Plasmonics最新文献

Silver ion (Ag⁺) is one of the heavy metals (HMs) of interest that must be regularly profiled, by virtue of its toxicity and eco-physiological implications. Herein, a colorimetric assay for sensitive detection of Ag⁺ ion in solution is developed. To avoid the introduction of toxic chemicals in the material synthesis stage, ascorbic acid (AA) was employed as the reducing/stabilizing agent at room temperature (RT), for the gold nanoparticle (AuNPs) synthesis. The biocompatibility of the synthesized AA-AuNPs was demonstrated by the cytotoxicity test using MTT assay on mouse macrophage cells (RAW 264.7), which revealed that AA-AuNPs imparted no destruction on the tested cells. Further, AA capping on the AuNP surfaces was confirmed by Raman and Fourier transform infrared spectroscopy (FTIR). At the optimal detection conditions, the addition of Ag⁺ to AA-AuNPs solution (pH 10) resulted in naked-eye color transitions from red to orange and yellow, with a blue shift in the absorption maximum from 522 to 400 nm. This is attributed to the reduction of Ag⁺ on the initially synthesized AA-AuNPs probe, induced by the capping agent, forming Au@Ag core–shell nanomaterials. The analytic response (A_f-A₀)400 nm plotted against Ag⁺ concentrations was linear within 0.05–12.50 and 12.50–150.00 µM, with estimated limit of detection (LOD) of 15.8 nM. For practical usage, the probe was deployed for Ag⁺ detection in lake water sample, showing impressive accuracy (95.5–104.7%) and precision.

Owing to the detrimental effect on human health, the contamination of drinking water and water sources by metal and heavy metal ions has received significant attention from the scientific community. Among the metal ions, copper has drawn considerable attention, since at a certain dose, it holds significance in the physiological processes of the living being, but when used excessively, it could be very toxic and can cause many diseases. Hence, the ongoing research focus is on creating accurate and affordable analytical techniques or procedures for detecting copper ions in drinking water. With advancements in different analytical methods, currently, nanoparticle-based sensors are widely developed especially plasmonic (Ag and Au) due to a wide range of optical properties that offer fast real-time visualization. This review paper briefly covers the synthetic process of plasmonic (silver) nanoparticles and provides a comprehensive overview of the recent trends in developing silver-based plasmonic nano-sensors for copper metal ions. The review revealed that silver-based plasmonic nano-sensors are promising tools for copper metal ion sensing and could detect with high selectivity and sensitivity with the minimum set-up in real water samples.

Graphical Abstract

The present work deals with the study of the plasmonic modes of core–shell nanostructures (silver–aluminum nanocylinders) using the finite-difference time-domain (FDTD) numerical method. The nanocylinders are placed in a two-dimensional square periodic array under normal radiation in the spectral range of 200–800 nm. This study has tried to reduce radiation losses and create strong surface lattice resonances (SLR) in the ultraviolet (UV) region by using a suitable combination of materials and nanostructures. In this regard, it is demonstrated that by changing the dimensions and geometry of the cores of nanocylinders, as well as the characteristics of incident light radiation, one can obtain a suitable optical response in the near-UV spectral region. The calculations show that a new SLR peak related to the hybrid nanostructure is formed in the near-UV region under s-polarized radiation, and for the core with a circular cross-section, in addition to the primary modes related to an array composed of individual nanoparticles. This peak, with a quality factor of 41 at the wavelength of 372 nm, is close to the diffraction modes of the dielectric substrate. Also, by reducing the height of the core, another peak is formed with a quality factor of 12 at the wavelength of 260 nm under the shell’s plasmonic effects and close to the environment’s diffraction modes. These modes (SLRs) provide the possibility of achieving high-energy spectral regions with a suitable quality factor, which is not usually possible in other nanostructures. By changing the polarization of the incident light to p-polarization, depending on the period of the array, the principle resonance peak is formed with a shift to higher wavelengths in the visible region with a quality factor of 20 at the wavelength of 452 nm, as compared to s-polarization. This demonstrates the different spectral responses of nanocylinders under the influence of changes in the polarization of the incident light. The effects of the refractive index of the substrate on the plasmonic modes are also studied. The results indicate that the location and intensity of the core–shell modes (372 and 260 nm) are highly dependent on the substrate refractive index. The findings of the present study suggest the use of nanocylinders (core–shell) as a suitable option for application in sensors, nanolasers, and other optoelectronic devices.

The recurring consumption of formalin, a notorious preservative, can lead to a variety of lethal diseases and cause significant morbidity, highlighting the pressing need for its precise detection in developing nations. Hence, in this article, a Kretschmann configuration–based hybrid surface plasmon resonance (SPR) biosensor is proposed and analyzed numerically for formalin detection. The sensor heterostructure consists of five monolayers, namely, BAK1 prism, WS₂, silver, FASnI₃ halide perovskite (HP), and 2D black phosphorous (BP). The influence of an additional metal oxide layer (ZnO, TiO₂, SiO₂, Al₂O₃, and MoO₃) over the metallic layer is also investigated w.r.t. major performance indicators such as sensitivity, detection accuracy, quality factor, and figure of merit. Here, BP and HP jointly act as biomolecular recognition elements. Chitosan serves as a probe to react with formalin, which acts as the target molecule. Using the attenuated total reflection (ATR) concept and Fresnel equations, we have employed angular interrogation and transfer matrix approaches to detect the concentration of formalin by monitoring the variations in the minimum reflectance and maximum transmittance attributors in relation to SPR angle and SPR frequency (SPRF), respectively. The simulation findings demonstrate a minimal variation in SPR angle and SPRF for improper formalin sensing, confirming its absence in liquid solution. In contrast, the aforesaid attributors show significantly measurable changes when formalin is properly sensed, confirming its presence. We demonstrate that adding MoO₃ over the Ag layer can enhance the detection accuracy of our primary HP-based SPR biosensor to a maximum of 55.6%. The finite difference time domain (FDTD) technique is utilized to examine the distribution of electric fields within this biosensor structure to showcase the distinct contributions of HP and metal oxide. In the end, our simulation work is validated by a comparative study of the performance parameters with a few of the previous works on formalin detection.

In this research, a new model of the photonic crystal fiber (PCF) biosensor, which uses the surface plasmon resonance (SPR) principle, is presented, with a focus on effectively identifying various cancerous cells in the human body. We specifically targeted six different types of cells, namely, Basal, Hela, Jurkat, PC 12, MDA MB 231, and MCF 7, which are linked to skin, cervical, blood, adrenal gland, and two types of breast cancers. The biosensor works by detecting shifts in resonance wavelength (RW) between healthy and infected cells. Our exploration involved a dual-mode investigation, considering both transverse magnetic (TM) and transverse electric (TE) polarization. The wavelength sensitivities (({{varvec{S}}}_{{varvec{W}}})) of 4000, 3333.33, 6071.42, 6428.57, 8428.57, and 13,571.42 nm/RIU and 3520, 2916.66, 5000, 7142.85, 8571.42, and 12,857.14 nm/RIU, and amplitude sensitivities (({{varvec{S}}}_{{varvec{A}}})) of 2482, 6124, 9773, 13,452, 15,289, and 18,651 RIU⁻¹ and 1467, 2683, 5845, 7243, 10,089, and 16,864 RIU⁻¹, are obtained for TM and TE polarizations, respectively. A sensor resolution (({{varvec{S}}}_{{varvec{R}}})) of the order 10⁻⁶ is achieved for both polarizations. Owing to its high sensing parameters and a novel combination of materials, the proposed dual-mode PCF SPR sensor shows significant promise as a valuable tool for perceiving cancer cells, potentially aiding in the early detection and management of various forms of cancer.

This work reports the synthesis of blue-emitting graphene quantum dots (GQDs) with an average diameter of 3.8 ± 0.5 nm from paddy straw, a sustainable biomass resource, via hydrothermal synthesis. These GQDs demonstrate excellent performance in bilirubin (BR) detection. The GQD photoluminescence (PL) intensity exhibits a proportional decrease with increasing BR concentration, indicating efficient quenching. The limit of detection for BR reaches a low value of 87.9 nM, highlighting the high sensitivity and selectivity of the GQD-based sensor. The observed quenching likely arises from a combined mechanism involving static quenching due to GQD-BR complex formation, inner filter effect (IFE), and Förster resonance energy transfer facilitated by spectral overlap.

This research presents a novel approach to effectively modify the characteristics of bifacial porous silicon (B-PSi) layers using tri-metallic nanoparticles. The B-PSi was synthesized by double beam laser-induced etching (D-LIE) of an n-type silicon substrate using 533-nm wavelength lasers at 80-mW power. Tri-metallic nanoparticles with a core/shell configuration, composed of Au, Ag, and Pd, were then incorporated onto the B-PSi surface through a dipping process in a solution with a 1:1:1 volumetric ratio of HAuCl4, AgNO3, and PdCl2 at 2-mM concentration for 4 min. The structural, spectroscopic, and morphological properties of the bare B-PSi were significantly modified by the deposition of the tri-metallic nanoparticles. Notably, the bifacial faces of the porous silicon layer exhibited a high degree of symmetry in terms of grain sizes of the tri-metallic nanoparticles, surface morphology, photoluminescence emission, and chemical bonding, both before and after nanoparticle deposition. This simple yet novel approach demonstrates an effective method for tailoring the characteristics of bifacial porous silicon layers through the integration of tri-metallic nanostructures.

In this paper, we propose a new plasmonic metamaterial-based biosensor using graphene-coated titanium nitride nano-cuboids with a tunable absorbance peak for the use in the first biological window in the infrared region between 830 and 950 nm. Using the finite element simulations, we study the absorbance of the proposed graphene/TiN hybrid metamaterial and demonstrate the possibility of achieving narrow and sensitive peaks to ambient medium index of refraction. The proposed nanostructure is highly tunable across the first biological window as the optical response of the metamaterial can be simply adjusted by varying the bias voltage of graphene nano-films. We demonstrate that graphene coating of the titanium nitride nano-films not only introduce tunability in the structure, but also improves the average absorption of the metamaterial by more than 20%, and the sensitivity by more than double while acting as a surface protection layer for the TiN nano-cuboids. The optimized structure demonstrates an average linear spectral sensitivity of 1014 nm/RIU, and a detection limit of 9.86 × 10^–6 RIU has been obtained for RI variations between 1.3 and 1.42. The proposed structure also demonstrates an amplitude sensitivity of 5 RIU⁻¹ with 850 nm excitation in IR region for liquid analytes. We also showed that the proposed sensor has a linear response for small variations in analyte RI with a tunable peak in IR region. This enables the development of a highly tunable and accurate refractometer for the detection of biomaterials, biological molecules, and liquid analytes in the infrared region. Finally, we demonstrate that small variation in design parameters due to fabrication-induced imperfection does not change the sensing performance of the proposed biosensor, resulting in a viable platform for sensing and narrowband applications with higher stability, sensitivity, and durability than previously reported structures based on traditional plasmonic materials like gold and silver.

This study presents an innovative surface plasmon resonance (SPR) biosensor model constructed with a glass prism coated first with a layer of silver followed by a graphene layer (glass prism/Ag/graphene). The biosensor was analyzed using a finite element method-based simulation platform. Evaluation of the SPR sensor was conducted using a range of normal and cancer cell lines, including Basal (skin cancer), HeLa (cervical cancer), Jurkat (blood cancer), PC12 (adrenal gland cancer), and MCF-7 (breast cancer) cells. The results demonstrate the biosensor’s effectiveness in detecting various cancerous cells across a wide range of refractive index variations. Sensitivity values for skin, cervical, blood, adrenal gland, and breast cancer cells are reported as 120.0 °/RIU, 200.0 °/RIU, 142.9 °/RIU, 114.3 °/RIU, and 114.3 °/RIU, respectively. This proposed biosensor model offers significant potential for a variety of bio-sensing applications.

The reduction of the photoluminescence (PL) decay time of a colloidal quantum dot (QD) inserted into an Ag or Au surface nanohole and the efficiency enhancement of the Förster resonance energy transfer (FRET) from a green-emitting QD into a red-emitting QD are first experimentally demonstrated. Besides the factor of metal dissipation in the induced surface plasmon (SP) coupling process, the reduced PL decay time is attributed to the QD emission efficiency increase caused by the SP-coupling-involved nanoscale-cavity effect. Numerical simulation studies are undertaken to confirm the feasible enhancements of QD emission, FRET, and color conversion efficiencies. In particular, by artificially changing the dielectric constant of Ag based on the Drude model, the effects of cavity resonance and SP coupling in producing the enhanced radiated power peaks can be differentiated. Such a peak can be formed when both conditions of cavity resonance and SP resonance are satisfied. In the case of a weaker (stronger) SP resonance, the combined resonance can lead to a stronger and sharper (weaker and broader) radiated power peak. The results in this paper indicate that a nanoscale metal cavity can be used for enhancing the emission and color conversion efficiencies of inserted light emitters.