Superoxide dismutase-based third-generation biosensor for superoxide anion

Real-time monitoring of cellular superoxide anion release in THP-1 cells using a catalytically amplified superoxide dismutase-based microbiosensor

Reactive oxygen species (ROS) including the superoxide anion (O2•-) are typically studied in cell cultures using fluorescent dyes, which provide only discrete single-point measurements. These methods lack the capabilities for assessing O2•- kinetics and release in a quantitative manner over long monitoring times. Herein, we present the fabrication and application of an electrochemical biosensor that enables real-time continuous monitoring of O2•- release in cell cultures for extended periods (> 8 h) using an O2•- specific microelectrode. To achieve the sensitivity and selectivity requirements for cellular sensing, we developed a biohybrid system consisting of superoxide dismutase (SOD) and Ti3C2Tx MXenes, deposited on a gold microwire electrode (AuME) as O2•- specific materials with catalytic amplification through the synergistic action of the enzyme and the biomimetic MXenes-based structure. The biosensor demonstrated a sensitivity of 18.35 nA/μM with a linear range from 147 to 930 nM in a cell culture medium. To demonstrate its robustness and practicality, we applied the biosensor to monitor O2•- levels in human leukemia monocytic THP-1 cells upon stimulation with lipopolysaccharide (LPS). Using this strategy, we successfully monitored LPS-induced O2•- in THP-1 cells, as well as the quenching effect induced by the ROS scavenger N-acetyl-L-cysteine (NAC). The biosensor is generally useful for exploring the role of oxidative stress and longitudinally monitoring O2•- release in cell cultures, enabling studies of biochemical processes and associated oxidative stress mechanisms in cellular and other biological environments.

H/D Exchange of Aromatic Sulfones via Base Promotion and Silver Catalysis

Aromatic sulfones are the prevailing scaffolds in pharmaceutical and material sciences. However, compared to their widespread application, the selective deuterium labeling of these structures is restricted due to their electron-deficient properties. This study presents two comprehensive strategies for the deuteration of aromatic sulfones. The base-promoted deuteration uses DMSO-d6 as the deuterium source, resulting in a rapid H/D exchange within 2 h. Meanwhile, a silver-catalyzed protocol offers a much milder option by using economical D2O to furnish the labeled sulfones.

Advancements in Brain Research: The In Vivo/In Vitro Electrochemical Detection of Neurochemicals

Neurochemicals, crucial for nervous system function, influence vital bodily processes and their fluctuations are linked to neurodegenerative diseases and mental health conditions. Monitoring these compounds is pivotal, yet the intricate nature of the central nervous system poses challenges. Researchers have devised methods, notably electrochemical sensing with micro-nanoscale electrodes, offering high-resolution monitoring despite low concentrations and rapid changes. Implantable sensors enable precise detection in brain tissues with minimal damage, while microdialysis-coupled platforms allow in vivo sampling and subsequent in vitro analysis, addressing the selectivity issues seen in other methods. While lacking temporal resolution, techniques like HPLC and CE complement electrochemical sensing's selectivity, particularly for structurally similar neurochemicals. This review covers essential neurochemicals and explores miniaturized electrochemical sensors for brain analysis, emphasizing microdialysis integration. It discusses the pros and cons of these techniques, forecasting electrochemical sensing's future in neuroscience research. Overall, this comprehensive review outlines the evolution, strengths, and potential applications of electrochemical sensing in the study of neurochemicals, offering insights into future advancements in the field.

Direct real-time measurements of superoxide release from skeletal muscles in rat limbs and human blood platelets using an implantable Cytochrome C microbiosensor

Oxidative stress and excessive accumulation of the superoxide (O2.-) anion are at the genesis of many pathological conditions and the onset of several diseases. The real time monitoring of (O2.-) release is important to assess the extent of oxidative stress in these conditions. Herein, we present the design, fabrication and characterization of a robust (O2.-) biosensor using a simple and straightforward procedure involving deposition of a uniform layer of L-Cysteine on a gold wire electrode to which Cytochrome C (Cyt c) was conjugated. The immobilized layers, studied using conductive Atomic Force Microscopy (c-AFM) revealed a stable and uniformly distributed redox protein on the gold surface, visualized as conductivity and surface topographical plots. The biosensor enabled detection of (O2.-) at an applied potential of 0.15 V with a sensitivity of 42.4 nA/μM and a detection limit of 2.4 nM. Utility of the biosensor was demonstrated in measurements of real time (O2.-) release in activated human blood platelets and skeletal rat limb muscles following ischemia reperfusion injury (IRI), confirming the biosensor's stability and robustness for measurements in complex biological systems. The results demonstrate the ability of these biosensors to monitor real time release of (O2.-) and estimate the extent of oxidative injury in models that could easily be translated to human pathologies.

Bioinspired Cu-based metal-organic framework mimicking SOD for superoxide anion sensing and scavenging

Superoxide anion (O₂^•-) is typically produced in living cells and organisms, while excess O₂^•- may cause unexpected damage, so monitoring and scavenging the O₂^•- is of considerable significance to exploring physiological and pathological process. In this study, a Cu-based metal-organic framework (Cu-MOF) which comprise sequential Cu metal ion and conductive organic 2,5-dicarboxylic acid-3,4-ethylene dioxythiophene is synthesized to mimic superoxide dismutase (SOD), in which Cu is the essence of active site. On one hand, the Cu-MOF possesses excellent electrocatalytic activity to detect O₂^•- at -0.05 V, biased at which potential the electrode showed good linearity toward O₂^•- with detection limit of 0.283 μM and interference immunity for AA, DA, UA, 5-HT and H₂O₂. The Cu-MOF modified microelectrode was applied for measuring the O₂^•- released from living cells real time and monitoring O₂^•- generation in rat brain. On the other hand, this Cu-MOF has the catalytic activity to mimic the superoxide dismutase for scavenging O₂^•- in HeLa cells effectively. This work provides a methodology to design metal ion based enzyme mimetic for analyzing and scavenging O₂^•- in cells and in vivo.

Implantable Electrochemical Sensors for Brain Research

Implantable electrochemical sensors provide reliable tools for in vivo brain research. Recent advances in electrode surface design and high-precision fabrication of devices led to significant developments in selectivity, reversibility, quantitative detection, stability, and compatibility of other methods, which enabled electrochemical sensors to provide molecular-scale research tools for dissecting the mechanisms of the brain. In this Perspective, we summarize the contribution of these advances to brain research and provide an outlook on the development of the next generation of electrochemical sensors for the brain.

Review of Bacterial Nanocellulose-Based Electrochemical Biosensors: Functionalization, Challenges, and Future Perspectives

Electrochemical biosensing devices are known for their simple operational procedures, low fabrication cost, and suitable real-time detection. Despite these advantages, they have shown some limitations in the immobilization of biochemicals. The development of alternative materials to overcome these drawbacks has attracted significant attention. Nanocellulose-based materials have revealed valuable features due to their capacity for the immobilization of biomolecules, structural flexibility, and biocompatibility. Bacterial nanocellulose (BNC) has gained a promising role as an alternative to antifouling surfaces. To widen its applicability as a biosensing device, BNC may form part of the supports for the immobilization of specific materials. The possibilities of modification methods and in situ and ex situ functionalization enable new BNC properties. With the new insights into nanoscale studies, we expect that many biosensors currently based on plastic, glass, or paper platforms will rely on renewable platforms, especially BNC ones. Moreover, substrates based on BNC seem to have paved the way for the development of sensing platforms with minimally invasive approaches, such as wearable devices, due to their mechanical flexibility and biocompatibility.

Real-Time Monitoring of Neurotransmitters in the Brain of Living Animals

Neurotransmitters, as important chemical small molecules, perform the function of neural signal transmission from cell to cell. Excess concentrations of neurotransmitters are often closely associated with brain diseases, such as Alzheimer's disease, depression, schizophrenia, and Parkinson's disease. On the other hand, the release of neurotransmitters under the induced stimulation indicates the occurrence of reward-related behaviors, including food and drug addiction. Therefore, to understand the physiological and pathological functions of neurotransmitters, especially in complex environments of the living brain, it is urgent to develop effective tools to monitor their dynamics with high sensitivity and specificity. Over the past 30 years, significant advances in electrochemical sensors and optical probes have brought new possibilities for studying neurons and neural circuits by monitoring the changes in neurotransmitters. This Review focuses on the progress in the construction of sensors for in vivo analysis of neurotransmitters in the brain and summarizes current attempts to address key issues in the development of sensors with high selectivity, sensitivity, and stability. Combined with the latest advances in technologies and methods, several strategies for sensor construction are provided for recording chemical signal changes in the complex environment of the brain.

In Vivo Electrochemical Biosensors: Recent Advances in Molecular Design, Electrode Materials, and Electrochemical Devices

Electrochemical biosensors provide powerful tools for dissecting the dynamically changing neurochemical signals in the living brain, which contribute to the insight into the physiological and pathological processes of the brain, due to their high spatial and temporal resolutions. Recent advances in the integration of in vivo electrochemical sensors with cross-disciplinary advances have reinvigorated the development of in vivo sensors with even better performance. In this Review, we summarize the recent advances in molecular design, electrode materials, and electrochemical devices for in vivo electrochemical sensors from molecular to macroscopic dimensions, highlighting the methods to obtain high performance for fulfilling the requirements for determination in the complex brain through flexible and smart design of molecules, materials, and devices. Also, we look forward to the development of next-generation in vivo electrochemical biosensors.

Real-Time Tracking of Electrical Signals and an Accurate Quantification of Chemical Signals with Long-Term Stability in the Live Brain

The development of in vivo analytical tools and methods for recording electrical signals and accurately quantifying chemical signals is a key issue for a comprehensive understanding of brain events. The electrophysiological microelectrode was invented to monitor electrical signals in free-moving brains. On the other hand, electrochemical assays with excellent spatiotemporal resolution provide an effect way to monitor chemical signals in vivo. Unfortunately, the in vivo electrochemical biosensors still have three limitations. First, many biological species such as reactive oxygen species (ROS) and neurotransmitters demonstrate large overpotentials at conventional electrodes. Thus, it is hard to convert the chemical/electrochemical signals of these molecules into electric signals. Second, the interfacial properties of the recognition molecules assembled onto the electrode surfaces have a great influence on the transmission of electric charge through the interface and the stability of the modified recognition molecules. Meanwhile, the surface of biosensors implanted in the brain is easily absorbed by many proteins present in the brain, resulting in the loss of signals. Finally, activities in the brain including neuron discharges and electrophysiological signals may be affected by electrochemical measurements due to the application of extra potentials and/or currents.This Account presents a deep view of the fundamental design principles and solutions in response to the above challenges for developing in vivo biosensors with high performance while meeting the growing requirements, including high selectivity, long-time stability, and simultaneously monitoring electrical and chemical signals. We aim to highlight the basic criteria based on a double-recognition strategy for the selective biosensing of ROS, H₂S, and H_nS through the rational design of specific recognition molecules followed by electrochemical oxidation or reduction. Recent developments in designing functionalized surfaces through a systematic investigation of self-assembly with Au-S bonds, Au-Se bonds, and Au≡C bonds for facilitating electrochemical properties as well as improving the stability are summarized. More importantly, this Account highlights the novel methodologies for simultaneously monitoring electrical and chemical signals ascribed to the dynamic changes in K⁺, Na⁺, and Ca²⁺ and pH values in vivo. Additionally, SERS-based photophysiological microarray probes have been developed for quantitatively tracking chemical changes in the live brain together with recording electrophysiological signals.The design principles and novel strategies presented in this Account can be extended to the real-time tracking of electrical signals and the accurate quantification of more chemical signals such as amino acids, neurotransmitters, and proteins to understand the brain events. The final part also outlines potential future directions in constructing high-density microarrays, eventually enabling the large-scale dynamic recording of the chemical expression of multineuronal signals across the whole brain. There is still room to develop a multifiber microarray which can be coupled with photometric methods to record chemical signals both inside and outside neurons in the live brains of freely moving animals to understand physiological processes and screen drugs.

Involvement of O2·- release in zearalenone-induced hormesis of intestinal porcine enterocytes: An electrochemical sensor-based analysis

Relationship between mycotoxin-induced hormesis and reactive oxygen species (ROS) has not been systematically investigated due to the lack of an effective analysis method. To monitor cellular release and intracellular level of O2·-, carboxymethyl cellulose-Mn3(PO4)2 nanocomposite was synthesized to fabricate an electrochemical biosensor, which selectively detects O2·- over the range of 57.50 nM ∼ 2.95 μM (R2 = 0.99) with the sensitivity of 78.67 μA μM-1 cm-2 and the detection limit of 8.47 nM. Transient exposure to zearalenone (ZEA) induces the enhancement on cell viability, immediate O2·- release from cells, and reduction of intracellular O2·- level. After post-treatment culture, intracellular O2·- initially increases to a high level and then decreases to the normal level. Concurrently, the ZEA-induced hormesis disappears. Based on the findings, we propose a mechanism, involving the ROS release, increase of succinate dehydrogenase activity and recovery of intracellular ROS, to explain the occurrence and disappearance of hormesis in intestinal porcine enterocytes.

Au nanoflower film-based stretchable biosensors for in situ monitoring of superoxide anion release in cell mechanotransduction

Cell mechanotransduction plays an important role in vascular regulation and disease development.

Methods to evaluate the scavenging activity of antioxidants toward reactive oxygen and nitrogen species (IUPAC Technical Report)

This project was aimed to identify the quenching chemistry of biologically important reactive oxygen and nitrogen species (ROS/RNS, including radicals), to show antioxidant action against reactive species through H‐atom and electron transfer reactions, and to evaluate the ROS/RNS scavenging activity of antioxidants with existing analytical methods while emphasizing the underlying chemical principles and advantages/disadvantages of these methods. In this report, we focused on the applications and impact of existing assays on potentiating future research and innovations to evolve better methods enabling a more comprehensive study of different aspects of antioxidants and to provide a vocabulary of terms related to antioxidants and scavengers for ROS/RNS. The main methods comprise the scavenging activity measurement of the hydroxyl radical (•OH), dioxide(•1–) (O2 •–: commonly known as the superoxide radical), dihydrogen dioxide (H2O2: commonly known as hydrogen peroxide), hydroxidochlorine (HOCl: commonly known as hypochlorous acid), dioxidooxidonitrate(1–) (ONOO−: commonly known as the peroxynitrite anion), and the peroxyl radical (ROO•). In spite of the diversity of methods, there is currently a great need to evaluate the scavenging activity of antioxidant compounds in vivo and in vitro. In addition, there are unsatisfactory methods frequently used, such as non-selective UV measurement of H2O2 scavenging, producing negative errors due to incomplete reaction of peroxide with flavonoids in the absence of transition metal ion catalysts. We also discussed the basic mechanisms of spectroscopic and electrochemical nanosensors for measuring ROS/RNS scavenging activity of antioxidants, together with leading trends and challenges and a wide range of applications. This project aids in the identification of reactive species and quantification of scavenging extents of antioxidants through various assays, makes the results comparable and more understandable, and brings a more rational basis to the evaluation of these assays and provides a critical evaluation of existing ROS/RNS scavenging assays to analytical, food chemical, and biomedical/clinical communities by emphasizing the need for developing more refined, rapid, simple, and low‐cost assays and thus opening the market for a wide range of analytical instruments, including reagent kits and sensors.

Extremophilic Oxidoreductases for the Industry: Five Successful Examples With Promising Projections

In a global context where the development of more environmentally conscious technologies is an urgent need, the demand for enzymes for industrial processes is on the rise. Compared to conventional chemical catalysts, the implementation of biocatalysis presents important benefits including higher selectivity, increased sustainability, reduction in operating costs and low toxicity, which translate into cleaner production processes, lower environmental impact as well as increasing the safety of the operating staff. Most of the currently available commercial enzymes are of mesophilic origin, displaying optimal activity in narrow ranges of conditions, which limits their actual application under industrial settings. For this reason, enzymes from extremophilic microorganisms stand out for their specific characteristics, showing higher stability, activity and robustness than their mesophilic counterparts. Their unique structural adaptations allow them to resist denaturation at high temperatures and salinity, remain active at low temperatures, function at extremely acidic or alkaline pHs and high pressure, and participate in reactions in organic solvents and unconventional media. Because of the increased interest to replace chemical catalysts, the global enzymes market is continuously growing, with hydrolases being the most prominent type of enzymes, holding approximately two-third share, followed by oxidoreductases. The latter enzymes catalyze electron transfer reactions and are one of the most abundant classes of enzymes within cells. They hold a significant industrial potential, especially those from extremophiles, as their applications are multifold. In this article we aim to review the properties and potential applications of five different types of extremophilic oxidoreductases: laccases, hydrogenases, glutamate dehydrogenases (GDHs), catalases and superoxide dismutases (SODs). This selection is based on the extensive experience of our research group working with these particular enzymes, from the discovery up to the development of commercial products available for the research market.

Nonenzymatic Electrochemical Sensor with Ratiometric Signal Output for Selective Determination of Superoxide Anion in Rat Brain

There is still an urgent need to develop reliable analytical methods of O₂^•- in vivo for deeply elucidating the roles of O₂^•- playing in the brain. Herein, a nonenzymatic electrochemical sensor with ratiometric signal output was developed for an in vivo analysis of O₂^•- in the rat brain. Diphenylphosphonate-2-naphthol ester (ND) was designed and synthesized as a specific recognition molecule for the selective determination of O₂^•-. An anodic peak ascribed to the oxidation of 2-naphthol was generated via the nucleophilic substitution between ND and O₂^•- and was increased with the increasing concentration of O₂^•-. Meanwhile, the inner reference of methylene blue (MB) was co-assembled at the electrode surface to enhance the determination accuracy of O₂^•-. The anodic peak current ratio between 2-naphthol and MB exhibited a good linear relationship with the concentration of O₂^•- from 2 to 200 μM. Because of the stable molecule character of ND and its specific reaction with O₂^•-, the developed electrochemical sensor demonstrated excellent selectivity toward various potential interferences in the brain and good stability even after storage for 7 days. Accordingly, the present electrochemical sensor with high selectivity, high stability, and high accuracy was successfully exploited in monitoring the levels of O₂^•- in the rat brain and that of the diabetic model followed by cerebral ischemia.

DFT/B3LYP and BP86 examination of mononuclear half-sandwich nd7 metallo drug complexes based on N∩O dendritic scaffolds

In this paper, we have explored the bonding properties of a series of mononuclear half-sandwich nd⁷ anticancer complexes based on N∩O dendritic scaffolds (L) using two functionals (B3LYP and BP86) with generic basis set (LanL2DZ for transition metals (as well as halogen atoms) and 6-311 + G (d,p) for others atoms. The geometry optimization of structures have led to the adoption of the piano-stool environment and the formation of kings of intermolecular hydrogen bonding: CH … X (Cl,Br) (2.619-2.954) and CH...O (2.266-2.973 Å) interaction. The metal (M)-bromine bond distances have shown to be significantly higher than metal-chlorine ones. In chloride complexes, salicylaldimine ligand-Co²⁺ (-3097.15 kJ/mol) and salicylaldimine ligand-Ir²⁺ (-3436.78 kJ/mol) interactions are stronger. Except for cobalt complexes, the interaction energies are underestimated by B3LYP functional, by contrast B3LYP HOMO-LUMO gaps obtained are highly greater. The metal ion affinity (MIA) is increasing in the order: Ir⁺²<Rh⁺²<Co⁺² for both halogen ligands adopted, exception for picolinate and salicylaldimine ligands. Our results also show that the metal … oxygen, metal … nitrogen and metal … halogen interactions are closed-shell interaction. From the contribution of the ΔE_orb term in the ranges 4.06-98.61% (X = Cl) and 10.29-99.87% (X = Br), the nature of the [Formula: see text] … X^- interaction turned out to be mainly dependent on the transition metal and halogen atom involved. The smallest back-donation observed for chloride complexes corresponding to the highest barrier to the formation of [MLCP^∗]-X bond traduces that the fact that chloride complexes are the least reactive. In the majority of cases, larger donation is obtained compared to back-donation showing that the possibility of [Formula: see text] [Formula: see text] charge separation can be expected. For α rings of chloride complexes, B3LYP HOMA indexes are higher than those estimated by PB86 functional. Conversely, opposite results were found for their bromide counterparts.

Self-assembled mono- and bilayers on gold electrodes to assess antioxidants—a comparative study

Oxidative stress is considered as an imbalance of reactive species over antioxidants, leading to diseases and cell death. Various methods have been developed to determine the antioxidant potential of natural or synthetic compounds based on the ability to scavenge free radicals. However, most of them lack biological relevance. Here, a gold-based self-assembled monolayer (SAM) was compared with a gold-supported lipid bilayer as models for the mammalian cell membrane to evaluate the free radical scavenging activity of different antioxidants. The oxidative damage induced by reactive species was verified by cyclic and differential pulse voltammetry and measured by the increase of electrochemical peak current of a redox probe. Trolox, caffeic acid (CA), epigallocatechin gallate (EGCG), ascorbic acid (AA), and ferulic acid (FA) were used as model antioxidants. The change in the decrease of the electrochemical signal reflecting oxidative membrane damage confirms the expected protective role. Both model systems showed similar efficacies of each antioxidant, the achieved order of radical scavenging potential is as follows: Trolox > CA > EGCG > AA > FA. The results showed that the electrochemical assay with SAM-modified electrodes is a stable and powerful tool to estimate qualitatively the antioxidative activity of a compound with respect to cell membrane protection against biologically relevant reactive species.

In Vivo Electrochemical Sensors for Neurochemicals: Recent Update

In vivo electrochemical sensing based on implantable microelectrodes is a strong driving force of analytical neurochemistry in brain. The complex and dynamic neurochemical network sets stringent standards of in vivo electrochemical sensors including high spatiotemporal resolution, selectivity, sensitivity, and minimized disturbance on brain function. Although advanced materials and novel technologies have promoted the development of in vivo electrochemical sensors drastically, gaps with the goals still exist. This Review mainly focuses on recent attempts on the key issues of in vivo electrochemical sensors including selectivity, tissue response and sensing reliability, and compatibility with electrophysiological techniques. In vivo electrochemical methods with bare carbon fiber electrodes, of which the selectivity is achieved either with electrochemical techniques such as fast-scan cyclic voltammetry and differential pulse voltammetry or based on the physiological nature will not be reviewed. Following the elaboration of each issue involved in in vivo electrochemical sensors, possible solutions supported by the latest methodological progress will be discussed, aiming to provide inspiring and practical instructions for future research.

Tailoring pore structures with optimal mesopores to remarkably promote DNA adsorption guiding the growth of active Mn3(PO4)2 toward sensitive superoxide biomimetic enzyme sensors

The great challenge in preparing a biomimetic enzyme sensor is to have sensitivity and selectivity equal to or better than its corresponding biological sensor. Porous electrodes possess a large surface area and are often used to greatly improve the sensor sensitivity. However, how to tailor the pore structure, especially the pore size distribution to further improve the sensitivity and selectivity of a biomimetic sensor, has not been investigated yet. The superoxide anion (O2˙-) plays essential roles in various biological processes and is of importance in clinical diagnosis and life science research. It is generally detected by the superoxide dismutase enzyme. Herein, we delicately tailor the pore structure of carbon nanofibers (CNFs) by pyrolysis to obtain an optimal mesopore structure for strong adsorption of DNA, followed by guiding the growth of Mn3(PO4)2 as a biomimetic enzyme toward highly sensitive detection of O2˙-. The Mn3(PO4)2-DNA/CNF sensor achieves the best sensitivity among the reported O2˙- sensors while possessing good selectivity. The enhancement mechanism is also investigated, indicating that the mesopore ratio of CNFs plays an essential role in the high sensitivity and selectivity due to their strong adsorption of DNA for guiding the growth of a large amount of uniform sensing components, Mn3(PO4)2, toward high sensitivity and selectivity. The biomimetic sensor was further used to in situ monitor O2˙- released from human keratinocyte cells and human malignant melanoma cells under drug stimulation, showing high sensitivity to real-time quantitative detection of O2˙-. This work provides a highly sensitive in situ real-time biomimetic O2˙- sensor for applications in biological research and diagnosis, while shedding light on the enhancement mechanism of the pore structure, especially the pore size distribution of a porous electrode for high performance sensing processes.

Designing Recognition Molecules and Tailoring Functional Surfaces for In Vivo Monitoring of Small Molecules in the Brain

The in vivo analysis of chemical signals in brain extracellular fluid (ECF) using implanted electrochemical biosensors is a vital way to study brain functions and brain activity mapping. This approach offers excellent spatial (10-200 μm) and temporal (approximately second) resolution and the major advantage of long-term stability. By implantation of a microelectrode in a specific brain region, changes in the concentration of a variety of ECF chemical species can be monitored through applying a suitable electrical signal and, typically, recording the resulting Faradaic current. However, the high performance requirements for in vivo biosensors greatly limit our understanding of the roles that biomolecules play in the brain. Since a large number of biological species, including reactive oxygen species (ROS), metal ions, amino acids, and proteins, coexist in the brain and interact with each other, developing in vivo biosensors with high selectivity is a great challenge. Meanwhile, it is difficult to quantitatively determine target molecules in the brain because of the variation in the distinct environments for monitoring biomolecules in vitro and in vivo. Thus, there are large errors in the quantification of concentrations in the brain using calibration curves obtained in artificial cerebrospinal fluid (aCSF). More importantly, to gain a full understanding of the physiological and pathological processes in the brain, the development of novel approaches for the simultaneous determination of multiple species in vivo is urgently needed. This Account provides insight into the basic design principles and criteria required to convert chemical/electrochemical reactions into electric signals, while satisfying the increasing requirements, including high selectivity, sensitivity, and accuracy, for the in vivo analysis of biomolecules in the brain. Recent developments in designing various functional surfaces, such as self-assembled monolayers, gold nanostructures, and nanostructured semiconductors for facilitating electron transfer from specific enzymes, including superoxide dismutase (SOD), and further application to an O₂^•- biosensor are summarized. This Account also aims to highlight the design principles for the selective biosensing of Cu²⁺ and pH in the brain through the rational design and synthesis of specific recognition molecules. Additionally, electrochemical ratiometric biosensors with current signal output have been constructed to correct the effect of distinct environments in a timely manner, thus greatly improving the accuracy of the determination of Cu²⁺ in the live brain. This method of using a built-in element has been extended to biosensors with the potential signal output for in vivo pH analysis. More importantly, the new concept of both current and potential signal outputs provides an avenue to simultaneously determine dual species in the brain. The extension of the design principles and developed strategy demonstrated in this Account to other biomolecules, which may be closely correlated to the biological processes of brain events, is promising. The final section of this Account outlines potential future directions in tailoring functional surfaces and designing recognition molecules based on recent advances in molecular science, nanoscience and nanotechnology, and biological chemistry for the design of advanced devices with multiple target species to map the molecular imaging of the brain. There are still opportunities to engineer surfaces that improve on this approach by constructing implantable, multifunctional nanodevices that promise to combine the benefits of multiple sensing and therapeutic modules.

Novel Spectroscopic and Electrochemical Sensors and Nanoprobes for the Characterization of Food and Biological Antioxidants

Since an unbalanced excess of reactive oxygen/nitrogen species (ROS/RNS) causes various diseases, determination of antioxidants that can counter oxidative stress is important in food and biological analyses. Optical/electrochemical nanosensors have attracted attention in antioxidant activity (AOA) assessment because of their increased sensitivity and selectivity. Optical sensors offer advantages such as low cost, flexibility, remote control, speed, miniaturization and on-site/in situ analysis. Electrochemical sensors using noble metal nanoparticles on modified electrodes better catalyze bioelectrochemical reactions. We summarize the design principles of colorimetric sensors and nanoprobes for food antioxidants (including electron-transfer based and ROS/RNS scavenging assays) and important milestones contributed by our laboratory. We present novel sensors and nanoprobes together with their mechanisms and analytical performances. Our colorimetric sensors for AOA measurement made use of cupric-neocuproine and ferric-phenanthroline complexes immobilized on a Nafion membrane. We recently designed an optical oxidant/antioxidant sensor using N,N-dimethyl-p-phenylene diamine (DMPD) as probe, from which ROS produced colored DMPD-quinone cationic radicals electrostatically retained on a Nafion membrane. The attenuation of initial color by antioxidants enabled indirect AOA estimation. The surface plasmon resonance absorption of silver nanoparticles as a result of enlargement of citrate-reduced seed particles by antioxidant addition enabled a linear response of AOA. We determined biothiols with Ellman reagent-derivatized gold nanoparticles.

Effect of Nanoparticles on Modified Screen Printed Inhibition Superoxide Dismutase Electrodes for Aluminum

A novel amperometric biosensor for the determination of Al(III) based on the inhibition of the enzyme superoxide dismutase has been developed. The oxidation signal of epinephrine substrate was affected by the presence of Al(III) ions leading to a decrease in its amperometric current. The immobilization of the enzyme was performed with glutaraldehyde on screen-printed carbon electrodes modifiedwith tetrathiofulvalene (TTF) and different types ofnanoparticles. Nanoparticles of gold, platinum, rhodium and palladium were deposited on screen printed carbon electrodes by means of two electrochemical procedures. Nanoparticles were characterized trough scanning electronic microscopy, X-rays fluorescence, and atomic force microscopy. Palladium nanoparticles showed lower atomic force microscopy parameters and higher slope of aluminum calibration curves and were selected to perform sensor validation. The developed biosensor has a detection limit of 2.0 ± 0.2 μM for Al(III), with a reproducibility of 7.9% (n = 5). Recovery of standard reference material spiked to buffer solution was 103.8% with a relative standard deviation of 4.8% (n = 5). Recovery of tap water spiked with the standard reference material was 100.5 with a relative standard deviation of 3.4% (n = 3). The study of interfering ions has also been carried out.

Manganese Phosphate Self-assembled Nanoparticle Surface and Its application for Superoxide Anion Detection

Quantitative analysis of superoxide anion (O2(·-)) has increasing importance considering its potential damages to organism. Herein, a novel Mn-superoxide dismutase (MnSOD) mimics, silica-manganous phosphate (SiO2-Mn3(PO4)2) nanoparticles, were designed and synthesized by surface self-assembly processes that occur on the surface of silica-phytic acid (SiO2-PA) nanoparticles. The composite nanoparticles were characterized by fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), scanning electronic microscopy (SEM), electron diffraction pattern, energy dispersive spectroscopy (EDS) and elemental mapping. Then the electrochemical measurements of O2(·-) based on the incorporation of SiO2-Mn3(PO4)2 onto the surface of electrodes were performed, and some satisfactory results were obtained. This is the first report that manganous phosphate (Mn3(PO4)2) nanoparticles with shape-controlled, but not multilayer sheets, were utilized for O2(·-) detection. The surface self-assembly technology we proposed will offer the ideal material to construct more types biosensor and catalytic system for its nanosized effect.

New faces of porous Prussian blue: interfacial assembly of integrated hetero-structures for sensing applications

Prussian blue (PB), the oldest synthetic coordination compound, is a classic and fascinating transition metal coordination material. Prussian blue is based on a three-dimensional (3-D) cubic polymeric porous network consisting of alternating ferric and ferrous ions, which provides facile assembly as well as precise interaction with active sites at functional interfaces. A fundamental understanding of the assembly mechanism of PB hetero-interfaces is essential to enable the full potential applications of PB crystals, including chemical sensing, catalysis, gas storage, drug delivery and electronic displays. Developing controlled assembly methods towards functionally integrated hetero-interfaces with adjustable sizes and morphology of PB crystals is necessary. A key point in the functional interface and device integration of PB nanocrystals is the fabrication of hetero-interfaces in a well-defined and oriented fashion on given substrates. This review will bring together these key aspects of the hetero-interfaces of PB nanocrystals, ranging from structure and properties, interfacial assembly strategies, to integrated hetero-structures for diverse sensing.

A novel fabrication of a polymeric ionic liquid hybrid film modified electrode and its successful application to the electrogeneration of a superoxide anion in aqueous media

An ionene polymer-ionic liquid hybrid was fabricated by electro-oxidative polymerization of N,N-dimethylaniline in [MPP]⁺[N(Tf)₂]⁻, which can be applied for the electrogeneration of a superoxide anion in aqueous media.

Direct Electrochemistry and Electrocatalysis of Horseradish Peroxidase Immobilized in a DNA/Chitosan-Fe₃O₄ Magnetic Nanoparticle Bio-Complex Film

A DNA/chitosan-Fe₃O₄ magnetic nanoparticle bio-complex film was constructed for the immobilization of horseradish peroxidase (HRP) on a glassy carbon electrode. HRP was simply mixed with DNA, chitosan and Fe₃O₄ nanoparticles, and then applied to the electrode surface to form an enzyme-incorporated polyion complex film. Scanning electron microscopy (SEM) was used to study the surface features of DNA/chitosan/Fe₃O₄/HRP layer. The results of electrochemical impedance spectroscopy (EIS) show that Fe₃O₄ and enzyme were successfully immobilized on the electrode surface by the DNA/chitosan bio-polyion complex membrane. Direct electron transfer (DET) and bioelectrocatalysis of HRP in the DNA/chitosan/Fe₃O₄ film were investigated by cyclic voltammetry (CV) and constant potential amperometry. The HRP-immobilized electrode was found to undergo DET and exhibited a fast electron transfer rate constant of 3.7 s⁻¹. The CV results showed that the modified electrode gave rise to well-defined peaks in phosphate buffer, corresponding to the electrochemical redox reaction between HRP(Fe^(III)) and HRP(Fe^(II)). The obtained electrode also displayed an electrocatalytic reduction behavior towards H₂O₂. The resulting DNA/chitosan/Fe₃O₄/HRP/glassy carbon electrode (GCE) shows a high sensitivity (20.8 A·cm⁻²·M⁻¹) toward H₂O₂. A linear response to H₂O₂ measurement was obtained over the range from 2 μM to 100 μM (R² = 0.99) and an amperometric detection limit of 1 μM (S/N = 3). The apparent Michaelis-Menten constant of HRP immobilized on the electrode was 0.28 mM. Furthermore, the electrode exhibits both good operational stability and storage stability.

Two-photon ratiometric fluorescent sensor based on specific biomolecular recognition for selective and sensitive detection of copper ions in live cells

In this work, we develop a ratiometric two-photon fluorescent probe, ATD@QD-E2Zn2SOD (ATD = amino triphenylamine dendron, QD = CdSe/ZnSe quantum dot, E2Zn2SOD = Cu-free derivative of bovine liver copper-zinc superoxide dismutase), for imaging and sensing the changes of intracellular Cu(2+) level with clear red-to-yellow color change based on specific biomolecular recognition of E2Zn2SOD for Cu(2+) ion. The inorganic-organic nanohybrided fluorescent probe features two independent emission peaks located at 515 nm for ATD and 650 nm for QDs, respectively, under two-photon excitation at 800 nm. Upon addition of Cu(2+) ions, the red fluorescence of QDs drastically quenches, while the green emission from ATD stays constant and serves as a reference signal, thus resulting in the ratiometric detection of Cu(2+) with high accuracy by two-photon microscopy (TPM). The present probe shows high sensivity, broad linear range (10(-7)-10(-3) M), low detection limit down to ∼10 nM, and excellent selectivity over other metal ions, amino acids, and other biological species. Meanwhile, a QD-based inorganic-organic probe demonstrates long-term photostability, good cell-permeability, and low cytotoxicity. As a result, the present probe can visualize Cu(2+) changes in live cells by TPM. To the best of our knowledge, this is the first report for the development of a QD-based two-photon ratiometric fluorescence probe suitable for detection of Cu(2+) in live cells.