Surface grafted silica adsorbent for efficient removal of Hg2+ ions from contaminated water.

A mesoporous silica hybrid functionalized with aromatic 1,2-phenyl dithiol (PT@MS NPs) was prepared in two steps such as sol-gel co-condensation of VTMS and tetraethyl orthosilicate (TEOS) using Pluronic P123 as a structure directing surfactant, and surface grafting reaction of 1,2-phenyl dithiol with vinyl groups via click-reaction. Surface area, average pore size, and mesopore volume of the produced PT@MS NPs are approximately 546 m2/g, 2.8 nm, and 0.63 cm3/g, respectively. With an adsorption quantity of 252 mg/g and a removal capacity of nearly 95% from the initial metal ion (100 mg/L of Hg2+ ions) solutions, the PT@MS NPs material showed highly selective adsorption of mercury (Hg2+) from a mixture of other competitive metal (Zn2+, Ni2+, Pb2+, Cd2+, and Fe2+) ions. By treating the adsorbent with an acidic aqueous solution (0.1 M HCl), the produced adsorbent can be recycled and reused up to five times. As a result, the PT@MS NPs adsorbent might be used in wastewater treatment as a highly efficient and selective adsorbent for harmful Hg2+ ions.

Anti-Inflammatory Effect of IKK-Activated GSK-3ß Inhibitory Peptide Prevented Nigrostriatal Neurodegeneration in the Rodent Model of Parkinson's Disease.

Parkinson's disease (PD) is a progressive movement disorder caused by nigrostriatal neurodegeneration. Since chronically activated neuroinflammation accelerates neurodegeneration in PD, we considered that modulating chronic neuroinflammatory response might provide a novel therapeutic approach. Glycogen synthase kinase 3 (GSK-3) is a multifunctional serine/threonine protein kinase with two isoforms, GSK-3α and GSK-3ß, and GSK-3ß plays crucial roles in inflammatory response, which include microglial migration and peripheral immune cell activation. GSK-3ß inhibitory peptide (IAGIP) is specifically activated by activated inhibitory kappa B kinase (IKK), and its therapeutic effects have been demonstrated in a mouse model of colitis. Here, we investigated whether the anti-inflammatory effects of IAGIP prevent neurodegeneration in the rodent model of PD. IAGIP significantly reduced MPP+-induced astrocyte activation and inflammatory response in primary astrocytes without affecting the phosphorylations of ERK or JNK. In addition, IAGIP inhibited LPS-induced cell migration and p65 activation in BV-2 microglial cells. In vivo study using an MPTP-induced mouse model of PD revealed that intravenous IAGIP effectively prevented motor dysfunction and nigrostriatal neurodegeneration. Our findings suggest that IAGIP has a curative potential in PD models and could offer new therapeutic possibilities for targeting PD.

Cost-Effective Electrochemical Activation of Graphitic Carbon Nitride on the Glassy Carbon Electrode Surface for Selective Determination of Serotonin.

A simple one-step electrochemical deposition/activation of graphitic carbon nitride (g-C3N4) is highly desired for sensor configurations and remains a great challenge. Herein, we attempt an electrochemical route to exfoliate the g-C3N4 nanosheets in an aqueous solution of pH 7.0 for constructing a sensor, which is highly sensitive for the detection of serotonin (5-HT). The significance of our design is to exfoliate the g-C3N4 nanosheets, a strong electrocatalyst for 5-HT detection. Investigations regarding the effect of neutral pH (pH 7.0) on the bulk g-C3N4 and g-C3N4 nanosheets, physical characterization, and electrochemical studies were extensively carried out. We demonstrate that the g-C3N4 nanosheets have a significant electrocatalytic effect for the 5-HT detection in a dynamic linear range from 500 pM to 1000 nM (R2 = 0.999). The limit of detection and sensitivity of the designed 5-HT sensor was calculated to be 150 pM and 1.03 µA µM-1 cm-2, respectively. The proposed sensor has great advantages such as high sensitivity, good selectivity, reproducibility, and stability. The constructed g-C3N4 nanosheets-based sensor platform opens new feasibilities for the determination of 5-HT even at the picomolar/nanomolar concentration range.

Electrochemical reactive oxygen species detection by cytochrome c immobilized with vertically aligned and electrochemically reduced graphene oxide on a glassy carbon electrode.

A new amperometric biosensor for hydrogen peroxide (H2O2) and superoxide anion (SO) has been developed. The biosensor developed uses cytochrome c (Cyt c) modified glassy carbon electrodes coupled with electrochemically reduced graphene oxide (ErGO). To immobilize Cyt c, the "one step" electrochemical deposition of vertically aligned and ErGO (VAErGO) has been performed by using a pulse reverse technique, thus resulting in a very simple and efficient system. The well-established vertical alignment of ErGO was confirmed by atomic force microscopy and the electrochemical characteristics of the biosensor were investigated by cyclic voltammetric, electrochemical impedance spectroscopy and amperometric techniques. The surface coverage (Γ) of immobilized Cyt c was effectively increased by the vertical alignment of ErGO and found to be 1.03 × 10-10 mol cm-2. The direct electron transfer property of Cyt c was also improved by VAErGO and the heterogeneous electron transfer rate constant (ket) was estimated to be 6.40 s-1. To detect H2O2 and SO, amperometric measurements were carried out at different operating potentials (0.0 V vs. Ag/AgCl for H2O2 and +0.2 V for SO). The sensitivity and detection limit for H2O2 were found to be 46.3 µA mM-1 cm-2 and 2.3 µM, and for SO were found to be 32.1 µM nA-1 cm-2 and 6.84 nM s-1, respectively. Additionally, the designed biosensor exhibited strong anti-interference ability and satisfactory reproducibility.

Conductive Polymer-Based Hydrogels for Wearable Electrochemical Biosensors.

Hydrogels are gaining popularity for use in wearable electronics owing to their inherent biomimetic characteristics, flexible physicochemical properties, and excellent biocompatibility. Among various hydrogels, conductive polymer-based hydrogels (CP HGs) have emerged as excellent candidates for future wearable sensor designs. These hydrogels can attain desired properties through various tuning strategies extending from molecular design to microstructural configuration. However, significant challenges remain, such as the limited strain-sensing range, significant hysteresis of sensing signals, dehydration-induced functional failure, and surface/interfacial malfunction during manufacturing/processing. This review summarizes the recent developments in polymer-hydrogel-based wearable electrochemical biosensors over the past five years. Initially serving as carriers for biomolecules, polymer-hydrogel-based sensors have advanced to encompass a wider range of applications, including the development of non-enzymatic sensors facilitated by the integration of nanomaterials such as metals, metal oxides, and carbon-based materials. Beyond the numerous existing reports that primarily focus on biomolecule detection, we extend the scope to include the fabrication of nanocomposite conductive polymer hydrogels and explore their varied conductivity mechanisms in electrochemical sensing applications. This comprehensive evaluation is instrumental in determining the readiness of these polymer hydrogels for point-of-care translation and state-of-the-art applications in wearable electrochemical sensing technology.

Glutamate oxidase sheets-Prussian blue grafted amperometric biosensor for the real time monitoring of glutamate release from primary cortical neurons.

Glutamate (GLU) is a primary excitatory neurotransmitter, and its dysregulation is associated with several neurodegenerative disorders. A major challenge in GLU estimation is the existence of other biomolecules in the brain that could directly get oxidized at the electrode. Hence, highly selective electroenzymatic biosensors that enable rapid estimation of GLU are needed. Initially, a copolymer, poly(2-dimethylaminoethyl methacrylate- styrene) was synthesized through reversible addition-fragmentation chain transfer polymerization to noncovalently functionalize reduced graphene oxide (rGO), named DS-rGO. Glutamate oxidase macromolecule immobilized DS-rGO formed enzyme nanosheets, which was drop-coated over Prussian blue electrodeposited disposable electrodes to fabricate the GLU biosensor. The interconnectivity between the enzyme nanosheets and the Prussian blue endows the biosensor with enhanced conductivity and electrochemical activity. The biosensor exhibited a linearity: 3.25-250 µM; sensitivity: 3.96 µA mM-1 cm-2, and a limit of detection: 0.96 µM for GLU in the Neurobasal Medium. The biosensor was applied to an in vitro primary rat cortical model to discriminate GLU levels in Neurobasal Medium, before and after KCl mediated depolarization, which provides new insights for elucidating neuronal functioning in the brain.

Ruthenium-Anchored Carbon Sphere-Customized Sensor for the Selective Amperometric Detection of Melatonin.

Melatonin (MT), a pineal gland hormone, regulates the sleep/wake cycle and is a potential biomarker for neurodegenerative disorders, depression, hypertension, and several cancers, including prostate cancer and hepatocarcinoma. The amperometric detection of MT was achieved using a sensor customized with ruthenium-incorporated carbon spheres (Ru-CS), possessing C- and O-rich catalytically active Ru surfaces. The non-covalent interactions and ion-molecule adducts between Ru and CS favor the formation of heterojunctions at the sensor-analyte interface, thus accelerating the reactions towards MT. The Ru-CS/Screen-printed carbon electrode (SPCE) sensor demonstrated the outstanding electrocatalytic oxidation of MT owing to its high surface area and heterogeneous rate constants and afforded a lower detection limit (0.27 µM), high sensitivity (0.85 µA µM -1 cm-2), and excellent selectivity for MT with the co-existence of crucial neurotransmitters, including norepinephrine, epinephrine, dopamine, and serotonin. High concentrations of active biomolecules, such as ascorbic acid and tyrosine, did not interfere with MT detection. The practical feasibility of the sensor for MT detection in pharmaceutical samples was demonstrated, comparable to the data provided on the product labels. The developed amperometric sensor is highly suitable for the quality control of medicines because of its low cost, simplicity, small sample size, speed of analysis, and potential for automation.

Enzyme Nanosheet-Based Electrochemical Aspartate Biosensor for Fish Point-of-Care Applications.

Bacterial infections in marine fishes are linked to mass mortality issues; hence, rapid detection of an infection can contribute to achieving a faster diagnosis using point-of-care testing. There has been substantial interest in identifying diagnostic biomarkers that can be detected in major organs to predict bacterial infections. Aspartate was identified as an important biomarker for bacterial infection diagnosis in olive flounder (Paralichthys olivaceus) fish. To determine aspartate levels, an amperometric biosensor was designed based on bi-enzymes, namely, glutamate oxidase (GluOx) and aspartate transaminase (AST), which were physisorbed on copolymer reduced graphene oxide (P-rGO), referred to as enzyme nanosheets (GluOx-ASTENs). The GluOx-ASTENs were drop casted onto a Prussian blue electrodeposited screen-printed carbon electrode (PB/SPCE). The proposed biosensor was optimized by operating variables including the enzyme loading amount, coreactant (α-ketoglutarate) concentration, and pH. Under optimal conditions, the biosensor displayed the maximum current responses within 10 s at the low applied potential of -0.10 V vs. the internal Ag/AgCl reference. The biosensor exhibited a linear response from 1.0 to 2.0 mM of aspartate concentrations with a sensitivity of 0.8 µA mM-1 cm-2 and a lower detection limit of approximately 500 µM. Moreover, the biosensor possessed high reproducibility, good selectivity, and efficient storage stability.

Screen-printed carbon electrode modified with de-bundled single-walled carbon nanotubes for voltammetric determination of norepinephrine in ex vivo rat tissue.

A voltammetric sensor for norepinephrine (NE) detection was developed by modifying a disposable screen-printed carbon electrode (SPCE) with de-bundled single-walled carbon nanotubes (D-SWCNTs). The de-bundling was carried out using a newly synthesized polymeric dispersant, a co-polymer of polystyrene sulfonate and methacrylate of lipoic acid. The D-SWCNTs/SPCE showed better sensitivity towards NE compared to the bare SPCE and that modified with bundled SWCNTs. The sensor was optimized for detecting NE by differential pulse voltammetry (DPV) in terms of the D-SWCNTs concentration, DPV parameters, and solution pH. Under the optimum conditions, the sensor exhibited a dynamic linear range of 100 nM-2.0 µM NE, and the detection limit was 62.0 nM (S/N = 3). Additionally, the effects of possible interferents were investigated. The relative standard deviation for five successive measurements of 2.0 µM NE was 7.6%, and approximately 75.8% of the sensor activity was retained after four weeks of storage. The practical potential of this sensor was demonstrated by quantifying NE in ex vivo rat tissue samples.

Disposable Voltammetric Sensor Modified with Block Copolymer-Dispersed Graphene for Simultaneous Determination of Dopamine and Ascorbic Acid in Ex Vivo Mouse Brain Tissue.

Dopamine (DA) and ascorbic acid (AA) are two important biomarkers with similar oxidation potentials. To facilitate their simultaneous electrochemical detection, a new voltammetric sensor was developed by modifying a screen-printed carbon electrode (SPCE) with a newly synthesized block copolymer (poly(DMAEMA-b-styrene), PDbS) as a dispersant for reduced graphene oxide (rGO). The prepared PDbS-rGO and the modified SPCE were characterized using a range of physical and electrochemical techniques including Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, cyclic voltammetry, electrochemical impedance spectroscopy, and linear sweep voltammetry. Compared to the bare SPCE, the PDbS-rGO-modified SPCE (PDbS-rGO/SPCE) showed better sensitivity and peak-to-peak separation for DA and AA in mixed solutions. Under the optimum conditions, the dynamic linear ranges for DA and AA were 0.1-300 and 10-1100 µM, and the detection limits were 0.134 and 0.88 µM (S/N = 3), respectively. Furthermore, PDbS-rGO/SPCE exhibited considerably enhanced anti-interference capability, high reproducibility, and storage stability for four weeks. The practical potential of the PDbS-rGO/SPCE sensor for measuring DA and AA was demonstrated using ex vivo brain tissues from a Parkinson's disease mouse model and the control.

Robust Nanozyme-Enzyme Nanosheets-Based Lactate Biosensor for Diagnosing Bacterial Infection in Olive Flounder (Paralichthys olivaceus).

Bacterial infections in fish farms increase mass mortality and rapid detection of infection can help prevent its widespread. Lactate is an important biomarker for early diagnosis of bacterial infections in farmed olive flounder (Paralichthys olivaceus). To determine the lactate levels, we designed a disposable amperometric biosensor based on Prussian blue nanozyme and lactate oxidase (LOX) entrapped in copolymer-reduced graphene oxide (P-rGO) on screen-printed carbon electrodes. Because LOX is inherently unstable, P-rGO nanosheets were utilized as a base matrix to immobilize it. After optimization in terms of enzyme loading, operating potential, and pH, the biosensor displayed maximum current responses within 5 s at the applied potential of -0.1 V vs. internal Ag/AgCl. The biosensor had Langmuir-type response in the lactate concentration range from 10 µM to 1.6 mM, a dynamic linear response range of 10-100 µM, a sensitivity of 15.9 µA mM-1 cm-2, and a lower detection limit of 3.1 µM (S/N = 3). Additionally, the biosensor featured high reproducibility, good selectivity, and stability till four weeks. Its practical applicability was tested in olive flounder infected by Streptococcus parauberis against the uninfected control. The results were satisfactory compared to those of a standard colorimetric assay kit, validating our method.

In situ synthesis of copper-ruthenium bimetallic nanoparticles on laser-induced graphene as a peroxidase mimic.

A new type of disposable flexible sensor for hydrogen peroxide (H2O2) detection was developed by in situ synthesis of copper-ruthenium bimetallic nanoparticles on a laser-induced graphene surface (Cu-Ru/LIG). The approach produced Cu-Ru/LIG via a solid phase transfer mechanism which loaded the metal precursor onto LIG, followed by laser scribing without demanding chemical vapor deposition or solution-based reactions. Cu-Ru/LIG showed a high electrocatalytic response toward H2O2 reduction at -0.4 V vs. Ag/AgCl. The sensor also showed good selectivity and reproducibility. This method provides an alternative route to easily synthesize various catalysts on conductive substrates for sensor applications.

Anti-Inflammatory Effects of the Novel Barbiturate Derivative MHY2699 in an MPTP-Induced Mouse Model of Parkinson's Disease.

Parkinson's disease (PD) is one of the most common neurodegenerative disorders, and is caused by the death of dopamine neurons and neuroinflammation in the striatum and substantia nigra. Furthermore, the inflammatory response in PD is closely related to glial cell activation. This study examined the neuroprotective effects of the barbiturate derivative, MHY2699 [5-(4-hydroxy 3,5-dimethoxybenzyl)-2 thioxodihydropyrimidine-4,6(1H,5H)-dione] in a mouse model of PD. MHY2699 ameliorated MPP⁺-induced astrocyte activation and ROS production in primary astrocytes and inhibited the MPP⁺-induced phosphorylation of MAPK and NF-κB. The anti-inflammatory effects of MHY2699 in protecting neurons were examined in an MPTP-induced mouse model of PD. MHY2699 inhibited MPTP-induced motor dysfunction and prevented dopaminergic neuronal death, suggesting that it attenuated neuroinflammation. Overall, MHY2699 has potential as a neuroprotective treatment for PD.

Polymer-dispersed reduced graphene oxide nanosheets and Prussian blue modified biosensor for amperometric detection of sarcosine.

A new disposable amperometric biosensor for sarcosine (Sar, a biomarker for prostate cancer) was designed based on screen-printed carbon electrodes, Prussian blue, polymer dispersed reduced graphene oxide (P-rGO) nanosheets, and sarcosine oxidase (SOx). Poly(sodium 4-styrenesulfonate-r-LAHEMA) denoted as PSSL was newly synthesized as dispersant for rGO. The P-rGO was utilized for SOx immobilization, the sulfonate and disulfide functionalities in PSSL enable physical adsorption of SOx and its bioactivity and stability properties were improved. The biosensor was optimized by various enzyme concentration, applied potential, and operating pH. Under the optimized conditions, the biosensor exhibited maximum current responses within 5 s at an applied potential of -0.1 V vs. integrated Ag/AgCl reference electrode. The biosensor had a dynamic linear range of 10-400 µM, with a sensitivity of 9.04 µA mM-1 cm-2 and a low detection limit of 0.66 µM (S/N = 3). Additionally, the biosensor possesses strong anti-interference capability, high reproducibility, and storage stability over 3 weeks. Furthermore, its clinical applicability was tested in urine samples from both prostate cancer patients and healthy control, and the analytical recoveries were satisfactory. Therefore, this biosensor has significant potential in the rapid and non-invasive point-of-care testing for prostate cancer diagnosis.

Reagentless Amperometric Pyruvate Biosensor Based on a Prussian Blue- and Enzyme Nanoparticle-Modified Screen-Printed Carbon Electrode.

We report a facile strategy for developing reagentless amperometric pyruvate biosensors based on enzyme nanoparticles (EnNPs). The EnNPs were prepared using pyruvate oxidase crosslinked with graphene quantum dots. Before EnNP immobilization, screen-printed carbon electrodes (SPCEs) were modified with Prussian blue, a biocompatible coordination polymer. The biosensor system was optimized in terms of the working potential and pH value. At pH 7.0 in 50 mM phosphate-buffered solution, the biosensor showed optimal characteristics under an applied potential of -0.10 V versus an internal pseudo-Ag reference electrode. Using these optimized conditions, the biosensor performance was characterized via the chronoamperometric technique. The EnNP-immobilized SPCE exhibited a dynamic linear range from 10 to 100 µM for pyruvate solution, and a sensitivity of 40.8 µA mM-1 cm-2 was recorded. The observed detection limit of the biosensor was 0.91 µM (S/N = 3) and it showed strong anti-inference capability under the optimized working potential. Furthermore, the practical applicability of the proposed biosensor was studied in fish serum samples.