Reduced Graphene Oxide Gold Nanoparticles Research Articles

The rGO@AuNPs modified label-free electrochemical immunosensor to sensitive detection of CP-BNYVV protein of Rhizomania disease agent in sugar beet

For the first time, a novel simple label-free electrochemical immunosensor was fabricated for sensitive detection of the coat protein of beet necrotic yellow vein virus (CP-BNYVV) as the causal agent of Rhizomania disease in sugar beet. To boost the amplification of the electrochemical signal, gold nanoparticles-reduced graphene oxide (AuNPs-rGO) nanocomposite was employed to modify the glassy carbon electrode. Anti-BNYVV polyclonal was immobilized onto a modified electrode by applying a thiol linker via a self-assembly monolayer (SAM) and activating the functionalized surface using (3-aminopropyl triethoxysilane) and glutaraldehyde. The determination step relied on the forming of an immunocomplex between the antigen and oriented antibody, resulting in a decrease in current in the [Fe (CN)6]3−/4− redox reaction. The response value exhibited direct proportionality to the concentrations of CP-BNYVV. Scanning electron microscopy, energy dispersive x-ray, cyclic voltammetry, and electrochemical impedance spectroscopy techniques collectively provided a comprehensive understanding of the structural, morphological, and electrochemical features during the modification steps. Under optimized experimental conditions, the fast Fourier transform square wave voltammetry responds to the logarithm of CP-BNYVV concentrations in a wide linear range from 0.5 to 50000 pg/mL and the limit of detection is calculated to be 150 fg/mL, implying the admirable sensitivity. Selectivity assay exhibited no cross-reactivity with other proteins from interfering virus samples. Satisfactory reproducibility and stability were achieved with a relative standard deviation of 3.1% and a stable value of 90% after 25 days, respectively. More importantly, the high performance of the immunosensor resulted in the direct detection of CP-BNYVV in spiked and infected plant samples, which affords a sensing platform with huge potential application for the early detection of BNYVV virus in field conditions.Graphical

One-pot radiolytically synthesized reduced graphene oxide-gold nanoparticles composites and exploration in energy storage

Graphene and its composites are of primary importance, particularly in the field of energy storage. Numerous bottom-up and top-down methods have been proposed in the literature to produce these materials with enhanced physicochemical properties. Recently, an innovative and green methodology was developed based on ionizing radiation, allowing the quantitative synthesis of graphene oxide-based materials. With the aim to extend this strategy for the preparation of hybrid nanomaterials, the objective of this work was the one-pot synthesis of nanocomposites composed of reduced graphene oxide – gold nanoparticles (rGO-AuNPs) via gamma ray-induced radiolytic reduction. UV–Vis Absorption Spectroscopy, Fourier Transform Infrared Spectroscopy, Raman Spectroscopy and X-ray Photoemission Spectroscopy were utilized to comprehensively evaluate the reduction degree of graphene oxide and the formation of gold nanoparticles. Atomic Force Microscopy and Scanning Electron Microscopy were employed to obtain the morphological and topographical information on synthesized nanocomposites. Thermal properties were investigated by Thermogravimetric Analysis and electrical properties were investigated using Cyclic Voltammetry and Potentiostatic Charge and Discharge method. The results demonstrated the successful reduction of graphene oxide and gold ions through the drastic transformation of oxygen-containing functional groups and the formation of gold nanoparticles. Electrical characterization results highlighted the excellent electrical properties of radiosynthesized rGO-AuNPs composites and their great potential for supercapacitance application.

β-Cyclodextrin Functionalized Reduced Graphene Oxide–Gold Nanoparticles for Electrochemical Detection of Stigmasterol in Ganoderma boninense-Infected Oil Palm Leaves

β-Cyclodextrin Functionalized Reduced Graphene Oxide–Gold Nanoparticles for Electrochemical Detection of Stigmasterol in Ganoderma boninense-Infected Oil Palm Leaves

Fabrication of a citrus flavonoid hesperetin-capped gold nanoparticles-reduced graphene oxide nanocomposites (Hes-Au/rGONCs) as a potential therapeutic agent for triple negative breast cancer and bacterial infections

Hesperetin (Hes) is a Citrus Flavonoid, which is confirmed to have extensive therapeutic effects, comprising antimicrobial, antioxidant, anticancer, cardiovascular protection, and so forth. To overcome the poor solubility, here we attempt to synthesize the Hes-mediated gold nanoparticles bio-functionalized in reduced Graphene oxide (Hes-Au/rGONCs) to increase the therapeutic efficacy of Hes. The characterization of synthesized Hes-Au/rGONCs were analysed using UV–vis spectrophotometry, FT-IR, Raman spectroscopy, X-ray diffraction analysis (XRD), XPS, HPLC, SEM, EDX and HR-TEM. The absence of vibrations at 1516 and 1381 cm−1 shows the involvement of hydroxyl groups of phenols and enols in anchoring Au on the surface of rGO. In XRD, the planes at (111), (200), (220) and (311) revealed the face centered cubic (fcc) crystalline structure of gold nanoparticles that were functionalized on rGO nanosheets. Hes-Au/rGONCs synthesised produced a highly negative zeta potential of -36.44 mV due to their stability. The Hes-rGO/Au-NPs were analysed for their surface morphology by SEM. The HR-TEM micrographs exhibited uniform distribution and homogenous spherical shaped AuNPs with an average size of 21.37±5.7 nm on rGO sheets. The bio reduction percentage was calculated as 98.86% by using HPLC. The inhibitory concentration (IC50) of free-Hes and nanocomposites were 157.57 and 38.41 µM, respectively. The Hes-Au/rGONCs possess effective bactericidal activity against gram positive bacterial species than against gram negative bacterial strains. The resazurin dye assay confirms the MIC values of Hes-Au/rGONCs. Hereby, the outcome of these studies suggested that the fabricated Hes-Au/rGONCs have potential biomedical applications.

Biomass-assisted fabrication of rGO-AuNPs as surface-enhanced Raman scattering substrates for in-situ monitoring methylene blue degradation

Reduced graphene oxide-gold nanoparticles nanocomposites (rGO-AuNPs) with high surface-enhanced Raman scattering (SERS) activity was created by biomass-assisted green synthesis with Lilium casa blanca petals biomass for the first time, and its application for methylene blue (MB) degradation was explored through in-situ monitoring. Lilium casa blanca petals biomass was used as a reducing agent to reduce GO and chloroauric acid successively when carrying out rGO-AuNPs in-situ synthesis while it also acted as a capping agent. The produced rGO had oxygen-containing functional groups which had an outstanding performance in enhancing the SERS effect. Characterization results confirmed that the AuNPs were grafted onto the rGO sheet, and the mechanism study showed that total flavonoids in Lilium casa blanca petals biomass were the main biological compounds involved in the reduction. rGO-AuNPs had a high Raman enhancement factor (EF) which could reach 3.88 × 107. The synthesized nanocomposite also had a good catalytic activity that could be employed as catalyst in MB degradation, and it could complete degradation within 15min. The reaction rate increased linearly with the amount of rGO-AuNPs, and the degradation could be in-situ monitored both by UV and SERS.

Development of conducting cellulose paper for electrochemical sensing of procalcitonin

An electrochemical paper-based sensor was developed for the detection of bacterial infection (BI)-specific biomarker procalcitonin (PCT). Reduced graphene oxide-gold nanoparticles (rGO-AuNP) and poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) were synthesized and were fabricated to a disposable, portable, and inexpensive cellulose fiber paper (CFP) substrate. rGO-AuNP-PEDOT:PSS nanocomposite-modified conductive paper-based biosensing platform was efficaciously fabricated by a constant and simple coating procedure. rGO-AuNP-PEDOT:PSS nanocomposite-modified conductive paper electrode was found to provide a sensitive and conductive substrate for PCT detection. The presence of rGO-AuNP-PEDOT:PSS nanocomposite on CFP substate was investigated by Fourier transform infrared spectrometry, field emission scanning electron microscopy, ultraviolet-visible spectroscopy, and X-ray diffraction studies. The electrochemical behavior of rGO-AuNP-PEDOT:PSS @CFP surface was studied with impedance spectroscopy, cyclic voltammetry, and chronoamperometry techniques. This low-cost paper-based biosensor has a linear range for PCT of 1 × 103 to 6 × 107fgmL-1. This developed sensor exhibited good reproducibility with a relative standard deviation (RSD) of about 3.7%. The proposed CFP-based biosensor has been proven as an accelerated simple point-of-care (POC) exploratory approach for early PCT diagnosis in inadequate areas with limited production facilities, computational techniques, and highly skilled experts.

Ionic liquid modified chloroperoxidase is immobilized on gold nanoparticles-reduced graphene oxide nanocomposites for efficient sensoring of nitrite by electroenzymatic catalysis

Electroenzymatic biosensors have wide applications due to its fastness and sensitivity. Here we propose a bio-nanocomposite to be dropped on glassy carbon electrode (GCE) for nitrite sensoring by electroenzymatic catalysis. The composite is constructed by ionic liquids (1-butyl-3-methylimidazolium bromide, ILBMB) modified chloroperoxidase (CPO) immobilized on gold nanoparticles (Au NPs) modified reduced graphene oxide (rGO). The ILBMB can facilitate the direct electron transfer (DET) of CPO on GCE without a redox mediator. The molecular docking indicates ILBMB is located at the opening of substrate channel rather than occupy the active site of CPO, which is beneficial to its DET. Circular dichroic spectrum (CD) verifies the α-helix content of CPO is increased, and ultraviolet-visible spectrum (UV–vis) demonstrates the heme prosthetic group become more exposed by ILBMB. These changes result in the enhancement of CPO activity. The rGO-Au NPs plays two roles enhancing the detection signal and improving the loading of CPO on GCE. The sensor (CPO-ILBMB/rGO-Au NPs/GCE) provides two models for nitrite detection as cyclic voltammetry and amperometry. The detection limit is 0.25 μmol·L−1 and 0.049 μmol·L−1, respectively with corresponding detection range of 2.0−2500 μmol·L−1 and 0.5–300 μmol·L−1. The high sensitivity, stability, and selectivity of this electroenzymatic biosensor ensure its potential practical application.

A multiplexed electrochemical quantitative polymerase chain reaction platform for single-base mutation analysis

Detection of single-based mutation (SbM), which is of ultra-low abundance against wild-type alleles, are typically constrained by the level of multiplexing, sensitivity for single-base resolution and quantification accuracy. In this work, an electrochemical quantitative polymerase chain reaction (E-PCR) platform was developed for multiplexed and quantitative SbM analysis in limited and precious samples with single-nucleotide discrimination. A locked nucleic acid (LNA)-mediated multiplexed PCR system in a single, closed tube setup was firstly constructed to selectively amplify the SbM genes while suppressing the wild-type alleles. The amplicons were detected simultaneously through hybridization with the sequence-specific hairpin probes anchored on a reduced graphene oxide-gold nanoparticles functionalized electrode surface. With the inclusion of an LNA-mediated PCR step upstream of the electrochemical detection, we improved the limit of detection (LOD) by 2 orders of magnitude, down to an ultralow-level of 5 copies μL−1. The platform achieved an ultra-sensitive and specific detection with 0.05% against a background of 10, 000 copies of wild-type alleles. It is highly adaptive and has the potential to enable expanded multiplexed detection in parallel, thus providing a universal tool for multiplexed SbM identification.

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.

Highly Sensitive Electrochemical Aptasensor for Detection of Glypican-3 Using Hemin-Reduced Graphene Oxide-Platinum Nanoparticles Coupled with Conductive Reduced Graphene Oxide-Gold Nanoparticles.

An electrochemical aptasensor for quantitatively detecting glypican-3 (GPC3) was constructed by combining hemin-reduced graphene oxide-platinum (H-rGO-Pt) nanoparticles (NPs) with reduced graphene oxide-gold (rGO-Au) nanoparticles (NPs). Herein, the rGO-Au NPs deposited onto screen-printed electrodes resulted in signal amplification due to their large surface areas. Meanwhile, highly conductive H-rGO-Pt NPs acted as a sensing medium that improved electrical conductivity and as an indicator for monitoring peak current for determination. A GPC3 aptamer (GPC3apt) with a low equilibrium dissociation constant was used as a bio-recognition molecule. GPC3apt specifically captured GPC3 proteins and formed aptamer-GPC3 complexes, which impeded electron transfer and thus hampered the redox signal of hemin in H-rGO-Pt NPs. This developed electrochemical aptasensor showed a linear response to GPC3 (from 0.001 μg/mL to 10 μg/mL) and had a detection limit of 0.001 μg/mL. This work provides a low-cost and highly sensitive detection with and good recovery for GPC3 and holds great promise for the clinical diagnosis of hepatocellular carcinoma.

Ultrasensitive electrochemical immunosensor for ProGRP detection based on 3D-rGO@Au nanocomposite

In this work, an ultrasensitive and low-cost electrochemical immunosensor has been constructed for ProGRP detection. The prepared three-dimensional reduced graphene oxide-gold nanoparticles (3D-rGO@Au) composite as substrate materials were applied for electrode modification, which can enhance electrical conductivity and enlarge the effective surface area for immobilizing capture antibody. Detection antibody-coated non-conductive SiO2 nanospheres were used for specifically recognize ProGRP and form a sandwich structure. The electrochemical response signal of the sandwich-type immunosensor was based on the electron transferability between the electrode and [Fe(CN)6]3−/4−. 3D-rGO@Au can significantly increase the initial current, while SiO2 can greatly reduce the response current. The combined effects of these nanomaterials can thus effectively enhance the sensitivity. Under optimal conditions, the constructed immunosensor exhibited a wide linear range (1 fg/mL to 10 ng/mL) with a low limit of detection (0.14 fg/mL). Moreover, the immunosensor exhibited superior stability, good reproducibility, favorable selectivity, and high sensitivity. Meanwhile, the concentration of ProGRP in human serum samples was measured with satisfactory results. This device is promising in the early screening of lung cancer, which can be applied as an over-the-counter test at home or in the community.

A molecularly imprinted polymer on reduced graphene oxide-gold nanoparticles modified screen-printed electrode for selective determination of ferulic acid in orange peels

This work reports the development of a molecularly imprinted polymer used for the sensitive and selective electrochemical detection of ferulic acid. The device was prepared by the electropolymerization of molecularly imprinted poly(phenol) film on screen-printed electrode modified with reduced graphene oxide and gold nanoparticles. The modified electrode was characterized by cyclic voltammetry, electrochemical impedance spectroscopy, scanning electron microscopy with field emission gun, energy dispersive X-ray spectroscopy, RAMAN spectroscopy and atomic force microscopy. Under optimized conditions, the proposed electrode presented a linear working range of 10 nM to 1 µM and a detection limit of 3.1 nM (n = 3). The sensor displayed good repeatability and stability over time, as well as excellent selectivity when applied for the detection of ferulic acid molecule. The method proposed here was successfully applied for ferulic acid detection in orange peels. The analyses were validated by recovery assays, where recovery values between 99 and 103% were obtained. The results of the study show that this electroanalytical methodology has good accuracy when employed for the detection of ferulic acid.

Microfluidic Rapid Prototype Enzymatic Biofuel Cell Based on a Nanocomposite

Here, a low-cost glucose/O2 Y-shaped microfluidic biofuel cell was developed using a printed circuit board for microelectrode construction. A double-side tape based on the pressure-sensitive adhesive was used for microchannel fabrication. A nanocomposite that consisted of reduced graphene oxide gold nanoparticles (AuNPs), and poly neutral red connected to enzymes was applied on the copper electrode surface. The Aspergillus niger glucose oxidase enzyme and Mytheliophthora thermophile laccase were used to prepare the modified anodic and cathodic electrodes. Different procedures such as cyclic voltammetry scanning electron microscope coupled with energy-dispersive x-ray spectroscopy (EDX), and atomic force microscopy were used to scan the modified electrodes. SEM/EDX microanalysis displayed the structural and morphological properties of the proposed nanocomposite. The biofuel cell performance demonstrated a maximum power density of 36 μW cm−2, an open-circuit voltage of 0.5 V, and a flow rate of 50 μl min−1. The proposed rapid technique with RGO/AuNPs/PNR bioelectrodes is a good approach for finding low-cost microfluidic biofuel cells.

A highly-sensitive vascular endothelial growth factor-A(165) immunosensor, as a tool for early detection of cancer.

Biomarkers can be ideal indicators for assessing the risk of the presence of a disease. In this study, a label-free electrochemical biosensor was designed to quantify the vascular endothelial growth factor A (165) (VEGF-A(165)) antigen, using reduced graphene oxide-gold nanoparticle for early detection of breast cancer. The conductivity of gold nanoparticle along with its biocompatibility provide an enhanced surface, suitable for anti-VEGF antibody immobilization. 11-mercaptoundecanoic acid was used to facilitate a single-step and convenient bonding of the antibodies to the surface, compared to previous studies. The dynamic range of the biosensor was between 20 to 120 pg/ml and its limit of detection of the biomarker VEGF-A(165) was obtained to be about 0.007 pg/ml, using different electric signal transduction modes. Hence, the biosensor is a beneficial immunosensor with high sensitivity and ideal dynamic range for early-stage diagnosis of breast cancer and other cancers diseases associated with expression of VEGF-A(165). The as-prepared immunosensor could be efficiently employed for designing a point-of-care diagnostic platform.

Nitrogen and sulfur co-doped reduced graphene oxide-gold nanoparticle composites for electrochemical sensing of rutin

The extraordinary biological and physiological properties of rutin have been used in the preparation of therapeutical drugs. So it is very significant to develop a simple and sensitive method for rutin determaination in pharmaceutical samples. Herein, nitrogen and sulfur co-doped reduced graphene oxide attached with gold nanoparticles (NS-rGO/AuNPs) was developed for electrochemical determination of rutin. The NS-rGO was first prepared by a simple one-step thermal annealing method, and AuNPs were embedded onto NS-rGO through the interaction force of Au with N and S atoms. Detailed characterizations showed that the AuNPs are well dispersed and the presence of nitrogen and sulfur are significant. The NS-rGO/AuNPs modified electrode exhibited a significantly enhanced electrocatalytic activity towards rutin compared with NS-rGO, N-rGO and S-rGO modified electrodes. The excellent performance was achieved by the synergistic effect of AuNPs and heteroatoms co-doping. As a consequence, the NS-rGO/AuNPs based sensor showed a wide linear range of 0.2–1400 nM with a nanomolar detection limit of 0.067 nM (S/N = 3). Also the sensor exhibited satisfying selectivity, reproducibility, and stability. Finally, the sensor was successfully used to determine rutin in pharmaceutical tablets.

Electrochemical Determination of Naloxone Using Molecularly Imprinted Poly(para-phenylenediamine) Sensor

A molecularly imprinted polymer (MIP)-based electrochemical sensor featuring an electrochemically grafted para-phenylenediamine functional monomer on a reduced graphene oxide-gold nanoparticles composite modified screen printed electrode is reported. The morphology and properties of the sensing material were characterized with microscopy, spectroscopy and electrochemical techniques. A number of factors affecting the performance of the MIP sensor were examined and optimized. Under an optimized condition, the imprinted electrochemical sensor yielded homogenous naloxone binding sites with a dissociation constant of 8.6 μM, and responded linearly up to 8 μM naloxone, with a limit of detection of 0.16 μM. The sensor showed good run-to-run repeatability and batch-to-batch performance reproducibility with relative standard deviation of 5.7%–9.6% (n = 4) and <9% (n = 3), respectively. The imprinted sensor retained 95% and 85% of its performance when stored at ambient conditions for one and two weeks, respectively, demonstrating the sensor’s good stability. Selectivity experiments showed that both the MIP sensor and non-imprinted polymer electrode had minimal response (<25%) to equal concentrations of structurally similar compounds such as morphine, naltrexone and noroxymorphone, indicating good selectivity of the MIP sensor towards naloxone. The MIP sensor was successfully used to quantify naloxone in artificial urine samples, yielding recoveries greater than 92%.

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.

A glassy carbon electrode modified with reduced graphene oxide and gold nanoparticles for electrochemical aptasensing of lipopolysaccharides from Escherichia coli bacteria.

An electrochemical aptasensor is described for the voltammetric determination of lipopolysaccharide (LPS) from Escherichia coli 055:B5. Aptamer chains were immobilized on the surface of a glassy carbon electrode (GCE) via reduced graphene oxide and gold nanoparticles (RGO/AuNPs). Fast Fourier transform infrared, X-ray diffraction and transmission electron microscopy were used to characterize the nanomaterials. Cyclic voltammetry, square wave voltammetry and electrochemical impedance spectroscopy were used to characterize the modified GCE. The results show that the modified electrode has a good selectivity for LPS over other biomolecules. The hexacyanoferrate redox system, typically operated at around 0.3V (vs. Ag/AgCl) is used as an electrochemical probe. The detection limit is 30fg·mL-1. To decrease the electrochemical potential for detection of LPS, Mg/carbon quantum dots were used as redox active media. They decrease the detection potentialto 0V and the detection of limit (LOD) to 1fg·mL-1. The electrode was successfully used to analyze serum of patients and healthy persons. Graphical abstractSchematic representation of the modification of reduced graphene oxide gold nanoparticles with aptamer chains to immobilize on the glassy carbon electrode surface for electrochemical detection of lipopolysaccharides.

Electrochemical biosensor for amplified detection of Pb2+ based on perfect match of reduced graphene oxide-gold nanoparticles and single-stranded DNAzyme.

In this study, a sensitive amplification strategy for Pb2+ detection using reduced graphene oxide (RGO) and gold nanoparticles (AuNPs) was proposed. Thiol-modified DNAzyme is specific for Pb2+ self-assembly on RGO-AuNPs-modified electrode surface. Ferrocene labeled single-stranded DNAzyme (Fc-ssDNAzyme) self-hybridizes to form a DNA hairpin structure. The amount of Fc adsorbed on the electrode surface changes after the appearance of Pb2+, leading to a change of electrical signal. This change can be sensitively identified by differential pulse voltammetry (DPV) assisted by ferricyanide ([Fe(CN)6]3-/4-) in the electrolyte. The high conductivity and specific surface area of RGO and the strong chemical bond adsorption effect between DNAzyme and AuNPs are responsible for the amplified detection of Pb2+, which realize a detection range of 0.05-400,000.0nM and a minimum detection limit of 0.015nM. Moreover, the selectivity test results indicated that the biosensor had specificity for Pb2+, even if there was interference from other high-concentration metal ions. This simple biosensor also exhibited good responsiveness in actual sample detection, which provides a good application prospect for field detection of Pb2+ in water. Graphical abstract.

Electrochemical Impedance Characterization of Cell Growth on Reduced Graphene Oxide–Gold Nanoparticles Electrodeposited on Indium Tin Oxide Electrodes

The improved binding ability of graphene–nanoparticle composites to proteins or molecules can be utilized to develop new cell-based assays. In this study, we fabricated reduced graphene oxide–gold nanoparticles (rGO-AuNP) electrodeposited onto a transparent indium tin oxide (ITO) electrode and investigated the feasibility of the electrochemical impedance monitoring of cell growth. The electrodeposition of rGO–AuNP on the ITO was optically and electrochemically characterized in comparison to bare, rGO-, and AuNP-deposited electrodes. The cell growth on the rGO–AuNP/ITO electrode was analyzed via electrochemical impedance measurement together with the microscopic observation of HEK293 cells transfected with a green fluorescent protein expression vector. The results showed that rGO–AuNP was biocompatible and induced an increase in cell adherence to the electrode when compared to the bare, AuNP-, or rGO-deposited ITO electrode. At 54 h cultivation, the average and standard deviation of the saturated normalized impedance magnitude of the rGO–AuNP/ITO electrode was 3.44 ± 0.16, while the value of the bare, AuNP-, and rGO-deposited ITO electrode was 2.48 ± 0.15, 2.61 ± 0.18, and 3.01 ± 0.25, respectively. The higher saturated value of the cell impedance indicates that the impedimetric cell-based assay has a broader measurement range. Thus, the rGO–AuNP/ITO electrode can be utilized for label-free and real-time impedimetric cell-based assays with wider dynamic range.