Highly sensitive immunoassay of lung cancer marker carcinoembryonic antigen using surface-enhanced Raman scattering of hollow gold nanospheres

Efficient electrochemiluminescence quenching of carbon-coated petalous CdS nanoparticles for an ultrasensitive tumor marker assay through coreactant consumption by G-quadruplex-hemin decorated Au nanorods

A novel competitive electrochemiluminescence aptasensor was designed for the detection of carcinoembryonic antigen using carbon-coated petalous CdS nanopaticles as an ECL emitter and DNAzyme/Au nanorods–complementary DNA as a quenching probe.

3D ordered silver nanoshells silica photonic crystal beads for multiplex encoded SERS bioassay

3D ordered silver nanoshell silica photonic crystal beads as a novel encoded surface enhanced Raman scattering substrate are proposed for the development of highly efficient multiplex bioassays.

Facile and sensitive detection of influenza viruses using SERS antibody probes

We report facile and sensitive influenza virus detection method using surface-enhanced Raman scattering antibody probes.

Surface Enhanced Raman Scattering Detection of Cancer Biomarkers with Bifunctional Nanocomposite Probes

This report describes new findings of an investigation of a bifunctional nanocomposite probe for the detection of cancer biomarkers, demonstrating the viability of magnetic focusing and SERS detection in a microfluidic platform. The nanocomposite probe consists of a magnetic nickel-iron core and a gold shell. Upon bioconjugation, the nanoprobes are magnetically focused on a specific spot in a microfluidic channel, enabling an enrichment of "hot spots" for surface enhanced Raman scattering detection of the targeted carcinoembryonic antigen. The detection sensitivity, with a limit of detection of ∼0.1 pM, is shown to scale with the magnetic focusing time and the nanoparticle size. The latter is also shown to exhibit an excellent agreement between the experimental data and the theoretical simulation. Implications of the findings to the development of rapid and sensitive microfluidic detection of cancer biomarkers are also discussed.

SERS immunoassay based on the capture and concentration of antigen-assembled gold nanoparticles

A simple, rapid, and sensitive immunoassay has been developed based on antigen-mediated aggregation of gold nanoparticles (AuNP) and surface-enhanced Raman spectroscopy (SERS). Central to this platform is the extrinsic Raman label (ERL), which consists of a gold nanoparticle modified with a mixed monolayer of a Raman active molecule and an antibody. ERLs are mixed with sample, and antigen induces the aggregation of the ERLs. A membrane filter is then used to isolate and concentrate the ERL aggregates for SERS analysis. Preliminary work to establish proof-of-principle of the platform technology utilized mouse IgG as a model antigen. The effects of membrane pore diameter and AuNP size on the analytical performance of the assay were systematically investigated, and it was determined that a pore diameter of 200 nm and AuNP diameter of 80 nm provide maximum sensitivity while minimizing signal from blank samples. Optimization of the assay provided a detection limit of 1.9 ng/mL, 20-fold better than the detection limit achieved by an ELISA employing the same antibody-antigen system. Furthermore, this assay required only 60 min compared to 24h for the ELISA. To validate this assay, mouse serum was directly analyzed to accurately quantify IgG. Collectively, these results demonstrate the potential advantages of this technology over current diagnostic tests for protein biomarkers with respect to time, simplicity, and detection limits. Thus, this approach provides a framework for prospective development of new and more powerful tools that can be designed for point-of-care diagnostic or point-of-need detection.

Ultra-sensitive immunoassay biosensors using hybrid plasmonic-biosilica nanostructured materials

We experimentally demonstrate an ultra-sensitive immunoassay biosensor using diatom biosilica with self-assembled plasmonic nanoparticles. As the nature-created photonic crystal structures, diatoms have been adopted to enhance surface plasmon resonances of metal nanoparticles on the surfaces of diatom frustules and to increase the sensitivity of surface-enhanced Raman scattering (SERS). In this study, a sandwich SERS immunoassay is developed based on the hybrid plasmonic-biosilica nanostructured materials that are functionalized with goat anti-mouse IgG. Our experimental results show that diatom frustules improve the detection limit of mouse IgG to 10 pg/mL, which is ˜100× better than conventional colloidal SERS sensors on flat glass. Ultra-sensitive immunoassay biosensor using diatom biosilica with self-assembled plasmonic nanoparticles.

Electric-Field Enhanced Molecule Detection in Suspension on Assembled Plasmonic Arrays by Raman Spectroscopy

One of the greatest challenges in surface enhanced Raman scattering (SERS) sensing is to detect biochemicals directly from suspension with ultrasensitivity. In this work, we employed strategically designed longitudinal nanocapsule structures with uniformly surface distributed Ag nanoparticles (Ag NPs) to dually focus and enhance SERS sensitivity of biochemicals in suspension assisted with electric fields. By tuning the reaction conditions, Ag NPs were synthesized and uniformly grown with optimized sizes and junctions on the surface of nanocapsules for well reproducible detection. The Ag NPs can further concentrate molecules from suspension due to induced electrokinetic effects in electric fields. As a result, the signals of Nile blue molecules can be enhanced by 34.4±3.1% at optimal alternating current (AC) frequencies and voltages compared to that without electric fields. This work demonstrates the dual roles of a new type of plasmonic NPs for molecule concentration and detection, which could inspire new Raman sensing devices for applications in microfluidics.

Direct identification of on-bead peptides using surface-enhanced Raman spectroscopic barcoding system for high-throughput bioanalysis

Recently, preparation and screening of compound libraries remain one of the most challenging tasks in drug discovery, biomarker detection, and biomolecular profiling processes. So far, several distinct encoding/decoding methods such as chemical encoding, graphical encoding, and optical encoding have been reported to identify those libraries. In this paper, a simple and efficient surface-enhanced Raman spectroscopic (SERS) barcoding method using highly sensitive SERS nanoparticles (SERS ID) is presented. The 44 kinds of SERS IDs were able to generate simple codes and could possibly generate more than one million kinds of codes by incorporating combinations of different SERS IDs. The barcoding method exhibited high stability and reliability under bioassay conditions. The SERS ID encoding based screening platform can identify the peptide ligand on the bead and also quantify its binding affinity for specific protein. We believe that our SERS barcoding technology is a promising method in the screening of one-bead-one-compound (OBOC) libraries for drug discovery.

Fast and sensitive detection of an anthrax biomarker using SERS-based solenoid microfluidic sensor

We report the application of a fully automated surface-enhanced Raman scattering (SERS)-based solenoid-embedded microfluidic device to the quantitative and sensitive detection of anthrax biomarker poly-γ-D-glutamic acid (PGA) in solution. Analysis is based on the competitive reaction between PGA and PGA-conjugated gold nanoparticles with anti-PGA-immobilized magnetic beads within a microfluidic environment. Magnetic immunocomplexes are trapped by yoke-type solenoids embedded within the device, and their SERS signals were directly measured and analyzed. To improve the accuracy of measurement process, external standard values for PGA-free serum were also measured through use of a control channel. This additional measurement greatly improves the reliability of the assay by minimizing the influence of extraneous experimental variables. The limit of detection (LOD) of PGA in serum, determined by our SERS-based microfluidic sensor, is estimated to be 100 pg/mL. We believe that the defined method represents a valuable analytical tool for the detection of anthrax-related aqueous samples.

Highly sensitive SERS-based immunoassay of aflatoxin B1 using silica-encapsulated hollow gold nanoparticles

Aflatoxin B1 (AFB1) is a well-known carcinogenic contaminant in foods. It is classified as an extremely hazardous compound because of its potential toxicity to the human nervous system. AFB1 has also been extensively used as a biochemical marker to evaluate the degree of food spoilage. In this study, a novel surface-enhanced Raman scattering (SERS)-based immunoassay platform using silica-encapsulated hollow gold nanoparticles (SEHGNs) and magnetic beads was developed for highly sensitive detection of AFB1. SEHGNs were used as highly stable SERS-encoding nano tags, and magnetic beads were used as supporting substrates for the high-density loading of immunocomplexes. Quantitative analysis of AFB1 was performed by monitoring the intensity change of the characteristic peaks of Raman reporter molecules. The limit of detection (LOD) of AFB1, determined by this SERS-based immunoassay, was determined to be 0.1 ng/mL. This method has some advantages over other analytical methods with respect to rapid analysis (less than 30 min), good selectivity, and reproducibility. The proposed method is expected to be a new analytical tool for the trace analysis of various mycotoxins.

Synthesis of magnetic Fe3O4–Au hybrids for sensitive SERS detection of cancer cells at low abundance

A facile and rapid SERS-based immunoassay for living cancer cells using magnetic Fe₃O₄–Au hybrid nanoparticles is reported.

Synthesis of micro sphere-like bismuth nanoparticles by microwave assisted polyol method; designing a novel electrochemical nanosensor for ultra-trace measurement of Pb2+ ions

Bi nanostructures were synthesized in the presence of propylene glycol as the solvent and surfactant through microwave method.

Fabrication of a SERS based aptasensor for detection of ricin B toxin

Poly(N-acryoyl-l-valine, AVAL) brushes were grafted onto a silicon substrateviaRAFT polymerization, and then ricin B aptamer was covalently conjugated to the poly(AVAL) brushes to recognize and detect ricin B toxinviaSERS-based sandwich assay.

Synthesis of novel gold mesoflowers as SERS tags for immunoassay with improved sensitivity

A new class of flowerlike gold mesostructure in high yield is successfully synthesized through a facile one-step route using ascorbic acid as a reducing agent of gold salt with cetyltrimethylammonium chloride (CTAC) as surfactant. The as-prepared Au particles have spherical profiles with an averaged diameter of 770 ± 50 nm, but showing a highly rough surface consisting of many irregular and randomly arranged protrusions. The Au mesoflowers exhibit strong surface-enhanced effects and near-infrared absorption which were utilized in the design of efficient surface-enhanced Raman scattering (SERS) tags as immunosensors for immunoassay with improved sensitivity. The experimental results indicate that a good linear relationship is found between the peak intensity at 1071 cm(-1) and the logarithm of H-IgG concentration in the range between 1 ng/mL and 1 fg/mL, and the limit of detection (LOD) is 1 fg/mL.

Electric field enhancement and far-field radiation pattern of the nanoantenna with concentric rings

The optical antennas have the potential in various applications because of their field enhancement and directivity control. The directivity of a dipole antenna can be improved by directivity-enhanced Raman scattering structure, which is a combination of a dipole antenna and a ring reflector layer on a ground plane. The concentric rings can collect the light into the center hole. Depending upon the geometry of the antenna inside the hole, different electric field enhancements can be achieved. In this paper, we propose to combine the concentric rings with the directivity-enhanced Raman scattering structure in order to study its electric field enhancement and the far-field radiation pattern by finite-difference time-domain simulations. Compared with the structure without the concentric rings over the ground plane, it is found that our proposed structure can obtain stronger electric field enhancements and narrower radiation beams because the gold rings can help to couple the light into the nanoantenna and they also scatter light into the far field and modify the far-field radiation pattern. The designed structures were fabricated and the chemical molecules of thiophenol were attached on the structures for surface-enhanced Raman scattering (SERS) measurements. The measured results show that the structure with concentric rings can have stronger SERS signals. The effects of the dielectric layer thickness in our proposed structure on the near-field enhancements and far-field radiation are also investigated. The proposed structure can be useful for several nanoantenna applications, such as sensing or detecting.

Surface-enhanced Raman scattering aptasensor for ultrasensitive trace analysis of bisphenol A

Surface-enhanced Raman scattering (SERS)-based aptasensor platform, using double strand DNA-embedded Au/Ag core-shell nanoparticles, has been developed for the ultrasensitive detection of bisphenol A (BPA) in water. By combining optimally controlled Au/Ag core-shell nanoparticles with the selective BPA binding characteristics of DNA aptamers, a highly sensitive limit of detection (LOD) of 10 fM could be achieved for BPA-spiked tap water over a wide concentration range from 100 nM to 10 fM. This LOD is two or three orders of magnitude lower than that reported for other BPA sensing techniques, and also yields a detection limit that is 100-1000 times lower than the US EPA-defined Predicted No Effect Concentration (PNEC) values in potable water. Total detection time is estimated to be about 40 min including the reaction between aptamer and BPA (30 min) and detection (10 min). This sensing platform is also suitable for field applications since measurement can be performed under aqueous colloidal conditions.

Assessment of tumor cells in a mouse model of diffuse infiltrative glioma by Raman spectroscopy

Glioma of infiltrative nature is challenging for surgeons to achieve tumor-specific and maximal resection. Raman spectroscopy provides structural information on the targeted materials as vibrational shifts. We utilized Raman spectroscopy to distinguish invasive tumors from normal tissues. Spectra obtained from replication-competent avian sarcoma-(RCAS-) based infiltrative glioma cells and glioma tissues (resembling low-grade human glioma) were compared with those obtained from normal mouse astrocytes and normal tissues. In cell analysis, the spectra at 950-1000, 1030, 1050-1100, 1120-1130, 1120-1200, 1200-1300, 1300-1350, and 1450 cm(-1) were significantly higher in infiltrative glioma cells than in normal astrocytes. In brain tissue analysis, the spectra at 1030, 1050-1100, and 1200-1300 cm(-1) were significantly higher in infiltrative glioma tissues than in normal brain tissues. These spectra reflect the structures of proteins, lipids, and DNA content. The sensitivity and specificity to predict glioma cells by distinguishing normal cells were 98.3% and 75.0%, respectively. Principal component analysis elucidated the significance of spectral difference between tumor tissues and normal tissues. It is possible to distinguish invasive tumors from normal tissues by using Raman spectroscopy.

Detecting endotoxin with a flow cytometry-based magnetic aptasensor

Endotoxin, which is also known as lipopolysaccharide (LPS), is a marker for intruding gram-negative pathogens. It is essential to detect endotoxin quickly and sensitively in a complex milieu. A new flow cytometry (FCM)-based magnetic aptasensor assay that employs two endotoxin-binding aptamers and magnetic beads has been developed to detect endotoxin. The endotoxin-conjugated sandwich complex on magnetic beads was observed by scanning confocal laser microscopy. The resulting magnetic aptasensor rapidly detected (<1 min) endotoxin within a broad dynamic detection range of 10(-8) to 10(0)mg/ml in the presence of bovine serum albumin (BSA), RNA, sucrose, and glucose, which are most likely to coexist with endotoxin in the majority of biological liquids. Only 2 μl of magnetic aptasensor was required to quantify the endotoxin solution. Furthermore, the magnetic aptasensor could be regenerated seven times and still presented an outstanding response to the endotoxin solution. Therefore, the magnetic aptasensor exhibited high sensitivity, selectivity, and reproducibility, thereby serving as a powerful tool for the quality control and high-throughput detection of endotoxin in the food and pharmaceutical industries.

Highly sensitive detection of zearalenone in feed samples using competitive surface-enhanced Raman scattering immunoassay

Accurate and quantitative analysis of mycotoxin (such as zearalenone) is particularly imperative in the field of food safety and animal husbandry. Here, we develop a sensitive and specific method for zearalenone detection using competitive surface-enhanced Raman scattering (SERS) immunoassay. In this assay, a functional gold nanoparticle was labeled with the Raman reporter and the zearalenone antibody, and a modified substrate was assembled with the zearalenone-bovine serum albumin. With the addition of free zearalenone, the competitive immune reaction between free zearalenone and zearalenone-bovine serum albumin was initiated for binding with zearalenone antibody labeled on gold nanoparticle, resulting in the change of SERS signal intensity. The proposed method exhibits high sensitivity with a detection limit of 1 pg/mL and a wide dynamic range from 1 to 1000 pg/mL. Furthermore, this method can be further applied to analyze the multiple natural feed samples contaminated with zearalenone, holding great potential for real sample detection.

Effect of hydration on plasmonic coupling of bioconjugated gold nanoparticles immobilized on a gold film probed by surface-enhanced Raman spectroscopy

Gold nanoparticle (AuNP)-Au film constructs were prepared using antibody-antigen interactions or a small organic cross-linker to systematically control the gap between the AuNP and Au film. Surface-enhanced Raman spectroscopy (SERS), scanning electron micrsocopy (SEM), and atomic force microscopy (AFM) were used to characterize each construct and elucidate structure-activity relationships. Interestingly, plasmonic coupling and SERS intensity were reversibly modulated with wetting/drying cycles for the protein immobilized AuNP, and this effect was attributed to changes in protein size with hydration state. This work provides insight into fundamental limitations of AuNP-enabled SERS bioassays and will facilitate rational design of novel biospecific ligands that maximize SERS sensitivity.

One-step synthesis of silver nanoshells with bumps for highly sensitive near-IR SERS nanoprobes

A seedless, one-step synthetic route to uniform bumpy silver nanoshells (AgNSs) as highly NIR sensitive SERS substrates is reported. These substrates can incorporate Raman label compounds and biocompatible polymers on their surface. AgNS based NIR-SERS probes are successfully applied to cell tracking in a live animal using a portable Raman system.

Label-free blood plasma test based on surface-enhanced Raman scattering for tumor stages detection in nasopharyngeal cancer

This study aims to evaluate the feasibility of a label-free nanobiosensor based on blood plasma surface-enhanced Raman spectroscopy (SERS) method for exploring variability of different tumor (T) stages in nasopharyngeal cancer (NPC). Au nanoparticles as the SERS-active nanostructures were directly mixed with human blood plasma to enhance the Raman scattering signals. High quality SERS spectra can be acquired from blood plasma samples belong to 60 healthy volunteers, 25 NPC patients with T1 stage and 75 NPC patients with T2-T4 stage. A diagnostic accuracy of 83.5% and 93.3%, respectively, can be achieved for classification between early T (T1) stage cancer and normal; and advanced T (T2-T4) stage cancer and normal blood groups. This exploratory study demonstrates that the nanobiosensor based on SERS technique in conjunction with PCA-LDA has great potential as a clinical complement for different T stages detection in nasopharyngeal cancer.

Au dotted magnetic network nanostructure and its application for on-site monitoring femtomolar level pesticide

A novel magnetically responsive and surface-enhanced Raman spectroscopy (SERS) active nanocomposite is designed and prepared by direct grafting of Au nanoparticles onto the surface of magnetic network nanostructure (MNN) with the help of a nontoxic and environmentally friendly reagent of inositol hexakisphosphate shortly named as IP6. The presence of IP6 as a stabilizer and a bridging agent could weave Fe3O4 nanoparticles (NPs) into magnetic network nanostructure, which is easily dotted with Au nanoparticles (Au NPs). It has been shown firstly that the huge Raman enhancement of Au-MNN is reached by an external magnetic collection. Au-MNN presenting the large surface and high detection sensitivity enables it to exhibit multifunctional applications involving sufficient adsorption of dissolved chemical species for enrichment, separation, as well as a Raman amplifier for the analysis of trace pesticide residues at femtomolar level by a portable Raman spectrometer. Therefore, such multifunctional nanocomposites can be developed as a smart and promising nanosystem that integrates SERS approach with an easy assay for concentration by an external magnet for the effective on-site assessments of agricultural and environmental safety.

Vibrational spectroscopy of biofluids for disease screening or diagnosis: translation from the laboratory to a clinical setting

There remains a need for objective and cost-effective approaches capable of diagnosing early-stage disease in point-of-care clinical settings. Given an increasingly ageing population resulting in a rising prevalence of chronic diseases, the need for screening to facilitate the personalising of therapies to prevent or slow down pathology development will increase. Such a tool needs to be robust but simple enough to be implemented into clinical practice. There is interest in extracting biomarkers from biofluids (e.g., plasma or serum); techniques based on vibrational spectroscopy provide an option. Sample preparation is minimal, techniques involved are relatively low-cost, and data frameworks are available. This review explores the evidence supporting the applicability of vibrational spectroscopy to generate spectral biomarkers of disease in biofluids. We extend the inter-disciplinary nature of this approach to hypothesise a microfluidic platform that could allow such measurements. With an appropriate lightsource, such engineering could revolutionize screening in the 21(st) century.

Capillary-driven surface-enhanced Raman scattering (SERS)-based microfluidic chip for abrin detection

Herein, we firstly demonstrate the design and the proof-of-concept use of a capillary-driven surface-enhanced Raman scattering (SERS)-based microfluidic chip for abrin detection. The micropillar array substrate was etched and coated with a gold film by microelectromechanical systems (MEMS) process to integrate into a lateral flow test strip. The detection of abrin solutions of various concentrations was performed by the as-prepared microfluidic chip. It was shown that the correlation between the abrin concentration and SERS signal was found to be linear within the range of 0.1 ng/mL to 1 μg/mL with a limit of detection of 0.1 ng/mL. Our microfluidic chip design enhanced the operability of SERS-based immunodiagnostic techniques, significantly reducing the complication and cost of preparation as compared to previous SERS-based works. Meanwhile, this design proved the superiority to conventional lateral flow test strips in respect of both sensitivity and quantitation and showed great potential in the diagnosis and treatment for abrin poisoning as well as on-site screening of abrin-spiked materials.

Emerging advances in nanomedicine with engineered gold nanostructures

Gold nanostructures possess unique characteristics that enable their use as contrast agents, as therapeutic entities, and as scaffolds to adhere functional molecules, therapeutic cargo, and targeting ligands. Due to their ease of synthesis, straightforward surface functionalization, and non-toxicity, gold nanostructures have emerged as powerful nanoagents for cancer detection and treatment. This comprehensive review summarizes the progress made in nanomedicine with gold nanostructures (1) as probes for various bioimaging techniques including dark-field, one-photon and two-photon fluorescence, photothermal optical coherence tomography, photoacoustic tomography, positron emission tomography, and surface-enhanced Raman scattering based imaging, (2) as therapeutic components for photothermal therapy, gene and drug delivery, and radiofrequency ablation, and (3) as a theranostic platform to simultaneously achieve both cancer detection and treatment. Distinct from other published reviews, this article also discusses the recent advances of gold nanostructures as contrast agents and therapeutic actuators for inflammatory diseases including atherosclerotic plaque and arthritis. For each of the topics discussed above, the fundamental principles and progress made in the past five years are discussed. The review concludes with a detailed future outlook discussing the challenges in using gold nanostructures, cellular trafficking, and translational considerations that are imperative for rapid clinical viability of plasmonic nanostructures, as well as the significance of emerging technologies such as Fano resonant gold nanostructures in nanomedicine.

Using well-defined Ag nanocubes as substrates to quantify the spatial resolution and penetration depth of surface-enhanced Raman scattering imaging

The multiplexing capability and high sensitivity of surface-enhanced Raman scattering (SERS) make this new imaging modality particularly attractive for rapid diagnosis. With 100 nm Ag nanocubes serving as the substrate, this work quantitatively evaluated, for the first time, some of the fundamental parameters of SERS imaging such as blur, spatial resolution and penetration depth. Our results imply that SERS is a high-resolution imaging technique with a blur value of 0.5 μm that is lower than many traditional modalities such as mammography. The spatial resolution was measured to be 1.1 μm, suggesting that SERS images could be collected effectively by adjusting the imaging step size to the same length scale, or no more than 2 μm. The major drawback of SERS imaging is its penetration depth, which is limited by the scattering and absorption of tissues. We demonstrated that enhancement of signal caused by aggregation of multiple nanoparticles could help overcome this potential road-block to in vivo imaging.

Nanoslit membrane-integrated fluidic chip for protein detection based on size-dependent particle trapping

This paper describes the fabrication of a nanoslit membrane-integrated fluidic chip (Nanoslit-Chip) used for trapping and concentrating micro-/nano-particles of desired size and its application in detecting biological molecules based on target-induced particle aggregation. To trap particles of a specific size, a large scale uniform sized nanoslit fluid channel array is fabricated on a silicon dioxide membrane. A small number of fluorescence labeled particles in a large volume of solution are concentrated into a monolayer of particles in a small nanoslit membrane, which enables us to effectively quantify them via fluorescence intensity. In addition, the particles of desired size (1.8 μm) are readily separated from the mixture of particles with a different size (450 nm) in Nanoslit-Chip size, and then quantified via fluorescence measurements. Finally, the Nanoslit-Chip is successfully applied to the sensitive detection of proteins by target-induced particle aggregation, trapping, and quantification. This shows its potential as a biological and clinical device for quantitative and sensitive detection of biological molecules.