Quantitative surface-enhanced resonant Raman scattering multiplexing of biocompatible gold nanostars for in vitro and ex vivo detection

Caged gold nanostars: a novel plasmonic nanoplatform with potential theranostic applications

Here, we first introduce caged gold nanostars (C-GNS), a novel hybrid nanoplatform combining the exceptional plasmonic properties of nanostars with the loading capability of hollow-shell structures. We present two synthetic routes used to produce C-GNS particles and highlight the benefits of the galvanic replacement-free approach. FEM simulations explore the enhanced plasmonic properties of this novel nanoparticle morphology. Finally, in a proof-of-concept study, we successfully demonstrate in vivo hyperspectral imaging and photothermal treatment of tumors in a mouse model with the C-GNS nanoplatform.

Ultra-trace SERS detection of cocaine and heroin using bimetallic gold-silver nanostars (BGNS-Ag)

A rapid, in-field, and reliable method for the detection of illegal drugs of abuse in biological fluids without any sample pretreatment would potentially be helpful for law enforcement, drug control officials, and public healthcare. In this study, we presented a cost-effective and highly reproducible solution-based surface-enhanced Raman scattering (SERS) platform utilizing a portable Raman instrument for fast sensitive SERS detection of illegal drugs, such as cocaine, and heroin in human urine without any sample preprocessing. The SERS platform was constructed for the first time by combining the superior SERS enhancement properties of bimetallic silver-coated gold nanostars (BGNS-Ag) and the advantages of suitable alkaline metal salts such as NaI for SERS signal amplification. The effects of the silver thickness of BGNS-Ag and alkaline salts on the SERS performance were investigated in detail; we observed that the maximum SERS enhancement was obtained for BGNS-Ag with the maximum silver thickness (54 ± 5 nm) in presence of NaI salt. Our SERS platform shows ultra-high sensitivity of cocaine and heroin with a limit of detection (LOD) as low as 10 pg/mL for cocaine and 100 pg/mL for heroin, which was 100 times lower than that of the traditional silver nanoparticle-based illegal drug detection. As a demonstration, the platform was further applied to detect cocaine and heroin spiked in human urine without any sample preprocessing achieving a LOD of 100 pg/mL for cocaine and 1 ng/mL for heroin. Overall, our SERS detection platform shows potential for rapid, onsite, ultra-low-cost portable applications for trace detection of illegal drugs and biomarkers.

Design and Synthesis of SERS Materials for In Vivo Molecular Imaging and Biosensing

Surface-enhanced Raman scattering (SERS) is a feasible and ultra-sensitive method for biomedical imaging and disease diagnosis. SERS is widely applied to in vivo imaging due to the development of functional nanoparticles encoded by Raman active molecules (SERS nanoprobes) and improvements in instruments. Herein, the recent developments in SERS active materials and their in vivo imaging and biosensing applications are overviewed. Various SERS substrates that have been successfully used for in vivo imaging are described. Then, the applications of SERS imaging in cancer detection and in vivo intraoperative guidance are summarized. The role of highly sensitive SERS biosensors in guiding the detection and prevention of diseases is discussed in detail. Moreover, its role in the identification and resection of microtumors and as a diagnostic and therapeutic platform is also reviewed. Finally, the progress and challenges associated with SERS active materials, equipment, and clinical translation are described. The present evidence suggests that SERS could be applied in clinical practice in the future.

Microfluidic SERS devices: brightening the future of bioanalysis

A new avenue has opened up for applications of surface-enhanced Raman spectroscopy (SERS) in the biomedical field, mainly due to the striking advantages offered by SERS tags. SERS tags provide indirect identification of analytes with rich and highly specific spectral fingerprint information, high sensitivity, and outstanding multiplexing potential, making them very useful in in vitro and in vivo assays. The recent and innovative advances in nanomaterial science, novel Raman reporters, and emerging bioconjugation protocols have helped develop ultra-bright SERS tags as powerful tools for multiplex SERS-based detection and diagnosis applications. Nevertheless, to translate SERS platforms to real-world problems, some challenges, especially for clinical applications, must be addressed. This review presents the current understanding of the factors influencing the quality of SERS tags and the strategies commonly employed to improve not only spectral quality but the specificity and reproducibility of the interaction of the analyte with the target ligand. It further explores some of the most common approaches which have emerged for coupling SERS with microfluidic technologies, for biomedical applications. The importance of understanding microfluidic production and characterisation to yield excellent device quality while ensuring high throughput production are emphasised and explored, after which, the challenges and approaches developed to fulfil the potential that SERS-based microfluidics have to offer are described.

Expanding the Multiplexing Capabilities of Raman Imaging to Reveal Highly Specific Molecular Expression and Enable Spatial Profiling

Profiling the heterogeneous landscape of cell types and biomolecules is rapidly being adopted to address current imperative research questions. Precision medicine seeks advancements in molecular spatial profiling techniques with highly multiplexed imaging capabilities and subcellular resolution, which remains an extremely complex task. Surface-enhanced Raman spectroscopy (SERS) imaging offers promise through the utilization of nanoparticle-based contrast agents that exhibit narrow spectral features and molecular specificity. The current renaissance of gold nanoparticle technology makes Raman scattering intensities competitive with traditional fluorescence methods while offering the added benefit of unsurpassed multiplexing capabilities. Here, we present an expanded library of individually distinct SERS nanoparticles to arm researchers and clinicians. Our nanoparticles consist of a ∼60 nm gold core, a Raman reporter molecule, and a final inert silica coating. Using density functional theory, we have selected Raman reporters that meet the key criterion of high spectral uniqueness to facilitate unmixing of up to 26 components in a single imaging pixel in vitro and in vivo. We also demonstrated the utility of our SERS nanoparticles for targeting cultured cells and profiling cancerous human tissue sections for highly multiplexed optical imaging. This study showcases the far-reaching capabilities of SERS-based Raman imaging in molecular profiling to improve personalized medicine and overcome the major challenges of functional and structural diversity in proteomic imaging.

Boosting the Brightness of Thiolated Surface-Enhanced Raman Scattering Nanoprobes by Maximal Utilization of the Three-Dimensional Volume of Electromagnetic Fields

Self-assembled monolayers (SAMs) of thiols on plasmonic nanoparticles constitute one of the most common methods for fabricating surface-enhanced Raman scattering (SERS) nanoprobes with wide applications. However, this method greatly limits the sufficient utilization of electromagnetic fields derived from plasmon excitation of the nanoparticles, because the thickness of SAMs (<1 nm) is usually much smaller than the attenuation length (>10 nm) of the fields. To overcome this, we propose a three-dimensional (3D) volume-active SERS (VASERS) technique to break the SAM limit, which integrates large amounts of thiol reporters into polydopamine shells on silver nanoparticles via Michael addition and allows sufficient utilization of 3D electromagnetic fields, leading to a dramatic increase in the intensity of the signal of the nanoprobes by about one order of magnitude. We demonstrate the universality of this strategy on various thiol reporters and plasmonic substrates. We also show that orthogonal VASERS nanoprobes with alkyne readout allow for high-precision in vivo tumor targeting and margin delineation.

Ultra-high SERS detection of consumable coloring agents using plasmonic gold nanostars with high aspect-ratio spikes

Solution-based SERS detection by using a portable Raman instrument has emerged as an important tool due to its simplicity, and flexibility for rapid and on-site screening of analyte molecules. However, this method has several shortcomings, including poor sensitivity especially for weak-affinity analyte molecules, where there is no close contact between the plasmonic metal surface and analyte molecule. Examples of weak-affinity molecules include pigment molecules that are commonly used as a consumable coloring agent, such as allura red (AR), and sunset yellow (SY). As high consumption of colorant agents has been shown to cause adverse effects on human health, there is a strong need to develop a simple and practical sensing system with high sensitivity for these agents. Here we present a novel, highly sensitive solution-based SERS detection method for AR, and SY by using CTAC capped gold nanostars (GNS) having different aspect ratios (GNS-2, GNS-4, and GNS-5) without utilizing any aggregating agents which can enhance SERS signal however it reduces batch to batch reproducibility. The influence of the aspect ratio of GNS on SERS properties was investigated. We have achieved a limit of detection (LOD) of AR and SY as low as 0.5 and 1 ppb, respectively by using GNS-5 with the advantages of minimal sample preparation by just mixing the analyte solution into a well plate containing GNS solution. In addition, excellent colloidal stability and reproducibility have further enhanced the applicability in real-world samples. Overall, our results evidence that the solution-based SERS detection platform using high aspect-ratio GNS can be applied for practical application to detect pigment molecules in real samples with satisfactory results.

Surface-enhanced Raman probes based on gold nanomaterials for in vivo diagnosis and imaging

Surface-enhanced Raman scattering (SERS) has received considerable attention from researchers due to its high molecular specificity, high sensitivity, non-invasive and multiplexing. Recently, various metal substrates have been exploited for SERS analysis and imaging. Among them, gold nanomaterials are important SERS substrates with outstanding surface plasmon resonance effects, structural adjustability and good biocompatibility, making them widely used in biomedical diagnosis and clinical fields. In this minireview, we discuss the latest progress about the application of gold-based nanomaterials as SERS probes in biomedical research, primarily for in vivo disease diagnosis and imaging. This review mainly includes the basic shapes and morphologies of gold based SERS probes, such as gold nanoparticles (AuNPs), gold nanorods (AuNRs), gold nanostars (AuNSs), as well as other gold nanostructures. Finally, a brief outlook for the future development of SERS technique in the context of efficient diagnostics and therapy guidance is provided. We hope that this minireview will facilitate the design and future development of Surface-enhanced Raman probes based on gold nanomaterials.

Design and synthesis of gold nanostars-based SERS nanotags for bioimaging applications

Surface-enhanced Raman spectroscopy (SERS) nanotags hold a unique place among bioimaging contrast agents due to their fingerprint-like spectra, which provide one of the highest degrees of detection specificity. However, in order to achieve a sufficiently high signal intensity, targeting capabilities, and biocompatibility, all components of nanotags must be rationally designed and tailored to a specific application. Design parameters include fine-tuning the properties of the plasmonic core as well as optimizing the choice of Raman reporter molecule, surface coating, and targeting moieties for the intended application. This review introduces readers to the principles of SERS nanotag design and discusses both established and emerging protocols of their synthesis, with a specific focus on the construction of SERS nanotags in the context of bioimaging and theranostics.

Noninvasive and Highly Multiplexed Five-Color Tumor Imaging of Multicore Near-Infrared Resonant Surface-Enhanced Raman Nanoparticles In Vivo

In vivo multiplexed imaging aims for noninvasive monitoring of tumors with multiple channels without excision of the tissue. While most of the preclinical imaging has provided a number of multiplexing channels up to three, Raman imaging with surface-enhanced Raman scattering (SERS) nanoparticles was suggested to offer higher multiplexing capability originating from their narrow spectral width. However, in vivo multiplexed SERS imaging is still in its infancy for multichannel visualization of tumors, which require both sufficient multiplicity and high sensitivity concurrently. Here we create multispectral palettes of gold multicore-near-infrared (NIR) resonant Raman dyes-silica shell SERS (NIR-SERRS) nanoparticle oligomers and demonstrate noninvasive and five-plex SERS imaging of the nanoparticle accumulation in tumors of living mice. We perform the five-plex ratiometric imaging of tumors by varying the administered ratio of the nanoparticles, which simulates the detection of multiple biomarkers with different expression levels in the tumor environment. Furthermore, since this method does not require the excision of tumor tissues at the imaging condition, we perform noninvasive and longitudinal imaging of the five-color nanoparticles in the tumors, which is not feasible with current ex vivo multiplexed tissue analysis platforms. Our work surpasses the multiplicity limit of previous preclinical tumor imaging methods while keeping enough sensitivity for tumor-targeted in vivo imaging and could enable the noninvasive assessment of multiple biological targets within the tumor microenvironment in living subjects.

Gap-enhanced resonance Raman tags for live-cell imaging

Surface-enhanced Raman scattering (SERS) nanotags are widely used in the biomedical field including live-cell imaging due to the high specificity from their fingerprint spectrum and the multiplexing capability from the ultra-narrow linewidth. However, long-term live-cell Raman imaging is limited due to the photodamage from a relatively long exposure time and a high laser power, which are needed for acquiring detectable Raman signals. In this work, we attempt to resolve this issue by developing ultrabright gap-enhanced resonance Raman tags (GERRTs), consisting of a petal-like gold core and a silver shell with the near-infrared resonant reporter of IR-780 embedded in between, for long-term and high-speed live-cell imaging. GERRTs exhibit an ultrahigh Raman intensity down to a single-nanoparticle level in aqueous solution and the solid state upon 785 nm excitation, allowing for high-resolution time-lapse live-cell Raman imaging with an exposure time of 1 ms per pixel and a laser power of 50 μW. Under these measurement conditions, we can possibly capture dynamic cellular processes with a high temporal resolution, and track living cells for long periods of time owing to the reduced photodamage to cells. These nanotags open new opportunities for ultrasensitive, low-phototoxic, and long-term live-cell imaging.

Silica-Coated, Waxberry-like Surface-Enhanced Raman Resonant Scattering Tag-Pair with Near-Infrared Raman Dye Encoding: Toward In Vivo Duplexing Detection

Surface-enhanced Raman resonant scattering (SERRS) tags encoded with near-infrared (NIR) Raman reporters showed great potential for in vivo detection owing to their ultrasensitivity. However, in vivo signal stability of such tags is a remaining problem due to the lack of suitable silica coating method because the weakly adsorbed NIR reporters tend to detach from traditional gold nanosubstrates in the ethanol-rich and high pH conditions, which are commonly used for silica coating. Herein, we propose a silica coating method for NIR SERRS tags by using waxberry-like gold nanoparticles (NPs) as substrates. The lipid bilayer of the NPs played a crucial role in the coating, which can encapsulate the NIR Raman reporter via hydrophobic interactions and prevent the interference from a harsh medium. Thus, the silica-coated tags well preserved ultrasensitivity of bare tags and simultaneously gained satisfactory signal stability in vivo. Moreover, the coating method is compatible for the encapsulation of a variety of thiol group-free NIR reporters (as exemplified by DTTC, Cy7, IR792, and DIR), relying on which a tag-pair with distinguishable peaks can be screened (labeling with DTTC and Cy7, respectively). In vivo duplexing detection revealed that the tag-pair-labeled liposome was cleared faster in the liver than polydopamine NPs within one mouse. The developed method paves an easy way for gaining high-quality SERRS tags and will promote their in vivo multiplex analysis and diagnostics applications.

Recent advances in applications of nanoparticles in SERS in vivo imaging

Surface-enhanced Raman scattering (SERS) technique has been regarded as one of the most important research methods in the field of single-molecule science. Since the previous decade, the application of nanoparticles for in vivo SERS imaging becomes the focus of research. To enhance the performance of SERS imaging, researchers have developed several SERS nanotags such as gold nanostars, copper-based nanomaterials, semiconducting quantum dots, and so on. The development of Raman equipment is also necessary owing to the current limitations. This review describes the recent advances of SERS nanoparticles and their applications for in vivo imaging in detail. Specific examples highlighting the in vivo cancer imaging and treatment application of SERS nanoparticles. A perspective on the challenges and opportunities of nanoparticles in SERS in vivo imaging is also provided. This article is categorized under: Diagnostic Tools > in vivo Nanodiagnostics and Imaging Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

AuNanostar@4-MBA@Au Core-Shell Nanostructure Coupled with Exonuclease III-Assisted Cycling Amplification for Ultrasensitive SERS Detection of Ochratoxin A

The "turn-on" mode surface-enhanced Raman scattering (SERS) aptasensor for ultrasensitive ochratoxin A (OTA) detection was developed based on the SERS "hot spots" of AuNanostar@4-MBA@Au core-shell nanostructures (AuNS@4-MBA@Au) and exonuclease III (Exo III)-assisted target cycle amplification strategy. Compared with conventional gold nanoparticles, AuNS@4-MBA@Au provides a much higher SERS enhancement factor because AuNS exhibits a larger surface roughness and the lightning rod effect, as well as an excellent electromagnetic field between the AuNS core and the Au shell, which contribute to the superstrong SERS signal. Meanwhile, Exo III-assisted target cycle amplification can be used as an effective method for the further amplified detection of OTA. Additionally, the utilization of streptavidin magnesphere paramagnetic particles offers a green, economical, and facile technology for the accumulation and separation of the signal probe AuNS@4-MBA@Au from solution. All these factors lead to a significant enhancement of detectable signals and superhigh sensitivity. As a result, the limit of detection as low as 0.25 fg mL^-1 could be achieved, which was lower than that in the other reported literatures on SERS methods for OTA detection as we know. The developed SERS aptasensor also provides a promising tool for foodstuff detection.

A Rapid Detection Method for On-site Screening of Estazolam in Beverages with Au@Ag Core-shell Nanoparticles Paper-based SERS Substrate

Estazolam (EST) is a common sedative-hypnotic drug with a risk of abuse. Therefore, rapid on-site detection of EST is necessary to control the abuse of EST. In this paper, a fast, simple, and sensitive method is demonstrated for the detection of EST in both water and beverages, using surface-enhanced Raman spectroscopy (SERS) techniques. Au@Ag core-shell nanoparticles (NPs) assembled on the filter paper as a SERS substrate exhibit good applicability and practicality. At the same time, density functional theory (DFT) is used to assign the vibration mode of the EST molecules, which can be used as a guide for subsequent experiments. The lowest detectable concentration of EST in aqueous solution can be as low as 5 mg/L, and signal uniformity is excellent (RSD687 = 5.56%, RSD1000 = 4.35%). In addition, EST components artificially added to orange juice and pomegranate juice can be effectively detected by simple pretreatment with a minimum detection concentration as low as 10 mg/L. Therefore, this study found that the use of Au@Ag core-shell nanoparticles paper-based SERS substrate provides a quick and easy method for the detection of illegally added drugs in beverages.

Surface-Enhanced Raman Scattering and Fluorescence on Gold Nanogratings

Surface-enhanced Raman scattering (SERS) spectroscopy is a sensitive sensing technique. It is desirable to have an easy method to produce SERS-active substrate with reproducible and robust signals. We propose a simple method to fabricate SERS-active substrates with high structural homogeneity and signal reproducibility using electron beam (E-beam) lithography without the problematic photoresist (PR) lift-off process. The substrate was fabricated by using E-beam to define nanograting patterns on the photoresist and subsequently coat a layer of gold thin film on top of it. Efficient and stable SERS signals were observed on the substrates. In order to investigate the enhancement mechanism, we compared the signals from this substrate with those with photoresist lifted-off, which are essentially discontinuous gold stripes. While both structures showed significant grating-period-dependent fluorescence enhancement, no SERS signal was observed on the photoresist lifted-off gratings. Only transverse magnetic (TM)-polarized excitation exhibited strong enhancement, which revealed its plasmonic attribution. The fluorescence enhancement showed distinct periodic dependence for the two structures, which is due to the different enhancement mechanism. We demonstrate using this substrate for specific protein binding detection. Similar periodicity dependence was observed. Detailed theoretical and experimental studies were performed to investigate the observed phenomena. We conclude that the excitation of surface plasmon polaritons on the continuous gold thin film is essential for the stable and efficient SERS effects.

One-Pot Aqueous Synthesis of Icosahedral Au as Bifunctional Candidates for Enhanced Glucose Electrooxidation and Surface-Enhanced Raman Scattering

Bifunctional candidates, which could provide catalytic and plasmonic properties simultaneously, could activate a promising development for biomedicine. Here, we kinetically controlled and synthesized a penta-twinned icosahedral Au (Ih Au) by a facile wet-chemical protocol without assistance of stabilizers. Benefiting from icosahedral morphology and kinetic synthesis process, the Ih Au nanoparticles (NPs) incorporate three key advantages: (i) ample active sites/"hot spots" and surface strain, (ii) good stability/chemical inertness and easy functionalization, and (iii) biological compatibility and a clean surface, which could promote their electrocatalysis and photonic capacity. Ih Au NPs, as bifunctional nanomaterials, exert excellent electrocatalytic and surface-enhanced Raman scattering (SERS) performances. Ih Au delivers the highest glucose electrooxidation (GEO) peak current density with 6.87 mA cm^-2, which is 14 times larger than that of Turkevich Au (0.49 mA cm^-2) under the same condition. Moreover, the SERS signals of rhodamine 6G (R6G) on Ih Au are much stronger than that on the other corresponding Au counterparts. Particularly, the SERS intensity of R6G on Ih Au increases by about four times compared to that on Au NPs. This study motivates the great prospect for combining Ih Au's bifunctionalities and indicates the potential of bifunctional nanomaterials in biologically implanted devices.

Present and Future of Surface-Enhanced Raman Scattering

The discovery of the enhancement of Raman scattering by molecules adsorbed on nanostructured metal surfaces is a landmark in the history of spectroscopic and analytical techniques. Significant experimental and theoretical effort has been directed toward understanding the surface-enhanced Raman scattering (SERS) effect and demonstrating its potential in various types of ultrasensitive sensing applications in a wide variety of fields. In the 45 years since its discovery, SERS has blossomed into a rich area of research and technology, but additional efforts are still needed before it can be routinely used analytically and in commercial products. In this Review, prominent authors from around the world joined together to summarize the state of the art in understanding and using SERS and to predict what can be expected in the near future in terms of research, applications, and technological development. This Review is dedicated to SERS pioneer and our coauthor, the late Prof. Richard Van Duyne, whom we lost during the preparation of this article.

In situ synthesis of silver nanoparticles on periodic supports as highly active and flexible surface-enhanced Raman spectroscopy substrates

With regard to surface-enhanced Raman spectroscopy (SERS), the preparation of substrates with high homogeneity and low cost remains a challenge. In this paper, cheap commercial DVD-R plates were adopted as supports, whose 3D periodic structure was transferred onto the surface of flexible polydimethylsiloxane (PDMS) easily. Then, silver nanoparticles were grown both on DVD and PDMS substrates by the in situ reduction method, and the SERS performances of these two substrates were investigated. The results confirmed that the PDMS-based substrate exhibited better enhancement performance and higher uniformity (RSD=4.16%). In addition, due to the flexibility and transparency of PDMS, it is not restricted by the surface shape of the object when applied in in situ detection. This low-cost, simple method will be widely used in the in situ detection of surfaces of objects of any shape.

Polymerase chain reaction - surface-enhanced Raman spectroscopy (PCR-SERS) method for gene methylation level detection in plasma

Gene promoter hypermethylation is a vital step in tumorigenesis. This paper set out to explore the use of polymerase chain reaction - surface-enhanced Raman spectroscopy (PCR-SERS) for the detection of gene methylation levels, with a focus on cancer diagnosis. Methods: PCR with methylation independent primers were used on DNA samples to amplify target genes regardless of their methylation states. SERS was used on the obtained PCR products to generate spectra that contained peak changes belonging to CG and AT base pairs. Multiple linear regression (MLR) was then used to deconvolute the SERS spectra so that the CG/AT ratios of the sample could be obtained. These MLR results were used to calculate methylation levels of the target genes. For protocol verification, three sets of seven reference DNA solutions with known methylation levels (0%, 1%, 5%, 25%, 50%, 75%, and 100%) were analysed. Clinically, blood plasma samples were taken from 48 non-small-cell lung cancer (NSCLC) patients and 51 healthy controls. The methylation levels of the genes p16, MGMT, and RASSF1 were determined for each patient using this method. Results: Verification experiment on the mixtures with known methylation levels resulted in an error of less than 6% from the actual levels. When applied to our clinical samples, the frequency of methylation in at least one of the three target genes among the NSCLC patients was 87.5%, but this percentage decreased to 11.8% for the control group. The methylation levels of p16 were found to be significantly higher in NSCLC patients with more pack-years smoked (p=0.04), later cancer stages (p=0.03), and cancer types of squamous cell and large cell versus adenocarcinoma (p=0.03). Prediction accuracy of 88% was achieved from classification and regression trees (CART) based on methylation levels and states, respectively. Conclusion: This research showed that the PCR-SERS protocol could quantitatively measure the methylation levels of genes in plasma. The methylation levels of the genes p16, MGMT, and RASSF1 were higher in NSCLC patients than in controls.

In situ synthesis of graphene oxide/gold nanocomposites as ultrasensitive surface-enhanced Raman scattering substrates for clenbuterol detection

A highly sensitive approach to detect trace amount of clenbuterol (CB) based on graphene oxide/gold nanoparticles (GO/Au NPs) by surface-enhanced Raman spectroscopy (SERS) was presented. To be specific, the GO/Au nanocomposites were formed by depositing Au NPs onto the surface of GO through an in situ reduction process, where a high density of inherent hot spots was created between Au NPs. By optimizing the depositing density of Au NPs, the strongest electromagnetic coupling effect originating from highly dense hot spots was obtained. The optimized GO/Au was demonstrated to enhance the Raman signals of CB by 4.8 times more than that of CB enhanced by Au NPs. Moreover, GO/Au nanocomposites exhibit good biocompatibility and accessible surface for high adsorption of target molecules through the pi-pi stacking with graphene oxide. Hence, the proposed GO/Au nanocomposites were utilized to capture aromatic molecules like CB and served as excellent sensitive SERS-active substrates for sensing of it, which exhibited an excellent linear performance in the range of 5 × 10^-8 to 1 × 10^-6 mol/L with a limit of detection (LOD) of 3.34 × 10^-8 mol/L (S/N = 3). Due to high-density hot spots with easy operation, this proposed GO/Au nanocomposite-based SERS technique holds great potential in the application of food safety analysis and biomedical science.

Direct and Label-Free Detection of MicroRNA Cancer Biomarkers using SERS-Based Plasmonic Coupling Interference (PCI) Nanoprobes

MicroRNAs (miRNAs), small noncoding endogenous RNA molecules, are emerging as promising biomarkers for early detection of various diseases and cancers. Practical screening tools and strategies to detect these small molecules are urgently needed to facilitate the translation of miRNA biomarkers into clinical practice. In this study, a label-free biosensing technique based on surface-enhanced Raman scattering (SERS), referred to as plasmonic coupling interference (PCI), was applied for the multiplex detection of miRNA biomarkers. The sensing mechanism of the PCI technique relies on the formation of a nanonetwork consisting of nanoparticles with Raman labels located between adjacent nanoparticles that are interconnected by DNA duplexes. Because of the plasmonic coupling effect of adjacent nanoparticles in the nanonetwork, the Raman labels exhibit intense SERS signals. Such effect can be modulated by the addition of miRNA targets of interest that act as inhibitors to interfere with the formation of this nanonetwork, resulting in a diminished SERS signal. In this study, the PCI technique is theoretically analyzed, and the multiplex capability for detection of multiple miRNA cancer biomarkers is demonstrated, establishing the great potential of PCI nanoprobes as a useful diagnostic tool for medical applications.

Boosting the analytical properties of gold nanostars by single particle confinement into yolk porous silica shells

Herein we illustrate an effective protocol to boost the optical enhancing properties of gold nanostars. By coating single nanostars with a mesoporous silica layer of the appropriate size (yolk capsules), to localize them under optical microscopy, it is possible to enumerate single particles and design SERS quantitative methods with minute amounts of metallic particles.

Quantitative Evaluation of Surface-Enhanced Raman Scattering Nanoparticles for Intracellular pH Sensing at a Single Particle Level

Intracellular pH is one of the key factors for understanding various biological processes in biological cells. Plasmonic gold and silver nanoparticles (NPs) have been extensively studied for surface-enhanced Raman scattering (SERS) applications for pH sensing as a local pH probe in a living cell. However, the SERS performance of NPs depends on material, size, and shape, which can be controlled by chemical synthesis. Here, we synthesized 18 types of gold and silver NPs with different morphologies such as sphere, rod, flower, star, core/shell, hollow, octahedra, core/satellites, and chainlike aggregates, and quantitatively compared their SERS performance for pH sensing. The SERS intensity from the most commonly utilized SERS probe molecule ( para-mercaptobenzoic acid, p-MBA) for pH sensing was measured at the single nanoparticle level under the same measurement parameters such as low laser power (0.5 mW/μm²), short integration time (100 ms) at wavelengths of 405, 488, 532, 584, 676, and 785 nm. In our measurement, the Ag chain, Ag core/satellites, Ag@Au core/satellites, and Au core/satellites nanoassemblies showed efficient pH sensing at the single particle level. By using p-MBA-conjugated Au@Ag core/satellites, we performed time-lapse pH measurements during apoptosis of HeLa cells. These experimental results confirmed that the pH measurement using p-MBA-conjugated Au@Ag core/satellites can be applied for long-term measurements of intracellular pH during cellular events.

Gold-nanostar-based SERS substrates for studying protein aggregation processes

Aggregation of proteins has been related to some neurodegenerative diseases such as Alzheimer's and Parkinson's among others. Raman spectroscopy is a useful technique for the investigation of protein conformation and of changes in their secondary structure. In this study, a surface enhanced Raman spectroscopy (SERS) substrate based on the immobilization of plasmonic gold nanostars on a glass slide via silanization of the surface has been prepared and characterized. Gold nanostars were synthesized via a seed-growth method using gold nanoparticles as seeds obtained via stainless steel as the reducing agent. The plasmonic substrate provided an enhancement of 5.7 × 102 fold, as shown for the Raman signal of crystal violet. Using this SERS-active substrate, the investigation of aggregation processes of bovine serum albumin (BSA) and myoglobin proteins upon temperature and solvent modification has been enabled with enhanced sensitivity. Both curve fitting and deconvolution of the amide I band, as well as 2D correlation analysis, were employed for the evaluation of the changes in the SERS spectra of the protein samples. The amide I band within the SERS spectra of the BSA protein revealed a decrease in the α-helix structures within the secondary structure of the protein while the presence of β-sheet structures increased with temperature and solvent concentration.

Cell penetrating peptides in preclinical and clinical cancer diagnosis and therapy

Delivery of imaging reagents and drugs to tumors is essential for cancer diagnosis and therapy. In addition to therapeutic and diagnostic functionalities, peptides have potential benefits such as biocompatibility, ease to synthesize, smaller size, by-passing off-target side effects, and achieving the beneficial effects with lower-administered dosages. A particular type of peptide known as cell penetrating peptides (CPP) have been predominantly studied during last twenty years as they are not only capable to translocate themselves across membranes but also allow carrier drugs to translocate across plasma membrane, by different mechanisms depending on the CPP. This is of great potential importance in drug delivery systems, as the ability to pass across membranes is crucial to many drug delivery systems. In spite of significant progress in design and application of CPP, more investigations are required to further improve their delivery to tumors, with reduced side-effect and enhanced therapeutic efficacy. In this review, we emphasis on current advancements in preclinical and clinical trials based on using CPP for more efficient delivery of anti-cancer drugs and imaging reagents to cancer tissues and individual cells associated with them. We discuss the evolution of the CPPs-based strategies for targeted delivery, their current status and strengths, along with summarizing the role of CPPs in targeted drug delivery. We also discuss some recently reported diagnostic applications of engineered protease-responsive substrates and activable imaging complexes. We highlight the recent clinical trial data by providing a road map for better design of the CPPs for future preclinical and clinical applications.

Synthesis and SERS activity of super-multibranched AuAg nanostructure via silver coating-induced aggregation of nanostars

The super-multibranched AuAg bimetallic nanostructures are synthesized due to the aggregation of Au nanostars in the process of silver coating. The super-multibranched bimetallic nanostructures with different silver coating thickness are obtained by changing the concentration of silver nitrate and ascorbic acid. It has been found that the formation of these nanostructures is due to the stacking of several nanostars during the process of silver coating. By comparing the silver coating process of gold nanostars with different branch lengths, we found that the nanostars with longish branches are easy to aggregate and form the super-multibranched nanostructures in the process of silver coating. In the AuAg bimetallic nanostructures, the silver layer is mainly covered on the surface of the cores and the thickness increases with the increasing of the AgNO₃, which leads to the change of the surface-enhanced Raman scattering (SERS) activity. It has been found that the SERS activity is stronger when the silver layer is thin and the Au branches are still exposed to the outside of the Ag shell. The sample with the strongest SERS activity has been used to detect thiram with different concentrations. The Raman intensity increases linearly with the logarithmic concentration of thiram ranging from 10^-3 to 10^-7 M with a detection limit of 6.3 × 10^-7 M. These experimental results show that the super-multibranched bimetallic nanostructures have a broad application prospect in molecular detection and biologic sensing based on SERS.

Picoanalysis of Drugs in Biofluids with Quantitative Label-Free Surface-Enhanced Raman Spectroscopy

The enormous increase of Raman signal in the vicinity of metal nanoparticles allows surface-enhanced Raman spectroscopy (SERS) to be employed for label-free detection of substances at extremely low concentrations. However, the ultimate potential of label-free SERS to identify pharmaceutical compounds at low concentrations, especially in relation to biofluid sensing, is far from being fully realized. Opioids are a particular challenge for rapid clinical identification because their molecular structural similarities prevent their differentiation with immunolabeling approaches. In this paper, a new method called quantitative label-free SERS (QLF-SERS) which involves the formation of halide-conjugated gold nanoclusters trapping the analyte of interest near the SERS hot spots is reported, and it is demonstrated that it yields a 105 fold improvement in the detection limit over previously reported results for the entire class of clinically relevant opioids and their metabolites. Measurements of opioid concentrations in multicomponent mixtures are also demonstrated. QLF-SERS has comparable detection limits as currently existing laboratory urine drug testing techniques but is significantly faster and inexpensive and, therefore, can be easily adapted as part of a rapid clinical laboratory routine.

iSERS microscopy guided by wide field immunofluorescence: analysis of HER2 expression on normal and breast cancer FFPE tissue sections

Surface-enhanced Raman scattering (SERS) microscopy is an emerging imaging technique for tissue-based cancer diagnostics. Specifically, immuno-SERS (iSERS) microscopy employs antibodies labelled by molecularly functionalized noble metal colloids for antigen localization on tissue specimen. Spectrally resolved iSERS acquisition schemes are typically rather time-consuming when large tissue areas must be scanned. Here, we demonstrate the application of iSERS imaging guided by wide field immunofluorescence (IF) for localization of the human epidermal growth factor receptor 2 (HER2) on breast tissue sections. The addition of unlabelled anti-HER2 primary antibodies to the tissue is followed by the incubation with secondary antibodies labelled with both Alexa-647 (for IF) and hydrophilically stabilized gold nanostars coated with aromatic thiols (for iSERS). False-color iSERS images clearly reveal the different HER2 expression levels on normal and breast cancer tissue, respectively. A series of negative controls confirms that the binding specificity of the secondary antibody is maintained after conjugation to the SERS nanoparticles.

Plasmonic Au nanostar Raman probes coupling with highly ordered TiO2/Au nanotube arrays as the reliable SERS sensing platform for chronic myeloid leukemia drug evaluation

The accurate therapeutic evaluation for chronic myeloid leukemia (CML) drug is of great importance to minimize side effects and enhance efficacy. Herein, a facile and precise surface-enhanced scattering (SERS) approach based on coupled plasmonic field has been introduced to evaluate the therapeutic outcomes of antileukemia drug through ultrasensitive assay of caspase-3 activity in apoptotic cells. Caspase-3 as an apoptosis indicator could specifically cleave the N-terminus of biotinylated DEVD-peptide (biotin-Gly-Asp-Gly-Asp-Glu-Val-Asp-Gly-Cys) immobilized on the Au nanoparticle-decorated TiO₂ nanotube arrays (TiO₂/Au NTAs) substrate. After the enzyme cleavage with caspase-3, Raman-labelled Au nanostar (AuNS) probes captured the residual DEVD-peptides via the recognition between streptavidin and biotin, thus resulting in an enhanced Raman response on the SERS platform. The variation of Raman intensity revealed caspase-3 activity that reflected the chemotherapeutic effect. On this platform, AuNS nanoprobes offered a large number of binding sites and intrinsic "hot spots" for Raman reporters, while TiO₂/Au NTAs rendered a homogenously coupled electromagnetic field between the adjacent repeated units over the large area. In particular, a spatially expanding plasmonic field formed by coupling AuNSs with TiO₂/Au NTAs would further heighten Raman enhancement. Taking these advantages, the strong and uniform Raman signals were achieved. Furthermore, the practicability investigation witnessed that the proposed SERS strategy was available to evaluate the therapeutic effect of dasatinib on CML K562 cells. The developed method possesses fascinating advantages of cost-effectiveness, excellent reproducibility and high sensitivity, which endows it with promising potential in apoptosis monitoring and anticancer drug development.

Surface Enhanced Raman Spectroscopy (SERS) for the Multiplex Detection of Braf, Kras, and Pik3ca Mutations in Plasma of Colorectal Cancer Patients

In this paper, we discuss the use of a procedure based on polymerase chain reaction (PCR) and surface enhanced Raman spectroscopy (SERS) (PCR-SERS) to detect DNA mutations.

Methods: This method was implemented by first amplifying DNA-containing target mutations, then by annealing probes, and finally by applying SERS detection. The obtained SERS spectra were from a mixture of fluorescence tags labeled to complementary sequences on the mutant DNA. Then, the SERS spectra of multiple tags were decomposed to component tag spectra by multiple linear regression (MLR).

Results: The detection limit was 10^-11 M with a coefficient of determination (R²) of 0.88. To demonstrate the applicability of this process on real samples, the PCR-SERS method was applied on blood plasma taken from 49 colorectal cancer patients to detect six mutations located at the BRAF, KRAS, and PIK3CA genes. The mutation rates obtained by the PCR-SERS method were in concordance with previous research. Fisher's exact test showed that only two detected mutations at BRAF (V600E) and PIK3CA (E542K) were significantly positively correlated with right-sided colon cancer. No other clinical feature such as gender, age, cancer stage, or differentiation was correlated with mutation (V600E at BRAF, G12C, G12D, G12V, G13D at KRAS, and E542K at PIK3CA). Visually, a dendrogram drawn through hierarchical clustering analysis (HCA) supported the results of Fisher's exact test. The clusters drawn by all six mutations did not conform to the distributions of cancer stages, differentiation or cancer positions. However, the cluster drawn by the two mutations of V600E and E542K showed that all samples with those mutations belonged to the right-sided colon cancer group.

Conclusion: The suggested PCR-SERS method is multiplexed, flexible in probe design, easy to incorporate into existing PCR conditions, and was sensitive enough to detect mutations in blood plasma.

Ultrasensitive NIR-SERRS Probes with Multiplexed Ratiometric Quantification for In Vivo Antibody Leads Validation

Immunotargeting ability of antibodies may show significant difference between in vitro and in vivo. To select antibody leads with high affinity and specificity, it is necessary to perform in vivo validation of antibody candidates following in vitro antibody screening. Herein, a robust in vivo validation of anti-tetraspanin-8 antibody candidates against human colon cancer using ratiometric quantification method is reported. The validation is performed on a single mouse and analyzed by multiplexed surface-enhanced Raman scattering using ultrasensitive and near infrared (NIR)-active surface-enhanced resonance Raman scattering nanoprobes (NIR-SERRS dots). The NIR-SERRS dots are composed of NIR-active labels and Au/Ag hollow-shell assembled silica nanospheres. A 93% of NIR-SERRS dots is detectable at a single-particle level and signal intensity is 100-fold stronger than that from nonresonant molecule-labeled spherical Au NPs (80 nm). The result of SERRS-based antibody validation is comparable to that of the conventional method using single-photon-emission computed tomography. The NIR-SERRS-based strategy is an alternate validation method which provides cost-effective and accurate multiplexing measurements for antibody-based drug development.

Nanoplasmonic sensors for detecting circulating cancer biomarkers

The detection of cancer biomarkers represents an important aspect of cancer diagnosis and prognosis. Recently, the concept of liquid biopsy has been introduced whereby diagnosis and prognosis are performed by means of analyzing biological fluids obtained from patients to detect and quantify circulating cancer biomarkers. Unlike conventional biopsy whereby primary tumor cells are analyzed, liquid biopsy enables the detection of a wide variety of circulating cancer biomarkers, including microRNA (miRNA), circulating tumor DNA (ctDNA), proteins, exosomes and circulating tumor cells (CTCs). Among the various techniques that have been developed to detect circulating cancer biomarkers, nanoplasmonic sensors represent a promising measurement approach due to high sensitivity and specificity as well as ease of instrumentation and operation. In this review, we discuss the relevance and applicability of three different categories of nanoplasmonic sensing techniques, namely surface plasmon resonance (SPR), localized surface plasmon resonance (LSPR) and surface-enhanced Raman scattering (SERS), for the detection of different classes of circulating cancer biomarkers.

Gold nanostar-mediated neural activity control using plasmonic photothermal effects

Nanomaterials have emerged as an essential tool for the understanding of cellular level mechanism in the fields of biology and medical science. Recently, researchers have been studying the regulation of neuronal activity using plasmonic nanoparticles and light, and it has been reported that photothermal effects could lead to both excitation and inhibition of neuronal cells. So far, only a few photothermal transducers have been applied to modulate neural activity. In this paper, we synthesized biocompatible gold nanostars (AuNSs) which generate heat by absorbing near-infrared (NIR) light. And we used the AuNS to inhibit the activity of neurons through light stimulation. We have demonstrated that AuNS inhibits the neural activity by NIR laser in both chip-attached mode and cell-attached mode. We also confirmed the suppression of single neuron signal by using digital micromirror device (DMD) set up. This approach is possible to inhibit the neural firing by controlling the intensity of light, and overcome the disadvantages of conventional electrochemical stimulation methods. This method of NIR-mediated stimulating neurons using light sensitive AuNS will be a powerful tool for neuromodulation researches and neuroscience studies.

Rational Design of Ultrabright SERS Probes with Embedded Reporters for Bioimaging and Photothermal Therapy

Plasmonic nanoparticles can be utilized as surface-enhanced Raman scattering (SERS) probes for bioimaging and as photothermal (PT) agents for cancer therapy. Typically, their SERS and PT efficiencies reach maximal values under the on-resonant condition, when the excitation wavelength overlaps the localized surface plasmon resonance (LSPR) wavelength preferably in the near-infrared (NIR) biological window. However, the photogenerated heat may inevitably disturb or even destroy biological samples during the imaging process. Herein, we develop ultrabright SERS probes composed of metallic Au@Ag core-shell rodlike nanomatryoshkas (RNMs) with embedded Raman reporters. By rationally controlling the Ag shell thickness, the LSPR of RNMs can be tuned from UV to NIR range, resulting in highly tunable SERS and PT properties. As bright NIR SERS imaging nanoprobes, RNMs with a thick Ag shell are designed for minimal PT damage to the biological targets under the off-resonance condition, as illustrated through monitoring the changes in mitochondrial membrane potential of cancer cells during SERS imaging procedure. By contrast, RNMs with a thin Ag shell are designed as multifunctional NIR theranostic probes that combine enhanced photothermal therapy capability, as exemplified by efficient PT killing of cancer cells, with reduced yet still efficient imaging properties at the on-resonance excitation.

Indocyanine green-loaded gold nanostars for sensitive SERS imaging and subcellular monitoring of photothermal therapy

We have demonstrated that a typical nanothermometer was incorporated in a bovine serum albumin stabilized gold nanostar-indocyanine green (denoted as GNS-ICG-BSA) nanoprobe to realize surface-enhanced Raman scattering (SERS) imaging-based real-time sensitive monitoring of intracellular temperature in photothermal therapy (PTT), which significantly improved the spatial resolution compared to infrared thermal imaging. Herein, an exogenous thermosensitive molecule, ICG, acting as a tri-functional agent, was selected as the Raman reporter instead of direct cellular biochemical changes. The triggering of the obtained probe was unaffected by the cellular microenvironment, so it can act as a monitor of PTT in various cell types. High-resolution mass spectrometry (HRMS) was used to investigate the thermosensitive mechanism of ICG. The actively targeted GNS-ICG-BSA nanotags were used to induce SERS mapping-guided in vitro PTT of U87 glioma cells. Meanwhile, small temperature variations within a cell during PTT can be precisely monitored through the SERS fingerprint information, with a spatial resolution at the subcellular level and a sensitivity of 0.37 °C. Thus, the integrated GNS-ICG-BSA nanotags can be treated as a theranostic probe, a SERS imaging probe and an intracellular thermometer. Moreover, the good biocompatibility and the low cytotoxicity of GNS-ICG-BSA nanotags, together with their superior photothermal ablation effect on U87 glioma cells have been confirmed. This suggested that the implanted nanothermometry approach would be promising for a better understanding of the biological processes at subcellular level and provide new insights into the fabrication of a multifunctional nanoplatform. Furthermore, this study revealed that the SERS-based monitoring technique can offer great potential for theranostics as an emerging strategy.

Cancer imaging using surface-enhanced resonance Raman scattering nanoparticles

The unique spectral signatures and biologically inert compositions of surface-enhanced resonance Raman scattering (SERRS) nanoparticles make them promising contrast agents for in vivo cancer imaging. Our SERRS nanoparticles consist of a 60-nm gold nanoparticle core that is encapsulated in a 15-nm-thick silica shell wherein the resonant Raman reporter is embedded. Subtle aspects of their preparation can shift their limit of detection by orders of magnitude. In this protocol, we present the optimized, step-by-step procedure for generating reproducible SERRS nanoparticles with femtomolar (10^-15 M) limits of detection. We provide ways of characterizing the optical properties of SERRS nanoparticles using UV/VIS and Raman spectroscopy, and their physicochemical properties using transmission electron microscopy and nanoparticle tracking analysis. We introduce several applications of these nanoprobes for biomedical research, with a focus on intraoperative cancer imaging via Raman imaging. A detailed account is provided for successful i.v. administration of SERRS nanoparticles such that delineation of cancerous lesions can be achieved in vivo and ex vivo on resected tissues without the need for specific biomarker targeting. This straightforward, yet comprehensive, protocol-from initial de novo gold nanoparticle synthesis to SERRS nanoparticle contrast-enhanced preclinical Raman imaging in animal models-takes ∼96 h.

Raman Imaging in Cell Membranes, Lipid-Rich Organelles, and Lipid Bilayers

Raman-based optical imaging is a promising analytical tool for noninvasive, label-free chemical imaging of lipid bilayers and cellular membranes. Imaging using spontaneous Raman scattering suffers from a low intensity that hinders its use in some cellular applications. However, developments in coherent Raman imaging, surface-enhanced Raman imaging, and tip-enhanced Raman imaging have enabled video-rate imaging, excellent detection limits, and nanometer spatial resolution, respectively. After a brief introduction to these commonly used Raman imaging techniques for cell membrane studies, this review discusses selected applications of these modalities for chemical imaging of membrane proteins and lipids. Finally, recent developments in chemical tags for Raman imaging and their applications in the analysis of selected cell membrane components are summarized. Ongoing developments toward improving the temporal and spatial resolution of Raman imaging and small-molecule tags with strong Raman scattering cross sections continue to expand the utility of Raman imaging for diverse cell membrane studies.

Hydrophobic IR-780 Dye Encapsulated in cRGD-Conjugated Solid Lipid Nanoparticles for NIR Imaging-Guided Photothermal Therapy

This is high demand to enhance the accumulation of near-infrared theranostic agents in the tumor region, which is favorable to the effective phototherapy. Compared with indocyanine green (a clinically applied dye), IR-780 iodide possesses higher and more stable fluorescence intensity and can be utilized as an imaging-guided PTT agent with laser irradiation. However, lipophilicity and short circulation time limit its applications in cancer imaging and therapy. Moreover, solid lipid nanoparticles (SLNs) conjugated with c(RGDyK) was designed as efficient carriers to improve the targeted delivery of IR-780 to the tumors. The multifunctional cRGD-IR-780 SLNs exhibited a desirable monodispersity, preferable stability and significant targeting to cell lines overexpressing α_vβ₃ integrin. Additionally, the in vitro assays such as cell viability and in vivo PTT treatment denoted that U87MG cells or U87MG transplantation tumors could be eradicated by applying cRGD-IR-780 SLNs under laser irradiation. Therefore, the resultant cRGD-IR-780 SLNs may serve as a promising NIR imaging-guided targeting PTT agent for cancer therapy.

Tumor-triggered drug release from calcium carbonate-encapsulated gold nanostars for near-infrared photodynamic/photothermal combination antitumor therapy

Different stimulus including pH, light and temperature have been used for controlled drug release to prevent drug inactivation and minimize side-effects. Herein a novel nano-platform (GNS@CaCO₃/ICG) consisting of calcium carbonate-encapsulated gold nanostars loaded with ICG was established to couple the photothermal properties of gold nanostars (GNSs) and the photodynamic properties of indocyanine green (ICG) in the photodynamic/photothermal combination therapy (PDT/PTT). In this study, the calcium carbonate worked not only a drug keeper to entrap ICG on the surface of GNSs in the form of a stable aggregate which was protected from blood clearance, but also as the a pH-responder to achieve highly effective tumor-triggered drug release locally. The application of GNS@CaCO₃/ICG for in vitro and in vivo therapy achieved the combined antitumor effects upon the NIR irradiation, which was superior to the single PDT or PTT. Meanwhile, the distinct pH-triggered drug release performance of GNS@CaCO₃/ICG implemented the tumor-targeted NIR fluorescence imaging. In addition, we monitored the bio-distribution and excretion pathway of GNS@CaCO₃/ICG based on the NIR fluorescence from ICG and two-photon fluorescence and photoacoustic signal from GNSs, and the results proved that GNS@CaCO₃/ICG had a great ability for tumor-specific and tumor-triggered drug release. We therefore conclude that the GNS@CaCO₃/ICG holds great promise for clinical applications in anti-tumor therapy with tumor imaging or drug tracing.

Surface-Enhanced Raman Scattering-Based Immunoassay Technologies for Detection of Disease Biomarkers

Detection of biomarkers is of vital importance in disease detection, management, and monitoring of therapeutic efficacy. Extensive efforts have been devoted to the development of novel diagnostic methods that detect and quantify biomarkers with higher sensitivity and reliability, contributing to better disease diagnosis and prognosis. When it comes to such devastating diseases as cancer, these novel powerful methods allow for disease staging as well as detection of cancer at very early stages. Over the past decade, there have been some advances in the development of platforms for biomarker detection of diseases. The main focus has recently shifted to the development of simple and reliable diagnostic tests that are inexpensive, accurate, and can follow a patient’s disease progression and therapy response. The individualized approach in biomarker detection has been also emphasized with detection of multiple biomarkers in body fluids such as blood and urine. This review article covers the developments in Surface-Enhanced Raman Scattering (SERS) and related technologies with the primary focus on immunoassays. Limitations and advantages of the SERS-based immunoassay platform are discussed. The article thoroughly describes all components of the SERS immunoassay and highlights the superior capabilities of SERS readout strategy such as high sensitivity and simultaneous detection of a multitude of biomarkers. Finally, it introduces recently developed strategies for in vivo biomarker detection using SERS.

Synthesis of optically tunable bumpy silver nanoshells by changing the silica core size and their SERS activities

Size-tunable AgNSs with a broad extinction band are fabricated, all exhibit strong SERS activities at single-particle levels. The SERS activities of the AgNSs increased with reduced size and seemed to correlate with their roughness factors.