Shift Of Surface Plasmon Resonance Research Articles

Highly sensitive visual colorimetric sensor for trichlorfon detection based on the inhibition of metallization of gold nanorods

In this study, a highly sensitive visual colorimetric sensor was designed for the detection of trichlorfon based on inhibiting ascorbate oxidase (AAO)-induced metallization of gold nanorods (Au NRs). Ascorbic acid (AA) can reduce silver ion (Ag+) to metal silver (Ag) that will be deposited on the surface of Au NRs, which results in the blue shift of longitudinal localized surface plasmon resonance (LSPR) peak of Au NRs, accompanying by perceptible color changes from red to cyan to red to yellow. In the presence of trichlorfon, the activity of AAO will be inhibited, resulting in less AA is hydrolyzed to dehydroascorbic acid (DHA), and therefore more Ag+ is reduced to Ag by AA. Under the optimized conditions, detection of trichlorfon has a wide linear range of 27.8–11111.1 μg/L with a limit of detection as low as 132.6 ng/L. Moreover, the sensor has a good sample spiked recovery (84.7–96.8%) for the determination of trichlorfon in lake water samples. The proposed method can achieve rapid analysis (about 10 min) of trichlorfon with simple operation when there are no other types of organophosphorus pesticides in the real samples.

Wide range tunability of surface plasmon resonance of nanostructured Ag deposited by off-axis magnetron sputtering

In this work, nanostructured Ag showing size distribution dependent tunable surface plasmon resonance (SPR) are grown on glass substrate using off-axis DC magnetron sputtering at a sputtering power of 74 W. Argon gas pressure is set at 8.0 Pa and the deposition time is varied in the range 5–300 s. The structural, morphological, and optical properties are examined by using X-ray diffractometer (XRD), field emission scanning electron microscope (FESEM), and UV–Visible spectrophotometer. XRD patterns of all samples reveal characteristic (111) and (200) peaks of fcc Ag. Broad XRD peaks suggest formation of nanosized Ag crystallites with mean crystallite size of 3 nm. FESEM images depict near spherical Ag grains up to 120 s deposition time and elongated grains with greater substrate coverage with extended deposition time of 300 s. SPR features are well distinct in the optical absorption spectra which are highly sensitive to the deposition time. Within a short deposition time of 5–60 s, nanostructured Ag demonstrates wide range SPR tunability from 438 nm to 530 nm. It is observed that the variations in the size distribution as estimated from FESEM images are crucial to observe systematic red shift of SPR with increasing deposition time. Nanosized Ag produced by off-axis magnetron sputtering may be used as a vital component in plasmonic devices and sensors.

Comprehensive study of -Alanine passivated colloidal gold nanoparticles and GNP-PVP thin films: Linear optical properties and very large nonlinear refractive index, absorption coefficient, third-order nonlinear susceptibility measurements and effect of passivation

We synthesized gold nanoparticles (GNPs) stabilized in various concentration of l-alanine by chemical reduction method. We measured NLO responses of GNPs when they are dispersed in the l-alanine stabilizer with 1, 2.5 and 5 mM concentrations and when they are implanted into the PVP matix, by using single beam Z- Scan technique with 632 nm He–Ne CW laser for excitation. GNPs exhibited blue shift in localised surface plasmon resonance (LSPR) peak with the l-alanine concentration. The fcc structured GNPs of reducing size with the stabilizer concentration were obtained and characterized by the TEM as well as XRD. The FTIR spectral investigation revealed the formation of strong bond between the surface of GNPs and the l-alanine functional groups and established that l-alanine is very good candidate for stabilization of MNPs. It was observed that these samples show very large nonlinear refractive index, absorption coefficient and third-order nonlinear susceptibility in the order of 10−8cm2W−1, 10−6 cmW−1 and 10−9esu respectively for colloidal suspension of GNPs, and for the GNP-PVP thin films these parameter values were found in the order of 10−6cm2W−1, 10−5cmW−1and 10−6esu respectively. The thermally stimulated, l-alanine concentration dependant, very large NLO responses attributed to the local field effect from Mie resonance and thermal lensing effect originated from thermo-optic phenomenon. The obtained results validate the influence of the stabilizer (l-alanine) on NLO properties.

Design of Gelatin-Capped Plasmonic-Diatomite Nanoparticles with Enhanced Galunisertib Loading Capacity for Drug Delivery Applications.

Inorganic diatomite nanoparticles (DNPs) have gained increasing interest as drug delivery systems due to their porous structure, long half-life, thermal and chemical stability. Gold nanoparticles (AuNPs) provide DNPs with intriguing optical features that can be engineered and optimized for sensing and drug delivery applications. In this work, we combine DNPs with gelatin stabilized AuNPs for the development of an optical platform for Galunisertib delivery. To improve the DNP loading capacity, the hybrid platform is capped with gelatin shells of increasing thicknesses. Here, for the first time, full optical modeling of the hybrid system is proposed to monitor both the gelatin generation, degradation, and consequent Galunisertib release by simple spectroscopic measurements. Indeed, the shell thickness is optically estimated as a function of the polymer concentration by exploiting the localized surface plasmon resonance shifts of AuNPs. We simultaneously prove the enhancement of the drug loading capacity of DNPs and that the theoretical modeling represents an efficient predictive tool to design polymer-coated nanocarriers.

A Novel Dual-Wavelength Method for Evaluating Temperature Effect in Fiber-Optic SPR Sensors

The temperature effect is one of the critical factors to induce the resonance wavelength shift in fiber-optic surface plasmon resonance (SPR) sensors, which leads to the inaccuracy measurement of refractive index (RI) in practical applications. In this study, a novel dual-wavelength method is presented for fiber-optic SPR sensors to measure the changes of RI and temperature simultaneously in real time. A typical model of an SPR-based fiber optical sensor is constructed for theoretical analysis of temperature effect. Both the thermo-optic effect in the fiber core and phonon–electron scattering along with electron–electron scattering in the metal layer are studied systematically in the theoretical model. The linear and independent relationship, about the dependence of defined output signals on the RI and temperature, is validated by a theoretical calculation in specific dual wavelengths. A proof-of-concept experiment is conducted to demonstrate the capability of the presented dual-wavelength technique. The experimental results indicate that the presented dual-wavelength method is technically feasible and can be applied for practical application. Since the presented method only depends on the full advantages of the transfer spectrum data, it can be applied directly to the conventional single-channel fiber-optic SPR without any specific design structure of the sensor probe. The proposed method provides a new way to detect the RI under different thermal conditions and could lead to a better design for the fiber-optic SPR sensors.

Thermoplasmonic Patterning of Silver Nanocrystal/Polymer Composite Thin Films

AbstractThe lithographic patterning of polymer films is ubiquitous in manufacturing processes. In this work, the high photothermal conversion efficiency utilizes plasmonic nanoparticles to locally pattern polystyrene films. Silver nanocubes on polystyrene thin films are used as a heat source for photothermal lithographic patterning using a continuous‐wave, visible laser. Distinct states of the nanocomposite defined by their own far‐field optical properties and microscale topography are observed. At low intensities the nanocubes can be embedded into the polymer at a nanometer scale displacement precision and produce a notable shift in the distinct localized surface plasmon resonance, enabling two‐color optical patterning. Numerical modelling indicates the temperatures reached in the film surpass polystyrene's glass transition temperature (Tg, ≈90 °C). At higher laser intensities sufficient temperatures are reached to achieve pronounced polymer film displacement enabling direct‐write lithography. Temperature estimates highlight the role of collective contribution of nanoparticle heating in the process. The process can be controlled by selecting excitation wavelengths to tune the power absorbed by the nanocubes in accordance with their plasmonic absorption spectrum. The approach here outlines a general method of 2D optical patterning utilizing thermoplasmonics, which can be further expanded to other materials, applications, and potentially to subdiffraction length scales.

Gold-embellished mixed-valence manganite as a smart, self-regulating magnetoplasmonic nanomaterial

In the present study, lanthanum-strontium manganite (LSM) particles were embellished with gold nanoparticles to create a magnetoplasmonic composite core-shell material enabling bimodal heating regimens upon exposure to an alternate current (AC) magnetic field and/or near-infrared (NIR) radiation. The composite particles were prepared by combined solid-state synthesis, mechanochemical processing and wet chemistry. The core crystals were round but faceted, often growing into an equilibrium shape conforming to the Wulff construction and the orthorhombic Pbnm crystal symmetry. They were also multi-domain but nanocrystalline, exhibiting superparamagnetic behavior as the result of evening the local anisotropies by the exchange interaction. The deposition of the gold nanoparticles onto the manganite core resulted in the red shift of the localized surface plasmon resonance due to interfacial effects. This deposition also improved the conditions for colloidal stability in water by increasing the surface charge density in the electric double layer surrounding the particles. The hybrid magnetoplasmonic particles were evaluated for their potential for use in cancer ablation therapies by measuring their aqueous heating dynamics in an ultralow AC magnetic field mimicking the magnetic hyperthermia (MH) condition of deep-seated tumors and the NIR light mimicking the photothermal (PT) condition. Aggregation of spherical, 5–10 nm sized gold nanoparticles on the surface of LSM enhanced their NIR light absorption capacity. The heating of the particle suspensions was more intense in the PT mode than in the MH mode, but the latter mode allowed for the display of the smart, thermostatic behavior by the material. Namely, the stoichiometry of the manganite phase, La0·76Sr0·24MnO3, was adjusted to display the Curie temperature at 45.8 °C after decoration with gold and the thermostatic effect at 43–44 °C, with a potential to prevent the overheating of tissues during the MH treatments of cancer. The bimodal heating potential endows the particles with the ability to be used in personalized cancer therapies. These therapies would be able to adjust in situ the ratio between the two heating modes, one more suitable for superficial ablation (PT) and another one for the treatment of deeper tumors (MH).

Simulation and Experimental Studies of Size Effects on Plasmonic Gas Sensing with Nanohole Arrays

Simulation and Experimental Studies of Size Effects on Plasmonic Gas Sensing with Nanohole Arrays

The Effect of Ag Concentration of Core-Shell Fe<sub>3</sub>O<sub>4</sub>@Ag Nanoparticles for Sensitivity Enhancement of Surface Plasmon Resonance (SPR) - Based Biosensor

The objective of this research is to advance the affectability of Surface Plasmon Resonance (SPR) biosensor utilizing core-shell Fe3O4@Ag nanoparticles (Fe3O4@Ag NPs) with a variation of Ag concentration (20, 40, 60, 80, 100) mM. Fe3O4@Ag NPs were synthesized by the aqueous solution method. The characterization by utilizing X-ray Diffractometer (XRD) depicts that the crystal structure of Fe3O4 compares to the cubic inverse spinel structure and based on Transmission Electron Microscopy (TEM) estimation, the particle size average of Fe3O4@Ag NPs is 14.45 nm. The magnetic properties of Fe3O4@Ag NPs were evaluated by Vibrating Sample Magnetometer (VSM), the result appears that the more concentration of Ag increases, the more remanent magnetization (Mr), saturation magnetization (Ms), and coercitivity field (Hc) diminishes. In this research, a Fe3O4@Ag NPs, a spherical nanoparticle consisting of a spherical Fe3O4 core covered by an Ag shell, was used as an active material to enhance the signal detection of SPR, with a wavelength of 632.8 nm in the Kretschmann configuration. The system consists of a four-layer material, i.e., prism/Au film/ Fe3O4@Ag NPs. The results show that the SPR angle shifted to the larger angle of incident light by using Fe3O4@Ag NPs. However, the effect of Ag concentration appears that the more concentration of Ag extends, the lower angle of SPR shifts. The addition of a core-shell in the conventional SPR-based biosensor leads to the enhancement of the SPR biosensor sensitivity if the fractional volume of the core-shell is large.

Au integrated 2D ZnO heterostructures as robust visible light photocatalysts

Integration of semiconducting nanostructures with noble metal nanoparticles are turning highly desirable for cost efficient energy and environmental related applications. From this viewpoint, we report on a facile aqueous synthesis of polymer capped gold (Au) nanoparticles on free standing 2D layered structures of zinc oxide (ZnO) to result with ZnO/Au nanocomposites. Concentration of Au nanoparticles were observed to promote the preferential growth of ZnO along the (002) wurtzite plane. The ZnO/Au structures and their morphological dissemination was noted to be of few. This flake like structure was also noted to be greatly influenced by the concentration of Au in the colloidal blend. Optical band edge transformations noted in the absorption spectra across the lower wavelength region and the shift in surface plasmon resonance (SPR) towards the red region of the visible spectrum signify the improved absorptivity of the heterostructures along the visible spectrum. These heterostructures exhibited remarkable visible light driven photocatalytic activity (99% efficiency) on par with pristine ZnO. The findings also attest this new class of composite structures to open up new openings in diversified solar energy conversion related functions.

Determination of pseudo-refractive index in self-assembled ligand layers from spectral shift of surface plasmon resonances in colloidal silver nanoplates

Abstract We examined systematically how self-assembled monolayers (SAMs) of different mercaptoacids affect the spectral shift of the localized surface plasmon resonance in silver nanoplates and nanospheres. We observed a clear trend in the magnitude of a redshift with a molecular length or the SAM thickness within a homologous series of aliphatic mercaptoacids: the thicker shell the stronger the red shift. Using classic Mie theory for plasmonic core-dielectric shell spheres and oblate spheroids we developed the method for determination of a pseudo-refractive index in SAM of different molecules and obtained a good correlation with the reference refractive indices for bulk long-chain aliphatic acids, but only in case of silver nanoplates. Calculations for silver core–shell nanospheres gave overestimated values of refractive index perhaps due to restrictions of Mie theory on the minimum particle size.

Coagulation-Inspired Direct Fibrinogen Assay Using Plasmonic Nanoparticles Functionalized with Red Blood Cell Membranes.

The fast measurement of fibrinogen is essential in evaluating life-threatening sepsis and cardiovascular diseases. Here, we aim to utilize biomimetic plasmonic Au nanoparticles using red blood cell membranes (RBCM-AuNPs) and demonstrate nanoscale coagulation-inspired fibrinogen detection via cross-linking between RBCM-AuNPs. The proposed biomimetic RBCM-AuNPs are highly suitable for fibrinogen detection because hemagglutination, occurring in the presence of fibrinogen, induces a shift in the localized surface plasmon resonance of the NPs. Specifically, when the two ends of the fibrinogen protein are bound to receptors on separate RBCM-AuNPs, cross-linking of the RBCM-AuNPs occurs, yielding a corresponding plasmon shift within 10 min. This coagulation-inspired fibrinogen detection method, with a low sample volume, high selectivity, and high speed, could facilitate the diagnosis of sepsis and cardiovascular diseases.

Understanding blue shift of the longitudinal surface plasmon resonance during growth of gold nanorods

We have investigated in detail the growth dynamics of gold nanorods with various aspect ratios in different surrounding environments. Surprisingly, a blue shift in the temporal evolution of colloidal gold nanorods in aqueous medium has been observed during the growth of nanorods by UV–visible absorption spectroscopy. The longitudinal surface plasmon resonance peak evolves as soon as the nanorods start to grow from spheres, and the system undergoes a blue shift in the absorption spectra. Although a red-shift is expected as a natural phenomenon during the growth process of all nano-systems, our blue shift observation is regarded as a consequence of competition between the parameters of growth solution and actual growth of nanorods. The growth of nanorods contributes to the red-shift which is hidden under the dominating contribution of the growth solution responsible for the observed massive blue shift.

Template-assisted Cu2O@Fe(OH)3 yolk-shell nanocages as biomimetic peroxidase: A multi-colorimetry and ratiometric fluorescence separated-type immunosensor for the detection of ochratoxin A

The convenient and effective detection of toxins is urgently demanded for food security and human health. Herein, based on the catalytic activity of mimetic peroxidase from the Cu2O@Fe(OH)3 yolk-shell nanocages, a dual-modal multi-colorimetric and ratiometric fluorescence immunosensor for the sensitive detection of ochratoxin A (OTA) was successfully developed. For the multi-colorimetric detection, H2O2 can be effectively decomposed by Cu2O@Fe(OH)3 to form ·OH groups, thus Au nanorods (Au NRs) can be etched to exhibit vivid color variations and localized surface plasmon resonance (LSPR) shifts. For the ratiometric fluorescence detection, o-phenylenediamine was oxidized by Cu2O@Fe(OH)3 to form 2,3-diaminophenazine (DAP) in the presence of H2O2. Interestingly, the exogenous fluorescence signal source of carbon dots can be quenched by DAP via inner filter effect, while a new emission peak at 563 nm can be discovered, forming a ratiometric fluorescence signal. Due to the independent signals and mutual confirmation, the performance of the dual-modal immunosensor for the detection of OTA was significantly improved, where a broad linear range from 1 ng/L to 10 μg/L with a detection limit of 0.56 ng/L (S/N = 3) was achieved. The sensing strategy was also used to monitor OTA in millet and lake water samples with a satisfied performance.

Au-Ag core-shell composite nanoparticles as a selective and sensitive plasmonic chemical probe for l-cysteine detection in Lens culinaris (lentils).

The present work reported is a simple and selective method for the colorimetrical detection of l-cysteine in Lens culinaris (or lentils) using Au–Ag core–shell (Au core Ag shell) composite nanoparticles as a chemical probe. The phenomenon is based on the color change of composite nanoparticles from yellowish brown to light blue, followed by a shift of the localized surface plasmon resonance (LSPR) absorption band in the UV-visible region (i.e., 200–800 nm) with the addition of l-cysteine into the solution of bimetallic nanoparticles. The mechanism for the detection of l-cysteine is based on the electrostatic interaction of the metal ion with the thiol group of the amino acid, which causes the red shift of the LSPR band at 685 nm. The size distribution, morphology, composition and optical properties of the Au–Ag core–shell composite nanoparticles were characterized by transmission electron microscopy (TEM), dynamic light scattering (DLS), energy dispersive X-ray diffraction (EDX), UV-visible spectrophotometer and Fourier transform infrared spectroscopy (FTIR) techniques. An excellent linearity range for the present method was observed in the range of 20–140 μg mL−1 with a limit of detection at 1.95 μg mL−1 and correlation coefficient (R2) of 0.986. A good% recovery of 4.0% showed the selectivity of the method for l-cysteine determination from sample matrices. The advantageous features of the present method are being simple, rapid, low cost and selectivity towards the determination of l-cysteine in lentils.

Localized surface plasmon resonance shift and its application in scanning near-field optical microscopy

Quantifiable information on refractive index changes due to surface chemistry, structure, and topography is accessibleviaplasmon-enhanced nanoscale imaging.

Spectroscopic investigation on the affinity of SARS-CoV-2 spike protein to gold nano-particles

The affinity of the SARS-CoV-2 spike protein (S protein) to gold nano-particles was examined through spectral shifts of SPR (Surface Plasmon Resonance) band. Gold nano-colloidal particles are sensitive to the conformational change of the protein adsorbed over the particles' surface. As the pH value was gradually lowered from approximately neutral pH to an acidic pH (ca. pH 2), all mixtures of S protein with the gold colloids ≥30 nm in diameter exhibited a drastic red-shift of the average SPR band peak at one pH value more than that observed for bare gold colloids. The surface coverage fraction (Θ) of S protein over the nano-particle's surface was extracted and all showed relatively small coverage values (i.e., Θ ~ 0.30). The SPR band peak shift was also examined as the pH values were hopped between pH ~ 3 and pH ~ 10 (pH hopping). As the pH values hopped, an alternation of the average SPR band peaks were observed. A significant amplitude of an alternation was especially observed for the mixture of S protein with gold ≥30 nm of gold size implying the reproduction of pH induced reversible protein folding. We hypothesize that the pH hopping scheme captured a reversible transition between folded or Down conformation (pH ≥ ~7) and unfolded or Up (pH ~ 3) conformation of RBD (receptor binding domain). The acidic condition may also dimerize the S protein through RBD. The Up conformation or dimerization of S protein are considered to be connected to the other gold nano particles forming gold nano-particle aggregates.

A photoelectrochemical/colorimetric immunosensor for broad-spectrum detection of ochratoxins using bifunctional copper oxide nanoflowers

Abstract The detection of ochratoxins is of great significance for rapid and accurate food safety screening. This work was aimed to design a photoelectrochemical/colorimetric immunosensor for the broad-spectrum detection of ochratoxin A (OTA), ochratoxin B (OTB) and ochratoxin C (OTC). In order to provide a comprehensive and accurate assessment of ochratoxins contamination, the broad spectrum antibodies were used as recognized elements and the bifunctional copper oxide nanoflowers (CuO NFs) were used as dual-signal probe to trigger the response of photoelectrochemical (PEC) and colorimetric detection. In PEC mode, Cu2+ released by CuO NFs can replace Cd2+ in photoactive material to form a new band gap, which accelerated the electron-hole recombination to change the PEC current. In colorimetric mode, Cu2+ efficiently assisted etching of Au nanorods (Au NRs), causing multiply color changes and localized surface plasmon resonance (LSPR) shifts of Au NRs. Two independent modes from different detection mechanisms were used to reflect the concentrations of ochratoxins with more accuracy and reliability. Therefore, this work not only realized the broad-spectrum detection of OTA, OTB and OTC, but also provided a new strategy for the development of accurate, visual and multi-signal immunosensing platform.

Gold nanorods assisted silver mirror reaction for consecutive color change based on-site visual semi-quantification of indoor formaldehyde

In the present study, a multicolor conversion strategy based on gold nanorods (AuNRs) assisted silver mirror reaction is developed for visual quantification of formaldehyde (HCHO). The method involves the silver deposition on the surface of AuNRs via the reduction reaction of Tollens' reagent in the presence of HCHO. The peak shifts of the longitudinal localized surface plasmon resonance (LSPR) and color variations of AuNRs solution are sensitive to the thickness of silver layer deposited on the surface of AuNRs. Under the optimized conditions, there is a good linear relationship between the peak shift and the concentration of HCHO (for both liquid sample and gas sample) in a wide range of concentration, thus an AuNRs based colorimetric assay for quantitative analysis of HCHO is established. Moreover, a series of consecutive color changes (from mauve to dusty blue, nattier blue, blue, mazarine blue, dark green, clay bank and finally orange red) responding to the presence and amount of HCHO enables visual semi-quantitative determination of HCHO within 15 min, and the clearly discernible dosage scale is as low as 0.10 μM. This assay exhibits desirable selectivity for HCHO over several common interfering organic molecular species and potential gas interferents, which has been successfully applied to measure the concentration of HCHO indoor.

Optimized Silica Shell Synthesis Surrounding Gold Nanorods for Enhanced Spectroscopies

We present a precise study for coating gold nanorods (GNRs) by a silica shell layer. Different parameters like pH, reaction time, and, most importantly, the ratio between the selected surfactant and the tetraethyl orthosilicate (TEOS) are studied and discussed. This latter is the key parameter to increase reproducibility, stability, reaction time, and the control of the targeted silica shell thickness. Moreover, the silica shell growth induces an optical shift of the localized surface plasmon resonance (LSPR) bands, which is explained by the change of the local refractive index. Both extinction spectroscopy and scanning electronic microscopy (SEM) are used to characterize the growth of the silica shell in time. Based on these results, it is thus possible to follow the growth process just by extinction spectroscopy, which ensures a rapid control of the reaction and makes it possible to stop it on time depending on the targeted shell thickness. Controlling the thickness is mandatory for further GNRs functionalization and surface plasmon enhanced spectroscopies.