Colloidal Silver Nanoparticles Research Articles

Simple two-step synthesis of Ag/ZnO nanoparticles with enhanced photocatalytic response

This study presents a simple two-step synthesis method for the fabrication of Ag/ZnO nanocomposites to improve the photocatalytic response of ZnO. The synthesis involves ZnO nanoparticles that were fabricated from the thermal decomposition of commercial zinc acetate. In order to produce Ag/ZnO nanoparticles in a simple two-step process, ZnO nanoparticles were mixed with Ag nanoparticle suspensions previously obtained by the laser ablation of solids in liquids technique at three different fluences. Structural characterization of ZnO powders revealed the presence of single phase wurtzite ZnO nanoparticles with crystal sizes of 20 nm. On the other hand, XRD patterns for a composite sample revealed the presence of signals associated to both ZnO and Ag suggesting that silver nanoparticles were attached to the ZnO particles surface. Optical characterization of the ZnO powders, carried out by UV–vis spectroscopy, showed a strong absorption band centered at 380 nm, which is associated to excitonic transitions in ZnO nanoparticles, whilst absorption measurements of silver nanoparticles colloids revealed the presence of a strong band centered near 412 nm. This band shifts to shorter wavelengths with increasing fluence from 2.6 to 6.2 J cm−2, indicating changes in nanoparticles size. Photocatalytic degradation tests of methylene blue under UV irradiation were carried out using pure ZnO, Ag colloids and Ag/ZnO nanoparticles. After the first 30 min of irradiation, it was observed that the silver nanoparticles reached degradation percentages of 16, 22 and 29% for samples synthesized at 2.6, 4.2 and 6.2 J cm−2, respectively. Meanwhile the ZnO sample reached a value of 13% after 30 min. Regarding the Ag/ZnO composite sample, the percentage of degradation after 30 min was 36%, demonstrating a considerable enhanced photocatalytic activity as compared to ZnO. After 24 h irradiation, Ag/ZnO degraded 95% of the methylene blue solution. It was observed that decorating ZnO with laser produced silver nanoparticles accelerates the photocatalytic response of ZnO by enhancing the activity at short times.

Discrimination of Genetic Biomarkers of Disease through Machine-Learning-Based Hypothesis Testing of Direct SERS Spectra of DNA and RNA.

Cancer is globally a leading cause of death that would benefit from diagnostic approaches detecting it in its early stages. However, despite much research and investment, cancer early diagnosis is still underdeveloped. Owing to its high sensitivity, surface-enhanced Raman spectroscopy (SERS)-based detection of biomarkers has attracted growing interest in this area. Oligonucleotides are an important type of genetic biomarkers as their alterations can be linked to the disease prior to symptom onset. We propose a machine-learning (ML)-enabled framework to analyze complex direct SERS spectra of short, single-stranded DNA and RNA targets to identify relevant mutations occurring in genetic biomarkers, which are key disease indicators. First, by employing ad hoc-synthesized colloidal silver nanoparticles as SERS substrates, we analyze single-base mutations in ssDNA and RNA sequences using a direct SERS-sensing approach. Then, an ML-based hypothesis test is proposed to identify these changes and differentiate the mutated sequences from the corresponding native ones. Rooted in "functional data analysis," this ML approach fully leverages the rich information and dependencies within SERS spectral data for improved modeling and detection capability. Tested on a large set of DNA and RNA SERS data, including from miR-21 (a known cancer miRNA biomarker), our approach is shown to accurately differentiate SERS spectra obtained from different oligonucleotides, outperforming various data-driven methods across several performance metrics, including accuracy, sensitivity, specificity, and F1-scores. Hence, this work represents a step forward in the development of the combined use of SERS and ML as effective methods for disease diagnosis with real applicability in the clinic.

A compact 3D printed magnetically stirred tank reactor cascade coupled with a free impinging jet for continuous production of colloidal nanoparticles

Most colloidal nanoparticle production processes involve more than one step, such as particle nucleation, growth and stabilisation, that often take place at different time scales. Flow chemistry offers an attractive platform for nanoparticle synthesis, as it can provide excellent control of conditions for each individual step. In this work, a free impinging jet reactor (FIJR), known for its rapid mixing capability and fouling-proof operation, is followed by a cascade of 5 miniaturised (3 ml) continuous stirred tank reactors (mCSTR) that provides longer residence time and efficient temperature control for subsequent synthesis steps, while still being resistant to clogging due to active mixing. The small (0.1 mm) diameter nozzle design allowed the FIJR to provide excellent mixing even at relatively low flowrates (2 ml/min/jet). The mCSTR cascade was arranged in a vertical configuration (one tank on top of another), offering a compact design that is simple to use and requiring only one magnetic stirrer. It provided near-ideal macromixing with limited dead volumes and interconnections, as reflected by a residence time distribution comparable with the theoretical one for a CSTR cascade. Most parts of the reactor system were 3D printed with features that facilitated the assembly. The proposed FIJR design overcomes the accuracy limitations of 3D printing by combining it with micromilling to achieve one of the smallest FIJR reported and by allowing for rotation of the nozzles to easily resolve issues with jet alignment. The reactor system was employed for the synthesis of colloidal (∼10 nm size) silver nanoparticles via NaBH4 reduction of AgNO3, in a 0.06 g/day scale for 50 min continuous operation and (∼6 nm core size) iron oxide nanoparticles via co-precipitation of Fe3+/Fe2+, producing colloidally stable nanoparticles in a 16.1 g/day scale for over 2 h continuous operation.

Investigation of Melphalan interaction as an alkylating agent with nucleotides by using surface enhanced Raman spectroscopy (SERS)

SERS (Surface Enhanced Raman Spectroscopy) is a new Raman spectroscopy which relies on Surface Plasmon Resonance (SPR) of metal nanoparticles. We have applied colloidal silver and gold nanoparticles as amplifier agents to enhance nucleotide Raman signals. It is observed that without these enhancing agents, it is impossible to investigate nucleotide spectrum due to weak Raman signals. Interaction mechanism of Melphalan, an anticancer drug with four nucleotides (Adenine, Cytosine, Guanine, Thymine) was investigated using SERS to detect and identify changes due to alkylating process in Raman spectra. After incubating Melphalan drug with nucleotides for 24 h at 37 °C, some changes occurred in SERS spectrum and interpretation of SERS spectra revealed the influence of the alkyl substitution on peaks and Raman shifts. After incubation of Melphalan with each nucleotide, intensity of relevant SERS signals assigned to Amid III group of Cytosine and Amid I of Thymine decreased significantly, confirming alkylating taking place. In this study, we also investigated the effect of nanoparticles type on nucleotide spectrum. We could not obtain useful information in the cases of guanine nucleotide. The SERS spectrum of Cytosine as an example of nucleotides in aqueous solution compared to solid state and results demonstrated that in solid state better signals were obtained than in liquid state.

In English

Changes in the light absorption spectrum when mixing colloids of Ag nanoparticles with a diameter of 7 nm in a quercetin shell with a nutrient medium were studied in the present article. Colloids of silver nanoparticles were prepared by chemical reduction of AgNO3 silver salt with sodium tetrahydroborate (NaBH4) in an aqueous solution. Quercetin is a flavonoid of plant origin. It was chosen to stabilize nanoparticles due to its capability to form complexes with metals. The quercetin shell is capable to preserve the bactericidal effect of silver NPs on bacteria and weaken their toxic effect on healthy cells of the human body. The absorption spectra of solutions from which nanoparticle colloids were synthesized were used to control the synthesis result. The Luria-Bertani nutrient medium was studied in the work. Absorption spectra of the nutrient medium and nanoparticle colloids were again obtained immediately before mixing. Then, the nutrient medium and the nanoparticle colloid were mixed in volume proportion 1:1, and the absorption spectrum of the mixture was mesured. The absorption spectrum of the mixture did not reproduce a simple overlay of the nanoparticle colloid spectrum on the absorption spectrum of the nutrient medium. To describe the experimental spectra, a colloid of stabilized silver nanoparticles, a nutrient medium, and a mixture of a colloid and a nutrient medium were considered by nanocomposites of various organic and inorganic nanoparticles in a liquid. As a result, experimental absorption spectra were theoretically approximated by related to these nanoparticles elementary oscillators. The error of the discrepancy between experimental and simulated spectra did not exceed 3%. Analysis of the complex spectra of the mixture of the nanoparticle colloid and the nutrient medium has shown that the frequency of the localized plasmon resonance in the nanoparticles most likely does not change. It means that for studying the effect of nanoparticles on biological objects (microbes or viruses), the wavelength of external irradiation must be chosen equal to the wavelength of LPR in the colloid.

Nanometals incorporation into active and biodegradable chitosan films

This study investigates the effects of incorporating ZnO, TiO2, and colloidal Ag nanoparticles on the antioxidant, antimicrobial, and physical properties of biodegradable chitosan films. The research focuses on addressing the growing demand for sustainable packaging solutions that offer efficient food preservation while mitigating environmental concerns. In this investigation, the physical properties including thickness, water content, solubility, swelling degree, tensile strength, and elasticity of the chitosan films were examined. Additionally, the samples were analyzed for total polyphenol content, antimicrobial activity, and antioxidant capacity. Notably, the incorporation of ZnO nanoparticles led to the lowest water content and highest strength values among the tested films. Conversely, the addition of colloidal Ag nanoparticles resulted in films with the highest antioxidant capacities (DPPH: 32.202 ± 1.631 %). Remarkably, antimicrobial tests revealed enhanced activity with the inclusion of colloidal silver nanoparticles, yet the most potent antimicrobial properties were observed in films containing ZnO (E.coli: 2.0 ± 0.0 mm; MRSA: 2.0 ± 0.5 mm). The findings of this study hold significant implications for the advancement of edible biodegradable films, offering potential for more efficient food packaging solutions that address environmental sustainability concerns. By elucidating the effects of nanoparticle incorporation on film properties, this research contributes to the ongoing discourse surrounding sustainable packaging solutions in the food industry.

Comparing silver and gold nanoislands’ surface plasmon resonance for bisacodyl and its metabolite quantification in human plasma

Gold and silver nanoparticles have witnessed increased scientific interest due to their colourful colloidal solutions and exceptional applications. Comparing the localized surface plasmon resonance (LSPR) of gold and silver nanoparticles is crucial for understanding and optimizing their optical properties. This comparison informs the design of highly sensitive plasmonic sensors, aids in selecting the most suitable nanoparticles for applications like surface-enhanced infrared spectroscopy (SEIRA) and biomedical imaging, and guides the choice between gold and silver nanoparticles based on their catalytic and photothermal properties. Ultimately, the study of LSPR facilitates the tailored use of these nanoparticles in diverse scientific and technological applications. Two SEIRA methods combined with partial least squares regression (PLSR) chemometric tools were developed. This development is based on the synthesis of homogeneous, high-dense deposited metal nanoparticle islands over the surface of glass substrates to be used as lab-on-chip SEIRA sensors for the determination of bisacodyl (BIS) and its active metabolite in plasma. SEM micrographs revealed the formation of metallic islands of colloidal citrate-capped gold and silver nanoparticles of average sizes of 29.7 and 15 nm, respectively. BIS and its active metabolite were placed on the nanoparticles’ coated substrates to be directly measured, then PLSR chemometric modelling was used for the quantitative determinations. Plasmonic citrate-capped gold nanoparticle substrates showed better performance than those prepared using citrate-capped silver nanoparticles in terms of preparation time, enhancement factor, PLSR model prediction, and quantitative results. This study offers a way to determine BIS and its active metabolite in the concentration range 15–240 ng/mL in human plasma using inexpensive disposable glass-coated substrates that can be prepared in 1 h to get results in seconds with good recovery between 98.77 and 100.64%. The sensors provided fast, simple, selective, molecular-specific and inexpensive procedures to determine molecules in their pure form and biological fluid.

Vibrational Analysis and Concentration Dependent SERS Study of Cefoperazone

Cefoperazone is a broad-spectrum antibiotic that is extremely efficient in the treatment of respiratory, abdominal, or genital infections. Vibrational spectroscopic techniques, FT-IR, Raman, and SERS, along with DFT calculations, were involved in investigating the normal modes of vibration and adsorption behavior of this antibiotic. Using both the experimental and theoretical data, the bands in the Raman and IR spectra were assigned to the normal vibrational modes. The SERS spectra were successively obtained by using silver and gold colloidal nanoparticles as a substrate. Their analysis revealed that the molecule is chemisorbed on the nanostructured surface through the as-denoted nitrogen ring. Changes observed in the SERS spectra recorded at different cefoperazone concentrations, i.e., modifications in the relative intensity of specific bands suggest the reorientation of adsorbed molecules towards the metal surface.

Surface adsorption of L-phenylalanine on silver colloidal nanoparticles investigated by surface-enhanced Raman spectroscopy

L-phenylalanine (L-Phe) is one of three aromatic amino acids frequently used in numerous vibrational applications, including surface-enhanced Raman spectroscopy (SERS). Despite the wide applications, the spectral analyses and vibrational assignments of the Raman spectra of L-Phe based on surface adsorption on metallic nanosurfaces are limited. In this work, we report pH-dependent SERS of L-Phe adsorbed on borohydride-reduced silver colloidal nanoparticles, where the spectral changes upon protonation of amine group are understood as the modification in the surface adsorption via the carboxylate and amino group. In-plane and out-of-plane ring stretching and aromatic ν(CH) modes appear sensitive to the surface orientation of the phenyl ring, and the peripheral vibrational modes, including the stretching and bending of carboxylate and amine groups, are crucial to understanding the detailed surface adsorption mechanisms of L-Phe in anionic and zwitterionic forms depending on the solution pH. The pH-dependent intensity changes of the major ring stretching modes show that the surface pKa of L-Phe decreases to ∼6 from the bulk value of 9.13.

A facile approach for selective detection of arsenite ions using plasmonic behaviour of silver nanoparticles.

A specific reagent/aptamer-free easy redox strategy between silver(I) moieties present in a citrate-stabilized colloidal silver nanoparticle (NP) system and arsenite ions is described that enables plasmonic change of AgNPs for the selective quantification of arsenite ions in the range of 0 to 30 μM with a low limit of quantification value of 50 nM (5.3 ppb).

Synthesis Optimization and Antibacterial Performance of Colloidal Silver Nanoparticles in Chitosan

Colloidal silver nanoparticles were successfully synthesized via the chemical reduction method. The synthesis used AgNO3 as the precursor, chitosan as the reducing and stabilizing agents, and NaOH as the accelerator. The synthesis parameters were optimized. The samples were tested with a UV-vis spectrophotometer to observe their localized surface plasmon resonance (LSPR) phenomenon, a transmission electron microscope (TEM), and a particle size analyzer (PSA) to investigate their particle shape and size distribution. Further, silver nanoparticles were tested for their storage stability and antibacterial performance. The UV-vis spectroscopy data exhibited that the silver nanoparticles have been successfully synthesized, validating via the emergence of the LSPR absorption band at 402–418 nm. At 50 °C, the optimum synthesis was achieved for 100 min of reaction time by adding 0.033 M NaOH and AgNO3 4.00% (w/w, AgNO3/chitosan). TEM results showed spherical silver nanoparticles of 1–8 nm, while the PSA results exhibited particles sizes of about 12–59 nm. The colloidal silver nanoparticles were stable in storage for 8 weeks and had good antibacterial performance against E. coli, S. aureus, extended-spectrum beta-lactamases (ESBL), and methicillin-resistant S. aureus (MRSA). Therefore, colloidal silver nanoparticles have the potential as a material for medical applications.

High removal efficiency of ammonium from aqueous solution by colloidal silver nanoparticles: batch adsorption

ABSTRACT This study aimed to use colloidal silver nanoparticles (AgNPs) for ammonium adsorption. Several factors were considered, including pH value, contact time, amount of adsorbent, and beginning ammonium content. The ideal parameters for ammonium adsorption onto the AgNPs were an a pH of 9, a contact period of 60 minutes, a concentration of 1.824 mg AgNPs/25 mL of ammonium solution, and a starting concentration of 80 mL, as determined. The optimum ammonium adsorption capacity onto the AgNPs was 276.84 mg/g, and the Langmuir model described the isotherm adsorption with R2, KL, and calculated qmax values of 0.9339, 0.518 L/mg, and 263.37 mg/g, respectively. The experimental data were most closely matched by the Elovich model, as seen by its R2, α, and β values of 0.885, 0.055, and 0.180, respectively. Temperature release values for the exothermic adsorption were 23,084 kJ/mol at 20°C, −23872 kJ/mol at 30°C, and 24,660 kJ/mol at 40°C.

A Green Chemistry Approach to the Synthesis and Characterization of Silver Nanoparticles

Traditional synthesis of nanoparticles employed only physical and chemical methods. More often the chemical synthesis methods employed in this production usually makes presence and absorbance of some toxic chemical substance on their surface and this may result in an adverse effect in several medical and other applications. No such adverse effects appear if they are biosynthesized using technology of green synthesis. This paper emphasizes on the synthesis and characterization of silver nanoparticles that can be applied in cleaning up of an environment such as an anti-biofouling compound synthesis by an environmentally friendly green synthesis technique. Aqueous extracts from the leaves of plant S. siamea were used as the reducing agents to produce the nanoparticles. UV-Visible spectroscopy monitored the synthesis of colloidal silver Nanoparticles and it showed a peak at 429 nm corresponding to the Plasmon absorbance of the silver nanoparticles. SEM analysis and FTIR and EDS XRD were employed to characterize other aspects like that of the size and shape.

Synthesis of Colloidal Silver Nanoparticles Using Alginate as Reducing and Stabilizing Agents and its Application as Antibacterial Material

Synthesis of colloidal silver nanoparticles has been successfully conducted through the chemical reduction technique. The synthesis used AgNO3, NaOH, and alginate as the precursor, accelerator reagent, and reducing agent and stabilizer, respectively. The effects of heating temperature, reaction time, accelerator concentration, and precursor concentration were investigated according to the localized surface plasmon resonance (LSPR) phenomenon using a UV-Vis spectrophotometer. The nanoparticle size distribution was observed via a Particle Size Analyzer (PSA). The stability of silver nanoparticles was studied for 8 weeks based on the LSPR phenomenon. Then, their antibacterial performance toward S. Aureus ATCC 25923 and E. Coli ATCC 25922 was examined. The results showed the absorbance intensities representing the number of silver nanoparticles formed were influenced by temperature, reaction time, NaOH concentration, and AgNO3 concentration. At 50°C heating, the optimum synthesis of silver nanoparticles was achieved at 50 min with a NaOH concentration of 0.013M. The higher AgNO3 concentration resulted in a greater concentration of silver nanoparticles produced. From the PSA characterization, the average particle sizes for the samples were 1.82 nm and 1.30 nm for AgNO3 concentrations (% w/w; AgNO3/Alginate) of 1.6% and 2.4%, respectively. Based on the LSPR phenomenon, colloidal silver nanoparticles were stable in storage for 8 weeks at room temperature. The increase in the concentration of silver nanoparticles within colloidal could enhance antibacterial performance against S. Aureus and E. Coli. Accordingly, silver nanoparticles synthesized with alginate as a stabilizer have the potential as an antibacterial compound for medical applications.

Stability and conductivity of water-based colloidal silver nanoparticles conductive inks for sustainable printed electronics

BackgroundDeveloping conductive inks for printed electronics has gained increasing interest in recent years as a low-cost and environmentally friendly alternative to traditional organic metal-based inks. This study aims to investigate the influence of silver nitrate (AgNO3) concentration at different temperatures and the effect of polyvinylpyrrolidone (PVP) surfactant concentration on the properties of the colloidal silver nanoparticles (AgNPs) conductive inks. MethodsIn this study, water-based AgNPs were prepared using a chemical reduction method. The effect of AgNO3 concentration, the reaction temperature, and the amount of PVP as a stabilizing agent on the size, shape, and purity of the synthesized AgNPs was investigated. The stability, thermal characteristics, and functional groups of the water-based AgNPs were also evaluated. The printed AgNPs patterns were examined for morphological and electrical properties. Significant findingsResults indicated that the concentration of AgNO3 and reaction temperature influence the size of AgNPs particles and their clustering. A high concentration of AgNO3 results in a higher yield of AgNPs and subsequently increases the electrical conductivity to 2.69×10° S/m. Adding PVP improves the stability of AgNPs for up to 45 days. Therefore, the development of water-based colloidal AgNPs conductive ink in this study can be used in inkjet printing to fabricate environmentally friendly printed electronics.

Silk fibroin-based green colloidal silver nanoparticle synthesis and their antibacterial and anticancer properties

Aqueous silk fibroin (SF), derived from Bombyx mori silk, was used to synthesize colloidal silver nanoparticles (AgNPs) in situ under white light and at ambient temperature. A characteristic surface plasmon resonance (SPR) band at 425–435 nm from the UV–Vis spectrum provided evidence of the formation of AgNPs by UV–Visible spectroscopy. The nanoparticles that were synthesized were spherical with smooth surfaces, as evidenced by the transmission electron microscope (TEM) photographs. The size of the particles was between 35 and 40 nm. Additionally, X-ray diffraction (XRD) investigation supports the existence of silver's nanocrystalline phase with FCC crystal structure. The human bacterial pathogens Escherichia coli (E. coli) and Bacillus subtilis (B. subtilis) were significantly inhibited by the biogenic silver nanoparticles' antibacterial activity. The synthesized nanoparticles also show an excellent anti-cancer activity in lowest dosage.

Colloid transport by an oscillatory electroosmotic flow between microelectrodes of axially variable shape

In this work, an analytic solution for the hydrodynamic dispersion of silver colloidal nanoparticles released into an oscillatory electroosmotic flow between microelectrodes of axially variable shape is presented. The long-time colloid concentration response is derived using the homogenization method together with multiple-scale analysis. The results indicate that the deposition of nanoparticles onto the surface of the microelectrodes depends on the rate constant β of solute reaction at the wall, on the angular frequency ω, and mainly on the induced pressure gradient that arises due to the variable geometrical shape of the walls. For suitable values of the previous parameters, we show that colloidal nanoparticle concentration can be enhanced as well as choosing the location where it will happen.

Design and synthesis of silver bio-nanocomposite for photocatalytic applications.

One of the major concerns faced by humanity since Industrial Revolution is the contamination of water by the effluents released to the water bodies as a part of modernization and socio-economic development. Water purification is the most researched topic and numerous researches carried out in the past and are still going on in the present which pinpoints the seriousness of the grave issues raised by contamination of water bodies. In this work we have tried to develop a bio-nanocomposite utilizing colloidal silver nanoparticles synthesized via green protocol and arrowroot powder. Nano Silver well known for its photocatalytic properties has been incorporated into biodegradable and ecofriendly arrowroot powder for enhanced photocatalytic action and carried out degradation studies on the common contaminant dye Methylene Blue (MB). The synthesized bio nanocomposite exhibits promising photocatalytic action to be used for water purification.

Systematic Photophysical Interaction Studies Between Newly Synthesised Oxazole Derivatives and Silver Nanoparticles: Experimental and DFT Approach.

In this study, the photophysical properties of oxazole derivatives such as 5-(furan-2-yl) -4-tosyloxazole (OX-1) and 5-(2-bromothiazol-4-yl)-4-tosyloxazoles (OX-2) were investigated using theoretical and experimental techniques. The ground and excited state dipole moments were empirically obtained utilising the solvatochromic shift technique and several solvatochromic correlations such as Lippert's, Bakhshiev's, KawskiChamma- Viallet's, and solvent polarity equations. The ground state dipole moments, HOMO-LUMO and molecule electrostatic potential map were also computed using ab initio calculations and evaluated using Gaussian 09 W software. Furthermore, spectroscopic interactions between newly synthesised dyes (OX-1 and OX-2) and freshly synthesised silver nanoparticles (size 40nm) were studied. Increased absorbance and widening of absorption spectra for both dyes in the presence of varied quantities of silver nanoparticles show the potential of dye-nanoparticle interactions. Fluorescence quenching has been detected for both dyes in the presence of colloidal silver nanoparticles, indicating dynamic quenching, and a significant overlap between the absorption and emission spectra of the silver nanoparticle reveals that fluorescence quenching is also due to energy transfer.

Concentration dependence of NaBH4 reductant on the optical properties of colloidal silver nanoparticles synthesized from AgNO3 solution

Synthesis of silver nanoparticles was successfully synthesized by a chemical reduction method using silver nitrate (AgNO3) as a precursor and sodium borohydride (NaBH4) as a reducing agent. The optical properties of silver nanoparticles were studied based on their surface plasmon resonance (SPR) phenomenon using UV-Visible spectrophotometry. The absorbance spectra of colloidal silver nanoparticles show the peak at the wavelength range of 380 nm to 450 nm. Colloidal silver nanoparticles have good stability after storage at room temperature.