Facile displacement of citrate residues from gold nanoparticle surfaces

Thiol-polyethylene glycol-folic acid (HS-PEG-FA) induced aggregation of Au@Ag nanoparticles: A SERS and extinction UV-Vis spectroscopy combined study

Plasmonic colloidal nanoparticles (NPs) functionalised with polymers are widely employed in diverse applications, offering advantages demonstrated over non-functionalised NPs such as enhanced colloidal stability or increased biocompatibility. However, functionalisation with polymers does not always increase the stability of the colloidal system. This work explores the intricate relationship between the functionalisation of plasmonic core@shell Au@Ag nanoparticles (NPs) with thiol-polyethylene glycol-folic acid (HS-PEG-FA) polymer chains and the resulting stability and spectral characteristics of Surface-Enhanced Raman Scattering (SERS) nanotags based on these NPs. We demonstrate that varying levels of HS-PEG-FA grafting influence nanotag stability, with a low level of grafting causing aggregation and subsequently affecting the spectral signature of Raman-reporter molecules attached to the surface of the NP. Electrostatic destabilisation is identified as the primary mechanism driving aggregation, impacting the SERS spectrum of Malachite Green isothiocyanate (MGITC) whose spectral shape is different between the aggregated and non-aggregated NPs. The findings provide valuable insights into NPs stability under different conditions, offering essential considerations for the design and optimisation of SERS nanotags in bio-analytical applications, particularly those involving data processing based on spectral shape, such as in multiplex approaches where experimental spectra are decomposed with several reference components.

Mixed-charge hyperbranched polymer nanoparticles with selective antibacterial action for fighting antimicrobial resistance

The escalating menace of antimicrobial resistance (AMR) presents a profound global threat to life and assets. However, the incapacity of metal ions/reactive oxygen species (ROS) or the indiscriminate intrinsic interaction of cationic groups to distinguish between bacteria and mammalian cells undermines the essential selectivity required in these nanomaterials for an ideal antimicrobial agent. Hence, we devised and synthesized a range of biocompatible mixed-charge hyperbranched polymer nanoparticles (MCHPNs) incorporating cationic, anionic, and neutral alkyl groups to effectively combat multidrug-resistant bacteria and mitigate AMR. This outcome stemmed from the structural, antibacterial activity, and biocompatibility analysis of seven MCHPNs, among which MCHPN7, with a ratio of cationic groups, anionic groups, and long alkyl chains at 27:59:14, emerged as the lead candidate. Importantly, owing to inherent differences in membrane potential among diverse species, alongside its nano-size (6 - 15 nm) and high hydrophilicity (Kow = 0.04), MCHPN7 exhibited exceptional selective bactericidal effects over mammalian cells (selectivity index > 564) in vitro and in vivo. By inducing physical membrane disruption, MCHPN7 effectively eradicated antibiotic-resistant bacteria and significantly delayed the emergence of bacterial resistance. Utilized as a coating, MCHPN7 endowed initially inert surfaces with the ability to impede biofilm formation and mitigate infection-related immune responses in mouse models. This research heralds the advent of biocompatible polymer nanoparticles and harbors significant implications in our ongoing combat against AMR. STATEMENT OF SIGNIFICANCE: The escalating prevalence of antimicrobial resistance (AMR) has been acknowledged as one of the most significant threats to global health. Therefore, a series of mixed-charge hyperbranched polymer nanoparticles (MCHPNs) with selective antibacterial action were designed and synthesized. Owing to inherent differences in membrane potential among diverse species and high hydrophilicity (Kow = 0.04), the optimal nanoparticles exhibited exceptional selective bactericidal effects over mammalian cells (selectivity index >564) and significantly delayed the emergence of bacterial resistance. Importantly, they endowed surfaces with the ability to impede biofilm formation and mitigate infection-related immune responses. Furthermore, the above findings focus on addressing the problem of AMR in Post-Pandemic, which will for sure attract attention from both academic and industry research.

Hydrogen on Colloidal Gold Nanoparticles

Colloidal gold nanoparticles (AuNPs) have myriad scientific and technological applications, but their fundamental redox chemistry is underexplored. Reported here are titration studies of oxidation and reduction reactions of aqueous AuNP colloids, which show that the AuNPs bind substantial hydrogen (electrons + protons) under mild conditions. The 5 nm AuNPs are reduced to a similar extent with reductants from borohydrides to H2 and are reoxidized back essentially to their original state by oxidants, including O2. The reactions were monitored via surface plasmon resonance (SPR) optical absorption, which was shown to be much more sensitive to surface H than to changes in solution conditions. Reductions with H2 occurred without pH changes, demonstrating that hydrogenation forms surface H rather than releasing H+. Computational studies suggested that an SPR blueshift was expected for H atom addition, while just electron addition likely would have caused a redshift. Titrations consistently showed a maximum redox change of the 5 nm NPs, independent of the reagent, corresponding to 9% of the total gold or ∼30% hydrogen surface coverage (∼370 H per AuNP). Larger AuNPs showed smaller maximum fractional surface coverages. We conclude that H binds to the edge, corner, and defect sites of the AuNPs, which explains the stoichiometric limitation and the size effect. The finding of substantial and stable hydrogen on the AuNP surface under mild reducing conditions has potential implications for various applications of AuNPs in reducing environments, from catalysis to biomedicine. This finding contrasts with the behavior of bulk gold and with the typical electron-focused perspective in this field.

Influence of the linkage between long alkyl tails and cationic groups on membrane activity of nano-sized hyperbranched polyquaterniums

The recurrent emergence of serious pathogens necessitates novel insights and highly efficient antibacterial agents. However, the innate inability of metal ions and reactive oxygen species (ROS) to differentiate between bacteria and mammalian cells presents a challenge, limiting the selectivity crucial for an ideal antimicrobial solution. Herein, we present a systematic exploration involving two variants of nano-sized hyperbranched polyquaterniums (NHBPQs) - one featuring a lengthy alkyl tail linked to the ammonium unit at the N-atom center (NHBPQ-A), and the other in a segregated configuration (NHBPQ-B). The exterior alkyl chain chains act as a barrier to the cationic group's non-specific adsorption due to spatial site resistance, causing NHBPQ-A in broad-spectrum cytotoxicity. Conversely, the distinct molecular configuration of NHBPQ-B in the segregated state affords greater flexibility, allowing the cationic groups to be released and interact non-specifically, finally resulting in selective bactericidal activity. Leveraging this selectivity, the optimized NHBPQ-B exhibits robust anti-infectious performance in a model of methicillin-resistant Staphylococcus aureus (MRSA)-infected wounds. This work establishes a promising avenue for biocompatible NHBPQs, holding significant potential in addressing MRSA infections and ameliorating both genetically encoded and phenotypic antibiotic resistance mechanisms.

An "on-off-on" Fluorescent Sensor Based on Carbon Dots for the Detection of Au (III) and Creatinine

The present study proposes a new approach for detecting trace amounts of creatinine (Cre) through the utilization of a fluorescence sensor system consisting of nitrogen doped carbon dots (NCDs) and gold ions (Au3+). Yellow fluorescent carbon dots were prepared using a one-step hydrothermal method with o-phenylenediamine and isopropanol as raw materials. First, gold ions are reduced to gold nanoparticles (Au NPs), which bind to NCDs, resulting in electron transfer and fluorescence quenching of NCDs. After adding creatinine, Cre and Au NPs were preferentially combined to form non-fluorescent complexes, and the NCDs fluorescence was restored. The study achieved a detection limit of 1.06 × 10-7 M for Au3+ and 9.29 × 10-9 M for creatinine, indicating a high level of sensitivity. The sensing system has also been successfully utilized for detecting Au3+ in lake water and Cre in human urine, indicating its promising potential and practical applications in the areas of environmental monitoring and biosensing.

NaYF4:Yb/Ho upconversion nanoprobe incorporated gold nanoparticle (AuNP) based FRET immunosensor for the "turn-on" detection of cardiac troponin I

Cardiac troponin I (cTnI) is a significant biomarker for acute heart attack. Hence, fast, economical, easy and real time monitoring of cardiac troponin I (cTnI) is of great importance in diagnosis and prognosis of heart failure in the healthcare domain. In this work, an immunoassay based on NaYF4:Yb/Ho based photon-upconversion nanoparticle (UCNP) with narrow emission peaks at 540 nm and 655 nm respectively, is synthesized. Then, it is encapsulated with amino functionalized silica using 3-aminopropyltriethoxysilane (APTES) to form APTES@SiO2-NaYF4:Yb/Ho UCNPs. When AuNPs is added to this system, the fluorescence is quenched by the electrostatic interaction with APTES@SiO2-NaYF4:Yb/Ho UCNPs, thereby exhibiting a FRET-based biosensor. When the cTnI antigen is introduced into the developed probe, an antibody-antigen complex is formed on the surface of the UCNPs resulting in fluorescence recovery. The developed sensor shows a linear response towards cTnI in the range from 0.1693 ng mL-1 to 1.9 ng mL-1 with a low limit of detection (LOD) of 5.5 × 10-2 ng mL-1. The probe exhibits adequate selectivity and sensitivity when compared with coexisting cardiac biomarkers, biomolecules and in real human serum samples.

Biomimetic Antithrombotic Tissue-Engineered Vascular Grafts for Converting Cholesterol and Free Radicals into Nitric Oxide

Small-diameter tissue-engineered vascular grafts (sdTEVGs) are essential materials used in bypass or replacement surgery for cardiovascular diseases; however, their application efficacy is limited because of patency rates, especially under hyperlipidemia, which is also clinically observed in patients with cardiovascular diseases. In such cases, improving sdTEVG patency is challenging because cholesterol crystals easily cause thrombosis and impede endothelialization. Herein, the development of a biomimetic antithrombotic sdTEVG incorporating cholesterol oxidase and arginine into biomineralized collagen-gold hydrogels on a sdTEVG surface is described. Biomimetic antithrombotic sdTEVGs represent a multifunctional substrate for the green utilization of hazardous substances and can convert cholesterol into hydrogen peroxide, which can react with arginine to generate nitric oxide (NO). NO is a vasodilator that can simulate the antithrombotic action of endothelial cells under hyperlipidemic conditions. In vivo studies show that sdTEVGs can rapidly produce large amounts of NO via a cholesterol catalytic cascade to inhibit platelet aggregation, thereby improving the blood flow velocity and patency rates 60 days after sdTEVG transplantation. A practical and reliable strategy for transforming "harmful" substances into "beneficial" factors at early transplantation stages is presented, which can also promote vascular transplantation in patients with hyperlipidemia.

Localized surface plasmon resonance shift of biosynthesized and functionalized quasi-spherical gold nanoparticle systems

Rapid and more environment-friendly means of gold nanoparticle synthesis is necessary in many applications, as in ion detection. Leaf extracts have become effective and economical reducing agents for gold nanoparticle formation, however, effects of extract combinations have not been thoroughly investigated. With the exploitation of combined extract effects, gold nanoparticles were synthesized then functionalized and investigated to produce selected nanoparticle systems which are capable of detecting aqueous lead(ii) ions with minimum detection limits of 10-11 ppm. The measured localized surface plasmon resonance absorption peaks of the gold nanoparticles were 541-800 nm for the synthesis and 549 nm for the functionalization. The diameters of different gold nanoparticle systems were 17-37 nm. These were mostly quasi-spherical in morphology with some rod-, triangular-, and hexagonal plate-like particles. The biosynthesis used polyphenols and acids present in the extracts in the reduction of gold ions into gold nanoparticles, and in the nanoparticle capping and stabilization. Functionalization replaced the capping compounds with alliin, S-allylcysteine, allicin, and ajoene. Gold nanoparticle stability in aqueous systems was verified for two weeks up to five months. The investigations concluded the practicability of the gold nanoparticles in lead(ii) ion detection with selectivity initially verified for other divalent cations.

Investigation of the Influence of Wound-Treatment-Relevant Buffer Systems on the Colloidal and Optical Properties of Gold Nanoparticles

Biocompatible gold nanoparticles (AuNPs) are used in wound healing due to their radical scavenging activity. They shorten wound healing time by, for example, improving re-epithelialization and promoting the formation of new connective tissue. Another approach that promotes wound healing through cell proliferation while inhibiting bacterial growth is an acidic microenvironment, which can be achieved with acid-forming buffers. Accordingly, a combination of these two approaches appears promising and is the focus of the present study. Here, 18 nm and 56 nm gold NP (Au) were prepared with Turkevich reduction synthesis using design-of-experiments methodology, and the influence of pH and ionic strength on their behaviour was investigated. The citrate buffer had a pronounced effect on the stability of AuNPs due to the more complex intermolecular interactions, which was also confirmed by the changes in optical properties. In contrast, AuNPs dispersed in lactate and phosphate buffer were stable at therapeutically relevant ionic strength, regardless of their size. Simulation of the local pH distribution near the particle surface also showed a steep pH gradient for particles smaller than 100 nm. This suggests that the healing potential is further enhanced by a more acidic environment at the particle surface, making this strategy a promising approach.

Gold Nanoparticles Functionalized with 2-Thiouracil for Antiproliferative and Photothermal Therapies in Breast Cancer Cells

Nanoparticles have been used to transport drugs to various body parts to treat cancer. Our interest is in gold nanoparticles (AuNPs) since they have the capacity to absorb light and convert it to heat, inducing cellular damage. This property is known as photothermal therapy (PTT) and has been studied in cancer treatment. In the present study, biocompatible citrate-reduced AuNPs were functionalized with a biologically active compound, 2-thiouracil (2-TU), of potential anticancer activity. Both the unfunctionalized (AuNPs) and functionalized (2-TU-AuNPs) were purified and characterized by UV-Vis absorption spectrophotometry, Zeta potential, and Transmission Electron Microscopy. Results showed monodispersed, spherical AuNPs with a mean core diameter of 20 ± 2 nm, a surface charge of -38 ± 5 mV, and a localized surface plasmon resonance peak at 520 nm. As a result of functionalization, the mean core diameter of 2-TU-AuNPs increased to 24 ± 4 nm, and the surface charge increased to -14 ± 1 mV. The functionalization of AuNPs and the load efficiency were further established through Raman spectroscopy and UV-Vis absorption spectrophotometry. The antiproliferative activities of AuNPs, 2-TU and 2-TU-AuNPs were examined by a 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide (MTT) assay in the MDA-MB-231 breast cancer cell line. It was established that AuNPs significantly enhanced the antiproliferative activity of 2-TU. Furthermore, the irradiation of the samples with visible light at 520 nm decreased the half-maximal inhibitory concentration by a factor of 2. Thus, the 2-TU drug concentration and its side effect during treatments could be significantly reduced by synergistically exploiting the antiproliferative activity of 2-TU loaded onto AuNPs and the PTT effect of AuNPs.

Influence of cationic groups on the antibacterial behavior of cationic nano-sized hyperbranched polymers to enhance bacteria-infected wound healing

With the continuous emergence of drug-resistant pathogens, new strategies with high antibacterial efficacy are urgently needed. Herein, five cationic nano-sized hyperbranched polymers (CNHBPs) with cationic functional groups have been constructed, and their antibacterial mechanism has been studied in detail. CNHBPs bearing secondary ammonium salt groups and long alkyl chains (S₁₂-CNHBP) exhibited weak antibacterial and antibiofilm ability, while CNHBPs bearing quaternary ammonium salt groups and long alkyl chains (Q₁₂-CNHBP) showed the highest antimicrobial and strongest antibiofilm activities. ζ potential and isothermal titration microcalorimetry (ITC) results suggest that the negatively charged surfaces of bacterial cells provided Q₁₂-CNHBP with a higher intrinsic electrostatic driving force for bacterial killing than that with S₁₂-CNHBP. Fluorescent tracing and morphological observations indicate that the bacterial genome might be another antibacterial target for S₁₂-CNHBP in addition to the cell wall and membrane, which are mainly antibacterial targets for Q₁₂-CNHBP, making it less likely to induce bacterial resistance. Surprisingly, Q₁₂-CNHBP exhibited superior in vivo therapeutic efficacy in a mouse wound model of methicillin-resistant Staphylococcus aureus (MRSA) infection with low toxicity during treatment. These advantages and ease of preparation will undoubtedly distinguish Q₁₂-CNHBP as a new class of suitable candidates to combat multidrug-resistant pathogen infections. This study opens up a new avenue for exploiting antibacterial biomaterials to treat infections caused by drug-resistant bacteria.

Interaction of Metallic Nanoparticles With Biomimetic Lipid Liquid Crystalline Cubic Interfaces

In the past decades, events occurring at the nano-bio interface (i.e., where engineered nanoparticles (NPs) meet biological interfaces such as biomembranes) have been intensively investigated, to address the cytotoxicity of nanomaterials and boost their clinical translation. In this field, lamellar synthetic model membranes have been instrumental to disentangle non-specific interactions between NPs and planar biological interfaces. Much less is known on nano-biointeractions occurring at highly curved biological interfaces, such as cubic membranes. These non-lamellar architectures play a crucial -but far from understood-role in several biological processes and occur in cells as a defence mechanism against bacterial and viral pathologies, including coronaviruses infections. Despite its relevance, the interaction of cubic membranes with nano-sized objects (such as viral pathogens, biological macromolecules and synthetic NPs) remains largely unexplored to date. Here, we address the interaction of model lipid cubic phase membranes with two prototypical classes of NPs for Nanomedicine, i.e., gold (AuNPs) and silver NPs (AgNPs). To this purpose, we challenged lipid cubic phase membranes, either in the form of dispersed nanoparticles (i.e., cubosomes) or solid-supported layers of nanometric thickness, with citrate-stabilized AuNPs and AgNPs and monitored the interaction combining bulk techniques (UV-visible spectroscopy, Light and Synchrotron Small-Angle X-ray Scattering) with surface methods (Quartz Crystal Microbalance and Confocal Laser Scanning Microscopy). We show that the composition of the metal core of NPs (i.e., Au vs Ag) modulates their adsorption and self-assembly at cubic interfaces, leading to an extensive membrane-induced clustering of AuNPs, while only to a mild adsorption of isolated AgNPs. Such differences mirror opposite effects at the membrane level, where AuNPs induce lipid extraction followed by a fast disruption of the cubic assembly, while AgNPs do not affect the membrane morphology. Finally, we propose an interaction mechanism accounting for the different behaviour of AuNPs and AgNPs at the cubic interface, highlighting a prominent role of NPs’ composition and surface chemistry in the overall interaction mechanism.

Natural organic matter composition and nanomaterial surface coating determine the nature of platinum nanomaterial-natural organic matter corona

Natural organic matter corona (NOM corona) is an interfacial area between nanomaterials (NMs) and the surrounding environment, which gives rise to NMs' unique surface identity. While the importance of the formation of natural organic matter (NOM) corona on engineered nanomaterials (NMs) to NM behavior, fate, and toxicity has been well-established, the understanding of how NOM molecular properties affect NOM corona composition remains elusive due to the complexity and heterogeneity of NOM. This is further complicated by the variation of NOMs from different origins. Here we use eight NOM isolates of different molecular composition and ultrahigh resolution Fourier-transform ion cyclotron resonance-mass spectrometry (ESI-FT-ICR-MS) to determine the molecular composition of platinum NM-NOM corona as a function of NOM composition and NM surface coating. We observed that the composition of PtNM-NOM corona varied with the composition of the original NOM. The percentage of NOM formulas that formed PVP-PtNM-NOM corona was higher than those formed citrate-PtNM-NOM corona, due to increased sorption of NOM formulas, in particular condensed hydrocarbons, to the PVP coating. The relative abundance of heteroatom formulas (CHON, CHOS, and CHOP) was higher in the PVP-PtNM-NOM corona than in citrate-PtNM-corona which was in turn higher than those in the original NOM isolate, indicating preferential partitioning of heteroatom-rich molecules to NM surfaces. The relative abundance of CHO, CHON, CHOS, CHOP and condensed hydrocarbons in PtNM-NOM corona increased with their increase in NOM isolates. Furthermore, PtNM-NOM corona is rich with compounds with high molecular weight. This study demonstrates that the composition and properties of PtNM-NOM corona depend on NOM molecular properties and PtNM surface coating. The results here provide evidence of molecular interactions between NOM and NMs, which are critical to understanding NM colloidal properties (e.g., surface charge and stability), interaction forces (e.g., van der Waals and hydrophobic), environmental behaviors (e.g., aggregation, dissolution, sulfidation, etc.), and biological effects (e.g., uptake, bioaccumulation, and toxicity).

Localized Surface Plasmon Resonance-Based Colorimetric Assay Featuring Thiol-Capped Au Nanoparticles Combined with a Mobile Application for On-Site Parathion Organophosphate Pesticide Detection

In this study, we employed a dual strategy for parathion organophosphate pesticide (parathion) detection; first, we used a localized surface plasmon resonance (LSPR)-based colorimetric sensor featuring thiol-capped Au NPs, namely cysteine (Cys)@Au NPs, 11-mercaptoundecanoic acid (11-MUA)@Au NPs, and glutathione (GSH)@Au NPs, via acetylcholinesterase (ACHE) and acetylthiocholine (ATCH) enzyme-mediated hydrolysis reactions; second, we developed a color analysis toxicity-sensing app (Toxin APP). Positively charged thiocholine (TCH) molecules, which were continuously generated via hydrolysis, subsequently conjugated with thiol-capped Au NPs, causing Au NP aggregation through electrostatic attractions. The degree of aggregation of the thiol-capped Au NPs was influenced by parathion concentrations in the range 0 to 10⁸ ppt, because parathion acted as an ACHE inhibitor by controlling the amount of TCH generated. Based on the values of LSPR absorbance ratio, the limits of detection (LODs) of three types thiol-capped Au NPs were determined to be 100 ppt using ultraviolet-visible spectroscopy measurements. However, the aggregation efficiency of GSH@Au NPs was lower than that of the others regarding gradual changes in their color and LSPR absorbance band. Furthermore, we designed Toxin APP for color analysis which consists of three modules: processing, database collection, and communication. Toxin APP could on-site and precisely detect the color changes of GSH@Au NPs at parathion concentrations in the ranges of 100 ppt to 1, 10, and 100 ppm and could distinguish between OP and non-OP pesticides (e.g., fipronil) in tap water samples with high sensitivity and selectivity. Moreover, the concentration of residual parathion in real samples (tomato and strawberry) was quantified based on the color changes of GSH@Au NPs detected using Toxin APP. Therefore, the combination of an LSPR-based colorimetric assay and Toxin APP can be a reliable method for the facile and rapid detection of parathion in food and water samples.

How to Use Localized Surface Plasmon for Monitoring the Adsorption of Thiol Molecules on Gold Nanoparticles?

The functionalization of spherical gold nanoparticles (AuNPs) in solution with thiol molecules is essential for further developing their applications. AuNPs exhibit a clear localized surface plasmon resonance (LSPR) at 520 nm in water for 20 nm size nanoparticles, which is extremely sensitive to the local surface chemistry. In this study, we revisit the use of UV-visible spectroscopy for monitoring the LSPR peak and investigate the progressive reaction of thiol molecules on 22 nm gold nanoparticles. FTIR spectroscopy and TEM are used for confirming the nature of ligands and the nanoparticle diameter. Two thiols are studied: 11-mercaptoundecanoic acid (MUDA) and 16-mercaptohexadecanoic acid (MHDA). Surface saturation is detected after adding 20 nmol of thiols into 1.3 × 10⁻³ nmol of AuNPs, corresponding approximately to 15,000 molecules per AuNPs (which is equivalent to 10.0 molecules per nm²). Saturation corresponds to an LSPR shift of 2.7 nm and 3.9 nm for MUDA and MHDA, respectively. This LSPR shift is analyzed with an easy-to-use analytical model that accurately predicts the wavelength shift. The case of dodecanehtiol (DDT) where the LSPR shift is 15.6 nm is also quickly commented. An insight into the kinetics of the functionalization is obtained by monitoring the reaction for a low thiol concentration, and the reaction appears to be completed in less than one hour.

p-Co-BDC/AuNPs-based multiple signal amplification for ultra-sensitive electrochemical determination of miRNAs

In this work, we report AuNPs-decorated pyrolyzed Co-BDC nanosheets (p-Co-BDC/AuNPs) as high-performance electrocatalyst for developing an electrochemical platform. p-Co-BDC/AuNPs as a new electrocatalyst showed superior electrocatalytic activity towards the electrochemical oxidation of methylene blue (MB). Besides, magnetic p-Co-BDC/AuNPs can be well immobilized on the magnetic glassy carbon electrode without further assistance. The oxidation of MB can be reduced by ascorbic acid. Inspired by this phenomenon, an electrochemical biosensor was constructed based on multiple signal amplification for the diagnosis of miRNAs. Firstly, p-Co-BDC/AuNPs enhanced the electrochemical oxidation of MB. Then, strand displacement amplification reaction can form lots of double helix structure DNA to embed more MB molecules. Finally, ascorbic acid in the electrolyte was utilized to reduce the oxidation of MB and improve the electrochemical signal of MB electro-oxidation. The linear detection range for the detection of miRNAs is 100 aM to 10 nM, and the limit of detection is 86 aM. Furthermore, the constructed biosensor also displayed satisfactory selectivity, good reproducibility, and excellent recovery in the detection of real samples. We are convinced that our proposed multiple signal amplification strategy will provide more promising methods for the diagnosis of cancer.

A Martini Coarse Grained Model of Citrate-Capped Gold Nanoparticles Interacting with Lipid Bilayers

Citrate capping is one of the most common strategies to achieve the colloidal stability of Au nanoparticles (NPs) with diameters ranging from a few to hundreds of nanometers. Citrate-capped Au nanoparticles (CNPs) represent a step of the synthesis of Au NPs with specific functionalities, as CNPs can be further functionalized via ligand-exchange reactions, leading to the replacement of citrate with other organic ligands. In vitro, CNPs are also used to address the fundamental aspects of NP-membrane interactions, as they can directly interact with cells or model cell membranes. Their affinity for the bilayer is again mediated by the exchange of citrate with lipid molecules. Here, we propose a new computational model of CNPs compatible with the coarse grained Martini force field. The model, which we develop and validate through an extensive comparison with new all-atom molecular dynamics (MD) simulations and UV-vis and Fourier transform infrared spectroscopy data, is aimed at the MD simulation of the interaction between citrate-capped NPs and model phosphatidylcholine lipid membranes. As a test application we show that, during the interaction between a single CNP and a flat planar 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine bilayer, the citrate coating is spontaneously replaced by lipids on the surface of Au NPs, while the NP size and shape determine the final structural configuration of the NP-bilayer complex.

Systematic process evaluation of the conjugation of proteins to gold nanoparticles

The present work addresses some fundamental aspects in the preparation of protein-conjugated gold nanoparticles, in order to ensure an appropriate final product. Ten broadly available and/or easy to implement analytical tools were benchmarked and compared in their capacity to provide reliable and conclusive information for each step of the procedure. These techniques included transmission electron microscopy, UV/VIS spectroscopy, dynamic light scattering, zeta-potential, Fourier-transformed infrared spectroscopy, colloidal stability titration, end-point colloidal stability analysis, cyclic voltammetry, agarose gel electrophoresis and size-exclusion chromatography (SEC). Four different proteins widely used as adaptors or blocking agents were tested, together with 13 nm gold nanoparticles containing different surface chemistries. Among all tested techniques, some of the least popular among nanomaterial scientists probed to be the most informative, including colloidal stability, gel electrophoresis and SEC; the latter being also an efficient purification procedure. These three techniques provide low-cost, low time consuming, sensitive and robust ways to assess the success of the nanoparticle bioconjugation steps, especially when used in adequate combinations.

Plasmonic Gold Nanomaterials as Photoacoustic Signal Resonant Enhancers for Cysteine Detection

The development of photoacoustic systems is important for the real-time detection of cysteine (Cys), a biothiol in biological systems that serves as a significant biomarker for human health. Advanced photoacoustic (PA) signals with colloidal plasmonic Au nanomaterials rely on the efficient conversion of light to energy waves under moderately pulsed laser irradiation. In this study, we synthesized Cys-capped Au nanorods (Au@Cys NRs) and Cys-capped Au nanoparticles (Au@Cys NPs) through a conjugate of three Cys concentrations (10, 100, and 1000 μM). These plasmonic Au nanomaterials can be used as a PA resonance reagent due to their maximum localized surface plasmon resonance (LSPR) absorption bands at 650 nm and 520 nm in Au NRs and Au NPs, respectively. Subsequently, the PA signals were noticeably increased proportionally to the concentrations in the Au@Cys NRs and Au@Cys NPs under 658 nm and 520 nm laser irradiation, respectively, according to our portable photoacoustic system. Furthermore, PA signal amplitudes in Cys detection are boosted by ~233.01% with Au@Cys NRs and ~102.84% with Au@Cys NPs enhancement, compared to free Cys, according to ultrasound transducers at frequencies of 3 MHz.

Influence of Surface Ligand Molecular Structure on Phospholipid Membrane Disruption by Cationic Nanoparticles

Cationic nanoparticles are known to interact with biological membranes and often cause serious membrane damage. Therefore, it is important to understand the molecular mechanism for such interactions and the factors that impact the degree of membrane damage. Previously, we have demonstrated that spatial distribution of molecular charge at cationic nanoparticle surfaces plays an important role in determining the cellular uptake and membrane damage of these nanoparticles. In this work, using diamond nanoparticles (DNPs) functionalized with five different amine-based surface ligands and small phospholipid unilamellar vesicles (SUVs), we further investigate how chemical features and conformational flexibility of surface ligands impact nanoparticle/membrane interactions. ³¹P-NMR T₂ relaxation measurements quantify the mobility changes in lipid dynamics upon exposing the SUVs to functional DNPs, and coarse-grained molecular dynamics simulations further elucidate molecular details for the different modes of DNP-SUV interactions depending on the surface ligands. Collectively, our results show that the length of the hydrophobic segment and conformational flexibility of surface ligands are two key factors that dictate the degree of membrane damage by the DNP, while the amount of surface charge alone is not predictive of the strength of interaction.

Factors Influencing the Surface Functionalization of Citrate Stabilized Gold Nanoparticles with Cysteamine, 3-Mercaptopropionic Acid or l-Selenocystine for Sensor Applications

Thiols and selenides bind to the surface of gold nanoparticles (AuNPs) and thus provide suitable platforms for the fabrication of sensors. However, the co-existence of adsorbed citrate on the surface of the nanoparticles can influence their functionalization behavior and potentially their sensing performance measured by the extent of particle aggregation. In this study, the functionalization of purchased (7.3 ± 1.2 nm) and in-house prepared AuNPs (13.8 ± 1.2 nm), under the same experimental conditions with either cysteamine (Cys), 3-mercaptopropionic acid (3-MPA), or l-selenocystine (SeCyst) was investigated. 1H-NMR measurements showed distinct citrate signatures on the in-house synthesized citrate-stabilized AuNPs, while no citrate signals were detected on the purchased AuNPs other than evidence of the presence of α-ketoglutaric acid. Carboxylate-containing species attributed to either citrate or α-ketoglutaric acid were identified in all functionalized AuNPs. ATR-FTIR spectroscopy confirmed the functionalization of AuNPs with Cys and 3-MPA, and energy dispersive X-ray (EDX) spectroscopy measurements suggested the formation of SeCyst functionalized AuNPs. Co-adsorption rather than displacement by the functionalizing agents and carboxylate-containing molecules was indicated, which for Cys and SeCyst functionalized AuNPs was also the aggregation limiting factor. In contrast, the behavior of 3-MPA functionalized AuNPs could be attributed to electrostatic repulsions between the functionalized groups.

Good's buffers have various affinities to gold nanoparticles regulating fluorescent and colorimetric DNA sensing

Citrate-capped gold nanoparticles (AuNPs) are highly important for sensing, drug delivery, and materials design. Many of their reactions take place in various buffers such as phosphate and Good's buffers. The effect of buffer on the surface properties of AuNPs is critical, yet this topic has not been systematically explored. Herein, we used halides such as fluoride, chloride, and bromide as probes to measure the relative adsorption strength of six common buffers. Among them, HEPES had the highest adsorption affinity, while MES, citrate and phosphate were weakly adsorbed with an overall ranking of HEPES > PIPES > MOPS > MES > citrate, phosphate. The adsorption strength was reflected from the inhibited adsorption of DNA and from the displacement of pre-adsorbed DNA. This conclusion is also supported by surface enhanced Raman spectroscopy. Furthermore, some buffer molecules did not get adsorbed instantaneously, and the MOPS buffer took up to 1 h to reach equilibrium. Finally, a classic label-free AuNP-based colorimetric sensor was tested. Its sensitivity increased by 15.7-fold when performed in a MES buffer compared to a HEPES buffer. This study has articulated the importance of buffer for AuNP-based studies and how it can improve sensors and yield more reproducible experimental systems.

Aside from maintaining pH, Good's buffers can be adsorbed on gold nanoparticles with different affinities, affecting the stability and its fluorescent and colorimetric sensing performance.

Influence of the Spatial Distribution of Cationic Functional Groups at Nanoparticle Surfaces on Bacterial Viability and Membrane Interactions

While positively charged nanomaterials induce cytotoxicity in many organisms, much less is known about how the spatial distribution and presentation of molecular surface charge impact nanoparticle-biological interactions. We systematically functionalized diamond nanoparticle surfaces with five different cationic surface molecules having different molecular structures and conformations, including four small ligands and one polymer, and we then probed the molecular-level interaction between these nanoparticles and bacterial cells. Shewanella oneidensis MR-1 was used as a model bacterial cell system to investigate how the molecular length and conformation of cationic surface charges influence their interactions with the Gram-negative bacterial membranes. Nuclear magnetic resonance (NMR) and X-ray photoelectron spectroscopy (XPS) demonstrate the covalent modification of the nanoparticle surface with the desired cationic organic monolayers. Surprisingly, bacterial growth-based viability (GBV) and membrane damage assays both show only minimal biological impact by the NPs functionalized with short cationic ligands within the concentration range tested, yet NPs covalently linked to a cationic polymer induce strong cytotoxicity, including reduced cellular viability and significant membrane damage at the same concentration of cationic groups. Transmission electron microscopy (TEM) images of these NP-exposed bacterial cells show that NPs functionalized with cationic polymers induce significant membrane distortion and the production of outer membrane vesicle-like features, while NPs bearing short cationic ligands only exhibit weak membrane association. Our results demonstrate that the spatial distribution of molecular charge plays a key role in controlling the interaction of cationic nanoparticles with bacterial cell membranes and the subsequent biological impact. Nanoparticles functionalized with ligands having different lengths and conformations can have large differences in interactions even while having nearly identical zeta potentials. While the zeta potential is a convenient and commonly used measure of nanoparticle charge, it does not capture essential differences in molecular-level nanoparticle properties that control their biological impact.

A study of the influence of plasmonic resonance of gold nanoparticle doped PEDOT: PSS on the performance of organic solar cells based on CuPc/C60

This work studied the role of gold nanoparticles (AuNPs) with different spherical sizes mixed with poly (3, 4-ethylene dioxythiophene): polystyrene sulfonate (PEDOT: PSS) as a hole transfer layer to enhance the efficiency (ITO/PEDOT:PSS (AuNPs)/CuPc/C₆₀/Al) organic photovoltaic cell (OPV). AuNPs were synthesized using the thermochemical method and the results of the transmission electron microscope (TEM) images showed that the gold nanoparticles mostly dominated by spherical shapes and sizes were calculated in the range (12–23 nm). Measurements of UV-VIS spectra for AuNPs have shown that the surface plasmon resonance shifted to a higher wavelength with decreasing the particle size. Surface morphology and absorption spectra of OPV cells were studied using atomic force microscope and UV-VIS spectrometer techniques. The efficiency of the OPV cell was calculated without and with AuNPs. Efficiency was increased from 0.78% to 1.02% due to the embedded of AuNPs with (12 nm) in PEDOT/PSS. The increase in the light absorption in CuPc is due to the good transparent conducting of PEDOT:PSS and the increase in the electric field around AuNPs embedded in PEDOT:PSS and inbuilt electric field at the interfacial between CuPc and C₆₀ is due to the surface plasmon resonance of AuNPs. The increase in these two factors increase the exciton generation in CuPc, dissociation at the interfacial layer, and charge carrier transfer which increases the collection of electrons and holes at cathode and anode.

Surface Plasmon Resonance, Formation Mechanism, and Surface Enhanced Raman Spectroscopy of Ag+-Stained Gold Nanoparticles

A series of recent works have demonstrated the spontaneous Ag⁺ adsorption onto gold surfaces. However, a mechanistic understanding of the Ag⁺ interactions with gold has been controversial. Reported herein is a systematic study of the Ag⁺ binding to AuNPs using several in-situ and ex-situ measurement techniques. The time-resolved UV-vis measurements of the AuNP surface plasmonic resonance revealed that the silver adsorption proceeds through two parallel pseudo-first order processes with a time constant of 16(±2) and 1,000(±35) s, respectively. About 95% of the Ag⁺ adsorption proceeds through the fast adsorption process. The in-situ zeta potential data indicated that this fast Ag⁺ adsorption is driven primarily by the long-range electrostatic forces that lead to AuNP charge neutralization, while the time-dependent pH data shows that the slow Ag⁺ binding process involves proton-releasing reactions that must be driven by near-range interactions. These experimental data, together with the ex-situ XPS measurement indicates that adsorbed silver remains cationic, but not as a charged-neutral silver atom proposed by the anti-galvanic reaction mechanism. The surface-enhanced Raman activities of the Ag⁺-stained AuNPs are slightly higher than that for AuNPs, but significantly lower than that for the silver nanoparticles (AgNPs). The SERS feature of the ligands on the Ag⁺-stained AuNPs can differ from that on both AuNPs and AgNPs. Besides the new insights to formation mechanism, properties, and applications of the Ag⁺-stained AuNPs, the experimental methodology presented in this work can also be important for studying nanoparticle interfacial interactions.

Mimicking the bioelectrocatalytic function of recombinant CotA laccase through electrostatically self-assembled bioconjugates

Unprecedented 3D nanobiosystems composed of recombinant CotA laccases and citrate-stabilised gold nanoparticles have been successfully achieved by an electrostatic self-assembly strategy. The bioelectrochemical reduction of O2 driven by CotA laccase at the spore coat was mimicked. Consequently key insights into its bioelectrocatalytic function were unravelled.

Real-Time Monitoring of Ligand Exchange Kinetics on Gold Nanoparticle Surfaces Enabled by Hot Spot-Normalized Surface-Enhanced Raman Scattering

Nanoparticle surface coatings dictate their fate, transport, and bioavailability. We used a gold nanoparticle-bacterial cellulose substrate and "hot spot"-normalized surface-enhanced Raman scattering (HSNSERS) to achieve in situ and real-time monitoring of ligand exchange reactions on the gold surface. This approach enables semiquantitative determination of citrate surface coverage. Following exposure of the citrate-coated nanoparticles to a suite of guest ligands (thiolates, amines, carboxylates, inorganic ions, and proteins), the guest ligand signal exhibited first-order growth kinetics, while the desorption mediated decay of the citrate signal followed a first-order model. Guest ligand functional group chemistry dictated the kinetics of citrate desorption, while the guest ligand concentration played only a minor role. Thiolates and BSA were more efficient at ligand exchange than amine-containing chemicals, carboxylate-containing chemicals, and inorganic salts due to their higher binding energies with the AuNP surface. Amine-containing molecules overcoated rather than displaced the citrate layer via electrostatic interaction. Citrate exhibited low resistance to replacement at high surface coverages, but higher resistance at lower coverage, thus suggesting a transformation of the citrate-binding mode during desorption. High resistance to replacement in streamwater suggests that the role of surface-adsorbed citrate in nanomaterial fate and transport must be better understood.