Search Results (134)

Total antioxidant capacity (TAC) reflects the collective ability of biological systems to counteract oxidative stress and is therefore an important indicator in redox biology, nutritional evaluation, and clinical assessment. Conventional TAC assays often suffer from insufficient sensitivity, pronounced matrix interference, and limited reliability in complex biological samples. Herein, we developed a redox-active lanthanide metal–organic framework (CeMOF@Tb) through mild aqueous-phase synthesis followed by post-synthetic incorporation of Tb³⁺ ions, serving as a luminescent probe for sensitive and reliable TAC analysis. The reversible Ce⁴⁺/Ce³⁺ redox couple serves as the antioxidant-responsive recognition unit, while Tb³⁺ provides a characteristic green luminescence output. The antioxidant-mediated reduction of Ce⁴⁺ to Ce³⁺ regulates the energy transfer process, thereby producing a concentration-dependent enhancement in Tb³⁺ emission and reduction in Ce³⁺ fluorescence. The sensing platform also exhibits high selectivity and strong resistance to interference from common coexisting species, supporting reliable TAC determination in complex biological matrices. Furthermore, the probe was applied to human serum samples, yielding recoveries of 91.6–122.6%. This study establishes an integrated redox-to-luminescence transduction strategy for TAC analysis and provides a versatile design framework for developing Ln-MOF-based probes for clinical biochemical applications. Full article

Hydrogen sulfide (H₂S) has emerged as an important gaseous signaling molecule involved in numerous physiological and pathological processes, including redox regulation, inflammation, and cellular signaling. Accurate detection of H₂S in biological systems is therefore essential for understanding its roles in health and disease. Among various fluorescent platforms, the 1,8-naphthalimide scaffold has attracted considerable attention due to its unique photophysical properties, structural tunability, and high sensitivity to substituent modification. This review summarizes recent advances in the development of 1,8-naphthalimide-based fluorescent probes for H₂S detection. The fundamental photophysical mechanisms associated with the 1,8-naphthalimide fluorophore, including intramolecular charge transfer (ICT), photoinduced electron transfer (PET), and Förster resonance energy transfer (FRET), are discussed in relation to probe design. Emphasis is placed on reaction-based sensing strategies, highlighting organic reactions that enable selective recognition of H₂S, such as reduction, nucleophilic addition, nucleophilic substitution, and intramolecular cyclization. Representative probes are summarized and compared with respect to sensing mechanisms and photophysical behavior. In addition, the current challenges of 1,8-naphthalimide-based H₂S probes are discussed. We hope this review will provide useful perspectives for the development of efficient 1,8-naphthalimide-based fluorescent probes for H₂S detection. Full article

The performance of coatings, corrosion barriers, photocatalysts, and tribological materials is greatly influenced by in situ surface properties, requiring highly sensitive and reproducible operando surface characterization methods. We previously developed a temperature-programmed photoelectron emission (TPPE) method to clarify electron transfer behavior on light-irradiated metal surfaces. TPPE is sensitive to surface temperature and prior chemical exposure, which affect the total photoemitted electron count (N_T), the photothreshold, and the activation energy derived from Arrhenius plots of N_T obtained during heating–cooling cycles. This study examines the reproducibility of TPPE data and the TPPE mechanisms for Cu₂O/Cu surfaces subjected to mechanical abrasion, cleaning, plasma treatment, and subsequent immersion in organic liquids. The resulting Arrhenius plots reveal both positive and negative activation energies, depending on the treatment conditions. Negative activation energies during cooling are associated with photoredox-mediated emission. TPPE is attributed to oxygen vacancies within the Cu₂O surface layer, which is interfaced with metallic Cu, serving as a direct probe of these vacancy-related states. The TPPE characteristics (N_T intensity and activation energy) following exposure to various polar and nonpolar organic molecules (e.g., acetone, toluene, hexane, and ethanol) correlate with the electronic properties of these vacancies, consistent with previous observations for ambient air, alcohol, and water vapor exposure. Under illumination, Cu₂O vacancy states enhance photocarrier extraction (electrons and holes) and accelerate surface redox reactions within adsorbed thin films, thereby improving photocatalytic performance. Notably, the solvent’s reciprocal dielectric constant significantly influences TPPE, indicative of electrostatic surface–solvent interactions. Finally, the TPPE mechanism is discussed in the context of antiviral inactivation at the metallic copper–environment interface. Full article

Foam cell formation of macrophages is a core pathological event in the progression of atherosclerosis. Investigating the changes in active molecules during macrophage foaming is critical for the early warning and mechanistic research of atherosclerosis. Superoxide anion (O₂^•−) and nitric oxide (NO) are two typical representatives of these active species; evaluating the fluctuations of O₂^•− and NO during macrophage foaming is vital for understanding the early diagnosis and pathological mechanisms of atherosclerosis. Herein, we report a fluorescent probe for the detection of O₂^•− and NO concentration changes based on the quenching effect of the urea bond and trifluoromethanesulfonate group on the fluorophore. MB-ROS features favorable sensitivity, selectivity and biocompatibility, enabling imaging of O₂^•− and NO fluctuations in macrophages. It was further validated in ox-LDL-stimulated foam cell models to visually track abnormal ROS/RNS changes during foam formation. This work offers a reliable chemical imaging tool to uncover redox imbalance underlying early atherosclerotic macrophage foaming. Full article

Reactive oxygen species (ROS) regulate cellular signaling at physiological concentrations and drive tissue damage when their generation exceeds antioxidant defenses. The conceptual reframing of the field into oxidative eustress (low, controlled redox signaling) and oxidative distress (supraphysiological levels causing biomolecular damage), alongside parallel advances in detection chemistry and genetically encoded biosensors, has transformed how investigators measure ROS in living systems. This review provides a critical, methods-focused update covering the contemporary toolkit, with particular emphasis on advances from 2015 to 2026 while incorporating earlier foundational work where it remains indispensable to interpretation. Consistent with the title and reflecting both the maturity of the available chemistry and the weight of the recent literature, our emphasis falls on hydrogen peroxide and mammalian experimental systems; superoxide, the hydroxyl radical, and singlet oxygen are addressed primarily where their detection intersects with the platforms reviewed here, and non-mammalian models are considered only selectively. Readers seeking dedicated coverage of these other species or of plant, microbial, and invertebrate systems are directed to the specialized reviews cited throughout. Five complementary measurement platforms are evaluated: (i) electron paramagnetic resonance spectroscopy with classical nitrone spin traps and the newer cyclic hydroxylamine probes; (ii) small-molecule fluorescent probes, with particular emphasis on the boronate-based, activity-based sensing platform that has supplanted 2′,7′-dichlorofluorescin diacetate for hydrogen peroxide imaging; (iii) genetically encoded biosensors of the HyPer and roGFP families, which now permit ratiometric, organelle-resolved, and longitudinal measurements; (iv) mass-spectrometry-based quantification of oxidation products and radical adducts, including isoprostanes, 2-hydroxyethidium, and redox-modified cysteines via chemical proteomics; and (v) electrochemical and nanosensor approaches enabling real-time single-cell measurements. The selectivity, sensitivity, temporal resolution, spatial resolution, and quantitative capability of each platform are critically compared. Reliance on a single non-specific probe is no longer sufficient as the sole evidence base for quantitative or species-specific claims; contemporary investigators are expected to apply complementary approaches and to validate findings across modalities. Standardization of reporting, integration with single-cell omics, and clinical translation of validated mass-spectrometry biomarkers are identified as priorities for the coming decade. Full article

The reliable detection of the peanut allergen Ara h2 in processed foods remains a major challenge, since thermal and high-pressure treatments can alter protein structure and limit the performance of immunoassays. DNA-based methods provide a robust alternative to this approach. In this work, a highly sensitive label-free electrochemical genoassay for Ara h2 DNA detection was developed using streptavidin-coated magnetic beads (MBs). A biotinylated capture probe (CP) immobilized on the MBs’ surface enabled specific target recognition through a sandwich hybridization strategy with a secondary probe, allowing for direct electrochemical detection without enzymatic labels. Two transduction strategies were evaluated: (i) electrochemical impedance spectroscopy (EIS) with ferri/ferrocyanide as a redox probe, and (ii) differential pulse voltammetry (DPV) using methylene blue. The ferri/ferrocyanide-based EIS approach showed the best sensitivity and discrimination between hybridized and non-hybridized states. A linear dependence was observed with the concentration of the synthetic Ara h2 target over the 0.05 to 20 nM range, with a detection limit of 0.025 nM. CP-MBs showed good stability for at least 20 days. Applicability was demonstrated in soy beverages, rice beverages, and low-fat cow’s milk, with recoveries close to 100% and negligible matrix effects. Full article

Photobiological hydrogen (H₂) production by microalgae and cyanobacteria is widely seen as a promising and sustainable alternative to H₂ produced from fossil fuels. However, its efficiency remains limited because the enzymes responsible for H₂ production are highly sensitive to oxygen (O₂), while photosynthesis itself generates O₂ that can suppress their activity. This mini-review explores how different photosynthesis inhibitors affect H₂ production in these microorganisms, with a focus on their molecular targets and their physiological effects. In both microalgae and cyanobacteria, compounds such as DCMU, atrazine, DBMIB, CCCP, and KCN influence H₂ metabolism by altering electron transport, O₂ release, proton gradients, and cellular redox balance. The reviewed studies indicate that complete inhibition of photosynthetic electron flow is usually unfavorable for sustained H₂ production because it reduces the electron supply required by H₂-evolving enzymes. Therefore, anaerobiosis is more reliably established by physiological or cultivation-based strategies, whereas photosynthetic and respiratory inhibitors are best used as mechanistic probes or as auxiliary modulators under carefully optimized conditions. Their effects are strongly context-dependent, reflecting the balance between O₂ suppression, residual electron transport, respiratory O₂ consumption, and competing electron sinks. Full article

Copper ions (Cu²⁺) and intracellular biothiols are tightly coupled in cellular redox regulation, where copper–thiol coordination governs oxidative stress and metal homeostasis. However, analytical platforms capable of sequentially monitoring Cu²⁺ and biothiols within a single molecular system remain scarce. Herein, we report a coumarin-based fluorescent probe XDP that enables sequential ON–OFF–ON sensing of Cu²⁺ and biothiols through a coordination–competition mechanism. The imine (C=N) site of XDP selectively coordinates Cu²⁺, leading to fluorescence quenching arising from coordination-induced electronic perturbation and enhanced nonradiative decay. The probe exhibits a linear response toward Cu²⁺ over 1–80 μM with a detection limit of 0.108 μM. Subsequent competitive binding of biothiols (GSH, Cys, and Hcy) releases Cu²⁺ from the complex, thereby restoring fluorescence and enabling detection within 1–30 μM with submicromolar sensitivity. XDP also displays a large Stokes shift (135 nm), which minimizes spectral overlap and improves signal reliability. Notably, Cu²⁺ binding triggers a distinct color change that supports naked-eye detection and smartphone-based RGB quantification. The probe further enables visualization of Cu²⁺ and thiol-triggered signal recovery in living cells and zebrafish. This work establishes a versatile analytical platform for probing copper–thiol interactions in environmental and biological systems. Full article

A capacitive screen-printed electrode immunosensor operating in non-faradaic mode by dispensing redox probes was developed for the Coronavirus 2 Spike (S) protein. This new strategy enabled direct detection of the S protein by measuring changes in the electrochemical capacitance resulting from antigen–antibody interactions on the electrode surface, altering interfacial dielectric properties. To enhance analytical sensitivity and provide an electrode surface with attractive capacitive and conductive properties, an in-house graphite ink-based screen-printed electrode was developed and subsequently modified with a polypyrrole (PPy) layer in bulk-synthesized in the presence of Cetyltrimethylammonium bromide (CTAB). CTAB acted as a dispersing and structure-directing agent, promoting homogeneous distribution and guiding the PPy polymerization, resulting in a composite with improved charge density storage and high conductivity. Analytical signals of the S proteins in spiked serum were detected by measuring the Specific Capacitances taken from cyclic voltammograms. This capacitive immunosensor achieved a linear range from 1 to 100 µg/mL (R² = 0.989, p < 0.05), with a limit of detection of 0.45 µg/mL of S protein, which falls within the clinical range for COVID-19 diagnostics. Probe-free detection without ferri/ferrocyanide steps minimizes errors by probe adsorptions and is easy to use as a point-of-care, unlike conventional immunosensors. Full article

C-reactive protein (CRP) is one of the most essential biomarkers for the early detection of inflammation and infection. In this study, we developed a sensitive and selective electrochemical immunosensor for CRP detection, leveraging the unique properties of gold nanoparticles (AuNPs). A nanostructured layer of AuNPs was deposited onto a screen-printed carbon electrode (SPCE), followed by the formation of a self-assembled monolayer (SAM) of L-cysteine and EDC/sulfo-NHS chemistry. The antibody was covalently immobilized onto the modified electrode through optimized dual-crosslinking chemistry. Detection conditions were systematically optimized, with pH 8.0 in Tris buffer providing the best electrochemical response. Electrochemical characterization was performed using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and differential pulse voltammetry (DPV) in a 5 mM K₃[Fe(CN)₆]/K₄[Fe(CN)₆] redox probe solution containing 0.1 M KCl. CRP detection was achieved by monitoring the increase in charge transfer resistance (Rct) upon specific binding of the target CRP antigen to the immobilized antibody. Spiked recovery experiments showed spiked recovery rates ranging from 98.01% to 107.14%, with a standard deviation below 4%. Regeneration studies demonstrated high efficiency, confirming the suitability of the sensor interface for repeated and reliable measurements. Under optimized conditions, the immunosensor exhibited excellent analytical performance, including a low limit of detection (LOD) of 0.16 µg/mL, a wide linear detection range of 5–100 µg/mL, high selectivity against 13 potential interferents (including inflammatory cytokines), and good reproducibility with a relative standard deviation (RSD) of 3.69%. The sensor also showed strong stability, retaining more than 95% of its signal after 15 days, and high regeneration efficiency of 97% over seven cycles. These results highlight the strong potential of the proposed immunosensor for point-of-care (POC) applications due to its simple fabrication, cost-effectiveness, user accessibility, and robust analytical performance. Full article

Tumor oxygenation is a key determinant of cancer biology and treatment response, correlating with angiogenesis, recurrence, and malignant progression. Hypoxia is a defining feature of glioblastoma (GBM) and adult diffuse gliomas, generating low-oxygen niches that promote invasion, stem-like states, immune suppression, and resistance to radiotherapy and temozolomide, contributing to poor outcomes. Measuring tissue partial pressure of oxygen (pO₂) and mapping its spatial heterogeneity can, therefore, inform mechanistic understanding and therapeutic development, including hypoxia-activated prodrugs, hypoxia-responsive gene therapy, and optimized radiotherapy planning. Although direct pO₂ assessment is challenging, invasive probes and multimodal imaging can characterize regional hypoxia pre-operatively, support patient stratification, monitor treatment effects, and improve outcome prediction. This review summarizes oxygen dynamics in GBM; analyzes causes of hypoxia (rapid growth outpacing supply, diffusion-limited hypoxia, and abnormal/chaotic vasculature); compares methods to quantify oxygenation from direct measurements to noninvasive imaging surrogates; and evaluates preclinical and clinical strategies that target hypoxia to enhance standard therapy, including barriers to translation. We further integrate oxygenation with cell signaling and redox biology: oxygen gradients are transduced via hypoxia-inducible factor programs and redox-sensitive pathways (NRF2/KEAP1, NOX-derived ROS, nitric oxide/S-nitrosylation, and sulfur metabolic routes), shaping mesenchymal-like transitions and cell-death programs such as ferroptosis. Framing oxygenation as both a microenvironmental and redox-signaling variable positions oxygen imaging as an entry point to biomarker-guided therapies that exploit oxidative vulnerabilities. Full article

Fibromyalgia (FM) is a complex chronic syndrome marked by widespread musculoskeletal pain, neurocognitive dysfunction (“fibro-fog”), and autonomic disturbances. Clinical management remains challenging due to subjective symptom reporting and the lack of definitive diagnostics. Emerging evidence points to a multifactorial origin involving central sensitization, neuroendocrine imbalance, and systemic immune-inflammatory alterations. A wide array of candidate biomarkers has been reported in FM, encompassing neurotransmitters (serotonin, norepinephrine), excitatory and inhibitory amino acids, metabolic and glycolytic enzymes, stress-related proteins, autoantibodies, oxidative stress markers and pro-inflammatory cytokines. This molecular heterogeneity reflects the systemic and multidimensional nature of FM. However, most of these biomarkers have been primarily investigated in serum or plasma, where analytical validation and reference ranges are more established. In contrast, the exploration of salivary biomarkers—although highly attractive due to its non-invasive, stress-free, and repeatable collection—remains comparatively limited. Saliva contains a reduced concentration range of many systemic markers and is strongly influenced by circadian rhythms, stress, flow rate, and oral health conditions. While promising candidates such as α-amylase, cortisol, calgranulins, and selected metabolic enzymes have shown potential in saliva, many proposed FM-related biomarkers lack full analytical validation, standardized protocols, and clinically defined reference intervals in this matrix. In this context, non-invasive electrochemical biosensors represent a transformative technological approach. Advanced electrode architectures incorporating nucleic acid probes, redox reporters, and nanostructured materials offer high sensitivity in low-volume and low-concentration biofluids such as saliva. The integration of multiplexed biomarker panels into portable platforms could enable real-time, longitudinal monitoring of FM pathophysiology, supporting phenotype stratification, personalized therapeutic adjustment, and objective disease activity tracking. Full article

Neopterin, a low-molecular-weight pteridine, is a biomarker of pro-inflammatory immune activity. Its levels rise in viral infections, transplant rejection, autoimmune, cardiovascular, and neurodegenerative diseases, and cancer. In healthy human serum, neopterin concentration values are up to 10 nM. Detection is challenging due to its low concentration and limited solubility. In this work, a sensitive and selective electrochemical sensor for neopterin was developed using polydopamine molecularly imprinted polymers on a glassy carbon electrode. The polymer films were electro-polymerized directly on the electrode, varying the ratio of polymer to neopterin, while non-imprinted films were prepared without the template for comparison. Rebinding and template removal were monitored by cyclic voltammetry using ferricyanide as a redox probe. All imprinted films exhibited a concentration-dependent response from 1.2 nM to 1.2 mM, with a rapid increase at low concentrations up to 120 nM and a slower approach to a plateau at higher concentrations. The highest response was observed in films with the greatest neopterin content, consistent with increased binding site availability. Full article

Harmful algal blooms pose significant risks to water resource management and aquatic ecosystem health, rendering early detection of algal bloom proliferation essential. In this study, we present an electrochemical strategy for the real-time detection of individual Chlorella cells using the single-particle collision method at an ultramicroelectrode (UME). The detection principle relies on monitoring changes in the redox probe flux at the UME induced by attachment of the target. Both diffusional and migrational transport were considered to promote particle collision at the UME. Detection sensitivity for negatively charged microalgae was enhanced by exploiting migration effects. To control migration strength, neutral and charged redox probes were selected, and the ionic strength was adjusted to tune electrostatic attraction, yielding microalgae capture on the UME with a collision frequency that depended on the solution composition. Conversely, migration was suppressed by increasing the ionic strength, and inverse migration was implemented, and resulting collision responses were compared. Furthermore, COMSOL Multiphysics simulations were used to estimate the size of detected Chlorella cells. The collision frequencies expected from diffusion and migration were compared with the experimental values, and a calibration curve relating collision frequency to Chlorella concentration was established. Consequently, this methodology provides a promising platform for the early monitoring of algal blooms by simultaneously determining microalgal size and concentration. Full article

Copper ions are essential trace elements that play critical roles in redox reactions, signal transduction, energy metabolism, and regulation of the central nervous system. However, excess copper can induce cytotoxicity and contribute to various pathological conditions, highlighting the need for sensitive and selective detection methods. We report a novel near-infrared (NIR) optical sensor, IRPhen, based on a heptamethine cyanine scaffold conjugated with a 1,10-phenanthroline Cu²⁺-binding receptor. IRPhen exhibits strong NIR absorption and emission (E_x: 750 nm, E_m: 808 nm), high sensitivity, and good selectivity toward Cu²⁺ over competing metal ions. Spectroscopic studies revealed a rapid, reversible 1:1 binding interaction with a binding constant of 1.3 × 10⁶ M⁻¹ and a detection limit of 0.286 µM. The probe demonstrated excellent stability across physiological pH ranges and maintained its performance under competitive conditions. Importantly, IRPhen is cell-permeable and capable of detecting dynamic Cu²⁺ changes in living fibroblast (WS1) cells using confocal microscopy. This sensor design offers a versatile platform for developing NIR optical sensors to study copper homeostasis, elucidating copper-related biological mechanisms, and potentially developing similar NIR probes for other biologically relevant metal ions. Full article