Localized Surface Plasmon Resonance Spectra Research Articles

Synthesis of carbon quantum dots from waste Phaseolus vulgaris for the development of a fluorescence sensing probe to detect plasticizer in cookies

Dibutyl phthalate (DBP) is a commonly used plasticizer in the fabrication of various packaging materials, however upon exposure, it poses significant health and environmental hazards. These plasticizers consist of low-molecular-weight components, which permeate easily into the food matrix. Hence, the development of a cost-effective detection technique is necessary for the detection and monitoring of DBP. Therefore, this research focuses on the utilization of broken Phaseolus vulgaris-derived carbon quantum dots (PV-CQDs) as a fluorescent probe for the detection of DBP in cookies. Herein, PV-CQDs were synthesized through a hydrothermal reaction, which exhibited a blue color under UV-luminescence and localized surface plasmon resonance spectrum at 238 and 270 nm. The highest fluorescence emission intensity was recorded at 428 nm. The resulting PV-CQDs exhibited an average particle size of 1.22 ± 0.05 nm and prominent peaks obtained during infrared spectroscopy were found to be of carboxylic and hydroxyl functional groups, respectively. Transmission electron microscopy and energy dispersive spectroscopy analyses confirmed the spherical morphology and elemental composition, which include C (58.05% by weight) and O (41.92% by weight), respectively. The topographical height profile of the PV-CQDs was observed by atomic force microscopy and it was found to be approximately 100 µm with a thickness of 2.9 µm . The inherent fluorescence of CQDs demonstrated notable quenching efficiency when exposed to varying concentrations of 0.1, 0.2, 0.3, 0.4, 0.5, 1, 5, and 10 µM of DBP residue, resulting in a linear relationship with a high detection sensitivity of 3.19634 µM. Furthermore, the developed method was successfully implemented to determine DBP in cookies, achieving recovery rates within the range of 97–99%. Thus, the rapid sensing capabilities of CQDs could be highlighted as their promising potential for the detection of DBP in food products.

Single-Particle Spectroelectrochemistry: Promoting the Electrocatalytic Activity of Gold Nanorods via Oxygen Plasma Treatment without Structural Deformation.

Understanding of the electrocatalytic activity enhancement in gold nanoparticles is still limited. Herein, we present the effect of the oxygen plasma treatment on the electrochemical activity of gold nanorods (AuNRs). Oxygen plasma treatment resulted in the blueshift and line width narrowing of the localized surface plasmon resonance (LSPR) spectra obtained from individual AuNRs immobilized on an indium tin oxide (ITO) surface. These changes can be attributed to increases in the surface charges of the AuNRs. The formation of a Au-ITO heterojunction provided structural stability to the immobilized AuNRs regardless of the duration of oxygen plasma exposure. The electrocatalytic oxidation of hydrogen peroxide (H2O2) was induced by increases in the free-electron densities on the surfaces of these AuNRs owing to oxygen plasma treatment, and Au did not dissolve under the experimental conditions. However, the potential-dependent LSPR spectra of the individual AuNRs showed similar patterns of LSPR behavior, irrespective of the duration of oxygen plasma treatment and the concentration of H2O2. Therefore, this study based on single-particle spectroelectrochemistry and cyclic voltammetry improves the understanding of the role of oxygen plasma treatment in promoting the catalytic activity of structurally stable AuNRs immobilized on an ITO surface.

Dark-Field Microscopy of Au@Ag Core Shell Nanoparticles during Electrochemical Conversion Reactions

Nanoparticles (NPs), which can nowadays be synthesized in various shapes and compositions, provide special physical properties that can strongly differ from their respective macroscopic counterparts. In particular due to the highly increased surface-to-volume ratios, NPs are frequently used as catalyst material.(1) Furthermore, metal NPs exhibit adjustable spectral properties arising from the interaction of the conduction band electrons with electromagnetic radiation, called localized surface plasmon resonance (LSPR).(2) The NPs appear colorful, where spectra of single NPs contain fundamental information about the size, shape and composition of the NP. Using Dark-Field Microscopy (DFM), the LSPR spectra of individual NPs can be precisely detected by hyperspectral imaging and CCD imaging. Combining this method with electrochemistry allows the monitoring of electrochemical processes on a single NP level.(3) In our work we focus on Au@Ag Core Shell NPs which are a promising candidate for catalytic applications. The LSPR spectra of the core shell NPs were herein tracked during the electrochemically induced dissolution of the Ag shell in nitrate solution exhibiting a “naked” Au core with possibly increased catalytic activities. With this spectro-electrochemical approach, an intensity decrease accompanied by a spectral red-shift was found during the dissolution of the Ag, which correlated with the simultaneously obtained current responses.Figure 1: Left: DFM CCD images of core shell NPs before and after linear sweep voltammetry (LSV) are displayed (-0.2 to 0.6 V vs Pt, 5 mV/s), center: LSPR intensity gradient of > 600 core shell NPs which were individually tracked during the LSV (black) including the current response (red), right: LSPR spectra of a representative core shell NP before and after the LSV.References(1) Ealia S. A. M.; Saravanakumar M. P. IOP Conf. Ser.: Mater. Sci. Eng. 2017, 263, 032019.(2) Sambur J. B.; Chen P. Annu Rev Phys Chem 65, 395–422.(3) K. Wonner et al. J. Am. Chem. Soc. 2018, 140, 12658–12661. Figure 1

Click reaction-based single-particle dark-field microscopy: A visual platform for the highly sensitive and selective detection of pyrophosphatase

Inorganic pyrophosphatase (PPase) plays significant roles in diverse pathophysiological processes, therefore, developing a reliable method to measure PPase activity is crucial for the early diagnosis of the related diseases. In this work, a novel platform with single-particle dark-field microscopy (DFM), consisting of core gold nanoparticles (AuNPs), satellite AuNPs, pyrophosphate ions (PPi), copper ions (Cu2+), and sodium ascorbate (NaAsc), is designed for the selective and sensitive analysis of PPase according to a click reaction. After the introduction of PPase, the coordination between PPi and Cu2+ can be destroyed by catalyzing the hydrolysis of PPi to release free Cu2+ which can be reduced by NaAsc to produce cuprous ions (Cu+). Then the formed Cu+ promotes the click reaction between azide-modified core AuNPs and alkynyl-modified satellite AuNPs to cause the significant redshift of the localized surface plasmon resonance (LSPR) spectra of core AuNPs. Thus, PPase can be ultra-sensitively detected with a low detection limit of 0.003 U/L in a wide linear range from 0.01 to 1 U/L. This click reaction-based DFM technique can also be used to assess PPase inhibition, which suggests that it has a lot of potential for both the screening of PPase inhibitors and the diagnosis of PPase-related disorders.

Elucidating Surface Plasmon Damping and Fano Resonance Induced by Epitaxial Growth of Palladium on Single Gold Nanorods.

Plasmon damping and Fano resonance induced in the growth of palladium (Pd) on gold nanorods (AuNRs) have been poorly understood. Herein, we investigated the optical properties and morphologies of single AuNRs@Pd (core@shell) synthesized using epitaxial Pd growth at different Pd concentrations. The localized surface plasmon resonance (LSPR) spectra of single AuNRs@Pd showed characteristic subradiant and superradiant peaks as well as Fano resonance as a spectral dip, which was highly influenced by the Pd shell thickness. The occurrence of the Fano resonance during the Pd growth was further verified by in situ real-time observation experiments. We then elucidated time-dependent, real-time variations in LSPR peak wavelength, metal-induced surface damping, and Fano resonance mode of single AuNRs@Pd during Pd shell formation in three successive phases: Pd reduction, nucleation, and growth. Therefore, this study provides new insights into metal interface damping, the Fano resonance, and optical tunability by engineering the Fano resonance energy and Pd shell thickness.

Single-Particle Spectroelectrochemistry: Electrochemical Approaches for Tuning Chemical Interfaces and Plasmon Damping in Single Gold Nanorods.

The strong adsorption of thiol molecules on gold nanorods (AuNRs) results in localized surface plasmon resonance (LSPR) energy loss via chemical interface damping (CID). This study investigated the CID effect induced by thiophenol (TP) adsorption on single AuNRs and the in situ tuning of LSPR properties and chemical interfaces through electrochemical potential manipulation. The potential-dependent LSPR spectrum of bare AuNRs exhibited redshifts and line width broadening owing to the characteristics of capacitive charging, Au oxidation, and oxidation dissolution. However, TP passivation provided stability to the AuNRs from oxidation in an electrochemical environment. Electrochemical potentials induced electron donation and withdrawal, causing changes in the Fermi level of AuNRs at the Au-TP interface, thereby controlling the LSPR spectrum. Additionally, the desorption of TP molecules from the Au surface was electrochemically achieved at the anodic potentials further away from the capacitive charging region, which can be used to tune chemical interfaces and the CID process in single AuNRs.

Localized surface plasmon resonance sensing of SO2 and H2S using zeolitic imidazolate framework-8

A localized surface plasmon resonance (LSPR) sensor for SO2 and H2S has been developed by coating a Au nanopattern with zeolitic imidazolate framework-8 (ZIF-8), which is one of the most common metal–organic frameworks. SO2 and H2S were detected by the change in the absorbance at a certain wavelength in the LSPR spectrum. The sensitivity to SO2 and H2S was enhanced by ZIF-8 and with increasing relative humidity, and 0.1–20 ppm SO2 and 0.1–10 ppm H2S could be detected within 5 min at 70% relative humidity. The ZIF-8-coated sensor was more sensitive to SO2. The changes in the absorbance increased during exposure to SO2 and H2S, and only slightly decreased for SO2 and remained almost constant for H2S after stopping exposure. These responses indicate that the sensor can measure the integrated concentrations of SO2 and H2S. If the sensor was not exposed to ≥ 20 ppm SO2 or ≥ 10 ppm H2S, the sensitivity and LSPR spectrum of the sensor could be recovered approximately a dozen times by heating it at 200 °C in air. This study demonstrates the potential of metal–organic-framework-coated LSPR sensors for highly sensitive detection of SO2 and H2S.

Multispectral Localized Surface Plasmon Resonance (msLSPR) Reveals and Overcomes Spectral and Sensing Heterogeneities of Single Gold Nanoparticles.

Metal nanoparticles can be sensitive molecular sensors due to enhanced absorption and scattering of light near a localized surface plasmon resonance (LSPR). Variations in both intrinsic properties such as the geometry and extrinsic properties such as the environment can cause heterogeneity in nanoparticle LSPR and impact the overall sensing responses. To date, however, few studies have examined LSPR and sensing heterogeneities, due to technical challenges in obtaining the full LSPR spectra of individual nanoparticles in dynamic assays. Here, we report multispectral LSPR (msLSPR), a wide-field imaging technique for real-time spectral monitoring of light scattering from individual nanoparticles across the whole field of view (FOV) at ∼0.5 nm spectral and ∼100 ms temporal resolutions. Using msLSPR, we studied the spectral and sensing properties of gold nanoparticles commonly used in LSPR assays, including spheres, rods, and bipyramids. Complemented with electron microscopy imaging, msLSPR analysis revealed that all classes of gold nanoparticles exhibited variations in LSPR peak wavelengths that largely paralleled variations in morphology. Compared with the rods and spheres, gold nanobipyramids exhibited both more uniform and stronger sensing responses as long as the bipyramids are structurally intact. Simulations incorporating the experimental LSPR properties demonstrate the negative impact of spectral heterogeneity on the overall performance of conventional, intensity-based LSPR assays and the ability of msLSPR in overcoming both particle heterogeneity and measurement noise. These results highlight the importance of spectral heterogeneity in LSPR-based sensors and the potential advantage of performing LSPR assays in the spectral domain.

Highly Responsive Plasmon Modulation in Dopant-Segregated Nanocrystals.

Electron transfer to and from metal oxide nanocrystals (NCs) modulates their infrared localized surface plasmon resonance (LSPR), revealing fundamental aspects of their photophysics and enabling dynamic optical applications. We synthesized and chemically reduced dopant-segregated Sn-doped In2O3 NCs, investigating the influence of radial dopant segregation on LSPR modulation and near-field enhancement (NFE). We found that core-doped NCs show large LSPR shifts and NFE change during chemical titration, enabling broadband modulation in LSPR energy of over 1000 cm-1 and of peak extinction over 300%. Simulations reveal that the evolution of the LSPR spectra during chemical reduction results from raising the surface Fermi level and increasing the donor defect density in the shell region. These results establish dopant segregation as a useful strategy to engineer the dynamic optical modulation in plasmonic semiconductor NC heterostructures going beyond what is possible with conventional plasmonic metals.

Single-Particle Measurements of Nanocatalysis with Dark-Field Microscopy

Due to the complexity of heterogeneous reactions and heterogeneities of individual catalyst particles in size, morphology, and the surrounding medium, it is very important to characterize the structure of nanocatalysts and measure the reaction process of nanocatalysis at the single-particle level. Traditional ensemble measurements, however, only provide averaged results of billions of nanoparticles (NPs), which do not help reveal structure–activity relationships and may overlook a few NPs with high activity. The advent of dark-field microscopy (DFM) combined with plasmonic resonance Rayleigh scattering (PRRS) spectroscopy provides a powerful means for directly recording the localized surface plasmon resonance (LSPR) spectrum of single plasmonic nanoparticles (PNPs), which also enables quantitative measurements. In recent years, DFM has developed rapidly for a series of single-particle catalytic reactions such as redox reactions, electrocatalytic reactions, and DNAzyme catalysis, with the ability to monitor the catalytic reaction process in real time and reveal the catalytic mechanism. This review provides a comprehensive overview of the fundamental principles and practical applications of DFM in measuring various kinds of catalysis (including chemocatalysis, electrocatalysis, photocatalysis, and biocatalysis) at the single-particle level. Perspectives on the remaining challenges and future trends in this field are also proposed.

LOCALIZED SURFACE PLASMON RESONANCE OF COPPER NANOPARTICLES USING FINITE ELEMENT METHOD

The aim of this paper is to study the interaction of the electromagnetic wave with plasmonic nanoparticles. Localized Surface Plasmon resonance (LSPR) characteristics are governed by the intrinsic properties of the nanoparticle (size, shape and dielectric environment). The extinction cross-section spectra of Cu nanoparticles are calculated using finite element method (FEM). By increasing both the size of the nanoparticle and the dielectric environment, the simulations show a red-shifting and broadening on the LSPR spectrum with enhancement of the spectral amplitude. The extinction cross section spectra are calculated using polarized light for non-spherical or assembled nanoparticles. We investigated the LSPR of Cu nanospheres of different arrangements, showing that the optical response depends on the order of nanospheres and the light polarization.

How Light Polarizations Affect the Localized Surface Plasmon Resonance of Asymmetric Palladium Nanostructures

Divers spectroscopy techniques and advances imaging are elucidated when employing light in a controlled manner. One of the features of the light focusing fields is the localized surface plasmon resonance (LSPR). In this paper, we study the LSPRs for different arrangements of palladium (Pd) nanostructures with respect to light polarization in the visible and near-infrared regions. The extinction cross-section spectrum of asymmetric nanostructures is measured using far field spectroscopy technique and is calculated using Finite Element Method (FEM). The spectra of the nanostructures various arrangements recorded from the two methods are in very good agreement. Depending on the light polarization, the nanostructures produce strong plasmonic coupling. This is represented by the induction of dipole and quadrupole LSPR modes. A clear enhancement of the extinction spectrum has been evidenced by increasing the number of particles of nanostructures. The main advantage of the transition metallic nanostructures of different arrangements lies in the generation of a highly enhanced electromagnetic field accompanied by a redshift of LSPR spectrum that can be exploited in diverse applications.

Optimizing and Quantifying Gold Nanospheres Based on LSPR Label-Free Biosensor for Dengue Diagnosis

The localized surface plasmon resonance (LSPR) due to light–particle interaction and its dependence on the surrounding medium have been widely manipulated for sensing applications. The sensing efficiency is governed by the refractive index-based sensitivity () and the full width half maximum (FWHM) of the LSPR spectra. Thereby, a sensor with high precision must possess both requisites: an effective and a narrow FWHM of plasmon spectrum. Moreover, complex nanostructures are used for molecular sensing applications due to their good values but without considering the wide-band nature of the LSPR spectrum, which decreases the detection limit of the plasmonic sensor. In this article, a novel, facile and label-free solution-based LSPR immunosensor was elaborated based upon LSPR features such as extinction spectrum and localized field enhancement. We used a 3D full-wave field analysis to evaluate the optical properties and to optimize the appropriate size of spherical-shaped gold nanoparticles (Au NPs). We found a change in Au NPs’ radius from 5 nm to 50 nm, and an increase in spectral resonance peak depicted as a red-shift from 520 nm to 552 nm. Using this fact, important parameters that can be attributed to the LSPR sensor performance, namely the molecular sensitivity, FWHM, , and figure of merit (FoM), were evaluated. Moreover, computational simulations were used to assess the optimized size (radius = 30 nm) of Au NPs with high FoM (2.3) and sharp FWHM (44 nm). On the evaluation of the platform as a label-free molecular sensor, Campbell’s model was performed, indicating an effective peak shift in the adsorption of the dielectric layer around the Au NP surface. For practical realization, we present an LSPR sensor platform for the identification of dengue NS1 antigens. The results present the system’s ability to identify dengue NS1 antigen concentrations with the limit of quantification measured to be 0.07 μg/mL (1.50 nM), evidence that the optimization approach used for the solution-based LSPR sensor provides a new paradigm for engineering immunosensor platforms.

Control of Surface Plasmon Resonance in Silver Nanocubes by CEP-Locked Laser Pulse

Localized surface plasmon resonance (LSPR) of metal nanoparticles has attracted increasing attention in surface-enhanced Raman scattering, chemical and biological sensing applications. In this article, we calculate the optical extinction spectra of a silver nanocube driven by an ultrashort carrier envelope phase (CEP)-locked laser pulse. Five LSPR modes are clearly excited in the optical spectra. We analyze the physical origin of each mode from the charge distribution on different parts of the cubic particle and the dipole and quadrupole excitation features at the LSPR peaks. The charge distribution follows a simple rule that when the charge concentrates from the face to the corners of the cubic particle, the resonant wavelength red-shifts. Then we modulate the LSPR spectra by changing CEP. The results show that CEP has selective plasmon mode excitation functionality and can act as a novel modulation role on LSPR modes. Our work suggests a novel means to regulate LSPR modes and the corresponding optical properties of metal nanoparticles via various freedoms of controlled optical field, which can be useful for optimized applications in chemical and biological sensors, single molecule detection, and so on.

Localized surface plasmon resonance (LSPR) of coupled metal nanospheres in longitudinal, transverse and three-dimensional coupling configurations

localized surface plasmon resonance of metal nanoparticles is highly regarded by researchers due to its special applications. In the paper, the spectral response of the coupled metal nanospheres located in a silica fiber is explored using the boundary element method as a fast and appropriate numerical method for phenomena related to scattered waves. Three different coupling configurations including longitudinal, transverse, and three-dimensional coupling is simulated and investigated. The results declare that the coupling distance and the angle between nanoparticles relative position vector and direction of light propagation, in addition to the radii of the metal nanoparticles and the refractive index of the environment, can affect the shape of scattering cross-sectional spectrum and also the position and linewidth of the resonance peaks. Furthermore, the effects of coupling in the LSPR spectrum of longitudinal coupled structures are observed even up to long coupling distances (about 300 nm for gold nanospheres), while these effects are negligible in the transverse coupled structures in the studied range. Also, a threshold can be defined for effective coupling distance, which determines whether the coupling effects are significant or not. The results show that this threshold value is independent of the radius of metal spherical nanoparticles. Finally, the results prove that the dominant coupling in the three-dimensional structures is the longitudinal coupling that controls the threshold coupling value of the structure and it is 300 nm for structures based on gold spherical nanoparticles. This threshold value is an important quantity for better decisions about LSPR-based applications.

All-solid-state Z-scheme plasmonic Si@Au nanoparticles on CuBi2O4/BiVO4 for efficient photocatalytic activity

Development of plasmon-mediated catalysis emerged as an attractive alternative to propel chemical reactions. Novel plasmonic material in the form of Si@Au as core@shell nanostructure was experimentally synthesized with good colloidal stability. The Si@Au showed broad tunable light absorption spectra which benefits an effective light harvesting. The observed gold nanoparticles have narrow particle size distribution of 5 nm with lattice fringe of 1.23 Å corresponding to {311} gold lattice spacing. Whereas the silicon nanoparticles emitted photoluminescence under ultraviolet light irradiation, indicating successful alteration towards direct bandgap by quantum confinement effect in zero-dimensional structure. The Si@Au nanostructures were confirmed using high-resolution transmission electron microscopy and selected area electron diffraction, with the obtained localized surface plasmon resonance spectrum conformed to the simulated pattern corresponding to core@shell structure with a 5 nm-thin-shell Au layer. The vanishing photoluminescence in Si@Au nanostructure suggested suppression of the charge recombination, meaning that photogenerated charge carrier could be preferably used for photocatalytic reactions. The presence of novel Si@Au did not only show broad absorption spectra which is useful for effective light harvesting, but also acted as solid-state mediator driving the photocarrier transfer mode into Z-scheme system. As the result, an enhanced phenol degradation can be achieved, as indicated by 95% phenol degradation under visible light irradiation within 3 h.

Reconfigurable localized surface plasmon resonance spectrum based on acousto-dynamic coupling in arrays gold nanoparticles induced by shear horizontal vibration

Reconfigurable localized surface plasmon resonance (LSPR) is an essential characteristic for various applications to support Society 5.0. However, many LSPR spectrum have poor reconfigurability. As a novelty, we proposed a reconfigurable LSPR spectrum by acousto-dynamic coupling in arrays of gold nanoparticles (AuNPs) induced by shear-horizontal vibrations. The vibrations were produced by piezoelectric phenomena especially shear horizontal surface acoustic waves (SH-SAWs) on a 36XY-LiTaO3 substrate after applying an electric signal, the ON-condition. The experimental results demonstrated that the ON-condition produced a blueshift effect on the peak position (λP) with an adjustment quality factor compared to the OFF-condition. Moreover, in order to perform the finite-difference time-domain (FDTD) analysis, we reproduced the morphological structure of AuNPs base on scanning electron microscope (SEM) images. The different coupling distances and different arrays structures were utilized as ON-condition approaches for dimer AuNPs and arrays AuNPs, respectively. The FDTD simulation obtained a blueshift effect compared to the initial structure. Finally, the proposed structure successfully combines piezoelectric phenomena with plasmonic phenomena to produce reconfigurable LSPR. The LSPR spectrum can be switched comfortably and reverses easily. The proposed method can be applied for multifunctional sensors with the high possibility of integration into a wireless network.

Scanning probe microscopy by localized surface plasmon resonance at fiber taper tips.

Plasmonic antenna probes have been widely investigated for detecting electrical permittivity changes on the nanometer scale by employing high-sensitivity localized surface plasmon resonance (LSPR). Although it is intuitive to integrate such a probe onto an atomic force microscope (AFM) to add one more measurable quantity to the family of scanning probe microscopy techniques, the strong scattering background of the AFM tip overwhelms the LSPR scattering signal. To solve this problem, we combined evanescent coupling, polarization and spatial filtering, confocal spectroscopy, and numerical methods to extract clean LSPR spectra from a gold nanosphere-antenna probe attached to the tip of a fiber taper. By mounting the fiber taper on a custom quartz-tuning-fork SPM, we achieved high-quality nanometer-scale imaging of gold nanospheres on glass slides by mapping the LSPR wavelength shift. In addition, we reported an LSPR wavelength shift enhancement by more complicated probe designs and the consequent promise for higher-sensitivity microscopy. Our optical system and spectral processing method provide an effective solution to the long-standing quest for LSPR scanning microscopy.

Alkaline Phosphatase-Triggered Etching of Au@FeOOH Nanoparticles for Enzyme Level Assay under Dark-Field Microscopy.

In clinical diagnosis, the level of biological enzymes in serum has been generally regarded as markers of human diseases. In this work, a kind of simple and sensitive plasmonic probe (indicated as Au@FeOOH) has been synthesized with the guidance of plasmonic imaging and subsequently developed for the alkaline phosphatase (ALP) level detection under dark-field microscopy (DFM). As a kind of hydrolysis enzyme, ALP can promote the hydrolysis of l-ascorbic acid 2-phosphate to ascorbic acid (AA). AA further acts as a strong reduction reagent for the decomposition of the FeOOH shell, which results in a blue shift of localized surface plasmon resonance spectra and an obvious color change under DFM. RGB analyses show that using a ΔR/G value instead of scattering wavelength or R/G value as the analytical signal, the deviation attributed to the size distribution of the initial Au NPs is greatly suppressed, and a linear range from 0.2 to 6.0 U/L (R2 = 0.99) and a limit of detection of 0.06 U/L are acquired with various concentrations of ALP during the detection. Besides, this approach exhibits excellent selectivity in complex biological serum samples, which is expected to be applied for the early diagnosis of clinical diseases by monitoring various biomarkers in the future.

Gold Nanostar Spatial Distribution Impacts the Surface-Enhanced Raman Scattering Detection of Uranyl on Amidoximated Polymers.

The plasmonic properties of carboxylated gold nanostars distributed on amidoximated polyacrylonitrile (AO PAN) electrospun polymer films scale with surface-enhanced Raman scattering (SERS) intensities for coordinated uranium(VI) oxide (uranyl) species. This two-step plasmonic sensor first isolates uranyl from solution using functionalized polymers; then carboxylated gold nanostars are subsequently deposited for SERS. Spatially resolved localized surface plasmon resonance (LSPR) and SERS facilitate correlated nanostar optical density and uranyl quantification. To reduce sampling bias, gold nanostars are deposited in an inverted drop-coating geometry and measurements are conducted inside resulting nanoparticle coffee rings that form on the polymer substrates. This approach naturally preserves the plasmonic properties of gold nanostars while reducing the deposition of nanoparticle aggregates in active sensing regions, thereby maximizing both the accuracy and the precision of SERS measurements. Several advances are made. First, second-derivative analysis of LSPR spectra facilitates the quantification of local nanostar density across large regions of the sensor substrate by reducing background variations caused by the polymeric and gold materials. Second, local nanostar densities ranging from 140 to 200 pM·cm are shown to result in uranyl signals that are independent of nanostar concentration. Third, the Gibbs free energy of uranyl adsorption to carboxylated nanostars is estimated at 8.4 ± 0.2 kcal/mol. Finally, a linear dynamic range from ∼0.3 to 3.4 μg U/mg polymer is demonstrated. Signals vary by 10% or less. As such, the uniformity of the plasmonic activity of distributed gold nanostars and the employment of spatially resolved spectroscopic measurements on the composite nanomaterial sensor interface facilitate the quantitative detection of uranyl while also reducing the dependence on user expertise and the selected sampling region. These important advances are critical for the development of a user-friendly SERS-based sensor for uranyl.