Localized Surface Plasmon Resonance Properties Research Articles

Chromogenic Mechanisms of Colorimetric Sensors Based on Gold Nanoparticles.

The colorimetric signal readout method is widely used in visualized analyses for its advantages, including visualization of test results, simple and fast operations, low detection cost and fast response time. Gold nanoparticles (Au NPs), which not only exhibit enzyme-like activity but also have the advantages of tunable localized surface plasmon resonance (LSPR), high stability, good biocompatibility and easily modified properties, provide excellent platforms for the construction of colorimetric sensors. They are widely used in environmental monitoring, biomedicine, the food industry and other fields. This review focuses on the chromogenic mechanisms of colorimetric sensors based on Au NPs adopting two different sensing strategies and summarizes significant advances in Au NP-based colorimetric sensing with enzyme-like activity and tunable LSPR characteristics. In addition, the sensing strategies based on the LSPR properties of Au NPs are classified into four modulation methods: aggregation, surface modification, deposition and etching, and the current status of visual detection of various analytes is discussed. Finally, the review further discusses the limitations of current Au NP-based detection strategies and the promising prospects of Au NPs as colorimetric sensors, guiding the design of novel colorimetric sensors.

Fe3O4-carboxyl modified AuNPs-chitosan@AgNPs as a robust surface-enhanced Raman scattering substrate for rapid analysis of tryptamine and ofloxacin in aquatic products

Rapid and accurate quantification of trace targets in complex samples is an extremely challenging issue in fast analysis field. Herein, we developed Fe3O4-carboxyl modified AuNPs-chitosan@AgNPs composite (Fe3O4–AuNCs–Cs@AgNPs) as a robust surface-enhanced Raman scattering (SERS) substrate for rapid analysis of tryptamine (TPA) and ofloxacin (OFX). The substrate possessed abundant surficial active sites of –NH2, –OH and –COOH groups. The substrate exhibited good SERS activity for several different model molecules with enhancement factors (EFs) of 1.2 × 108 for 4-mercaptobenzoic acid. The substrate presented good stability for detection of TPA at pH 6.0 and OFX at pH 8.0, and relative standard deviations less than 5.0% for intra-batch and 6.0% for inter-batch. Also, the substrate possessed good time-stability within 50 days. The substrate integrated advantages of efficient enrichment, fast magnetic separation, and strong localized surface plasmon resonance properties of AgNPs. With versatile merits, TPA and OFX can be enriched and separated within 10 min. SERS methods for analysis of TPA and OFX were developed with detection limits of 35.5 μg/L and 15.8 μg/L, respectively. TPA and OFX were actually found in aquatic product, and recoveries during sample analysis were 89.3%–110% for TPA and 89.3%–96.8% for OFX. The analytical process completed within 30 min via enrichment-separation-detection all-in-one, exhibiting great potential for rapid analysis of toxic biogenic monoamines and antibiotic residues in food.

Growth time dependency on the formation of gold nanobipyramids for efficient detection towards chlorpyrifos-based LSPR sensor

The structure of gold nanobipyramids (GNBPs) is very promising for specific Localized Surface Plasmon Resonance (LSPR) properties, and thus potentially to be used in various applications, especially in sensing. This work reported growth time dependency on the formation of GNBPs for application in LSPR sensors for chlorpyrifos detection. The study on the growth time found that GNBPs formation at the initial stage is dominated by elongation direction and its optimum growth time is 2 h. The optimum GNBPs with 106.32 ± 2.50 in length, 42.17 ± 0.82 in width and an aspect ratio of 2.55 ± 0.08 were implemented as a sensing material for direct and rapid localized surface plasmon resonance (LSPR) sensors to detect chlorpyrifos. The mechanism is based on the change in spectrum intensity and wavelength shift between GNBPs when tested in deionized water and chlorpyrifos solution. The change arises from molecular interaction between the targeted analyte and the sensing material and effectively changes the dielectric features of the medium. The presence of chlorpyrifos in the 1 – 100 mg/mL concentration range has been successfully detected. The proposed sensor offers better sensitivity as high as 1.22 times for transverse LSPR mode and 2.04 for longitudinal LSPR mode than the LSPR sensor based on gold nanosphericals. Moreover, the sensor stability and repeatability response showed a reliable performance for determining chlorpyrifos. Furthermore, this sensor also shows high selectivity towards chlorpyrifos compared to other organophosphate and organochlorine pesticides such as malathion, chlorothalonil, and triclopyr-butotyl.

Thermochromic performance enhancement by geometric structure optimization of VO2 nanoarrays for smart window application

The localized surface plasmon resonance (LSPR) exhibited by vanadium dioxide (VO2) has expanded its utility in thermochromic smart windows. Here, guided by the absorption characteristics of a single VO2 nanoparticle (NP) with a radius between 10 to 60 nm on a glass substrate, we numerically conducted an extensive analysis of the optical properties of VO2 nano-cylinder arrays. We achieved a significant enhancement in the performance of thermochromic smart windows by optimizing the geometric structure of the VO2 arrays. Such a performance enhancement relies on the on-off switch properties of LSPR in VO2 nano-cylinder arrays. Smaller (r≤ 60) ones with high aspect ratios (> 0.75) shows a higher absorption contribution in their extinction effect and a more energetic LSPR peak located in the near-infrared spectra. Those characteristics significantly improve the thermochromic performance of smart windows via enhancing the transmission contrast between the high-temperature rutile state and the low-temperature monoclinic state of VO2. At a transmittance luminous (Tlum) efficacy of 60.03%, an excellent 20.03% in solar spectrum modulation ability (ΔTsol) can be attained. Compared to flat films with an identical Tlum, ΔTsol of the periodically cylindrical-structured film is raised by 234%.

Dual-Function Meta-Grating Based on Tunable Fano Resonance for Reflective Filter and Sensor Applications.

Localized surface plasmon resonance (LSPR)-based sensors exhibit enormous potential in the areas of medical diagnosis, food safety regulation and environmental monitoring. However, the broadband spectral lineshape of LSPR hampers the observation of wavelength shifts in sensing processes, thus preventing its widespread applications in sensors. Here, we describe an improved plasmonic sensor based on Fano resonances between LSPR and the Rayleigh anomaly (RA) in a metal-insulator-metal (MIM) meta-grating, which is composed of silver nanoshell array, an isolation grating mask and a continuous gold film. The MIM configuration offers more freedom to control the optical properties of LSPR, RA and the Fano resonance between them. Strong couplings between LSPR and RA formed a series of narrowband reflection peaks (with a linewidth of ~20 nm in full width at half maximum (FWHM) and a reflectivity nearing 100%) within an LSPR-based broadband extinction window in the experiment, making the meta-grating promising for applications of high-efficiency reflective filters. A Fano resonance that is well optimized between LSPR and RA by carefully adjusting the angles of incident light can switch such a nano-device to an improved biological/chemical sensor with a figure of merit (FOM) larger than 57 and capability of detecting the local refractive index changes caused by the bonding of target molecules on the surface of the nano-device. The figure of merit of the hybrid sensor in the detection of target molecules is 6 and 15 times higher than that of the simple RA- and LSPR-based sensors, respectively.

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.

Growth dynamics and its correlation with plasmonic properties of silver nanoparticles grown by solid state dewetting

Surface morphology and growth dynamics of silver nanoparticles grown by solid-state dewetting of sputtered precursor silver films are studied using atomic force microscopy (AFM) with advanced statistical analysis. Height-height correlation function (HHCF) and power spectral density function (PSDF) were extracted from AFM data, and scaling exponents αlocal,β,1/z and α were determined using analysis. HHCF analysis reveals that interface width w follows power law dependence with precursor film thickness (t) as ∼t0.48±0.01 for as-deposited films and ∼t1.27±0.08 for annealed films. Similarly, lateral correlation length ξ is observed to scale with precursor film thickness as ∼t0.58±0.08 for as-deposited films and ∼t0.65±0.05 for annealed films. The HHCF and PSDF analysis confirmed mound-like growth of the nanoparticles for the higher thickness of the precursor films. A direct correlation between morphology and the localized surface plasmon resonance (LSPR) properties of the silver nanoparticles is also observed.

Development of a method to diagnose endometrial cancer based on the AuNRs-AntiVimentin optical probe.

Endometrial cancer is one of the common gynecological malignancies, and its incidence has been increasing year by year in recent years, raising higher requirements for its rapid diagnosis. In this article, gold nanorods (AuNRs) with localized surface plasmon resonance properties (LSPR) has used to prepare AuNRs-antibody to waveform protein (AuNRs-AntiVimentin) optical probes, and a new method has been constructed that could rapidly detect and identify endometrial cancer tissue sections by polarized light microscopy. AuNRs were prepared by seed growth method using gold chloride as raw material, and the morphology of AuNRs and the optical characteristics of AuNRs-AntiVimentin has characterized by transmission electron microscopy (TEM), ultraviolet-visible spectroscopy (UV-Vis), and zeta potential; immunohistochemistry (IHC) and AuNRs-AntiVimentin optical probes have used to detect clinical endometrial cancer, respectively. The AuNRs-AntiVimentin optical probe has been used to detect endometrial cancer tissue sections and found to have good bio-specificity, with no significant difference in the detection of AuNRs-AntiVimentin compared with conventional IHC techniques (p > .05). An optical probe generated by coupling AuNRs with Vimentin antibodies has been obtained to detect and identify endometrial cancer with simple operation and comparable effect to conventional IHC, providing a new method and idea for the rapid detection of endometrial cancer.

Plasmonic scattering imaging of single Cu2-xSe nanoparticle for Hg2+ detection

The development of new efficient contrast nanoprobe has been greatly concerned in the field of scattering imaging for sensitive and accurate detection of trace analytes. In this work, the non-stoichiometric Cu2-xSe nanoparticle with typical localized surface plasmon resonance (LSPR) properties originating from their copper deficiency as a plasmonic scattering imaging probe was developed for sensitive and selective detection of Hg2+ under dark-field microscopy. Hg2+ can compete with Cu(I)/Cu(II) which were sources of optically active holes coexisting in these Cu2-xSe nanoparticles for its higher affinity with Se2−. The plasmonic properties of Cu2-xSe were adjusted effectively. Thus, the color scattering images of Cu2-xSe nanoparticles was changed from blue to cyan, and the scattering intensity was obviously enhanced with the dark-field microscopy. There was a linear relationship between the scattering intensity enhancement and the Hg2+ concentration in the range of 10–300 nM with a low detection limit of 1.07 nM. The proposed method has good potential for Hg2+ detection in the actual water samples. This work provides a new perspective on applying new plasmonic imaging probe for the reliable determination of trace heavy metal substances in the environment at a single particle level.

Hybrid gold-silica nanoparticles for plasmonic applications: A comparison study of synthesis methods for increasing gold coverage

The current work focuses on the synthesis of hybrid nanoparticles (NPs) made of a silica core (Si NPs) coated with discrete gold nanoparticles (Au NPs), which exhibit localized surface plasmon resonance (LSPR) properties. This plasmonic effect is directly related to the nanoparticles size and arrangement. In this paper, we explore a wide range of size for the silica cores (80, 150, 400, and 600 nm) and for the gold NPs (8, 10, and 30 nm). Some rational comparison between different functionalization techniques and different synthesis methods for the Au NPs are proposed, related to the optical properties and colloidal stability in time. An optimized, robust and reliable synthesis route is established, which improves the gold density and homogeneity. The performances of these hybrid nanoparticles are evaluated in order to be used in the shape of a dense layer for pollutant detection in gas or liquids, and find numerous applications as a cheap and new optical device.

Colorimetric sensing of Cu(II) ions in water on the basis of selective chemical etching of EDA-capped Ag nanoplates

Cu(II) ions are one of the essential mineral elements in the human body, but can pose a substantial health risk to people exposed to high concentrations of Cu(II) ions over a long period. Therefore, the ability to detect Cu(II) ions in drinking water is important. In this study, a novel colorimetric sensing probe for the easy and onsite detection of Cu(II) ions in drinking water was developed. The probe was constructed through selective chemical etching of triangular Ag nanoplates with tunable localized surface plasmon resonance (LSPR) properties. Ethylenediamine (EDA) was used as an organic capping agent to improve the chemical stability of triangular Ag nanoplates. Selective chemical etching of the EDA-capped Ag nanoplates in the presence of Cu(II) ions as a result of the formation of a coordination complex between the EDA and Cu(II) ions caused remarkable changes in the nanoplates’ LSPR characteristics. On the basis of this phenomenon, a novel colorimetric sensing probe capable of detecting Cu(II) ions in drinking water at concentrations above the safety limit was developed. Our findings were also extended to develop a portable and paper-based sensing probe with good long-term stability to overcome the shortcomings of liquid-phase colorimetric sensors without requiring a spectrometer. The proposed colorimetric sensing probes provide accurate results even with a real sample and offer numerous advantages over conventional sensing platforms, including clearly distinguishable color changes that can be observed by the naked eye; thus, the proposed probes can be used for the selective, reliable, and low-cost point-of-care detection of Cu(II) ions in water.

Emission peak shifted incoherent random laser through the combined effects of coupling of surface plasmons in a triangular shaped silver nanostructure, microbubbles, and the waveguiding mechanism

The random laser (RL) is now becoming an essential tool for various photonics applications, and a plethora of research advancements in RL coupled with developments in the field of techniques of syntheses of various nanostructured materials is taking place. But the realization of tuning the peak emission wavelength of RL is still very challenging. However, in this report we have demonstrated an emission peak shifted tunable low threshold incoherent RL in the visible region in a gain medium of a commercially available dye laser material and by employing the rarely used scatterer materials of triangular silver nanoparticles (TSN), microbubbles, and the waveguiding mechanism. The scattering properties of trapped microbubbles, along with the localized surface plasmon resonance property of TSN of appropriate concentration within waveguided thin films composed of glass substrates, have been methodically investigated to demonstrate the reduction in lasing threshold and tunability in the peak emission wavelength. A two-fold reduction in RL threshold by addition of TSN in the disordered system, along with a considerable narrowing down of the emission spectra to a few nanometers, are obtained. Furthermore, the peak emission wavelength shift of 6 nm is reported by suitably changing the system configuration by the addition of an optimum concentration of TSN along with trapped microbubbles. The as-developed system shows high-quality laser performance with the maximum value of η=0.64, a quantity describing the ratio of the number of stimulated radiative photons within RL and the total number of emissive photons. We propose that the total internal reflections from the microbubble surface, along with plasmonic enhancement and scattering from the TSN, mediate the waveguided RL to achieve the low threshold. Therefore, this report is an early step towards demonstrating efficient RL in a ternary scattering system. Many more avenues for investigating this developing research issue may be helpful for the future development of affordable and robust optoelectronic devices.

Dual-Functional Capping Agent-Mediated Transformation of Silver Nanotriangles to Silver Nanoclusters for Dual-Mode Biosensing.

The localized surface plasmon resonance (LSPR) property, depending on the structure (morphology and assembly) of nanoparticles, is very sensitive to the environmental fluctuation. Retaining the colorimetric effect derived from the LSPR property while introducing new optical properties (such as fluorescence) that provide supplementary information is an effective means to improve the controllability in structures and reproducibility in optical properties. DNA as a green and low-cost etching agent has been demonstrated to effectively control the morphology and optical properties (the blue shift of the LSPR peak) of the plasmonic nanoparticles. Herein, taking silver nanotriangles (AgNTs) as a proof of concept, we report a novel strategy to induce precisely tunable LSPR and fluorescence-composited dual-mode signals by using mono-DNA first as an etching agent for etching the morphology of AgNTs and later as a template for synthesizing fluorescent silver nanoclusters (AgNCs). In addition, common templates for synthesizing AgNCs, such as l-glutathione and bovine serum albumin, were demonstrated to have the capability to serve as etching agents. More importantly, these biomolecules as dual-functional capping agents (etching agents and templates) follow the size-dependent rule: as the size of the thiolated biomolecule increases, the blue shift of the LSPR peak increases; at the same time, the fluorescence intensity increases. The enzyme that can change the molecular weight (size) of the biomolecular substrates (DNA, peptides, and proteins) through an enzymatic cleavage reaction was explored to regulate the LSPR and fluorescent properties of the resulting nanoparticles (by etching of AgNTs and synthesis of AgNCs), achieving excellent performance in detection of cancer-related proteases. This study can be expanded to other biopolymers to impact both fundamental nanoscience and applications and provide powerful new tools for bioanalytical biosensors and nanomedicine.

Plasmon enhanced photocatalytic degradation of 4-chlorophenol using zinc oxide nanorods decorated with gold nanoparticles as supported catalysts under natural sunlight

The photocatalytic degradation of 4-chlorophenol (4-CP) was evaluated under natural sunlight using zinc oxide nanorods (ZnO NRs) and gold nanoparticles (AuNPs) decorated ZnO NRs catalysts. Microwave-assisted hydrothermal growth of ZnO NRs followed by photoinduced deposition of AuNPs on ZnO NRs was carried out to fabricate the ZnO-Au catalysts. The photocatalytic degradation of 4-CP with different AuNPs sizes and surface coverage obtained from varying Au loading on ZnO NRs was studied. 0.1 mM AuNPs concentration exhibited the best result, with a degradation efficiency of 97% for 10 ppm of 4-CP within 180 min. The degradation enhancement for the ZnO-Au catalysts was owing to enhanced absorption in the visible region. The visible-light-induced localized surface plasmon resonance property of AuNPs reduced the recombination and promoted the electrons and holes separation. The substantial change in the binding energy of the valance band maximum exhibited the charge transfer from AuNPs to ZnO NRs. Photocatalytic degradation of four different concentrations (10, 50, 100, and 200 ppm) of 4-CP was studied. During the photocatalytic degradation, various hydroxylated intermediates formed, namely hydroquinone, benzoquinone, 4-chlorocatechol, and 4-chlororesorcinol. The photocatalytic results indicate that the ZnO-Au catalyst is a promising candidate for environmental decontamination of organic pollutants in the aqueous media.

Au Nanowires Decorated Ultrathin Co3 O4 Nanosheets toward Light-Enhanced Nitrate Electroreduction.

Nitrate is a reasonable alternative instead of nitrogen for ammonia production due to the low bond energy, large water-solubility, and high chemical polarity for good absorption. Nitrate electroreduction reaction (NO3 RR) is an effective and green strategy for both nitrate treatment and ammonia production. As an electrochemical reaction, the NO3 RR requires an efficient electrocatalyst for achieving high activity and selectivity. Inspired by the enhancement effect of heterostructure on electrocatalysis, Au nanowires decorated ultrathin Co3 O4 nanosheets (Co3 O4 -NS/Au-NWs) nanohybrids are proposed for improving the efficiency of nitrate-to-ammonia electroreduction. Theoretical calculation reveals that Au heteroatoms can effectively adjust the electron structure of Co active centers and reduce the energy barrier of the determining step (*NO → *NOH) during NO3 RR. As the result, the Co3 O4 -NS/Au-NWs nanohybrids achieve an outstanding catalytic performance with high yield rate (2.661mg h-1 mgcat -1 ) toward nitrate-to-ammonia. Importantly, the Co3 O4 -NS/Au-NWs nanohybrids show an obviously plasmon-promoted activity for NO3 RR due to the localized surface plasmon resonance(LSPR) property of Au-NWs, which can achieve an enhanced NH3 yield rate of 4.045mg h-1 mgcat -1 . This study reveals the structure-activity relationship of heterostructure and LSPR-promotion effect toward NO3 RR, which provide an efficient nitrate-to-ammonia reduction with high efficiency.

Adjustment of eccentricity and split angle for improved SERS and refractive index sensing of TiN nanodonuts

The unique refractory plasmonic properties and strong enhancement of the electric field within the inherent gap of titanium nitride (TiN) nanodonuts make them excellent candidates for surface-enhanced Raman scattering (SERS)- and refractive index (RI)-sensing applications. The eccentricity and split angles are critical parameters for tuning the localized surface plasmon resonance (LSPR) properties of the donuts, which were numerically investigated using the finite element method herein. We demonstrated that the proposed donuts provided efficient SERS and RI sensing substrates capable of working in regions ranging from ultraviolet (UV) to near-infrared (NIR). By adjusting the eccentricity and split angles, the corresponding optimized RI sensitivity and SERS enhancement factor reached 1,374 nm RIU−1 and 6.8 × 104, respectively. Moreover, the effects of both incident polarisation and electromagnetic (EM) field distributions on the LSPR properties were elucidated and discussed. This study provides new insights for understanding the LSPR properties of TiN nanoparticles and enables the rational design of efficient refractory plasmon-based SERS and RI-sensing substrates.

Amplification-Free, High-Throughput Nanoplasmonic Quantification of Circulating MicroRNAs in Unprocessed Plasma Microsamples for Earlier Pancreatic Cancer Detection.

Pancreatic ductal adenocarcinoma (PDAC) is a deadly malignancy that is often detected at an advanced stage. Earlier diagnosis of PDAC is key to reducing mortality. Circulating biomarkers such as microRNAs are gaining interest, but existing technologies require large sample volumes, amplification steps, extensive biofluid processing, lack sensitivity, and are low-throughput. Here, we present an advanced nanoplasmonic sensor for the highly sensitive, amplification-free detection and quantification of microRNAs (microRNA-10b, microRNA-let7a) from unprocessed plasma microsamples. The sensor construct utilizes uniquely designed -ssDNA receptors attached to gold triangular nanoprisms, which display unique localized surface plasmon resonance (LSPR) properties, in a multiwell plate format. The formation of -ssDNA/microRNA duplex controls the nanostructure-biomolecule interfacial electronic interactions to promote the charge transfer/exciton delocalization processes and enhance the LSPR responses to achieve attomolar (10-18 M) limit of detection (LOD) in human plasma. This improve LOD allows the fabrication of a high-throughput assay in a 384-well plate format. The performance of nanoplasmonic sensors for microRNA detection was further assessed by comparing with the qRT-PCR assay of 15 PDAC patient plasma samples that shows a positive correlation between these two assays with the Pearson correlation coefficient value >0.86. Evaluation of >170 clinical samples reveals that oncogenic microRNA-10b and tumor suppressor microRNA-let7a levels can individually differentiate PDAC from chronic pancreatitis and normal controls with >94% sensitivity and >94% specificity at a 95% confidence interval (CI). Furthermore, combining both oncogenic and tumor suppressor microRNA levels significantly improves differentiation of PDAC stages I and II versus III and IV with >91% and 87% sensitivity and specificity, respectively, in comparison to the sensitivity and specificity values for individual microRNAs. Moreover, we show that the level of microRNAs varies substantially in pre- and post-surgery PDAC patients (n = 75). Taken together, this ultrasensitive nanoplasmonic sensor with excellent sensitivity and specificity is capable of assaying multiple biomarkers simultaneously and may facilitate early detection of PDAC to improve patient care.

Seed-Mediated Synthesis of Thin Gold Nanoplates with Tunable Edge Lengths and Optical Properties

Thin Au nanoplates show intriguing localized surface plasmon resonance (LSPR) properties with potential applications in various fields. The conventional synthesis of Au nanoplates usually involves the formation of spherical nanoparticles or produces nanoplates with large thicknesses. Herein, we demonstrate a synthesis of uniform thin Au nanoplates by using Au-Ag alloy nanoframes obtained by the galvanic replacement of Ag nanoplates with HAuCl4 as the seeds and a sulfite (SO32-) as a ligand. The SO32- ligand not only complexes with the Au salt for the controlled reduction kinetics but also strongly adsorbs on Au {111} facets for effectively constraining the crystal growth on both basal sides of the Au nanoplates for controlled shape and reduced thicknesses. This seed-mediated synthesis affords Au nanoplates with a thickness of only 7.5 nm, although the thickness increases with the edge length. The edge length can be customizable in a range of 48-167 nm, leading to tunable LSPR bands in the range of 600-1000 nm. These thin Au nanoplates are applicable not only to surface-enhanced Raman spectroscopy with enhanced sensitivity and reliability but also to a broader range of LSPR-based applications.

Colorimetric and visual determination of iodide ions via morphology transition of gold nanobipyramids

The gold nanobipyramids (Au NBPs) are widely used in the analytical detection of biochemistry due to their unique localized surface plasmon resonance (LSPR) properties. In our developed approach, I− in kelp was detected by etching Au NBPs in the presence of IO3−. Under acidic conditions, IO3− reacted rapidly with I− to form I2, subsequently I2 reacted with I− to form the intermediate I3−. In the presence of CTAB, Au NBPs were etched by I2 derived from I3−, resulting in a decrease in the aspect ratio of Au NBPs, to form a significant blue shift of LSPR longitudinal peak and color variation of colloid which changed from blue-green to magenta and could be employed to quantitatively detect the concentration of I− with the naked eye. A linear relationship can be found between the LSPR peak changes with the I− concentration in a wide range from 4.0 μM to 15.0 μM, and the sensitive limit of detection (LOD) was 0.2 μM for UV–vis spectroscopy and the obvious color changes with a visual LOD was 4.0 μM for the naked eye. Benefiting from the high specificity, the proposed colorimetric detection of I− in kelp samples was achieved, indicating the available potential of the colorimetric detection for the determination of I− in real samples. What's more, this detection procedure was time-saving and could avoid tedious procedures.

Single-Probe-Based Colorimetric and Photothermal Dual-Mode Identification of Multiple Bacteria.

Effective identification of multiple pathogenic bacteria in unknown samples is important for disease prevention and control but remains a challenge yet. A single-mode array-based sensing approach is simple and sensitive, but it usually relies on the use of multiple cross-reactive receptors to construct sensor arrays, which is cumbersome and insufficiently accurate. Here, we developed a sensor array with colorimetric and photothermal dual mode of differentiating multiple pathogenic bacteria. The sensor array was based on boronic acid-functionalized Au-Fe3O4 nanoparticles (BA-GMNPs), which not only possess localized surface plasmon resonance properties, showing a burgundy color similar to that of AuNPs, but also exhibit mild superparamagnetism, allowing for the differentiation of bacteria before and after binding to the nanoparticles. Immobilization of BA-GMNPs on the bacterial cell surface by covalent bonding would diminish NaCl-induced assembly of BA-GMNPs. Different BA-GMNPs@bacterial complexes differed in their ability to resist assembly and produced different colorimetric and photothermal response signals. A unique molecular fingerprint of each bacterium was obtained by linear discriminant analysis of the response patterns, demonstrating an effective differentiation among the six species studied. Compared with single-mode sensing arrays based on multiple receptors, this method only requires the preparation of a single nanomaterial, which produces two signal outputs for the identification of multiple bacteria with better differentiation. It can distinguish not only multiple pathogenic bacteria but also Gram-negative and Gram-positive bacteria, and, more importantly, it can perform preliminary discrimination of unknown samples.