Transmission Surface Plasmon Resonance Research Articles

Asymmetrical Absorption and Surface‐Enhanced Raman Scattering Enhancement by Silver Nanoflower Metasurface

A metasurface composed of silver nanoflower arrays, which exhibit asymmetrical absorption and surface‐enhanced Raman scattering (SERS) due to hybrid plasmonic effects, is reported. The silver nanoflowers are fabricated by oblique deposition of silver on a polymer nanohole array on a glass substrate, forming petal‐like semicontinuous thin films on the inner walls of the holes. Depending on the deposition angle, three‐ or five‐petal nanoflowers are obtained. The nanoflower arrays show strong reflection from the air side and broadband and wide‐angle absorption from the glass side, as a result of transmission surface plasmon resonance and localized surface plasmon resonance, respectively. The three‐petal structure, which absorbs most of the incident light from the glass side, induces a localized enhancement of electric field in the center of each nanohole, providing a high‐sensitivity SERS substrate. The SERS performance of the metasurface by direct measurement and near‐field simulation is demonstrated.

An axisymmetric metal and metal-oxide grating-structured self-reference fiber optic SPR sensor

An optical-fiber-based surface plasmon resonance (SPR) sensing probe consisting of axisymmetrical grating is proposed and studied theoretically for the detection of the refractive index (RI). The sensing probe is formed by depositing a plasmonic metal layer on a bare core of optical fiber, followed by an axisymmetric grating layer and an analyte. The grating consists of metal and metal oxide in an alternate manner. The proposed structure of a single channel provides two resonance modes in the transmission SPR spectra. It is found that the mode present at the lower wavelength remains fixed, and the mode present at the higher wavelength is varied when the RI of the analyte is varied, so that the previous one works as a reference mode while the latter one works as a sensing mode. These properties provide the self-referencing capability of the proposed RI sensor in ambient conditions. We have calculated the sensitivity, detection accuracy (DA) and signal to width ratio (SWR) using the SPR spectra of various probes of different combinations of plasmonic metal and metal-oxide gratings to enhance the study. The best performing probe is found to be Ag/Cu-ITO. This optimum probe attained a maximum SWR of 42, sensitivity of 5400 nm RIU−1 and DA of 0.08 nm−1 with the self-referencing capability. The optimum probe also works well for a dispersive analyte within the spectral range. The use of metal oxide provides better adsorption of the analyte as well as high sensitivity. The cumulative properties of self-referencing and the metal oxide of the designed probe make it accurate and useful for the detection of biological elements in the ambient atmosphere.

Combination of Capped Gold Nanoslit Array and Electrochemistry for Sensitive Aqueous Mercuric Ions Detection.

Label-free surface plasmon resonance (SPR) detection of mercuric ions in various aqueous solutions, using capped gold nanoslit arrays combined with electrochemical (EC) sensing technique, is demonstrated. The nanoslit arrays are fabricated on flexible cyclo-olefin polymer substrates by a nanoimprinting lithography method. The EC and SPR signals for the investigation of current responses and transmission SPR spectra are simultaneously measured during metal ions electrodeposition. Glycerol–water solution is studied to evaluate the resonant peak wavelength sensitivity (480.3 nm RIU−1) with a FOM of 40.0 RIU−1 and the obtained intensity sensitivity is 1819.9%. The ferrocyanide/ferricyanide redox couple performs the diffusion controlled electrochemical processes (R2 = 0.99). By investigating the SPR intensity changes and wavelength shifts of various mercuric ion concentrations, the optical properties are evaluated under chronoamperometric conditions. The sensors are evaluated in the detection range between 100 μM and 10 nM with a detection limit of 1 μM. The time dependence of SPR signals and the selectivity of 10 μM Hg2+ in the presence of 10 μM interfering metal ion species from Ca2+, Co2+, Ni2+, Na+, Cu2+, Pb2 + and Mn2+ are determined. The capped gold nanoslit arrays show the selectivity of Hg2+ and the EC sensing method is effectively utilized to aqueous Hg2+ detection. This study provides a label-free detection technique of mercuric ions and this developed system is potentially applicable to detecting chemicals and biomolecules.

Promising urinary miRNA biomarkers t-SPR profiling for urothelial cell carcinoma

An integrated transmission surface plasmon resonance platform with microfluidic sensor has a high potential to be a medical diagnostic tool. There has been extensive research into the potential use of transmission surface plasmon resonance, but here we demonstrate the practical application of transmission surface plasmon resonance to monitor and compare the urinary microRNA expression between the urothelial cell carcinoma patient group and the healthy control group. Furthermore, the expression levels are compared with the conventional real-time quantitative polymerase chain reaction method to verify the results. The relative expression of miR-21–3p and miR–214–3p have demonstrated to be upregulated in urothelial cell carcinoma patient group when measured using both real-time quantitative polymerase chain reaction and transmission surface plasmon resonance. Using receiver operating characteristics of miR-21–3p and miR-214–3p the area under curve reaches an excellent score of 0.99 and 0.917, respectively. Our work has demonstrated the ability of clinical application of transmission surface plasmon resonance as a rapid and cost effective point-of-care.

High-Sensitive Assay of Nucleic Acid Using Tetrahedral DNA Probes and DNA Concatamers with a Surface-Enhanced Raman Scattering/Surface Plasmon Resonance Dual-Mode Biosensor Based on a Silver Nanorod-Covered Silver Nanohole Array.

A novel surface-enhanced Raman scattering/surface plasmon resonance (SERS/SPR) dual-mode biosensor prepared on a silver nanorod-covered silver nanohole (Ag NR-NH) array by surface modification of tetrahedral DNA probes is proposed for highly sensitive detecting nucleic acids by a special signal amplification strategy of DNA supersandwich. The Ag NR-NH with a large area and uniformly arrayed nanostructure possesses excellent anisotropic extraordinary optical transmission and strong localized surface plasmon resonance, which lead to sensitive SPR response to the change of a local refractive index and strong localized electric fields for excellent SERS activity. To obtain high sensitivity and specificity, smart tetrahedral DNA probes are immobilized onto the Ag NR-NH array and the DNA supersandwich sensing strategy, including the signal amplification of DNA concatamers, is used. About 10 times signal enhancement for SPR and 4 times for SERS are achieved by this sensing strategy. In the detection of the target DNA in the human serum, the two sensing modes have complementary performances, i.e., the limit of detection for the SPR array is high (0.51 pM), while for SERS, it is low (0.77 fM), but the specificity for SPR is much higher than that of SERS. This improves the robustness of the DNA sensors, and subsequent recovery tests also confirm good reliability of the biosensor. The proposed SERS/SPR dual-mode biosensor has a great potential for high performance and reliable detection of trace disease-related nucleic acid biomarkers in the serum and is a powerful sensing platform for early-stage disease diagnosis.

Long-range surface plasmon resonance enhanced transmission of light through silver-coated Cytop gratings

In this study, transmission surface plasmon resonance (TSPR) signal of a silver-coated Cytop grating/glass slide substrate was investigated in combination with a hyperspectral imaging technique. The TSPR excitation peaks, corresponding to surface plasmon (SP) dispersion modes of +2 (−SP+2) and −1 (+SP−1), were simultaneously observed. The TSPR signal of −SP+2 mode at the visible light region was further enhanced by increasing Cytop thickness. A 2-time stronger in TSPR intensity of the developed substrate than that of conventional silver-coated polycarbonate grating substrate was observed. Since the structure of the substrate was the silver film bound by Cytop and water that had similar dielectric constants, this enhancement was due to a long-range SP resonance effect. TSPR hyperspectral image of developed substrate while injecting different concentrations of ethylene glycol solutions into a five-microchannel assembled to the substrate were recorded and TSPR hyperspectra were then plotted to acquire the sensitivity of this technique. This technique gave a sensitivity of 315.0 nm RIU−1. According to the sensitive changes of TSPR hyperspectral image to the refractive index of an environment, this technique showed high potential with respect to further development of sensing devices based TSPR imaging system.

Simultaneous detection of ammonia and humidity using transmission surface plasmon resonance technique

Gas sensing by using the transmission surface plasmon resonance (T-SPR) technique was demonstrated. Polyacrylic acid (PAA)/5-nm-thick gold/40-nm-thick silver/polycarbonate grating substrate structure (Sensor A) responded to ammonia; however, it exhibited a strong humidity dependence. Polyvinyl alcohol (PVA)/5-nm-thick gold/40-nm-thick silver/polycarbonate grating substrate structure (Sensor B) as the sensing material was also prepared and it mainly responded to humidity. The T-SPR properties of Sensors A and B were observed simultaneously by a stacking arrangement that enabled us to obtain the responses by using a single spectrophotometer. The ammonia concentration under various humidity conditions could be accurately obtained by simultaneous measurement of Sensors A and B.

Transmission surface plasmon resonance image detection by a smartphone camera

Abstract

Controlling Surface Plasmon Optical Transmission by Stretching a Silver-Coated Elastomeric Grating Substrate

In this study, transmission surface plasmon resonance (TSPR) of a silver-coated elastomeric grating substrate was tuned via mechanical stretching. The wavelengths of TSPR excitation peaks, corresponding to surface plasmon dispersion modes of + 1 and − 1, were simultaneously observed. The TSPR excitation wavelength was dramatically shifted up to 80 nm when the strain of the substrate reached 13.3%. The fine control of TSPR properties of the silver-coated elastomeric grating substrate has potential applications in mechanically tunable band pass filters, optical sensors, etc.

Surface Plasmon Resonance of A Bimetallic Nanostructured Film for Enhanced Optical Sensitivity

AbstractA bimetallic (Ag/Au) nanoslit film is reported on surface plasmon (SP) generation and refractive index (RI) sensitivity. These were compared to gold devices in transmission surface plasmon resonance (tSPR). The bimetallic films have a primary resonant peak that shifts with periodicity and correlates well with Finite‐Difference Time‐Domain (FDTD) simulation studies. The SPR of bimetallic nanoslit structures is analyzed via a semi‐analytical model. The model enables decomposition and quantitative analysis of SP generation at the aperture under plane‐wave illumination. The nanostructured, metallic, thin films provide flexibility to integrate with microfluidics, allowing for simplified instrumentation and alignment. Calculation and experimentation demonstrate that bimetallic films afford an increase in RI sensitivity due to the addition of silver along with the biocompatibility of gold. The Ag/Au films were found to be non‐diffusing, long‐term stable (over several months), and provided an increase in sensitivity (about 53/RIU) over gold equivalents.

Supercharging as a General Strategy for Making Proteins into Conformational Switches and their Use in Biosensing

Greatly increasing the magnitude of a protein's net charge using surface supercharging transforms that protein into a ligand-gated or counterion-gated conformational molecular switch. To demonstrate this we first modified the designed helical bundle hemoprotein H4 using simple molecular modeling to create a highly charged protein which both unfolds reversibly at low ionic strength and undergoes the ligand-induced folding transition commonly observed in signal transduction in biology. To demonstrate this process using more complex proteins, we then modified green fluorescent protein and the cytochrome B562, using a combination of simple modeling and electrostatic calculations to create proteins that unfold reversibly with decreasing ionic strength. These simple model systems allow us to derive and then experimentally validate a mass-action model for the coupled folding and binding behavior of ligand-gated conformational switches, establishing a set of engineering principles which can be used to convert natural and designed soluble proteins into molecular switches useful in biodesign and synthetic biology. We have applied these principles to a biosensing project in which supercharged IDPs are attached to nanostructured gold surfaces and conformational changes are sensed using surface plasmon resonance. An increase of the refractive index at the gold surface is caused by the ligand induced conformational change and can be detected via transmission surface plasmon resonance (SPR) spectroscopy. We calculate that the shift in the resonance wavelength of the surface plasmons is almost two orders of magnitude more than simple ligand binding to an already folded protein. Continuing SPR studies provide practical insight into the use of our model as conformational switches for biosensing devices.

Interfacial preparation and optical transmission surface plasmon resonance of Janus metamaterials membrane

Janus metamaterials membrane had been fabricated using self-assembly strategy at the oil/water interface with thiol-terminated polymers. Janus metamaterials membrane exhibits a characteristic surface plasmon absorption band, in which the peak position is sensitive to the addition of polymer. The optical transmission surface plasmon resonance (T-SPR) peak has a blue shift at the visible region with addition of thiol-terminated polystyrene (PS-SH). With thiol-terminated poly (ethylene glycol) (PEG-SH) attachment onto the surface side of gold nanoparticles (AuNPs), the T-SPR band has a successive blue shift. One surprising thing is that it has a flat terrace on T-SPR band from 580 to 740 nm. In addition, The T-SPR of Janus metamaterials membrane dramatically changed with the addition PS-SH when the PEG-SH was capped on the opposite side. The morphologies of AuNPs membrane and Janus metamaterials membrane support the above mentioned result of SPR. In virtue of tunable SPR band, the Janus metamaterials membrane has great potential application in science-based design of optical sensing sensors and surface-enhanced optic sensitive detection.

Multiplex detection of urinary miRNA biomarkers by transmission surface plasmon resonance.

The clinical assessment of short-stranded nucleic acid biomarkers such as miRNAs could potentially provide useful information for monitoring disease progression, prompting definitive treatment decisions. In the past decade, advancements in biosensing technology have led to a shift towards rapid, real-time and label-free detection systems; as such, surface plasmon resonance (SPR) biosensor-based technology has become of high interest. Here, we developed an automated multiplex transmissive surface plasmon resonance (t-SPR) platform with the use of a capped gold nanoslit integrated microfluidic surface plasmon resonance (SPR) biosensor. The automated platform was custom designed to allow the analysis of spectral measurements using wavelength shift (dλ), intensity (dI) and novel area change (dA) for surface binding reactions. A simple and compact nanostructure based biosensor was fabricated with multiplex real-time detection capabilities. The sensitivity and specificity of the microfluidic device was demonstrated through the use of functionalised AuNPs for target molecule isolation and signal enhancement in combination with probes on the CG nanoslit surface. Our work allows for the multiplex detection of miRNA at femtomolar concentrations in complex media such as urine.

Protein Trapping in Plasmonic Nanoslit and Nanoledge Cavities: The Behavior and Sensing.

A novel plasmonic nanoledge device was presented to explore the geometry-induced trapping of nanoscale biomolecules and examine a generation of surface plasmon resonance (SPR) for plasmonic sensing. To design an optimal plasmonic device, a semianalytical model was implemented for a quantitative analysis of SPR under plane-wave illumination and a finite-difference time-domain (FDTD) simulation was used to study the optical transmission and refractive index (RI) sensitivity. In addition, total internal reflection fluorescence (TIRF) imaging was used to visualize the migration of fluorescently labeled bovine serum albumin (BSA) into the nanoslits; and fluorescence correlation spectroscopy (FCS) was further used to investigate the diffusion of BSA in the nanoslits. Transmission SPR measurements of free prostate specific antigen (f-PSA), which is similar in size to BSA, were performed to validate the trapping of the molecules via specific binding reactions in the nanoledge cavities. The present study may facilitate further development of single nanomolecule detection and new nanomicrofluidic arrays for effective detection of multiple biomarkers in clinical biofluids.

Transmission surface plasmon resonance imaging of silver nanoprisms enhanced propagating surface plasmon resonance on a metallic grating structure

The localized surface plasmon resonance of in-plane dipole plasmon resonance of silver nanoprisms was used to facilitate transmission surface plasmon resonance (TSPR). The TSPR signal was detected by a camera coupled with liquid crystal tunable filters. This technique was further utilized for the multiple detection of hydrogen peroxide.

Microfluidic transmission surface plasmon resonance enhancement for biosensor applications

The microfluidic transmission surface plasmon resonance (MTSPR) constructed by assembling a gold-coated grating substrate with a microchannel was employed for biosensor application. The transmission surface plasmon resonance spectrum obtained from the MTSPR sensor chip showed a strong and narrow surface plasmon resonance (SPR) peak located between 650 and 800 nm. The maximum SPR excitation was observed at an incident angle of 35°. The MTSPR sensor chip was employed for glucose sensor application. Gold-coated grating substrates were functionalized using 3-mercapto-1-propanesulfonic acid sodium salt and subsequently functionalized using a five-bilayer poly(allylamine hydrochloride)/poly(sodium 4-styrenesulfonate) to facilitate the coupling/decoupling of the surface plasmon and to prepare a uniform surface for sensing. The detection limit of our developed system for glucose was 2.31 mM. This practical platform represents a high possibility of further developing several biomolecules, multiplex systems, and a point-of-care assay for practical biosensor applications.

Lectin binding studies on a glycopolymer brush flow-through biosensor by localized surface plasmon resonance.

A localized surface plasmon resonance biosensor in a flow-through configuration was applied for investigating kinetics of lectin binding to surface-grafted glycopolymer brushes. Polycarbonate filter membranes with pore sizes of 400nm were coated with a 114-nm thick gold layer and used as substrate for surface-initiated atom-transfer radical polymerization of a glycomonomer. These grafted from glycopolymer brushes were further modified with two subsequent enzymatic reactions on the surface to yield an immobilized trisaccharide presenting brush. Specific binding of lectins including Clostridium difficile toxin A receptor domain to the glycopolymer brush surface could be investigated in a microfluidic setup with flow-through of the analytes and transmission surface plasmon resonance spectroscopy. Graphical abstract Glycopolymer brushes serve as high affinity ligands for lectin and toxin interactions in a sensitive, disposable flow-through LSPR biosensor.

In Situ Study of Electropolymerized Poly(3-aminobenzoic acid) Thin Film on BD-R and DVD-R Grating Substrates by Electrochemical-Transmission Surface Plasmon Resonance Spectroscopy

The electropolymerization process and doping/dedoping properties of poly(3-aminobenzoic acid) (PABA) thin films on gold-coated commercial BD-R and DVD-R grating substrates were simultaneously studied by the combination of electrochemical technique and transmission surface plasmon resonance (TSPR) spectroscopy. The optical property as a function of the applied potentials and time dependence during electropolymerization were studied. The obtained TSPR wavelength scan spectra after electropolymerization showed that the maximum wavelength slightly shifted to longer wavelength indicating the increase of film thickness. In addition, the change during construction of PABA-based immunosensor for label-free detection of human immunoglobulin G can be observed.

The relationship between the diameter of chemically-functionalized multi-walled carbon nanotubes and their organ biodistribution profiles in vivo

Carbon nanotubes (CNTs) exhibit unique properties which have led to their applications in the biomedical field as novel delivery systems for diagnosis and therapy purposes. We have previously reported that the degree of functionalization of CNTs is a key factor determining their biological behaviour. The present study broadens the spectrum by investigating the impact of the diameter of CNTs using two series of multi-walled CNTs (MWNTs) with distinct differences in their diameters. Both MWNTs were doubly functionalized by 1,3-dipolar cycloaddition and amidation reactions, allowing the appended functional groups to be further conjugated with radionuclide chelating moieties and antibodies or antibody fragments. All constructs possessed comparable degree of functionalization and were characterized by thermogravimetric analysis, transmission electron microscopy, gel electrophoresis and surface plasmon resonance. The MWNT conjugates were radio-labelled with indium-111, which thereby enabled in vivo single photon emission computed tomography/computed tomography (SPECT/CT) imaging and organ biodistribution study using γ-scintigraphy. The narrow MWNTs (average diameter: 9.2 nm) demonstrated enhanced tissue affinity including non-reticular endothelial tissues compared to the wider MWNTs (average diameter: 39.5 nm). The results indicate that the higher aspect ratio of narrow MWNTs may be beneficial for their future biological applications due to higher tissue accumulation.

Label-free detection and molecular profiling of exosomes with a nano-plasmonic sensor.

Exosomes show potential for cancer diagnostics because they transport molecular contents of the cells from which they originate. Detection and molecular profiling of exosomes is technically challenging and often requires extensive sample purification and labeling. Here we describe a label-free, high-throughput approach for quantitative analysis of exosomes. Our nano-plasmonic exosome (nPLEX) assay is based on transmission surface plasmon resonance through periodic nanohole arrays. Each array is functionalized with antibodies to enable profiling of exosome surface proteins and proteins present in exosome lysates. We show that this approach offers improved sensitivity over previous methods, enables portable operation when integrated with miniaturized optics and allows retrieval of exosomes for further study. Using nPLEX to analyze ascites samples from ovarian cancer patients, we find that exosomes derived from ovarian cancer cells can be identified by their expression of CD24 and EpCAM, suggesting the potential of exosomes for diagnostics.