Plasmonics

The resonance of surface plasma waves in metallic layers is a strongly polarization-dependent phenomenon by the very nature of the physical effect responsible of that resonance. This implies the necessity of polarization-controlling elements to be added to any operative surface-plasmon-resonance-based sensor. A fully symmetrical, circular-section double deposition of a metallic and a dielectric layer on a uniform-waist tapered optical fiber (SymDL-UWT) permits us to completely eliminate the dependence on polarization of the plasmon excitation, with the corresponding operative advantages and basic theoretical consequences. We depict the fabrication process of these transducers, which is based on the use of a simple and efficient rotating element developed by us, and show the characteristics of the produced devices. No such device has been depicted up to date. As our experimental results show, this kind of devices can be considered a very good option for the development of simple, compact, and efficient chemical and biological sensors.

Graphene bilayered split rings (BSRs) are proposed to generate tunable circular dichroism (CD). BSRs with traditional materials do not elicit the CD effect because of C4 symmetry. By contrast, BSRs with graphene can achieve the CD effect by varying the Fermi energy of each part of the split rings. The CD signal can be reversed from positive to negative or vice versa by exchanging the Fermi energy. CD effects can also be tuned by varying the Fermi energies of the different parts. This phenomenon indicates that the chirality of BSRs gradually change as the Fermi energy varies. This concept provides a method to change chirality and dynamically vary the CD effect without rebuilding the structures.

CuS nanostructures with high surface areas were produced through a hydrothermal method using simple materials. These included pure CuS, as well as CuS doped with Fe, Ag, and Mn, as well as dual-doped with Fe/Mn and Ag/Mn. X-ray diffraction (XRD), field-emission scanning electron microscopes (FE-SEM), chemical composition (EDX) analysis, zeta potential, ultraviolet–visible (UV–vis) absorption spectra, and compositional chemicals (FTIR) have been used to characterize the produced nanoparticles. The XRD patterns indicate that the CuS is in hexagonal covellite polycrystalline phases with estimated crystalline sizes of 25.14–14.25 nm. The optical measurements showed that the band gaps ranged from 3.19 to 2.24 eV. The inhibitory effects of pristine CuS, as well as CuS doping with Fe, Ag, and Mn and dual-doping with (Fe/Mn, Ag/Mn), against Pseudomonas aeruginosa, Staphylococcus aureus, and Escherichia coli, were evaluated using the inhibition zone method. All samples exhibited robust antibacterial activity against all strains. The highest level of inhibition against all strains was observed with a concentration of 4 mg/ml of copper sulfide. Out of all the tested samples, (Ag/Mn) dual-doped copper sulfide showed the highest antibacterial activity against both negative-gram and positive-gram bacteria. Hence, (Ag/Mn) dual-doped copper sulfide might be applied as an antibacterial agent with antibiotics to kill and prevent resistance bacterial development.

With continuous mutations of SARS-CoV-2 virus, new highly contagious and fast-spreading variants have emerged, including Delta and Omicron. The popular label-free immunosensor based on surface plasmon resonance (SPR) technique can be used for real-time monitoring of the ligand-analyte or antibody-antigen interactions occurring on the sensor surface. In this work, an SPR-based biosensor combined with a nanodisk array was presented to enhance the sensitivity toward virus detection. The nanodisk arrays were employed to enhance the adsorption of molecules for better detection by increasing the SPR field. Four optimal sensing configurations of silver or gold nanodisks on gold thin films with different aspect ratios were achieved through systematic optimization of all parameters to yield the best sensor performance. The resonance angle can be modulated simply by the aspect ratio of nanodisk array. The sensitivity of the optimized sensors has been improved, and the detection limit is smaller than that of bare gold-based sensor. The multi-jump resonance angle curves at tiny refractive index can clearly distinguish the difference of trace concentrations, which is very important for the accurate detection of trace substances.

A theoretical study of photon statistics of an optically driven quantum dot located near a metal nanoparticle cluster (composed of one or two nanoparticles) is presented. Considering the system in the weak Rabi frequency regime, an analytical formula for anti-bunching time is derived. Using a photon Green’s function method based on the exact quantization of electromagnetic field in a dissipative medium, the dependence of the anti-bunching time on the geometrical parameters (quantum dot radius and quantum dot distance from the metal nanoparticle) is studied. The results show that these geometrical parameters have pronounced impacts on the photon statistics. Furthermore, our findings reveal that the quantum dot dipole orientation possesses an important role in the quantum dot photon emission.

Bột nano hợp kim lõi-vỏ Fe3O4 và Fe3O4/Ag đã được tổng hợp bằng phương pháp đồng kết tủa. Cấu trúc, vi cấu trúc, tính chất từ tính và quang học của Fe3O4/Ag và Fe3O4 đã được nghiên cứu. Các mẫu XRD và phổ UV-Vis cho thấy rằng các hạt Fe3O4 và Fe3O4/Ag có cấu trúc nano đã được tổng hợp thành công. Hình ảnh chế độ AFM và MFM của bột Fe3O4 và Fe3O4/Ag xác nhận sự hình thành của các hạt Fe3O4 trong khoảng nano. Cả hai loại bột composite Fe3O4 và Fe3O4/Ag đều cho thấy hành vi siêu từ tính do sự hình thành của các hạt Fe3O4 kích thước nano. Hơn nữa, việc tổng hợp Ag tại bề mặt của các hạt nano magnetite đã làm tăng kích thước hạt, dẫn đến sự giảm biên độ từ trường bão hòa. Ngoài ra, dựa trên lý thuyết chất môi hiệu quả Maxwell-Garnet, một mô hình lý thuyết đã được phát triển để xác định các tính chất quang học của các hạt nano lõi-vỏ treo lơ lửng. Một sự phù hợp rất tốt đã được tìm thấy giữa các kết quả lý thuyết và thực nghiệm. Thêm vào đó, trường điện cục bộ trong các hạt, được đánh giá bằng phương pháp phần tử hữu hạn số, cho thấy rằng trường điện trong lõi magnetite có thể được khuếch đại lên tới 20 lần tại chế độ bước sóng SPR đối xứng, tùy thuộc vào độ dày lớp vỏ bạc.

A broadband plasmonic optical modulator based on a dual back-to-back U-shaped silicon waveguide and double layers of graphene has been investigated. The proposed structure is designed at TE mode over a range of wavelengths extending from 1.1 to 1.9 μm. By adjusting the geometry of the U-shaped structure, the modulator’s performance has been tuned. Utilizing propagation loss, bandwidth, power consumption, and modulation depth, the proposed modulator’s performance has been characterized. According to the results, at a wavelength of 1.55 μm, the loss, modulation depth, and small footprint read 0.0415 dB/μm, 0.6337 dB/μm, and (0.5 μm × 12.17 μm), respectively. Furthermore, the proposed modulator has a modulation bandwidth of about 151.7 GHz and a power consumption of 21.068 fJ/bit.

An efficient strategy involves the use of antibiotic-conjugated nanoparticles. This research primarily aimed to enhance the biosynthesis of gold nanoparticles by binding them with ciprofloxacin. We investigated the biological, optical, and structural characteristics of gold nanoparticles (AuNPs) and their combination with ciprofloxacin (CIP@AuNPs). We performed a number of analyses using Fourier-transform infrared (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM), and UV–VIS spectroscopy using a cost-effective pulsed-laser ablation technique (PLAL). The size and morphology of the nanoparticles were notably determined by the TEM analysis, which showed an average particle size of less than 20 nm. We also investigated the antibacterial effects of AuNPs, ciprofloxacin, and CIP@AuNPs against two bacterial strains: the gram-negative Klebsiella pneumonia and the gram-positive Streptococcus pneumonia. Utilizing the well-diffusion method, we observed that CIP@AuNPs exhibited greater effectiveness compared to ciprofloxacin alone or AuNPs alone. The bacterial strains tested in this study exhibited a high degree of resistance to the antibiotics under investigation. The antimicrobial activity assay revealed the most significant inhibition zone when dealing with S. pneumonia, as compared to K. pneumonia. Notably, Ciprofloxacin-conjugated gold nanoparticles displayed a more pronounced inhibitory effect when contrasted with Ciprofloxacin or standalone AuNPs. We further delved into the nanoparticles’ capacity to prevent biofilm formation, supported by atomic force microscopy (AFM) research examining how Ciprofloxacin-conjugated gold nanoparticles influenced bacterial biofilm development within nebulizer masks. The combination of Ciprofloxacin-conjugated gold nanoparticles holds promise as a preservative for nebulizer masks, effectively curbing the formation of microbial biofilms. Additionally, Ciprofloxacin-conjugated gold nanoparticles demonstrated antioxidant activity through the DPPH assay. These investigations underscore the potential utility of these particles in the development of antioxidant drugs. In vitro assessments revealed that Ciprofloxacin-conjugated gold nanoparticles (Ciprofloxacin@Au) proved effective against multidrug-resistant bacteria, establishing their credentials as potent antibacterial agents. In summary, addressing the challenges associated with biofilm formation in nebulizer masks is paramount for safeguarding the health and well-being of respiratory patients. Preventing biofilm development not only mitigates infection risks but also fosters patient comfort, aids in the healing process, ensures efficient medication delivery, and ultimately contributes to reducing healthcare costs.