Localized Surface Plasmon Resonance Band Research Articles

Ultra-Broadband Plasmon Resonance in Gold Nanoparticles Precipitated in ZnO-Al2O3-SiO2 Glass

Optical materials with a tunable localized surface plasmon resonance (LSPR) are of great interest for applications in photonics and optoelectronics. In the present study, we explored the potential of generating an LSPR band with an ultra-broad range of over 1000 nm in gold nanoparticles (NPs), precipitated through a thermal treatment in ZnO-Al2O3-SiO2 glass. Using optical absorption spectroscopy, we demonstrated that the LSPR band’s position and shape can be finely controlled by varying the thermal treatment route. Comprehensive methods including Raman spectroscopy, X-ray diffraction, and high-resolution transmission electron microscopy were used to study the glass structure, while computational approaches were used for the theoretical description of the absorption spectra. The obtained results allowed us to suggest a scenario responsible for an abnormal LSPR band broadening that includes a possible interparticle plasmonic coupling effect taking place during the liquid–liquid phase separation of the heat-treated glass. The formation of gold NPs with an ultra-broad LSPR band in glasses holds promise for sensitizing rare earth ion luminescence for new photonics devices.

Localized surface plasmon resonance sensing of Trenbolone acetate dopant using silver nanoparticles

In this work, localized surface plasmon resonance (LSPR) sensing as applicable in the detection of Trenbolone acetate dopant is demonstrated. We show that the LSPR of the Trenbolone acetate/silver nanoparticle (Tren Ac/AgNPs) complex is sensitive to changes in the adsorbent concentration. The results show an average redshift of + 18 nm in the LSPR peak with variations in intensity and broadening behavior of the LSPR band of the Tren Ac/AgNPs complex. AgNPs were synthesized using laser ablation in liquid (LAL) technique with water as the solvent. UV–Vis spectroscopy was used for absorbance measurements and particle size and morphology were monitored using scanning electron microscopy (SEM). The aggregation behavior of the Tren Ac/AgNPs complex was monitored using energy-dispersive X-ray spectroscopy (EDS). Molecular Electrostatic Potential (MEP) and the HOMO–LUMO orbitals of the optimized Trenbolone acetate structure were obtained using Density Function Theory (DFT). The molecule was optimized at the B3LYP level of theory using the 6–311 basis set carried out using the Gaussian 09 software package. The results showed that O2− is Trenbolone acetate’s active site that would interact with Ag+ to form a complex that would influence the plasmon behavior. The results presented in this work demonstrate the feasibility of LSPR for anabolic androgenic steroid detection.

Enhancing photocatalytic H2 production and dye degradation: Comparative analysis of gold reduction techniques on Au/TiO2 nanocomposites

This study compares the impact of two reduction techniques, thermal reduction (TR) and photocatalytic reduction (PR), on Au/TiO2 photocatalysts synthesized using the deposition-precipitation with urea method. Characterization methods, including temperature-programmed reduction, UV-Vis diffuse reflectance spectroscopy, electrochemical assessments (open-circuit potential and linear sweep voltammetry), and transmission electron microscopy, were employed. The 2-h. PR treatment yielded a highly effective photocatalyst (0.5Au-PR2), with 93.6% of gold nanoparticles below 4 nm, outperforming the TR counterpart (76.8%). All Au-loaded samples exhibited an absorption band between 400 and 800 nm, indicating the localized surface plasmon resonance (LSPR) effect. Interestingly, the TR catalyst had a broader LSPR band than the PR catalyst. Additionally, the 0.5Au-PR2 sample showed higher photocurrent and superior photocatalytic activity in the degradation of methyl orange and hydrogen production, which is attributed to its smaller particle size (2.9 nm) and weaker metal-support interaction. This smaller particle size emphasizes the crucial role of reduction techniques in tailoring Au/TiO2 photocatalysts for enhanced performance.

Experimental and Theoretical Studies on Ag Nanoparticles with Enhanced Plasmonic Response, Formed Within Al2O3 Thin Films Deposited by Magnetron Sputtering

AbstractReactive magnetron sputtering was employed to prepare nanocomposite thin films of Ag/Al2O3, on a glass substrate. The films are characterized by the formation of Ag nanoparticles embedded in the Al2O3 matrix, after thermal treatment at 600 °C, which are responsible for the appearance of an outstanding pronounced and narrow localized surface plasmon resonance (LSPR) band. Electron microscopy analysis also revealed the presence of larger Ag fractal aggregates at the film’s surface, responsible for a broad band absorption. Noteworthily, the LSPR band maximum remains at the same position (about 412 nm) for Ag concentrations ranging from 23 to 34 at.%, despite some discernible alterations in both LSPR band intensity and width. An optimized thin film is characterized by full transparency in non-resonant wavelengths due to suppression of Ag aggregates at the film’s surface, while maintaining the LSPR behavior. To better explain the plasmonic behavior of the Ag/Al2O3 films, discrete dipole approximation was used to determine the extinction, scattering, and absorption efficiencies of Ag spheres surrounded by an Al2O3 cap layer. This allowed to ascertain some nanostructural features of the films, pointing to the formation of Ag nanoparticles with average sizes in the order of 40 nm.

One-pot synthesis of near-infrared absorbing silver nanoprisms via a simple photochemical method using an ultraviolet-C light source

This study describes a simple one-pot photochemical method to synthesize triangular silver nanoprisms (T-AgNPs), for which a mixture of silver nitrate (AgNO3) and citrate was irradiated with an ultraviolet-C (UVC) lamp reactor. We successfully synthesized T-AgNPs with edge lengths ranging from 50 to 150 nm, showing a significant localized surface plasmon resonance (LSPR) band over a wavelength of 1200 nm. This photochemical reaction appears to be unrestricted by plasmon resonance conditions, allowing for the formation of colloidal T-AgNPs with an LSPR band in the near-IR region. In addition, this new method does not require any highly reactive reducing agents or initially prepared silver seed solution. The reduction of Ag+ ions by citrate is induced by UVC light, and the nascent Ag first undergoes nucleation to form spherical or quasi-spherical silver nanoparticles (S-AgNPs). Subsequently, continuous irradiation with UVC light facilitates the transformation of these S-AgNPs into T-AgNPs. The growth kinetics of the nanoparticles with different reaction conditions were examined using ultraviolet–visible–near-infrared spectroscopy and transmission electron microscopy. This new method offers a simple, efficient, and cost-effective means to synthesize T-AgNPs with near-IR LSPR, contributing to wider applications in the fields of optoelectronics, spectroscopics, photovoltaics, etc.

In Situ Monitoring of the Polymerization Kinetics of Organic Pollutants during Persulfate-Based Advanced Oxidation Processes Using Plasmonic Colorimetry.

Using sulfate radicals to initiate polymer production in persulfate-based advanced oxidation processes (AOPs) is an emerging strategy for organics removal. However, our understanding of this process remains limited due to a dearth of efficient methods for in situ and real time monitoring of polymerization kinetics. This study leverages plasmonic colorimetry to monitor the polymerization kinetics of an array of aromatic pollutants in the presence of sulfate radicals. We observed that the formation of polymer shells on the surfaces of gold nanoparticles (AuNPs) led to an increase and red shift in their localized surface plasmon resonance (LSPR) band as a result of an increased refractive index surrounding the AuNP surfaces. This observation aligns with Mie theory simulations and transmission electron microscopy-electron energy loss spectroscopy characterizations. Our study demonstrated that the polymerization kinetics exhibits a significant reliance on the electrophilicity and quantity of benzene rings, the concentration of aromatic pollutants, and the dosage of oxidants. In addition, we found that changes in LSPR band wavelength fit well into a pseudo-first-order kinetic model, providing a comprehensive and quantitative insight into the polymerization kinetics involving diverse organic compounds. This technique holds the potential for optimizing AOP-based water treatment by facilitating the polymerization of aromatic pollutants.

Development of silver nanocubes created by pulsed laser ablation in liquid

This paper describes a simple approach for creating silver (Ag) nanocubes using pulsed laser ablation in a liquid medium. The development of nanocubical formations of Ag obtained by laser ablation using Nd: YAG laser was conducted for 5, 10, 15, and 20[Formula: see text]min. The surface morphological analysis was performed using field-emission scanning electron microscopy (FESEM) to show the formation of silver nanocubes with edge lengths ranging from 150[Formula: see text]nm to 250[Formula: see text]nm. The UV-visible spectroscopy demonstrates that the concentration of Ag nanostructures, evidenced by the characteristic localized surface plasmon resonance band near 400[Formula: see text]nm in the colloidal solution containing Ag nanoparticles, increased with the increasing laser ablation duration from 5[Formula: see text]min to 20[Formula: see text]min. The growth mechanism for Ag nanocubes can be easily understood with the change in laser ablation time from 5 to 10, 15, and then 20[Formula: see text]min. The Ag sheets with no specific shape start to develop after 5 min of laser ablation, and after 10[Formula: see text]min, larger particles form. Then, after 15[Formula: see text]min, a small number of cube-like nanostructures with rough and uneven edges was obtained. At the end of 20[Formula: see text]min, a complete cubic formed with fine and distinct edges and a very large amount of nanocubes. The elemental silver signal was present in Ag nanocubes, as revealed by the energy-dispersive X-ray spectroscopy (EDS) spectra. The produced Ag nanocubes may be used to construct two-dimensional nanocomposites with practical applications in the electrical, optoelectronic, electrochemical, and biological areas.

Streptomyces monashensis MSK03-mediated synthesis of gold nanoparticles: characterization and antibacterial activity.

Nanotechnology is a cutting-edge field with diverse applications, particularly in the utilization of gold nanoparticles (AuNPs) due to their stability and biocompatibility. AuNPs serve as pivotal components in medical applications, with a specific emphasis on their significant antibacterial efficacy. This study focuses on synthesizing AuNPs using the cell-free supernatant of Streptomyces monashensis MSK03, isolated from terrestrial soil in Thailand. The biosynthesis process involved utilizing the cell-free supernatant of S. monashensis MSK03 and hydrogen tetrachloroauric acid (HAuCl4) under controlled conditions of 37 °C and 200 rpm agitation. Characterization studies revealed spherical AuNPs with sizes ranging from 7.1 to 40.0 nm (average size: 23.2 ± 10.7 nm), as confirmed by TEM. UV-Vis spectroscopy indicated a localized surface plasmon resonance (LSPR) band at 545 nm, while XRD analysis confirmed a crystalline structure with characteristics of cubic lattice surfaces. The capping molecules on the surface of AuNPs carry a negative charge, indicated by a Zeta potential of -26.35 mV, and FTIR analysis identified functional groups involved in reduction and stabilization. XANES spectra further confirmed the successful reduction of Au3+ to Au0. Moreover, the synthesized AuNPs demonstrated antibacterial activity against drug-resistant strains of Pseudomonas aeruginosa and Acinetobacter baumannii. Interestingly, the AuNPs showed non-toxicity to Vero cell lines. These significant antibacterial properties of the produced nanoparticles mean they hold great promise as new antimicrobial treatments for tackling the increasing issue of antibiotic resistance.

(Invited) Metal and Nonmetal Plasmonic Nanostructures for Surface-Enhanced Raman Spectroscopy Detection

Toxic small molecules such as pesticides, food additives, plasticizers and dyes have been posing increasing threat to human health. Surface-enhanced Raman scattering spectroscopy (SERS) is a powerful sensing strategy for these small molecules with advantages including fast response, high sensitivity and fingerprint identification.Based on the surface plasmon effect, gold and silver nanostructures are the typical plasmonic sensing materials for rapid detection with SERS. However, the crucial challenges for realizing on-site real detection application is to fabricate reproducible and highly sensitive SERS substrates and portable instrument. We fabricated several long-range ordered sensitive nanostructure arrays based on anodic aluminum oxide templates which could provide reproducible structural patterns. Then, we developed a portable instrument integrated with database of the standard Raman spectra of common contaminants and a software for automatic identification and comparison of the test spectrum with the standard database, which can identify the specific analytes. Combined with the sensitive and reproducible SERS substrates, we realized the on-site and rapid detection of various toxic contaminants.Recently, as an inexpensive candidate, nonmetal plasmonic materials like oxide semiconductors have attracted increasing interests, which induced by the increase of free charge carriers via introducing oxygen vacancies. We synthesized oxygen-deficient WO3-x and NayWO3-x nanosheets and realized the localized surface plasmon resonance (LSPR) band in visible range (~530 nm) as same as the gold nanoparticles, which is the bluest. Then, SERS detection of dyes has also been realized on nonmetal substrate. Moreover, the plasmonic oxygen-deficient oxides showed wide LSPR tuning window from visible to infrared range and plasmon-driven photocatalysis, which may open potentials for biological applications.

Influence of Carboxymethyl Cellulose on the Green Synthesis of Gold Nanoparticles Using Gliricidia sepium and Petiveria alliacea Extracts: Surface-Enhanced Raman Scattering Effect Evaluation.

Gold nanoparticles (AuNPs) were synthesized and stabilized using ecological strategies: the extracts of the leaves of the plants Gliricidia sepium (GS) and Petiveria alliacea (PA) reduced the metallic Au ions to AuNPs. The AuNPs were analyzed as surface-enhanced Raman scattering (SERS) substrates for pyridoxine detection (vitamin B6). UV-vis spectroscopy was carried out to assess the stability of the AuNPs. As a result, absorption bands around 530 and 540 nm were obtained for AuNPs-PA and AuNPs-GS, respectively. Both cases associated it with localized surface plasmon resonance (LSPR). In the final stage of the synthesis, to stabilize the AuNPs, carboxymethyl cellulose (CMC) was added; however, LSPR bands do not exhibit bathochromic or hypsochromic shifts with the addition of CMC. Transmission electron microscopy (TEM) micrographs show relatively spherical morphologies; the particle diameters were detected around 7.7 and 12.7 nm for AuNPs-PA and AuNPs-GS, respectively. The nanomaterials were evaluated as SERS substrates on pyridoxine, revealing an intensification in the vibrational mode centered at 688 cm-1 associated with the pyridinic ring. Complementarily, different density functional theory functionals were included to obtain molecular descriptors on the Aun-cluster-pyridoxine interaction to study the SERS behavior.

{111}‐ Faceted Silver Nanoplates: An Automated and Customized Design for Functionality

AbstractSilver nanoparticles (Ag‐NPs) exhibit the highest efficiency of localized surface plasmon resonance (LSPR) excitation that can be tuned to any wave length in the visible spectrum. Its performance depends to a large extent on its physicochemical characteristics such as size and shape; which, in turn, can be modulated by the selective growth of their crystalline facets. We used a simple direct chemical reduction method with a precise manipulation of seed‐mediated growth control through an automated single‐phase continuous flow‐batch system to induce customized geometries on Ag‐NPs. Optimization of the experimental design was carried out from a multivariate analysis, where the height/width ratio of LSPR band was used as response signal. Proposed methodology controls the critical steps in the synthesis of Ag‐NPs that modulate their morphology to attain customized surface plasmon resonance in an interval of 380 nm (spherical‐shaped nanoparticles) to 925 nm ({111}‐ faceted prism‐shaped nanoplates) absorptions, leading to a versatile platform to extend their potential applications. Although the present work focused on silver nanoparticles, we believe that this methodology can be extended to any free‐electron metals.

Label-free SERS for rapid identification of interleukin 6 based on intrinsic SERS fingerprint of antibody‑gold nanoparticles conjugate

A label-free surface-enhanced Raman scattering (SERS) was designed for sensitive detection of interleukin-6 (IL-6). The sensing element composed of anti-IL-6 antibodies adsorbed on the surface of spherical gold nanoparticles (AuNPs) as SERS-active surface. The principle of detection was probing antibody conformational changes using its intrinsic SERS fingerprint after binding to IL-6. Comparison of SERS spectra of antibody before and after binding to IL-6 showed that secondary structure of antibody does not change upon binding to IL-6. Vibrational information from disulfide bonds ν(SS) in antibody structure indicated some changes of geometry around SS bridges as a consequence of the immunocomplex formation. Transmission electron microscopy (TEM) and UV–Vis spectroscopy were used to confirm AuNPs conjugation with antibody as well as IL-6 binding to antibody on the surface of AuNPs. The SERS-based immunoassay showed a wide linear range (2.0–1000 pg mL−1) and a high sensitivity with a limit of detection (LOD) as low as 0.91 pg mL−1 (0.04 pM) without using any extrinsic Raman label. UV–Vis spectroscopy was employed as a conventional method for IL-6 detection based on observation of any change in the position of localized surface plasmon resonance (LSPR) band of AuNPs-antibody conjugates with LOD of 10 ng mL−1.

Solid-Phase Spectrometric Determination of Organic Thiols Using a Nanocomposite Based on Silver Triangular Nanoplates and Polyurethane Foam.

Adsorption of silver nanoparticles on polymers may affect the processes in which they participate, adjusting the analytical characteristics of methods for the quantitation of various substances. In the present study, a composite material based on silver triangular nanoplates (AgTNPs) and polyurethane foam was proposed for chemical analysis. The prospects of its application for the solid-phase/colorimetric determination of organic thiols were substantiated. It was found that aggregation of AgTNPs upon the action of thiols is manifested by a decrease in the AgTNPs' localized surface plasmon resonance band and its significant broadening. Spectral changes accompanying the process can be registered using household color-recording devices and even visually. Four thiols differing in their functional groups were tested. It was found that their limits of detection increase in the series cysteamine < 2-mercaptoethanol < cysteine = 3-mercaptopropionic acid and come to 50, 160, 500, and 500 nM, respectively. The applicability of the developed approach was demonstrated during the analysis of pharmaceuticals and food products.

Comparison of Gold Nanoparticles Prepared Using Monobasic Sodium Citrate or Sodium Borohydride for Neomycin Determination in Saliva after Solid-Phase Extraction (SPE) on a Molecularly Imprinted Polymer (MIP)

Two distinct spherical gold nanoparticles (AuNPs) were compared for the spectrophotometric determination of neomycin in saliva. The AuNPs were produced using AuCl3 and monobasic sodium citrate (in water bath at 100 °C) under magnetic stirring (AuNPs-citrate) and using HAuCl4 and NaBH4, at room-temperature under mechanical agitation in a commercial reactor (AuNPs-H). Both AuNPs were spherical with diameters of 7.7 nm (AuNPs-H) and 26.1 nm (AuNPs-citrate) and the maximum wavelength of the localized surface plasmon resonance (LSPR) bands were at 511 nm (AuNPs-H) and 529 nm (AuNPs-citrate). Equivalent spectral extinctions were found despite the fact the large difference in concentrations of AuNPs in dispersions: 4.2 × 10−9 mol L−1 for the AuNPs-H and 8.7 × 10−11 mol L−1 for the AuNPs-citrate. Both AuNPs interacted with aminoglycosides (AMG), affecting intensity of the LSPR band as the concentration of AMG increased. The response of the AuNPs-H was more sensitive toward AMG covering the following ranges: 0.6–600 µg L−1 (gentamicin), 7.3–550 µg L−1 (neomycin) and 14–520 µg L−1 (kanamycin). AuNPs-H optical response was more robust in function of the pH with AuNPs-citrate response only observed in acid solution, favoring electrostatic interaction with AMG. Catalytic activity of AuNPs-H, in reducing the 4-phenolate ion, presented a higher rate constant (4.3 × 10−3 s−1) and was used as analytical probe to determine neomycin in saliva after solid phase extraction with a commercially available AMG imprinted polymer enabling quantification to 0.36 μg of the analyte.

Formation of plasmonic silver nanoparticles by glucosamine reduction: Application to a colorimetric sensor for determination of glucosamine in its pharmaceutical preparations

The purpose of this study is to develop a novel method for synthesizing silver nanoparticles using glucosamine as reducing agent and to utilize the developed method for colorimetric detection and quantitative determination of the non-chromophoric drug, glucosamine. Silver nanoparticles are prepared by reducing 0.02 mol/L silver nitrate by glucosamine in 0.075 mol/L ammonia and stabilizing the nanoparticles with 0.1% polyvinylpyrrolidone and the mixture is heated at 90 °C for 5 min. The prepared silver nanoparticles dispersed in water exhibit a bright yellow color due to a localized surface plasmon resonance band at 412 nm. The principle of glucosamine sensing is based on measuring the intensity of the surface plasmon resonance band at 412 nm which is directly proportional to the concentration of glucosamine with a linearity range (1 – 9 μg/mL), limit of detection 0.33 μg/mL and limit of quantitation 1.0 μg/mL. The proposed method was validated according to the ICH guidelines, and it was found to be accurate, precise, selective, and robust. The method was applied for determination of glucosamine in Joflex® capsules using the standard addition approach with mean % recovery ± standard deviation of 100.077 ± 1.786. The method is simple, rapid, and cost-effective and can be used for determination of glucosamine in bulk and in its pharmaceutical preparations.

Plasmonic oxygen-deficient sodium tungsten bronze NayWO3-x microstructures for SERS detection

Nonmetal plasmonic semiconductors have attracted increasing research interests for the low cost and promising surface plasmon properties. Here, oxygen-deficient sodium tungsten bronze NayWO3-x microstructures on tungsten foil has been facilely fabricated, showing nonmetal plasmonic behavior and surface-enhanced Raman scattering (SERS) detection potential. The NayWO3 was firstly grown on tungsten sheets with Na doping in the solvothermal processing. Then, the oxygen vacancies have been introduced with thermal treatment in a hydrogen-containing atmosphere, resulting in NayWO3-x microstructures which revealed a localized surface plasmon resonance band at 620 nm. The NayWO3-x microstructures was used as SERS substrate for detecting methylene blue of 10-7 M, showing application potentials of plasmonic nonmetal materials.

Using laser ablation in liquid (LASIS) method to synthesize silver nanoparticles for SERS applications

In this work, colloid formation with laser ablation in distilled water was used to investigate the influence of ablation time and pulse repetition frequency in generating silver nanofluids. The nature (size and shape) of the nanoparticles were investigated using transmission electron microscopy (TEM) while the elemental composition of the generated nanoparticles was explored using energy-dispersive X-ray fluorescence (EDXRF). The EDXRF spectra confirmed the presence of silver as the dominant element in the nanofluid. TEM showed that the size of the generated nanoparticles varies with the concentration of silver based on the change in Laser ablation time (LAT) and the pulse repetition frequency (PRF). The localized surface plasmon resonance band of silver in the fluid was explored using UV–VIS with the absorption band observed at around 408 nm. The generated nanofluid was then used as a substrate in surface enhanced Raman spectroscopy (SERS). The conclusion drawn from this work is that the laser ablation time and pulse repetition rate can be modified to produce reproducible silver nanofluids for subsequent SERS applications.

LSPR-Based Aptasensor for Rapid Urinary Detection of NT-proBNP.

N-terminal pro-brain natriuretic peptide (NT-proBNP) is a myocardial stress biomarker that can be found in serum or plasma, saliva, and urine in the context of cardiovascular disease. In this study, we developed a rapid (~25 min) and straightforward localized surface plasmon resonance (LSPR)-based assay for detecting NT-proBNP in urine. The assay employs citrate-capped gold nanoparticles (AuNPs) and an aptamer specific for NT-proBNP, which initially interacts with NT-proBNP. The remaining unbound aptamer then interacts with the AuNPs, and the addition of NaCl induces the aggregation of the unprotected AuNPs, resulting in a decrease in absorbance at the LSPR band (A521) and an increase in absorbance at 750 nm (A750). The concentration of NT-proBNP showed a linear correlation with the aggregation ratio (A521/A750), and the assay demonstrated a limit of detection (LOD) of 0.303 µg·L-1 and a detection range of 0.566-8 µg·L-1. However, the presence of sulfur-containing proteins in saliva and fetal bovine serum hindered the detection of NT-proBNP in these biofluids. Nevertheless, the assay successfully detected NT-proBNP in diluted urine with an LOD of 0.417 µg·L-1 and a detection range of 0.589-6 µg·L-1. The observed values in urine samples from preterm infants with cardiovascular disease fell within this range, indicating the potential clinical relevance of the assay. The recovery percentages ranged from 92.3 to 116.3%. Overall, our findings suggest that the LSPR-based assay for NT-proBNP detection in urine can be a valuable tool for the diagnosis and treatment of cardiovascular disease.

Chlorophyll Coated Silver Nanoparticles Synthesized by Microwave Assisted Method for the Colorimetric Detection of Cr (VI) Ions in Aqueous Medium

The study aims at synthesizing a simple, cost-effective, selective, and sensitive colorimetric sensor based on chlorophyll-coated silver nanoparticles (Chl-AgNPs) using microwave-assisted method for the determination of Cr(VI) ions in an aqueous medium. The characterization reveals that synthesized nanoparticles are 20–30 nm in size and spherical in shape. The presence of methyl, carboxyl, aldehyde, and ketone groups on the surface of Chl-AgNPs results in the formation of size controlled, well dispersed, and stable silver nanoparticles. The prepared nano-colloidal solution has been used for selective and sensitive determination of Cr(VI) in water samples. The addition of single drop of Chl-AgNPs solution immediately changes the color of water samples containing Cr(VI) to red displaying good sensitivity from 10 to 100 µM and high selectivity even in the presence of other metal ions. The ultraviolet–visible spectra show that in the presence of Cr(VI), the localized surface plasmon resonance (LSPR) band of Chl-AgNPs at 410 nm shifts to 470 nm with a new peak at 357 nm. Furthermore, the absorbance of the LSPR band decreases and the absorbance at 357 nm increases linearly with the concentration of Cr(VI). The functional groups on the surface of nanoparticles bind Cr(VI) on the surface leading to agglomeration and alterations in interparticle distance that are observed as changes in the color and LSPR profile. The limits of detection and quantification for Cr(VI) ions were determined to be 0.62 µM and 1.88 µM, respectively.

Contact lenses that transform gold into nanoparticles for prophylaxis of light-related events and photothermal therapy

This work describes for first time how anisotropic gold nanoparticles (AuNPs) can be spontaneously formed inside preformed contact lenses (CLs) avoiding the use of additional reductant agents (reagent-free) through a precise tunning of the monomeric composition, the saline concentration, and the application of steam heat sterilization. Protocols to generate AuNPs in solution using inorganic or small organic reductants are widely available. Differently, gold precursors interactions with polymer networks have been overlooked and, thus, the interest of chemically cross-linked hydrogels as organic reductants is still to be elucidated. In the ocular field, incorporation of AuNPs to CLs may expand their applications in prophylaxis, therapy and diagnosis. To carry out the work, a variety of hydrogels and commercially available CLs were incubated with gold salt solution without any other chemical reagent. AuNPs formation was monitored by changes in localized surface plasmon resonance (LSPR) bands and quantifying the gold sorbed. Only silicone hydrogels induced AuNPs formation at room temperature in few days; methacrylic acid red-shifted the LSPR band (550–600 nm), while monomers bearing F hindered the reduction. Storage of hydrogels in the gold precursor solution allowed a gradual formation of anisotropic AuNPs, which could be stopped at any time by washing the hydrogel with water. The developed CLs behave as efficient filters against highly penetrant light and also exhibit photoresponsiveness as demonstrated as rapid (10 s), focused mild hyperthermia when irradiated with green, red and NIR lasers.