Electrochemical codeposition of silver-gold nanoparticles on CNT-based electrode and their performance in electrocatalysis of dopamine

Targeted color design of silver-gold alloy nanoparticles

This research article focuses on the targeted color design of silver-gold alloy nanoparticles (NPs), employing a multivariate optimization approach. NP synthesis involves interconnected process parameters, making independent variation challenging. Data-based property-process relationships are established to optimize optical properties effectively. We define a color target, employ a green chemical co-reduction method at room temperature and optimize process parameters accordingly. The CIEL*a*b* color space (Commission Internationale de l'Éclairage - International Commission on Illumination) and Euclidean distances facilitate accurate color matching to establish the property-process relationship. Concurrently, theoretical Mie calculations explore the structure-property relationship across particle sizes, concentrations, and molar gold contents. The theoretically optimal structure agrees very well with experimental particle structures at the property-process relationship's optimum. The data-driven property-process relationship provides valuable insights into the formation mechanism of a complex particle system, sheds light on the role of relevant process parameters and allows to evaluate the practically available property space. Model validation beyond the original grid demonstrates its robustness, yielding colors close to the target. Additionally, Design of Experiments (DoE) methods reduce experimental work by threefold with slight accuracy trade-offs. Our novel methodology for targeted color design demonstrates how data-based methods can be utilized alongside structure-property relationships to unravel property-process relationships in the design of complex nanoparticle systems and paves the way for future developments in targeted property design.

Electrochemical Sensor for Tryptophan Determination Based on Trimetallic-CuZnCo-Nanoparticle-Modified Electrodes

The superior properties of electrodeposited trimetallic CuZnCo nanoparticles, arising from the synergistic effect of combining the unique features of metallic components, were confirmed using voltametric measurements. The surface morphology and structure of the as-prepared electrocatalysts were determined using scanning electron microscopy, energy-dispersive X-ray, and X-ray photoelectron spectroscopy techniques. Here, the trimetallic CuZnCo nanoparticles were synthesized as a powerful redox probe and highly efficient signal amplifier for the electrochemical oxidation of tryptophan. Differential pulse voltammetry studies showed a linear relationship with a tryptophan concentration of 5-230 μM, and the low detection limit was identified at 1.1 μM with a sensitivity of 0.1831 μA μM-1 cm-2.

Radiolysis-Assisted Direct Growth of Gold-Based Electrocatalysts for Glycerol Oxidation

The electrocatalytic oxidation of glycerol by metal electrocatalysts is an effective method of low-energy-input hydrogen production in membrane reactors in alkaline conditions. The aim of the present study is to examine the proof of concept for the gamma-radiolysis-assisted direct growth of monometallic gold and bimetallic gold-silver nanostructured particles. We revised the gamma radiolysis procedure to generate free-standing Au and Au-Ag nano- and micro-structured particles onto a gas diffusion electrode by the immersion of the substrate in the reaction mixture. The metal particles were synthesized by radiolysis on a flat carbon paper in the presence of capping agents. We have integrated different methods (SEM, EDX, XPS, XRD, ICP-OES, CV, and EIS) to examine in detail the as-synthesized materials and interrogate their electrocatalytic efficiency for glycerol oxidation under baseline conditions to establish a structure-performance relationship. The developed strategy can be easily extended to the synthesis by radiolysis of other types of ready-to-use metal electrocatalysts as advanced electrode materials for heterogeneous catalysis.

Green room temperature synthesis of silver-gold alloy nanoparticles

Metallic alloy nanoparticles (NPs) exhibit interesting optical, electrical and catalytic properties, dependent on their size, shape and composition. In particular, silver-gold alloy NPs are widely applied as model systems to better understand the syntheses and formation (kinetics) of alloy NPs, as the two elements are fully miscible. Our study targets product design via environmentally friendly synthesis conditions. We use dextran as the reducing and stabilizing agent for the synthesis of homogeneous silver-gold alloy NPs at room temperature. Our approach is a one-pot, low temperature, reaction-controlled, green and scalable synthesis route of well-controlled composition and narrow particle size distribution. The composition over a broad range of molar gold contents is confirmed by scanning transmission electron microscopy-energy-dispersive X-ray spectroscopy (STEM-EDX) measurements and auxiliary inductively coupled plasma-optical emission spectroscopy measurements (ICP-OES). The distributions of the resulting particles in size and composition are obtained from multi-wavelength analytical ultracentrifugation using the optical back coupling method and further confirmed by high-pressure liquid chromatography. Finally, we provide insight into the reaction kinetics during the synthesis, discuss the reaction mechanism and demonstrate possibilities for scale-up by a factor of more than 250 by increasing the reactor volume and NP concentration.

Disproportional surface segregation in ligand-free gold-silver alloy solid solution nanoparticles, and its implication for catalysis and biomedicine

Catalytic activity and toxicity of mixed-metal nanoparticles have been shown to correlate and are known to be dependent on surface composition. The surface chemistry of the fully inorganic, ligand-free silver-gold alloy nanoparticle molar fraction series, is highly interesting for applications in heterogeneous catalysis, which is determined by active surface sites which are also relevant for understanding their dissolution behavior in biomedically-relevant ion-release scenarios. However, such information has never been systematically obtained for colloidal nanoparticles without organic surface ligands and has to date, not been analyzed in a surface-normalized manner to exclude density effects. For this, we used detailed electrochemical measurements based on cyclic voltammetry to systematically analyze the redox chemistry of particle-surface-normalized gold-silver alloy nanoparticles with varying gold molar fractions. The study addressed a broad range of gold molar fractions (Ag₉₀Au₁₀, Ag₈₀Au₂₀, Ag₇₀Au₃₀, Ag₅₀Au₅₀, Ag₄₀Au₆₀, and Ag₂₀Au₈₀) as well as monometallic Ag and Au nanoparticle controls. Oxygen reduction reaction (ORR) measurements in O₂ saturated 0.1 M KOH revealed a linear reduction of the overpotential with increasing gold content on the surface, probably attributed to the higher ORR activity of gold over silver, verified by monometallic Ag and Au controls. These findings were complemented by detailed XPS studies revealing an accumulation of the minor constituent of the alloy on the surface, e.g., silver surface enrichment in gold-rich particles. Furthermore, highly oxidized Ag surface site enrichment was detected after the ORR reaction, most pronounced in gold-rich alloys. Further, detailed CV studies at acidic pH, analyzing the position, onset potential, and peak integrals of silver oxidation and silver reduction peaks revealed particularly low reactivity and high chemical stability of the equimolar Au₅₀Ag₅₀ composition, a phenomenon attributed to the outstanding thermodynamic, entropically driven, stabilization arising at this composition.

Multidimensional characterization of noble metal alloy nanoparticles by multiwavelength analytical ultracentrifugation

In this study, we introduce a method for the simultaneous retrieval of two-dimensional size-composition distributions of noble metal Ag-Au alloy nanoparticles utilizing an analytical ultracentrifuge equipped with a multiwavelength extinction detector (MWL-AUC). MWL-AUC is used to measure coupled optical and sedimentation properties of the particles. The optical response of the nanoparticles is calculated using Mie's theory, where the particles' complex refractive index is corrected due to the effect of reduced mean free path of electrons. Using a combined analysis of the hydrodynamic and spectral data captured by MWL-AUC, the size and composition of the alloy particles is retrieved. Our method is validated through the analysis of synthetic data and by the very good agreement between experimental scanning transmission electron microscopy and our AUC data. The presented comprehensive characterization approach contributes to improved synthesis, scale-up and production of particulate systems as it provides a simple, fast and direct method to determine noble metal alloy nanoparticle size and composition distributions simultaneously.

State of the Art in Gold Nanoparticle Synthesisation via Pulsed Laser Ablation in Liquid and Its Characterisation for Molecular Imaging: A Review

With recent advances in nanotechnology, various nanomaterials have been used as drug carriers in molecular imaging for the treatment of cancer. The unique physiochemical properties and biocompatibility of gold nanoparticles have developed a breakthrough in molecular imaging, which allows exploration of gold nanoparticles in drug delivery for diagnostic purpose. The conventional gold nanoparticles synthetisation methods have limitations with chemical contaminations during the synthesisation process and the use of higher energy. Thus, various innovative approaches in gold nanoparticles synthetisation are under development. Recently, studies have been focused on the development of eco-friendly, non-toxic, cost-effective and simple gold nanoparticle synthesisation. The pulsed laser ablation in liquid (PLAL) technique is a versatile synthetic and convincing technique due to its high efficiency, eco-friendly and facile method to produce gold nanoparticle. Therefore, this study aimed to review the eco-friendly gold nanoparticle synthesisation method via the PLAL method and to characterise the gold nanoparticles properties for molecular imaging. This review paper provides new insight to understand the PLAL technique in producing gold nanoparticles and the PLAL parameters that affect gold nanoparticle properties to meet the desired needs in molecular imaging.

Enhanced Tb(III) fluorescence on gelatin-coated silver nanoparticles in dopamine detection

A composite fluorescent nanoprobe based on metal enhanced fluorescence (MEF) effect of gelatin-coated silver nanoparticles (AgNPs@gel) was developed for selective and sensitive detection of dopamine (DA). The characteristic fluorescence of Tb(III) was using as the detection signal and AgNPs@gel served as substrates of the MEF. Gelatin with rich amine and carboxylic groups was used not only as a co-ligand of Tb(III) complex, but also as a bridging substance and a spacing material for improving the MEF of AgNPs@gel on the intrinsic luminescent intensity of Tb(III). Under the optimal conditions, the increment of the fluorescence intensity (measured at 307/544 nm as excitation/emission wavelength) of the system increased linearly with the concentration of DA in the range of 0.80-100 nM (R² = 0.9937) and 100-1000 nM (R² = 0.9978). The fluorescent probe greatly improved Tb(III) luminescence, which paved the way for sensitive detection with a low detection limit of 0.54 nM. It also showed good selectivity among other neurotransmitters. This work was successfully applied to the determination of DA in human serum samples with recoveries ranging from 99.8 to 102.2%. We believe that the Tb(III)-DA-AgNPs@gel composite fluorescent probe can be developed as a new approach for DA detection.

A Review on the Development of Gold and Silver Nanoparticles-Based Biosensor as a Detection Strategy of Emerging and Pathogenic RNA Virus

The emergence of highly pathogenic and deadly human coronaviruses, namely SARS-CoV and MERS-CoV within the past two decades and currently SARS-CoV-2, have resulted in millions of human death across the world. In addition, other human viral diseases, such as mosquito borne-viral diseases and blood-borne viruses, also contribute to a higher risk of death in severe cases. To date, there is no specific drug or medicine available to cure these human viral diseases. Therefore, the early and rapid detection without compromising the test accuracy is required in order to provide a suitable treatment for the containment of the diseases. Recently, nanomaterials-based biosensors have attracted enormous interest due to their biological activities and unique sensing properties, which enable the detection of analytes such as nucleic acid (DNA or RNA), aptamers, and proteins in clinical samples. In addition, the advances of nanotechnologies also enable the development of miniaturized detection systems for point-of-care (POC) biosensors, which could be a new strategy for detecting human viral diseases. The detection of virus-specific genes by using single-stranded DNA (ssDNA) probes has become a particular interest due to their higher sensitivity and specificity compared to immunological methods based on antibody or antigen for early diagnosis of viral infection. Hence, this review has been developed to provide an overview of the current development of nanoparticles-based biosensors that target pathogenic RNA viruses, toward a robust and effective detection strategy of the existing or newly emerging human viral diseases such as SARS-CoV-2. This review emphasizes the nanoparticles-based biosensors developed using noble metals such as gold (Au) and silver (Ag) by virtue of their powerful characteristics as a signal amplifier or enhancer in the detection of nucleic acid. In addition, this review provides a broad knowledge with respect to several analytical methods involved in the development of nanoparticles-based biosensors for the detection of viral nucleic acid using both optical and electrochemical techniques.

Electrochemical synthesis of chitosan/silver nanoparticles multilayer hydrogel coating with pH-dependent controlled release capability and antibacterial property

By coupling in situ electrochemical synthesis of silver nanoparticles (AgNPs) with the pre-deposited chitosan multilayer hydrogel, a novel type of nanocomposite coating was successfully fabricated on the stainless-steel needle electrode. Experimental results demonstrated the chitosan film can serve as a versatile medium for metal salt adsorption and stabilization, and finally electrochemical reduction of loaded silver ions to nanoparticles. The AgNPs were fabricated with a spherical shape and an average size of ∼15 nm endowing considerable antibacterial property to the hydrogel. Furthermore, the unique layered architecture consisted of porous segments and compact boundaries is almost retained, resulting in a pH-dependent and staged release pattern of silver nanoparticles based on acid triggered dissolution of the multi-membrane layer by layer. Thus, considering the mild synthesizing approach, multi-functionalities and relatively low cytotoxicity, this antibacterial hydrogel would show great potential either to be used as a newly coating material for interfacial improvement of implants or as a free-standing film after being peeled off for wound dressing.

Silver or gold? A comparison of nanoparticle modified electrochemical genosensors based on cobalt porphyrin-DNA

We applied a cobalt-porphyrin modified DNA as electrochemical marker, which was attached to nanoparticles, to detect specific DNA sequences. We compare the performance of gold and silver NPs in oligonucleotide sensors to determine if a change in metal will lead to either higher sensitivity or different selectivity, based on the redox behaviour of silver vs. gold. Surprisingly, we find that using either gold or silver NPs yields very similar overall performance. The electrochemical measurements of both types of sensors show the same redox behaviour which is dominated by the cobalt porphyrin, indicating that the electron pathway does not include the NP, but there is direct electron transfer between the porphyrin and the electrode. Both sensors show a linear response in the range of 5 × 10^-17-1 × 10^-16 M; the limit of detection (LOD) is 3.8 × 10^-18 M for the AuNP sensor, and 5.0 × 10^-18 M for the AgNP sensor, respectively, which corresponds to the detection of about 20-50 DNA molecules in the analyte. Overall, the silver system results in a better DNA economy and using cheaper starting materials for the NPs, thus shows better cost-effectivness and could be more suitable for the mass-production of highly sensitive DNA sensors.

Synthesis of La2O3/MWCNT nanocomposite as the sensing element for electrochemical determination of theophylline

In this study, an electrochemical sensor was applied for the determination of theophylline, a bronchodilator drug, using differential pulse voltammetry (DPV). A glassy carbon electrode (GCE) surface was modified with the La2O3/MWCNT nanocomposite. The design is simplistic, efficient, greener and solvent-free microwave procedure for synthesizing La2O3/MWCNT nanocomposites. Fourier transform infrared (FT-IR) spectroscopy, field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD) techniques are used to characterize the features of the La2O3/MWCNT nanocomposite morphology and structure. The use of the modified sensor remarkably enhanced the current density and displayed a linear response ranging between 0.1 and 400.0 μM, with a limit of detection of 0.01 μM (S/N = 3). Using optimized conditions, the modified sensor demonstrated very good stability, selectivity and improved accuracy. Acceptable outputs were achieved in the analysis of real specimens, indicating that it is possible to use the modified sensor for practical analyses.

Highly branched gold-copper nanostructures for non-enzymatic specific detection of glucose and hydrogen peroxide

The development of highly sensitive and highly selective sensors for non-enzymatic glucose and hydrogen peroxide (H₂O₂) detection using gold-copper alloy nanoparticles (AuCu alloy NPs) is reported. The AuCu NPs are nanostructures with branches and can be used as an electrochemical catalyst. Series of AuCu alloy NPs with various metal ratios are synthesized through a coreduction reaction. The morphology of AuCu alloy NPs is altered from highly branched structures (nanourchin, nanobramble, nanostar, nanocrystal) to a spherical shape by increasing Au content in the synthesis reaction. Cu-rich AuCu nanobramble and Au-rich AuCu nanostar exhibit selective electrocatalysis behaviors toward electro-oxidation of glucose and electroreduction of H₂O₂, respectively. The AuCu nanobramble-based sensor holds great potential in glucose detection with a linear working range of 0.25 to 10 mM. The sensor possesses a sensitivity of 339.35 μA mM^-1 cm^-2, a limit of detection (LOD) of 16.62 μM, which is an acceptable selectivity and good stability. In addition, the AuCu nanostar-based sensor shows excellent electrochemical responses toward H₂O₂ reduction with good selectivity, reproducibility, and a short response time of about 2-3 s. The linear range for H₂O₂ determination is 0.05 to 10 mM, with LOD and sensitivity of 10.93 μM and 133.74 μA mM^-1 cm^-2, respectively. The good sensing performance is a result of the synergistic surface structure and atomic composition effects, which leads AuCu alloys to be a promising nanocatalyst for sensing both glucose and H₂O₂. Graphical abstract Schematic illustration presents the construction of gold-copper alloy nanoparticles (AuCu alloy NPs) on the surface of screen-printed carbon electrode (SPCE). The highly branched nanostructures of AuCu alloys with different surface structure and metal ratios give selective electrocatalysis behaviors. Cu-rich AuCu nanobramble-based sensor reveals prominent electrocatalytic activity for glucose detection. Au-rich AuCu nanostar-based sensor provides good electrochemical response for H₂O₂ detection.

A dopamine electrochemical sensor based on a platinum–silver graphene nanocomposite modified electrode

A platinum–silver graphene nanocomposite was synthesized and characterized. A nanocomposite modified electrode was fabricated in order to investigate the electrochemical detection of dopamine.

Development of Dopamine Sensor Using Silver Nanoparticles and PEG-Functionalized Tapered Optical Fiber Structure

This article presents a localized surface plasmon resonance (LSPR) phenomenon based optical fiber sensor (OFS) for the detection of dopamine (DA). DA functions as a hormone and a neurotransmitter in the human body and plays a crucial role in the peripheral system. To develop the OFS for DA detection, taper fiber probe was fabricated and immobilized with silver nanoparticles (AgNPs) and functionalized with Polyethylene glycol (PEG). The developed sensor shows the great selectivity in the presence of ascorbic acid (AA) oxidation due to PEG coating. The morphology of the AgNPs and uniformity of coating over the surface of sensing probe were confirmed with UV-visible spectrophotometer, transmission electron microscope (TEM), energy-dispersive X-ray spectroscopy (EDS), and scanning electron microscope (SEM). The calibration curve is found to be linear over the range of 10 nM-1 μM with the lowest detection limit of 0.058 μM. Also provides a wide dynamic range of detection (10 nm-100 μM). The parameters responsible for the performance of OFS, such as sensitivity, detection limit, and selectivity are greatly improved in the proposed sensor. The applicability of the proposed sensor has been validated and have the potential to use for routine diagnosis.