Developing an Electrochemically Reversible Switch for Modulating the Optical Signal of Gold Nanoparticles

Gold nanoparticles (AuNPs) possess remarkable optical properties and electrical conductivity, making them highly relevant in various fields such as medical diagnoses, biological imaging, and electronic sensors. However, the existing methods for modulating the optical properties of AuNPs are often under limitations such as a high cost, the complexity of detection, a narrow range of application settings, and irreversibility. In this study, we propose a novel approach to address these challenges by constructing a reversible electrochemical switch. The switch (ITO-OMAD) involves covalently linking nitroxide radicals and AuNPs (AuNPs-NO•), followed by tethering this nanocomposite to a siloxane-derived indium tin oxide (ITO) electrode. By simply electrochemically oxidizing/reducing the nitroxide units, one is able to reversibly modulate the optical properties of AuNPs at will. The surface morphology and structure of the as-prepared ITO-OMAD electrode were characterized through scanning electron microscopy (SEM) and cyclic voltammetry (CV). SEM imaging confirmed the successful anchoring of AuNPs on the ITO electrode. Electrochemical tests performed in the three-electrode system demonstrated that the local surface plasmon resonance (LSPR) of AuNPs can be reversibly regulated by alternatively imposing ± 0.5V (vs. Ag/AgCl) to the modified electrode. The development of this electrochemical switch presents a novel approach to effectively control the optical properties of AuNPs. The further exploration and utilization of this reversible electrochemical switch could significantly enhance the versatility and practicality of AuNPs in numerous applications.

A fluorescent sensing platform based on collagen peptides-protected Au/Ag nanoclusters and WS2 for determining collagen triple helix integrity

The unique triple helix structure of collagen plays an important role in its biological properties, and the triple helix integrity is closely correlated with its molecular behavior and biological functions. Nevertheless, there is still a lack of convenient, accurate and practical methods for quantitatively determining collagen triple helix integrity. Herein, we first prepared bovine skin collagen peptide (BSCP)-protected Au/Ag nanoclusters (Au/AgNCs@BSCP) with excellent optical properties, high stability and good biocompatibility, which could adsorb on WS₂ surface leading to fluorescence quenching. Upon the addition of collagen, the interaction of collagen and Au/AgNCs@BSCP led to the detachment of Au/AgNCs@BSCP from the WS₂ surface, causing an increase in the fluorescence signal. Using the difference in the fluorescence recovery of the different samples, we achieved the quantitative determination of collagen triple helix integrity. This developed strategy exhibited excellent accuracy, selectivity, and practicality, thus showing promising potentials in biomedical applications.

Fabrication of Microbicidal Silver Nanoparticles: Green Synthesis and Implications in the Containment of Bacterial Biofilm on Orthodontal Appliances

Among various metal-based nanoparticles, silver nanoparticles (AgNPs) manifest superior inhibitory effects against several microorganisms. In fact, the AgNP-based treatment has been reported to inhibit both sensitive and resistant isolates of bacteria and other disease-causing microbes with equal propensity. Keeping this fact into consideration, we executed bio-mediated synthesis of AgNPs employing extract of flower and various other parts (such as bud and leaf) of the Hibiscus rosa-sinensis plant. The physicochemical characterization of as-synthesized AgNPs was executed employing transmission electron microscopy (TEM), dynamic light scattering (DLS), zeta potential, Fourier transform infrared (FTIR) spectroscopy, and UV-Vis spectroscopy, etc. The as-synthesized AgNPs demonstrated strong antimicrobial activity against both Gram-positive and Gram-negative bacteria with equal propensity. The as-synthesized AgNPs successfully inhibited Streptococcus mutans (S. mutans), one of the main causative bacteria responsible for dental caries. Considering the fact that orthodontic appliances facilitate infliction of the oral cavity with a range of microbes including S. mutans, we determined the growth inhibitory and anti-adherence activities of AgNPs on orthodontic appliances. We performed microbiological assays employing AgNPs adsorbed onto the surface of nickel–titanium (Ni-Ti) orthodontic wires. A topographic analysis of the decontaminated Ni-Ti orthodontic wires was performed by scanning electron microscopy. In addition to antimicrobial and anti-biofilm activities against oral S. mutans, the as-fabricated AgNPs demonstrated significant inhibitory and anti-biofilm properties against other biofilm-forming bacteria such as Escherichia coli and Listeria monocytogenes.

Toxicological evaluation of fluorescent 11-mercaptoundecanoic gold nanoclusters as promising label-free bioimaging probes in different cancer cell lines

Due to advancement in nanomaterials and increasing use of functionalized gold nanoclusters (AuNCs) in different biomedical applications, better understanding of their potential cytotoxicity is necessary. Interactions of ultra-small fluorescent AuNCs with mammalian cells remains up to this day poorly understood, therefore, cytotoxic evaluation of thoroughly characterized ca. 2.5 nm spherical water-soluble 11-mercaptoundecanoic acid coated AuNCs (AuNC@M) with diverse fluorescent properties in variety of mammalian cancer cell lines was performed. Cell viability was assessed by traditional MTT assay and xCELLigence real time cell analyzer. Cell apoptosis was evaluated via an Annexin V-FITC/propidium iodide (PI) assay. Confocal fluorescence imaging confirmed that tested AuNC@M entered live cells and were homogeneously distributed in their cytoplasm. The results suggested that the cytotoxicity of tested nanoclusters was very low, or near the control level at concentrations 0.1 and 0.5 mg/mL in the cell lines after 24 h exposition. The purity of tested AuNC@M had no relevant effect on cell viability and no differences were observed after 24 h in our study. The low toxicity toward cancer cells further strengthens our view that AuNC@M are promising label-free fluorescent probes for bio-labelling and bio-imaging, or they can even serve as platforms for antitumor drug delivery systems.

Reversing the Thermodynamics of Galvanic Replacement Reactions by Decreasing the Size of Gold Nanoparticles

Here, we describe the surprising reactivity between surface-attached (a) 0.9, 1.6, and 4.1 nm diameter weakly stabilized Au nanoparticles (NPs) and aqueous 1.0 × 10^-4 M Ag⁺ solution, and (b) 1.6 and 4.1 nm diameter weakly stabilized Au NPs and aqueous 1.0 × 10^-5 M PtCl₄^2-, which are considered to be antigalvanic replacement (AGR) reactions because they are not thermodynamically favorable for bulk-sized Au under these conditions. Anodic Stripping Voltammetry (ASV) and Scanning Transmission Electron Microscopy with Energy-Dispersive X-ray Spectroscopy (STEM-EDS) mapping provide quantitation of the extent of Ag and Pt replacement as a function of Au NP diameter. The extent of the reaction increases as the Au NP size decreases. The percentage of Ag in the AuAg alloy following AGR based on ASV is 17.8 ± 0.6% for 4.1 nm diameter Au NPs, 87.2 ± 2.9% for 1.6 nm Au NPs, and an unprecedented full 100% Ag for 0.9 nm diameter Au NPs. STEM-EDS mapping shows very close agreement with the ASV-determined compositions. In the case of PtCl₄^2-, STEM-EDS mapping shows AuPt alloy NPs with 3.9 ± 1.3% and 41.1 ± 8.7% Pt following replacement with 4.1 and 1.6 nm diameter Au NPs, respectively, consistent with qualitative changes to the ASV. The size-dependent AGR correlates well with the negative shift in the standard potential (E⁰) for Au oxidation with decreasing NP size.

Nanocomposite of Ag nanoparticles and catalytic fluorescent carbon dots for synergistic bactericidal activity through enhanced reactive oxygen species generation

Microwave mediated synthesis of catalytic fluorescent carbon dots (Cdots) has been reported using biodegradable starch as precursor. The as-synthesized Cdots were then characterized using various techniques such as fluorescence spectroscopy, fourier-transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM) and x-ray photoelectron spectroscopy (XPS) analysis. Interestingly, Cdots showed high catalytic activity in the photo-reduction of Ag⁺ to silver nanoparticles (Ag NPs). During the photo-reduction process, no additional surface passivating agents was needed to stabilize the Ag NPs. Further, TEM results indicated the formation of Cdot-Ag NP nanocomposite i.e. Ag NPs surrounded with Cdots, and the emission intensity of Cdots was significantly decreased whereas the lifetime of Cdots remained almost unaltered in the presence of Ag NPs following static quenching. Finally, combination therapy of Cdots and Ag NPs using Cdot-Ag NP nanocomposite was performed which indicated synergistic bactericidal activity against antibiotic resistant recombinant E. coli bacteria. The treatment elevated the reactive oxygen species (ROS) level as compared to its individual components. Additionally, the flow cytometer study demonstrated that combination therapy causing bacterial cell wall perforation that was possibly leading to synergistic bactericidal activity against both Gram positive and Gram negative bacteria. The presence of Cdots on the surface of the Ag NPs due to their ground state complexation, possibly facilitated electrons towards Ag NPs which enhanced the ROS production in comparison to only Ag NPs.

Gold embedded chitosan nanoparticles with cell membrane mimetic polymer coating for pH-sensitive controlled drug release and cellular fluorescence imaging

In this work, gold embedded chitosan nanoparticles (Au@CS NPs) were fabricated by a one-pot method. The benzaldehyde-terminated poly[(2-methacryloyloxy) ethyl phosphorylcholine] (PMPC) was applied to modification of the gold doped chitosan nanoparticles. The obtained Au@CS-PMPC NPs had the diameter of 135 nm with a narrow distribution. The size of the Au@CS-PMPC NPs, as well as the size of the embedded gold NPs, might be well-controlled by adjusting the feeding ratio between chitosan and HAuCl₄. Furthermore, the Au@CS-PMPC NPs showed increased colloidal stability, high drug loading content, pH-responsive drug release, excellent biocompatibility and bright fluorescence emission. The results demonstrated that Au@CS-PMPC NPs showed a great potential for tumor therapy via the combination advantages of pH-sensitive controlled drug release and cellular fluorescence imaging.

Smartphone controlled interactive portable device for theranostics in vitro

In this work, a smartphone controlled interactive theranostic device has been developed to perform in vitro photodynamic therapy (PDT) and diagnostic assays for treatment assessment on a single platform. Further, silver nanorod (Ag NR) was identified as a photosensitizer and its effect was studied in three different cell lines. PDT was achieved with Ag NRs using low irradiation (1.4 mW/cm² at 632 nm) from light emitting diodes (LEDs) in the device. Specifically, PDT in conjugation with widely used chemotherapeutic drug doxorubicin (Dox) proved effective in killing of HeLa cancer cells and multicellular tumor spheroids at a minimum dose of Ag (2.5 μg/mL). The MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) and LDH (lactate dehydrogenase) assays performed with the device indicated the therapeutic success of the delivered PDT. The device is portable and can be adapted for different wavelength irradiations and radiation doses. Additionally, wireless operation using a custom designed smartphone application makes it convenient to use in complex environments without much of human intervention.

Inhibitor-conjugated harmonic nanoparticles targeting fibroblast activation protein

The recent progress in the engineering of nanosized inorganic materials presenting tailored physical properties and reactive surface for post-functionalization has opened promising avenues for the use of nanoparticles (NPs) in diagnosis and therapeutic intervention. Surface decoration of metal oxide NPs with ligands modulating circulation time, cellular uptake, affinity and extravasation through active targeting led to efficient cancer specific bioimaging probes. The most relevant cancer biomarkers studied so far include surface and transmembrane cancer cell receptors. More recently, tumor microenvironments and more specifically the fibroblastic element of the tumor stroma have emerged as a valuable target for diagnosis and treatment of several types of cancers. In this study, a low molecular weight ligand targeting fibroblast activation protein α (FAP), which is specifically expressed by activated fibroblasts of the tumor stroma, was synthesized. This ligand demonstrated nanomolar inhibition of FAP with high selectivity with respect to prolyl oligopeptidase (PREP) and dipeptidyl peptidase (DPP) IV, as well as good biocompatibility toward a human lung tissue model. Bismuth ferrite (BFO) harmonic nanoparticles (HNPs) conjugated to this ligand showed target-specific association to FAP as demonstrated by reverse ELISA-type assay using Human Fibroblast Activation Protein alpha/FAP Alexa Fluor® 594-conjugated Antibody and multiphoton multispectral microscopy experiments. These functionalized HNPs may provide new nanocarriers to explore the role of FAP in tumorigenesis and to target the fibroblastic component of the tumor microenvironment.

Gold-Nanocluster-Embedded Mucin Nanoparticles for Photodynamic Therapy and Bioimaging

Effective delivery of a photosensitizer with the ability to trace its eventual progress forms an important aspect in photodynamic therapy (PDT). Further, the delivery mechanism might require possessing the ability to traverse through the complex mucus barrier that offers retention of therapeutic molecules. In this work, gold nanocluster (Au NC)-embedded mucin nanoparticles were synthesized by a rapid green synthetic procedure for application as nanocarriers and to achieve image-guided PDT. The mucin-based nanocarrier exhibited excellent biocompatibility toward normal cells (HEK 293T). The photosensitizer methylene blue (MB) was loaded onto these Au NC-mucin nanoparticles (NPs). HeLa cancer cells were treated with MB-loaded Au NC-mucin nanoparticles under irradiation of 640 nm light. The cell viability assay revealed that the viability of HeLa cells was reduced to 50% after treatment with MB-loaded Au NC-mucin NPs under 640 nm irradiation. The luminescence exhibited by Au NCs in the nanocarrier was applied for tracking the delivery of MB inside the HeLa cells using confocal microscopy. The flow cytometry assays elucidated the mechanism of cell death.

Single Platform for Gene and Protein Expression Analyses Using Luminescent Gold Nanoclusters

A single platform for gene and protein expression studies is proposed to pursue rapid diagnostics. A common method to synthesize gold (Au) nanoclusters on both DNA and protein template was developed using a benchtop device. The method of synthesis is rapid and versatile and can be applied to different classes of DNA/protein. Employing luminescent Au nanoclusters as the signal-generating agents, the device enables carrying out reverse transcriptase polymerase chain reaction and array-based analyses of multiple genes/proteins simultaneously using switchable holders and custom-designed software. The device and methods were applied to evaluate gene profiling related to apoptosis in HeLa cancer cells and further to analyze the protein expressions of glutathione-S-transferase (GST) and GST-tagged human granulocyte macrophage colony-stimulating factor (GST-hGMCSF) recombinant proteins purified from bacterial strains of BL21(DE3) Escherichia coli (E. coli). The device with user-friendly methods for diagnosis using the luminescence of Au nanoclusters offers potential use in disease diagnostics with a vision to extend health care facilities especially to remote geographical locations.

Antitumor Activity of Alloy and Core-Shell-Type Bimetallic AgAu Nanoparticles

Nanoparticles (NPs) of noble metals, namely gold and silver, remain promising anticancer agents capable of enhancing current surgery- and chemotherapeutic-based approaches in cancer treatment. Bimetallic AgAu composition can be used as a more effective agent due to the synergetic effect. Among the physicochemical parameters affecting gold and silver nanoparticle biological activity, a primary concern relates to their size, shape, composition, charge, etc. However, the impact of metal components/composition as well as metal topological distribution within NPs is incompletely characterized and remains to be further elucidated and clarified. In the present work, we tested a series of colloidal solutions of AgAu NPs of alloy and core-shell type for an antitumor activity depending on metal molar ratios (Ag:Au = 1:1; 1:3; 3:1) and topological distribution of gold and silver within NPs (AucoreAgshell; AgcoreAushell). The efficacy at which an administration of the gold and silver NPs inhibits mouse Lewis lung carcinoma (LLC) growth in vivo was compared. The data suggest that in vivo antitumor activity of the studied NPs strongly depends on gold and silver interaction arising from their ordered topological distribution. NPs with Ag core covered by Au shell were the most effective among the NPs tested towards LLC tumor growth and metastasizing inhibition. Our data show that among the NPs tested in this study, AgcoreAushell NPs may serve as a suitable anticancerous prototype.

An in vitro assessment of novel chitosan/bimetallic PtAu nanocomposites as delivery vehicles for doxorubicin

AIM

To synthesize and functionalize platinum (core)-gold (shell) bimetallic nanoparticles (PtAuBNps) with chitosan and doxorubicin to display favorable pharmacokinetics, biodegradability, biological activity and safety in vitro.

MATERIALS & METHODS

PtAuBNps and their drug nanocomposites were morphologically and physico-chemically characterized. Binding studies determined the efficiency and stability of the platform. In vitro release kinetics were evaluated under simulated environments, cytotoxicity profiles through MTT and Sulforodhamine B assays and apoptosis induction using the dual EtBr/AO staining.

RESULTS & DISCUSSION

The results obtained indicate that functionalized PtAuBNps displayed favorable physio-chemical attributes, high binding capabilities, pH-triggered drug release through zero-order release kinetics, cell-specific cytotoxicity and good colloidal stability.

CONCLUSION

The positive attributes of this novel delivery system bodes well for future in vivo studies.

Nanowire networks and hollow nanospheres of Ag-Au bimetallic alloys at room temperature

Due to their physicochemical properties, metallic nanoalloys have potential applications in biomedicine, electrocatalysis and electrochemical sensors, among many other fields. New alternative procedures have emerged in order to reduce production costs and the use of toxic substances. In this study we present a novel low-toxicity synthesis method for the fabrication of nanowire networks (NWNs) and Ag-Au hollow nanospheres. The synthesis process is performed at room temperature without any sophisticated equipment, such as special cameras or furnaces, etc. Transmission electron microscopy showed that the NWNs contain random alloys with a diameter of between 10-13 nm. The radius for the hollow nanospheres is approximately located between 70-130 nm. The absorption bands in the UV-vis spectrum associated with the surface plasmon in Ag-Au bimetallic nanoparticles are highlighted at 385 nm for the NWNs and 643 nm for the hollow nanospheres. The study was performed with low-toxicity substances, such as rongalite, ascorbic acid and sucrose, and showed high efficiency for the fabrication of these types of nanostructures, as well as good stability for long periods of time.

Fluorescent metal quantum clusters: an updated overview of the synthesis, properties, and biological applications

A brief history of metal quantum clusters, their synthesis methods, physical properties, and an updated overview of their applications is provided.

Green synthesis of folic acid-conjugated gold nanoparticles with pectin as reducing/stabilizing agent for cancer theranostics

The one pot aqueous green synthesis of gold nanoparticles (GNPs) decorated with folic acid and loaded with doxorubicin suitable for anti-cancer drug delivery was potentially promising as a new therapeutic system for cancer treatment.