Surface-enhanced Raman Scattering Probes Research Articles

Purines recognition and quantitative analysis by surface-enhanced Raman spectroscopy

The common quantification methods of purines, including high-performance liquid chromatography, micellar electrokinetic chromatography, reverse phase ion pair chromatography, and capillary zone electrophoresis, have been used for the analysis of purines. These conventional techniques are limited by long operation times, large sample volumes, requirements for pretreatment and separation processes, or sophisticated, bulky and expensive equipment. Here, we have developed a simple method to prepare a probe for the quantitative analysis of purines using the surface-enhanced Raman scattering (SERS) method. The SERS probe is a rough Ag wire obtained with simple electrochemical treatment, which is optimized to reach the maximum SERS signal enhancement. The Raman enhancement factor (EF) of Ag wire after roughening can reach ∼106. Under optimized conditions, the rough Ag wire is capable of recognizing four purine bases (namely, guanine, adenine, hypoxanthine, and xanthine) in the range of 10−5 to 10−1 mg/mL with a linear relationship between SERS intensity of signature peak and purine concentration. The recovery rate of each purine base is higher than 80% in the mixture of four purines. The overall method was successfully applied to the monitoring of the level of purines in marketplace beer beverages. The novel wire-based SERS sensor used with portable Raman spectroscopy is prospective in diet safety and personalized point-of-care medical detection.

In-situ SERS monitoring of membrane receptor PTK7 for assessing cancer cell migration at single-cell level on a microfluidic chip

Protein tyrosine kinase-7 (PTK7), an important membrane receptor, is crucial in cell migration. Accumulated evidence suggests that aberrant PTK7 expression is associated with the occurrence of cancer. Lots of research has focused on revealing the role of PTK7 in the development of cancers, the conventional methods need transwell and western blot, masking intrinsic differences among cells, and the integrity of the cells cannot be preserved, which is important for revealing the role of PTK7 on cancer development. Herein, we present a method to monitor the expression of PTK7 receptor at single-cell level using a surface-enhanced Raman scattering (SERS) microfluidic chip. Cell migration channel arrays were designed, and controllable chemical stimulation was generated on the microfluidic chip, enabling the cell migration at single-cell level. Raman reporter-embedded gold@silver core–shell nanoparticles (Au@4-Mercaptobenzonitrile@AgNPs) modified with DNA aptamers (Sgc8) exhibit promising binding ability to cell membrane receptor PTK7. The different migration abilities of cancer cells were accurately distinguished in the microfluidic chip. We explored the reduced expression of PTK7 on high migration ability cells at single-cell level. And the discrimination of different colorectal cancer cells was successfully realized using the SERS probes. The developed platform is expected to provide a powerful tool for investigating tumor heterogeneity and promoting clinical precision medicine.

An aptamer and Au/Si CCA based SERS sensor for ultra-sensitive detection of Vimentin during EMT in gastric cancer.

Introduction: In this study, a surface-enhanced Raman scattering (SERS) sensor based on a functionalized Au/Si cap-cone array (Au/Si CCA) was constructed using the identity-release strategy to detect Vimentin changes during epithelial-mesenchymal transition (EMT) in gastric cancer (GC). Methods: The periodic structure of Au/Si CCA, which can form "hot spots" with high density and regular arrangement, is a substrate with excellent performance. Au/Si CCA was functionalized with aptamers as the capture substrate, and Au nanocubes (AuNCs) were modified with 5-carboxyfluorescein (5-FAM) labelled complementary strand as SERS probe. The capture substrate and SERS probe were assembled by hybridization, and the SERS signal intensity of 5-FAM was greatly enhanced. The binding of Vimentin to the aptamer resulted in a broken connection between the SERS sensor Au/Si CCA array and AuNCs, which resulted in a decrease in the signal intensity of 5-FAM. The identity-release strategy requires only a simple step of reaction to achieve rapid detection of target proteins, which has clinical practicability. Results: Using this protocol, the concentration of Vimentin in GES-1 cells could be successfully detected, and the detection limit was as low as 4.92pg/mL. Biological experiments of Vincristine, Oncovin (VCR)-treated GES-1 cells effectively mimicked the EMT process, and Vimentin changes during EMT could be accurately detected by this method. Discussion: This study provides a selective, ultra-sensitive and accurate assay for Vimentin detection, which may provide a means for the future detection of EMT process in GC.

A Microfluidics-Based Multiplex SERS Immunoassay Device for Analysis of Acute Ischemic Stroke Biomarkers.

Sensitive and accurate methods for early detection of acute ischemic stroke (AIS) are essential for timely treatment and prognostic assessment of patients. In this study, we report a microfluidics-based ultrasensitive surface-enhanced Raman scattering (SERS) immunoassay device for the quantitative determination of multiplex biomarkers in AIS. By preparing 5,5'-dithiobis-2-nitrobenzoic acid (DTNB) antibody-modified gold nanoparticles (AuNPs) on SERS devices as SERS probes, the biomarkers in whole blood of AIS were accurately captured and further visualized for SERS signal intensity quantitative analysis of six biomarkers in the blood samples. It is worth mentioning that the limit of detection (LOD) of the method can reach the level of fg/mL, with excellent sensitivity and selectivity. Meanwhile, the analytical comparison with ELISA method showed that the detection results of both methods were consistent, which verified the feasibility of the assembled device. The SERS immunoassay device detection provides a powerful strategy for the prediction, early diagnosis and dynamic monitoring of prognosis of AIS with a wide range of clinical practice prospects.

Enhancing the Reliability of SERS Detection in Ampicillin Using Oriented Tetrahedral Framework Nucleic Acid Probes and a Long-Range SERS Substrate.

Indirect surface-enhanced Raman scattering (SERS)-based methods are highly efficient in detecting and quantitatively analyzing trace antibiotics in complex samples. However, the poor reproducibility of indirect SERS assays caused by the diffusion and orientation changes of the probing molecules on SERS substrates still presents a significant challenge. To address this issue, this study reports the construction of a novel SERS sensing platform using tetrahedral framework nucleic acid (tFNA) as SERS probes in conjunction with a long-range SERS (LR-SERS) substrate. The tFNA was modified with sulfhydryl groups at three vertices and appended with a probing DNA at the remaining vertex, anchored on the substrate surface with a well-ordered orientation and stable coverage density, resulting in highly reproducible SERS signals. Owing to the weak SERS signal of tFNA inherited from its size being larger than the effective range of the enhancing electric field (E-field) of conventional SERS substrates, we utilized an LR-SERS substrate to enhance the signal of tFNA probes by capitalizing on its extended E-field. Correspondingly, the LR-SERS substrate demonstrated a 54-fold increase in the intensity of tFNA probes compared to the conventional substrate. Using this novel platform, we achieved a highly reliable detection of the antibiotic ampicillin with a wide linear range (10 fM to 1 nM), low detection limit (3.1 fM), small relative standard deviation (3.12%), and yielded quantitative recoveries of 97-102% for ampicillin in water, milk, and human serum samples. These findings, therefore, effectively demonstrate the achievement of highly reliable SERS detection of antibiotics using framework nucleic acids and an LR-SERS substrate.

Engineering Surface-Enhanced Raman Scattering Probe for Enhanced Detection of Acute Diseases with Paper Microfluidics

Effective and fast detection of acute diseases is still a main challenge for early diagnosis and monitoring treatment. In this work, surface-enhanced Raman scattering (SERS) probes are incorporated into a microfluidic paper strip for antigen biomarker detection. First, a new material is designed to tune plasmon band position and intensity. Second, geometry is optimized to maximize the SERS enhancement factor. The Finite-Difference Time-Domain simulation has confirmed that more hotspots are generated by the above optimization. As a results, the paper microfluidic strip has achieved the limit of detection at pg/mL level toward antigen detection in blood plasma. The paper microfluidic device shows a great potential in early detection of acute diseases at home, clinics, and remote areas with limited resources.

Preparation of gold nanoparticles loaded MOF-199 for SERS detection of 5-hydroxyindole-3-acetic acid in serum

5-Hydroxyindole-3-acetic acid (5-HIAA) is regarded as a biomarker for diagnosis of carcinoid tumors, and it is of great significance to developing a precision assay for monitoring 5-HIAA levels. In this work, gold nanoparticles loading on the surface of MOF-199 (Au NPs/MOF-199) is prepared to propose a surface enhanced Raman scattering (SERS) assay for 5-HIAA. When 4-mercaptopyridine (4-MPy) is used as a SERS probe, on Au NPs/MOF-199, limit of detection (LOD) at 10−9 mol/L can be achieved. In addition, Au NPs/MOF-199 substrate with good preparation reproducibility shows long-term storage stability at 4 °C. Under optimal condition, the Au NPs/MOF-199-based SERS method is applied to determine 5-HIAA in serum. The concentration linear range is from 10−9 to 10−5 mol/L and LOD is of 6.40 × 10−11 mol/L. Much importantly, Au NPs/MOF-199 substrate exhibits specific response toward 5-HIAA against other metabolites in the serum due to the capturing selectivity from porous MOF-199. The recoveries obtained on spiked human serum samples locate in the span from 94.30% to 106.00% with RSD of 4.01–7.43%. Au NPs/MOF-199-based SERS sensing strategy is a promising avenue for on-field monitoring biomedical species for clinic diagnosis purpose.

Self-assembly of Au@AgNR along M13 framework: A SERS nanocarrier for bacterial detection and killing

Self-assembled functional nanomaterials with electromagnetic hot spots are crucial and highly desirable in surface-enhanced Raman scattering (SERS). Due to its versatile biological scaffold, the M13 phage has been employed to produce novel nano-building blocks and devices. In this study, we propose a novel M13 phage-based SERS nanocarrier, that utilizes the pVIII capsid in M13 to conjugate Au@Ag core-shell nanorod (Au@AgNR) with linker carboxy-PEG-thiol (M13-Au@AgNR) and the pIII capsid to specifically target Escherichia coli (E. coli). The M13-Au@AgNR@DTTC (3,3′- diethylthiocarbocyanine iodide) SERS probe was used to detect E. coli in a concentration range of 6 to 6 × 105 cfu/mL, achieving a limit of detection (LOD) of 0.5 cfu/mL. The proposed SERS platform was also tested in real samples, showing good recoveries (92%–114.3%) and a relative standard deviation (RSD) of 1.2%–4.7%. Furthermore, the system demonstrated high antibacterial efficiency against E. coli, approximately 90%, as measured by the standard plate-count method. The investigation provides an effective strategy for in vitro bacteria detection and inactivation.

SERS Endoscopy for Monitoring Intracellular Drug Dynamics.

Understanding the dynamics and distribution of medicinal drugs in living cells is essential for the design and discovery of treatments. The tools available for revealing this information are, however, extremely limited. Here, we report the application of surface-enhanced Raman scattering (SERS) endoscopy, using plasmonic nanowires as SERS probes, to monitor the intracellular fate and dynamics of a common chemo-drug, doxorubicin, in A549 cancer cells. The unique spatio-temporal resolution of this technique reveals unprecedented information on the mode of action of doxorubicin: its localization in the nucleus, its complexation with medium components, and its intercalation with DNA as a function of time. Notably, we were able to discriminate these factors for the direct administration of doxorubicin or the use of a doxorubicin delivery system. The results reported here show that SERS endoscopy may have an important future role in medicinal chemistry for studying the dynamics and mechanism of action of drugs in cells.

A dual-amplification strategy-intergated SERS biosensor for ultrasensitive hepatocellular carcinoma-related telomerase activity detection.

Telomerase has been considered as a biomarker for early diagnosis and prognosis assessment of hepatocellular carcinoma (HCC), while the highly sensitive and specific methods remain challenging. To detect telomerase, a novel surface-enhanced Raman scattering (SERS) biosensor was constructed using the dual DNA-catalyzed amplification strategy composed of strand displacement amplification (SDA) and catalytic hairpin assembly (CHA). This strategy relies on the extension reaction of telomerase primer induced by telomerase, forming long-stranded DNAs with repetitive sequence to catalyze the follow-up SDA event. Subsequently, the SDA products can trigger the CHA reaction between the SERS probes (Au-Ag nanocages (Au-AgNCs) modified with hairpin DNA1 and Raman reporters) and capture substrate (Au@SiO2 array labeled with hairpin DNA2), resulting in the formation of numerous "hot spots" to significantly enhance the SERS signal. Results are promising that the established biosensor presented excellent reproducibility, specificity and sensitivity. Moreover, ELISA was applied as the golden standard to verify the application of the proposed biosensor in real samples and the results confirmed the satisfactory accuracy of our method. Therefore, the proposed SERS biosensor has the potential to be an ideal tool for the early screening of HCC.

Microfluidic Droplet-SERS Platform for Single-Cell Cytokine Analysis via a Cell Surface Bioconjugation Strategy.

A microfluidic-based surface-enhanced Raman scattering (SERS) platform for analyzing cytokines secreted by single cells is reported based on the elaborate bioconjugation of the immuno-sandwich complex on the probed cell surface. This platform integrates the dual functions of microfluidic droplet separation of single cells and SERS measurement. Two immune nanoprobes (capture probe and SERS probe) are introduced into a microfluidic droplet along with a single cell. They were anchored to the cell membrane protein surface by capturing secreted cytokines to form an immune sandwich structure, realizing the enrichment effect of cytokines above the cell membrane surface and the amplification effect of SERS detection probes. This single-cell analytical platform was applied to track specific cell-secreted vascular endothelial growth factor (VEGF) of different cell lines (MCF-7, SGC, and T24), and highly sensitive detection of VEGF was achieved. Chemometric methods (principal component analysis and t-distributed stochastic neighbor embedding) were adopted for the SERS data analysis, and the support vector machine (SVM) discriminant model was established to test the data. These chemometric methods successfully identify significant differences in the secreting ability of cytokines among three kinds of cancer cell lines, revealing cell heterogeneity. In addition, the behavior of single cells secreting VEGF was monitored time-dependently and was shown to increase with time. This work demonstrates the importance of tracking specific cells secreting cytokines based on the cell surface bioconjugation strategy. Our developed platform provides guidelines for using the single-cell exocytosis factors as biomarkers to assess the early diagnosis of cancer and provide physiological cues for learning single-cell secretions.

Dynamically Monitoring pH in Living Organisms Based on a SERS‐Active Optical Fiber

AbstractTo dynamically monitor pH in living organisms, a pH‐sensitive surface‐enhanced Raman scattering (SERS)‐active optical fiber is designed and developed. A 2‐cm‐long optical fiber is processed with an inclined end to facilitate entering the body of the optical fiber, and a hole is etched near the inclined end to integrate pH‐sensitive SERS probes and protect them from being erased during entering the body. The pH‐sensitive SERS probes in the hole respond thoroughly to the buffer environment in 5 min and the body environment in 15 min, respectively. The fabricated SERS‐active optical fiber is used to dynamically monitor the change in pH in tissues of living rats, such as muscle and brain. The SERS‐active optical fibers will be a versatile platform to integrate optical probes such as SERS probes and fluorescence probes to dynamically monitor life activities in living organisms.

A Raman immunosensor based on SERS and microfluidic chip for all-fiber detection of brain natriuretic peptide

Early diagnosis of chronic heart failure (CHF) relies on the ultra-sensitive detection assay of its main biomarker, Brain natriuretic peptide (BNP). To meet such demand, we designed a near-infrared immunoassay biosensor, utilizing a fiber-embedded microfluidic chip for surface-enhanced Raman scattering (SERS) detection. A SERS probe, consisting of metal–organic framework and Au-HEPES coupling nanoparticles (AuHPs), was used to enhance the Raman signal of the toluidine blue (TB) dye. The probe anchored with TB is used as a SERS tag, which is linked to BNP through sandwich method. To enhance the Raman signal further, we embedded a SERS substrate at the bottom of the microfluidic channel, which serves an enhancer when the SERS tagged BNP passes through the microfluidic chip. The amplified Raman signal was collected by an optical fiber probe of a simple and portable Raman detection system with an all-fiber connected configuration. Such design resulted in the lowest detection limit of pg/mL, indicating that the proposed platform can be used for rapid and highly sensitive detection of BNP. In addition, our platform also has the advantages of low sample consumption and high throughput rate, providing an effective scheme for the early diagnosis of CHF.

Application of Dual-Enhanced Surface-Enhanced Raman Scattering Probe Technology in the Diagnosis of Tumor Cells in Vitro.

With the development of precision medicine, antigen/antibody-targeted therapy has brought great hope to tumor patients; however, the migration of tumor cells, especially a small number of cells flowing into blood or other tissues, remains a clinical challenge. In particular, it is difficult to use functional gold nanomaterials for targeted clinical tumor diagnosis while simultaneously obtaining stable and highly sensitive Raman signals. Therefore, we developed a detection method for functional Au Nanostars (AuNSs) with dual signal enhancement that can specifically track location and obtain high-intensity surface-enhanced Raman scattering (SERS) signals. First, AuNSs with specific optical properties were synthesized and functionalized. The Raman dye 4-mercapto-hydroxybenzoic acid and polyethylene glycol were coupled with the tumor marker, epidermal growth factor receptor, to obtain the targeted SERS probes. In addition, a detection chip was prepared for Raman detection with physical enhancement, exhibiting a 40-times higher signal intensity than that of quartz glass. This study combines physical enhancement and SERS enhancement technologies to achieve dual enhancement, enabling the detection of a highly sensitive and stable Raman signal; this has potential clinical value for antigen/antibody-targeted tumor diagnosis and treatment.

Silica-Encapsulated Core–Satellite Gold Nanoparticle Assemblies as Stable, Sensitive, and Multiplex Surface-Enhanced Raman Scattering Probes

Silica-Encapsulated Core–Satellite Gold Nanoparticle Assemblies as Stable, Sensitive, and Multiplex Surface-Enhanced Raman Scattering Probes

Visible-light and near-infrared fluorescence and surface-enhanced Raman scattering point-of-care sensing and bio-imaging: a review.

This review article deals with the concepts, principles and applications of visible-light and near-infrared (NIR) fluorescence and surface-enhanced Raman scattering (SERS) in in vitro point-of-care testing (POCT) and in vivo bio-imaging. It has discussed how to utilize the biological transparency windows to improve the penetration depth and signal-to-noise ratio, and how to use surface plasmon resonance (SPR) to amplify fluorescence and SERS signals. This article has highlighted some plasmonic fluorescence and SERS probes. It has also reviewed the design strategies of fluorescent and SERS sensors in the detection of metal ions, small molecules, proteins and nucleic acids. Particularly, it has provided perspectives on the integration of fluorescent and SERS sensors into microfluidic chips as lab-on-chips to realize point-of-care testing. It has also discussed the design of active microfluidic devices and non-paper- or paper-based lateral flow assays for in vitro diagnostics. In addition, this article has discussed the strategies to design in vivo NIR fluorescence and SERS bio-imaging platforms for monitoring physiological processes and disease progression in live cells and tissues. Moreover, it has highlighted the applications of POCT and bio-imaging in testing toxins, heavy metals, illicit drugs, cancers, traumatic brain injuries, and infectious diseases such as COVID-19, influenza, HIV and sepsis.

Emergence of Surface-Enhanced Raman Scattering Probes in Near-Infrared Windows for Biosensing and Bioimaging.

Emergence of Surface-Enhanced Raman Scattering Probes in Near-Infrared Windows for Biosensing and Bioimaging.

SERS-based boronate affinity biosensor with biomimetic specificity and versatility: Surface-imprinted magnetic polymers as recognition elements to detect glycoproteins

Glycoproteins are a class of proteins with significant biological functions and clinical implications. Due to glycoproteins’ reliability for the quantitative analysis, they have been used as biomarkers and therapeutic targets for disease diagnosis. We propose a sandwich structure-based boronate affinity biosensor that can separate and detect target glycoproteins by magnetic separation and Surface-enhanced Raman scattering (SERS) probes. The biosensor relies on boronic acid affinity magnetic molecularly imprinted polymer (MMIPs) with pH response as "capturing probe" for glycoproteins, and Au-MPBA@Ag modified with 4-mercaptophenylboronic acid (MPBA) as SERS probes, among which, MPBA has both strong SERS activity and can specifically recognize and bind to glycoproteins. MMIPs ensured specific and rapid analysis, and SERS detection provided high sensitivity. The proposed boronate affinity SERS strategy exhibited universal applicability and provided high sensitivity with limit of detection of 0.053 ng/mL and 0.078 ng/mL for horseradish peroxidase and acid phosphatase, respectively. Ultimately, the boronate affinity SERS strategy was successfully applied in detection of glycoprotein in spiked serum sample with recovery between 90.6% and 103.4%, respectively. In addition, this study used a portable Raman meter, which can meet the requirements of point-of-care testing. The biosensor presented here also has advantages in terms of cost-effectiveness, stability, and detection speed.

Porous Au-Ag Nanoparticles from Galvanic Replacement Applied as Single-Particle SERS Probe for Quantitative Monitoring.

Plasmonic nanostructures have raised the interest of biomedical applications of surface-enhanced Raman scattering (SERS). To improve the enhancement and produce sensitive SERS probes, porous Au-Ag alloy nanoparticles (NPs) are synthesized by dealloying Au-Ag alloy NP-precursors with Au or Ag core in aqueous colloidal environment through galvanic replacement reaction. The novel designed core-shell Au-Ag alloy NP-precursors facilitate controllable synthesis of porous nanostructure, and dealloying degree during the reaction has significant effect on structural and spectral properties of dealloyed porous NPs. Narrow-dispersed dealloyed NPs are obtained using NPs of Au/Ag ratio from 10/90 to 40/60 with Au and Ag core to produce solid core@porous shell and porous nanoshells, having rough surface, hollowness, and porosity around 30-60%. The clean nanostructure from colloidal synthesis exhibits a redshifted plasmon peak up to near-infrared region, and the large accessible surface induces highly localized surface plasmon resonance and generates robust SERS activity. Thus, the porous NPs produce intensely enhanced Raman signal up to 68-fold higher than 100nm AuNP enhancement at single-particle level, and the estimated Raman enhancement around 7800, showing the potential for highly sensitive SERS probes. The single-particle SERS probes are effectively demonstrated in quantitative monitoring of anticancer drug Doxorubicin release.

Development of porous silicon‐coated gold nanoparticles as potential theragnostic material

AbstractGold nanoparticles (AuNPs) have been used widely as multifunctional materials for several biomedical applications due to their attractive characteristics. However, toxicity and aggregation of AuNPs are critical issues, and methods of effective surface modification are required to overcome these problems. In this study, porous silicon‐coated gold nanoparticles (AuNP@pSi) were fabricated as a hybrid nanocomposite capable of surface‐enhanced Raman scattering (SERS)‐sensing and drug carrier. First, size‐controlled AuNPs were coated with a silica nano‐shell, and the resulting silica layers were converted to porous silicon through magnesiothermic reduction. Overall results suggest that AuNP@pSi can be exploited as a SERS probe with efficient Raman signal improvement of benzenethiol as well as a drug carrier based on its high surface area (113.7 m2 g−1) and porosity (13.38 nm, 0.3805 cm3 g−1). Since the porous silicon possibly can serve as magnetic resonance imaging probes with DNP technology, this hybrid platform potentially can be utilized as powerful material capable of theragnosis system.