlighting the applications where the reviewed triad paradigm was employed.

Recent Progress in Nanomaterial-Based Surface-Enhanced Raman Spectroscopy for Food Safety Detection

Food safety has recently become a widespread concern among consumers. Surface-enhanced Raman scattering (SERS) is a rapidly developing novel spectroscopic analysis technique with high sensitivity, an ability to provide molecular fingerprint spectra, and resistance to photobleaching, offering broad application prospects in rapid trace detection. With the interdisciplinary development of nanomaterials and biotechnology, the detection performance of SERS biosensors has improved significantly. This review describes the advantages of nanomaterial-based SERS detection technology and SERS's latest applications in the detection of biological and chemical contaminants, the identification of foodborne pathogens, the authentication and quality control of food, and the safety assessment of food packaging materials. Finally, the challenges and prospects of constructing and applying nanomaterial-based SERS sensing platforms in the field of food safety detection are discussed with the aim of early detection and ultimate control of foodborne diseases.

Surface-Enhanced Raman Scattering Nanosensing and Imaging in Neuroscience

Monitoring neurochemicals and imaging the molecular content of brain tissues in vitro, ex vivo, and in vivo is essential for enhancing our understanding of neurochemistry and the causes of brain disorders. This review explores the potential applications of surface-enhanced Raman scattering (SERS) nanosensors in neurosciences, where their adoption could lead to significant progress in the field. These applications encompass detecting neurotransmitters or brain disorders biomarkers in biofluids with SERS nanosensors, and imaging normal and pathological brain tissues with SERS labeling. Specific studies highlighting in vitro, ex vivo, and in vivo analysis of brain disorders using fit-for-purpose SERS nanosensors will be detailed, with an emphasis on the ability of SERS to detect clinically pertinent levels of neurochemicals. Recent advancements in designing SERS-active nanomaterials, improving experimentation in biofluids, and increasing the usage of machine learning for interpreting SERS spectra will also be discussed. Furthermore, we will address the tagging of tissues presenting pathologies with nanoparticles for SERS imaging, a burgeoning domain of neuroscience that has been demonstrated to be effective in guiding tumor removal during brain surgery. The review also explores future research applications for SERS nanosensors in neuroscience, including monitoring neurochemistry in vivo with greater penetration using surface-enhanced spatially offset Raman scattering (SESORS), near-infrared lasers, and 2-photon techniques. The article concludes by discussing the potential of SERS for investigating the effectiveness of therapies for brain disorders and for integrating conventional neurochemistry techniques with SERS sensing.

Antibody-Driven Assembly of Plasmonic Core-Satellites to Increase the Sensitivity of a SERS Vertical Flow Immunoassay

Here, we describe a SERS-based vertical flow assay as a platform technology suitable for point-of-care (POC) diagnostic testing. A capture substrate is constructed from filter paper embedded with spherical gold nanoparticles (AuNPs) and functionalized with an appropriate capture antibody. The capture substrate is loaded into a filtration device and connected to a syringe to rapidly and repeatedly pass the sample through the sensor for efficient antigen binding. The antigen is then labeled with a SERS-active detection probe. We show that only a few Raman reporter molecules, exclusively located adjacent to the plasmonic capture substrate, generate detectible signals. To maximize the signal from underutilized Raman reporter molecules, we employ a secondary signal enhancing probe that undergoes antibody-directed assembly to form plasmonic core-satellites. This facile enhancement step provides a 3.5-fold increase in the signal and a detection limit of 0.23 ng/mL (1.6 pM) for human IgG. This work highlights the potential to rationally design plasmonic architectures using widely available and reproducible spherical AuNPs to achieve large SERS enhancements for highly sensitive POC diagnostics.

Application and Method of Surface Plasmon Resonance Technology in the Preparation and Characterization of Biomedical Nanoparticle Materials

Surface Plasmon Resonance (SPR) technology, as a powerful analytical tool, plays a crucial role in the preparation, performance evaluation, and biomedical applications of nanoparticles due to its real-time, label-free, and highly sensitive detection capabilities. In the nanoparticle preparation process, SPR technology can monitor synthesis reactions and surface modifications in real-time, optimizing preparation techniques and conditions. SPR enables precise measurement of interactions between nanoparticles and biomolecules, including binding affinities and kinetic parameters, thereby assessing nanoparticle performance. In biomedical applications, SPR technology is extensively used in the study of drug delivery systems, biomarker detection for disease diagnosis, and nanoparticle-biomolecule interactions. This paper reviews the latest advancements in SPR technology for nanoparticle preparation, performance evaluation, and biomedical applications, discussing its advantages and challenges in biomedical applications, and forecasting future development directions.