Gold Alloy Nanoparticles Research Articles

Surface gold atoms determine peroxidase mimic activity in gold alloy nanoparticles.

The development of peroxidase mimic nanocatalysts is relevant for oxidation reactions in biosensing, environmental monitoring and green chemical processes. Several nanomaterials have been proposed as peroxidase mimic, the majority of which consists of noble metals and oxide nanoparticles (NPs). Yet, there is still limited information about how the change in the composition influences their catalytic activity. Here, the peroxidase mimic behaviour of gold NPs is compared to a traditional nanoalloy as Au-Ag and to the Au-Fe and the Au-Co nanoalloys, which were not tested before as oxidation catalysis. Since the alloys of gold with iron and cobalt are thermodynamically unstable, laser ablation in liquid (LAL) is exploited for the synthesis of these NPs. Using LAL, no chemical stabilizers or capping agents are present on the NPs surface, allowing the evaluation of the oxidation behaviour as a function of the alloy composition. The results point to the importance of surface gold atoms in the catalytic process, but also indicate the possibility of obtaining active nanocatalysts with a lower content of Au by alloying it with iron, which is earth-abundant, non-toxic and low cost. Overall, Au nanoalloys are worth consideration as a more sustainable alternative to pure Au nanocatalysts for oxidation reactions.

Tailoring the Reaction Pathway for Control of Size and Composition of Silver–Gold Alloy Nanoparticles

Tailoring the Reaction Pathway for Control of Size and Composition of Silver–Gold Alloy Nanoparticles

Anti-biofilm properties of laser-synthesized, ultrapure silver–gold-alloy nanoparticles against Staphylococcus aureus

Staphylococcus aureus biofilm-associated infections are a common complication in modern medicine. Due to inherent resilience of biofilms to antibiotics and the rising number of antibiotic-resistant bacterial strains, new treatment options are required. For this purpose, ultrapure, spherical silver–gold-alloy nanoparticles with homogenous elemental distribution were synthesized by laser ablation in liquids and analyzed for their antibacterial activity on different stages of S. aureus biofilm formation as well as for different viability parameters. First, the effect of nanoparticles against planktonic bacteria was tested with metabolic activity measurements. Next, nanoparticles were incubated with differently matured S. aureus biofilms, which were then analyzed by metabolic activity measurements and three dimensional live/dead fluorescent staining to determine biofilm volume and membrane integrity. It could be shown that AgAu NPs exhibit antibacterial properties against planktonic bacteria but also against early-stage and even mature biofilms, with a complete diffusion through the biofilm matrix. Furthermore, AgAu NPs primarily targeted metabolic activity, to a smaller extend membrane integrity, but not the biofilm volume. Additional molecular analyses using qRT-PCR confirmed the influence on different metabolic pathways, like glycolysis, stress response and biofilm formation. As this shows clear similarities to the mechanism of pure silver ions, the results strengthen silver ions to be the major antibacterial agent of the synthesized nanoparticles. In summary, the results of this study provide initial evidence of promising anti-biofilm characteristics of silver–gold-alloy nanoparticles and support the importance of further translation-oriented analyses in the future.

Multiplexed immunolabelling of cancer using bioconjugated plasmonic gold-silver alloy nanoparticles.

Reliable protein detection methods are vital for advancing biological research and medical diagnostics. While immunohistochemistry and immunofluorescence are commonly employed, their limitations underscore the necessity for alternative approaches. This study introduces immunoplasmonic labelling, utilizing plasmonic nanoparticles (NPs), specifically designed gold and gold-silver alloy NPs (Au:Ag NPs), for multiplexed and quantitative protein detection. These NPs, when coupled with antibodies targeting proteins of interest, enable accurate counting and evaluation of protein expression levels while overcoming issues such as autofluorescence. In this study, we compare two nanoparticle functionalization strategies-one coating based on thiolated PEG and one coating based on calix[4]arenes-on gold and gold-silver alloy nanoparticles of varying sizes. Overall results tend to demonstrate a greater versatility for the calix[4]arene-based coating. With this coating and using the classical EDC/sulfo-NHS cross-linking procedure, we also demonstrate the successful multiplexed immunolabelling of Her2, CD44, and EpCAM in breast cancer cell lines (SK-BR-3 and MDA-MB-231). Furthermore, we introduce a user-friendly software for automatic NP detection and classification by colour, providing a promising proof-of-concept for the practical application of immunoplasmonic techniques in the quantitative analysis of biopsies in the clinical setting.

SERS Reveals the Presence of Au–O–O–H and Enhanced Catalytic Activity of Electrochemically Dealloyed AgAu Nanoparticles

Due to their high surface-to-volume ratio and large proportion of low coordinated surface atoms, dealloyed nanoparticles have gained increasing attention as porous catalysts for the electrochemical oxygen evolution reaction (OER). Here, we characterize and rationalize the physical and chemical properties of operando gold-enriched porous nanoparticles fabricated by electrochemical dealloying of citrate-capped silver gold alloy nanoparticles in 250 mM KNO3. We combine surface-enhanced Raman spectroscopy (SERS) with electrochemistry for catalyst tracking. With SERS, we observe at 1.05 V (vs platinum quasi-reference electrode) the formation of Au–O–O–H species, a known intermediate of OER, while this is not observed for monometallic gold nanoparticles or bare electrodes. In agreement, qualitative measurements of the catalytic activity prove that appreciable OER currents are detected at lower potentials for gold-enriched porous nanoparticles compared to gold nanoparticles of the same size. Our results pave the way for the application of dealloying-derived nanoparticles as promising catalyst materials.

Picosecond Laser-Ablated Nanoparticles Loaded Filter Paper for SERS-Based Trace Detection of Thiram, 1,3,5-Trinitroperhydro-1,3,5-triazine (RDX), and Nile Blue.

Recently, filter paper (FP)-based surface-enhanced Raman scattering (SERS) substrates have stimulated significant attention owing to their promising advantages such as being low-cost, easy to handle, and practically suitable for real-field applications in comparison to the solid-based substrates. Herein, a simple and versatile approach of laser-ablation in liquid for the fabrication of silver (Ag)-gold (Au) alloy nanoparticles (NPs). Next, the optimization of flexible base substrate (sandpaper, printing paper, and FP) and the FP the soaking time (5–60 min) was studied. Further, the optimized FP with 30 min-soaked SERS sensors were exploited to detect minuscule concentrations of pesticide (thiram-50 nM), dye (Nile blue-5 nM), and an explosive (RDX-1,3,5-Trinitroperhydro-1,3,5-triazine-100 nM) molecule. Interestingly, a prominent SERS effect was observed from the Au NPs exhibiting satisfactory reproducibility in the SERS signals over ~1 cm2 area for all of the molecules inspected with enhancement factors of ~105 and relative standard deviation values of <15%. Furthermore, traces of pesticide residues on the surface of a banana and RDX on the glass slide were swabbed with the optimized FP substrate and successfully recorded the SERS spectra using a portable Raman spectrometer. This signifies the great potential application of such low-cost, flexible substrates in the future real-life fields.

Gold–Silver Bimetallic Alloy Nanoparticles in a Covalent Organic Framework for Real-Time Monitoring of Hydrogen Peroxide from Live Cells

An efficient and simple way has been described to prepare gold and silver bimetallic alloy nanoparticles (Au-AgNPs) in an organic framework with a metal-free core. The growth of alloy Au-AgNPs was monitored by UV–visible spectroscopy (UV–vis) and confirmed using various spectral, microscopy, and electrochemical techniques. The field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) results revealed that the covalent organic framework (COF) had a uniform flake-like morphology, and the alloy-based Au-AgNPs had a flower-like structure. The results of X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) indicated that Au-AgNPs are metallic in nature and highly crystalline. The surface of a glassy carbon electrode (GCE) was then modified with Au-AgNPs-COF, which was subsequently employed for enzyme-free electrochemical reduction of H2O2. The electrocatalytic cyclic voltammetry performance of the different modified electrodes was in the following order: COF (−14.82 μA) < AgNPs-COF (−26.95 μA) < AuNPs-COF (−31.78 μA) < Au-AgNPs-COF (−46.15 μA). The Au-AgNPs-COF/GCE displayed an excellent electrocatalytic activity toward reduction of H2O2, over a dynamic range of 2.0 nM–1.0 mM with a limit of detection (LOD) of 0.44 nM (S/N = 3). Furthermore, the present sensor showed appreciable selectivity, stability, and reproducibility against the reduction of H2O2. Practicality was demonstrated in fetal bovine serum (FBS), cat blood serum (CBS), and living cells (RAW 264.7).

Robust Colloidal Synthesis of Palladium-Gold Alloy Nanoparticles for Hydrogen Sensing.

Metal nanoparticles are currently used in a variety of applications, ranging from life sciences to nanoelectronic devices to gas sensors. In particular, the use of palladium nanoparticles is gaining increasing attention due to their ability to catalyze the rapid dissociation of hydrogen, which leads to an excellent response in hydrogen-sensing applications. However, current palladium-nanoparticle-based sensors are hindered by the presence of hysteresis upon hydride formation and decomposition, as this hysteresis limits sensor accuracy. Here, we present a robust colloidal synthesis for palladium–gold alloy nanoparticles and demonstrate their hysteresis-free response when used for hydrogen detection. The obtained colloidal particles, synthesized in an aqueous, room-temperature environment, can be tailored to a variety of applications through changing the size, ratio of metals, and surface stabilization. In particular, the variation of the viscosity of the mixture during synthesis resulted in a highly tunable size distribution and contributed to a significant improvement in size dispersity compared to the state-of-the-art methods.

Rapid visual detection for nitroreductase based on the copper ions-induced and NADH-mediated aggregation of gold-silver alloy nanoparticles

Hypoxia refers to the lack of oxygen supply to cells or tissues. The overexpression of nitroreductase has been shown to be closely related to the degree of hypoxia, which leads to the level of nitroreductase (NTR) being used as an indicator of hypoxia. We reported a facile visual detection of NTR based on the aggregation of gold and silver alloy nanoparticles. Compared with gold nanoparticles (AuNPs), the aggregation behavior of Au80Ag20 NPs caused a more prominent color change. Copper ions (Cu2+) can be rapidly reduced by nicotinamide adenine dinucleotide (NADH) under the catalysis of Au80Ag20 NPs. But NADH is consumed as an electron donor during the catalytic reduction reaction of p-nitrophenol (pNP) by NTR. A decrease of NADH amount results in the aggregation of Au80Ag20 NPs by the excess Cu2+ and different aggregation degrees of Au80Ag20 NPs lead to observable color change. A linear correlation of A600/A505 = 0.0285 [NTR]+0.361 (R2 = 0.980) was obtained with a limit of detection (LOD) of 0.23 μg/mL for UV–vis spectrophotometer. For visual detection, the values of R/B against the concentration of NTR obtains a calibration curve of R/B = −0.031 [NTR]+ 1.54 (R2 = 0.985) with a LOD of 0.76 μg/mL, which is of the same order of magnitude as the UV–vis spectrophotometer analysis. As a comparison, Au80Ag20 NPs was replaced by several different composition nanoparticles (Au NPs, Au70Ag30 NPs, Au50Ag50 NPs) to be a chromogenic substrate, and the results suggest the Au80Ag20 NPs is the most sensitive substrate in our assay. Selectivity tests showed that the detection system did not respond to other common substances, and the reaction mechanism was verified by inhibitor research. Finally, the assay was used on the human serum samples with spiking NTR, and the recovery rates of this assay with UV–vis spectrophotometer were basically consistent with RGB analysis.

Antibacterial and Immunomodulatory Potentials of Biosynthesized Ag, Au, Ag-Au Bimetallic Alloy Nanoparticles Using the Asparagus racemosus Root Extract.

Two noble metals, such as silver and gold alloy nanoparticles, were successfully synthesized by the microwave assisted method in the presence of the Asparagus racemosus root extract and were used as an antibacterial and immunomodulatory agent. The nanostuctures of the synthesized nanoparticles were confirmed by various spectroscopic and microscopic techniques. The UV-vis spectrum exhibits a distinct absorption peak at 483 nm for the bimetallic alloy nanoparticles. The microscopic analysis revealed the spherical shaped morphology of the biosynthesized nanoparticles with a particle size of 10–50 nm. The antibacterial potential of the green synthesized single metal (AgNPs and AuNPs) and bimetallic alloy nanoparticles was tested against five bacterial strains. The bimetallic alloy nanoparticles displayed the highest zone of inhibition against P. aeurgnosia and S.aureus strains when compared to single metal nanoparticles and plant extract. In addition, the inmmunomodulatory potential of the root extract of A. racemosus, AgNPs, AuNPs, and Ag-Au alloy NPs is achieved by measuring the cytokine levels in macrophages (IL-1β, IL-6, and TNF-α) and NK cells (IFN-γ) of NK92 and THP1 cells using the solid phase sandwich ELISA technique. The results showed that the root extract of A. racemosus, AgNPs, and AuNPs can reduce the pro-inflammatory cytokine levels in the macrophages cells, while Ag-Au alloy NPs can reduce cytokine responses in NK92 cells. Overall, this study shows that the microwave assisted biogenic synthesized bimetallic nanoalloy nanoparticles could be further explored for the development of antibacterial and anti-inflammatory therapies.

Optical properties of polymer-graphene composites coated with gold and silver alloy nanoparticles

The plasmon resonance phenomenon occurring in the system of graphene-polymer-nanoparticles of an alloy of gold and silver is investigated. The possibility of controlling the attenuation of the intensity of electromagnetic radiation passing through the sample by changing the composition and thickness of the deposited coating is shown. For the investigated gold and silver alloy nanoparticles, the highest degree of radiation attenuation falls on the wavelength range from 400 to 600 nm. It was shown that by changing the composition of the nanoparticles (changing the ratio of gold and silver in the alloy), it is possible to achieve the maximum selective light attenuation by more than 2.5 times in the 500 nm region. In the 700 nm region, light attenuation by not more than 2 times is achieved. It was revealed that the use of films with different metal ratios allows us to shift the position of plasmon absorption in the entire visible wavelength range.

Hyperthermia-Induced Controlled Local Anesthesia Administration Using Gelatin-Coated Iron-Gold Alloy Nanoparticles.

The lack of optimal methods employing nanoparticles to administer local anesthesia often results in posing severe risks such as non-biocompatibility, in vivo cytotoxicity, and drug overdose to patients. Here, we employed magnetic field-induced hyperthermia to achieve localized anesthesia. We synthesized iron–gold alloy nanoparticles (FeAu Nps), conjugated an anesthetic drug, Lidocaine, and coated the product with gelatin to increase the biocompatibility, resulting in a FeAu@Gelatin–Lidocaine nano-complex formation. The biocompatibility of this drug–nanoparticle conjugate was evaluated in vitro, and its ability to trigger local anesthesia was also evaluated in vivo. Upon exposure to high-frequency induction waves (HFIW), 7.2 ± 2.8 nm sized superparamagnetic nanoparticles generated heat, which dissociated the gelatin coating, thereby triggering Lidocaine release. MTT assay revealed that 82% of cells were viable at 5 mg/mL concentration of Lidocaine, indicating that no significant cytotoxicity was induced. In vivo experiments revealed that unless stimulated with HFIW, Lidocaine was not released from the FeAu@Gelatin–Lidocaine complex. In a proof-of-concept experiment, an intramuscular injection of FeAu@Gelatin–Lidocaine complex was administered to the rat posterior leg, which upon HFIW stimulation triggered an anesthetic effect to the injected muscle. Based on our findings, the FeAu@Gelatin–Lidocaine complex can deliver hyperthermia-induced controlled anesthetic drug release and serve as an ideal candidate for site-specific anesthesia administration.

Nonlinear optical investigations of laser generated gold, silver and gold-silver alloy nanoparticles and optical limiting applications

Laser induced synthesis of gold, silver and gold-silver alloy nanoparticles in water and their nonlinear optical investigations are reported. The tunability of localized surface plasmon resonance band of the gold-silver alloy nanoparticles in the wavelength region between gold and silver was established using the UV–Visible absorption studies. The third order nonlinear optical properties like two photon absorption coefficient, optical limiting threshold, non linear refractive index and third order nonlinear optical susceptibility χ(3) of the nanoparticles could be fine tuned by controlling the volume ratios of gold and silver in the gold-silver alloy nanoparticles. The nonlinear optical behavior and optical limiting properties of the gold, silver and gold-silver alloy nanoparticles were found to be considerably affected by the position of inter and intra band absorption wavelength. Dual beam thermal lens method was utilized to determine the variations in photo thermal parameters like thermal diffusivity and thermal lens signal amplitude. The ability to tailor the nonlinear optical characteristics and photo thermal properties of the gold and silver nanoparticles employing the alloy nanoparticles makes them promising candidates in optical limiting, bio photonic, opto-electronic applications.

Improving Photocatalytic Energy Conversion via NAD(P)H

Wilm Jones received his PhD from Cardiff University; his research concerned photocatalytic hydrogen production using supported gold and gold alloy nanoparticles. He then worked at the UK Catalysis Hub on CO2 hydrogenation, followed by a research fellowship at the University of Aberdeen, working on photocatalytic NADH regeneration. Currently Wilm works as a research associate for UCL at the Research Complex at Harwell on a project developing photocatalytic materials for the depollution of air. Joseph Burnett is a final year PhD student at the University of Aberdeen, where his research is focused on heterogeneous systems, utilizing both supported metal catalysts and photocatalysts for the regeneration of the biocofactor NADH. He obtained his BS in chemistry from Manchester Metropolitan University, where his initial curiosity for catalysis was sparked, and later went on to study an MS in catalysis at Cardiff University. Jiafu Shi is an associate professor at School of Environmental Science and Engineering of Tianjin University. He obtained his PhD in chemical technology from Tianjin University. After graduation, he joined the faculty of Tianjin University and started working at the School of Environmental Science and Engineering. He was a visiting scholar at the University of California at Berkeley from 2016 to 2017. His research interests include biocatalysis, photo-biocatalysis, and hierarchically structured materials, which are related to energy and the environment. Russell Howe is a professor in materials chemistry at the University of Aberdeen. His research focuses on the use of spectroscopic methods to investigate catalysts and catalytic reaction mechanisms. Xiaodong Wang is a senior lecturer in chemical engineering at Lancaster University. Prior to this, he was a lecturer in chemical engineering at the University of Aberdeen. He obtained his PhD at Heriot-Watt University and completed both MS and BE studies at Tianjin University. Xiaodong’s research interests are heterogeneous catalysis and reaction engineering; his recent work focuses on the innovative use of heterogeneous catalysts (e.g., supported metals) in enzymatic transformations via cofactor regeneration.

Bare laser-synthesized palladium–gold alloy nanoparticles as efficient electrocatalysts for glucose oxidation for energy conversion applications

Laser-synthesized PdAu nanoparticles demonstrate a strong synergetic effect on glucose oxidation combining high catalytic activity with ultrafast kinetics at low potentials.

Glioma-sensitive delivery of Angiopep-2 conjugated iron gold alloy nanoparticles ensuring simultaneous tumor imaging and hyperthermia mediated cancer theranostics

Gliomas display a poor disease prognosis causing death within 15 months after diagnosis. Chemotherapy has offered some hope to target this, however, it is majorly ineffective due to the low therapeutic window, poor efficacy and high cytotoxicity. To overcome these challenges, we conjugated Angiopep-2, a cell penetrating peptide (CPP) to Iron Gold (Fe-Au) alloy nanoparticles and investigated the ability of Ang-Fe-Au Nps conjugate to limit glioma growth via magnetic field induced hyperthermia. Our results show that 6.44 nm sized conjugated Fe-Au Nps were superparamagnetic, enhanced negative Glioma image contrast and displayed a 12 °C temperature elevation when magnetically stimulated, indicating applications in medical imaging and hyperthermia-based therapy. Angiopep-2 conjugation resulted in 1.5-fold higher ingestion by C6 glioma cells than L929 fibroblasts, indicating specific glioma targeting and resulting in 90 % decrement in cell viability due to magnetic field induced hyperthermia. Immunohistochemical analysis showed an enhanced coagulative necrosis, glial fibrillary acidic protein (GFAP) expression and decreased Ki67 labelling index in rat treated with Ang-Fe-Au Nps which translated to a 5-fold decrement in tumor volume, consequently resulting in an increased survival time by 7 days. The dual application of this platform opens new doors towards cancer theranostics with minimal invasiveness.

Tailoring thermo-optical properties of eosin B dye using surfactant-free gold-silver alloy nanoparticles.

Surfactant free gold, silver and gold-silver alloy nanoparticles were synthesized using a laser mediated method for localized surface plasmon resonance tuning. The effect of these nanoparticles on the thermo-optical properties of eosin B dye was investigated. Dual beam mode matched thermal lens method was implemented to evaluate the thermal diffusivity of the eosin B with gold, silver and gold-silver alloy nanoparticles. Concentration and composition dependant changes in thermo-optical properties of the eosin B-nanoparticle systems were quantified. As the concentration of nanoparticles incorporated into the dye solution increased, the thermal diffusivity and fluorescence emission intensity of the samples were found to be decreased. At the same time an enhancement of the thermal lens signal was observed with the introduction of nanoparticles into the system. Further enhancement in signal and reduction in thermal diffusivity and fluorescence intensity can be obtained with fine tuning of surface plasmon resonance wavelength by gold, silver and gold-silver alloy nanoparticles.

Multicolor High-Speed Tracking of Single Biomolecules with Silver, Gold, and Silver–Gold Alloy Nanoparticles

Gold nanoparticles have been used as imaging probes to track the motions of single biomolecules. To investigate behaviors of various biomolecules simultaneously, increase of the color palette is ne...

Biosynthesis of silver, gold and silver–gold alloy nanoparticles using Persea americana fruit peel aqueous extract for their biomedical properties

While several green biomolecules have been used to synthesize functional and biologically compatible nanoparticles, little attention has been paid to Persea americana (PA) (avocado) fruit extract as a potential reducing agent. This study used avocado fruit peel aqueous extracts to synthesize silver nanoparticles (PAAgNPs), gold nanoparticles (PAAuNPs) and bimetallic alloy nanoparticles (PAAg–AuNPs). The particles were characterized using UV–vis spectroscopy, Fourier-transform infrared spectroscopy (FTIR), transmission electron microscopy, selected area electron diffraction (SAED), energy-dispersive X-ray spectroscopy and X-ray diffraction among others. The particles were assessed for their antibacterial, antifungal and antioxidant properties. The UV–vis spectroscopy showed PAgNPs, PAAuNPs and PAAg–AuNPs with surface plasmon resonance at 455.5, 538 and 540.5 nm, respectively. The significant FTIR peaks: PAAgNPs (3358 cm−1), PAAuNPs (3503 cm−1) and PAAg–AuNPs (3651 cm−1) pointed to protein as both capping and stabilizing agents for the synthesized nanoparticles. Generally, the particles were spherical, with size range of 18–80 nm for PAAgNPs, 16–71 nm for PAAuNPs and 44–55 nm for PAAg–AuNPs. The energy-dispersive X-ray spectra showed silver, gold and silver/gold as conspicuous metals in PAAgNPs, PAAuNPs and PAAg–AuNPs colloids, respectively. SAED showed ring-shaped patterns for the particles. The nanoparticles effectively inhibited growth of tested bacteria (11–94%) for PAAgNPs, (10–77%) for PAAuNPs and (20–85%) for PAAg–AuNPs. The effectiveness of the biosynthesized nanoparticles can be placed as PAAg–AuNPs > PAAgNPs > PAAuNPs. The fungal inhibition performances are 33–76%, 50–82% and 27–88% for PAAgNPs, PAAuNPs and PAAg–AuNPs, respectively, while DPPH-scavenging activities were 57.82–63.25%, 15.28–54.50% and 53.05–54.26%, which were dose dependent at the tested concentrations of 20–100 µg/ml with good antioxidant activities compared to standard BHA (41.46–84.57%) and ascorbic acid (43.56–91.10%). The bleaching inhibition assay of ABTS showed activities of 56.15–85.43% (PAAgNPs), 34.67–50.93% (PAAuNPs) and 45.31–94.01% (PAAg–AuNPs). The lower concentrations of EC50 were obtained in nanoparticles (24.45–58.33 µg/ml) compared with the standards (38.42–69.04 µg/ml), indicating that the nanoparticles could suffice as good agents in drug consignment. This study has demonstrated the potential of P. americana fruit peel aqueous extracts to synthesize AgNPs, AuNPs and Ag–AuNPs for antimicrobial and antioxidant applications. The current work, to the best of our knowledge, is the first to use avocado peel extract to synthesis nanoparticles.

Ultrafast excited state dynamics and femtosecond nonlinear optical properties of laser fabricated Au and Ag50Au50 nanoparticles

The localized surface plasmon dynamics of laser ablated gold and gold-silver alloy nanoparticles (NPs) near interband and intraband excitation wavelengths were investigated using femtosecond (fs) transient absorption spectroscopy. Interband excitation with 70 fs laser pulses at a wavelength of 400 nm demonstrated plasmon photo-bleach and a transient absorption in the wings of the bleach spectrum. With intraband excitation, Ag50Au50 alloy NPs depicted a fast electron thermalization time of ~180 fs. A slower decay of positive absorption from alloy NPs was observed when compared to pure Au NPs. These NPs demonstrated a rapid initial electron thermalization and exhibited similar electron-phonon relaxation times. The third-order nonlinear optical (NLO) properties were measured using the Z-scan technique with 1 kHz repetition rate fs pulses at 800 nm. It is observed that the alloy NPs possessed large value of the NLO susceptibility χ(3) (~10−13 esu) compared to pure gold NPs at 800 nm finding applications in different areas of photonics.