Polyvinyl alcohol/polyacrylamide double-network hydrogel-based semi-dry electrodes for robust electroencephalography recording at hairy scalp for noninvasive brain-computer interfaces.

Objective.Reliable and user-friendly electrodes can continuously and real-time capture the electroencephalography (EEG) signals, which is essential for real-life brain-computer interfaces (BCIs). This study develops a flexible, durable, and low-contact-impedance polyvinyl alcohol/polyacrylamide double-network hydrogel (PVA/PAM DNH)-based semi-dry electrode for robust EEG recording at hairy scalp.Approach.The PVA/PAM DNHs are developed using a cyclic freeze-thaw strategy and used as a saline reservoir for semi-dry electrodes. The PVA/PAM DNHs steadily deliver trace amounts of saline onto the scalp, enabling low and stable electrode-scalp impedance. The hydrogel also conforms well to the wet scalp, stabilizing the electrode-scalp interface. The feasibility of the real-life BCIs is validated by conducting four classic BCI paradigms on 16 participants.Main results.The results show that the PVA/PAM DNHs with 7.5 wt% PVA achieve a satisfactory trade-off between the saline load-unloading capacity and the compressive strength. The proposed semi-dry electrode exhibits a low contact impedance (18 ± 8.9 kΩ at 10 Hz), a small offset potential (0.46 mV), and negligible potential drift (1.5 ± 0.4µV min-1). The temporal cross-correlation between the semi-dry and wet electrodes is 0.91, and the spectral coherence is higher than 0.90 at frequencies below 45 Hz. Furthermore, no significant differences are present in BCI classification accuracy between these two typical electrodes.Significance.Based on the durability, rapid setup, wear-comfort, and robust signals of the developed hydrogel, PVA/PAM DNH-based semi-dry electrodes are a promising alternative to wet electrodes in real-life BCIs.

An Efficient Voltammetric Sensor Based on Graphene Oxide-Decorated Binary Transition Metal Oxides Bi2O3/MnO2 for Trace Determination of Lead Ions.

Herein we present a facile synthesis of the graphene oxide-decorated binary transition metal oxides of Bi2O3 and MnO2 nanocomposites (Bi2O3/MnO2/GO) and their applications in the voltammetric detection of lead ions (Pb2+) in water samples. The surface morphologies, crystal structures, electroactive surface area, and charge transferred resistance of the Bi2O3/MnO2/GO nanocomposites were investigated through the scanning electron microscopy (SEM), power X-ray diffraction (XRD), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) techniques, respectively. The Bi2O3/MnO2/GO nanocomposites were further decorated onto the surface of a glassy carbon electrode (GCE), and Pb2+ was quantitatively analyzed by using square-wave anodic stripping voltammetry (SWASV). We explored the effect of the analytical parameters, including deposition potential, deposition time, and solution pH, on the stripping peak current of Pb2+. The Bi2O3/MnO2/GO nanocomposites enlarged the electroactive surface area and reduced the charge transferred resistance by significant amounts. Moreover, the synergistic enhancement effect of MnO2, Bi2O3 and GO endowed Bi2O3/MnO2/GO/GCE with extraordinary electrocatalytic activity toward Pb2+ stripping. Under optimal conditions, the Bi2O3/MnO2/GO/GCE showed a broad linear detection range (0.01-10 µM) toward Pb2+ detection, with a low limit of detection (LOD, 2.0 nM). The proposed Bi2O3/MnO2/GO/GCE electrode achieved an accurate detection of Pb2+ in water with good recoveries (95.5-105%).

Ultrasensitive, label-free voltammetric determination of norfloxacin based on molecularly imprinted polymers and Au nanoparticle-functionalized black phosphorus nanosheet nanocomposite.

Norfloxacin (NOR) is an antibiotic commonly used to treat humans and food-producing animals. Owing to NOR abuse, its residues are frequently found in animal-derived food products and the surrounding environment. Therefore, development of an efficient analytical technique for the selective determination of trace NOR is greatly significant for food safety and environmental protection. Here, we fabricated an ultrasensitive, label-free molecularly imprinted polymer (MIP) voltammetric sensor for the selective determination of NOR, based on an Au nanoparticle-functionalized black phosphorus nanosheet nanocomposite (BPNS-AuNP) covered by a polypyrrole-imprinted film. BPNS-AuNP nanocomposites were prepared via an in-situ one-step method without the use of reducing agents. The imprinted polypyrrole film was formed on the surface of the BPNS-AuNPs in the presence of NOR. The physical properties and electrochemical behavior of the MIP/BPNS-AuNPs were investigated using various characterization techniques, and the analytical parameters were optimized. We found that BPNS-AuNPs improve the ambient stability and electrocatalytic activity, providing a large surface area for locating a higher number of specific recognition sites. Consequently, the MIP/BPNS-AuNP/GCE showed excellent sensing performance toward NOR, with a wide linear response range (0.1 nM - 10 µM), an extremely low limit of detection (0.012 nM), and extraordinary selectivity. Moreover, the MIP/BPNS-AuNP/GCE was used to determine NOR in various experimental samples with satisfactory results.

Recent advances in black phosphorus-based electrochemical sensors: A review.

Since the discovery of liquid-phase-exfoliated black phosphorus (BP) as a field-effect transistor in 2014, BP, with its 2D layered structure, has attracted significant attention, owing to its anisotropic electroconductivity, tunable direct bandgap, extraordinary surface activity, moderate switching ratio, high hole mobility, good biocompatibility, and biodegradability. Several pioneering research efforts have explored the application of BP in different types of electrochemical sensors. This review summarizes the latest synthesis methods, protection strategies, and electrochemical sensing applications of BP and its derivatives. The typical synthesis methods for BP-based crystals, nanosheets, and quantum dots are discussed in detail; the degradation of BP under ambient conditions is introduced; and state-of-the-art protection methodologies for enhancing BP stability are explored. Various electrochemical sensing applications, including chemically modified electrodes, electrochemiluminescence sensors, enzyme electrodes, electrochemical aptasensors, electrochemical immunosensors, and ion-selective electrodes are discussed in detail, along with the mechanisms of BP functionalization, sensing strategies, and sensing properties. Finally, the major challenges in this field are outlined and future research avenues for BP-based electrochemical sensors are highlighted.

Non-local orientation filtered imaging with incoherent light source.

A non-local spatial filtered imaging experiment using an orientation filter has been performed with spatially incoherent thermal light, which is based on Abbe-Porter imaging system. A two-dimensional periodic grid object and an orientation filter are placed in two correlated light beams, namely a test beam and a reference beam, generated by splitting the thermal light beam via a beam splitter. The filtering process has been produced by manipulating the orientation of a slit aperture, which is in the back focal plane of the biconvex imaging lens in the reference beam. The detected object is placed in the test beam, whose modulated images have been achieved through optical field intensity correlation measurement between the two correlated beams. The experimental results are in good agreement with theoretical analysis. The research results here show considerable possibilities to distributively manipulate the image of an object with spatially incoherent light source, which could find potential applications in the remote imaging technology in the fields of geological survey and spectral analysis.

A practical gas chromatography flame ionization detection method for the determination of octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, and dodecamethylcyclohexasiloxane in silicone emulsions.

A gas chromatography with flame ionization detection (GC-FID) method for analysis of D4, D5, and D6 cyclic siloxanes in silicone emulsions is described. Sample preparation involves breaking the emulsion with methanol and hexanes, and then analyzing the hexanes phase after derivatization with hexamethyldisilazane (HMDS). Silylation is performed to reduce the potential for formation of cyclic siloxanes during the course of the GC analysis. The accuracy of the method was verified by performing analyses on samples spiked with known levels of D4, D5 and D6 and by comparison to a referee method using atmospheric pressure chemical ionization liquid chromatography with mass spectrometry detection (APCI-LC-MS). Absolute differences of the results obtained between the two techniques were 0.03 weight percent or less, and relative differences were 15% or less. The reproducibility and ruggedness of the method was demonstrated by performing a global round robin test at four different geographic sites on four different types of silicone emulsions. The %RSDs obtained were less than 10% for all analytes and all emulsions examined.

Inhibitory activities of Lignum Sappan extractives on growth and growth-related signaling of tumor cells.

AIM: To investigate the active constituents of Lignum Sappan (Caesalpinia sappan L.) on growth-related signaling and cell mitosis. METHOD: The influence of the ethyl acetate (EtOAc) extract of Lignum Sappan and its constituents on growth-related signaling were evaluated by a luciferase assay in cells stably-transfected with NF-κB, STAT1, or STAT3 responsive luciferase reporter plasmid. The inhibitory effect on the cell cycle was determined by flow cytometric analysis. The anti-tumor activities were assessed in vitro and in vivo. RESULTS: The EtOAc extract of Lignum Sappan had inhibitory activities on growth-related signaling and cell mitosis. Three major active compounds were sappanchalcone, brazilin, and butein. Sappanchalcone blocked cell cycle progression in the G2/M phase, brazilin inhibited TNFα/NF-κB signaling, while butein inhibited IL-6/STAT3 signaling, as well as TNFα/NF-κB signaling. The three compounds all demonstrated cytotoxic activities against human tumor cells in vitro. In a S180 tumor cell-bearing mice model, the anti-tumor efficacy of the EtOAc extract was better than the individual compounds acting alone. CONCLUSION: These results indicate that Lignum Sappan contains multiple active compounds with different antitumor activities, which act synergistically to enhance their anti-tumor effects. The EtOAc extract of Lignum Sappan may be better than individual active constituent as a novel medicine for the treatment of cancer.

[Study on chemical constituents from stem of Mallotus apelta].

Eight compounds were isolated from the ethyl-acetate extract of the stem of Mallotus apelta Muell. -Arg. The structures of eight compounds were identified by means of spectroscopic analysis as 12-ursen-3-one (I), 3-hydroxy-12-ursen (II), mussaenoside (III), 6-methoxy-2H-1-benzopyron4-one (IV), ursolic acid (V), acetyl aleuritolic acid (VI), beta-sitosterol-3-O-beta-D-glucopyranoside (daucosterol VII), beta-sitosterol (VII). Compound I to approximately V were obtained from this plant for the first time.