Peroxynitrite activity of hemin-functionalized reduced graphene oxide

A hemin/rGO/MWCNT nanocomposite-based dual signal electrochemical aptasensor for sensitive detection of NSE

Neuron-specific enolase (NSE), a tumor marker of small cell lung cancer (SCLC), has high application value in the early diagnosis of SCLC. In this study, a dual signal electrochemical aptasensor for NSE was constructed based on hemin/reduced graphene oxide/multi-walled carbon nanotube (H-rGO-MWCNT) nanocomposites. Hemin played a dual role, functioning not only as an in situ electrochemical probe but also exhibiting excellent peroxidase-like properties, effectively catalyzing the electroreduction of H2O2. Reduced graphene oxide and multi-walled carbon nanotubes exhibited excellent conductivity. Through their binding with hemin, the nanocomposites achieved a larger specific surface area, providing numerous active sites for capturing the NSE aptamer. In the presence of NSE, the specific adsorption between the antigen and the aptamer formed a stable antigen-aptamer structure, which inhibited the performance of hemin, resulting in the weakening of the electrochemical signals of hemin and H2O2. Leveraging these characteristics, the sensitive and cost-effective dual-signal electrochemical aptasensor has been fabricated for the detection of NSE. One signal corresponded to differential pulse voltammetry (DPV) of hemin, while the other signal was derived from chronoamperometry, capturing the catalytic reduction of H2O2. The linear ranges for NSE were 1 pg mL-1 to 1 μg mL-1 and 100 pg mL-1 to 100 ng mL-1 with the limit of detection (LOD) of 0.21 pg mL-1 and 11.22 pg mL-1 by DPV and chronoamperometry, respectively. In addition, this aptasensor exhibited good reproducibility, stability and specificity. The recovery of NSE in human blood serum samples was from 89% to 131%. It provided a promising strategy for the detection of NSE in clinical diagnostics.

Sustainable and cascaded catalytic hairpin assembly for amplified sensing of microRNA biomarkers in living cells

The sensing of intracellular microRNAs (miRNAs) is of significance for early-stage disease diagnosis and therapeutic monitoring. DNA is an interesting building material that can be programed into assemblies with rigid and branched structures, especially suitable for imaging intracellular biomolecules or therapeutic drug delivery. Here, by introducing the palindromic sequences into the programmable DNA hairpins, we describe an endogenous target-responsive three-way branched and palindrome-assisted catalytic hairpin assembly (3W-pCHA) approach for imaging miRNA-155 of living tumor cells with high sensitivity. The miRNA-155 triggers autonomous assembly of the fluorescently quenched signal hairpin and two hairpin dimers formed via hybridization of their respective palindromic sequences to yield branched DNA junctions, which carry the unopened hairpins and thus provide addressable substrates for continuous assembly formation of DNA nanostructures. During the formation of the DNA nanostructures, the miRNA-155 is cyclically reused and many signal probes are unfolded to show highly intensified fluorescence for detecting miRNA-155 down to 6.9 pM in vitro with high selectivity. More importantly, these probes can be transfected into live cancer cells to initiate the assembly process triggered by intracellular miRNA-155, which provides a new way for imaging highly under-expressed miRNAs in cells. Besides, this approach can also be employed to differentiate miRNA-155 expression variations in different cells, indicating its promising potentials for early-stage disease diagnosis and biological studies in cells.

GNP-CeO2- polyaniline hybrid hydrogel for electrochemical detection of peroxynitrite anion and its integration in a microfluidic platform

Peroxynitrite anion (ONOO^-) is an important in vivo oxidative stress biomarker whose aberrant levels have pathophysiological implications. In this study, an electrochemical sensor for ONOO^- detection was developed based on graphene nanoplatelets-cerium oxide nanocomposite (GNP-CeO₂) incorporated polyaniline (PANI) conducting hydrogels. The nanocomposite-hydrogel platform exhibited distinct synergistic advantages in terms of large electroactive surface coverage and providing a conductive pathway for electron transfer. Besides, the 3D porous structure of hydrogel integrated the GNP-CeO₂ nanocomposite to provide hybrid materials for the evolution of catalytic activity towards electrochemical oxidation of ONOO^-. Various microscopic and spectroscopic characterization techniques endorsed the successful formation of GNP-CeO₂-PANI hydrogel. Cyclic voltammetry (CV) measurements of GNP-CeO₂-PANI hydrogel modified screen-printed electrodes (SPE) were carried out to record the current changes influenced by ONOO^-. The prepared sensor demonstrated a significant dose-dependent increase in CV peak current within a linear range of 5-100 µM (at a potential of 1.12 V), and a detection limit of 0.14 with a sensitivity of 29.35 ± 1.4 μA μM^-1. Further, a customized microfluidic flow system was integrated with the GNP-CeO₂-PANI hydrogel modified SPE to enable continuous electrochemical detection of ONOO^- at low sample volumes. The developed microfluidic electrochemical device demonstrated an excellent sensitivity towards ONOO^- under optimal experimental conditions. Overall, the fabricated microfluidic device with hybrid hydrogels as electrochemical interfaces provides a reliable assessment of ONOO^- levels. This work offers considerable potential for understanding the oxidative stress-related disease mechanisms through determination of ONOO^- in biological samples.

The Scavenging Effect of Myoglobin from Meat Extracts toward Peroxynitrite Studied with a Flow Injection System Based on Electrochemical Reduction over a Screen-Printed Carbon Electrode Modified with Cobalt Phthalocyanine: Quantification and Kinetics

The scavenging activity of myoglobin toward peroxynitrite (PON) was studied in meat extracts, using a new developed electrochemical method (based on cobalt phthalocyanine-modified screen-printed carbon electrode, SPCE/CoPc) and calculating kinetic parameters of PON decay (such as half-time and apparent rate constants). As reactive oxygen/nitrogen species (ROS/RNS) affect the food quality, the consumers can be negatively influenced. The discoloration, rancidity, and flavor of meat are altered in the presence of these species, such as PON. Our new highly thermically stable, cost-effective, rapid, and simple electrocatalytical method was combined with a flow injection analysis system to achieve high sensitivity (10.843 nA µM⁻¹) at a nanomolar level LoD (400 nM), within a linear range of 3–180 µM. The proposed biosensor was fully characterized using SEM, FTIR, Raman spectroscopy, Cyclic Voltammetry (CV), Differential Pulse Voltammetry (DPV), and Linear Sweep Voltammetry (LSV). These achievements were obtained due to the CoPc-mediated reduction of PON at very low potentials (around 0.1 V vs. Ag/AgCl pseudoreference). We also proposed a redox mechanism involving two electrons in the reduction of peroxynitrite to nitrite and studied some important interfering species (nitrite, nitrate, hydrogen peroxide, dopamine, ascorbic acid), which showed that our method is highly selective. These features make our work relevant, as it could be further applied to study the kinetics of important oxidative processes in vivo or in vitro, as PON is usually present in the nanomolar or micromolar range in physiological conditions, and our method is sensitive enough to be applied.

Enhanced chemodynamic therapy at weak acidic pH based on g-C3N4-supported hemin/Au nanoplatform and cell apoptosis monitoring during treatment

Chemodynamic therapy (CDT), inducing tumor cell apoptosis through Fenton reaction to produce hydroxyl radical (·OH), is an emerging cancer treatment technology. Highly efficient Fenton catalytic reactions usually take place at a low pH environment. Utilizing graphitic carbon nitride supported hemin and Au nanoparticles (g-C₃N₄/hemin/Au) as a novel biomimetic nanocatalyst, we achieve an enhanced CDT for inducing tumor cell apoptosis in the presence of excess H₂O₂, and reveal the molecular events during the CDT-induced apoptosis. The prepared g-C₃N₄/hemin/Au nanohybrids exhibit excellent Fenton catalytic activity for the generation of highly toxic ·OH at weak acidic and neutral condition, which breaks through the limitation of traditional acidity-dependent response. The Fenton catalytic mechanism was also studied. The Fenton efficiency is primarily enhanced by the high affinity between nanohybrids and H₂O₂, and the transformation of Fe(III) to Fe(IV)=O without the formation of iron hydrate precipitation. Moreover, the intracellular molecular events during the CDT process were monitored. Phenylalanine metabolism was perturbed with protein degradation and DNA structures were damaged, which eventually lead to cell apoptosis. This study provides a significant guidance for the further development of more effective CDT platforms.

A novel Fe-hemin-metal organic frameworks supported on chitosan-reduced graphene oxide for real-time monitoring of H2O2 released from living cells

Herein, a kind of novel hemin-based metal organic frameworks (Fe-hemin-MOFs) with unique peroxidase-like bioactivity was developed for the first time. The synthesized Fe-hemin-MOFs exhibited satisfactory catalytic activity toward hydrogen peroxide (H₂O₂). When it was further supported on Chitosan-reduced graphene oxide (CS-rGO), amplified electrochemical signal could be obtained. The Fe-hemin-MOFs/CS-rGO composite was used to construct a novel H₂O₂ electrochemical sensor. The electrocatalytic reduction of H₂O₂ displayed two segments linearity range from 1 to 61 μM and 61-1311 μM, as well as a low detection limit of 0.57 μM. Furthermore, the proposed sensor was successfully used for real-time monitoring of H₂O₂ released from living cells, which extended the practical application of MOFs-based sensors in monitoring the pathological process in living cells.

Synthetic melanin nanoparticles as peroxynitrite scavengers, photothermal anticancer and heavy metals removal platforms

Melanin is a ubiquitous natural polyphenolic pigment with versatile applications including physiological functions. This polymeric material is found in a diversity of living organisms from bacteria to mammals. The biocompatibility and thermal stability of melanin nanoparticles make them good candidates to work as free radical scavengers and photothermal anticancer substrates. Research studies have identified melanin as an antioxidative therapeutic agent and/or reactive oxygen species (ROS) scavenger that includes neutralization of peroxynitrite. In addition, melanin nanoparticles have emerged as an anticancer photothermal platform that has the capability to kill cancer cells. Recently, melanin nanoparticles have been successfully used as chelating agents to purify water from heavy metals, such as hexavalent chromium. This review article highlights some selected aspects of cutting-edge melanin applications. Herein, we will refer to the recent literature that addresses melanin nanoparticles and its useful physicochemical properties as a hot topic in biomaterial science. It is expected that the techniques of Dynamic Light Scattering (DLS), Scanning Electron Microscopy (SEM), and time-resolved Electron Paramagnetic Resonance (EPR) will have a strong impact on the full characterization of melanin nanoparticles and the subsequent exploration of their physiological and chemical mechanisms.

A novel electrochemical sensor based on microporous polymeric nanospheres for measuring peroxynitrite anion released by living cells and studying the synergistic effect of antioxidants

Peroxynitrite anion (ONOO-) is a crucial reactive nitrogen species (RNS), which has aroused immense research interest in the biological and biomedical fields because aberrant expression levels of ONOO- are related to many diseases. In this work, a novel electrochemical sensor is described for the detection of peroxynitrite anion (ONOO-) released from living cells. It is constructed with a glassy carbon electrode (GCE) decorated with a nanocomposite (CTS-MPNS) synthesized from chitosan (CTS) functionalized microporous polymeric nanospheres (MPNS). The prepared CTS-MPNS/GCE sensor shows a supernormal manifestation in measuring ONOO- in a wide range of concentrations from 3.83 nM to 0.104 mM, and the detection limit is as low as 1.28 nM (S/N = 3), which makes it possible to detect trace amounts of ONOO- released from U87 cells. Significantly, the synergistic effect of different antioxidants on scavenging ONOO- in biological systems is further studied by an electrochemical method for the first time, which provides an efficient strategy for protecting cells against oxidative stress. The developed platform and the efficient strategy may pave the way for their future applications in the field of biomedicine and the treatment of cancer diseases.

Analysis of poly(ADP-ribose) polymerase-1 by enzyme-initiated auto-PARylation-controlled aggregation of hemin-graphene nanocomposites

Poly(ADP-ribose) polymerase-1 (PARP-1) is a highly conserved nuclear enzyme, which binds tightly to damaged DNA and plays a key role in DNA repair, recombination, proliferation, and genomic stability. However, due to the poor electrochemical and optical activity of PARP-1 and its product PAR, only a few studies on its activity detection method have been reported. Herein, we report a simple and sensitive colorimetric strategy to monitor PARP-1 activity based on enzyme-initiated auto-PARylation-controlled aggregation of hemin-graphene nanocomposites (H-GNs). PARP, activated by dsDNA, catalyzed its substrate nicotinamide adenine dinucleotide (NAD+) to polymerize as a poly(ADP-ribose) polymer (PAR). PAR possesses several negative charges, and its charge density is twice that of a single-stranded DNA, which greatly impacts the dispersibility of H-GNs; due to their peroxidase-like catalytic activities, H-GNs can catalyze the chromogenic reaction of TMB and H2O2. As a result, in the presence of different PARP-1 activities, the supernatant of the corresponding solution contained different amounts of dispersed H-GNs and showed different colors after the chromogenic reaction that could be discerned easily by the absorbance or the color changes of the solution. The method was simple, sensitive, and reliable. The proposed method displays a linear range from 0.05 to 1 U with a detection limit of 0.03 U. In addition, this new method has been successfully applied to detect PARP-1 activity in human serum and different cancer cells and evaluate PARP-1 inhibitors.

A novel absorption spectrometric method, based on graphene nanomaterials, for detection of hepatocellular carcinoma-specific T lymphocyte cells

Introduction

Detection of antigen-specific cytotoxic T lymphocytes (CTLs) is the foundation for understanding hepatocellular carcinoma immune pathology and hepatocellular carcinoma immunotherapy. However, the classical method for labeling CTLs, major histocompatibility complex (MHC)–peptide tetramer, has drawbacks and needs further improvement.

Materials and methods

Here, as a new detection probe, a graphene-based MHC–peptide multimer was developed for sensitively and selectively identifying hepatocellular carcinoma-specific T-cells. To assess its detection efficiency, reduced graphene oxide (RGO) was functionalized with hemin and streptavidin to prepare a functionalized HRGO–streptavidin complex. Biotinylated MHC–peptide monomer was subsequently constructed onto HRGO to generate a detection probe for CTL labeling. The number of T-cells was detected through the reaction between HRGO and tetramethylbenzidine.

Results

Using HRGO/MHC–peptide multimers, the number of T-cells was efficiently detected in both the induction system in vitro and in peripheral blood of patients.

Conclusion

HRGO/MHC-peptide multimers methodology has application prospects in the detection of antigen peptide-specific T cells.

Electrophoretic Approach for the Simultaneous Deposition and Functionalization of Reduced Graphene Oxide Nanosheets with Diazonium Compounds: Application for Lysozyme Sensing in Serum

Electrophoretic deposition (EPD) of reduced graphene oxide nanosheets (rGO) offers several advantages over other surface coating approaches, including process simplicity, uniformity of the deposited films, and good control of the film thickness. The EPD conditions might also be of interest for the reduction of diazonium salts, which upon the release of N₂ molecules and generation of radicals, can form covalent bonds with the sp² hybridized carbon lattice atoms of rGO films. In this work, we report on the coating of gold electrodes in one step with rGO/polyethylenimine (PEI) thin films and their simultaneous modification using different phenyl (Ph) diazonium salt precursors bearing various functionalities such as -B(OH)₂, -COOH, and -C≡CH. We show further the interest of such interfaces for designing highly sensitive sensing platforms. Azide-terminated lysozyme aptamers were clicked onto the rGO/PEI/Ph-alkynyl matrix and used for the sensing of lysozyme levels in patients suffering from inflammatory bowel disease (IBD), where lysozyme levels are up-regulated. The approach attained the required demand for the determination of lysozyme level in patients suffering from IBD with a 200 fM detection limit and a linear range up to 20 pM without signal amplification.

Bioapplications of Electrochemical Sensors and Biosensors

Recent progress in the electrochemical field enabled development of miniaturized sensing devices that can be used in biological settings to obtain fundamental and practical biochemically relevant information on physiology, metabolism, and disease states in living systems. Electrochemical sensors and biosensors have demonstrated potential for rapid, real-time measurements of biologically relevant molecules. This chapter provides an overview of the most recent advances in the development of miniaturized sensors for biological investigations in living systems, with focus on the detection of neurotransmitters and oxidative stress markers. The design of electrochemical (bio)sensors, including their detection mechanism and functionality in biological systems, is described as well as their advantages and limitations. Application of these sensors to studies in live cells, embryonic development, and rodent models is discussed.

Peroxynitrite Sensor Based on a Screen Printed Carbon Electrode Modified with a Poly(2,6-dihydroxynaphthalene) Film

For the first time the electropolymerization of 2,6-dihydroxynaphthalene (2,6-DHN) on a screen printed carbon electrode (SPCE) was investigated and evaluated for peroxynitrite (PON) detection. Cyclic voltammetry was used to electrodeposit the poly(2,6-DHN) on the carbon electrode surface. The surface morphology and structure of poly(2,6-DHN) film were investigated by SEM and FTIR analysis, and the electrochemical features by cyclic voltammetry. The poly(2,6-DHN)/SPCE sensor showed excellent electrocatalytic activity for PON oxidation in alkaline solutions at very low potentials (0-100 mV vs. Ag/AgCl pseudoreference). An amperometric FIA (flow injection analysis) system based on the developed sensor was optimized for PON measurements and a linear concentration range from 2 to 300 μM PON, with a LOD of 0.2 μM, was achieved. The optimized sensor inserted in the FIA system exhibited good sensitivity (4.12 nA·μM^-1), selectivity, stability and intra-/inter-electrode reproducibility for PON determination.

Low potential detection of indole-3-acetic acid based on the peroxidase-like activity of hemin/reduced graphene oxide nanocomposite

An amperometric sensor was firstly established for the detection of indole-3-acetic acid (IAA) at low potential based on the hemin/reduced graphene oxide (hemin/rGO) composite. The hemin/rGO nanocomposite was prepared by a simple and facile hydrothermal method without using any reducing agent. It exhibited peroxidase-like activity for the catalytic oxidation of IAA in the presence of oxygen. The consumption of oxygen has a linear relationship with the concentration of IAA in the range from 0.1 to 43μM and from 43 to 183μM. The detection limit was down to 0.074μM. This sensor was unaffected by many interfering substances and stable over time. Such work broadened the application of hemin/rGO and provided a new method for IAA detection.

Electrochemical detection of peroxynitrite using hemin-PEDOT functionalized boron-doped diamond microelectrode

Peroxynitrite is a potent nitroxidation agent and highly reactive metabolite, clinically correlated with a rich pathophysiology. Its sensitive and selective detection is challenging due to its high reactivity and short sub-second lifetime. Boron-doped diamond (BDD) microelectrodes have attracted interest because of their outstanding electroanalytical properties that include a wide working potential window and enhanced signal-to-noise ratio. Herein, we report on the modification of a BDD microelectrode with an electro-polymerized film of hemin and polyethylenedioxythiophene (PEDOT) for the purpose of selectively quantifying peroxynitrite. The nanostructured modified polymer layer was characterized by Raman spectroscopy and scanning electron microscopy (SEM). The electrochemical response to peroxynitrite was studied by voltammetry and time-based amperometry. The measured detection limit was 10 ± 0.5 nM (S/N = 3), the sensitivity was 4.5 ± 0.5 nA nM(-1) and the response time was 3.5 ± 1 s. The hemin-PEDOT BDD sensors exhibited a response variability of 5% or less (RSD). The stability of the sensors after a 20-day storage in 0.1 M PB (pH 7.4) at 4 °C was excellent as at least 93% of the initial response to 50 nM PON was maintained. The presence of PEDOT was correlated with a sensitivity increase.

Highly stable biomolecule supported by gold nanoparticles/graphene nanocomposite as a sensing platform for H2O2 biosensor application

Highly stable biomolecule supported by AuNPs assisted with graphene nanocomposite as a sensing platform for H₂O₂ biosensor application.

Reduced graphene oxide-Hemin-Au nanohybrids: Facile one-pot synthesis and enhanced electrocatalytic activity towards the reduction of hydrogen peroxide

A facile and effective strategy is demonstrated for the synthesis of ternary reduced graphene oxide-Hemin-Au (rGO-H-Au) nanohybrids. The nanohybrids were synthesized through a one-pot in situ reduction of GO and HAuCl4 under alkaline conditions using GO, Hemin and HAuCl4 as the starting materials. The synthesis process can be finished within 1h in a solution phase, without adding any additional surfactant, stabilizing agent and toxic or harsh chemical reducing agents. The resulting nanohybrids were characterized by UV-vis spectroscopy, Raman spectroscopy, transmission electron microscopy (TEM), and so on. Electrochemical measurements showed that the rGO-H-Au nanohybrids exhibited good electrocatalytic activity for the reduction of hydrogen peroxide (H2O2). Based on this property, a simple and highly sensitive amperometric biosensor for H2O2 had been developed. The linear relationships were obtained from 0.1 µM to 40 µM and the detection limit was estimated to be 30 nM. The simple and sensitive sensing platform showed great promising applications in the pharmaceutical, clinical and industrial detection of H2O2.

Infrared Photothermal Therapy with Water Soluble Reduced Graphene Oxide: Shape, Size and Reduction Degree Effects

In this work, we investigate the effects of lateral size and reduction level of polyethylene glycol (PEG)-modified graphene oxide (GO) nanosheets on the photothermal properties. PEG-modified GO (GO–PEG) and reduced graphene oxide (rGO–PEG) matrices were synthesized through amide bond formation between the carboxyl groups of carboxylated GO and rGO and the amine groups of a PEG linker. We found that the reaction temperature has an important influence on the morphology and size of the pegylated nanostructures. While rGO–PEG formed at 80°C is of nanometer size, the GO–PEG, prepared at room temperature, has needle-like shape with micrometric dimensions. The rGO–PEG matrix was found to be highly soluble under physiological conditions with no aggregation observed even after 6 months of storage. The cytotoxicity of both matrices as well as their photothermal properties to ablate cervical HeLa cancer cells and MDA-MB-231 human breast carcinoma cells were studied. There was no sign of acute toxicity of rGO–PEG for HeLa and MDA-MB-31 cancer cells over a wide concentration range. A complete destruction of the tumor cells could be achieved with a laser power of 6 W cm-2 and a concentration of 60 μg mL-1 of rGO–PEG.

A graphene/hemin hybrid material as an efficient green catalyst for stereoselective olefination of aldehydes

A hemin/graphene composite was investigated for olefination of aldehydes using ethyl diazoacetate in the presence of triphenylphosphine.

Cobalt phthalocyanine tetracarboxylic acid modified reduced graphene oxide: a sensitive matrix for the electrocatalytic detection of peroxynitrite and hydrogen peroxide

The electrocatalytic properties of cobalt phthalocyanine modified reduced graphene oxide for peroxynitrite and hydrogen peroxide are investigated.

Laser-scribed graphene presents an opportunity to print a new generation of disposable electrochemical sensors

Graphene application within electrochemical sensing has been widely reported, but mainly as a composite, which adds summative effects to an underlying electrode. In this work we report the use of laser-scribed graphene as a distinct electrode patterned on a non-conducting flexible substrate. The laser-scribed graphene electrode compared favourably to established carbon macroelectrodes when evaluating both inner sphere and outer sphere redox probes, providing promise of extensive utility as an electrochemical sensor. The laser-scribed graphene electrode demonstrated the fastest heterogeneous electron transfer rate of all the electrodes evaluated with a k(0) of 0.02373 cm s(-1) for potassium ferricyanide, which exceeds commercially available edge plane pyrolytic graphite at 0.00260 cm s(-1), basal plane pyrolytic graphite at 0.00033 cm s(-1) and the very slow and effectively irreversible electrochemistry observed using single layer graphene. Finally and most significantly, a proof of principle system was fabricated using the laser-scribed graphene as working electrode, counter electrode and underlying base for the Ag/AgCl reference electrode, all in situ on the same planar flexible substrate, removing the requirement of macroscale external electrodes. The planar three electrode format operated with the same optimal electrode characteristics. Furthermore, the fabrication is inexpensive, scalable and compatible with a disposable biosensor format, considerably widening the potential applications in electrochemical bio-sensing for laser-scribed graphene.