Near-infrared Surface Plasmon Resonance Research Articles

Theoretical Design of Near-Infrared Tunable Surface Plasmon Resonance Biosensors Based on Gate-Controlled Graphene Plasmons

A tunable near-infrared surface plasmon resonance (SPR) biosensor based on gate-controlled graphene plasmons is numerically investigated by using the finite element method (FEM) and the transfer matrix method (TMM). The novel properties of chemical potential sensing make the proposed sensor promising in the application of ultra-sensitive and highly specific biosensing technology. The sensitivity of chemical potential sensing in wavelength interrogation mode can be calculated to be 1.5, 1.89, 2.29, 3.21, 3.73 and 4.68 nm/meV, respectively, at the resonance wavelengths of 1100, 1200, 1310, 1550, 1700 and 1900 nm. The figure of merit (FOM) achieves 129.3, 101.1, 84.5, 67.7, 69.5 and 59.7 eV−1, respectively, at these resonance wavelengths. The sensitivity of chemical potential sensing in gate voltage interrogation mode also can be calculated to be 156.9822, 143.6147, 131.0779, 111.0351, 101.3415 and 90.6038 mV/meV, respectively, at the incident wavelengths of 1100, 1200, 1310, 1550, 1700 and 1900 nm. The FOM achieves 135.6, 103.0, 88.9, 62.2, 66.6 and 61.5 eV−1, respectively, at these incident wavelengths. Theoretical estimates suggest that the limit of detection (LOD) of the sensor’s DNA sensing can reach the level of femtomolar or even attomolar, comparable to and even lower than that of 2D nanomaterial-enhanced metal SPR sensors with AuNPs as a sensitivity enhancement strategy. The feasibility of preparation and operation of this new concept SPR biosensor is also analyzed and discussed.

Synthesis and Characterization of Silver-Plated Gold Nanostars for Biomedical and Sensing Applications

The physiochemical and optical characteristics of nanoscale colloids rely on their chemical composition, shape, and size. Gold nanostars are anisotropic multibranched nanoparticles with a central core and several sharp delicate tips, command significant attention in nanodiagnostic, imaging and sensing applications. Anisotropic nanoparticle’s shape, size and tips are of a great importance dominating their properties and performance in biomedical applications and sensing strategies which require optimization. Several factors can affect these features. In this regard, silver seed mediated goldnanostars were synthesized and characterized using different characterization techniques. Furthermore, the effect of the gold solution concentration on the morphology of the synthesized gold nanostars was investigated. Result indicated successful synthesis of gold nanostars with high yield and multiple sharp branches. EDX line scanning profile of the gold nanostars showed that there is a thin coating of silver in the shell of the nanostructures. Moreover, further analysis of TEM images of AuNSs in atomic scale resolution demonstrated that there are no dislocations and defects in the structure of the synthesized gold nanostars. Positive zeta potential of 42.3 mV confirmed good stability against aggregation in terms of charge stabilization. Synthesized anisotropic gold nanostars with near-infrared surface plasmon resonance in which tissue absorption and autofluorescence are minimized, can be used for multiple purposes on the biomedical field and sensing assays.

Realization of Al:ZnO (AZO)-Ag nanocomposite as a novel photocatalyst capable of broadband photon harnessing driven by near-infrared plasmonics

The rising level of environmental pollution is a global concern and towards its mitigation, infrared photocatalysis emerges as a new concept, as the solar radiation at the earth’s surface has over 50% energy distribution in the near infrared (NIR) region. Al-doped ZnO (AZO) is a non-toxic congener of indium tin oxide (ITO) as transparent conducting oxide (TCO). A TCO-metal framework is developed as AZO-Ag@AZO nanocomposite by pulsed DC/DC magnetron sputtering. The consequences of diverse process conditions, viz, doping level, sputtering pressure, deposition time, and Ag/AZO co-sputtering time are noteworthy as the morphological, compositional, optical, and electrical properties are critically dependent on the process conditions. The structural and compositional analyses confirm wurtzite AZO and f.c.c. Ag with nanosized crystalline domains. A series of photocatalysis experiments reveal the significance of NIR plasmonics of AZO, realized by nanostructuring and generating optimum electron density (∼1020 cm−3). Notably, the optimal degradation rate (95%) of R6G is attained with tailored AZO-Ag@AZO nanocomposite. The gravity of visible surface plasmon resonance (SPR) due to Ag nanocrystallites and electron-hole pair creation in AZO cannot be undermined due to the remarkable participation of energetic electrons, and holes in redox reactions in harmony with actions of NIR SPR driven lower energy electrons.

Highly sensitive detection of nucleocapsid protein from SARS-CoV-2 using a near-infrared surface plasmon resonance sensing system

We report a near-infrared surface plasmon resonance (SPR) system to achieve highly sensitive, unlabeled detection of the SARS-CoV-2 nucleocapsid protein antigen. Use of the near-infrared light in SPR makes the SPR dip of the angular spectrum sharp and causes a large change of the reflected light intensity at a fixed incident angle. The present SPR system achieves the resolution of 10−5 refractive index unit in the refractive index measurement of glycerol solution samples. Additionally, we measured the nucleocapsid protein antigen of SARS-CoV-2 down to a molar concentration of 1 fM by immobilizing its corresponding antibody on the SPR sensor surface. This demonstration indicates a high potential of the present system for highly sensitive biosensing in medical diagnostics.

Near-infrared surface plasmon resonance sensor with a graphene-gold surface architecture for ultra-sensitive biodetection

Binding behaviors of proteins are important for applications in the field of biochemistry. Though a standard assay has a favorable limit of detection (LOD), it is mainly limited to indirect observation via fluorescence labeling. We reported and demonstrated a novel label-free sensing approach based on a near-infrared (NIR) surface plasmon resonance (SPR) sensing chip modified with a graphene-gold surface architecture in this paper. The NIR excitation wavelength can greatly improve the sensitivity of SPR sensing derived from the wavelength modulation-based methodology. Moreover, benefiting from the excellent electro-optical properties of graphene in NIR range, the graphene-gold surface architecture was built to further improve the sensing sensitivity. Experimental results proved the superiority over most of those reported previously in terms of ultra-sensitivity (39,160 nm/RIU) and resolution (5.107 × 10−7 RIU). We detected human immunoglobulin G (IgG) to confirm the ability to enhanced-sensitive detection with a graphene overlayer. This sensor provides surface-specific detection schemes with a large linear dynamic range of ng/ml (pM) to fg/ml (aM) and a LOD of 7.2 fg/ml (48 aM) using gold nanoparticles (GNPs) as amplification labels. The proposed method provides a simple and effective strategy to improve sensitivity and LOD for biochemical detection in a rapid, ultrasensitive, and nondestructive manner.

Near-infrared tunable surface plasmon resonance sensors based on graphene plasmons via electrostatic gating control.

A tunable near-infrared surface plasmon resonance sensor based on graphene plasmons via electrostatic gating control is investigated theoretically. Instead of the traditional refractive index sensing, the sensor can respond sensitively to the change of the chemical potential in graphene caused by the attachment of the analyte molecules. This feature can be potentially used for biological sensing with high sensitivity and high specificity. Theoretical calculations show that the chemical potential sensing sensitivities under wavelength interrogation patterns are 1.5, 2.21, 3, 3.79, 4.64 nm meV−1 at different wavebands with centre wavelengths of 1100, 1310, 1550, 1700, 1900 nm respectively, and the full width half maximum (FWHM) is also evaluated to be 10, 25.5, 43, 55.5, 77 nm at these different wavebands respectively. It can be estimated that the theoretical limit of detection (LOD) in DNA sensing of the proposed sensor can reach the femtomolar level, several orders of magnitude superior to that of noble metal-based SPR sensors (nanomolar or subnanomolar scale), and is comparable to that of noble metal-based SPR sensors with graphene/Au-NPs as a sensitivity enhancement strategy. The FWHM is much smaller than that of the noble metal-based SPR sensors, making the proposed sensor have a potentially higher figure of merit (FOM). This work provides a new way of thinking to detect in an SPR manner the analyte that can cause chemical potential change in graphene and provides a beneficial complement to refractive index sensing SPR sensors.

Highly sensitive near-infrared surface plasmon resonance (SPR) sensor based on birefringent six-core photonic crystal fibre

A new type of highly sensitive near-infrared birefringent six-core photonic crystal fibre sensor using surface plasmon resonance (SPR) is proposed. By using the full-vector finite element method, the impacts of the fibre parameters on the wavelength sensitivity and amplitude sensitivity are numerically studied. The numerical results indicate that, benefiting from the high birefringent multi-core fibre structure, an average sensitivity of 8083 nm/refractive index unit (RIU) within the wavelength range from 1.532 to 2.02 µm is achieved when the analyte refractive index (RI) lies in (1.372, 1.432). Moreover, the maximum amplitude sensitivity is as high as 226 RIU−1 if the analyte RI is adjusted from 1.372 to 1.382. In consideration of its excellent sensing performance, the proposed SPR multi-core PCF sensor can be applied in environmental, food safety, and (bio)chemical detection.

Near-infrared surface plasmon resonance sensor based on photonic crystal fiber with big open rings

A photonic crystal fiber (PCF) sensor based on surface plasmon resonance (SPR) is designed for near-infrared detection. The Ag-Au dual layers are selected as the plasmonic materials and the silver layer is covered by a gold layer for protection against oxidation. Influences of structural parameters on the confinement losses are investigated by the finite element method (FEM). The resonance wavelength of the sensor varies from 1470 nm to 2150 nm and a maximum wavelength sensitivity of 12400 nm/RIU and corresponding resolution of 8.06×10−6 RIU are obtained for analyte refractive indexes between 1.22 and 1.36.

In Situ-Generated Volatile Precursor for CVD Growth of a Semimetallic 2D Dichalcogenide.

Semimetallic-layered transition-metal dichalcogenides, such as TiS2, can serve as a platform material for exploring novel physics modulated by dimensionality, as well as for developing versatile applications in electronics and thermoelectrics. However, controlled synthesis of ultrathin TiS2 in a dry-chemistry way has yet to be realized because of the high oxophilicity of active Ti precursors. Here, we report the ambient pressure chemical vapor deposition (CVD) method to grow large-size, highly crystalline two-dimensional (2D) TiS2 nanosheets through in situ generating titanium chloride as the gaseous precursor. The addition of NH4Cl promoter can react with Ti powders and switch the solid-phase sulfurization reaction into a CVD process, thus enabling the controllability over the size, shape, and thickness of the TiS2 nanosheets via tuning the synthesis conditions. Interestingly, this semimetallic 2D material exhibits near-infrared surface plasmon resonance absorption and a memristor-like electrical behavior, both holding promise for further application developments. Our method hence opens a new avenue for the CVD growth of 2D metal dichalcogenides directly from metal powders and pave the way for exploring their intriguing properties and applications.

Characterizing Single Polymeric and Protein Nanoparticles with Surface Plasmon Resonance Imaging Measurements.

Near-infrared surface plasmon resonance imaging (SPRI) microscopy is used to detect and characterize the adsorption of single polymeric and protein nanoparticles (PPNPs) onto chemically modified gold thin films in real time. The single-nanoparticle SPRI responses, Δ%RNP, from several hundred adsorbed nanoparticles are collected in a single SPRI adsorption measurement. Analysis of Δ%RNP frequency distribution histograms is used to provide information on the size, material content, and interparticle interactions of the PPNPs. Examples include the measurement of log-normal Δ%RNP distributions for mixtures of polystyrene nanoparticles, the quantitation of bioaffinity uptake into and aggregation of porous NIPAm-based (N-isopropylacrylamide) hydrogel nanoparticles specifically engineered to bind peptides and proteins, and the characterization of the negative single-nanoparticle SPRI response and log-normal Δ%RNP distributions obtained for three different types of genetically encoded gas-filled protein nanostructures derived from bacteria.

Modulation of Visible and Near-Infrared Surface Plasmon Resonance of Au Nanoparticles Based on Highly Doped Graphene

We study an active modulation of surface plasmon resonance (SPR) of Au nanoparticles based on highly doped graphene in visible and near-infrared regions. We find that compared to the traditional metal SPR, the SPR of Au nanoparticles based on graphene causes a remarkable blue shift. The field intensity in the gap is redistributed to standing wave. The field intensity of standing wave is about one order of magnitude higher than the traditional model. Moreover, the SPR of Au nanoparticles can be actively modulated by varying the graphene Fermi energy. We find the maximum modulation of field intensity of absorption spectra is more than 21.6 % at λ = 822 nm and the amount of blue shift is 17.4 nm, which is about 2.14 % of the initial wavelength λ 0 = 813.4 nm, with increasing monolayer graphene Fermi energy from 1.0 to 1.5 ev. We find that the SPR sensitivity to the refractive index n of the environment is about 642 nm per refractive index unit (RIU). The SPR wavelengths have a big blue shift, which is about 33 nm, with increasing number of graphene layers from 1 to 3, and some shoulders on the absorption spectra are observed in the models with multilayer graphene. Finally, we study the Au nanorod array based on monolayer graphene. We find that the blue shift caused by the graphene increases from 14 to 24 nm, with increasing gap g y from 10 to 20 nm. Then, it decreases from 24 to 14 nm, with increasing gap g y from 20 to 50 nm. This study provides a new way for actively modulating the optical and optoelectronic devices.

Numerical investigations of a near-infrared plasmonic refractive index sensor with extremely high figure of merit and low loss based on the hybrid plasmonic waveguide-nanocavity system.

With vertically slotted hybrid plasmonic waveguides (VSHPWs)-nanocavity system fabricated on the silicon-on-insulator platform, a near-infrared surface plasmon resonances (SPRs)-based refractive index (RI) sensor with extremely high figure of merit FOM = 224.3 and transmission efficiency T = 97.6% is proposed and investigated. Based on the finite element method, effective mode index behaviors together with spectral properties are calculated to analyze and optimize the sensing performance. Within near-infrared region, the wavelength sensitivity (S) and optical resolution (FWHM) can be achieved as S = 1817.5nm/RIU and FWHM = 7.4nm. A mechanism of synergy between propagating SPRs and localized SPRs is also presented for further improving the sensitivity (as high as 2647.5nm/RIU). In addition, the VSHPWs-based RI sensor can be fully realized by CMOS-compatible fabrication technology. In general, the high FOM, S and T achieved by our designed structure may have extensive applications in nanophotonic circuits, environmental monitoring and even pharmaceutical research.

Measuring melittin uptake into hydrogel nanoparticles with near-infrared single nanoparticle surface plasmon resonance microscopy.

This paper describes how changes in the refractive index of single hydrogel nanoparticles (HNPs) detected with near-infrared surface plasmon resonance microscopy (SPRM) can be used to monitor the uptake of therapeutic compounds for potential drug delivery applications. As a first example, SPRM is used to measure the specific uptake of the bioactive peptide melittin into N-isopropylacrylamide (NIPAm)-based HNPs. Point diffraction patterns in sequential real-time SPRM differential reflectivity images are counted to create digital adsorption binding curves of single 220 nm HNPs from picomolar nanoparticle solutions onto hydrophobic alkanethiol-modified gold surfaces. For each digital adsorption binding curve, the average single nanoparticle SPRM reflectivity response, ⟨Δ%RNP⟩, was measured. The value of ⟨Δ%RNP⟩ increased linearly from 1.04 ± 0.04 to 2.10 ± 0.10% when the melittin concentration in the HNP solution varied from zero to 2.5 μM. No change in the average HNP size in the presence of melittin is observed with dynamic light scattering measurements, and no increase in ⟨Δ%RNP⟩ is observed in the presence of either FLAG octapeptide or bovine serum albumin. Additional bulk fluorescence measurements of melittin uptake into HNPs are used to estimate that a 1% increase in ⟨Δ%RNP⟩ observed in SPRM corresponds to the incorporation of approximately 65000 molecules into each 220 nm HNP, corresponding to roughly 4% of its volume. The lowest detected amount of melittin loading into the 220 nm HNPs was an increase in ⟨Δ%RNP⟩ of 0.15%, corresponding to the absorption of 10000 molecules.

Key Factors Affecting the Reproducibility of Synthesis and Growth Mechanism of Near-Infrared Absorbing Hollow Gold Nanospheres

Hollow gold nanospheres (HGNs) with near-infrared (NIR) surface plasmon resonance (SPR) absorption are highly desired for many applications including photothermal ablation therapy (PTA) of cancer; however, they are challenging to synthesize at relevant resonant wavelengths in a reproducible manner. In this work, we have systematically varied the reaction parameters to determine the origin of the irreproducibility of synthesis. This allows for much finer control of the synthesis, including homogeneous NIR absorbing HGNs that were characterized using UV–vis spectroscopy and electron microscopy (EM) techniques. We have found that cobalt seed particle growth time plays a more critical role than previously realized and is one of the most important parameters for high synthetic reproducibility. The results also provide new insight into the mechanism of cobalt seed and HGN growth, which further aids the successful synthesis of high quality HGNs with strong and tunable NIR SPR absorption.

Sensing with Prism-Based Near-Infrared Surface Plasmon Resonance Spectroscopy on Nanohole Array Platforms

Nanohole arrays exhibit unique surface plasmon resonance (SPR) characteristics according to hole periodicity, diameter, and excitation wavelength (λ(SPR)). This contribution investigates the SPR characteristics and surface sensitivity of various nanohole arrays with the aim of tuning the parameters for optimal sensing capability. Both the Bragg surface plasmons (SPs) arising from diffraction by the periodic holes and the traditional propagating SPs are characterized with emphasis on sensing capability of the propagating SPs. Several trends in bulk sensitivity and penetration depth were established, and the surface sensitivity was calculated from bulk sensitivity and penetration depth of the SPs for different analyte thicknesses. Increased accuracy and precision in penetration depth values were achieved by incorporating adsorbate effects on substrate permittivity. The optimal nanohole array conditions for highest surface sensitivity were determined (820 nm periodicity, 0.27 diameter/periodicity, and λ(SPR) = 1550 nm), which demonstrated an increase in surface sensitivity for the 10 nm analyte over continuous gold films at their optimal λ(SPR) (1300 nm) and conventional visible λ(SPR) (700 nm).

Single-Nanoparticle Near-Infrared Surface Plasmon Resonance Microscopy for Real-Time Measurements of DNA Hybridization Adsorption

A novel 814 nm near-infrared surface plasmon resonance (SPR) microscope is used for the real-time detection of the sequence-selective hybridization adsorption of single DNA-functionalized gold nanoparticles. The objective-coupled, high numerical aperture SPR microscope is capable of imaging in situ the adsorption of single polystyrene and gold particles with diameters ranging from 450 to 20 nm onto a 90 μm × 70 μm area of a gold thin film with a time resolution of approximately 1-3 s. Initial real-time SPR imaging (SPRI) measurements were performed to detect the accumulation of 40 nm gold nanoparticles for 10 min onto a gold thin film functionalized with a 100% complementary DNA surface at concentrations from 5 pM to 100 fM by counting individual particle binding events. A 100% noncomplementary DNA surface exhibited virtually no nanoparticle adsorption. In contrast, in a second set of SPRI measurements, two component complementary/noncomplementary mixed DNA monolayers that contained a very small percentage of complementary sequences ranging from 0.1 to 0.001%, showed both permanent and transient hybridization adsorption of the gold nanoparticles that could be tracked both temporally and spatially with the SPR microscope. These experiments demonstrate that SPR imaging measurements of single biofunctionalized nanoparticles can be incorporated into bioaffinity biosensing methods at subpicomolar concentrations.

Metallic-like Stoichiometric Copper Sulfide Nanocrystals: Phase- and Shape-Selective Synthesis, Near-Infrared Surface Plasmon Resonance Properties, and Their Modeling

In the realm of semiconductor nanomaterials, a crystal lattice heavily doped with cation/anion vacancies or ionized atomic impurities is considered to be a general prerequisite to accommodating excess free carriers that can support localized surface plasmon resonance (LSPR). Here, we demonstrate a surfactant-assisted nonaqueous route to anisotropic copper sulfide nanocrystals, selectively trapped in the covellite phase, which can exhibit intense, size-tunable LSPR at near-infrared wavelengths despite their stoichiometric, undoped structure. Experimental extinction spectra are satisfactorily reproduced by theoretical calculations performed by the discrete dipole approximation method within the framework of the Drude-Sommerfeld model. The LSPR response of the nanocrystals and its geometry dependence are interpreted as arising from the inherent metallic-like character of covellite, allowed by a significant density of lattice-constitutional valence-band free holes. As a consequence of the unique electronic properties of the nanocrystals and of their monodispersity, coherent excitation of symmetric radial breathing modes is observed for the first time in transient absorption experiments at LSPR wavelengths.

Spectral Characteristics of Near-Infrared Surface Plasmon Resonance

Intrinsic properties of surface plasmons (SPs) excited with Kretschmann configuration were analyzed as a function of wavelength, including the propagation length, the penetration depth, the Goos–Hanchen (GH) shift, and the field enhancement. The calculated results indicate that there exists a critical thickness (tcr) of the gold layer and that the maximum GH shift occurring exactly at the SP resonance wavelength (λR) rapidly varies from positive to negative with changing of the gold layer thickness from t tcr. The maximum field enhancement happens not at λR but at a wavelength smaller than λR due to the phase retardation between the transmitted and reflected light. Simulations also reveal that a broadband collimated near-infrared beam can simultaneously excite two SPs with different responses to a refractive index (RI) change: the shorter-wavelength SP able to make a small redshift and the longer-wavelength SP capable of yielding a large blueshift. Only the shorter-wavelength SP was experimentally observed and its RI sensitivity was measured to increase from 3,539 nm/RIU at λR = 707.6 nm to 57,143 nm/RIU at λR = 1,398 nm. The SP at λR = 1,013 nm moved to λR = 1,029 nm in response to the saturation adsorption of bovine serum albumin, and the corresponding surface coverage was determined to be Γ = 1.565 ng/mm2 based on a quasilinear dependence of Γ on the resonance wavelength shift (∆λR) deduced theoretically. Butyrylcholinesterase adsorption from a dilute solution of 10 nM protein in phosphate buffer solution leads to a redshift of ∆λR = 10 nm, corresponding to Γ ≈ 0.97 ng/mm2.

Molecular mechanism of monodisperse colloidal tin-doped indium oxide nanocrystals by a hot-injection approach

Molecular mechanisms and precursor conversion pathways associated with the reactions that generate colloidal nanocrystals are crucial for the development of rational synthetic protocols. In this study, Fourier transform infrared spectroscopy technique was employed to explore the molecular mechanism associated with the formation of tin-doped indium oxide (ITO) nanocrystals. We found that the reaction pathways of the indium precursor were not consistent with simple ligand replacements proposed in the literature. The resulting understanding inspired us to design a hot-injection approach to separate the ligand replacements of indium acetate and the aminolysis processes, generating quality ITO nanocrystals with decent size distributions. The hot-injection approach was readily applied to the synthesis of ITO nanocrystals with a broad range of tin doping. Structural, chemical, and optical analyses revealed effective doping of Sn4+ ions into the host lattices, leading to characteristic and tunable near-infrared surface plasmon resonance peaks. The size control of ITO nanocrystals by multiple hot-injections of metal precursors was also demonstrated.

Well‐Defined Multibranched Gold with Surface Plasmon Resonance in Near‐Infrared Region from Seeding Growth Approach Using Gyroid Block Copolymer Template

Well-defined multibranched gold (Au) in polymers, both as bulk or continuous thin films, can be fabricated by using a nanoporous polymer with gyroid nanochannels as a template. The nanoporous polymer template is obtained from the self-assembly of a degradable block copolymer, polystyrene-b-poly (L-lactide) (PS-PLLA), followed by the hydrolysis of PLLA blocks. Templated seeding growth approach can be conducted to create precisely controlled nanostructured Au giving remarkable surface plasmon resonance (SPR) in (branched Au with uniform distribution in PS matrix) near-infrared (NIR) region. Controlled growth conditions allow the fabrication of three-dimensionally ordered nanoporous Au particles that possess NIR SPR. Double gyroid Au with dual networks in the PS matrix is obtained after completing the seeding growth at which the NIR SPR diminishes resulting from the reduction in the density of nanostructured edge.