Surface-enhanced Raman Scattering Strategy Research Articles

Smart Nanoplatform for Visualizing Hydrogen Sulfide and Amplifying Oxidative Stress to Tumor Apoptosis.

Oxidative stress is involved in various signaling pathways and serves a key role in inducing cell apoptosis. Therefore, it is significant to monitor oxidative stress upon drug release for the assessment of therapeutic effects in cancer cells. Herein, a glutathione (GSH)-responsive surface-enhanced Raman scattering (SERS) nanoplatform is proposed for ultra-sensitively monitoring the substance related with oxidative stress (hydrogen sulfide, H2S), depleting reactive sulfur species and releasing anticancer drugs to amplify oxidative stress for tumor apoptosis. The Au@Raman reporter@Ag (Au@M@Ag) nanoparticles, where a 4-mercaptobenzonitrile molecule as a Raman reporter was embedded between layers of gold and silver to obtain sensitive SERS response, were coated with a covalent organic framework (COF) shell to form a core-shell structure (Au@M@Ag@COFs) as the SERS nanoplatform. The COF shell loading doxorubicin (DOX) of Au@M@Ag@COFs exhibited the GSH-responsive degradation capacity to release DOX, and its Ag layer as the sensing agent was oxidized to Ag2S by H2S to result in its prominent changes in SERS signals with a low detection limit of 0.33 nM. Moreover, the releasing DOX can inhibit the generation of H2S to promote the production of reactive oxygen species, and the depletion of reactive sulfur species (GSH and H2S) in cancer cells can further enhance the oxidative stress to induce tumor apoptosis. Overall, the SERS strategy could provide a powerful tool to monitor the dynamic changes of oxidative stress during therapeutic processes in a tumor microenvironment.

Direct Virus Gene Detection: A CRISPR/dCas9-Mediated Surface-Enhanced Raman Scattering Strategy with Enzyme-Catalyzed Signal Amplification.

The aberrant growth of cervical cells caused by the infection of human papillomavirus (HPV) may cause cervical cancer. In order to effectively prevent the occurrence of cervical cancer and for better follow-up treatment after surgery, a rapid and reliable detection method of HPV DNA is essential. Here, a surface-enhanced Raman scattering (SERS) detection method was developed based on the clustered regularly interspaced short palindromic repeats (CRISPR)/dCas9 technique and the enzyme catalysis amplification reaction, which achieved a simple and rapid detection of low-content HPV genes. The CRISPR/dCas9/sgRNA complex was anchored above a magnetic bead, which can precisely capture target DNA sequences, exhibiting high selectivity for HPV genes. When the biotinylated target DNAs exist, they can bridge a streptavidin-modified horse radish peroxidase (HRP) to the magnetic bead, producing an HRP-decorated conjugate. This conjugate allows an HRP-catalyzed reaction for its substrate (3,3',5,5'-tetramethylbenzidine, TMB). Gold nanostars with a silica shell exhibiting the lightning rod effect of SERS were employed to measure the SERS spectra of the oxidative product of TMB. Enzyme catalysis and SERS co-contribute to the SERS signal output, ensuring a high detection sensitivity. This method is a proof of concept for detecting HPV DNAs in a complex system. The current method can be applied to other target DNAs simply by changing the sgRNA sequence. Many superiors portend that the CRISPR/dCas9-based SERS method is promising for further clinical application.

Nondestructive separation/enrichment and rolling circle amplification-powered sensitive SERS enumeration of circulating tumor cells via aptamer recognition

Nondestructive separation/enrichment and reliable detection of extremely rare circulating tumor cells (CTCs) in peripheral blood are of considerable importance in tumor precision diagnosis and treatment, yet this remains a big challenge. Herein, a novel strategy for nondestructive separation/enrichment and ultra-sensitive surface-enhanced Raman scattering (SERS)-based enumeration of CTCs is proposed via aptamer recognition and rolling circle amplification (RCA). In this work the magnetic beads modified with "Aptamer (Apt)-Primer" (AP) probes were utilized to specifically capture CTCs, and then after magnetic separation/enrichment, the RCA-powered SERS counting and benzonase nuclease cleavage-assisted nondestructive release of CTCs were realized, respectively. The AP was assembled by hybridizing the EpCAM-specific aptamer with a primer, and the optimal AP contains 4 mismatched bases. The RCA enhanced SERS signal nearly 4.5-fold, and the SERS strategy has good specificity, uniformity and reproducibility. The proposed SERS detection possesses a good linear relationship with the concentration of MCF-7 cells spiked in PBS with the limit of detection (LOD) of 2 cells/mL, which shows good potential practicality for detecting CTCs in blood with recoveries ranging from 100.56% to 116.78%. Besides, the released CTCs remained good cellular activity with the normal proliferation after re-culture for 48 h and normal growth for at least three generations. The proposed strategy of nondestructive separation/enrichment and SERS-based sensitive enumeration is promising for reliable analysis of EpCAM-positive CTCs in blood, which is expected to provide a powerful tool for analysis of extremely rare circulating tumor cells in complex peripheral blood for liquid biopsy.

Phosphoric Acid Induced Controllable Nanoparticle Aggregation for Ultrasensitive SERS Detection of Malondialdehyde in a Microfluidic Chip

Malondialdehyde (MDA), one of the most important products of lipid peroxidation, has been widely accepted as a biomarker to indicate food rancidity as well as the progress of some human diseases. However, ready detection of MDA with ultra-high sensitivity remains a challenge. In this work, a microfluidic surface-enhanced Raman scattering (SERS) sensing chip based on phosphoric acid induced nanoparticles aggregation was proposed for ultrasensitive MDA detection. The sensing chip was composed of an ultrafast microfluidic mixer, which efficiently transferred analytes to hot spots via the mixer assisted hot spots occupying (MAHSO) SERS strategy. Phosphoric acid, a reagent used in MDA detection, played the role of aggregator to induce aggregation of silver nanoparticles (Ag NPs); meanwhile, as fast as a few milliseconds mixing time effectively prevented over-aggregation of Ag NPs. Therefore, this process generated a uniform and dense SERS substrate with analyte molecules located in hot spots. As a result, the MDA SERS sensing chip possessed a limit of detection (LOD) lower than 3.3 × 10−11 M, high spot-to-spot uniformity with a relative standard deviation (RSD) of 9.0% and an excellent batch-to-batch reproducibility with a RSD of 3.9%. This method also demonstrated excellent specificity and reliability in real sample detection with recoveries of 90.4–109.8% in spiked tests.

SERS monitoring of photoinduced-enhanced oxidative stress amplifier on Au@carbon dots for tumor catalytic therapy

Currently, artificial enzymes-based photodynamic therapy (PDT) is attractive due to its efficient capacity to change the immunosuppressive tumor microenvironment (TME). It is of great significance to study the therapeutic mechanism of novel artificial enzymes in TME through a monitoring strategy and improve the therapeutic effect. In this study, Au@carbon dots (Au@CDs) nanohybrids with a core-shell structure are synthesized, which not only exhibit tunable enzyme-mimicking activity under near-infrared (NIR) light, but also excellent surface-enhanced Raman scattering (SERS) properties. Therefore, Au@CDs show a good capability for monitoring NIR-photoinduced peroxidase-like catalytic processes via a SERS strategy in tumor. Moreover, the Au@CDs deplete glutathione with the cascade catalyzed reactions, thus elevating intratumor oxidative stress amplifying the reactive oxygen species damage based on the NIR-photoinduced enhanced peroxidase and glutathione oxidase-like activities, showing excellent and fast PDT therapeutic effect promoted by photothermal property in 3 min, finally leading to apoptosis in cancer cells. Through SERS monitoring, it is further found that after removing the NIR light source for 33 min, the reactive oxygen species (ROS) activity of the TME is counteracted and eliminated due to the presence of glutathione. This work presents a guidance to rationally design of artificial enzyme for ROS-involved therapeutic strategies and a new spectroscopic tool to evaluate the tumor catalytic therapy.

Rapid determination of thiram and atrazine pesticide residues in fruit and aqueous system based on surface-enhanced Raman scattering

In this work, a rapid and sensitive strategy was developed to determine thiram (THI) and atrazine (ATZ) by surface-enhanced Raman scattering (SERS) technology. β-cyclodextrin modified silver nanoparticles (β-CD-AgNPs) were synthesized using β-CD as a reducing agent and encapsulating agent under alkaline conditions and employed as SERS substrate. The existence of β-CD can capture the molecules to form host–guest complex and fix molecular orientation in its cavity, thus ensuring the enhanced SERS signal intensity of THI and ATZ. The linear response extends from 2.56 × 10-8 to 2.56 × 10-3 mol/L for THI and 3.08 × 10-8 to 3.08 × 10-3 mol/L for ATZ, with the limits of detection (LOD) of 2.42 × 10-9 mol/L for THI and 7.26 × 10-9 mol/L for ATZ, respectively. The application of the proposed method in real samples including apple and water were investigated, and the results would help promote the application of SERS technology as a powerful analytical tool for detecting other pesticide residues. It is expected that this SERS strategy will provide great value for rapid detecting pesticide residues in food products and environmental systems.

Hairpin-Structured Magnetic SERS Sensor for Tetracycline Resistance Gene tetA Detection.

Antibiotic resistance genes (ARGs) have become emerging environmental contaminants, and the effective on-site detection of ARGs is urgently needed. Herein, we constructed a hairpin-structured magnetic sensor for the analysis of a widespread ARG, tetA, using surface-enhanced Raman scattering (SERS). The SERS sensor was assembled by immobilizing core-satellite structured Fe3O4@SiO2-Au with single-stranded DNA in a folded hairpin structure. The SERS sensor exhibited good sensitivity and specificity for the detection of laboratory-synthesized tetA ssDNA fragments. In addition, this SERS strategy is the first of its kind to be employed for monitoring environmental samples in the field, with a limit of detection reaching as low as 25 copies μL-1. Univariate and multivariate linear regression equations verify the practicability of the SERS sensor for quantitative tetA determination, showing the prospect for an amplification-free alternative platform for sensitive and reliable on-site detection of ARGs in the environment.

Target-triggered configuration change of DNA tetrahedron for SERS assay of microRNA 122.

A surface-enhanced Raman scattering (SERS) method is proposed for the assay of microRNA 122 based on configuration change of DNA tetrahedron. Firstly, a DNA tetrahedron was self-assembled with one vertex labeled with toluidine blue (TB). Then, it was immobilized on the porous Ni/SiO2@PEI@Au as a SERS platform, which was characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). At this time, the DNA tetrahedron was contracted; so, the TB is close to AuNPs and the Raman signal is high. When target microRNA 122 existed, with the nicking enzyme amplification strategy, a great deal of DNA signal chains (S5) was obtained, which can extend the contracted DNA tetrahedron and change it into a three-dimensional DNA tetrahedron. In this case, the TB was far from AuNPs, resulting in a lower Raman signal. Due to the configuration change of DNA tetrahedron, the Raman signal at 1624cm-1 (with the excitation wavelength of 633nm) has a linear relationship with the logarithm concentration of microRNA 122. This SERS assay has high sensitivity for microRNA 122 with a determination range from 0.01aM to 10fM and a detection limit of 0.009aM. The recoveries from spiked samples were in the range 95 to 109%. This SERS strategy is designed based on the target-triggered configuration change of DNA tetrahedron, which can give new insight for DNA structures in bioanalysis. Graphical abstract A sensitive surface-enhanced Raman scattering (SERS) biosensor was developed to detect microRNA 122 using the configuration change of DNA tetrahedron to indirectly control the position of TB and hot spot.

Simultaneous Detection of Intracellular Nitric Oxide and Peroxynitrite by a Surface-Enhanced Raman Scattering Nanosensor with Dual Reactivity

A functional surface-enhanced Raman scattering (SERS) nanosensor which can simultaneously detect nitric oxide (NO) and peroxynitrite (ONOO-) in living cells is explored. The SERS nanosensor is fabricated through modifying gold nanoparticles (AuNPs) with newly synthesized 3,4-diaminophenylboronic acid pinacol ester (DAPBAP), which has two reactive groups. The simultaneous detection achieved in this work is not only because of the SERS spectral changes of the nanosensor resulting from the dual reactivity of DAPBAP on AuNPs with NO and ONOO- but also by the narrow SERS bands suitable for multiplex detection. Owing to the combination of SERS fingerprinting information and chemical reaction specificity, the nanosensor has great selectivity for NO and ONOO-, respectively. In addition, the nanosensor has a wide linearity range from 0 to 1.0 × 10-4 M with a submicromolar sensitivity. More importantly, simultaneous monitoring of NO and ONOO- in the Raw264.7 cells has been fulfilled by this functional nanosensor, which shows that the SERS strategy will be promising in comprehension of the physiological issues related with NO and ONOO-.

Dual-recognition surface-enhanced Raman scattering(SERS)biosensor for pathogenic bacteria detection by using vancomycin-SERS tags and aptamer-Fe3O4@Au

Rapid and reliable detection of pathogenic bacteria is vital to prevent and control bacterial diseases. In this study, we present a magnetically assisted surface-enhanced Raman scattering (SERS) biosensor based on the dual-recognition of bacterial cell by aptamer and antibiotic molecules. Aptamer-Fe3O4@Au magnetic nanoparticles (AuMNPs) were synthesized as magnetic and SERS activated substrate for specific bacteria enrichment, vancomycin-SERS tags (Au@MBA) were prepared for the sensitive quantification of pathogenic bacteria. Due to the Au-shell based dual-SERS enhancement and aptamer/vancomycin based dual-recognition ability, a detection limit of 3 cells/mL with a wide dynamic linear range from 10 to 107 cells/mL can be achieved within 50 min without other non-target bacteria interference. When applied in real samples, the approach shows recoveries from 95.0% to 106.4% with relative standard derivation (RSD) less than 5.3%. The SERS strategy could be used to detect a broad range of bacteria by using different aptamers, moreover, the simple operation and precise quantification ability empower this assay great potential in the application of food safety and infectious disease point-of-care diagnosis.

Surface-enhanced Raman spectroscopy of cell lysates mixed with silver nanoparticles for tumor classification.

The throughput of spontaneous Raman spectroscopy for cell identification applications is limited to the range of one cell per second because of the relatively low sensitivity. Surface-enhanced Raman scattering (SERS) is a widespread way to amplify the intensity of Raman signals by several orders of magnitude and, consequently, to improve the sensitivity and throughput. SERS protocols using immuno-functionalized nanoparticles turned out to be challenging for cell identification because they require complex preparation procedures. Here, a new SERS strategy is presented for cell classification using non-functionalized silver nanoparticles and potassium chloride to induce aggregation. To demonstrate the principle, cell lysates were prepared by ultrasonication that disrupts the cell membrane and enables interaction of released cellular biomolecules to nanoparticles. This approach was applied to distinguish four cell lines – Capan-1, HepG2, Sk-Hep1 and MCF-7 – using SERS at 785 nm excitation. Six independent batches were prepared per cell line to check the reproducibility. Principal component analysis was applied for data reduction and assessment of spectral variations that were assigned to proteins, nucleotides and carbohydrates. Four principal components were selected as input for classification models based on support vector machines. Leave-three-batches-out cross validation recognized four cell lines with sensitivities, specificities and accuracies above 96%. We conclude that this reproducible and specific SERS approach offers prospects for cell identification using easily preparable silver nanoparticles.

Tracing sialoglycans on cell membrane via surface-enhanced Raman scattering spectroscopy with a phenylboronic acid-based nanosensor in molecular recognition

Sialoglycan expression is critical for assessing various diseases progression. Especially, its abnormal levels are commonly believed to be associated with tumor and metastatic cancer types. While, complicated structures, multiple types and dynamic distributions make it challenging for in situ investigating sialoglycans at the physiological status. Herein, we developed a 4-mercaptophenylboronic acid (MPBA)-based surface-enhanced Raman scattering (SERS) nanosensor to in situ study sialoglycan levels and dynamic expression processes of different cell types based on molecular recognition between phenylboronic acid and sialoglycans at physiological condition. This nanosensor is designed by the MPBA decorated silver nanoparticle (AgNP), which is unique and multifunctional because of its three-in-one role involving the Raman signal enhancer (AgNP), the sensing reporter of MPBA and the target receptor based on the recognition of phenylboronic acid and sialoglycans. When this nanosensor binds to sialoglycans, the molecular vibrational modes of MPBA will change, which can be traced by ultrasensitive SERS technique. The superiority of this study is that we built the relation between the spectral changes of MPBA (relative intensities) in molecular recognition with the sialoglycan dynamic expression of cells. We believe that our SERS strategy could be further extended to explore crucial physiological processes and significant biological system that glycans are involved in.

SERS nanoprobes for the monitoring of endogenous nitric oxide in living cells

Nitric Oxide (NO) is a significant gaseous signalling molecule in various pathological and physiological pathways, whereas many of its functions are still ambiguous in part because of the shortage of powerful detection approaches. Herein, we present a type of reaction-based surface-enhanced Raman scattering (SERS) nanoprobes, o-phenylenediamine-modified gold nanoparticles (AuNPs/OPD), to detect the level of the endogenous NO in living cells. The detection is achieved through the SERS variation of AuNPs/OPD caused by the reaction between NO and OPD on the surface of AuNPs. The proposed SERS nanoprobes have a good stability and a rapid response to NO within 30s Moreover, as a result of the reaction specificity coupled with SERS fingerprinting, AuNPs/OPD nanoprobes demonstrate high selectivity towards NO over other biologically relevant species with a sensitivity at 10−7M level. Thereby, this SERS strategy can be used for monitoring NO that is endogenously produced in living macrophages, indicating immense potential in studying NO-involved pathophysiological processes in biological systems.