A SERS and fluorescence dual mode cancer cell targeting probe based on silica coated Au@Ag core–shell nanorods

Exosome detection via surface-enhanced Raman spectroscopy for cancer diagnosis

As nanoscale extracellular vesicles, exosomes are secreted by various cell types, and they are widely distributed in multiple biological fluids. Studies have shown that tumor-derived exosomes can carry a variety of primary tumor-specific molecules, which may represent a novel tool for the early detection of cancer. However, the clinical translation of exosomes remains a challenge due to the requirement of large quantities of samples when enriching the cancer-related exosomes in biological fluids, the insufficiency of traditional techniques for exosome subpopulations, and the complex exosome isolation of the current commercially available exosome phenotype profiling approaches. The evolving surface-enhanced Raman scattering (SERS) technology, with properties of unique optoelectronics, easy functionalization, and the particular interaction between light and nanoscale metallic materials, can achieve sensitive detection of exosomes without large quantities of samples and multiplexed phenotype profiling, providing a new mode of real-time and noninvasive analysis for cancer patients. In the present review, we mainly discussed exosome detection based on SERS, especially SERS immunoassay. The basic structure and function of exosomes were firstly introduced. Then, recent studies using the SERS technique for cancer detection were critically reviewed, which mainly included various SERS substrates, biological modification of SERS substrates, SERS-based exosome detection, and the combination of SERS and other technologies for cancer diagnosis. This review systematically discussed the essential aspects, limitations, and considerations of applying SERS technology in the detection and analysis of cancer-derived exosomes, which could provide a valuable reference for the early diagnosis of cancer through SERS technology. STATEMENT OF SIGNIFICANCE: Surface-enhanced Raman scattering (SERS) has been applied to exosomes detection to obtain better diagnostic results. In past three years, several reviews have been published in exosome detection, which were narrowly focus on methods of exosome detection. Selection and surface functionalization of the substrate and the combination detection with different methods based on SERS will provide new strategies for the detection of exosomes. This review will focus on the above aspects. This emerging detection method is constantly evolving and contributing to the early discovery of diseases in the future.

SERS nanotags for folate receptor α detection at the single cell level: discrimination of overexpressing cells and potential for live cell applications

Development of nanotags based on Surface-Enhanced Raman Scattering (SERS) for the discrimination of cancer cells overexpressing folate receptor α. Nanotags are also applicable for live cell measurements.

Gold/Silver Hybrid Nanoparticles with Enduring Inhibition of Coronavirus Multiplication through Multisite Mechanisms

As a large enveloped RNA virus, coronavirus is of considerable medical and veterinary significance, and anticoronavirus treatment is challenging due to its biodiversity and rapid variability. In this study, Au@Ag nanorods (Au@AgNRs) were successfully synthesized by coating AuNRs with silver and were shown for the first time to have activity against the replication of porcine epidemic diarrhea virus (PEDV). Viral titer analysis demonstrated that Au@AgNRs could inhibit PEDV infection by 4 orders of magnitude at 12 h post-infection, which was verified by viral protein expression analysis. The potential mechanism of action showed that Au@AgNRs could inhibit the entry of PEDV and decrease the mitochondrial membrane potential and caspase-3 activity. Additionally, we demonstrated that a large amount of virus proliferation can cause the generation of reactive oxygen species in cells, and the released Ag⁺ and exposed AuNRs by Au@AgNRs after the stimulation of reactive oxygen species has superior antiviral activity to ensure long-term inhibition of the PEDV replication cycle. The integrated results support that Au@AgNRs can serve as a potential therapeutic strategy to prevent the replication of coronavirus.

Renaissance of Stöber method for synthesis of colloidal particles: New developments and opportunities

Colloidal silica particles have received a widespread interest because of their potential applications in adsorption, ceramics, catalysis, drug delivery and more. Among many approaches towards fabrication of these colloidal particles, Stöber, Fink and Bohn (SFB) method, known as Stöber synthesis is an effective sol-gel strategy for production of uniform, monodispersed silica particles with highly tailorable size and surface properties. This review, after a brief introduction showing the importance of colloidal chemistry, is focused on the Stöber synthesis of silica spheres including discussion of the key factors affecting their particle size, porosity and surface properties. Next, further developments of this method are presented toward fabrication of polymer, carbon, and composite spheres.

Molecular-Imprinting-Based Surface-Enhanced Raman Scattering Sensors

Molecularly imprinted polymers (MIPs) receive extensive interest, owing to their structure predictability, recognition specificity, and application universality as well as robustness, simplicity, and inexpensiveness. Surface-enhanced Raman scattering (SERS) is regarded as an ideal optical detection candidate for its unique features of fingerprint recognition, nondestructive property, high sensitivity, and rapidity. Accordingly, MIP based SERS (MIP-SERS) sensors have attracted significant research interest for versatile applications especially in the field of chemo- and bioanalysis, showing excellent identification and detection performances. Herein, we comprehensively review the recent advances in MIP-SERS sensors construction and applications, including sensing principles and signal enhancement mechanisms, focusing on novel construction strategies and representative applications. First, the basic structure of the MIP-SERS sensors is briefly outlined. Second, novel imprinting strategies are highlighted, mainly including multifunctional monomer imprinting, dummy template imprinting, living/controlled radical polymerization, and stimuli-responsive imprinting. Third, typical application of MIP-SERS sensors in chemo/bioanalysis is summarized from both small and macromolecular aspects. Lastly, the challenges and perspectives of the MIP-SERS sensors are proposed, orienting sensitivity improvement and application expanding.

Lead Halide Perovskite Nanocrystals-Phospholipid Micelles and Their Biological Applications: Multiplex Cellular Imaging and in Vitro Tumor Targeting

Lead halide perovskite nanocrystals (NCs) are promising optical materials in many fields. However, their poor moisture stability, significant toxicity, and difficulty to be further functionalized greatly hinder their applications in bioimaging. Here, a universal strategy is demonstrated by simply encapsulating CsPbX₃ (X = Cl, Br, I) NCs into phospholipids to achieve CsPbX₃-phospholipid micelles (CsPbX₃@phospholipid) as probes for multiplex encoding cellular imaging or tumor-targeted imaging. The layer of phospholipids endows CsPbX₃ NCs with superior water-resistant characteristics, the ability to be further biofunctionalized, and greatly improved biocompatibility. The CsPbX₃@phospholipid micelles exhibited strong luminescence with narrow fwhm in water for more than four months. Specifically, even after being modified with folic acid, the bright fluorescence of the micelles was well retained, which were employed for the targeting of Hela cells. Finally, the greatly reduced toxicity of the CsPbX₃@phospholipid micelles was verified using HeLa cells and zebrafish as in vitro and in vivo models, respectively.

Surface modification of plasmonic noble metal-metal oxide core-shell nanoparticles

A comprehensive survey on the methods for the surface modification of plasmonic noble metal-metal oxide core-shell nanoparticles is presented. The review highlights various strategies for covalent attachment and electrostatic binding of molecules and molecular ions to core-shell nanoparticles with a focus on plasmonically active silver and gold nanoparticles encapsulated by SiO₂ and TiO₂ shells.

Applications of near infrared and surface enhanced Raman scattering techniques in tumor imaging: A short review

Imaging technologies play a vital role in clinical oncology and have undergone massive growth over the past few decades. Research in the field of tumor imaging and biomedical diagnostics requires early detection of physiological alterations so as to provide curative treatment in real time. The objective of this review is to provide an insight about near infrared fluorescence (NIRF) and surface enhanced Raman scattering (SERS) imaging techniques that can be used to expand their capabilities for the early detection and diagnosis of cancer cells. Basic setup, principle and working of the instruments has been provided and common NIRF imaging agents as well as SERS tags are also discussed besides the analytical advantages/disadvantages of these techniques. This review can help researchers working in the field of molecular imaging to design cost effective fluorophores and SERS tags to overcome the limitations of both NIRF as well as SERS imaging technologies.

One-Pot Synthesis of Epirubicin-Capped Silver Nanoparticles and Their Anticancer Activity against Hep G2 Cells

Epirubicin-capped silver nanoparticles (NPs) were synthesized through a one-pot method by using epirubicin as both the functional drug and the reducing agent of Ag⁺ to Ag⁰. The preparation process was accomplished in 1 h. In addition, the obtained epirubicin-capped silver nanoparticle was characterized by transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), and infrared spectroscopy. The results showed that a layer of polymer epirubicin had formed around the silver nanoparticle, which was 30-40 nm in diameter. We further investigated the antitumor activity of the prepared epirubicin-capped silver nanoparticle, and the half maximal inhibitory concentration (IC₅₀) against Hep G2 cells was 1.92 μg/mL, indicating a good antitumor property of the nanoparticle at low dosage.

The synthesis of Ag-coated tetrapod gold nanostars and the improvement of surface-enhanced Raman scattering

In this work, the novel tetrapod gold nanostars with four specific numbers of sharp tips were synthesized with good uniformity, high yield and chemical stability. The size of tetrapod gold nanostars has been increased effectively by increasing the amount of HAuCl₄ or DEA added to the reaction solution, and the corresponding in-plane localized surface plasmon resonance (LSPR) band can shift from 700 to 1100 nm. In order to combine the advantages of different metals, the Ag-coated tetrapod gold nanostars were prepared with different Ag coating thicknesses by increasing the volume of AgNO₃. With the increase of Ag coating thickness, the morphology of the nanoparticles has changed from gold nanostars with four sharp tips to bimetallic cuboids with four sharp tips and finally to crore-shell cuboids completely. The surface-enhanced Raman scattering (SERS) activity of Ag-coated tetrapod gold nanostars has also been improved with the different Ag coating thicknesses. Combined the tip effect and the enhancement effect of Ag, the SERS activity has the strongest enhancement when the four sharp tips of tetrapod gold nanostars are not completely coated by the Ag layer but still exposed to the outsides. For tetrapod gold nanostars with larger size to grow Ag-coated tetrapod gold nanostars, the bimetallic cuboids with four sharp tips nanostructure have the biggest SERS enhancement factor (EF) of 1.73 × 10⁶ for Rhodamine 6G (R6G), making it an ideal candidate in SERS-based sensing application.

APTES Duality and Nanopore Seed Regulation in Homogeneous and Nanoscale-Controlled Reduction of Ag Shell on SiO2 Microparticle for Quantifiable Single Particle SERS

Noble-metal nanoparticles size and packing density are critical for sensitive surface-enhanced Raman scattering (SERS) and controlled preparation of such films required to achieve reproducibility. Provided that they are made reliable, Ag shell on SiO₂ microscopic particles (Ag/SiO₂) are promising candidates for lab-on-a-bead analytical measurements of low analyte concentration in liquid specimen. Here, we selected nanoporous silica microparticles as a substrate for reduction of AgNO₃ with 3-aminopropyltriethoxysilane (APTES). In a single preparation step, homogeneous and continuous films of Ag nanoparticles are formed on SiO₂ surfaces with equimolar concentration of APTES and silver nitrate in ethanol. It is discussed that amine and silane moieties in APTES contribute first to an efficient reduction on the silica and second to capping the Ag nanoparticles. The high density and homogeneity of nanoparticle nucleation is further regulated by the nanoporosity of the silica. The Ag/SiO₂ microparticles were tested for SERS using self-assembled 4-aminothiophenol monolayers, and an enhancement factor of ca. 2 × 10⁶ is measured. Importantly, the SERS relative standard deviation is 36% when a single microparticle is considered and drops to 11% when sets of 10 microparticles are considered. As prepared, the microparticles are highly suitable for state-of-the-art quantitative lab-on-a-bead interrogation of specimens.

In Vivo Synthesis of Nanocomposites Using the Recombinant Escherichia coli

Biogenic gold nanorod (AuNR)-Ag core-shell nanocomposites (NCs) are synthesized by using recombinant Escherichia coli to demonstrate in vivo synthesis of biogenic NCs for the first time. The chemically synthesized AuNRs are internalized into the E. coli, and Ag ions are reduced and grown on the surface of the AuNRs with the assistance of metal-binding proteins, producing biogenic core-shell AuNR-Ag NCs. The core-shell structure of the biogenic AuNR-Ag NC is confirmed by transmission electron microscopy and energy-dispersive X-ray analysis. The biogenic AuNR-Ag NCs exhibit good plasmonic effects. While the core-shell morphology of the AuNR and Ag NCs is due to the similar lattice of Au and Ag, the shape of the biogenic NCs composed of gold nanoparticles and Fe is aciniform, and that of Fe₃ O₄ NPs and Au/Ag is a network structure, demonstrating the controllability of biogenic nanosynthesis using diverse metal combinations with different NC morphologies.

Etching-dependent fluorescence quenching of Ag-dielectric-Au three-layered nanoshells: The effect of inner Ag nanosphere

In this report, Ag-dielectric-Au three-layered nanoshells with controlled inner core size were synthesized. The fluorescence emission of the rhodamine 6G (R6G) could be quenched by the three-layered nanoshells distinctly. What's more, the fluorescence quenching efficiency could be further improved by tuning the etching of inner Ag nanosphere. The maximum fluorescence quenching efficiency is obtained when the separate layer just appears between the inner Ag core and the outer Au shell. Whereas the fluorescence quenching efficiency is weakened when no gaps take place around the inner Ag core or the separate layer is too thick and greater than 13nm. The fluorescence quenching properties of the Ag-dielectric-Au three-layered nanoshells with different initial sizes of the Ag nanoparticles are also studied. The maximum fluorescence quenching efficiency is obtained when the three-layered nanoshells are synthesized based on the Ag nanoparticles with 60nm, which is better than others two sizes (42 and 79nm). Thus we believe that the size of initial Ag nanospheres also greatly affects the optimized fluorescence quenching efficiency. These results about fluorescence quenching properties of Ag-dielectric-Au three-layered nanoshells present a potential for design and fabrication of fluorescence nanosensors based on tuning the geometry of the inner core and the separate layer.

Determination of brain injury biomarkers by surface-enhanced Raman scattering using hollow gold nanospheres

The development of rapid, highly sensitive detection methods for neuron-specific enolase (NSE) and S100-β protein is very important as the levels of NSE and S100-β protein in the blood are closely related to brain injury.

Click-Functionalized SERS Nanoprobes with Improved Labeling Efficiency and Capability for Cancer Cell Imaging

Precise identification and detection of cancer cells using nanoparticle probes are critically important for early cancer diagnosis and subsequent therapy. We herein develop novel folate receptor (FR)-targeted surface-enhanced Raman scattering (SERS) nanoprobes for cancer cell imaging based on a click coupling strategy. A Raman-active derivative (5,5'-dithiobis(2-nitrobenzoic acid)-N₃ (DNBA-N₃)) is designed with a disulfide bond for covalently anchoring to the surface of hollow gold nanoparticles (HAuNPs) and a terminal azide group for facilitating highly efficient conjugation with the bioligand. Modification of HAuNPs with DNBA-N₃ yields monolayer coverage of Raman labels absorbed on the nanoparticle surface (HAuNP-DNBA-N₃) and strong SERS signals. HAuNP-DNBA-N₃ can be simply and effectively conjugated with folate bicyclo[6.1.0]nonyne derivatives via a copper-free click reaction. The synthesized nanoprobes (HAuNP-DNBA-folic acid (FA)) exhibit excellent targeted capacities to FR-positive cancer cells relative to FR-negative cells through SERS mappings. The receptor-mediated delivery behaviors are confirmed by comparison with the uptake of HAuNP-DNBA-N₃ and free FA competition experiments. In addition to its good stability and benign biocompatibility, the developed SERS nanoprobes have great potential for applications in targeted tumor imaging.

Emergence of Gold-Mesoporous Silica Hybrid Nanotheranostics: Dox-Encoded, Folate Targeted Chemotherapy with Modulation of SERS Fingerprinting for Apoptosis Toward Tumor Eradication

Strategically fabricated theranostic nanocarrier delivery system is an unmet need in personalized medicine. Herein, this study reports a versatile folate receptor (FR) targeted nanoenvelope delivery system (TNEDS) fabricated with gold core silica shell followed by chitosan-folic acid conjugate surface functionalization by for precise loading of doxorubicin (Dox), resembled as Au@SiO₂ -Dox-CS-FA. TNEDS possesses up to 90% Dox loading efficiency and internalized through endocytosis pathway leading to pH and redox-sensitive release kinetics. The superior FR-targeted cytotoxicity is evaluated by the nanocarrier in comparison with US Food and Drug Administration (FDA)-approved liposomal Dox conjugate, Lipodox. Moreover, TNEDS exhibits theranostic features through caspase-mediated apoptosis and envisages high surface plasmon resonance enabling the nanoconstruct as a promising surface enhanced Raman scattering (SERS) nanotag. Minuscule changes in the biochemical components inside cells exerted by the TNEDS along with the Dox release are evaluated explicitly in a time-dependent fashion using bimodal SERS/fluorescence nanoprobe. Finally, TNEDS displays superior antitumor response in FR-positive ascites as well as solid tumor syngraft mouse models. Therefore, this futuristic TNEDS is expected to be a potential alternative as a clinically relevant theranostic nanomedicine to effectively combat neoplasia.

A magneto-fluidic nanoparticle trapping platform for surface-enhanced Raman spectroscopy

A microfluidic device utilizing magnetically activated nickel (Ni) micropads has been developed for controlled localization of plasmonic core-shell magnetic nanoparticles, specifically for surface enhanced Raman spectroscopy (SERS) applications. Magnetic microfluidics allows for automated washing steps, provides a means for easy reagent packaging, allows for chip reusability, and can even be used to facilitate on-chip mixing and filtration towards full automation of biological sample processing and analysis. Milliliter volumes of gold-coated 175-nm silica encapsulated iron oxide nanoparticles were pumped into a microchannel and allowed to magnetically concentrate down into 7.5 nl volumes over nano-thick lithographically defined Ni micropads. This controlled aggregation of core-shell magnetic nanoparticles by an externally applied magnetic field not only enhances the SERS detection limit within the newly defined nanowells but also generates a more uniform (∼92%) distribution of the SERS signal when compared to random mechanical aggregation. The microfluidic flow rate and the direction and strength of the magnetic field determined the overall capture efficiency of the magneto-fluidic nanoparticle trapping platform. It was found that a 5 μl/min flow rate using an attractive magnetic field provided by 1 × 2 cm neodymium permanent magnets could capture over 90% of the magnetic core-shell nanoparticles across five Ni micropads. It was also observed that the intensity of the SERS signal for this setup was 10-fold higher than any other flow rate and magnetic field configurations tested. The magnetic concentration of the ferric core-shell nanoparticles causes the SERS signal to reach the steady state within 30 min can be reversed by simply removing the chip from the magnet housing and sonicating the retained particles from the outlet channel. Additionally, each magneto-fluidic can be reused without noticeable damage to the micropads up to three times.

Microfluidic chip based micro RNA detection through the combination of fluorescence and surface enhanced Raman scattering techniques

We present a novel microfluidic chip based method for the detection of micro RNA (miRNA) via the combination of fluorescence and surface enhanced Raman scattering (SERS) spectroscopies. First, silver nanoparticles (Ag NPs) are immobilized onto a glass slide, forming a SERS enhancing substrate. Then a specificially designed molecular beacon (MB) is attached to the SERS substrate. The 3' end of the MB is decorated with a thiol group to facilitate the attachment of the MB, while the 5' end of the MB is labeled with an organic dye 6-FAM, which is used both as the fluorophore and SERS reporter. In the absence of target miRNA, the MB will form a hairpin structure, making 6-FAM close to the Ag NPs. Hence, the fluorescence of 6-FAM will be quenched and the Raman signal of 6-FAM will be enhanced. On the contrary, with target miRNA present, hybridization between the miRNA and MB will unfold the MB and increase the distance between 6-FAM and the Ag NPs. Thus the fluorescence of 6-FAM will recover and the SERS signal of 6-FAM will decrease. So the target miRNA will simultaneously introduce opposite changing trends in the intensities of the fluorescence and SERS signals. By combining the opposite changes in the two optical spectra, an improved sensitivity and linearity toward the target miRNA is achieved as compared with using solely fluorescence or SERS. Moreover, introducing the microfluidic chip can reduce the reaction time, reagent dosage and complexity of detection. With the improved sensitivity and simplicity, we anticipate that the presented method can have great potential in the investigation of miRNA related diseases.

Detection of Adhesion Molecules on Inflamed Macrophages at Early-Stage Using SERS Probe Gold Nanorods

In recent years, it has been shown that inflammatory biomarkers can be used as an effective signal for disease diagnoses. The early detection of these signals provides useful information that could prevent the occurrence of severe diseases. Here, we employed surface-enhanced Raman scattering (SERS) probe gold nanorods (GNRs) as a tool for the early detection of inflammatory molecules in inflamed cells. A murine macrophage cell line (Raw264.7) stimulated with lipopolysaccharide (LPS) was used as a model in this study. The prepared SERS probe GNRs containing 4-mercaptobenzoic acid as a Raman reporter to generate SERS signals were used for detection of intracellular adhesion molecule-1 (ICAM-1) in macrophages after treatment with LPS for varying lengths of time. Our results show that SERS probe GNRs could detect significant differences in the expression of ICAM-1 molecules in LPS-treated macrophages compared to those in untreated macrophages after only 1 h of LPS treatment. In contrast, when using fluorescent labeling or enzyme-linked immunosorbent assays (ELISA) to detect ICAM-1, significant differences between inflamed and un-inflamed macrophages were not seen until the cells had been treated with LPS for 5 h. These results indicate that our SERS probe GNRs provide a higher sensitivity for detecting biomarker molecules in inflamed macrophages than the conventional fluorescence and ELISA techniques, and could therefore be useful as a potential diagnostic tool for managing disease risk.

Human Induced Pluripotent Stem Cells for Tumor Targeted Delivery of Gold Nanorods and Enhanced Photothermal Therapy

How to improve effective accumulation and intratumoral distribution of plasmonic gold nanoparticles has become a great challenge for photothermal therapy of tumors. Herein, we reported a nanoplatform with photothermal therapeutic effects by fabricating Au nanorods@SiO2@CXCR4 nanoparticles and loading the prepared nanoparticles into the human induced pluripotent stem cells(AuNRs-iPS). In virtue of the prominent optical properties of Au nanorods@SiO2@CXCR4 and remarkable tumor target migration ability of iPS cells, the Au nanorods delivery mediated by iPS cells via the nanoplatform AuNRs-iPS was found to have a prolonged retention time and spatially even distribution in MGC803 tumor-bearing nude mice observed by photoacoustic tomography and two-photon luminescence. On the basis of these improvements, the nanoplatform displayed a robust migration capacity to target the tumor site and to improve photothermal therapeutic efficacy on inhibiting the growth of tumors in xenograft mice under a low laser power density. The combination of gold nanorods with human iPS cells as a theranostic platform paves an alternative road for cancer theranostics and holds great promise for clinical translation in the near future.

Dual peptides modified fluorescence-SERS dual mode imaging nanoprobes with improved cancer cell targeting efficiency

We designed dual-peptide-functionalized fluorescence-SERS dual mode imaging nanoprobes possessing an improved cancer cell targeting efficiency.

Nanostructured gold microelectrodes for SERS and EIS measurements by incorporating ZnO nanorod growth with electroplating

In this paper, a fine gold nanostructure synthesized on selective planar microelectrodes in micro-chip is realized by using an advanced hybrid fabrication approach incorporating growth of nanorods (NRs) with gold electroplating. By this developed nanostructure, integration of in-situ surface-enhanced Raman spectroscopy (SERS) detection with electrochemical impedance spectroscopy (EIS) measurement for label-free, nondestructive, real-time and rapid monitoring on a single cell has been achieved. Moreover, parameters of Au nanostructures such as size of nanoholes/nanogaps can be controllably adjusted in the fabrication. We have demonstrated a SERS enhancement factor of up to ~2.24 × 10⁶ and double-layer impedance decrease ratio of 90% ~ 95% at low frequency range below 200 kHz by using nanostructured microelectrodes. SERS detection and in-situ EIS measurement of a trapped single cell by using planar microelectrodes are realized to demonstrate the compatibility, multi-functions, high-sensitivity and simplicity of the micro-chip system. This dual function platform integrating SERS and EIS is of great significance in biological, biochemical and biomedical applications.

pH-sensitive nanocarrier based on gold/silver core-shell nanoparticles decorated multi-walled carbon manotubes for tracing drug release in living cells

We fabricate a multifunctional nanocarrier based on multi-walled carbon nanotubes (MWCNTs) decorated with gold/silver core-shell nanoparticles (Au@Ag NPs) and fluorescein isothiocyanate (FITC) for tracking the intracellular drug release process. In the demonstrated nanocarrier, the Au@Ag NPs adsorbed on the surface of MWCNTs were labeled with the pH-dependent SERS reporter 4-Mercaptobenzoic acid (4MBA) for SERS based pH sensing. FITC was conjugated on MWCNTs to provide fluorescence signal for tracing the MWCNTs. Fluorescent doxorubicin (DOX) was used as the model drug which can be loaded onto MWCNTs via π-π stacking and released from the MWCNTs under acidic condition. By detecting the SERS spectrum of 4MBA, the pH value around the nanocarrier could be monitored. Besides, by tracing the fluorescence of FITC and DOX, we can also investigate the drug release process in cells. Experimental results show that the proposed nanocarrier retained a well pH-sensitive performance in living cells, and the DOX detached from MWCNTs inside the lysosomes and entered into the cytoplasm with the MWCNTs being left in lysosomes. To further investigate the drug release dynamics, 2-D color-gradient pH mapping were plotted, which were calculated from the SERS spectra of 4MBA. The detailed release process and carrier distribution have been recorded as environmental pH changes during cell endocytosis. Furthermore, we also confirmed that the proposed nanocarrier has a good biocompatibility. It indicates that the designed nanocarrier have a great potential in intraceable drug delivery, cancer cells imaging and pH monitoring.

Raman Imaging from Microscopy to Nanoscopy, and to Macroscopy

Raman spectroscopy can not only provide intrinsic fingerprint information about a sample, but also utilize the merits of the narrow bandwidth and low background of Raman spectra, offering itself as a promising multiplex analytical technique. Raman microscopy has become particularly attractive recently because it has demonstrated itself as an important imaging technique for various samples, from biological samples and chemical systems to industrially important silicon-based wafers. In this Concept article, some of the most recent advances in Raman imaging techniques are critically reviewed, and the advantages and problems associated with the current techniques are discussed. Particular emphasis is placed on its future directions, from both the technical and application sides.

Fluorescence quenching studies on the interaction of catechin-quinone with CdTe quantum dots. Mechanism elucidation and feasibility studies

Changes of the photoluminescent properties of QD in the presence of oxidized catechin (CQ) were investigated by absorption, steady-state fluorescence, fluorescence lifetime and dynamic light scattering measurements. Photoluminescence intensity and fluorescence lifetime was decreasing with increasing CQ concentration. Dynamic light scattering technique found the hydrodynamic diameter of QD suspension in water is in range of 45 nm, whereas in presence of CQ increased to mean values of 67 nm. Calculated from absorption peak position of excition band indicated on average QD size of 3.2 nm. Emission spectroscopy and time-resolved emission studies confirmed preservation of electronic band structure in QD-CQ aggregates. On basis of the presented results, the elucidated mechanism of QD fluorescence quenching is a result of the interaction between QD and CQ due to electron transfer and electrostatic attraction. The results of fluorescence quenching of water-soluble CdTe quantum dot (QD) capped with thiocarboxylic acid were used to implement a simple and fast method to determine the presence of native antioxidant quinones in aqueous solutions. Feasibility studies on this method carried out with oxidized catechin showed a linear relation between the QD emission and quencher concentration, in range from 1 up to 200 μM. The wide linear range of concentration dependence makes it possible to apply this method for the fast and sensitive detection of quinones in solutions.

SERS investigation of ciprofloxacin drug molecules on TiO2 nanoparticles

TiO₂ nanoparticles with different crystallinity were synthesized and served as SERS-active substrates for SERS detection of ciprofloxacin (CIP) drug molecules.

Dual-functional sensor based on switchable plasmonic structure of VO2 nano-crystal films and Ag nanoparticles

Utilizing the insulator-metal phase transition of vanadium dioxide (VO2) crystal films, we develop a dual-functional sensor based on the coupling between VO2 nano-crystal films and Ag nanoparticles, which can probe fluorescence or Raman signals on the same substrate and it is switchable by changing temperature. At room temperature, the VO2 crystal films is insulator phase and the fluorescence signals of probe molecules (R6G) is detectable (Raman is in "off"). At high temperature (such as 85 °C), the VO2 crystal films become metallic phase. Ag nanoparticles interact with the metal phase of VO2 crystal films to produce stronger localized electric field. The stronger electric field can excite the Raman signals of probe molecules (R6G) and the coupled structure can also emit the Raman signals out efficiently (Raman is in "on"). The switchable probe of fluorescence and Raman signals would have potential applications in active photoelectric components, such as intelligent switch and multifunctional active sensor etc.

Distinguishing Cancerous Liver Cells Using Surface-Enhanced Raman Spectroscopy

Raman spectroscopy has been widely used in biomedical research and clinical diagnostics. It possesses great potential for the analysis of biochemical processes in cell studies. In this article, the surface-enhanced Raman spectroscopy (SERS) of normal and cancerous liver cells incubated with SERS active substrates (gold nanoparticle) was measured using confocal Raman microspectroscopy technology. The chemical components of the cells were analyzed through statistical methods for the SERS spectrum. Both the relative intensity ratio and principal component analysis (PCA) were used for distinguishing the normal liver cells (QSG-7701) from the hepatoma cells (SMMC-7721). The relative intensity ratio of the Raman spectra peaks such as I937/I1209, I1276/I1308, I1342/I1375, and I1402/I1435 was set as the judge boundary, and the sensitivity and the specificity using PCA method were calculated. The results indicated that the surface-enhanced Raman spectrum could provide the chemical information for distinguishing the normal cells from the cancerous liver cells and demonstrated that SERS technology possessed the possible applied potential for the diagnosis of liver cancer.

Optimization of SERS tag intensity, binding footprint, and emittance

Nanoparticle surface enhanced Raman scattering (SERS) tags have attracted interest as labels for use in a variety of applications, including biomolecular assays. An obstacle to progress in this area is a lack of standardized approaches to compare the brightness of different SERS tags within and between laboratories. Here we present an approach based on binding of SERS tags to beads with known binding capacities that allows evaluation of the average intensity, the relative binding footprint of particles in a SERS tag preparation, and the size-normalized intensity or emittance. We tested this on four different SERS tag compositions and show that aggregated gold nanorods produce SERS tags that are 2-4 times brighter than relatively more monodisperse nanorods, but that the aggregated nanorods are also correspondingly larger, which may negate the intensity if steric hindrance limits the number of tags bound to a target. By contrast, SERS tags prepared from smaller gold nanorods coated with a silver shell produce SERS tags that are 2-3 times brighter, on a size-normalized basis, than the Au nanorod-based tags, resulting in labels with improved performance in SERS-based image and flow cytometry assays. SERS tags based on red-resonant Ag plates showed similarly bright signals and small footprint. This approach to evaluating SERS tag brightness is general, uses readily available reagents and instruments, and should be suitable for interlab comparisons of SERS tag brightness.

Biocompatible surface-enhanced Raman scattering nanotags for in vivo cancer detection

The advancement of surface-enhanced Raman scattering (SERS) is significantly increasing as an ultra-sensitive sensing technology in biomedical research. In this review, we focus on the most recent developments of biocompatible nanoprobes for cancer research. First, we discuss coating approaches to enhance the biocompatibility of SERS substrate and Raman reporters. Furthermore, interesting ligands such as antibodies, aptamers and polypeptides are attached to the surface of nanotags for targeting the cancerous cells in vitro. The unique multiplexing capabilities of the SERS technique have been applied for simultaneous multiple target recognition. Finally, these noninvasive, ultrasensitive tools are mostly highlighted for in vivo tumor detection. Potential application of SERS nanotags in therapeutic study and the possibility of SERS nanotags in biomedical applications are outlined briefly in this review.

Focused ultrasound delivery of Raman nanoparticles across the blood-brain barrier: potential for targeting experimental brain tumors

Spectral mapping of nanoparticles with surface enhanced Raman scattering (SERS) capability in the near-infrared range is an emerging molecular imaging technique. We used magnetic resonance image-guided transcranial focused ultrasound (TcMRgFUS) to reversibly disrupt the blood-brain barrier (BBB) adjacent to brain tumor margins in rats. Glioma cells were found to internalize SERS capable nanoparticles of 50nm or 120nm physical diameter. Surface coating with anti-epidermal growth factor receptor antibody or non-specific human immunoglobulin G, resulted in enhanced cell uptake of nanoparticles in-vitro compared to nanoparticles with methyl terminated 12-unit polyethylene glycol surface. BBB disruption permitted the delivery of SERS capable spherical 50 or 120nm gold nanoparticles to the tumor margins. Thus, nanoparticles with SERS imaging capability can be delivered across the BBB non-invasively using TcMRgFUS and have the potential to be used as optical tracking agents at the invasive front of malignant brain tumors.

FROM THE CLINICAL EDITOR

This study demonstrates the use of magnetic resonance image-guided transcranial focused ultrasound to open the BBB and enable spectral mapping of nanoparticles with surface enhanced Raman scattering (SERS)-based molecular imaging for experimental tumor tracking.

Design strategies of hybrid metallic nanoparticles for theragnostic applications

Metallic nanoparticles (MNPs) such as iron oxide and gold nanoparticles are interesting platforms to build theragnostic nanocarriers which combine both therapeutic and diagnostic functions within a single nanostructure. Nevertheless, their surface must be functionalized to be suitable for in vivo applications. Surface functionalization also provides binding sites for targeting ligands, and for drug loading. This review focuses on the materials and surface chemistry used to build hybrid nanocarriers that are inorganic cores functionalized with organic materials. The surface state of the MNPs largely depends on their synthesis routes, and dictates the strategies used for functionalization. Two main strategies can be found in the literature: the design of core-shell nanosystems, or embedding nanoparticles in organic materials. Emerging tendencies such as the use of clusters or alternative coating materials are also described. To present both hydrophilic and lipophilic nanosystems, we chose the doxorubicin anticancer agent as an example, as the molecule presents an affinity for both types of materials.

SERS substrates formed by gold nanorods deposited on colloidal silica films

We describe a new approach to the fabrication of surface-enhanced Raman scattering (SERS) substrates using gold nanorod (GNR) nanopowders to prepare concentrated GNR sols, followed by their deposition on an opal-like photonic crystal (OPC) film formed on a silicon wafer. For comparative experiments, we also prepared GNR assemblies on plain silicon wafers. GNR-OPC substrates combine the increased specific surface, owing to the multilayer silicon nanosphere structure, and various spatial GNR configurations, including those with possible plasmonic hot spots. We demonstrate here the existence of the optimal OPC thickness and GNR deposition density for the maximal SERS effect. All other things being equal, the analytical integral SERS enhancement of the GNR-OPC substrates is higher than that of the thick, randomly oriented GNR assemblies on plain silicon wafers. Several ways to further optimize the strategy suggested are discussed.

Nanoparticles for Improving Cancer Diagnosis

Despite the progress in developing new therapeutic modalities, cancer remains one of the leading diseases causing human mortality. This is mainly attributed to the inability to diagnose tumors in their early stage. By the time the tumor is confirmed, the cancer may have already metastasized, thereby making therapies challenging or even impossible. It is therefore crucial to develop new or to improve existing diagnostic tools to enable diagnosis of cancer in its early or even pre-syndrome stage. The emergence of nanotechnology has provided such a possibility. Unique physical and physiochemical properties allow nanoparticles to be utilized as tags with excellent sensitivity. When coupled with the appropriate targeting molecules, nanoparticle-based probes can interact with a biological system and sense biological changes on the molecular level with unprecedented accuracy. In the past several years, much progress has been made in applying nanotechnology to clinical imaging and diagnostics, and interdisciplinary efforts have made an impact on clinical cancer management. This article aims to review the progress in this exciting area with emphases on the preparation and engineering techniques that have been developed to assemble "smart" nanoprobes.