Surface Plasmon Resonance Phenomenon Research Articles

The effect of surface roughness on the performance of 3D printed surface plasmon resonance sensors for refractive index measurements

AbstractIn this study, a polymer-based surface plasmon resonance (SPR) sensor for refractive index measurements was designed and manufactured via inkjet 3D printing; then, it was optically characterized. Next, it was investigated how the surface finish of the 3D printed optical waveguide affects the sensor performance, i.e., its sensitivity. More in detail, it was studied how the surface roughness changes with the placement of the 3D printed items on the building platform. To achieve this purpose, a Phase I distribution-free quality monitoring analysis of the selected manufacturing process was implemented for a small pilot production run. The aim was to check the stability of surface roughness versus the placement of the 3D printed parts on the building platform. The 3D printed sensor’s surface roughness was assessed through a profilometry study. In particular, the surface roughness was determined for the core of the optical waveguide used to excite the SPR phenomena. Furthermore, the SPR sensors were optically characterized to find the existing relationship between their sensitivity and the considered quality of surface finish. In particular, by varying the surface roughness of the used waveguide, the light scattering in the waveguide changes, and the SPR sensitivity changes too, similarly to the light-diffusing fibers covered by gold nanofilms where the guided light is scattered through a plurality of voids distributed in the core. The procedure followed to investigate the sensor roughness, and establishing their performance enabled the optimal operative range for their application in practice to be identified. Finally, a better knowledge of the 3D printing manufacturing process has been achieved to improve quality of surface finish.

Toward Nano- and Microplastic Sensors: Identification of Nano- and Microplastic Particles via Artificial Intelligence Combined with a Plasmonic Probe Functionalized with an Estrogen Receptor.

Nano- and microplastic particles are a global and emerging environmental issue that might pose potential threats to human health. The present work exploits artificial intelligence (AI) to identify nano- and microplastics in water by monitoring the interaction of the sample with a sensitive surface. An estrogen receptor (ER) grafted onto a gold surface, realized on a nonexpensive and easy-to-produce plastic optical fiber (POF) platform in order to excite a surface plasmon resonance (SPR) phenomenon, has been developed in order to carry out a "smart" sensitive interface (ER-SPR-POF interface). The ER-SPR-POF interface offers output data useful for exploiting a machine learning-based approach to achieve nano- and microplastic particle sensors. This work developed a proof-of-concept sensor through a training phase carried out by different particles, in terms of materials and size. The experimental results have demonstrated that the proposed "smart" ER-SPR-POF interface combined with AI can be used to identify the kind of particles in terms of the materials (polystyrene; poly(methyl methacrylate)) and size (20 μm; 100 nm) with an accuracy of 90.3%.

Phthalocyanine and Porphyrin Derivatives and Their Hybrid Materials in Optical Sensors Based on the Phenomenon of Surface Plasmon Resonance

In this review, the state of research over the past fifteen years in the field of the applications of metal phthalocyanines and porphyrin derivatives as well as their hybrid materials with carbon nanotubes, metal oxides, and polymers in optical sensors based on the phenomenon of surface plasmon resonance (SPR) is analyzed. The first chapter of the review presents an analysis of works on the use of porphyrins and phthalocyanines in classical SPR sensors for the detection of gases and volatile organic vapors, as well as their improved modifications, such as total internal reflection ellipsometry (TIRE) and magneto-optical SPR (MOSPR) methods, while the second chapter is devoted to their application for the detection of various analytes in solutions. The third chapter of the review summarizes publications describing recent advances in the use of porous materials based on hybrids of carbon nanotubes and oxides with metal phthalocyanines. The fourth chapter describes two-dimensional metal-organic frameworks (MOFs) based on metal porphyrin derivatives as SPR sensitizers.

Optimizing PCF-SPR sensor design through Taguchi approach, machine learning, and genetic algorithms

Designing Photonic Crystal Fibers incorporating the Surface Plasmon Resonance Phenomenon (PCF-SPR) has led to numerous interesting applications. This investigation presents an exceptionally responsive surface plasmon resonance sensor, seamlessly integrated into a dual-core photonic crystal fiber, specifically designed for low refractive index (RI) detection. The integration of a plasmonic material, namely silver (Ag), externally deposited on the fiber structure, facilitates real-time monitoring of variations in the refractive index of the surrounding medium. To ensure long-term functionality and prevent oxidation, a thin layer of titanium dioxide (TiO2) covers the silver coating. To optimize the sensor, five key design parameters, including pitch, air hole diameter, and silver thickness, are fine-tuned using the Taguchi L8(25) orthogonal array. The optimal results obtained present spectral and amplitude sensitivities that reach remarkable values of 10,000 nm/RIU and 235,882 RIU-1, respectively. In addition, Artificial Neural Network (ANN) optimization techniques, specifically Multi-Layer Perceptron (MLP) and Particle Swarm Optimization (PSO), are used to predict a critical optical property of the sensor confinement loss (αloss). These predictions are derived from the same input structure parameters that are present in the full L32(25) design experiment. A genetic algorithm (GA) is then applied for optimization with the goal of maximizing the confinement loss. Our results highlight the effectiveness of training PSO artificial neural networks and demonstrate their ability to quickly and accurately predict results for unknown geometric dimensions, demonstrating their significant potential in this innovative context. The proposed sensor design can be used for various applications including pharmaceutical inspection and detection of low refractive index analytes.

Optical force on yeast cells generated from surface plasmon polaritons

The surface plasmon resonance phenomenon is widely used in sensing, near-field control, and nonlinear optics. In this paper, the optical near-field generated by the surface plasmon resonance phenomenon is applied to trap yeast cells. The effect of the relative axial distance between the gold film surface and the waist of the focused beam on the trap stiffness is studied. There is a maximized trap stiffness at a specific relative axial distance for trapping yeast cells. The trap stiffness is significantly higher than the value at other locations. This study can be applied to screening of particles with different sizes.

Green synthesis of Ag/Yb2O3 nanostructures based-MIP for tamoxifen detection: Advancing from refractometers to sensor

This study presents a novel optical fiber refractometer based on a single smart functional layer of Ag/Yb2O3 nanostructure, synthesized by a green chemistry method using oak fruit extract. The optical phenomena of surface plasmon resonance (SPR) and lossy mode resonance (LMR) were investigated based on the performance of the real and imaginary parts of the dielectric constant function of nanoparticles and nanostructures coated on the optical fiber. The Ag/Yb2O3 nanostructure enhances the LMR phenomenon and acts as an electron mediator for the detection of tamoxifen (TAM) drug, a widely used anticancer agent. The Ag/Yb2O3 nanostructure was coated on a curved optical fiber surface along with a molecularly imprinted polymer (MIP) layer, which provided selective recognition of TAM molecules. The sensor probe showed rapid and reversible adsorption/desorption of TAM, with a high sensitivity of 5.3611 nm/µM and a limit of detection (LOD) and limit of quantification (LOQ) of 0.0987 μM and 0.32902 μM, respectively. The sensor also exhibited good recovery rate and effectiveness in real samples, demonstrating its potential for sensivity applications.

Optical and thermo-plasmonic properties of spherical and hollow gold nanoparticles injected in cell organelles

The advent of nanotechnology has profoundly altered many traditional treatment approaches, due to the beneficial physicochemical and functional characteristics of gold nanoparticles (AuNPs). These gold nanostructures are attracting particular interest in a wide range of biomedical applications, such as thermotherapy, diagnostics, detection, and drug delivery. Due to their exceptional characteristics, AuNPs have long been considered as a potential means of combating cancer. These features include surface plasmon resonance (SPR), surface chemistry and multi-functionalization. In addition to targeting tissues and cancer cells, AuNPs with the ability to specifically target organelles are attracting growing interest and are seen as the next evolutionary step in nanomedicine, forming the third generation of this technology. Subcellular targeting offers unique advantages over free targeting, as it enables specific delivery of encapsulated NPs to the intracellular site of action. This translates into greater therapeutic efficacy with a reduced dose and, above all, the ability to overcome immune resistance. AuNPs act as small heat sources taking advantage of SPR phenomenon, enabling targeted heating of specific organelles. The thermoplasmonic effect disrupts organelle function in targeted cancer cells, leading to their destruction. In this work, we used the finite element method (FEM) to examine the properties associated with the SPR of both spherical and hollow AuNPs when they are embedded in the main cellular components, including the lysosome, cell membrane, mitochondria, nucleus, cytoplasm and extracellular medium. In order to predict the thermal destructive power of solid spheres (SAuNPs) and hollow (HAuNPs) gold nanoparticles embedded in these different organelles, we simulated their absorption capacity, field enhancement effect and temperature distribution. The results obtained show that the thermoplasmonic effect is very important for HAuNPs compared with SAuNPs. In addition, the optical and thermoplasmonic properties of SAuNPs and HAuNPs show differential behavior for different cell organelles.

Modified Ag-ZnO coated graphene oxide ternary composite for superior photocatalytic degradation of crystal violet dye under visible light irradiation

The enhancement of advanced nanomaterials into photocatalytic applications has preserved a significant curiosity for its potential to address environmental challenges. To address this concern, a green and eco-friendly catalyst was fabricated. In this study, we examined the enhancement of the photocatalytic activity of various synthesized composites with the modification of graphene oxide (GO) and Ag over the surface of semiconductor zinc oxide (ZnO). The simple wet chemical method was used for the synthesis of ZnO, GO(x)@ZnO, Ag2@ZnO and GO(x)Ag2-ZnO composites [x = 1,3,5 wt%]. The synthesized samples were characterized by different techniques such as XRD, SEM-EDS, DRS, Raman, and PL. Ternary GO5@Ag2-ZnO photocatalyst exhibited superior degradation efficiency up to 97 % in degrading crystal violet (CV) dye, a persistent and environmentally concerning pollutant under visible light irradiation. The significant photocatalytic activity was attributed to the surface plasmon resonance (SPR) phenomenon of Ag, whose broad absorption band was observed in DRS, better electron mobility, and a large surface area of GO facilitates the charge transfer. The highly efficient catalyst was effectively employed for five repeating cycles with only an 11 % decrease in removal rate, demonstrating that it can be easily reused. Kinetic study reveals that the prepared composite follows a pseudo-first-order reaction model with the highest rate constant value of 0.02491 min−1 respectively. The possible degradation pathway was determined using the HRMS technique.

Citrus sinensis Seed-Mediated Gold Nanoparticles for Combating Diabetes and Bacterial Infections: A Promising Multifunctional Nano Formulation

This investigation explores the successful synthesis and comprehensive characterization of Citrus sinensis seed-mediated gold nanoparticles designated as C-AuNPs. Visual confirmation of synthesis was achieved through a distinct ruby red color change in the reaction mixture, followed by UV-Visible spectroscopy, which revealed a characteristic peak absorbance at 522 nm due to the Surface Plasmon Resonance (SPR) phenomenon associated with gold nanoparticles. Transmission Electron Microscopy (TEM) analysis demonstrated uniform, spherical nanoparticles with an average size of 19 nm, ideal for biomedical applications. Dynamic Light Scattering (DLS) revealed a hydrodynamic size of 55 nm in the hydrated state, while a negative zeta potential of −17 mV indicated colloidal stability. C-AuNPs exhibited significant antibacterial activity against both Gram-negative and Gram-positive bacterial strains, surpassing the performance of levofloxacin. Lower Minimum Inhibitory Concentration (MIC) values against bacterial strains further supported their enhanced efficacy, potentially due to interactions with bacterial cell membranes. Furthermore, C-AuNPs demonstrated potent inhibition of α-amylase and α-glucosidase enzymes involved in glucose metabolism, with IC50 values comparable to the anti-diabetic drug acarbose. This suggests their potential as anti-diabetic agents, with the ability to regulate blood sugar levels. C-AuNPs exhibit unique optical, structural, and electrostatic properties, making them promising candidates for diverse biomedical applications. Their small size, stability, antibacterial efficacy, and anti-diabetic properties position C-AuNPs as valuable assets in the realm of nanomedicine and therapeutics, warranting further exploration and development.

Cascaded plastic optical fiber based SPR sensor for simultaneous measurement of refractive index and temperature.

A cascaded side-polish plastic optical fiber (POF) and FONTEX optical fiber based surface plasmon resonance (SPR) sensor is proposed for simultaneous measurement of refractive index (RI) and temperature. The side-polish POF and FONTEX optical fiber are connected by using the UV glue in a Teflon plastic tube. The SPR phenomenon can be excited at both of the side-polish region and the FONTEX fiber cladding. The polydimethylsiloxane (PDMS) is coated on the side-polish POF to get a temperature sensing channel. Due to the low RI sensitivity of the FONTEX optical fiber, the cascaded fiber sensor can obtain a broader RI measurement range with a low crosstalk. An RI sensitivity of 700 nm/RIU in the RI measurement range of 1.335-1.39 and a temperature sensitivity of -1.02 nm/°C measured in deionized water with a range of 20-60 °C are obtained. In addition, the cascaded POF based SPR sensor has potential application prospects in the field of biochemical sensing.

Effects of thickness and roughness on plasmonic characteristics of gold thin films deposited on polished optical fiber

The thickness and roughness of metal layers substantially affect the performance of surface plasmon resonance (SPR)-based sensors. The deposition methods, control parameters, and substrate characteristics influence the layer thickness and roughness. This study investigates the SPR characteristics of a polished optical fiber surface coated with gold (Au) metal of different thicknesses. The Au layer is deposited via the thermal evaporation method, and its thickness is varied by controlling the deposition time (3–6 min). A proportionality relationship between thickness and deposition time is observed. Island-shaped structures in gold (Au) morphology are formed due to low adhesion to the substrate. The shape of this island creates gaps in the layer, causing scattering. In addition, the roughness on the gold surface triggers the Localized Surface Plasmon Resonance (LSPR) phenomenon. As a result, the measured dielectric characteristics differ from the reference. The SPR curve calculation simulation was carried out based on reference optical parameters and measurement results by an ellipsometer, which were then compared with experiments. The obtained results show that the substrate roughness, morphology, and thickness of the Au layer play an essential role in determining the characteristics of the SPR curve in a fiber optic plasmonic sensor. As a result, in basic experiments, the sample with an Au thickness of 27.37 nm (deposition time = 3 min) shows better characteristics (half-maximum full width, minimum transmittance, and resonance wavelength) compared with the sample with an Au thickness of 53.97 nm (deposition time = 4 min), Although 53.97 nm is the optimal thickness from the simulation using reference optical parameters (smooth substrate surface and smooth gold layer).

Laser Fragmentation of Green Tea-synthesized Silver Nanoparticles and Their Blood Toxicity: Effect of Laser Wavelength on Particle Diameters

Background: The efficacy of fractionation is significantly impacted by the colloidal particles’ spontaneous absorption of laser beam radiation. The classification of silver nanoparticles during fragmentation processing is regulated through the collection of a combination of laser pulses with wavelengths of 1064 nm and 532 nm. Aims and Objectives: This study presents an investigation of the efficacy of a plant extract in conjunction with the incorporation of supplementary silver nanoparticles, as well as the generation of smaller-sized silver nanoparticles using laser fragmentation.and then measure thier toxity on the blood. Results: Ag nanoparticles were synthesized using pulsed laser fragmentation on green tea AgNPs. The synthesis process involved the utilization of a Q-switch Nd:YAG laser with wavelengths of 1064 nm and 532 nm, with energy ranging from 200 to 1000 mJ. Initially, a silver nano colloid was synthesized through the process of fragmented of the Ag target using the second harmonic generation of 532 nm at various energy levels. The optimal energy within the selected wavelengths was determined in order to facilitate the ultimate comparison. Transmission electron microscopy (TEM) was used to determine surface morphology and average particle size, while a spectrophotometer was used to analyses UV light’s spectrum characteristics. The measurements focused on the surface plasmon resonance (SPR) phenomenon. The absorption spectra of silver nanoparticles exhibit distinct and prominent peaks at wavelengths of 405 nm and 415 nm. The mean diameter of the silver nanoparticles was found to be 16 nm and 20 nm, corresponding to wavelengths of 1064 nm and 532 nm, respectively. Conclusion: As a consequence, there is a decrease in the range of particle sizes and a decrease in the mean size to lower magnitudes, resulting in a very stable colloid. This particular methodology has demonstrated considerable efficacy in the production of colloidal suspensions with the intended particle dimensions. Moreover, by the analysis of nanoparticles in human blood, no discernible alterations in the blood constituents were seen, indicating their non-toxic nature.

Atomic layer deposition of Pt nanoparticles using dimethyl (N, N–dimethyl-3-butene-1-amine−N) platinum and H2 reactant and its application to 2D WS2 photodetectors

2D transition metal dichalcogenides (2D TMDCs) have thin and flexible structures and can be widely applied to nanoelectronics technology as a representative of 2D materials. Research studies on the surface functionalization of 2D TMDCs with nanoparticles have been actively conducted for fabrication of high-performance devices. Specifically, platinum (Pt) has attracted significant attention as a surface functionalization material in various applications, including photosensors, biosensors, and gas sensors due to its effective catalytic effect and excellent corrosion resistance. However, solution-based methods and PVD technologies, widely used for Pt nanoparticle synthesis, have difficulties forming fine particles dispersed on nanomaterials. Atomic layer deposition (ALD) is emerging as an advantageous method for forming nanoparticles, and dimethyl (N,N-dimethyl-3-buten-1-amine-N) platinum (DDAP) can overcome disadvantages of conventional ALD Pt precursors. In this study, we successfully synthesized Pt films using hydrogen as a new reactant in the DDAP-based ALD Pt process and evaluated formation of nanoparticles on SiO2/Si substrates. Subsequently, the ALD Pt-functionalized photodetector was fabricated with 2D WS2, a representative visible-light photodetector material, and improvement of photocurrent was confirmed by providing additional carriers via the localized surface plasmon resonance phenomenon. Furthermore, preferentially growing at high surface energy points, such as defects on WS2 nanosheets, can suppress the capture of photoexcited electrons by defects, consequently extending the carrier lifetime and preventing surface oxidation of the device. In the wavelength range of 500–1200 nm, the photoresponsivity of the ALD Pt-functionalized WS2 photodetector was improved more than 10–20 times compared to pristine WS2, and the response time was also noticeably improved. This study presents a novel approach to Pt functionalization using ALD, opening new possibilities for advanced nanodevice applications.

Silver-coated hollow fiber surface plasmon resonance sensor for glucose detection with enhanced limit of detection.

A fiber-optic surface plasmon resonance (SPR) biosensor based on a silver-coated hollow fiber (HF) structure for glucose detection is presented. The sensor surface was immobilized with 4-mercaptophenylboronic acid (PMBA) acting as a glucose recognition monolayer. Then, gold nanoparticles (AuNPs) modified with 2-aminoethanethiol (2-AET) and PMBA were introduced onto the sensor surface after glucose was captured to enhance the wavelength shift of the SPR phenomenon excited by the light transmitted in the wall of the HF sensor. Instead of the conventional one-step sensitization pretreatment commonly used in the deposition process of silver films for fiber-optic SPR sensors, a sensitization-activation two-step activation method was adopted in the fabrication of the proposed sensor. Experiments for glucose detection were performed on the fabricated sensors in the concentration range of 1 nM-1 mM. Results showed that the sensor fabricated by the two-step activation method has a much larger shift of resonance wavelength than the sensor fabricated using the one-step sensitization method. The resonance wavelength shift was found to be linear to the logarithm of the concentration in the range of 1 nM-1 mM. The sensor achieved a limit of detection (LOD) of as low as 1 nM, which is at least an order of magnitude lower than that of other fiber-optic sensors for glucose detection reported previously. The presented HF glucose sensor has the potential for biosensing applications and provides a large reference value in the study of optical fiber SPR sensors for biosensing.

Pengaruh Variasi Prekursor Terhadap Morfologi dan Aktivitas Antibakteri Nanopartikel Tembaga Menggunakan Reduktor Ekstrak Daun Gambir

Research on synthesis copper nanoparticles has been carried out by the bioreduction method with a green synthesis approach using extracts of gambir leaves (Uncaria gambir Roxb). Gambir leaf extract contains polyphenol compounds uses as a natural reducing agent to reduce copper cation from variations of prekursor (CuSO45.H2O, Cu(NO3)2.3H2O and CuCl2.2H2O). The formation of copper nanoparticles (CuNP) colloid is visually shown by color change from light brown to dark brown. Absorption peak in UV-Vis spectrophotometer analysis at 405 -427 nm which is a specific wavelength of copper nanoparticles base on phenomenon of Surface Plasmon Resonance (SPR). The X-Ray Diffraction (XRD) analysis showed formation of CuNP with a face centered cubic (fcc) crystal structure. The result of Transmission Electron Microscope show the synthesized CuNP was spherical with particle size diameter 15nm for CuSO4 prekursor, 25 nm for Cu(NO3) prekursor and 28 nm for CuCl2 prekursor. The size of nanoparticles influenced of type prekursor anions. The antibacterial activity of the synthesized nanoparticles was also tested using pathogenic bacteria Escherichia coli and Staphylococcus aureus. The results showed that copper nanoparticles were promising antibacterial agents. Antibacterial activity test on copper nanoparticles were found to have higher antibacterial activity against Gram positive bacteria S. aureus than Gram negatif E. coli.

ВПЛИВ ОПТИЧНОГО СКЛА ЯК ПІДКЛАДКИ В ППР-СЕНСОРАХ НА ТЕМПЕРАТУРНУ СТАБІЛЬНІСТЬ РЕЗУЛЬТАТІВ ВИМІРЮВАННЯ

The influence of the properties of the substrate made from optical glass of surface plasmon resonance (SPR) sensors on the temperature stability of measurements at a temperature change from 20 to 30°C, in which research is most often carried out, was studied. The phenomenon of surface plasmon resonance is very sensitive to any changes at the metal-dielectric interface, so studying the influence of the temperature factor is an actual task. Research in the infrared region of the spectrum is important because in this case the possible thickness of the research object increases, and it is also possible to reduce the thickness of the gold layer that is sprayed to the glass substrate of the sensory element from 50 nm to 30 nm. But heating the sensitive element with an IR laser can introduce an additional error into the measurement results. The sensitive element of the SPR device consists of a plate made of optical glass and a thin layer of gold deposited on it. It is known that materials expand when heated. The difference in temperature coefficients of linear expansion of glass and gold applied to it can lead to unequal expansion of glass (74x10 -7 ) and gold (14.2x10 -6 ), respectively, causing elastic stresses in the gold sensitive layer of the sensor. Sensory elements with a 30 nm gold layer are used for the IR range of measurements, and 50 nm for the visible range. Therefore, we investigated the stability of the results of measuring the angle of surface plasmon resonance minimum at a wavelength of 650 nm (Plasmon-6 device). It was determined that the optical glass of the substrate affects the stability of measurements of the SPR index of air from temperature fluctuations. The period of stabilization of measurement results in the visible range when the temperature changes from 20 to 30 °C to the change in the angle of the SPR minimum changes from 0.0006 degrees/min for Zerodur to 0.0032 degrees/min for flints, i.e. almost 5 times with the thickness of the gold nanolayer 50 nm, and for a thickness of 30 nm it varies from 0.0010 deg/min for crowns and quartz to 0.0013 deg/min for flints. The lowest value corresponds to Zerodur substrates with practically zero temperature coefficient of linear expansion and quartz in this temperature range. To ensure the stability of the results of measurements of SPR characteristics against temperature fluctuations in the range of 20-30°С, it is recommended to use Zerodur, quartz and crowns for the substrates of SPR sensors

Super-resolution imaging for the detection of low-energy ion tracks in fine-grained nuclear emulsions

We propose a new wide-field imaging method that exploits the Localized Surface Plasmon Resonance phenomenon to produce super-resolution images with an optical microscope equipped with a custom design polarization analyzer module. In this paper we describe the method and apply it to the analysis of low-energy carbon ion tracks implanted in a nuclear emulsion film. The result is then compared with the measurements of the same tracks carried out at an electronic microscope. The images set side by side show their close similarity. The resolution achieved with the current microscope setup is estimated to be about 50 nm.

Nematic liquid crystal filled D-shaped voltage sensor with enhanced performance for power monitoring and fault detection in extreme environments

A nematic liquid crystal voltage sensor with enhanced performance is proposed in this paper. The sensor is designed D-shaped using a single NLC filled core without the presence of air holes, which has made the sensor fabrication much simpler than previous sensors. The sensor also consists of a circular slot that provides a vast space for the surface plasmon resonance (SPR) phenomenon with a minimum amount of gold. The performance of the proposed sensor is carried out using a finite element method (FEM) based simulation. Following this, the sensor obtains a maximum wavelength sensitivity of 10 nm/V for a wide range of 190 V to 250 V with 5 V increments. The sensor also has a linearity of 0.9926 and a figure of merit (FOM) of 0.2V−1. It has a resolution of 0.01 V. The proposed sensor is a promising technology with a wide range of extreme and sophisticated applications. The sensor’s simple structure, high sensitivity, resolution, linearity, and FOM make it perfectly suitable for a variety of sensing applications, including power monitoring, fault detection, medical diagnosis, voltage lines, electronics, etc.

Synthesis Optimization and Antibacterial Performance of Colloidal Silver Nanoparticles in Chitosan

Colloidal silver nanoparticles were successfully synthesized via the chemical reduction method. The synthesis used AgNO3 as the precursor, chitosan as the reducing and stabilizing agents, and NaOH as the accelerator. The synthesis parameters were optimized. The samples were tested with a UV-vis spectrophotometer to observe their localized surface plasmon resonance (LSPR) phenomenon, a transmission electron microscope (TEM), and a particle size analyzer (PSA) to investigate their particle shape and size distribution. Further, silver nanoparticles were tested for their storage stability and antibacterial performance. The UV-vis spectroscopy data exhibited that the silver nanoparticles have been successfully synthesized, validating via the emergence of the LSPR absorption band at 402–418 nm. At 50 °C, the optimum synthesis was achieved for 100 min of reaction time by adding 0.033 M NaOH and AgNO3 4.00% (w/w, AgNO3/chitosan). TEM results showed spherical silver nanoparticles of 1–8 nm, while the PSA results exhibited particles sizes of about 12–59 nm. The colloidal silver nanoparticles were stable in storage for 8 weeks and had good antibacterial performance against E. coli, S. aureus, extended-spectrum beta-lactamases (ESBL), and methicillin-resistant S. aureus (MRSA). Therefore, colloidal silver nanoparticles have the potential as a material for medical applications.

Enhancing the Extinction Efficiency and Plasmonic Response of Bimetallic Nanoparticles of Au-Ag in Robust Thin Film Sensing Platforms

The extinction efficiency of noble metal nanoparticles (NPs), namely gold (Au) and silver (Ag), are dependent on their size and surrounding dielectric. Exploiting the Localized Surface Plasmon Resonance (LSPR) phenomenon, the composition and structure of the NPs might be tailored to achieve a configuration that optimizes their response (sensitivity) to environmental changes. This can be done by preparing a bimetallic system, benefiting from the chemical stability of Au NPs and the higher scattering efficiency of Ag NPs. To enhance the LSPR sensing robustness, incorporating solid supports in the form of nanocomposite thin films is a suitable alternative. In this context, the NPs composed of gold (Au), silver (Ag), and their mixture in bimetallic Au-Ag NPs, were grown in a titanium dioxide (TiO2) matrix using reactive DC magnetron sputtering. Thermal treatment at different temperatures (up to 700 °C) tuned the LSPR response of the films and, consequently, their sensitivity. Notably, the bimetallic film with Au/Ag atomic ratio 1 exhibited the highest refractive index sensitivity (RIS), with a value of 181 nm/RIU, almost one order of magnitude higher than monometallic Au-TiO2. The nanostructural analysis revealed a wide NP size distribution of bimetallic NPs with an average size of 31 nm, covering about 20% of the overall surface area. These findings underscore the significant potential of bimetallic film systems, namely AuAg-TiO2, in LSPR sensing enhancement.