Detection of nucleic acids has become a promising approach in diagnostics, but current methods often have limitations such as the need for expensive equipment or reduced sensitivity and specificity. Tuberculosis caused by M. tuberculosis is a widespread infectious disease that is also prone to developing antibiotic resistance. In this study, we introduce a novel method for detection and genotyping of M. tuberculosis using a biosensor based on a four-way junction (4WJ) DNA probe and plasmon Au nanospheres.
An anisotropic Ag@Au nanostructure is fabricated via physical vapor deposition of gold at oblique incidence onto a glass substrate with a preformed silver nanoparticle array. Utilization of silver nanoparticles as a scaffold for subsequent gold deposition makes it possible to control the size and shape of the gold capping layer. The obtained Ag@Au nanostructures are characterized by adjustable absorption bands and linear dichroism. The proposed technique provides for new opportunities in creation of plasmonic nanoparticles with targeted optical characteristics for applications in nanophotonics.
Whispering Gallery Mode (WGM) microlasers were obtained by impregnating polystyrene microspheres in an aqueous solution of plasmonic nanoparticles and Rhodamine 6G. The emission spectra of Rhodamine-doped microspheres with diameters of 1 μm and 5-7 μm exhibited peaks corresponding to WGM, with a low Q-factor for 1-μm and a higher Q-factor for 5-7-μm spheres. The embedding of gold nanoparticles into microlasers results in a 40% decrease in the WGM intensity, while doping with silver nanoparticles increases it by 10%.
One of the most critical issues in the field of molecular diagnostics and medicine is the development of compact and sensitive assay devices for the precise detection of nucleic acids. Although there are several effective methods for detecting unique nucleic acid sequences, the high cost of equipment and reagents, as well as the need for highly trained personnel, necessitate the design of new and more affordable diagnostic assays that are comparable in selectivity and sensitivity to existing methods that can be used in developing countries and/or outside of specialized diagnostic laboratories. Sensing methods based on guanine quadruplexes (G-4)/hemin complexes, that have peroxidase activity are one of the promising directions for the detection of target nucleic acids. Target nucleic acid was analyzed by peroxidase-like DNA-nanomachine (PxDm) equipped with 1-3 long analyte binding arms to tightly bind and unwind single-stranded analytes. In this study, we present a technique for sequence-specific detection of nucleic acid. The technique is based on the measuring of a chemiluminescent (CL) emission induced by luminol oxidation utilizing a closed-type detection device. Moreover, the optical properties and potential use of plasmonic silver nanoparticles (Ag NPs) to enhance the CL intensity of chemiluminophore were investigated. Particular attention was paid to the possibility of synthesizing the silver nanoparticles with different spectral positions of plasmon resonance band, depending on the method and duration of synthesis. The CL intensity of luminol in the presence of the post-centrifuged colloidal Ag NPs obtained by laser ablation has been increased 3 times. The combination of AgNPs-luminol-DNA-nanomachine systems in the presence of a target analyte led to the significant increase of limit of detection and reached clinically relevant quantitative indications.
Efficient point-of-care (POC) molecular diagnostic techniques can be designed using highly selective hybridization of G-quadruplex-based DNA-nanomachine (G-4DNM) with specific analytes that produce readable outputs. We propose the design of G-4DNM that can unwind an analyte’s secondary structures, solving the problem of nucleic acid analytes’ recognition at ambient temperatures. S.aureus is a pathogen responsible for a number of nosocomial infections. For detection, we chose a specific gene that is constitutively expressed. S.aureus was analyzed by G-4DNM equipped with 3 long analyte binding arms to tightly bind and unwind single-stranded analytes. Only when all arms bind the analyte a G-quadruplex (G-4) structure is formed. This structure can form a complex with hemin, which exhibits peroxidase activity. In the presence of the G-4/hemin complex, the chemiluminescence (CL) of luminol molecules, activated by hydrogen peroxide, is enhanced. We evaluated the CL kinetics for several minutes, comparing them with the background signal using a highly sensitive photon counting head. The results indicated that S.aureus was recognized with high selectivity and sensitivity up to attomolar concentrations in a quartz cuvette. Our research provides the basis for rapid and affordable POC diagnostics. In the future, this system may become a full-fledged lab-on-a-chip for the detection of marker-sequenced nucleic acids.
Cu2-xS nanoparticles have the ability to absorb radiation in the near infrared (NIR) range. This is due to localized surface plasmon resonance (LSPR) of free holes in the valence band. This fact makes it possible to use copper sulfide nanoparticles for sensing application in the NIR range. Our study showed that Cu2-xS nanoparticles have a significant localized surface plasmon resonance. The LSPR of nanoparticles was tuned by adjusting the concentrations of Cu and S. In this case, the plasmon peak reaches a maximum at values of about 1210 nm. Thus, highly localized electromagnetic field of Cu2-xS NPs can be successfully applied for to detection of vibrational bands (overtones) of various molecules in the NIR region. We showed the splitting of longitudinal and transverse dipolar resonance modes of Cu1.4S was changed in the presence of NMethylamine molecules.
Hybrid nanostructures that couple plasmon and exciton resonances generate hybridized energy states, which may result in unusual light-matter interactions. In our work we studied island films from the inhomogeneous ensemble of gold nanoparticles obtained by thermal vacuum deposition, spin-coated with a molecular layer of cyanine dye, in which Jaggregates were formed. The influence of the cyanine dye length chain of conjugation and the thickness of the island film on the optical properties of the hybrid structure was studied. The increase of the molecule absorption is observed for pseudoisocyanine, in comparison with mono- and dicarbocyanine dyes. The transparency in the absorption spectrum of a hybrid film with pseudoisocyanine was observed at a wavelength of 583 nm corresponding to the maximum of the Jaggregate band, which can be explained by the strong coupling of the exciton transition in the J-aggregate with the plasmon resonance of nanoparticles.
Excitation of localized surface plasmon resonance in noble metal nanoparticles leads to enhancement and localization of electromagnetic fields in the immediate vicinity of nanoparticles. These properties may be employed to amplify the lightmatter interaction in the near-infrared range where the overtone molecular vibrations are situated. Since the overtone vibration bands are much weaker than the fundamental bands, the amplification is essential. Here we explored SENIRA in the framework of molecular overtones sensing, particularly, those overtones that correspond to the C-H (1676 nm) and NH (1494 nm) stretching modes overtones. The gold nanorods (GNRs) are placed on the dielectric substrate and embedded into a thin layer of organic probe molecules (N-Methylaniline). The dispersion characteristics of N-Methylaniline, namely, its wavelength-dependent absorption and refractive indices in the spectral vicinity of the overtone transitions were fully taken into account. To find out the enhancement of overtone transitions provided by the GNR, we numerically calculated the differential transmission (DT) as a function of the gold nanoantenna’s size and grating periods. The computational results evidence that in sparse arrays of GNRs when the near fields of the neighbor GNRs do not overlap with each other, the differential transmission of stretching overtone modes shows the resonance at the right spectral position which is around 8.8 times larger as compared to the absorption of the bare molecular film of the same thickness. Thus, the obtained results substantiate a new sensing spectroscopy concept for identification of versatile “fingerprints” in the near-IR range based on plasmon-overtones interactions.
Infrared spectroscopy is very powerful tool to analyze the chemicals based on their molecular signatures. The registration of the fundamental vibrational modes that lie in the far IR is extensively explored, however the excitation of derivatives namely high harmonics molecular vibrations overtones is still a mystery. Although the absorption crosssection of molecular transition overtones is order of magnitude smaller compared to their fundamental vibrations, the research of overtones is of high importance if just would be possible to detect them. In this work, we show that the challenge in detection of molecular overtones may be overcome with localized surface plasmon resonance effect in gold nanorods antennas. We use N-Methylaniline as a probe molecule since we confirmed the excitation its molecular transitions overtones in near-infrared around 1.5 μm. We calculate absorption cross-section of gold nanorods with fixed diameter of 10 nm and different lengths varying from 80 to 160 nm surrounded by a homogeneous medium with the optical properties of N-Methylaniline, using the finite element method (FEM). To single out the contribution of the overtone modes, computations were repeated with N-Methylaniline replaced by the dispersionless media mimicking only the mean value of N-Methylaniline refractive index, n = 1.5712, and eliminating absorption. We show, that the differential absorption in the spectral range of the first overtone of the -NH vibration located at 1492 nm and the first overtone of the -CH vibration located at 1676 nm have both positive and negative values due to the shifting of the gold nanorod plasmon resonance band.
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