Immobilization Of Gold Nanoparticles Research Articles

Citrate polymer optical fiber for measuring refractive index based on LSPR sensor

Fiber optic localized surface plasmon resonance (LSPR) sensors have become an effective tool in refractive index (RI) detection for biomedical applications because of their high sensitivity. However, using conventional optical fiber has caused limitations in implanting the sensor in the body. This research presents the design and construction of a new type of polymer-based LSPR sensors to address this issue. Also, finite element method (FEM) is used to design the sensor and test it theoretically. The proposed polymer optical fiber (POF) based on citrate is biocompatible, flexible, and degradable, with a rate of 22% and 27 over 12 days. The step RI structure utilizes two polymers for light transmission: poly (octamethylene maleate citrate) (POMC) as the core and poly (octamethylene citrate) (POC) as the cladding. The POF core and cladding diameters and lengths are 700 µm, 1400 µm, and 7 cm, respectively. The coupling efficiency of light to the POF was enhanced using a microsphere fiber optic tip. The obtained results show that the light coupling efficiency increased to 77.8%. Plasma surface treatment was used to immobilize gold nanoparticles (AuNPs) on the tip of the POF, as a LSPR-POF sensor. Adsorption kinetics was measured based on the pseudo-first-order model to determine the efficiency of immobilizing AuNPs, in which the adsorption rate constant (k) was obtained be 8.6 × 10–3 min−1. The RI sensitivity of the sensor in the range from 1.3332 to 1.3604 RIU was obtained as 7778%/RIU, and the sensitivity was enhanced ~ 5 times to the previous RI POF sensors. These results are in good agreement with theory and computer simulation. It promises a highly sensitive and label-free detection biosensor for point-of-care applications such as neurosciences.

Coaxial electrospinning of Au@silicate/poly(vinyl alcohol) core/shell composite nanofibers with non-covalently immobilized gold nanoparticles for preparing flexible, freestanding, and highly sensitive SERS substrates amenable to large-scale fabrication

Coaxial electrospinning of Au@silicate/poly(vinyl alcohol) core/shell composite nanofibers with non-covalently immobilized gold nanoparticles for preparing flexible, freestanding, and highly sensitive SERS substrates amenable to large-scale fabrication

Protein quantification via LSPR-based biosensor platform utilizing chrono-growth for enhanced sensitivity

In this study an enhancement methodology, which utilizes time dependent growth of immobilized gold nanoparticles (GNPs) for LSPR-based biosensor platform was developed. The chrono-growth methodology was used for protein analysis and quantification. The method consisted GNP immobilization onto well-plates, GNP chrono-growth, and antibody functionalization. Success of each step was verified by UV–Vis spectrum measurement. Afterwards, the biosensor platform was tested to determine its characteristics. Bovine Serum Albumin (BSA) was chosen to be used as a model protein and an LoD value of 0.344 µM and a dynamic detection range of 1 to 1000 µM was calculated. The results were acquired within 30 min. Developed platform provides simple and rapid detection of the protein.

Electrodeposition of Au nanoparticles on ITO/PDAC/2H-MoS2 electrode for sensitive determination of bisphenol-A

Exfoliated 2H-MoS2 holds a promising future for various electrochemical applications. Nevertheless, its electrical conductivity and electrocatalytic efficiency are limited, restricting its standalone use. To address this limitation, this study proposes the electrochemical deposition of gold nanoparticles on layer-by-layer films of poly(diallyl dimethylammonium) hydrochloride interspersed with exfoliated 2H-MoS2, previously assembled on ITO substrate. This modified electrode, denoted as ITO/PDAC/2H-MoS2/Au, was assessed for its effectiveness in the voltametric detection of bisphenol-A (BPA). The optimal electrode architecture demonstrated a linear BPA detection range (0.9 µM-19 µM; R2 > 0.99), with a limit of detection of 23 nM. Notably, the electrochemical deposition was effective on both bare and film modified ITO substrates. However, it was on the ITO/PDAC/2H-MoS2/Au electrode that BPA detection achieved a reasonable level of sensitivity. During electrodeposition, superficial Mo(IV) is oxidized to Mo(VI) while sulfur vacancies are generated. These defect sites enhance the electrochemical activity of 2H-MoS2 and play a pivotal role in nucleating, growing, and immobilizing gold nanoparticles, which collectively enhance the sensor’s performance.

Functionalization of Carbon Electrode Surface Using Polyaniline and Gold Nanoparticles for Protein Immobilization

This study presents a screen-printed carbon electrode surface functionalization to immobilize proteins. The process involves the deposition of gold nanoparticles on the carbon electrode and subsequent surface modification to immobilize bovine serum albumin–fluorescein isothiocyanate conjugate (BSA-FITC). A combination of conducting polymer and gold nanoparticles was employed to enhance the electrode contact area and current transmission. The electrode surface morphology and properties were evaluated by scanning electron microscopy (SEM) and Raman spectroscopy, showing the porous polyaniline (PANI) film has been formed on the carbon electrode surface with the network of dendritic nanofibers. Gold nanoparticles were evenly distributed on the PANI film to form a nanocomposite material layer on the carbon electrode. The observed size of these gold nanoparticles was significantly smaller than those on the electrode without a PANI film. Additionally, the current transmission of this composite material layer has been verified by cyclic voltammetry (CV). The results show that the amplitude of the redox peak was doubled compared to the bare carbon electrode and gold nanoparticle-only deposited electrode. Moreover, the success of the process was verified by fluorescence and cyclic voltammetry. The fluorescent green color observed under the microscope indicated that BSA-FITC was on the electrode surface. The change of CV signal after each step verified the formation of a new layer on the electrode surface. These results are anticipated to play an important role in developing high-sensitivity immunosensors in the future.

Development of chrono-spectral gold nanoparticle growth based plasmonic biosensor platform

Plasmonic sensor platforms are designed for rapid, label-free, and real-time detection and they excel as the next generation biosensors. However, current methods such as Surface Plasmon Resonance require expertise and well-equipped laboratory facilities. Simpler methods such as Localized Surface Plasmon Resonance (LSPR) overcome those limitations, though they lack sensitivity. Hence, sensitivity enhancement plays a crucial role in the future of plasmonic sensor platforms. Herein, a refractive index (RI) sensitivity enhancement methodology is reported utilizing growth of gold nanoparticles (GNPs) on solid support and it is backed up with artificial neural network (ANN) analysis. Sensor platform fabrication was initiated with GNP immobilization onto solid support; immobilized GNPs were then used as seeds for chrono-spectral growth, which was carried out using NH2OH at varied incubation times. The response to RI change of the platform was investigated with varied concentrations of sucrose and ethanol. The detection of bacteria E.coli BL21 was carried out for validation as a model microorganism and results showed that detection was possible at 102 CFU/ml. The data acquired by spectrophotometric measurements were analyzed by ANN and bacteria classification with percentage error rates near 0% was achieved. The proposed LSPR-based, label-free sensor application proved that the developed methodology promises utile sensitivity enhancement potential for similar sensor platforms.

Enhancing gold nanoparticle immobilization on thiolated silica: utilizing neutral ligands to achieve maximum surface coverage for improved SERS substrates

This study achieved maximum surface coverage and high chemical stability of SERS substrates by replacing citrate with a neutral ligand and controlling the ligand thickness, addressing poor immobilization of citrate-AuNP on thiolated silica.

Polydopamine-mediated in situ synthesis of gold nanoparticles uniformly distributed on silk fibers as reusable catalysts for efficient 4-nitrophenol reduction

Developing green fibrous materials with uniformly distributed metal nanoparticles for highly efficient and recyclable catalysis remains a major challenge. Herein, we developed a simple, effective, and green method to immobilize gold nanoparticles (AuNPs) on polydopamine (PDA)-functionalized silk fibers (SFs) for efficient catalytic reduction of 4-nitrophenol (4-NP). The density and size of AuNPs on the PDA-coated SFs can be tuned by adjusting precursor concentration and synthesis duration, respectively. The AuNPs-PDA-SFs catalysts prepared under optimized conditions could catalyze the reduction of 4-NP, 4-nitroaniline (4-NA), and 4-amino-3-nitrophenol (4-A-3-NP) at the apparent rate constants of 0.087, 0.091, and 0.063 min−1, respectively. After six rounds of flow-through reduction of 4-NP, the AuNPs-PDA-SFs could maintain a 4-NP conversion rate greater than 92%, indicating their superior reusability and consistent catalytic activity. Due to the protein properties of SFs, the AuNPs-PDA-SFs can be degraded by enzymes and alkali solutions. This work may provide new insights for designing advanced fiber-supported recyclable catalysts with high catalytic performance and reusability in wastewater treatment.

Effects of green decorated AgNPs on lignin-modified magnetic nanoparticles mediated by Cydonia on cecal ligation and puncture-induced sepsis

Abstract Sepsis is a common and deadly syndrome that despite all the progress in its control, the death rate caused by it is high. Sepsis is a serious problem that needs immediate attention and treatment. This infection, especially if it is caused by bacteria resistant to several drugs, causes high mortality. About two-thirds of sepsis cases occur in hospitalized patients. Several factors such as increasing the age of the population, increasing the duration of chronic diseases, high consumption of antibiotics and corticosteroids, use of mechanical devices and intravascular devices play a role in increasing its incidence. We herein demonstrate the biogenic procedure for the in situ immobilizing gold nanoparticles over lignin (Lig)-modified Fe3O4 magnetic nanoparticles mediated by Cydonia leaf extract (Fe3O4@Lig-Ag NPs) and its catalytic activity on the acetylation of alcohols using acetic anhydride and subsequent biological performances. The successful synthesis of Fe3O4@Lig-Ag NPs was assessed using an array of advanced techniques like field emission scanning electron microscopy, fourier transformed infrared spectroscopy, transmission electron microscopy EDX, elemental mapping, vibrating-sample magnetometer, and X-ray diffraction. Cecal ligation and puncture was used for inducing the sepsis model in rats. Several doses of Fe3O4@Lig-Ag NPs (45, 15, and 5 µg/kg) on oxidant–antioxidant, inflammatory mediators mRNA such as IL-1 and TNF-α, and its effects on the levels of expression were assessed in the kidney, liver, duodenum, lung, and stomach. When septic rats kidney, liver, duodenum, lung, and stomach were compared with those of the control group, it was found that Fe3O4@Lig-Ag NPs dose-dependent administration raised glutathione levels and superoxide dismutase activity and significantly reduced the levels of malondialdehyde. The Fe3O4@Lig-Ag NPs (45 µg/kg) indicated greater anti-oxidative effects than the 5 and 15 µg/kg doses for all the assessed parameters. In addition, the expression of TNF-α mRNA in the CLP + 45 µg/kg group was decreased in comparison with the control group. Fe3O4@Lig-Ag NPs reduced oxidative stress by enhancing the free radicals scavenging effects and supporting endogenous antioxidants. The Fe3O4@Lig-Ag NPs potent antioxidant property may be related to the cytokine cascade suppression during sepsis. The above findings offer that Fe3O4@Lig-Ag NPs administration may indicate a modern treatment for the inhibition of liver, kidney, lung, duodenum, and stomach tissues damage caused by septic conditions.

Magnetic ZnFe2O4 composite advances SERS assay for Patent blue V

BackgroundPatent blue V (PbV) an Azo colorant because of its high toxicity to children has been severely limited in food industry. However, frequently the abuse of PbV in some artificial foods is still exposed by media. Current methods for the detection of PbV have to perform tedious pre-processing and the detection sensitivity and speed are required to be further improved. ResultsIn this work, we immobilize gold nanoparticles (Au NPs) on the surface of ZnFe2O4 with aid of Inositol hexaphosphate (IP6) to prepare a novel magnetic surface-enhanced Raman scattering (SERS) substrate (designated as ZnFe2O4–IP6–Au NPs) for rapid detection of PbV in beverages. Synergistic effect of magnetic enrichment, magnetic inducing improvement effect (MIIE) and efficient charge transfer (CT) enables ZnFe2O4–IP6–Au NPs-based SERS assay to achieve limit of detection of PbV down to 1.31 × 10−8 mol/L and a concentration linear relationship ranging from 8.6 × 10−4 to 8.6 × 10−8 mol/L. The detection recoveries for PbV in beverages locate in the range from 98.1 to 102.5 %, meaning the feasibility of method. In addition, the presence of IP6 protection greatly improves the storage stability of ZnFe2O4–IP6–Au NPs. SignificanceZnFe2O4–IP6–Au NPs substrates with excellent SERS performance could on-site, rapidly and sensitively detect PbV. As a perspective, magnetic-composite-based SERS assay has great scenario in food safety by using portable Raman spectrometer.

Nano‐Roughness‐Mediated Macrophage Polarization for Desired Host Immune Response

Macrophage polarization is a significant event in the host immune response, which can be modulated by modifying the surface of a biomaterial. Previous studies have demonstrated the modulation of macrophage polarization using different surface features; however, none of these studies reflect the effect of surface properties on unstimulated macrophage polarization for a prolonged period. To better understand the impact of surface features, in this work differentiated THP‐1 cells are employed to control macrophage polarization on nano‐rough surfaces for a duration of 7 days. Model nano‐rough substrates are fabricated by immobilizing gold nanoparticles (AuNPs) of predetermined sizes (16, 38, 68 nm) on a 2‐methyl‐2‐oxazoline thin film, followed by tailoring the outermost surface chemistry. All modified surfaces support high levels of cell adhesion and proliferation. Over time, the expression of pro‐inflammatory cytokines decreases, whereas the expression of anti‐inflammatory cytokines increases on all modified surfaces. Similarly, pro‐inflammatory interleukin (IL)‐1β gene expression is downregulated, and anti‐inflammatory IL‐10‐gene expression is upregulated, regardless of the surface roughness. Analysis of cell morphology reveals that the predominant cell type on the modified surfaces exhibits M2 anti‐inflammatory phenotype. Herein, how surface features can modulate macrophage responses over an extended period is highlighted, offering insights for the development of future biomaterial implants.

High Surface Area Assemblies of Gold Nanoparticles on Hydrophilic Carbon Fiber Paper with Ionomer Overlayers for Aqueous CO2 Reduction Electrocatalysis to Clean Syngas

We report a universal approach for the utilization of nanoparticles on inexpensive, high surface area carbon substrates in aqueous applications. We immobilized gold nanoparticles from aqueous colloid on hydrophilic carbon fiber paper and assessed this electrode assembly in aqueous carbon dioxide reduction electrocatalysis. Uniform distributions of gold nanoparticles on carbon fibers and stable electrocatalytic current generation indicated that immobilization of gold nanoparticles on hydrophilic carbon fiber paper was successful. Surface analysis before and after electroreduction revealed that the detachment of citrate capping ligands enhanced the amount of exposed surface gold and concomitantly increased the CO-to-H2 ratio in subsequent CO2 reduction electrocatalysis. Systematic variations of ionomer overlayers controlled the ratio of produced CO and H2 towards useful syngas compositions and revealed mechanistic insights into catalyst microenvironments, to enhance CO selectivity. Our results demonstrate that hydrophilic carbon fiber paper is an excellent high surface area electrode substrate for the utilization of nanoparticulate electrocatalysts in aqueous electrolyte.

Immobilization of Gold Nanoparticles on Postsynthetically Modified NU-1000 for Hydrogen Evolution Reaction

NU-1000, being a hydrothermally stable metal-organic framework (MOF), with structural robustness is viable for functionalization with various entities. A postsynthetic modification strategy called solvent-assisted ligand incorporation (SALI) is chosen for functionalizing NU-1000 with thiol moieties using 2-mercaptobenzoic acid. In accordance with soft acid-soft base interactions, the thiol groups on NU-1000, as a scaffold, can immobilize the gold nanoparticles without much aggregation. The catalytically active gold sites on thiolated NU-1000 are utilized for hydrogen evolution reaction (HER). The catalyst delivered an overpotential of 101 mV at a current density of 10 mAcm-2 in 0.5 M H2SO4. The faster charge transfer kinetics determined from the Tafel slope of 44 mV/dec enhances the HER activity. The sustainable performance of the catalyst for 36 h proves its utility as a potential catalyst to produce neat hydrogen.

Surface nanoengineering technology for the removal of sulfur compounds associated with negative attributes in wines

Volatile sulfur compounds (VSCs), such as hydrogen sulfide, methanethiol, and ethanethiol, are associated with ‘reductive’ aromas in wine and contribute to approximately 30% of all wine faults. These compounds can have a significant impact on wine aroma and perceived quality, and subsequently, consumer preference. In this communication, we report a method for the removal of VSC compounds based on nanoengineered surfaces that incorporate immobilized gold nanoparticles.

Activity and reusability of immobilized gold nanoparticles for the catalysis of both oxidation and reduction reactions

Colloidal gold nanoparticles (AuNP) are well-known to present a catalytic activity. However, they are characterized by certain limitations, as a rather poor stability and lack of both handling and reusability. Their immobilization on surfaces could help to overcome these drawbacks. This work evaluated the impact of the immobilization of AuNP towards their catalytic activity on reduction and oxidation reactions. Colloidal AuNP stabilized with citrate ions were synthesized, characterized, and immobilized by the dip-coating method, the obtained immobilized AuNP (iAuNP) were characterized. The catalytic activity of AuNP and iAuNP was evaluated and compared to each other through the p-nitrophenol reduction reaction. The kinetic of the catalytic activity of iAuNP was slower than colloidal AuNP. The catalytic activity appeared to be impacted by the less available surface of iAuNP. The reduction efficiency of iAuNP was also evaluated with the DPPH•/DPPH2 reduction reaction. The capacity of iAuNP to catalyze the reduction of DPPH• in DPPH2 was shown even after 130 days and 20 reuses of the nanostructured surface on the contrary to non-reusable colloidal AuNP. The oxidation efficiency of iAuNP was measured by the ability to catalyze the auto-oxidation of curcumin (HPLC-UV/vis). For all these experiments, the addition of 4-mercapto-phenol on the surface of iAuNP passivated the surface, decreasing the catalytic activity of the materials. In conclusion, iAuNP are redox catalysts with both anti- and pro-oxidant effects and high reusability over a very long period.

LSPR Sensing of Epithelial Cell Adhesion Molecules through Sphere and Cavity Plasmons of a Composite Ring Array of Poly[2-(dimethylamino)ethyl methacrylate]/Gold Nanoparticles.

Self-organization facilitates the formation of specific structures as a result of constituent interactions. In this study, the bottom of a 600 nm hole array photoresist template, which was deposited with a hydrophobic atom transfer radical polymerization (ATRP) initiator, was wetted by treatment with oxygen plasma. After the removal of the photoresist template, ring patterns of the ATRP initiator were formed at the interface between the hydrophobic and wetting regions. Poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) was grafted from the ring array of the initiator to immobilize gold nanoparticles (AuNPs) as a uniform ring array on a silicon substrate via repeated swelling/shrinking cycles. The localized surface plasmon resonance (LSPR) peak of the PDMAEMA-AuNP hybrid ring (PAHR) red-shifted after 12 swelling/shrinking cycles. In comparison to gold nanoparticles, scalable gold nanorings can effectively develop a variety of nanostructures to design LSPR-based sensors and optimize the sensing accuracy and stability. To detect epithelial cell adhesion molecules (EpCAM) during the structural change from a ring to a disk, antiEpCAM was anchored onto the PAHR as a biosensor during swelling/shrinking. The coupling of antiEpCAM and EpCAM led to asymptotical convergence from rings to disks as well as blue shifts of the LSPR peaks. Linear correlation between the blue shift and EpCAM concentration showed a limit of detection of ∼27 pg mL-1 and a linear range of 25-200 pg mL-1 for the detection of EpCAM within 30 min. The simple method of combining lithography and plasma technology provides a versatile platform for developing the scalable ring structure of AuNPs for highly sensitive and selective biosensing.

Ferrocene-Functionalized Covalent Organic Frameworks and Target Catalyzed Hairpin Assembly Strategy for Amplified Electrochemical Determination of MicroRNAs.

MicroRNAs (miRNAs) are considered as significant biomarkers in early diagnosis and treatment of diseases. Herein, an electrochemical biosensor that uses ferrocene (Fc)-functionalized covalent organic frameworks (COFs), a DNA tetrahedron nanostructure (DTN) biosensing interface, and a target catalyzed hairpin assembly (CHA) strategy has been fabricated and successfully developed for the sensitive and specific determination of microRNA-21 (miR-21). The COF served as a linked substrate for immobilization of gold nanoparticles (AuNPs), Fc-COOH, and complementary DNA probe L1 to prepare the electrochemical signal probe COF/Au/Fc/L1, which has a large surface area, extraordinary catalytic properties, and superior biocompatibility to amplify the current signal. The DTN containing a hairpin sequence H1 at one vertex was elaborately designed to construct the biosensing interface; thus, the CHA could be implemented on the electrode surface. In the presence of miR-21, the CHA reaction between H1 and the hairpin H2 was triggered to produce a great number of duplex DNA (H1/H2) with sticky ends. Then, the signal probe COF/Au/Fc/L1 was modified on the electrode surface through the hybridization between L1 and the sticky end of H1/H2, thereby obtaining an amplified Fc current signal. Under optimal conditions, the biosensor showed a wide linear response ranging from 1 fM to 10 nM miR-21, with a low detection limit of 0.33 fM (S/N = 3). Meanwhile, the method showed acceptable accuracy and precision for the determination of miR-21 in human serum.

Detection of tomato leaf curl New Delhi virus DNA using U-bent optical fiber-based LSPR probes

The detection of Tomato leaf curl New Delhi virus (ToLCNDV) DNA has been presented using U-bent fiber optic sensor (FOS) by an evanescent wave absorption method in the visible region. The localized surface plasmon resonance (LSPR) based FOS was developed by immobilizing gold nanoparticles on the amine-functionalized surface and the receptor probe was prepared by attaching a short segment of the complementary DNA (cDNA) on this surface. Further, the cDNA attachment was confirmed by monitoring the real-time change in LSPR absorption spectra. The conjugation protocol of single-strand DNA (ssDNA) from the viral genome of ToLCNDV was established like antibody-antigen-based assays by observing the real-time change in absorption kinetics. Consequently, a linear correlation between ssDNA concentration and the conjugation-dependent change in refractive index (RI) has been observed. The limit of detection (LOD) using two different cDNA immobilized FOS probes was determined to be 50±10 ng/μL and the change in RI was found 12.5±1.3×10−4 RIU/Abs. From this systematic binding study, a straightforward target-specific sensor has been constructed using a digital electronic logic gate analogy. This device has significant commercial potential for the development of a portable LSPR sensor for real-time detection of plant pathogens in addition to the possibility of multi-target environments.

Fabrication of scalable poly(N-isopropylacrylamide)/gold nanoparticles composite ring array as LSPR sensor for label-free biosensor application

Self-organization facilitates the formation of specific structures as a result of constituent interaction. In this study, the bottom of a 500-nm hole array photoresist template, which was deposited with a hydrophobic atom transfer radical polymerization (ATRP) initiator, was wetted by treatment with oxygen plasma. After the removal of the photoresist template, ring patterns of the ATRP initiator were formed at the interface between the hydrophobic and wetting regions. Poly(N-isopropylacrylamide) (PNIPAAm) was grafted from the ring array of the initiator to immobilize gold nanoparticles (AuNPs) as a uniform ring array on the silicon substrate via repeated swelling/shrinking cycles. The localized surface plasmon resonance (LSPR) peaks of the biotin-anchored AuNP–PNIPAAm composite ring (APCR) were employed to detect streptavidin as biosensors. The coupling of biotin and streptavidin led to asymptotical convergence from rings to disks as well as blue-shifts of the LSPR peaks. Linear correlation between the blue-shift and streptavidin concentration showed a limit of detection of ∼10 nM and a linear range of 10–150 nM for the detection of streptavidin within 30 min. The simple method of combining lithography and plasma technology provides a versatile platform for developing the scalable ring structure of AuNP for highly sensitive and sensitive biosensing.

Designing a new ligand based on pyridine for immobilization of gold nanoparticles on reduced magnetic graphene oxide: a new catalyst for the reduction of nitro compounds

Designing a new ligand based on pyridine for immobilization of gold nanoparticles on reduced magnetic graphene oxide: a new catalyst for the reduction of nitro compounds