Graphene Oxide-gold Nanocomposite Research Articles

An electrochemical PNA-based sensor for the detection of the SARS-CoV-2 RdRP by using surface-initiated-reversible-addition−fragmentation-chain-transfer polymerization technique

Coronavirus disease 2019 is one of the global health problems. Herein, a highly sensitive electrochemical biosensor has been designed to detect the RNA-dependent RNA polymerase (RdRP) of the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) (SARS-CoV-2 RdRP). Herein, the surface-initiated reversible-addition−fragmentation-chain-transfer polymerization was used to amplify the electrochemical signal. To do that, the thiol-terminated peptide nucleic acid (PNA) probes were first immobilized on the surface of a screen-printed electrode modified with reduced graphene oxide-gold nanocomposite and then the fixed concentration of the SARS-CoV-2 RdRP was added to the electrode surface to interact with PNA probes. Subsequently, the Zr 4+ ions were added to interact with the phosphate groups of the SARS-CoV-2 RdRP. It allowed us to polymerase the ferrocenylmethyl methacrylate (FcMMA) and 4-cyano-4-(phenylcarbonothioylthio)-pentanoic acid on the SARS-CoV-2 RdRP chain. Since the poly-FcMMA has an electrochemical signal, the response of the PNA-based sensor to SARS-CoV-2 RdRP was increased in the range of 5–500 aM. The limit of detection was calculated to be 0.8 aM which is lower than the previous sensor for SARS-CoV-2 RdRP detection. The proposed PNA-based sensor showed high selectivity to the SARS-CoV-2 RdRP in the presence of the gene fragments of influenza A and Middle East respiratory syndrome coronavirus.

Synthesis, Characterization, and Dye Removal Applications of Graphene Oxide-Gold Nanocomposite

Here, we report the facile synthesis of graphene oxide/gold nanocomposite, and dye removal ability as an adsorbent was studied. Sodium citrate as a reducing agent was used to reduce Au (III) ions to the formation of gold nanoparticles on the surface of graphene oxide sheets that were prepared by Hummers’ method. Transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction (XRD) was used to specify nanocomposite synthesis. Adsorption dosage and contact time were investigated and explained as influencing parameters in removing methylene blue and methyl orange. In optimum conditions, the amount of adsorbent 30 mg and contact time 15 min for methylene blue and the amount of adsorbent 30 mg and contact time 25 min for methyl orange were quantitatively removed from 10 mL of wastewater. The pseudo-second-order model explained the kinetic data. Since graphene oxide/gold nanocomposite could be reused reasonably and had adsorptive properties, it tends to be produced as a modest and elective adsorbent to treat wastewater.

A novel labeled and label-free dual electrochemical detection of endotoxin based on aptamer-conjugated magnetic reduced graphene oxide-gold nanocomposite

Lipopolysaccharide (LPS) or endotoxin is an amphiphilic macromolecule found in the outer membrane of gram-negative bacteria. Even low amounts of LPS could result in death. Therefore, sensitive detection of endotoxin in the range of ng.mL−1 is vital. The dual electrochemical detection of endotoxin was designed. Thiourea was utilized to conjugate the magnetic graphene-based nanocomposite to a pair of amino-modified aptamers to increase the selectivity and sensitivity through the increase of active space occupied by aptamers attached to the nanocomposite. X-ray diffraction, FT-IR spectroscopy, Raman spectroscopy, VSM, FE-SEM, and TEM were applied to study nanomaterials. Electrochemical techniques, including cyclic voltammetry (CV), Square‐wave voltammetry (SWV) and Electrochemical Impedance Spectroscopy (EIS) were accomplished to study electrochemical properties of the aptasensor. Both labeled, and label-free electrochemical detection of endotoxin were performed using methylene blue and ferrocyanide, respectively. The aptasensor exhibits the limit of detection as low as 4 fg/mL and 0.2 fg/mL, with linear range of detection 0.1–0.9 pg.mL−1 and 0.01–0.09 pg.mL−1 for ferrocyanide and methylene blue, respectively. The aptasensor showed a considerable response to LPS over other biomolecules like glucose. This aptasensor exhibited a good response to the serum of patient and normal people, which certificates its practicality in medical aims.

Catalytic and Medical Potential of a Phyto-Functionalized Reduced Graphene Oxide-Gold Nanocomposite Using Willow-Leaved Knotgrass.

In the current study, a simple, environmentally friendly, and cost-effective reduced graphene oxide–gold nanoparticle (rGO-AuNP) nanocomposite was successfully phytosynthesized using the aqueous leaf extract of a common weed found on the Nile banks, Persicaria salicifolia, for the first time. The phytosynthesis of rGO-AuNPs was first confirmed via the color transformation from brown to black as well as throughvarious techniques such as transmission electron microscopy (TEM) and Raman spectroscopy. Two UV–vis peaks at 275 and 530 nm were observed for the nanocomposite with a typical particle size of mostly spherical AuNPs of 15–20 nm. However, other shapes were occasionally detected including rods, triangles, and rhomboids. Existing phytoconstituents such as flavonoids and glycosides in the plant extract were suggested to be responsible for the phytosynthesis of rGO-AuNPs. The excellent catalytic efficacy of rGO-AuNPs against MB degradation was confirmed, and a high antibacterial efficiency against Escherichia coli and Klebsiella pneumonia was also confirmed. Promising antioxidant performance of rGO-AuNPs was also proved. Furthermore, it was concluded that rGO-AuNPs acquired higher efficiency than AuNPs synthesized from the same plant extract in all of the studied applications.

Graphene oxide/Au nanoparticles: Synthesis, properties, and application: A mini‐review

There has been rapid growth in research activities on the potential of graphene oxide/Au (GO:Au) composite for different applications. The GO:Au composite has been widely explored in applications such as biomedicine, electrochemical biosensors, optical limiters, and organic dye degradation. The increased interest in GO:Au for these applications is the consequence of harvesting the electronic bonding structure that is due to the formation of sp3 CC clusters from defected sp2 C═C and attachment of Au atoms onto the C═C carbon matrix. The defection of the sp2 cluster of GO can be achieved by the method of improved synthesis and functionalization with Au surfactants. The current review explores an overview of the different synthesis techniques for producing GO:Au composites, which is an important factor in controlling the particle and size distribution of the composites. The electronic, electrical, and magnetic properties of GO:Au composites are covered as it relates to photochemical, memristive, and biomedical imaging applications. The low coercivity and remanence are consistent with superparamagnetic behavior. Although, GO:Au-nanocomposite (NC) are widely explored for biomedicine and drug delivery applications, future applications of the composite can be useful for magnetic resonance imaging owing to the superparamagnetic behavior. The future possibilities of GO:Au-NP are promising in the field of bioimaging and electronic devices. The electrical property of GO:Au-NC can be fused with its electrochemical property for supercapacitor applications. In some cases, GO:Au-NC is used as an anchor material with conducting polymers to enhance the supercapacitor properties. Furthermore, the synthesis of mono-disperse few-layer graphene is still challenging owing to economic cost and the graphite exfoliation process. The review of GO:Au composite from a material physics perspective aims to elucidate the current trends as well the future possibilities offered by the composite for various promising applications. Novelty Statement This review focused on the graphene oxide-gold nanocomposite which is an outstanding composite material for different applications. The overview of graphene oxide/Au nanoparticles was first presented in this work. The synthesis, properties, and applications of graphene oxide/gold nanocomposites were emphasized. The disadvantages and promising prospect of GO:Au nanocomposites for the ferroelectric and magnetic resonance imaging applications were highlighted.

Green synthesis of graphene gold nanocomposites for optical sensing of ferritin biomarker

The combination of graphene oxide with gold nanoparticles offers enhanced optical properties with strong surface plasmon resonance, good biocompatibility, improved stability and ultrasensitive detection. This study aims to synthesize ecofriendly graphene oxide gold nanocomposites for sensing of ferritin biomarker, which is vital for diagnosing anemia as well as severe COVID conditions. Herein, an affordable and label free technique was proposed for detection of ferritin. The graphene oxide gold nanocomposites are synthesized by a simple one pot chemical reaction utilizing natural reducing agents. The alterations in the optical spectral characteristics of graphene gold nanocomposites upon interaction with the Fe3+ ions as well as ferritin protein are investigated. The proposed label free technique achieved a limit of detection of 1 μM for Fe3+ ions and 1 μg/ml for Ferritin protein.

Low hysteresis relative humidity sensing characteristics of graphene oxide–gold nanocomposite coated langasite crystal microbalance

We propose a relative humidity (RH) sensor made of langasite crystal microbalance (LCM) coated with graphene oxide (GO)–gold nanocomposite and report its excellent hysteresis and sensitivity characteristics. LCM has recently emerged as an alternative to the popular quartz crystal microbalance (QCM). However, only a few attempts have been reported that explore and elaborate the sensing characteristics of LCM. GO has extraordinary humidity sensing capability, yet it suffers from high hysteresis. In this work, we overcame this deficiency by employing an Au-GO nanocomposite as the sensing medium on the LCM electrode. We present the resonance frequency characteristics of the modified LCM under varying RH values in the range of 10% ‒ 80% in nitrogen. Our results suggest that the mass loading effect caused by water molecules altered the resonance frequency of the LCM linearly with a sensitivity of 3.64 Hz/% RH. More importantly, the sensor exhibited low hysteresis with an average value of 3.45% RH, and maximum and minimum hysteresis values of 5.6% RH, and 0.6% RH, respectively. Finally, the proposed Au-GO-LCM sensor displayed very high sensitivity to RH when tested for cross-sensitivity with a range of volatile organic compounds (VOCs).

Highly Sensitive Amperometric α-Ketoglutarate Biosensor Based on Reduced Graphene Oxide-Gold Nanocomposites.

Herein, a rapid and highly sensitive amperometric biosensor for the detection of α-ketoglutarate (α-KG) was constructed via an electrochemical approach, in which the glutamate dehydrogenase (GLUD) was modified on the surface of reduced graphene oxide-gold nanoparticle composite (rGO-Aunano composite). The rGO-Aunano composite was one-step electrodeposited onto glassy carbon electrode (GCE) surface and was characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and electrochemical techniques. In addition, the rGO-Aunano/GCE was also found to electrocatalyze the oxidation of β-nicotinamide adenine dinucleotide (NADH) at the peak potential of 0.3 V, which was negatively shifted compared with that at bare GCE or Aunano/GCE, illustrating better catalytic performance of rGO-Aunano. After the modification of GLUD, the GLUD/rGO-Aunano/GCE led to effective amperometric detection of α-KG through monitoring the NADH consumption and displayed a linear response in the range of 66.7 and 494.5 μM, with the detection limit of 9.2 μM. Moreover, the prepared GLUD/rGO-Aunano/GCE was further evaluated to be highly selective and used to test α-KG in human serum samples. The recovery and the RSD values were calculated in the range of 97.9–102.4% and 3.8–4.5%, respectively, showing a great prospect for its real application.

Ultrasensitive amperometric immunosensor for the prostate specific antigen by exploiting a Fenton reaction induced by a metal-organic framework nanocomposite of type Au/Fe-MOF with peroxidase mimicking activity

To increase the sensitivity of electrochemical sensor, Fe-MIL-88B-NH2 (Fe-MOF) with peroxidase-like activity is designed for the construction of immunoprobe. The Fe-MOF was prepared by one-step hydrothermalf method using 2-aminoterephthalic acid and iron(III) chloride. For the immunoprobe, it was fabricated by gold nanocomposite/Fe-MOF (Au/Fe-MOF) for the immobilization of labeling antibody (the antibody was used to conjuncting with label materials). The thin layer of Methylene Blue (MB) covered by reduced graphene oxide-gold nanocomposites (Au-rGO) serves as a substrate to covalently fix coating antibodies. The MB as a redox-active species was modified on the glass carbon electrode that can give a strong amperometric signal at 0.18V (vs. Ag/AgCl). With the participation of H2O2, Fe-MOF can induce the Fenton reaction which degrades MB covered by Au-rGO on the substrate. The rest of MB on the surface of electrode becomes oxidized thereby generating acurrent signal. Square wave voltammetry (SWV) was used to quantify PSA. Under optimal conditions, the immunoassay is stable, specific and reproducible. It has a lower detection limit of 0.13pgmL-1 (S/N = 3) and awide analytical range that extendsfrom 0.001 to 100ngmL-1. Graphical abstractA sandwich-type amperometric immunoassay based on Fe-MOF-induced Fenton reaction was designed for sensitive determination of prostate specific antigen.

Preparation of Molecularly Imprinted Magnetic Graphene Oxide-Gold Nanocomposite and Its Application to the Design of Electrochemical Sensor for Determination of Epinephrine

In this study, a new molecularly imprinted polymer (MIP) based nanocomposite was synthesized then used to determine epinephrine (EPN) by the use of an electrochemical sensor modified by it. Typical techniques for the synthesis of MIP have disadvantages, such as weak binding sites, low mass transfer and low selectivity. One of the ways to improve electrochemical properties is the use of graphene oxide (GR-Ox) and modification of its surface. For this purpose, GR-Ox was initially magnetized (MGR-Ox), then its surface was coated with a silica layer, and gold nanoparticles (AuNPs) were coated on its surface. Subsequently, copolymerization of methacrylic acid (MAA) and N,N'-methylene-bis-acrylamide (MBA) in the presence of EPN was performed on the MGO-AuNPs surface. Afterwards, a selective carbon paste electrode (CPE) with synthetic nanocomposite was fabricated to detect EPN. Under optimal conditions, a linear range from 10-8 to 5.0 × 10-7 M was obtained for the measurement of EPN in urine and blood with a detection limit of 5 × 10-9 M (S/N = 3).

Label-free electrochemical detection of Cloxacillin antibiotic in milk samples based on molecularly imprinted polymer and graphene oxide-gold nanocomposite

Detection of applied antibiotics in food productions could be the first step to avoid future health consequences. The aim of this work was to the synthesis of molecularly imprinted polymer (MIP) particles via non-covalent procedure and evaluation of efficiency MIP for the selective collection of Cloxacillin (CLO) from aqueous and biological samples and consequently quantification of separated CLO using an electrochemical nanosensor. The effect of operational parameters including pH, contact time and MIP dosage for optimization of CLO collection condition were studied. The CLO quantities were determined by a developed electrochemical nanosensor based on a screen-printed electrode modified with graphene oxide and gold nanoparticles. The results showed that the optimum conditions for removal of CLO (92%) were determined at pH = 8.5, with 89 min as contact time and 0.79 g MIP. The linear range was from 110 to 750 nM and the detection limit of the nanosensor was 36 nM. The performance of the MIP-based nanosensor for the spiked Cloxacillin detection in real milk samples showed the potential of the developed nanosensor to be considered in future real sample measurement analysis.

Disposable Nonenzymatic Uric Acid and Creatinine Sensors Using μPAD Coupled with Screen-Printed Reduced Graphene Oxide-Gold Nanocomposites.

Uric acid (UA) and creatinine are the imperative biological substance for clinical monitoring and diagnosis. Measuring the ratio between uric acid and creatinine in urine helps differentiate acute uric acid nephropathy from the hyperuricemia that secondarily occurs to renal failure. In general, the ratio is greater than 0.9 in acute uric acid nephropathy and less than 0.7 in hyperuricemia. In this work, disposable nonenzymatic screen-printed reduced graphene oxide-gold nanocomposites electrodes were firstly developed for the quantitative analysis of uric acid. Our sensors were also coupled with the paper-based colorimetric sensor of the determination of creatinine. Hence, an alternative high-throughput screening test for the uric acid to creatinine ratio with high sensitivity, specificity, simplicity, and rapidity was developed. Under the optimum conditions, our disposable nonenzymatic screen-printed electrode for the determination of uric acid shows the acceptable analytical performance in a wide range of linearity (2.5-1,000 μM) with a low detection limit of 0.74 μM. Our electrodes also showed no interference from common physiologic compound in urine. The determination of creatinine has been developed using Jaffé reaction between the creatinine and picric acid in alkaline condition. The alkaline picrate color on μPAD changed from yellow to orange in the presence of creatinine and the orange intensity is directly proportional to the creatinine amount in a linearity range of 0.20-6.0 mM as a detection limit of 180 μM. Finally, our device has been utilized to determine uric acid and creatinine simultaneously in control urine samples with acceptable result.

Eco-Friendly In Situ Fabrication of Reduced Graphene Oxide Gold Nanocomposites for Catalysis and Dye Degradation

The invention represents a development of robust eco-friendly method use for water waste management and polluted water. The inadvertent role of peanut peels extract helps to simultaneously convert and form reduced graphene oxide gold nanocomposite (rGO@AuNCs) in single step. Fabricated nanocomposite was evaluated for its catalytic performance using reduction of 4-nitrophenol to 4-aminophenol as well as elimination of methylene blue (MB) and malachite green (MG) dyes from water. Graphene oxide (GO) and rGO@AuNCs, were synthesized using simplified approaches and preliminary characterization was done using UV–Vis spectrophotometer and Fourier transform infrared spectroscopy. Least concentration of rGO@AuNCs is required to eliminate MB and MG around 77 and 93%, respectively. Furthermore, surface morphology and elemental analysis of rGO@AuNCs confirm successful fabrication methods as well as X‑ray diffraction pattern confirms the crystalline behavior of nanocomposite. The study illustrates an environment-friendly and cost effective in situ fabrication rGO@AuNCs from industrial agro waste for an environmental remediation.

Spectroscopic ellipsometry investigation of the optical properties of graphene oxide dip-coated on magnetron sputtered gold thin films

Despite intensive investigations on graphene oxide-gold nanocomposites, the interaction of graphene oxide sheets with magnetron sputtered gold thin films has not been studied yet. The optical constants of graphene oxide thin films dip-coated on magnetron sputtered gold thin films were determined by spectroscopic ellipsometry in the [300–1000] wavelength range. Moreover, the morphologic properties of the samples were investigated by SEM analysis. Graphene oxide absorbs mainly in the ultraviolet region, but when it is dip-coated on magnetron sputtered gold thin films, its optical constants show dramatic changes, becoming absorbing in the visible region, with a peak of the extinction coefficient at 3.1 eV. Using magnetron sputtered gold thin films as a substrate for graphene oxide thin films could therefore be the key to enhance graphene oxide optical sheets' properties for several technological applications, preserving their oxygen content and avoiding the reduction process.

An ultrasensitive and switch-on platform for aflatoxin B1 detection in peanut based on the fluorescence quenching of graphene oxide-gold nanocomposites

Graphene oxide-gold nanocomposites (GO/AuNCs) were prepared and used as a novel fluorescence quenching platform for ultrasensitive detection of aflatoxin B1 (AFB1) coupled with hybridization chain reaction (HCR) amplification. In the designed system, two fluorophore labeled hairpin probes (HP1/HP2) were introduced, and the fluorescence signals of them were effectively quenched due to the adsorption on GO/AuNCs. Associate probe (AP) was used for the specific recognition of AFB1, and the stem-loop structure of it was opened. Meanwhile, the exposed section of AP was utilized as an initiator for the happen of HCR between HP1 and HP2, a strong fluorescence signal was obtained due to the formation of long nicked dsDNA duplex and desorbed of them from the surface of GO/AuNCs. Under the optimal conditions, GO/AuNCs displayed 94% of the quenching efficiency to the fluorescent probes, and a detection limit down to 0.03pg/mL was obtained for AFB1 detection. In particular, the assay exhibited excellent selectivity for the detection of AFB1 against other interfering agents that normally coexist with AFB1 in mildewed agriculture products. Moreover, the assay could realize the detection of AFB1 effectively in peanut samples.

Electrochemical co-deposition of reduced graphene oxide-gold nanocomposite on an ITO substrate and its application in the detection of dopamine

The simultaneous deposition of rGO and gold nanostructures has been achieved by electrodeposition from mixed solutions containing graphene oxide (GO) and a gold precursor. Scanning electron microscope (SEM), Raman spectroscopy and atomic force microscopy (AFM) have been employed to reveal the morphology, uniformity and practical stability of the nanocomposite films on the indium tin oxide (ITO) substrate. The AFM data showed heights of tens of nanometers of the nanocomposite, suggesting that multilayers of rGO with gold nanoparticles had been formed as a result of the electrochemical co-deposition. Differential pulse voltammetry (DPV), as a widely used analytical technique, has been carried out on the rGO-Au/ITO electrode for the quantitative detection of dopamine (DA). The detection limit (S/N=3)for the determination of DA was evaluated as 0.6 μM.

A sensitive electrochemical sensor for direct phoxim detection based on an electrodeposited reduced graphene oxide–gold nanocomposite

The principal objective of this study was to develop a sensitive and selective electrochemical sensor for phoxim detection based on a reduced graphene oxide–gold nanocomposite (RGO–Au) modified grassy carbon electrode (GCE).

Aptamer-conjugated graphene oxide-gold nanocomposites for targeted chemo-photothermal therapy of cancer cells.

The current cancer therapies in clinical practice demonstrate the need for improvements such as improving the efficiency and reducing the severe side effects. Herein, we integrated the targeted chemotherapy and photothermal therapy in a multifunctional drug-delivery platform. The targeting DNA aptamer (Apt)-modified graphene oxide-gold nanoparticle (GO-AuNP) composites were successfully synthesized. The doxorubicin (DOX)-loaded GO-AuNP-Apt system showed heat-stimulative and sustained release characteristics. In vitro cell cytotoxicity experiments showed that combined therapy had the highest rate of death of tumor cells compared to that of single photothermal therapy or chemotherapy. Furthermore, aptamer-modification could significantly enhance the accumulation of nanocomposites within cancer cells. Our study demonstrates that aptamer-modified GO-Au nanocomposites may have potential in the development of targeted photothermal therapy and chemotherapy against cancer cells.

Acetylcholinesterase biosensor based on 3-carboxyphenylboronic acid/reduced graphene oxide–gold nanocomposites modified electrode for amperometric detection of organophosphorus and carbamate pesticides

A novel amperometric biosensor based on immobilizing acetylcholinesterase on 3-carboxyphenylboronic/reduced graphene oxide–gold nanocomposites modified electrode was developed for the detection of organophosphorus and carbamate pesticides. Acetylcholinesterase was successfully immobilized on the electrode with relatively high activity by the specific binding between the boronic acid group of 3-carboxyphenylboronic and the glycosyl of acetylcholinesterase. The biosensor enjoyed good sensitivity owing to the excellent properties of gold nanoparticles and reduced graphene oxide, which promoted electron transfer reaction and enhanced the electrochemical response. Parameters affecting the biosensor response such as pH, applied potential, enzyme loading and inhibition time were optimized. Based on the inhibition of an organophosphorus insecticide on the enzymatic activity of AChE, organophosphorus and carbamate pesticides were determined with satisfactory results in the presence of acetylthiocholine chloride as a substrate. Moreover, the fabricated biosensor had good repeatability and high stability.