In recent years, there have been a lot of papers and reports on the DNA-templated silver nanoclusters. These nanoclusters are ultra-bright and stable fluorescent beacons. Application of DNA-templated silver nanoclusters for biomolecules detection and bioimaging seems promising. However, direct conjugation between DNA-templated silver nanoclusters and antibodies is complicated while nanoclusters tend to degrade under conjugation conditions. To overcome this problem, it is possible to create a probe that not only can serve as an fluorescence reporter but also can contain the recognition motif that could selectively bind with target biomolecules. In the present work, we developed DNA-templated silver nanoclusters based on aptamer to lung cancer. Various sequences were added to core aptamer nucleotide sequence to form fluorescent nanoclusters. The synthesis of DNA-templated silver nanoclusters using borohydride reduction was conducted. Nanoclusters with 567 nm excitation and 630 nm emission were produced. The fluorescence quantum yield was 32 %. The storage technique of DNA-templated silver nanoclusters was optimized to ensure their photostability during the storage. Thus, bright and stable fluorescent red-emitting DNA-templated silver nanoclusters based on novel aptamer to lung cancer were developed. However, the potential use of DNA Ag NC for cell staining is complicated by the partial quenching of DNA Ag NC fluorescence in the presence of biomolecules.
Currently, GERTs tags are widely used nanoparticles in various fields of biosensing and bioimaging. This is due to their high SERS response and depends directly on their structure. Understanding Raman signal dependence on the GERTs structure is a key to creating custom tags with the required SESR response. In this regard, we obtained GERTs tags based on different nanocore and carried out a comparative analysis of their SERS properties. Three types of core were used: nanospheres, nanopolygons, and nanorods. Benzenedithiol-1,4 was used as a Raman reporter. Signal intensity increased in the spheres-polygons-rods series and maximum of SERS enhancement factor was obtained from GERTs based on nanorods of the order of 2E+06.
Bimetallic Au-Ag SERS tags with aromatic Raman reporters embedded between layers have emerged as new type of nanoparticles with high potential for application in various fields of biochemistry and biomedicine. Particular interest is based on their high SERS enhancement factor under non-resonant laser irradiation. The thickness and shape of the outer silver layer is one of the factors determining the SERS properties of bimetallic nanoprobes. Here we studied eight types of AuNR core@embedded Raman reporter (4-nitrobenzenthiol)@Ag shell nanoparticles with various shell thicknesses from 2 to 40 nm. The SERS enhancement factor for our samples varied in the range of 2.35-6.68×105; the maximum value was observed for particles with an outer shell thickness of 3 nm along the long nanorod axis of the rod and 16 nm along the short one. Simulation of the electromagnetic field by the FDTD method showed the presence of socalled “hot spots” at the boundary of the metal layers in a series of samples with high SERS EF.
It is now believed that the on-resonance excitation of the plasmonic nanoparticle is necessary to increase the Raman signal intensity of nearby molecules. On this basis, researchers try to fabricate rationally designed nanoparticles for surface-enhanced Raman scattering (SERS) applications with plasmon resonance close to wavelength of excitation. However, existing experiments show inconsistent results of measuring the dependence of the enhancement factor as a function of nanopaticle plasmon resonance. To fill the gap, we use the method of controllable etching to prepare set of Au nanorod colloids with the equal concentration, nanorod width, shape and tunable plasmon resonance that incrementally spanned 650-920 nm. Nanorods were functionalized with 4-nitrobenzenethiol and surface-enhanced Raman spectra were measured in colloid under 785 nm laser excitation. As a result we observe weak correlation between nanorod plasmon peak and SERS response. The ratio of SERS signals for on-resonance and of-resonance excitation was below 2. Nanorods were further overgrowth to have dumbbell morphology. This transformation leads to strong increase in SERS enhancement factor. Thus tuning of nanoparticles shape is more important factor towards highest SERS response compared to nanoparticle plasmonic peak.
The most common protocol for the synthesis of Au nanospheres is the reduction of gold salts by sodium citrate. However, the particles obtained by this method are not quite perfectly spherical and their optical and physical properties suffer from polydispersity and nonuniformity. In this work, we synthesized sets of quasispherical Au nanoparticles with sizes from 20 to 70 nm by citrate-based methods as well as single-crystal Au nanospheres with uniform diameters ranging from 20 to 130 nm. Particles were characterized by TEM, UV-VIS and Dynamic Light Scattering (DLS). We found that the extinction spectra of monodisperse Au nanospheres are equal to those calculated by using Mie theory (both in the position and width of the plasmonic band). The deviation of shape from a sphere that is typical of citratestabilized nanoparticles leads to a significant departure of the optical properties from those predicted by Mie theory. The non-sphericity of these particles also affects the measurement of their size by DLS. In particular, citrate-stabilized nanoparticles display a bimodal size distribution associated to rotational diffusion.
Polydopamine-coated Au nanorods (AuNRs) have attracted a great interest for various biomedical applications. Polydopamine (PDA) is a light absorbing biopolymer with nonzero imaginary part of the refractive index, which exerts a significant effect on the optical properties of PDA-coated AuNRs. In this paper, we study the changes in plasmonic properties of AuNRs after PDA coating. We observed that the longitudinal plasmon resonance decreases while the transversal one increases. To confirm the experimental observations, we performed theoretical simulations of the extinction and scattering spectra for AuNRs with different geometrical properties, PDA shell thickness and refractive index. The loss of plasmonic peak intensity becomes higher as the axial ratio of the AuNRs or the imaginary part of the refractive index of PDA increase.
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