Combined Extinction and Absorption UV–Visible Spectroscopy as a Method for Revealing Shape Imperfections of Metallic Nanoparticles

Interactions between gold nanoparticles with different morphologies and human serum albumin

Introduction: Three different shapes of gold nanoparticles were synthesized in this experiment. At the same time, studies compared their effects with human serum albumin (HSA). Methods: Gold nanoparticles (AuNPs) with three different morphologies, such as, nanospheres (AuNSs), nanorods (AuNRs), and nanoflowers (AuNFs) were synthesized via a seeding method and their characteristic absorption peaks were detected using ultraviolet-visible (UV-vis) absorption spectroscopy, Telectron microscopy (TEM), Dynamic Light Scattering (DLS) and Zeta potential measurements, circular dichroism (CD), and Fourier transform infrared spectroscopy (FTIR) to study the interactions between them and HSA. By comparing the thermodynamic parameters and quenching mechanism of the three materials, similarities and differences were determined in their interactions with HSA. Results: The results showed that with an increase in the concentration of the AuNPs with the three different morphologies, the UV-vis absorption peak intensity of the mixed solution increased, but its fluorescence intensity was quenched. This indicates that the three types of AuNPs interact with HSA, and that the interactions between them represent a static quenching process, which is consistent with the conclusions derived from three-dimensional fluorescence experiments. Through variable-temperature fluorescence experiments, the binding constants, number of binding sites, and thermodynamic parameters of the interactions between the three types of AuNPs and HSA were determined. The Gibbs free energy changes were <0, indicating that the reactions of the three types of AuNPs with HSA are spontaneous, resulting in associated matter. Binding constant measurements indicated that the strongest binding took place between the AuNFs and HSA. In addition, the results of fluorescence, CD spectroscopy, and FTIR showed that three different shapes of AuNPs can induce conformational changes in HSA and reduce the α-helix content. Among them, AuNFs have the smallest ability to induce conformational changes. Discussion: According to studies, AuNFs interact more favorably with HSA. This can be used as a reference for the administration of drugs containing AuNPs.

Hierarchical Nanoscale Structuring of Solution-Processed 2D van der Waals Networks for Wafer-Scale, Stretchable Electronics

Two-dimensional (2D) semiconductors are promising for next-generation electronics that are lightweight, flexible, and stretchable. Achieving stretchability with suppressed crack formation, however, is still difficult without introducing lithographically etched micropatterns, which significantly reduces active device areas. Herein, we report a solution-based hierarchical structuring to create stretchable semiconducting films that are continuous over wafer-scale areas via self-assembly of two-dimensional nanosheets. Electrochemically exfoliated MoS₂ nanosheets with large lateral sizes (∼1 μm) are first assembled into a uniform film on a prestrained thermoplastic substrate, followed by strain relief of the substrate to create nanoscale wrinkles. Subsequent strain-relief cycles with the presence of soluble polymer films produce hierarchical wrinkles with multigenerational structures. Stretchable MoS₂ films are then realized by curing an elastomer directly on the wrinkled surface and dissolving the thermoplastic. Three-generation hierarchical MoS₂ wrinkles are resistant to cracking up to nearly 100% substrate stretching and achieve drastically enhanced photoresponsivity compared to the flat counterpart over the visible and NIR regimes, while the flat MoS₂ film is beneficial in creating strain sensors because of its strain-dependent electrical response.

Cichorium intybus bio-callus synthesized silver nanoparticles: A promising antioxidant, antibacterial and anticancer compound

Cichorium intybus, commonly called chicory, has been widely used as a coffee substitute. It display a wide range of natural compounds and medicinally uses in treatment of gastrointestinal disorders. This study synthesized silver nanoparticles (Ci-AgNPs) using C. intybus leaf-derived callus extract to evaluate phytochemical content, antibacterial, antioxidant and anti-proliferative activities against human breast cancer cells (MDA-MB231). The optimal shape, size and stability of Ci-AgNPs was confirmed using UV-visible spectrophotometry, FESEM, EDX, XRD, DLS, Zeta potential, FTIR and sp-ICP-MS studies. The antibacterial activity of Ci-AgNPs was assessed using disk diffusion method against Staphylococcus aureus and Escherichia coli, and they displayed distinct zones of inhibition. Colorimetric phytochemical analysis of Ci-AgNPs revealed their higher total phenolic (TP) and total flavonoid (TF) content. Ci-AgNPs also indicated a high level of antioxidant activity using FRAP and DPPH assays. The Ci-AgNPs were investigated for their anticancer activities on the cancerous MDA-MB231 cells viability and apoptosis using MTT and flow cytometry, respectively. Ci-AgNPs showed dose dependent cytotoxicity against MDA-MB231 cells with IC50 value of 187.6 μg/mL at 48 h through induction of apoptosis. The biocompatibility test showed that Ci-AgNPs induced neglectable cytotoxicity (lower than 3 %) toward human erythrocytes. This is the first study that reports the bio-callus mediated synthesis of silver nanoparticle using C. intybus callus extract which provided a promising anticancer activity against human breast cancer MDA-MB231 cells and therefore could be used as an alternative and interesting benign strategy for biosynthesis of silver nanoparticles useful in cancer therapy.

Green synthesized Ag-nanoparticles using Scutellaria multicaulis stem extract and their selective cytotoxicity against breast cancer

Scutellaria multicaulis is a medicinal herb which has been extensively prescribed in Iranian traditional medicine for treatment of infections, constipation, wounds, and also as medication for anxiety. To evaluate biological activities of biosynthesized silver nanoparticles, silver nanoparticles (Sm-AgNPs) were synthesized using S. multicaulis extract as capping and reducing agent. Characterization studies using UV-vis, XRD, DLS, Zeta potential, FESEM, EDX, TEM, FTIR, RAMAN and TGA assays indicated that Sm-AgNPs had optimal shape, size (∼60 nm) and stability (-46.4 mV) to be used as a drug. Findings also demonstrated that Sm-AgNPs display higher Total Phenolics and Total Flavonoids Content and possesses higher antioxidant activity. HPLC-MSⁿ analysis of constituents in the S. multicaulis stem extract and Sm-AgNPs-free supernatant in negative ion mode showed that flavonoids, mainly jaceidin, skullcapflavon II, wogonin, oroxylin A and dihydroxy, trimethoxyflavone from extract have contributed to the synthesis of Sm-AgNPs. Additionally, Sm-AgNPs demonstrated effective anticarcinogenic properties on MDA-MB231 cells proliferation with IC₅₀ value of 81.2 μg/mL at 48 h by inducing cell apoptosis. Overall, results confirmed the potential role of S. multicaulis stem extract as a potential raw material for synthesis of biologically active Sm-AgNPs, for development of new antitumor agents which could be utilized to combat breast cancer.

Green synthesis of silver nanoparticles using green tea leaf extract, characterization and evaluation of antimicrobial activity

The use of nanoparticles in medicine, nanomedicine, is very important to diagnose and treat diseases; among the various metallic nanoparticles, silver nanoparticles (AgNPs) are very popular due to their physical, chemical, and biological properties, encompassing a range of activities such as antiviral, antifungal, anti-inflammatory, and anticancer activities. In this study, the synthesis of AgNPs was conducted by the use of a nontoxic, ecofriendly method. Green tea (GT) leaf extract was used as a reducing agent to convert silver ions into free AgNPs. The UV-vis spectrum showed a peak at 410 nm, confirming the presence of AgNPs. A Fourier-transform infrared (FTIR) analysis of the GT extract and GT AgNPs display spectra that is identical to those of polyphenols, polysaccharides, and proteins. All the vibrational peaks in the GT extract spectrum were shifted in the AgNP spectrum, becoming narrower after the encapsulation of nanoparticles. The scanning electron microscopy (SEM) images confirm the presence of AgNPs with different sizes, ranging from 15 to 33 nm. Furthermore, the antibacterial activity of the synthesized AgNPs in three different concentrations (10, 20, and 50 mg ml^-1) showed appreciable inhibition of bacterial growth against Staphylococcus aureus and Klebsiella sp. From the above findings, we can recommend the use of AgNPs from GT leaf extracts as an antimicrobial agent to treat chronic infections.

Raman spectroscopy and silver nanoparticles for efficient detection of membrane proteins in living cells

Molecular fingerprints revealed by Raman techniques show great potential for biomedical applications, like disease diagnostic through Raman detection of tumor markers and other molecules in the cell membrane. However, SERS substrates used in membrane molecule studies produce enhanced Raman spectra of high variability and challenging band assignments that limit their application. In this work, these drawbacks are addressed to detect membrane-associated hemoglobin (Hb_m) in human erythrocytes through Raman spectroscopy. These cells are incubated with silver nanoparticles (AgNPs) in PBS before Raman measurements. Our results showed that AgNPs form large aggregates in PBS that adhered to the erythrocyte membrane, which enhances Raman scattering by molecules around the membrane, like Hb_m. Also, deoxyHb markers may allow Hb_mdetection in Raman spectra of oxygenated erythrocytes (oxyRBCs). Raman spectra of oxyRBCs incubated with AgNPs showed enhanced deoxyHb signals with good spectral reproducibility, supporting the Hb_mdetection through deoxyHb markers. Instead, Raman spectra of oxyRBCs showed oxyHb bands associated with free cytoplasmic hemoglobin. Other factors influencing Raman detection of membrane proteins are discussed, like bothz-position and dimension of the sample volume. The results encourage membrane protein studies in living cells using Raman spectroscopy, leading to the characterization and diagnostic of different pathologies through a non-invasive technique.

Quantitative theory of integrating sphere throughput: comparison with experiments

We present a rigorous approach for measuring the throughput of an integrating sphere, from which the so-called sphere multiplier M can be derived. The critical ingredients of this approach are: (i) the transmitted power is measured at the base of an integrating port to avoid non-ideal port effects associated with reflections on the port wall; (ii) to implement this last point, optical fibers are used for light collection, providing a well-defined collection area and numerical aperture; (iii) the angular-dependent fiber throughput and detector sensitivity are determined experimentally and accounted for. We demonstrate in particular that a more realistic theory, accounting for the propagation of skew rays through the fiber, is needed to quantitatively model the fiber effect on the measured sphere throughput. We show experimentally that failure to fulfill these three points produces erroneous results, by as much as 50%. With an accurate experimentally derived sphere multiplier, agreement with theory is then obtained only if realistic ports (with non-zero reflectivity) are assumed. This provides experimental evidence for recent theoretical predictions of the importance of realistic ports [Tang et al., Appl. Opt.57, 1581 (2018)APOPAI0003-693510.1364/AO.57.001581]. Using the same experimental techniques, we also present clear experimental proof of two other predictions from that study: that the angular distribution exiting the port is strongly altered and that the overall port transmittivity is drastically reduced for high aspect ratio ports. This work will provide a solid basis for future quantitative measurements of absolute throughput and for further developments of the theory of integrating spheres.

Mie theory and the dichroic effect for spherical gold nanoparticles: an experimental approach

The attractive optical properties of metallic nanoparticles include the optically interesting but surprisingly not well understood dichroic effect, defined in this research as when particle colloids display different colours in transmitted and reflected light. Here we use a systematic experimental approach supplemented by theoretical Mie theory analysis to study the origin of this effect. The CloudSpec spectrophotometer has been utilised to produce quantitative scattering and absorption spectra for monodisperse spherical gold nanoparticles, allowing precise links to be made between the optical spectra and the colours observed. The source of the dichroic effect has been conclusively linked to particle size with no special particle shapes or size distributions required. These results experimentally demonstrate the relationship between particle size and the ratio of scattering to absorption predicted by Mie theory, which has important implications for users of Mie theory calculations.

Extinction-to-Absorption Ratio for Sensitive Determination of the Size and Dielectric Function of Gold Nanoparticles

Gold nanoparticles (AuNPs) have become an essential tool for a variety of fields across the biological, physical, and chemical sciences. The characterization of AuNPs by UV-vis spectroscopy is simple and commonly used but remains prone to error because of size and shape polydispersity and uncertainties in the dielectric function. We here propose and demonstrate a method to significantly improve this routine characterization technique by measuring not only the extinction but also the absorption spectrum. Specifically, we show that by considering the ratio of the extinction to absorption spectra, denoted η, we are able to determine the volume of AuNPs with a significant increase in accuracy compared to the UV-vis extinction method. We also prove an important property of η: it is independent of particle shape within the quasi-static/dipolar approximation, typically for particle sizes up to 100 nm. This shape independence results in very strong constraints for the theoretical predictions to agree with the experiments. We show that the spectral shape of η can therefore be used to discriminate between different proposed data sets for the dielectric function of gold, a long-standing challenge in plasmonics research.