Theoretical Investigation of Plasmonic Properties of Quantum-Sized Silver Nanoparticles

Plasmonic nanoparticles (NPs) like silver (Ag) strongly absorb the incident light and produce enhanced localized electric field at the localized surface plasmon resonance (LSPR) frequency. Enormous theoretical and experimental research has focused on the plasmonic properties of the metallic nanoparticles with sizes greater than 10 nm. However, such studies on smaller sized NPs in the size range of 3 to 10 nm (quantum-sized regime) are sparse. In this size regime, the conduction band of the metal particles discretizes, thus altering plasmon properties of the NPs from classical to the quantum regime. In this study, plasmonic properties of the spherical Ag NPs in size range of 3 to 20 nm were investigated using both quantum and classical modeling to understand the importance of invoking quantum regime to accurately describing their properties in this size regime. Theoretical calculations using standard Mie theory were carried out to monitor the LSPR peak shift and electric field enhancement as a function of the size of the bare plasmonic nanoparticle and the refractive index (RI) of the surrounding medium. Comparisons were made with and without invoking quantum regime. Also, the optical properties of metallic NPs conjugated with a chemical ligand using multi-layered Mie theory were studied, and interesting trends were observed.

     

A Localized Surface Plasmon Resonance Biosensor Based on Integrated Controllable Au2S/AuAgS-Coated Gold Nanorods Composite

In this work, we have demonstrated that the exquisite optical properties based on localized surface plasmon resonance (LSPR) of Au₂S/AuAgS-coated gold nanorods (Au₂S/AuAgS-coated GNRs) can be utilized to develop a simple and sensitive biosensor, and goat anti-human IgG can be detected by the human IgG probe as low as 0.2 nM. Moreover, we introduce an integrated LSPR biosensor constructed by integrating Au₂S/AuAgS-coated GNRs immobilized on glass slide and isolated Au₂S/AuAgS-coated GNRs in the form of liquid. The detection of target binding was performed via direct spectral changes induced by changes of refractive index in the vicinity of individual particles. The integrated LSPR optical biosensor is label-free, cost-effective, and easy to fabricate and requires only a visible/near-infrared spectrometer for detection purposes. Additionally, the investigation on the mutual influence of the two types of nanorods in the integrated LSPR biosensor was performed. The results of separate experiments indicate that the nanorods in the form of isolate or in integrated exhibit a similar behavior.     

Scattering Efficiency and LSPR Tunability of Bimetallic Ag,Au, and Cu Nanoparticles

Scattering efficiencies of Ag–Cu, Ag–Au, and Au–Cu alloy nanoparticles are studied based on Mie theory for their possible applications in solar cells. The effect of size (radius), surrounding medium, and alloy composition on the scattering efficiency at the localized surface plasmon resonance (LSPR) wavelengths has been reported. In the alloy nanoparticles of Ag_1?x Cu _x , Au_1?x Cu _x and Ag_1?x Au _x ; the scattering efficiency gets red-shifted with increase in x. Moreover, the scattering efficiency enhancement can be tuned and controlled with both the alloy composition and the surrounding medium refractive index. A linear relationship which is in good agreement to the experimental observations between the scattering efficiency and metal composition in the alloys are found. The effect of nanoparticle size and LSPR wavelength (scattering peak position) on the full width half maxima and scattering efficiency has also been studied. Comparison of Au–Ag, Au–Cu, and Ag–Cu alloy nanoparticles with 50-nm radii shows the optical response of Ag–Cu alloy nanoparticle with wide bandwidth in the visible region of the electromagnetic spectrum making them suitable for plasmonic solar cells. Further, the comparison of Ag–Cu alloy and core@shell nanoparticles of similar size and surrounding medium shows that Cu@Ag nanoparticle exhibits high scattering efficiency with nearly the same bandwidth.     

Dopamine-Induced Growth of Au and Ag Nanoparticles on ITO Substrate and Their Application in PCPDTBT-Based Polymer Solar Cell

The direct attachment and growth of gold or silver nanoparticles (NPs) on indium tin oxide (ITO) surfaces was demonstrated using a simple and inexpensive successive ionic layer adsorption and reaction (SILAR) method by chemical reduction of the precursor metal salts with dopamine aqueous solution. Ag NPs on ITO substrate were approximately spherical with an average particle size of about 57 nm, but had a wide particle size distribution. Compared with Ag NPs, under the same 10 SILAR cycles, Au NPs have higher density packing and smaller average particle size of about 36 nm. XRD characterization and surface chemistry analysis confirmed the formation of Ag and Au NPs on ITO substrate with small amounts of dopamine-quinone adsorbed on the surface of them. Although Au NPs showed characteristic plasmon absorption, this did not result in performance enhancement in solar cell with the structure of ITO/ZnO/PCPDTBT:[6,6]-phenyl C₇₁/MoO₃/Ag because of the energy level mismatch between ZnO and dopamine molecules adsorbed on the surface of metal NPs.     

Carbohydrate-directed synthesis of silver and gold nanoparticles: effect of the structure of carbohydrates and reducing agents on the size and morphology of the composites

A monosaccharide (β-d-glucose) and polysaccharide (soluble starch) were used as structure directing and subsequently stabilizing agents for the synthesis of spherical nanoparticles (NPs) and nanowires of silver and gold. Homogeneous monodispersed Ag(0) nanoparticles (Ag NPs) of 15 nm diameter were obtained when 10⁻⁴ M AgNO₃ precursor salt was reduced in starch (1 wt %)–water gel by 1 wt % β-d-glucose. For a second preparation the effect of reducing agents on the synthesis of Au(0) metallic nanoparticles (Au NPs) of 2 × 10⁻⁴ M concentration prepared in a β-d-glucose (0.03 M)–water dispersion was studied first in detail. Different equivalent amounts of NaBH₄ and a number of pH values were evaluated for the reduction of the Au salt HAuCl₄·3H₂O to obtain Au NPs. The type and the amount of reducing agent, as well as the pH of the solution was shown to affect the size and morphology of the NPs. NaBH₄ (4 equiv) produced the smallest (5.3 nm (σ 0.7)) metallic particles compared to larger particles (10.0 nm (σ 1.4)) when the salt was reduced by 1 equiv of NaBH₄. Addition of excess NaBH₄ caused the NPs to settle out as a precipitate forming a mesh or wire structure rather than monodispersed particles. Low pH (pH 6) resulted in incomplete reduction, while at pH 8 the salt was completely reduced. When the salt was reduced by NaOH at pH 8, the particles were larger (14.2 nm) and less homogeneous (σ 2.8) compared to those from NaBH₄ reduction.     

Investigation on the Sensitivity and FOM of Ag Nanoparticles and Nanoarrays

The localized surface plasmon resonance (LSPR) spectroscopy of Ag nanoparticles (NPs) is sensitive to the changes of the surrounding medium, which enables the NPs to serve as plasmonic nanosensors. In this paper, the refractive index (RI) sensitivity and figure of merit (FOM) of individual NPs and nanoarrays are investigated by employing the finite difference time domain (FDTD) method. The influence of shape and size are analyzed for individual NPs, and the influence of particle spacing is analyzed for nanoarrays. It is found that the NP with shorter size in incident direction or longer size in polarization direction exhibits better sensing performance. And when the a_eff is between 20 and 60 nm, the larger NP exhibits higher sensitivity but lower FOM. The results of nanoarrays show that when particle spacing is large, the sensitivity of nanoarrays is large, and the sensitivity of nanoarrays decreases first and then increases as particle spacing decreases. In addition, the FOM of nanoarrays exhibits the similar trend.

     

Silver Fused Conducting Fiber Formation of Au–Ag Core-Shell Nanoparticles Mediated by Ascorbic Acid

In this paper, we report the spontaneous formation of fibrous structures consisting of assemblies of Au–Ag core-shell nanoparticles (NPs) from a solution consisting of Au–Ag core-shell NPs and l-ascorbic acid (AA). AA acted both as the reducing agent for the generation of NPs and also as the mediator for the formation of fibers. The process of fiber formation involved three steps—reduction of HAuCl₄ to Au NPs by AA, subsequent formation of Au–Ag core-shell NPs after addition of AgNO₃, and spontaneous formation of fibers from the mixtures in water. It took typically about 30 days to form complete fibers that are of lengths of several hundred micrometers to millimeters, although nanofibers started forming from the first day of solution preparation. The width of each of these fibers was typically about 1–4 μm with length of each segment of fiber bundle, on the order of 40 μm. Formation of fibers was also observed in absence of AgNO₃. These fibers consisted of Au NPs and polymer of AA degradation products and were not electrically conducting. Also, low concentrations of AgNO₃ produced fibers with low electrical conductivity. However, it was observed that increase in the amount of AgNO₃ leads to the formation of fibers that were electrically conducting with conductivity values in the range of metallic conductivity. Spectroscopic and electron microscopic investigations were carried out to establish the formation of fibers. The details of fiber formation mechanism under different conditions and electrical conductivities of the fibers are discussed in the article.     

Single-Step Synthesis and Surface Plasmons of Bismuth-Coated Spherical to Hexagonal Silver Nanoparticles in Dichroic Ag:Bismuth Glass Nanocomposites

Here, we report for the first time the synthesis of bismuth-coated silver nanoparticles in dichroic bismuth glass nanocomposites by a novel and simple one-step melt quench technique without using any external reducing agent. The metallic silver nanoparticles (Ag NPs) were generated first, and subsequently, metallic bismuth was deposited on the Ag NPs and formed a thick layer. The reduction of Bi³⁺ to Bi^o and subsequently its deposition on the Ag NPs (which were formed earlier than Bi^o) in the K₂O–Bi₂O₃–B₂O₃ (KBB) glass system have been explained by their standard reduction potentials. The UV–vis absorption spectra show a prominent surface plasmon resonance (SPR) absorption band at 575 nm at lower concentrations (up to 0.01 wt%); three bands at 569, 624 and 780 nm at medium concentration (0.02–0.03 wt%); and two weak bands at 619 and 817 nm at highest concentration (0.06 wt%) of silver. They have been explained by the electrodynamics theories. TEM images reveal the conversion of spheroidal (5–15 nm) to hexagonal (10–35 nm) shaped Ag NPs with the increase in concentration of silver (up to 0.06 wt%). SAED pattern confirms the crystalline planes of rhombohedral bismuth and cubic silver. Thermal treatment at 360 °C, which is the glass transformation temperature (T _g) of the sample containing lower concentration of silver (0.007 wt%), shows red-shifted SPR band due to increase in size of NPs. Whereas the sample containing higher concentration (0.06 wt%) of silver under similar treatment exhibited changes in SPR spectral profile happened due to conversion to spherical NPs from hexagonal shape and reduction in size (10–20 nm) of NPs after heat treatment for 65 h. HRTEM images corroborate the different orientations of the NPs. FESEM images reveal hexagonal disk like structure having different orientations. Dichroic nature of the nanocomposites has been explained with the size and shape of Ag nanoparticles. We believe that this work will create new avenues in the area of nanometal–glass hybrid nanocomposites and the materials have significant applications in the field of optoelectronics and nanophotonics.     

Simultaneous detection of two tumor markers using silver and gold nanoparticles decorated carbon nanospheres as labels

In this work, a multiplexed electrochemical immunosensor was developed for sensitive detection of carcinoembryonic antigen (CEA) and α-fetoprotein (AFP) using silver nanoparticles (Ag NPs) or gold nanoparticles (Au NPs) coated-carbon nanospheres (CNSs) as labels. CNSs were employed as the carrier for the immobilization of nanoparticles (Ag NPs or Au NPs), thionine (Thi), and secondary antibodies (Ab₂) due to their good monodispersity and uniform structure. Au NPs reduced graphene oxide (rGO) nanocomposites were used as sensing substrate for assembling two primary antibodies (Ab₁). In the presence of target proteins, two labels were attached onto the surface of the rGO/Au NPs nanocomposites via a sandwich immunoreaction. Two distinguishable peaks, one at +0.16 V (corresponding to Ag NPs) and another at −0.33 V (corresponding to Thi), were obtained in differential pulse voltammetry (DPV). The peak difference was approximately 490 mV, indicating that CEA and AFP can be simultaneously detected in a single run. Under optimal conditions, the peak currents were linearly related to the concentrations of CEA or AFP in the range of 0.01–80 ng ml⁻¹. The detection limits of CEA and AFP were 2.8 and 3.5 pg ml⁻¹, respectively (at a signal-to-noise ratio of 3). Moreover, when the immunosensor was applied to serum samples, the results obtained were in agreement with those of the reference method, indicating that the immunosensor would be promising in the application of clinical diagnosis and screening of biomarkers.     

Investigating Fluorescence Quenching of ZnS Quantum Dots by Silver Nanoparticles

Water dispersible zinc sulfide quantum dots (ZnS QDs) with an average diameter of 2.9 nm were synthesized in an environment friendly method using chitosan as stabilizing agent. These nanocrystals displayed characteristic absorption and emission spectra having an absorbance edge at 300 nm and emission maxima (λ _emission) at 427 nm. Citrate-capped silver nanoparticles (Ag NPs) of ca. 37-nm diameter were prepared by modified Turkevich process. The fluorescence of ZnS QDs was significantly quenched in presence of Ag NPs in a concentration-dependent manner with K _sv value of 9 × 10⁹ M⁻¹. The quenching mechanism was analyzed using Stern–Volmer plot which indicated mixed nature of quenching. Static mechanism was evident from the formation of electrostatic complex between positively charged ZnS QDs and negatively charged Ag NPs as confirmed by absorbance study. Due to excellent overlap between ZnS QDs emission and surface plasmon resonance band of Ag NPs, the role of energy transfer process as an additional quenching mechanism was investigated by time-resolved fluorescence measurements. Time-correlated single-photon counting study demonstrated decrease in average lifetime of ZnS QDs fluorescence in presence of Ag NPs. The corresponding F?rster distance for the present QD–NP pair was calculated to be 18.4 nm.     

Modulation of Main Lobe for Superfocusing Using Subwavelength Metallic Heterostructures

A subwavelength metallic heterostructure is put forth for the purpose of suppressing sidelobes and improving superfocusing at a quasi-far field region. Improvement has been made by means of optimization of the heterostructure composed of structured Au and Ag thin films. By tuning thicknesses of both the structured Au and Ag films, we can modulate propagation distance of the plasmonic lens and beam width of main lobe for the superfocusing. A finite-difference and time-domain (FDTD) algorithm-based computational numerical calculation was carried out for analyzing the focusing performance and tuning ability of the metal films. Our computational calculation results show that the sidelobes which play negative role for the focusing can be suppressed significantly in the case of the metal film thicknesses of h _Au = 50 nm and h _Ag = 10 nm. Theoretically, the metallic structure with smaller thicknesses of the structured Au and Ag films is helpful for improving the focusing performance. This heterostructure-based device is possible to be used as a superlens or nanoprobe in data storage, nanometrology/inspection, and biosensing etc.     

Gas-Aggregated Copper Nanoparticles with Long-term Plasmon Resonance Stability

Metal nanoparticles (NPs) possessing localized surface plasmon resonance (LSPR) are of high interest for applications in optics, electronics, catalysis, and sensing. The practically important issue is the stability of the LSPR, which often limits the use of some metals due to their chemical reactivity leading to degradation of the NP functionality. In this work, copper NPs of two distinct sizes are produced by magnetron sputtering gas aggregation. This method ensures formation of the particles with high purity and monocrystallinity, enhancing the chemical inertness and providing a superior time stability of the plasmonic properties. Additionally, a simple UV-ozone treatment, which leads to the formation of an oxide shell around the copper NPs, is found to be an efficient method to prevent following gradual oxidation and assure the LSPR stability in ambient atmospheric conditions for periods over 100 days even for small (10–12 nm in diameter) NPs. The obtained results allow for significant improvement of the competitiveness of copper NPs with gold or silver nanostructures, which are traditionally used in plasmonics.

     

Study of the Adsorption of Human Hemoglobin to Silver (Ag) Nanoparticle Surface for the Detection of the Unfolding of Hemoglobin

In the present report, we focused on the detail study of the optical properties and structural characterization of the Ag NPs for the nanobioconjugate analysis and detection of the conformational structural change of the Hb. The detail optical and structural analysis of Ag NPs has been studied from UV–Vis absorption, emission spectrum, XRD, and HRTEM study. The proteins/Hb are attached immediately onto Ag NPs surface when NPs touch the biological fluids, forming protein corona (PC), which gives their biological identity. The NPs-PC bioconjugate is, more specifically, the true identity of NPs in the physiological world. The adsorption of Hb with Ag NP surfaces has been studied by monitoring the soret band and tryptophan band of Hb. The dynamics of the Hb adsorption on the Ag NPs showed the time constant of surface binding t₁?=?5.79 min and 10.23 min and surface reorganization t₂?=?500 min and 251.75 min with the use of small and large concentrations of Ag NPs, respectively. The absorption peak shape and size around the wavelength, λ ≈ 406.2 nm of the bioconjugate has been examined by Gaussian and Lorentz curve fitting analysis. The bioconjugate along with the PC formation has been analyzed by HRTEM images and DLS observations. The tertiary deformation of Hb and energy transfer efficiency connecting Ag NPs and Hb are discussed from the emission-quenching phenomenon. The change of the secondary structural elements (α-helix, β-sheets, intermolecular aggregates, intramolecular aggregates) of the bioconjugate has been analyzed from FTIR spectrum.

     

Surface Plasmon Resonance and Enhanced Fluorescence Application of Single-step Synthesized Elliptical Nano Gold-embedded Antimony Glass Dichroic Nanocomposites

A novel series of elliptical gold (Au⁰) nanoparticles (18–40 nm) embedded antimony glass (K₂O-B₂O₃-Sb₂O₃) dichroic nanocomposites have been synthesized by a single-step melt-quench in-situ thermochemical reduction technique. X-ray and selected area electron diffractions manifest growth of Au⁰ nanoparticles along the (111) and (200) crystallographic planes. The transmission electron microscopic image reveals elliptical Au⁰ nanoparticles having an aspect ratio varying in the range 1.2–2.1. The dichroic behavior of the nanocomposites arises due to elliptical shape of the Au⁰ nanoparticles. These nanocomposites show strong surface plasmon resonance (SPR) band of Au nanoparticles in the range 610–681 nm and it exhibit red-shifts with increasing Au concentration. They, when co-doped with Sm₂O₃ and excited at 949 nm, exhibit about sevenfold enhancement of the upconverted red emission transition of ⁴G_5/2→⁶H_9/2 at 636 nm due to local electric field enhancement effect of Au⁰ nanoparticles induced by its SPR. These nanocomposites are the promising materials for laser, display, and various nanophotonic applications.     

Green synthesis of nanoparticles and its potential application

Nanotechnology is a new and emerging technology with wealth of applications. It involves the synthesis and application of materials having one of the dimensions in the range of 1–100 nm. A wide variety of physico–chemical approaches are being used these days for the synthesis of nanoparticles (NPs). However, biogenic reduction of metal precursors to produce corresponding NPs is eco-friendly, less expensive, free of chemical contaminants for medical and biological applications where purity of NPs is of major concern. Biogenic reduction is a “Bottom Up” approach similar to chemical reduction where a reducing agent is replaced by extract of a natural products with inherent stabilizing, growth terminating and capping properties. Furthermore, the nature of biological entities in different concentrations in combination with reducing organic agents influence the size and shape of NPs. Present review focuses on microbes or plants based green synthesis of Ag, Au, Cu, Fe, Pd, Ru, PbS, CdS, CuO, CeO₂, Fe₃O₄, TiO₂, and ZnO NPs and their potential applications.     

Optimization of the Field Enhancement and Spectral Bandwidth of Single and Coupled Bimetal Core–Shell Nanoparticles for Few-Cycle Laser Applications

We have theoretically studied and optimized the field enhancement and temporal response of single and coupled bimetal Ag/Au core–shell nanoparticles (NPs) with a diameter of 160 nm and compared the results to pure Ag and Au NPs. Very high-field enhancements with an amplitude reaching 100 (with respect to the laser field centered at 800 nm) are found at the center of a 2-nm gap between Ag/Au core–shell dimers. We have explored the excitation of the bimetal core–shell particles by Fourier transform-limited few-cycle optical pulses and identified conditions for an ultrafast plasmonic decay on the order of the excitation pulse duration. The high-field enhancement and ultrafast decay makes bimetal core–shell particles interesting candidates for applications such as the generation of ultrashort extreme ultraviolet radiation pulses via nanoplasmonic field enhancement. Moreover, in first experimental studies, we synthesized small bimetal Ag/Au core–shell NPs and compared their optical response with pure Au and Ag NPs and numerical results.     

Laser-Driven Precipitation and Modification of Silver Nanoparticles in Soda Lime Glass Matrix Monitored by On-line Extinction Measurements

In this work, we investigated the effect of nanosecond laser irradiation at 532?nm on precipitation of Ag nanoparticles (NPs) in soda lime glasses doped with silver in the Ag^?+??CNa^?+? ion-exchange process. Formation and subsequent modification of Ag NPs during laser irradiation were studied by on-line extinction measurements making use of the localized surface plasmon resonance (LSPR). These investigations were further completed using scanning and transmission electron microscopies to examine the average size and distribution of nanoparticles within the sample. It has been shown that formation of NPs, its kinetics and the particle size strongly depend on the fluence and the total number of deposited laser pulses. It has been found that Ag NPs form after some specific number of pulses and they rapidly grow in size and number until some maximal value of extinction has been reached. Further irradiation of such samples only results in destruction of precipitated NPs due to photo-breakup, laser ablation confirmed by strong plasma emission observation. Moreover, due to strong irradiation, the host matrix can also be affected by changing its refractive index which manifests as the blue shift of the LSPR.     

Size-Dependent Toxicity of Silver Nanoparticles to Bacteria,Yeast, Algae,Crustaceans and Mammalian Cells In Vitro

The concept of nanotechnologies is based on size-dependent properties of particles in the 1–100 nm range. However, the relation between the particle size and biological effects is still unclear. The aim of the current paper was to generate and analyse a homogenous set of experimental toxicity data on Ag nanoparticles (Ag NPs) of similar coating (citrate) but of 5 different primary sizes (10, 20, 40, 60 and 80 nm) to different types of organisms/cells commonly used in toxicity assays: bacterial, yeast and algal cells, crustaceans and mammalian cells in vitro. When possible, the assays were conducted in ultrapure water to minimise the effect of medium components on silver speciation. The toxic effects of NPs to different organisms varied about two orders of magnitude, being the lowest (∼0.1 mg Ag/L) for crustaceans and algae and the highest (∼26 mg Ag/L) for mammalian cells. To quantify the role of Ag ions in the toxicity of Ag NPs, we normalized the EC₅₀ values to Ag ions that dissolved from the NPs. The analysis showed that the toxicity of 20–80 nm Ag NPs could fully be explained by released Ag ions whereas 10 nm Ag NPs proved more toxic than predicted. Using E. coli Ag-biosensor, we demonstrated that 10 nm Ag NPs were more bioavailable to E. coli than silver salt (AgNO₃). Thus, one may infer that 10 nm Ag NPs had more efficient cell-particle contact resulting in higher intracellular bioavailability of silver than in case of bigger NPs. Although the latter conclusion is initially based on one test organism, it may lead to an explanation for “size-dependent“ biological effects of silver NPs. This study, for the first time, investigated the size-dependent toxic effects of a well-characterized library of Ag NPs to several microbial species, protozoans, algae, crustaceans and mammalian cells in vitro.     

Tailored Electron Transfer Pathways in Aucore/Ptshell–Graphene Nanocatalysts for Fuel Cells

Au_core/Pt_shell–graphene catalysts (G‐Cys‐Au@Pt) are prepared through chemical and surface chemical reactions. Au–Pt core–shell nanoparticles (Au@Pt NPs) covalently immobilized on graphene (G) are efficient electrocatalysts in low‐temperature polymer electrolyte membrane fuel cells. The 9.5 ± 2 nm Au@Pt NPs with atomically thin Pt shells are attached on graphene via l ‐cysteine (Cys), which serves as linkers controlling NP loading and dispersion, enhancing the Au@Pt NP stability, and facilitating interfacial electron transfer. The increased activity of G‐Cys‐Au@Pt, compared to non‐chemically immobilized G‐Au@Pt and commercial platinum NPs catalyst (C‐Pt), is a result of (1) the tailored electron transfer pathways of covalent bonds integrating Au@Pt NPs into the graphene framework, and (2) synergetic electronic effects of atomically thin Pt shells on Au cores. Enhanced electrocatalytic oxidation of formic acid, methanol, and ethanol is observed as higher specific currents and increased stability of G‐Cys‐Au@Pt compared to G‐Au@Pt and C–Pt. Oxygen reduction on G‐Cys‐Au@Pt occurs at 25 mV lower potential and 43 A g_Pt^?1 higher current (at 0.9 V vs reversible hydrogen electrode) than for C–Pt. Functional tests in direct fomic acid, methanol and ethanol fuel cells exhibit 95%, 53%, and 107% increased power densities for G‐Cys‐Au@Pt over C–Pt, respectively.     

Identifying Metal Nanoparticle Size Effect on Sensing Common Human Plasma Protein by Counting the Sensitivity of Optical Absorption Spectra Damping

Colloidal nanoparticles (NPs) interact with biological fluids such as human plasma to form a protein coating (corona) on the surface of NPs (NP-protein complex). However, the impact of size and type of NPs on binding of the hard corona to the surface of NPs as well as damping of their optical spectra has not been systematically explored. To elucidate the interaction between biological environment (human plasma) and NPs, a photophysical measurement was conducted to quantify the interaction of two different types of NPs (gold (Au) and silver (Ag)) with common human plasma proteins. The colloidal AuNPs and AgNPs were electrostatically stabilized and varied in diameter from 10 to 80 nm in the presence of common human plasma. The sizes of the NPs were determined using transmission electron microscopy (TEM). Optical absorption spectra were obtained for the complexes. Dynamic light scattering (DLS) measurement and zeta potential were used to characterize the sizes, hydrodynamic diameters, and surface charges of the protein-NPs complexes. Protein separation was performed using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) to isolate and identify the protein bands. The absorption of proteins to the NPs was found to be strongly dependent on the size and type of NPs. The distance between surface of NPs by absorbed protein bound to the NPs gradually increased with size of NPs, particularly for AgNPs with primary diameter of < 50 nm. The chi-square test proved that AgNPs are a good candidate in sensing the protein complex in human plasma compared with AuNPs mainly for the AgNPs with diameter sized 50 nm.