Surface-enhanced Raman Scattering Analysis Research Articles

An enzymatic reaction-based SERS saliva analysis microporous array chip for chiral differentiation and high-throughput detection of D-amino acids.

ARaman-active boronate modified surface-enhanced Raman scattering (SERS) microporous array chip based on the enzymatic reaction was constructed for reliable, sensitive, and quantitative monitoring of D-Proline (D-Pro) and D-Alanine (D-Ala) in saliva. Initially, 3-mercaptophenylboronic acid (3-MPBA) was bonded to Au-coated Si nanocrown arrays (Au/SiNCA) via Au-S bonding. Following this, H2O2 obtained from D-amino acid oxidase (DAAO)-specific catalyzed D-amino acids (D-AAs) further reduced 3-MPBA to 3-hydroxythiophenol (3-HTP) with a new Raman peak at 882cm-1. Meanwhile, the original characteristic peak at 998cm-1 remained unchanged. Therefore, the I882/I998 ratio increased with increasing content ofD-AAs in the sample to be tested, allowing D-AAs to be quantitatively detected. TheAu/SiNCA with large-area periodic crown structure prepared provided numerous, uniform "hot spots," and the microporous array chip with 16 detection units was employed as the platform for SERS analysis, realizing high-throughput, high sensitivity, high specificity and high-reliability quantitative detection of D-AAs (D-Pro and D-Ala). The limits of detection (LOD) were down to 10.1µM and 13.7µM throughout the linear range of 20-500µM. The good results of the saliva detection suggested that this SERS sensor could rapidly differentiate between early-stage gastric cancer patients and healthy individuals.

A Machine Learning-Driven Surface-Enhanced Raman Scattering Analysis Platform for the Label-Free Detection and Identification of Gastric Lesions.

Gastric lesions pose significant clinical challenges due to their varying degrees of malignancy and difficulty in early diagnosis. Early and accurate detection of these lesions is crucial for effective treatment and improved patient outcomes. This paper proposed a label-free and highly sensitive classification method for serum of patients with different degrees of gastric lesions by combining surface-enhanced Raman scattering (SERS) and machine learning analysis. Specifically, we prepared Au lotus-shaped (AuLS) nanoarrays substrates using seed-mediated and liquid-liquid interface self-assembly method for measuring SERS spectra of serum, and then the collected spectra were processed by principal component analysis (PCA) - multi-local means based nearest neighbor (MLMNN) model to achieve differentiation. By employing this pattern analysis, AuLS nanoarray substrates can achieve fast, sensitive, and label-free serum spectral detection. The classification accuracy can reach 97.5%, the sensitivity is higher than 96.7%, and the specificity is higher than 95.0%. Moreover, by analyzing the PCs loading plots, the most critical spectral features distinguishing different degrees of gastric lesions were successfully captured. This discovery lays the foundation for combining SERS with machine learning for real-time diagnosis and recognition of gastric lesions.

SERS Analysis Platform Based on Aptamer Recognition-Release Strategy for Efficient and Sensitive Diagnosis of Colorectal Precancerous Lesions.

Colorectal cancer (CRC) has become a significant global public health challenge, demanding immediate attention due to its high incidence and mortality rates. Regular CRC screening is essential for the early detection of precancerous lesions and CRC. : We developed a novel surface-enhanced Raman scattering (SERS) analysis platform that employs high-throughput microarray chips as carriers and Au/SnO2 nanoring arrays (Au/SnO2 NRAs) as substrates. This platform utilizes an aptamer recognition-release strategy to achieve efficient and sensitive detection of protein tumor markers. In the detection process, the strong affinity and high specificity between the aptamer and the target protein result in competitive replacement of the SERS nanoprobes originally bound to the substrate surface. As a result, the SERS nanoprobes carrying Raman reporter genes are dislodged, leading to a reduction in the SERS signal intensity. The platform demonstrated excellent detection performance, with rapid detection completed within 15minutes and limits of detection (LOD) as low as 6.2×10-12 g/mL for hnRNP A1 and 6.51×10-12 g/mL for S100P. Clinical samples analyzed using the SERS platform showed high consistency with enzyme-linked immunosorbent assay (ELISA) results. This platform offers strong support for the early detection, risk assessment, and treatment monitoring of colorectal cancer precancerous lesions, with broad potential for clinical applications.

Label-Free Detection of DNA Base Mutation and Hybridized DNA by an Electrostatically Modified 3D Plasmonic Array.

Surface-enhanced Raman scattering (SERS) represents a promising avenue for DNA detection as it offers intrinsic chemical insights with high sensitivity compared to conventional methods. However, label-free and quantitative detection of unmodified DNA by SERS remains a major challenge in DNA analysis. To overcome this challenge, we propose a positively charged plasmonic nanosurface for DNA capture and quantitative analysis. Highly sensitive and uniform SERS enhancement was realized by a three-dimensional plasmonic array supporting well-designed hybrid plasmonic modes. Subsequently, the plasmonic array was modified with an electrostatically functionalized PDDA (poly(diene-dimethylammonium-chloride)) self-assembled monolayer in a single step. The effectiveness of the resulting PDDA-SERS substrate was demonstrated by the label-free and quantitative detection of base content and base mutation in hybridized DNA. The PDDA-SERS substrate provides a robust platform for SERS analysis not only of DNA but also of other electronegative analytes.

Laser-induced periodic surface structures on Fe ion doped LN crystal for pyroelectric SERS analysis

We proposed a sensor architecture for surface-enhanced Raman scattering (SERS) based on Fe ion doped LN (FLN) crystal, which was modified by large-area laser-induced periodic surface structures (LIPSS) and subsequently decorated with Ag nanoparticles (Ag NPs). Based on such a FLN/LIPSS/Ag substrate, strikingly boosted SERS enhancement was obtained at constant temperature owing to the LIPSS-related hot spot improvement. Benefiting from the pyroelectric effect of the FLN crystal, further enhanced SERS was achieved under heating and cooling processes, which can be ascribed to the additional charge transfer between molecules and Ag NPs triggered by pyroelectric potential. The experimental results highlight the high fabrication efficiency, ultrasensitivity, high uniformity, and high universality of the substrate, integrating the advantages of both LIPSS and the FLN crystal. More interestingly, selective suppression of Raman signals under cooling processes was observed, which further extends the applications of the FLN/LIPSS/Ag substrate for the detection of molecule complexes such as lake water polluted by crystal violet and 4-aminothiophenol molecules.

Large-area Ag “sesame cake-like” arrays with high-density hotspots for efficient SERS analysis

Nanogap-rich plasmonic metal nanostructures have attracted great attention in surface enhanced Raman scattering (SERS) applications due to their prominent performances. Herein, utilizing enhanced surface diffusion of Ag atoms on a low energy surface, a facile fabrication strategy is developed to construct a large-area Ag “sesame cake-like” (ASCL) array by combining the ultra-thin alumina mask (UTAM) and vapor deposition technique. Owing to the multiple plasmonic coupling effects, the proposed ASCL array possesses enormous hotspots responsible for remarkable sensitivity with an enhancement factor of 4.9 × 106, excellent reproducibility with a relative standard deviation (RSD) smaller than 7.12 % and obvious polarization independent in SERS analysis, which are confirmed by numerical simulations. In addition, the possibility to be fabricated on the flexible substrate makes the ASCL array substrate well meet the increasing demands for practical applications in the fields of food safety, health and environment monitoring.

A ratiometric SERS strategy for the prediction of cancer cell proportion and guidance of glioma surgical resection

Rapid and accurate identification of tumor boundaries is critical for the cure of glioma, but it is difficult due to the invasive nature of glioma cells. This paper aimed to explore a rapid diagnostic strategy based on a label-free surface-enhanced Raman scattering (SERS) technique for the quantitative detection of glioma cell proportion intraoperatively. With silver nanoparticles as substrate, an in-depth SERS analysis was performed on simulated clinical samples containing normal brain tissue and different concentrations of patient-derived glioma cells. The results revealed two universal characteristic peaks of 655 and 717 cm−1, which strongly correlated with glioma cell proportion regardless of individual differences. Based on the intensity ratio of the two peaks, a ratiometric SERS strategy for the quantification of glioma cells was established by employing an artificial neuron network model and a polynomial regression model. Such a strategy accurately estimated the proportion of glioma cells in simulated clinical samples (R2 = 0.98) and frozen samples (R2 = 0.85). More importantly, it accurately facilitated the delineation of tumor margins in freshly obtained samples. Taken together, this SERS-based method ensured a rapid and more detailed identification of tumor margins during surgical resection, which could be beneficial for intraoperative decision-making and pathological evaluation.

DHM/SERS reveals cellular morphology and molecular changes during iPSCs-derived activation of astrocytes.

The activation of astrocytes derived from induced pluripotent stem cells (iPSCs) is of great significance in neuroscience research, and it is crucial to obtain both cellular morphology and biomolecular information non-destructively in situ, which is still complicated by the traditional optical microscopy and biochemical methods such as immunofluorescence and western blot. In this study, we combined digital holographic microscopy (DHM) and surface-enhanced Raman scattering (SERS) to investigate the activation characteristics of iPSCs-derived astrocytes. It was found that the projected area of activated astrocytes decreased by 67%, while the cell dry mass increased by 23%, and the cells changed from a flat polygonal shape to an elongated star-shaped morphology. SERS analysis further revealed an increase in the intensities of protein spectral peaks (phenylalanine 1001 cm-1, proline 1043 cm-1, etc.) and lipid-related peaks (phosphatidylserine 524 cm-1, triglycerides 1264 cm-1, etc.) decreased in intensity. Principal component analysis-linear discriminant analysis (PCA-LDA) modeling based on spectral data distinguished resting and reactive astrocytes with a high accuracy of 96.5%. The increase in dry mass correlated with the increase in protein content, while the decrease in projected area indicated the adjustment of lipid composition and cell membrane remodeling. Importantly, the results not only reveal the cellular morphology and molecular changes during iPSCs-derived astrocytes activation but also reflect their mapping relationship, thereby providing new insights into diagnosing and treating neurodegenerative diseases.

Open Cross-gap Gold Nanocubes with Strong, Large-Area, Symmetric Electromagnetic Field Enhancement for On-Particle Molecular-Fingerprint Raman Bioassays.

Plasmonic nanoparticles with an externally open nanogap can localize the electromagnetic (EM) field inside the gap and directly detect the target via the open nanogap with surface-enhanced Raman scattering (SERS). It would be beneficial to design and synthesize the open gap nanoprobes in a high yield for obtaining uniform and quantitative signals from randomly oriented nanoparticles and utilizing these particles for direct SERS analysis. Here, we report a facile strategy to synthesize open cross-gap (X-gap) nanocubes (OXNCs) with size- and EM field-tunable gaps in a high yield. The site-specific growth of Au budding structures at the corners of the AuNC using the principle that the Au deposition rate is faster than the surface diffusion rate of the adatoms allows for a uniform X-gap formation. The average SERS enhancement factor (EF) for the OXNCs with 2.6 nm X-gaps was 1.2 × 109, and the EFs were narrowly distributed within 1 order of magnitude for ∼93% of the measured OXNCs. OXNCs consistently displayed strong EM field enhancement on large particle surfaces for widely varying incident light polarization directions, and this can be attributed to the symmetric X-gap geometry and the availability of these gaps on all 6 faces of a cube. Finally, the OXNC probes with varying X-gap sizes have been utilized in directly detecting biomolecules with varying sizes without Raman dyes. The concept, synthetic method, and biosensing results shown here with OXNCs pave the way for designing, synthesizing, and utilizing plasmonic nanoparticles for selective, quantitative molecular-fingerprint Raman sensing and imaging applications.

Surface-Enhanced Raman Scattering Using 2D Materials.

The use of surface-enhanced Raman scattering (SERS) as a technique for detecting small amounts of (bio)chemical analytes has become increasingly popular in various fields. While gold and silver nanostructures have been extensively studied as SERS substrates, the availability of other types of substrates is currently expanding the applications of this spectroscopic method. Recently, researchers have begun exploring two-dimensional (2D) materials (e. g., graphene-like nanostructures) as substrates for SERS analysis. These materials offer unique optical properties, a well-defined structure, and the ability to modify their surface chemistry. As a contribution to advance this field, this concept article highlights the significance of understanding the chemical mechanism that underlies the experimental Raman spectra of chemisorbed molecules onto 2D materials' surfaces. Therefore, the article discusses recent advancements in fabricating substrates using 2D layered materials and the synergic effects of using their metallic composites for SERS applications. Additionally, it provides a new perspective on using Raman imaging in developing 2D materials as analytical platforms for Raman spectroscopy, an exciting emerging research area with significant potential.

Acoustic Levitation Synthesis of Ultrahigh‐Density Spherical Nucleic Acid Architectures for Specific SERS Analysis

AbstractControllably regulating the electrostatic bilayer of nanogold colloids is a significant premise for synthesizing spherical nucleic acid (SNA) and building ordered plasmonic architectures. We develop a facile acoustic levitation reactor to universally synthesize SNAs with an ultra‐high density of DNA strands, which is even higher than those of various state‐of‐the‐art methods. Results reveal a new mechanism of DNA grafting via acoustic wave that can reconfigure the ligands on colloidal surfaces. The acoustic levitation reactor enables substrate‐free three‐dimentional (3D) spatial assembly of SNAs with controllable interparticle nanogaps through regulating DNA lengths. This kind of architecture may overcome the plasmonic enhancement limits by blocking electron tunneling and breaking electrostatic shielding in dried aggregations. Finite element simulations support the architecture with 3D spatial plasmonic hotspot matrix, and its ultrahigh surface‐enhanced Raman scattering (SERS) capability is evidenced by in situ untargeted tracking of biomolecular events during photothermal stimulation (PTS)‐induced cell death process. For biomarker diagnosis, the conjugation of adenosine triphosphate (ATP) aptamer onto SNAs enables in situ targeted tracking of ATP during PTS‐induced cell death process. Particularly, the CD71 receptor and integrin α3β1 protein on PL45 cell membrance could be well distinguished by label‐free SERS fingerprints when using specific XQ‐2d and DML‐7 aptamers, respectively, to synthesize SNA architectures. Our current acoustic levitation reactor offers a new method for synthesizing SNAs and enables both targeted and untargeted SERS analysis for tracking molecular events in living systems. It promises great potentials in biochemical synthesis and sensing in future.

Acoustic Levitation Synthesis of Ultrahigh-Density Spherical Nucleic Acid Architectures for Specific SERS Analysis.

Controllably regulating the electrostatic bilayer of nanogold colloids is a significant premise for synthesizing spherical nucleic acid (SNA) and building ordered plasmonic architectures. We develop a facile acoustic levitation reactor to universally synthesize SNAs with an ultra-high density of DNA strands, which is even higher than those of various state-of-the-art methods. Results reveal a new mechanism of DNA grafting via acoustic wave that can reconfigure the ligands on colloidal surfaces. The acoustic levitation reactor enables substrate-free three-dimentional (3D) spatial assembly of SNAs with controllable interparticle nanogaps through regulating DNA lengths. This kind of architecture may overcome the plasmonic enhancement limits by blocking electron tunneling and breaking electrostatic shielding in dried aggregations. Finite element simulations support the architecture with 3D spatial plasmonic hotspot matrix, and its ultrahigh surface-enhanced Raman scattering (SERS) capability is evidenced by in situ untargeted tracking of biomolecular events during photothermal stimulation (PTS)-induced cell death process. For biomarker diagnosis, the conjugation of adenosine triphosphate (ATP) aptamer onto SNAs enables in situ targeted tracking of ATP during PTS-induced cell death process. Particularly, the CD71 receptor and integrin α3β1 protein on PL45 cell membrance could be well distinguished by label-free SERS fingerprints when using specific XQ-2d and DML-7 aptamers, respectively, to synthesize SNA architectures. Our current acoustic levitation reactor offers a new method for synthesizing SNAs and enables both targeted and untargeted SERS analysis for tracking molecular events in living systems. It promises great potentials in biochemical synthesis and sensing in future.

Frequency shift Raman-based sensing of serum MicroRNA for ultrasensitive cervical cancer diagnosis

Cervical cancer is the most common gynaecological tumor. The development of a sensor for the ultrasensitive detection of cervical cancer is significant in guaranteeing its prognosis. Herein, we proposed a novel surface-enhanced Raman scattering (SERS) analysis platform using a frequency shifts-based sensing model for rapid and ultrasensitive microRNA (miRNA) assay. During the analysis process, miR-21 can be captured by the single-stranded DNA (ssDNA) modified on the platform which is complementary pairing with miR-21. The connection of miR-21 can lead to the variation of the molecular weight and result in the deformation extent of the Raman report molecule 6Thioguanine (6TG); thus, the peak at 1301 cm−1 due to the ring C–N stretches of 6TG shifts to lower frequency. The detection limit (LOD) of the proposed SERS analysis platform is as low as 8.32 aM. Moreover, the platform also has excellent specificity and repeatability, with the relative standard deviation (RSD) value of 6.53 %. Serum samples of cervical cancer patients and healthy subjects were analyzed via the platform and the accuracy of the detection results was verified by qRT-PCR, revealing that SERS results and qRT-PCR results have high homogeneity. Thus, the platform can serve as a potential tool for clinical diagnosis of cervical cancer.

Self-assembling photonic crystal film composed of TiO2/SiO2 hollow spheres for ultra-sensitive and reusable all-dielectric SERS substrates

Surface-enhanced Raman scattering (SERS) substrates were fabricated using an accurately designed arrangement of porous TiO2/SiO2 hollow spheres, notably devoid of noble metals. The synthesis of the SERS substrate involved the production of monodispersed composite materials through a hard-template technique. Subsequently, these hollow spheres were organized into an ordered photonic crystal (PC) film on glass slides using a dip-coating method. The porous SiO2 inter shell possessed a robust structure that significantly bolstered the durability of the SERS substrate. Moreover, the high specific surface area increased analyte absorbance, enhancing interaction with incident light. Simultaneously, the TiO2 outer shell facilitated charge transfer and heightened the reflective intensity of the substrate. The ordered arrangement of the TiO2/SiO2 hollow spheres, characterized by a substantial refractive-index contrast, resulted in a PC capable of augmenting the overall light reflectivity of the SERS substrate, thereby physically amplifying Raman signal intensity. Exploiting these distinctive properties, the TiO2/SiO2 substrate demonstrated an impressive detection limit of less than 10−10 M for both Methylene Blue and Rhodamine 6 G. Additionally, the enhancement factor (EF) reached a remarkable 4.7 × 107. The TiO2/SiO2 film's reusability and the straightforward preparation procedure position it as a promising candidate for future SERS analysis applications.

SERS analysis, DFT, and solution effects regarding the structural and optical characteristics of folic acid biomolecule adsorbed on a Cu3 metal cluster

The optical characteristics of folic acid (ABP) and metal clusters of copper (Cu3) at various locations were investigated by means of density functional theory (DFT) computations. Mulliken charge analysis and molecular electrostatic potential (MEP) surface show how charge moves from Cu3 to ABP through the various groups. The peak in the UV–Vis spectra of ABP-Cu3 is caused by bonding and anti-bonding orbitals. In both vacuum and aqueous conditions, the polarizability values of ABP-Cu3 cluster are significantly higher than those of pure ABP, indicating a possible enhancement of the nonlinear optical (NLO) effect. Our research investigates the possibility of using ABP adsorbed metal clusters for NLO materials. Surface enhanced Raman scattering (SERS) in the ABP adsorbed metal clusters enhances the vibrational modes of ABP. Adsorption energies are found to be in the range −17.08 to −58.52 kcal/mol in vacuum and −53.34 to −93.44 kcal/mol in aqueous medium for the different configurations for ABP-Cu3. It indicates that metal clusters adsorbed by ABP are stable in the aqueous media. Experimental IR and UV–Vis of ABP is in agreement with theoretically predicted ones.

Intra-nanoparticle plasmonic nanogap based spatial-confinement SERS analysis of polypeptides

Sensing and characterizing water-soluble polypeptides are essential in various biological applications. However, detecting polypeptides using Surface-Enhanced Raman Scattering (SERS) remains a challenge due to the dominance of aromatic amino acid residues and backbones in the signal, which hinders the detection of non-aromatic amino acid residues. Herein, intra-nanoparticle plasmonic nanogap were designed by etching the Ag shell in Au@AgNPs (i.e., obtaining AuAg cores) with chlorauric acid under mild conditions, at the same time forming the outermost Au shell and the void between the AuAg cores and the Au shell (AuAg@void@Au). By varying the Ag to added chloroauric acid molar ratios, we pioneered a simple, controllable, and general synthetic strategy to form interlayer-free nanoparticles with tunable Au shell thickness, achieving precise regulation of electric field enhancement within the intra-nanogap. As validation, two polypeptide molecules, bacitracin and insulin B, were successfully synchronously encapsulated and spatial-confined in the intra-nanogap for sensing. Compared with concentrated 50 nm AuNPs and Au@AgNPs as SERS substrates, our simultaneous detection method improved the sensitivity of the assay while benefiting to obtain more comprehensive characteristic peaks of polypeptides. The synthetic strategy of confining analytes while fabricating plasmonic nanostructures enables the diffusion of target molecules into the nanogap in a highly specific and sensitive manner, providing the majority of the functionality required to achieve peptide detection or sequencing without the hassle of labeling.

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.

Raman and Surface-Enhanced Raman Scattering Detection in Flowing Solutions for Complex Mixture Analysis.

Raman scattering provides a chemical-specific and label-free method for identifying and quantifying molecules in flowing solutions. This review provides a comprehensive examination of the application of Raman spectroscopy and surface-enhanced Raman scattering (SERS) to flowing liquid samples. We summarize developments in online and at-line detection using Raman and SERS analysis, including the design of microfluidic devices, the development of unique SERS substrates, novel sampling interfaces, and coupling these approaches to fluid-based chemical separations (e.g., chromatography and electrophoresis). The article highlights the challenges and limitations associated with these techniques and provides examples of their applications in a variety of fields, including chemistry, biology, and environmental science. Overall, this review demonstrates the utility of Raman and SERS for analysis of complex mixtures and highlights the potential for further development and optimization of these techniques.

Label-Free Surface-Enhanced Raman Scattering Detection of Fire Blight Pathogen Using a Pathogen-Specific Bacteriophage.

Fire blight is one of the most devastating plant diseases, causing severe social and economic problems. Herein, we report a novel method based on label-free surface-enhanced Raman scattering (SERS) combined with an Erwinia amylovora-specific bacteriophage that allows detecting efficiently fire blight bacteria E. amylovora for the first time. To achieve the highest SERS signals for E. amylovora, we synthesized and compared plasmonic nanoparticles (PNPs) with different sizes, i.e., bimetallic gold core-silver shell nanoparticles (Au@AgNPs) and monometallic gold nanoparticles (AuNPs) and utilized the coffee-ring effect for the self-assembly of PNPs and enrichment of fire blight bacteria. Furthermore, we investigated the changes in the SERS spectra of E. amylovora after incubation with an E. amylovora-specific bacteriophage, and we found considerable differences in the SERS signals as a function of the bacteriophage incubation time. The results indicate that our bacteriophage-based label-free SERS analysis can specifically detect E. amylovora without the need for peak assignment on the SERS spectra but simply by monitoring the changes in the SERS signals over time. Therefore, our facile method holds great potential for the label-free detection of pathogenic bacteria and the investigation of viral-bacterial interactions.

A dual-mode strategy for diacetyl detection based on colorimetry and surface-enhanced Raman scattering

Diacetyl is an important food additive with rich creamy flavor whose excessive intake may cause various diseases. Herein, for the first time, we designed a dual-mode method for diacetyl detection based on colorimetry and surface-enhanced Raman scattering (SERS) technology. Diacetyl exhibited excellent oxidase-like catalytic activity under light-mediated condition, facilitating the oxidation of colorless 3,3′,5,5′-tetramethylbenzidine (TMB) to blue ox-TMB for colorimetric detection. Notably, diacetyl could control the oxidation process of TMB by simply adjusting light irradiation, unlike traditional enzymatic reactions that required terminators to stop the reaction. Interestingly, ox-TMB was an ideal Raman marker for SERS analysis. Then, a three-dimensional flower-like zinc oxide/silver (ZnO/Ag) for sensitive SERS detection was prepared, which exhibited outstanding SERS effect with a high enhancement factor of 1.89 × 108 due to effective charge transfer and synergistic effect between ZnO and Ag. Based on these, SERS method was constructed to indirectly detect diacetyl, which has not been reported due to low Raman activity of diacetyl. The linear ranges of colorimetry and SERS were 0.5–60 μM and 10−9-10−5 M respectively, with detection limits of 0.41 μM and 0.73 nM. Obviously, the dual-mode strategy combined the simplicity and practicality of colorimetry and the high sensitivity of SERS, offering great potential applications in practical samples.