Spherical Gold Nanoparticles Research Articles

Nanoscale engineering of gold nanostars for enhanced photoacoustic imaging.

Photoacoustic (PA) imaging is a diagnostic modality that combines the high contrast resolution of optical imaging with the high tissue penetration of ultrasound. While certain endogenous chromophores can be visualized via PA imaging, many diagnostic assessments require the administration of external probes. Anisotropic gold nanoparticles are particularly valued as contrast agents, since they produce strong PA signals and do not photobleach. However, the synthesis of anisotropic nanoparticles typically requires cytotoxic reagents, which can hinder their biological application. In this work, we developed new PA probes based on nanostar cores and polymeric shells. These AuNS were obtained through one-pot synthesis with biocompatible Good's buffers, and were subsequently functionalized with polyethylene glycol, chitosan or melanin, three coatings widely used in (pre)clinical research. Notably, the structural features of the nanostar cores strongly affected the PA signal. For instance, despite displaying similar sizes (i.e. 45nm), AuNS obtained with MOPS buffer generated between 2 and 3-fold greater signal intensities in the region between 700 and 800nm than nanostars obtained with HEPES and EPPS buffers, and up to 25-fold stronger signals than spherical gold nanoparticles. A point source analytical model demonstrated that AuNS synthesized with MOPS displayed greater absorption coefficients than the other particles, corroborating the stronger PA responses. Furthermore, the AuNS shell not only improved the biocompatibility of the nanoconstructs but also affected their performance, with melanin coating enhancing the signal more than 4-fold, due to its own PA capacity, as demonstrated by both in vitro and ex vivo imaging. Taken together, these results highlight the strengths of gold nanoconstructs as PA probes and offer insights into the design rules for the nanoengineering of new nanodiagnostic agents.

Niosomes containing paclitaxel and gold nanoparticles with different coating agents for efficient chemo/photothermal therapy of breast cancer

Breast cancer (BC) is one of the most common cancers in women, and chemotherapy is usually used to overcome this cancer. To improve drug delivery to cancer sites and reduce their side effects, nanocarriers such as niosomes (NIOs) are used. Moreover, a combination of other therapeutic methods like photothermal therapy (PTT) can help to enhance the chemotherapy effect. The aim of this research is the design a nanocarrier that simultaneously delivers chemotherapy and PTT agents. To achieve this goal, NIOs containing paclitaxel (PTX) as a chemotherapeutic agent and spherical gold nanoparticles (AuNPs) coated with citrate, chitosan (CS), and polyamidoamine (PAMAM) as a PTT agent were synthesized by thin hydration methods. Their physicochemical properties were determined by dynamic light scattering, UV–Vis, Fourier-transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM) analysis. Cellular uptake, cell cytotoxicity, hyperthermia, and apoptosis effects of the proposed system were investigated in the MCF-7 BC cell line. The cellular uptake of NIOs/AuNPs–PAMAM (99.21%) and NIOs/AuNPs–CS (98.93%) by MCF-7 cells was higher than that of NIOs/AuNPs (79.55%), demonstrating that surface charge plays a key role in the cellular uptake of NPs. The MTT assay showed the cell viability of 45.48% for NIOs/AuNPs/PTX, 34.24% for NIOs/AuNPs–CS/PTX, and 37.67% for NIOs/AuNPs–PAMAM/PTX after 48 h of treatment. However, the application of hyperthermia significantly decreased the viability of cells treated with NIOs/AuNPs/PTX (37.72%), NIOs/AuNPs–CS/PTX (10.49%), and NIOs/AuNPs–PAMAM/PTX (4.1%) after 48 h. The apoptosis rate was high in NIOs/AuNPs–PAMAM/PTX (53.24%) and NIOs/AuNPs–CS/PTX (55.4%) confirming the data from MTT. In conclusion, the result revealed that combined PTT with chemotherapy increased cell cytotoxicity effects against the MCF-7 cells, and the AuNPs with various coating agents affected cellular uptake and hyperthermia which can be considered for efficient BC therapy.

Selective Colorimetric Detection of Pb(II) Ions by Using Green Synthesized Gold Nanoparticles with Orange Peel Extract

Gold nanoparticles (AuNPs) were prepared by using a green approach that employed orange (citrus sinensis) peel water extract (OPE) as a reducing agent. In this case, the organic compounds present in orange peel were able to reduce Au(III) to Au(0) and, at the same time, to act as a capping agent, functionalizing the surface of the AuNPs, stabilizing them in a water solution. This “green” approach valorizes orange peel waste as a resourceful material and makes the synthetic process of AuNPs more environmentally sustainable, safe, and economically feasible than the traditional methods. The obtained gold nanoparticles (AuNPs@OPE) were characterized by FT–IR, DLS, SEM analysis, and UV–Vis spectroscopy; the latter showed a characteristic surface plasmon resonance (SPR) band at 530 nm, typical of spherical gold nanoparticles. The AuNPs@OPE were then tested as colorimetric sensors for heavy metals in water, showing an affinity and selectivity toward Pb2+. In fact, in the presence of Pb2+, the added cation favors the aggregation process, and, in this case, nanoparticles form clusters due to the interactions between Pb2+ and the carboxyl/hydroxyl groups on the surface of the AuNPs@OPE, increasing the size of the nanostructure. This process is accompanied by a change in color of the AuNPs@OPE from pink to violet, with a formation of a second, new SPR band, at a higher wavelength, relative to the aggregate formation. The colorimetric assay was tested at different times with the addition of Pb2+ ions showing different LOD values of 13.31 µM and 0.05 µM after 15 min and 90 min, respectively. The proposed colorimetric assay was also tested for analyzing Pb2+ in drinking water samples demonstrating the reliability to use AuNPs@OPE with real samples.

A simulation study on the radiosensitization properties of gold nanorods

Objective. Gold nanorods (GNRs) have emerged as versatile nanoparticles with unique properties, holding promise in various modalities of cancer treatment through drug delivery and photothermal therapy. In the rapidly evolving field of nanoparticle radiosensitization (NPRS) for cancer therapy, this study assessed the potential of gold nanorods as radiosensitizing agents by quantifying the key features of NPRS, such as secondary electron emission and dose enhancement, using Monte Carlo simulations. Approach. Employing the TOPAS track structure code, we conducted a comprehensive evaluation of the radiosensitization behavior of spherical gold nanoparticles and gold nanorods. We systematically explored the impact of nanorod geometry (in particular size and aspect ratio) and orientation on secondary electron emission and deposited energy ratio, providing validated results against previously published simulations. Main results. Our findings demonstrate that gold nanorods exhibit comparable secondary electron emission to their spherical counterparts. Notably, nanorods with smaller surface-area-to-volume ratios (SA:V) and alignment with the incident photon beam proved to be more efficient radiosensitizing agents, showing superiority in emitted electron fluence. However, in the microscale, the deposited energy ratio (DER) was not markedly influenced by the SA:V of the nanorod. Additionally, our findings revealed that the geometry of gold nanoparticles has a more significant impact on the emission of M-shell Auger electrons (with energies below 3.5 keV) than on higher-energy electrons. Significance. This research investigated the radiosensitization properties of gold nanorods, positioning them as promising alternatives to the more conventionally studied spherical gold nanoparticles in the context of cancer research. With increasing interest in multimodal cancer therapy, our findings have the potential to contribute valuable insights into the perspective of gold nanorods as effective multipurpose agents for synergistic photothermal therapy and radiotherapy. Future directions may involve exploring alternative metallic nanorods as well as further optimizing the geometry and coating materials, opening new possibilities for more effective cancer treatments.

The enhancement of therapeutic effects of low-intensity ultrasound with spiky and spherical gold nanoparticles on CT26 cell line; an in vitro study

Introduction: The utilization of combination therapy has gained attention in the medical field as it can enhance treatment efficacy while minimizing side effects. Gold nanoparticles (AuNPs) have been identified as a promising candidate for enhancing the bioeffects of ultrasound (US) waves. Objectives: The primary objective of this study was to examine the impact of US irradiation when combined with spiky and spherical AuNPs on CT26 cells. Materials and Methods: Following a tailored composition, we devised and produced AuNPs with spiky and spherical morphologies. The properties of these nanoparticles were assessed using dynamic light scattering (DLS), voltammetry, and transmission electron microscopy (TEM). The CT26 cells were treated with the two types of nanoparticles and subsequently exposed to US radiation (1 W/cm2 , 1 MHz, and 10 minutes). The cytotoxic effects of various therapeutic interventions were assessed using MTT and flow cytometry assays. Results: This study’s findings indicate that nanoparticles’ morphology played a significant role in influencing the antitumor effects of US. Specifically, it was observed that the presence of spiky nanoparticles, when subjected to US, resulted in a significantly higher rate of cell death compared to spherical nanoparticles (P<0.001). Additionally, it was observed that the temperature changes induced by the spiky nanoparticles were comparatively lower. This observation implies that nanoparticles with spiky morphology enhance the non-thermal effects of US waves. Conclusion: The outcomes demonstrate a noteworthy augmentation in the biological impacts, specifically the non-thermal effects of US waves when employed in conjunction with spiky nanoparticles.

Effects of Spherical and Rod-like Gold Nanoparticles on the Reactivity of Human Peripheral Blood Leukocytes.

Gold nanoparticles (GNPs) are widely used in the technological and biomedical industries, which is a major driver of research on these nanoparticles. The main goal of this study was to determine the influence of GNPs (at 20, 100, and 200 μg/mL concentrations) on the reactivity of human peripheral blood leukocytes. Flow cytometry was used to evaluate the respiratory burst activity and pyroptosis in monocytes and granulocytes following incubation with GNPs for 30 and 60 min. Furthermore, the concentration of interleukin-1β (IL-1β) in human blood samples was assessed using enzyme-linked immunosorbent assay (ELISA) after their incubation with GNPs for 24 h. Under the conditions tested in the study, the GNPs did not significantly affect the production of reactive oxygen species in the granulocytes and monocytes that were not stimulated using phorbol 12-myristate 13-acetate (PMA) in comparison to the samples exposed to PMA (p < 0.05). Compared to the control sample, the greatest significant increase in the mean fluorescence intensity of the granulocytes occurred in the samples incubated with CGNPs = 100 and 200 µg/mL for tinc = 30 and 60 min (p < 0.05). From our results, we conclude that the physicochemical properties of the nanoparticles, chemical composition, and the type of nanoparticles used in the unit, along with the unit and incubation time, influence the induced toxicity.

Protein-Functionalized Gold Nanospheres with Tunable Photothermal Efficiency for the Near-Infrared Photothermal Ablation of Biofilms.

Temperature-responsive nanostructures with high antimicrobial efficacy are attractive for therapeutic applications against multidrug-resistant bacteria. Here, we report temperature-responsive nanospheres (TRNs) engineered to undergo self-association and agglomeration above a tunable transition temperature (Tt). The temperature-responsive behavior of the nanoparticles is obtained by functionalizing citrate-capped spherical gold nanoparticles (AuNPs) with elastin-like polypeptides (ELPs). Using protein design principles, we achieve a broad range of attainable Tt values and photothermal conversion efficiencies (η). Two approaches were used to adjust this range: First, by altering the position of the cysteine residue used to attach ELP to the AuNP, we attained a Tt range from 34 to 42 °C. Then, by functionalizing the AuNP with an additional small globular protein, we could extend this range to 34-50 °C. Under near-infrared (NIR) light exposure, all TRNs exhibited reversible agglomeration. Moreover, they showed an enhanced photothermal conversion efficiency in their agglomerated state relative to the dispersed state. Despite their spherical shape, TRNs have a photothermal conversion efficiency approaching that of gold nanorods (η = 68 ± 6%), yet unlike nanorods, the synthesis of TRNs requires no cytotoxic compounds. Finally, we tested TRNs for the photothermal ablation of biofilms. Above Tt, NIR irradiation of TRNs resulted in a 10,000-fold improvement in killing efficiency compared to untreated controls (p < 0.0001). Below Tt, no enhanced antibiofilm effect was observed. In conclusion, engineering the interactions between proteins and nanoparticles enables the tunable control of TRNs, resulting in a novel antibiofilm nanomaterial with low cytotoxicity.

Integrated magneto-plasmonic nanostructures-based immunoassay for galectin-3 detection.

Cardiovascular diseases remain a leading cause of global mortality, highlighting the need for accurate diagnostic tools and the detection of specific cardiac biomarkers. Surface-enhanced Raman scattering (SERS) spectroscopy has proved to be a promising alternative diagnostic tool to detect relevant biomarkers compared to traditional methods. To our knowledge, SERS methodology has never been used to detect galectin-3 (Gal-3), a crucial biomarker for cardiovascular conditions. Our study aimed to develop plasmonic and magneto-plasmonic nanoplatforms for the sensitive immunodetection of Gal-3 using SERS. Spherical gold nanoparticles (AuNPs) were synthesized and functionalized with 11-mercaptoundecanoic acid (MUDA) to enable antibody binding and 4-mercaptobenzoic acid (4MBA) that served as a Raman reporter due to its intense Raman signal. Following bioconjugation with Gal-3 antibody, the AuNPs were employed in the immunodetection of Gal-3 in phosphate-buffer saline (PBS) solution, offering a limit of detection (LOD) of 12.2 ng mL-1 and a working range up to 120 ng mL-1. Furthermore, our SERS-based immunosystem demonstrated selectivity for Gal-3 (40 ng mL-1) in the presence of other biomolecules such as α-amylase, bovine serum albumin and human C-reactive protein. As a proof of concept, we developed magneto-plasmonic nanoparticles composed of silica-coated magnetite decorated with the bioconjugated AuNPs aimed at enhancing the uptake and detection of Gal-3 via SERS coupled with Raman imaging. Our findings underscore the potential of SERS-based techniques for the sensitive and specific detection of biomarkers, holding significant implications for improved diagnosis and surveillance of cardiovascular diseases. Future research will focus on further optimizing these nanoplatforms and their translation into clinical settings.

Shape anisotropy induced jamming of nanoparticles at liquid interfaces: a tensiometric study.

The intersection of nanotechnology and interfacial science has opened up new avenues for understanding complex phenomena occurring at liquid interfaces. The assembly of nanoparticles at liquid/liquid interfaces provides valuable insights into their interactions with fluid interfaces, essential for various applications, including drug delivery. In this study, we focus on the shape and concentration effects of nanoscale particles on interfacial affinity. Using pendant drop tensiometry, we monitor the real-time interfacial tension between an oil droplet and an aqueous solution containing nanoparticles. We measure two different types of nanoparticles: spherical gold nanoparticles (AuNPs) and anisotropic gold nanorods (AuNRs), each functionalized with surfactants to facilitate interaction at the interface. We observe that the interface equilibrium behaviour is mediated by kinetic processes, namely, diffusion, adsorption and rearrangement of particles. For anisotropic AuNRs, we observe shape-induced jamming of particles at the interface, as evidenced by their slower diffusivity and invariant rearrangement rate. In contrast, the adsorption of spherical AuNPs is dynamic and requires more time to reach equilibrium, indicating weaker interface affinity. By detailed analysis of the interfacial tension data and interaction energy calculations, we show that the anisotropic particle shape achieves stable equilibrium inter-particle separation compared to the isotropic particles. Our findings demonstrate that anisotropic particles are a better design choice for drug delivery applications as they provide better affinity for fluid interface attachment, a crucial requirement for efficient drug transport across cell membranes. Additionally, anisotropic shapes can stabilize interfaces at low particle concentrations compared to isotropic particles, thus minimizing side effects associated with biocompatibility and toxicity.

Mechanisms of controlled stabilizer-free synthesis of gold nanoparticles in liquid aerosol containing plasma.

The interaction between low-temperature plasma and liquid enables highly reactive solution phase chemistry and fast reaction kinetics. In this work, we demonstrate the rapid synthesis of stabilizer-free, spherical and crystalline gold nanoparticles (AuNP). More than 70% of gold ion complex (AuCl- 4) conversion is achieved within a droplet residence time in the plasma of ∼10 ms. The average size of the AuNPs increases with an increase in the droplet residence time and the particle synthesis showed a power threshold effect suggesting the applicability of the classical nucleation theory. Leveraging UV-vis absorption and emission spectroscopy, and nanoparticle size distributions obtained from TEM measurements, we showed that the AuCl- 4 conversion exceeded by 250 times the maximum faradaic efficiency. We identified important roles of both short-lived reducing species including solvated electrons and possibly vacuum ultraviolet (VUV) photons, and long-lived species, H2O2, in the reduction of AuCl- 4. A quantitative investigation was performed by a 1-D reaction-diffusion model which includes transport, plasma-enabled interfacial reduction of AuCl- 4, classical nucleation, monomer absorption and autocatalytic surface growth enabled by H2O2. The model shows good agreement with the experimental results. The timescale analysis of the simulation revealed that nucleation is enabled by fast reduction of gold ions, and autocatalytic growth mainly determines the particle size and is responsible for the majority of the ion precursor conversion while also explaining the excessively large faradaic efficiency found experimentally.

Конформационная структура полиамфолитов на поверхности сферической металлической наночастицы при одновременном воздействии статического и переменного электрических полей

The simultaneous effect of external static and alternating electric fields on the composite nanosystem "gold spherical nanoparticle-polyampholyte" was studied. Radial and angular dependences of the polymer density were constructed, including in a narrow surface layer of the nanoparticle. In the case where the amplitude of the alternating dipole moment of the nanoparticle significantly exceeded the value of the static dipole moment, a ring-shaped fringe was formed in the equatorial region of the spherical gold nanoparticle. With an increase in the amplitude of the alternating electric field, the shape of the polyampholyte fringe changed from elongated in the direction of static polarization to swollen in the equatorial region of the nanoparticle. Oppositely charged links were located on those halves of the spherical nanoparticle relative to the equator, where opposite charges were induced due to the effect of the static electric field.

On-chip light sheet illumination for nanoparticle tracking in microfluidic channels.

A simple and inexpensive method is presented to efficiently integrate light sheet illumination in a microfluidic chip for dark-field microscopic tracking and sizing of nanoparticles. The basic idea is to insert an optical fiber inside a polydimethylsiloxane (PDMS) elastomer microfluidic chip and use it as a cylindrical lens. The optical fiber is in this case no longer seen as only an optical waveguide but as a ready-made micro-optical component that is inexpensive and easy to source. Upon insertion, the optical fiber stretches the PDMS microchannel walls, which has two effects. The first effect is to tone down the intrinsic ripples in the PDMS that would otherwise create inhomogeneities in the light sheet illumination. The second effect is to remove any obliqueness of the channel wall and constrain it to be strictly perpendicular to the propagation of the illumination, avoiding the formation of a prismatic diopter. Through calculations, numerical simulations and measurements, we show that the optimal configuration consists in creating a slowly converging light sheet so that its axial thickness is almost uniform along the tracked area. The corresponding thickness was estimated at 12 μm, or 10 times the depth of field of the optical system. This leads to an at least six-fold increase in the signal-to-noise ratio compared to the case without the cylindrical lens. This original light-sheet configuration is used to track and size spherical gold nanoparticles with diameters of 80 nm and 50 nm.

Rearrangement of the Conformations of Polyampholitic Macromolecules on the Surface of a Charged Spherical Metal Nanoparticle in an Alternating Electric Field: Molecular Dynamic Simulation

The rearrangement of the conformational structure of polyampholytic polypeptides on the surface of a charged spherical gold nanoparticle with its polarity intermittently changing over time was studied using molecular dynamics modeling. The angular distributions of the polypeptide atoms, as well as the radial distributions of the macrochain atomic density in the equatorial region of the nanoparticle with differentiation according to the types of links, were calculated. The polyampholyte shell acquired an annular shape, and the resulting macromolecular ring was located around the charged nanoparticle perpendicularly to the vector of the external electric field strength. With an increase in the charge of the nanoparticle, the ring belt was ordered according to the types of macrochain links, forming concentric annular layers. The diameter of the macromolecular ring depended on the law of distribution of charged units in the macrochain. At elevated temperatures the annular macromolecular ring was deformed at the moments of the highest polarization of the nanoparticle.

Ability of Antibodies Immobilized on Gold Nanoparticles to Bind Small Antigen Fluorescein

The analytical applications of antibodies are often associated with their immobilization on different carriers, which is accompanied by a loss of antigen-binding activity for a sufficient proportion of the bound antibodies. In contrast to data on plain carriers, minimal data are available on the properties of antibodies on the surfaces of nanoparticles. Protein antigens have been predominantly investigated, for which space restrictions do not allow them to occupy all active sites of immobilized antibodies. This study considered a low-molecular-weight compound, fluorescein, as an antigen. Spherical gold nanoparticles with five different sizes, two differently charged forms of fluorescein, and three different levels of surface coverage by immobilized antibodies were tested. For gold nanoparticles with diameters from 14 to 35.5 nm with monolayers of immobilized antibodies, the percentage of molecules capable of binding carboxyfluorescein varied from 6% to 17%. The binding of aminofluorescein was more efficient; for gold nanoparticles with an average diameter of 21 nm, the percentage of active binding sites for the immobilized antibodies reached 27% compared with 13% for the carboxyfluorescein case. A fourfold reduction in the coverage of the nanoparticles’ surface compared with that of the monolayer did not lead to reliable changes in the percentage of active binding sites. The obtained data demonstrate that an antigen’s binding to immobilized antibodies is limited even for small antigens and depends on the size of the nanoparticles and the electrostatic repulsion near their surface.

Mixed Nanosphere Assemblies at a Liquid-Liquid Interface.

The in-plane packing of gold (Au), polystyrene (PS), and silica (SiO2) spherical nanoparticle (NP) mixtures at a water-oil interface is investigated in situ by UV-vis reflection spectroscopy. All NPs are functionalized with carboxylic acid such that they strongly interact with amine-functionalized ligands dissolved in an immiscible oil phase at the fluid interface. This interaction markedly increases the binding energy of these nanoparticle surfactants (NPSs). The separation distance between the Au NPSs and Au surface coverage are measured by the maximum plasmonic wavelength (λmax) and integrated intensities as the assemblies saturate for different concentrations of non-plasmonic (PS/SiO2) NPs. As the PS/SiO2 content increases, the time to reach intimate Au NP contact also increases, resulting from their hindered mobility. λmax changes within the first few minutes of adsorption due to weak attractive inter-NP forces. Additionally, a sharper peak in the reflection spectrum at NP saturation reveals tighter Au NP packing for assemblies with intermediate non-plasmonic NP content. Grazing incidence small angle X-ray scattering (GISAXS) and scanning electron microscopy (SEM) measurements confirm a decrease in Au NP domain size for mixtures with larger non-plasmonic NP content. The results demonstrate a simple means to probe interfacial phase separation behavior using in situ spectroscopy as interfacial structures densify into jammed, phase-separated NP films.

Refractive Index-Modulated LSPR Sensing in 20–120 nm Gold and Silver Nanoparticles: A Simulation Study

Localized surface plasmon resonance (LSPR) based sensing has been a simple and cost-effective way to measure local refractive index changes. LSPR materials exhibit fascinating properties that have significant implications for various bio/chemical sensing applications. In many of these applications, the focus has traditionally been on analyzing the intensity of the reflected or transmitted signals in terms of the refractive index of the surrounding medium. However, limited simulation work is conducted on investigating the refractive index sensitivity of LSPR materials. Within this context, here we simulate the refractive index sensing properties of spherical gold (Au) and silver (Ag) nanoparticles ranging from 20–120 nm diameter within 1.0 to 1.50 refractive index units (RIU). After analyzing the peak optical efficiency and peak wavelength, we report the sensing performance of these materials in terms of sensitivity, linearity and material efficiency, which we refer to as the figure of merit (FOM). Overall, our observations have revealed greatest FOM values for the smallest sized nanoparticles, a FOM of 6.6 for 20 nm AuNPs and 11.9 for 20 nm AgNPs with refractive index of 1.

Acid-Responsive Aggregation of Gold Nanoparticles for the Photothermal Treatment of Bacterial Infections.

Photothermal therapy (PTT) is considered to be one of the promising methods to combat pathogenic bacteria. However, traditional PTT is prone to generate undesired temperature increase to surrounding normal tissues, which limits the application of PTT. Herein, an acid-responsive PTT system (Au nanoparticles system: AuNPs-S) was constructed based on the photothermal feature of spherical gold nanoparticles (AuNPs) and the low pH of the bacterial infected site. AuNPs-S is composed of two kinds of AuNPs: AuNPs modified with Asp-Asp-Asp-Asp-Asp-Cys (peptide A) were denoted as AuNPs-A; AuNPs modified with 2,3-dimethylmaleic anhydride (DA) grafted Lys-Gly-Gly-Lys-Gly-Gly-Lys-Cys (peptide B) were denoted as AuNPs-B/DA. AuNPs-B/DA with an acid-responsive moiety showed a charge-convertible feature. The negatively charged AuNPs-B/DA became positively charged AuNPs-B at low pH, aggregating with the negatively charged AuNPs-A via an electrostatic interaction, reaching the threshold to the interparticle plasmonic coupling effect among AuNPs, thereby killing bacteria precisely under the irradiation of near-infrared (NIR) light through the elevated temperature at the targeted area. This acid-responsive PTT strategy supplies an excellent mode for combating bacterial infections with no vital damage to normal tissues.

Dual-purpose nanoparticle assembly for identifying preferential intracellular targets of oxindolimine copper(II) complexes through SERS imaging

In this study, the main goal was to identify the intracellular targets of oxindolimine copper(II) complexes by SERS and Raman imaging of living HeLa cells, whose action as a cancer inhibitor has been previously determined. The used SERS probe was constituted of spherical gold nanoparticles together with the Raman reporter 5,5′-dithiobis-2-nitrobenzoic acid (DTNB) and oxindolimine copper(II) complexes, [Cu(isatp)Cl] and [Cu(nisatp)H2O]. Two excitation radiations were used to acquire living single HeLa cells images: 532 nm to acquire the conventional Raman information of the cells and 785 nm to acquire the localization of the modified SERS probe inside the cells. The Raman images of the main intracellular components were obtained by multivariate analysis, and the SERS images were obtained by univariate analysis using a Raman reporter. The SERS and Raman images showed that the complexes could enter the cells together with the gold nanoparticles, causing main damage to the nuclei and lipids-rich region. In addition, there was no evidence of water entry into the cell.

Analysis of Brownian motion trajectories of non-spherical nanoparticles using deep learning

As nanoparticles are being put to practical use as useful materials in the medical, pharmaceutical, and industrial fields, the importance of technologies that can evaluate not only nanoparticle populations of homogeneous size and density but also those of rich diversity is increasing. Nano-tracking analysis (NTA) has been commercialized and widely used as a method to measure individual nanoparticles in liquids and evaluate their size distribution by analyzing Brownian motion. We have combined deep learning (DL) for NTA to extract more property information and explored a methodology to achieve an evaluation for individual particles to understand their diversity. Practical NTA always assumes spherical shape when quantifying particle size using the Stokes–Einstein equation, but it is not possible to verify whether the measured particles are truly spherical. We developed a DL model that predicts the shape of nanoparticles using time series trajectory data of BM obtained from NTA measurements to address this problem. As a result, we were able to discriminate with ∼80% accuracy between spherical and rod-shaped gold nanoparticles of different shapes, which are evaluated to have nearly equal particle size without any discrimination by conventional NTA. Furthermore, we demonstrated that the mixing ratio of spherical and rod-shaped nanoparticles can be quantitatively estimated from measured data of mixed samples of nanoparticles. This result suggests that it is possible to evaluate particle shape by applying DL analysis to NTA measurements, which was previously considered impossible, and opens the way to further value-added NTA.

Label-free SERS for rapid identification of interleukin 6 based on intrinsic SERS fingerprint of antibody‑gold nanoparticles conjugate

A label-free surface-enhanced Raman scattering (SERS) was designed for sensitive detection of interleukin-6 (IL-6). The sensing element composed of anti-IL-6 antibodies adsorbed on the surface of spherical gold nanoparticles (AuNPs) as SERS-active surface. The principle of detection was probing antibody conformational changes using its intrinsic SERS fingerprint after binding to IL-6. Comparison of SERS spectra of antibody before and after binding to IL-6 showed that secondary structure of antibody does not change upon binding to IL-6. Vibrational information from disulfide bonds ν(SS) in antibody structure indicated some changes of geometry around SS bridges as a consequence of the immunocomplex formation. Transmission electron microscopy (TEM) and UV–Vis spectroscopy were used to confirm AuNPs conjugation with antibody as well as IL-6 binding to antibody on the surface of AuNPs. The SERS-based immunoassay showed a wide linear range (2.0–1000 pg mL−1) and a high sensitivity with a limit of detection (LOD) as low as 0.91 pg mL−1 (0.04 pM) without using any extrinsic Raman label. UV–Vis spectroscopy was employed as a conventional method for IL-6 detection based on observation of any change in the position of localized surface plasmon resonance (LSPR) band of AuNPs-antibody conjugates with LOD of 10 ng mL−1.