Sensitive electrochemical flow injection analysis of H2O2 released from cells with a pass-through mode.

Conventional plate electrodes were commonly used in electrochemical flow injection analysis and only part of molecules diffused to the plane of electrodes could be detected, which would limit the performance of electrochemical detection. In this study, a low-cost native stainless steel wire mesh (SSWM) electrode was integrated into a 3D-printed device for electrochemical flow injection analysis with a pass-through mode, which is different compared with previous flow-through mode. This strategy was applied for sensitive analysis of hydrogen peroxide (H2O2) released from cells. Under the optimal conditions (the applied potentials, the flow rate and the sample volume), the device exhibits high sensitivity toward H2O2. Linear relationships could be achieved between electrochemical responses and the concentration of H2O2 ranging from 1 nM to 1 mM. The excellent analytical performance of the SSWM-based device could be attributed to the pass-through mode based on the mesh microstructure and intrinsic catalytic properties for H2O2 by stainless steel. This approach could be further successfully extended for screening of H2O2 released from HeLa cells with electrochemical responses linear to the number of cells in a range of 3 - 1.35 × 104 cells with an injection volume of 30 µL. This study revealed the potential of mesh electrodes in electrochemical flow injection analysis for cellular function and pathology and its possible extension in cell counting and on-line analysis.

Water activating fresh NiMo foam for enhanced urea electrolysis.

Recently, production of hydrogen (H2) through the urea oxidation reaction (UOR) and hydrogen evolution reaction (HER) has acquired great attention because it is more environmentally friendly and energy-saving. Herein, an approach of water activation was developed for in situ growth of NiMo LDH nanosheet arrays on NiMo foam without using any binder or pressurizing or heating steps. The obtained NiMo foam electrodes showed exceptional catalytic activity and durability for both the UOR and HER. This work offers a new standpoint on designing electrodes with high activation for efficient and sustainable hydrogen production coupled with urea organic oxidation.

Vibration-enhanced disposable electroanalytical platform for selective analysis of tryptophan in fruits based on molecular imprinting.

Although electrochemical detection based on molecular imprinting polymers (MIP) could dramatically improve the selectivity, the procedure is time-consuming because of the essential incubation step. In addition, current MIP electrochemical detections were not suitable for analysis of microliter-level sample solutions, limiting their applications for real samples. This investigation aims at applying vibration to enhance efficiency of MIP electrochemical detection of 20 µL sample solutions. MIP analysis of Tryptophan (Trp) was used as the model with disposable MIP electrodes prepared by electrochemical polymerization of o-phenylenediamine on carbon ink coated on stainless steel sheets. The MIP electrode was integrated in a 3D-printed analytical device for vibration-enhanced electrochemical detection of Trp. Our results showed that this vibration-enhanced strategy could significantly increase electrochemical responses of Trp at the same incubation time. Such improvement might be attributed to the enhanced mass transfer at the surface of the working electrode brought by vibration. It needs to be emphasized that this strategy is suitable for analysis of sample solutions with the volume of microliters, which is superior to normal stirring in MIP electrochemical detection. Our approach could be successfully utilized for differentiation of Trp in different fruits, opening more opportunities for MIP electrochemical detection of real samples. The enhanced efficiency by vibration could pave foundation for extensive practical MIP detection of sample solutions at the level of microliters.

Unlocking the potential of a NiMo foam substrate for water splitting using an ultrafast two-step dipping strategy.

In this paper, a facile and ultrafast two-step dipping process was developed to in situ form an electrocatalyst on a NiMo foam substrate without consuming extra energy. The obtained electrode showed a porous coral-like structure decorated with nanosheets and exhibited excellent overall water splitting properties in alkaline solution. This study provides a feasible strategy for developing an environmentally friendly and energy-efficient non-noble metal electrode for hydrogen production from water splitting.

Plasma-spray-enabled microcosmic explosion to construct Ni mesh-based electrodes for water splitting.

Currently, the fabrication of low cost and high efficiency electrocatalysts is a hotspot in the study of water splitting. Herein, plasma spray (PS) was used to induce a microcosmic explosion (me) on Ni mesh to modify the nanoscale Ni for the preparation of me-PS-NM electrodes with excellent hydrogen evolution. We also demonstrated that oxygen evolution could be significantly enhanced after the me-PS-NM electrodes were doped with Fe3+. Both electrodes formed a system exhibiting superior activity and stability for overall water splitting without noble metals.

Vibration for enhancement of electrochemical analysis of biomolecules in a droplet on the rough surface of a disposable working electrode.

Although electrochemical detection of microliters-level solutions is attractive for analysis of low-amount biological samples, its performance could be weakened by limited mass transfer due to low Reynolds number and laminar flow. Herein we designed a 3D-printed electroanalytical device to apply vibration for improvement of mass transfer during electrochemical detection. In our approach, the droplet-size sample solution containing Indole-3-acetic acid (IAA, as a model) was directly applied on the effective surface of a disposable working electrode. We demonstrated that vibration could enhance electrochemical responses of IAA more on the rough surface than on the smooth surface of the working electrodes. After optimization, the sensitivity for electrochemical detection of a 20-µL droplet under vibration with the voltage of 7 V increased more than 100% compared with the static condition. The enhanced electrochemical responses brought by vibration could be achieved reproducibly, which could be ascribed to improved mass transfer. Our strategy could be practically applied for differentiation of IAA in different tissues of Marchantia polymorpha with enhanced responses. This study suggested that vibration might become a simple and effective method to improve mass transfer in analysis of microliter-volume solutions, which might be extended for more biochemical assays.

Facile method to activate substrate for oxygen evolution by a galvanic-cell reaction.

NiFe layered double hydroxide (NiFe LDH) is a promising material with multiple functions. In this communication, a novel method is used to prepare NiFe LDH. This synthesis method is achieved via galvanic-cell corrosion between nickel and iron substrates in aqueous solutions containing a halogen group anion (e.g., Cl) at ambient temperature. The as-prepared NiFe LDH electrodes are developed as electrocatalysts for the oxygen evolution reaction (OER) and exhibit excellent catalytic activities and durability. This work provides an energy-efficient, cost-effective, and scaled-up corrosion engineering approach for manufacturing NiFe LDH materials.

Acid etching followed by water soaking: a top-down strategy to induce highly reactive substrates for electrocatalysis.

A top-down strategy using acid etching followed by water soaking is utilized to in situ synthesize autologous NiFe LDH nanosheets on NiFe foam without other metal ions, oxidizing agents or heating steps. The NiFe foam serves as both the metal source and substrate, and the obtained nanosheets are firmly anchored on the foam. The obtained ultrathin nanosheet arrays could greatly increase the electrocatalytic active sites. This factor together with the synergistic effect between Fe and Ni simultaneously leads to an enhanced catalytic effect for water splitting and urea oxidation. This strategy could be scaled up to pave a viable way for low-cost fabrication of highly efficient electrodes for electrocatalysis.

A 3D-printed analytical device seamlessly integrating sample treatment for electrochemical detection of IAA in Marchantia polymorpha.

Because of the pivotal point of Marchantia polymorpha (M. polymorpha) in plant evolution, its auxin (mainly indole-3-acetic acid, IAA) levels could provide useful evidence for the study of the evolution of IAA. However, M. polymorpha could not be easily pretreated for electrochemical detection because they are at the entry level of land plants. Herein, we designed a three-dimensional (3D)-printed analytical device for seamless integration of sample treatment and electrochemical detection. Specifically, the electrochemical cell could be used as a mortar in which a tiny plant sample could be ground with a 3D-printed pestle, followed by mixing with the buffer solution under vibration for electrochemical detection of IAA with a disposable working electrode at the bottom of the cell. Using our strategy, the limits of quantification could reach 0.05 µmol L-1 after optimization of parameters. We were able to demonstrate that IAA in different tissues of wild-type and mutant M. polymorpha could be successfully differentiated after they were treated with the 3D-printed analytical device. The obtained results were comparable to the samples blended with zirconium beads while the differences of IAA levels in different tissues of M. polymorpha agreed well with previous reports. This study suggested the potential of sample treatment integrated with electrochemical detection for analysis of IAA using the 3D printing techniques and their possible applications in the research of plants and other fields.

Surface Reconstruction of an FeNi Foam Substrate for Efficient Oxygen Evolution.

Designing earth-abundant electrocatalysts that are highly active, low-cost, and stable for the oxygen evolution reaction (OER) is crucial for electrochemical water splitting. However, in conventional electrode fabrication strategies, NiFe layered double hydroxide (NiFe LDH) catalysts are usually coated onto substrates as external components, which suffers from poor conductivity, easily detaches from the substrate, and hinders their long-term utilization. Herein, the surface-reconstruction strategy is used to synthesize in situ autologous NiFe LDH to increase the surficial active sites numbers. The FeNi foam (FNF) serves as both the metal source and substrate, and the obtained NiFe LDH nanosheets (NSs) are firmly anchored in the monolithic FNF. What needs to be emphasized is that the strategy does not involve any high-temperature or high-pressure processes, apart from a cost-effective etching and a specified drying treatment. The nanostructure of NiFe LDH and the synergistic effect between Fe and Ni simultaneously lead to an enhanced catalytic effect for the OER. Remarkably, the sr-FNF46 requires only an ultralow overpotential of 283 mV to achieve a current density of 100 mA cm-2 for the OER in 1 M KOH electrolyte, and exhibits excellent stability. Thus, the obtained electrode holds promise for electrocatalytic applications. Finally, the formation mechanism of NiFe LDH NSs due to surface reconstruction is investigated and discussed in detail.

PNP Nanofluidic Transistor with Actively Tunable Current Response and Ionic Signal Amplification.

Inspired by electronic transistors, electric field gating has been adopted to manipulate ionic currents of smart nanofluidic devices. Here, we report a PNP nanofluidic bipolar junction transistor (nBJT) consisting of one polyaniline (PANI) layer sandwiched between two polyethylene terephthalate (PET) nanoporous membranes. The PNP nBJT exhibits three different responses of currents (quasi-linear, rectification, and sigmoid) due to the counterbalance between surface charge distribution and base voltage applied in the nanofluidic channels; thus, they can be switched by base voltage. Four operating modes (cutoff, active, saturation, and breakdown mode) occur in the collector response currents. Under optimal conditions, the PNP nBJT exhibits an average current gain of up to 95 in 100 mM KCl solution at a low base voltage of 0.2 V. The present nBJT is promising for fabrication of nanofluidic devices with logical-control functions for analysis of single molecules.

Enhanced analytical performance of disposable 3D carbon electrodes prepared with stainless steel wire mesh.

This paper aims to use low-cost stainless steel wire mesh (SSWM) as uniform templates to prepare disposable three-dimensional (3D) carbon electrodes to improve their analytical performance. Native SSWM electrodes were prepared with lamination and then coated with carbon cement for bulk preparation of disposable 3D carbon electrodes with drop-casting. The electrodes were then coupled in paper-based analytical devices. Meanwhile, disposable 2D carbon electrodes were prepared with the stainless steel sheets (SSSs) for comparison under the same condition using stripping analysis of heavy metals as a model. Our results demonstrated that the sensitivity of the 3D carbon electrodes was about three times as high as that of the 2D carbon electrodes on stripping analysis of both heavy metals. The electrochemical responses of 1 µg L-1 Pb2+ at the 3D carbon electrodes were about 6 times as high as those at the 2D carbon electrodes. The improved analytical performance of disposable 3D carbon electrodes could be attributed to their increased electrochemical effective area, which was brought by replacing SSSs with SSWM. The obtained disposable 3D carbon electrodes could be used for differentiation of Pb in teethers and corns. This study not only presented the potential of SSWM in the preparation of disposable 3D carbon electrodes but also suggested a simple and effective strategy for the preparation of disposable 3D electrodes for practical applications.

Horseshoe kidney with PLA2R-positive membranous nephropathy.

BACKGROUND: Horseshoe kidney (HSK) is a common congenital defect of the urinary system. The most common complications are urinary tract infection, urinary stones, and hydronephrosis. HSK can be combined with glomerular diseases, but the diagnosis rate of renal biopsy is low due to structural abnormalities. There are only a few reports on HSK with glomerular disease. Here, we have reported a case of PLA2R-positive membranous nephropathy occurring in a patient with HSK. CASE PRESENTATION: After admission to the hospital due to oedema of both the lower extremities, the patient was diagnosed with nephrotic syndrome due to abnormal 24-h urine protein (7540 mg) and blood albumin (25 g/L) levels. Abdominal ultrasonography revealed HSK. The patient's brother had a history of end-stage renal disease due to nephrotic syndrome. Therefore, the patient was diagnosed with PLA2R-positive stage II membranous nephropathy through renal biopsy under abdominal ultrasonography guidance. He was administered adequate prednisone and cyclophosphamide, and after 6 months of treatment, urinary protein excretion levels significantly decreased. CONCLUSION: The risk and difficulty of renal biopsy in patients with HSK are increased due to structural abnormalities; however, renal biopsy can be accomplished through precise positioning with abdominal ultrasonography. In the literature, 20 cases of HSK with glomerular disease have been reported thus far. Because of the small number of cases, estimating the incidence rate of glomerular diseases in HSK is impossible, and the correlation between HSK and renal pathology cannot be stated. Further studies should be conducted and cases should be accumulated to elucidate this phenomenon.

Stainless steel sheets as the substrate of disposable electrochemical sensors for analysis of heavy metals or biomolecules.

In this paper, low-cost stainless steel sheets with excellent electric conductivity were utilized as the robust substrate for fabrication of disposable working electrodes. The stainless steel electrodes were modified with carbon cement and then coupled in paper-based analytical devices for analysis of heavy metals (cadmium and lead) in toys or indole-3-acetic acid (IAA) in plants, respectively. For stripping analysis of cadmium and lead, the dilution ratio of the carbon cement, the pH value of the buffer solution, the pre-deposition potential and time, and the bismuth concentration were optimized with the detection limits reaching 1 µg•L-1. After optimization of the dilution ratio of carbon cement, the similar devices could also be used for analysis of IAA at the concentration of less than 0.5 µM. This strategy could be successfully applied for differentiation of migratable lead in toys or in situ amounts of IAA in root tips of Arabidopsis thaliana in real time, respectively. Our results implied that the electric conductivity of the substrate could possibly be critical for the improvement of the analytical performance of the modified electrodes. This study suggested that stainless steel could become a suitable and cost-effective substrate for fabrication of disposable carbon-based electrodes used in electrochemical detection.

Paper-based electroanalytical devices for stripping analysis of lead and cadmium in children's shoes.

Children's shoes are potential sources of toxic heavy metals, especially for younger children. Electrochemical detection could be applied for effective stripping analysis of heavy metals (such as Cd and Pb). However, the substrates of working electrodes are still limited and it is not well known which property is critical. Herein ITO glass was used as the substrate and the working electrode was modified with carbon cement for stripping analysis of Cd and Pb. The electrochemical impedance spectra of the ITO modified electrodes suggested the connection between the resistance and the electrochemical responses of heavy metals in stripping analysis, depending on the dilution ratio of the carbon cement. After optimization, the ITO modified electrodes in paper-based analytical devices could be used to sensitively quantify Cd and Pb with the concentration ranging from 10 to 1000 ppb. The detection limit of Pb2+ could reach less than 1 ppb while that of Cd2+ could reach 5 ppb, depending on the pH value of the sample solution. The paper-based electroanalytical devices could be used to quantify the concentration of Cd and Pb in children's shoes. This study implied the impact of the electric conductivity of the electrode substrates on stripping analysis, which might help to find more materials for the fabrication of the working electrodes.

Recent advances of ratiometric electrochemiluminescence biosensors.

Ratiometric electrochemiluminescence (ECL) assays have been widely applied in biosensing because of eliminated outside interferences and improved reliability in detection. In order to construct ratiometric ECL biosensors with high sensitivity and reliability, it is critical to find two signal emitters with suitable applied potentials or emission wavelengths. This review aims to discuss recent advances and trends of ratiometric ECL biosensors in terms of ECL materials and corresponding ratiometric sensing approaches. We focus on four types of ratiometric ECL biosensors based on particular ECL materials and ratiometric sensing strategies.

Multi-segmented CdS-Au nanorods for electrochemiluminescence bioanalysis.

In this study, we have developed a programmable electrochemiluminescence (ECL) system based on multi-segmented CdS-Au nanorod arrays with a sequential and highly tunable structure. The nanorod arrays were synthesized by an electrodeposition method using anodic aluminum oxide (AAO) as the template in which the Au and CdS segments were alternately electrodeposited. Compared to pure CdS nanorod arrays, multi-segmented CdS-Au nanorod arrays have showed a better ECL performance, which can be attributed to two factors: the favorable electron transfer and the surface plasma resonance (SPR) effect of the Au segment. On the one hand, we demonstrated that the Au segment can increase the charge transfer rate of CdS, which is beneficial for the ECL process because the generation of the radical state needs to accept electrons and then generate the radical state. On the other hand, the SPR of Au plasmon-induced local electromagnetic field enhancement can increase the radiative decay rate of CdS which makes the ECL process more efficient and lead to a higher ECL intensity. And also, an ECL sensor with multi-segmented CdS-Au nanorod arrays was constructed to detect prostate protein antigen (PSA). This study provides some basis for designing high-performance ECL emission materials and the construction of biosensors.

Electrochemiluminescence Resonance Energy Transfer System for Dual-Wavelength Ratiometric miRNA Detection.

In this study, we proposed a dual-wavelength electrochemiluminescence resonance energy transfer (ECL-RET) ratiometric sensor combined with duplex-specific nuclease (DSN)-assisted target recycling amplification to detect microRNAs (miRNAs). Due to the perfect overlapping of spectra, the gold-nanoparticle-luminol-layered-double-hydroxides (Au NP-luminol-LDH) nanocomposite and gold nanoclusters (Au NCs) exhibited excellent ECL-RET effect with high efficiency. The Au NP-luminol-LDH donor exhibits a strong and stable ECL emission at the wavelength peak of 440 nm, while the Au NC acceptor has an emission peak at 620 nm. Upon the introduction of DSN and target miRNAs, the specific DNA-RNA binding and nuclease cleaving could trigger the detachment of capture Au NCs-DNA from the surface of Au NP-luminol-LDH, resulting in an increased ECL signal of Au NP-luminol-LDH and a decreased fluorescence signal of Au NCs. By measuring the ratio of optical signals at 440 and 620 nm, the designed sensor provided a quantitative readout proportional to the target miRNAs concentration in the range of 10 aM to 100 pM with a lower detection limit (LOD) of 9.4 aM.

[Effects of LncRNA H19 on Proliferation of Human Colorectal Cancer SW620 Cells].

OBJECTIVE: To determine the expression level of long non-coding RNA (lncRNA) imprinted maternallyexpressed transcript (H19) in colorectal cancer tissues and its effect on proliferation of colorectal cancer SW620 cells. METHODS: Real-time quantitative PCR (qRT-PCR) was applied to detect the expression of H19 in 20 paired tumor tissues and adjacent normal tissues,and in normal NCM460 cells and colorectal cancer SW480,HCT116 and SW620 cells. The specific small interfering RNA for H19 (si-H19 group) or negative control sequence (si-NC group) were transfected into SW620 cells. Proliferation of the transfected cells was detected using flow cytometry,CCK8 assay and clone formation experiment. The expressions of CyclinD1 and cyclin dependent kinase 4 (CDK4) were detected by qRT-PCR and Western blot. RESULTS: The expression levels of H19 in colorectal cancer tissues and cells were higher compared with those in adjacent normal tissues and normal NCM460 cells. Lower H19 level,cell activities and cell clone numbers were found in si-H19 transfected cells compared with those in si-NC transfected cells ( P<0.05). si-H19transfected cells had decreased expression of CyclinD1 and CDK4 ( P<0.05). CONCLUSION: H19expression in colorectal cancer is high. Knock-down H19 expression can inhibit proliferation of colorectal cancer cells,which provides a potential strategy for targeted therapy of colorectal cancer.

Nanopore-Based Electrochemiluminescence for Detection of MicroRNAs via Duplex-Specific Nuclease-Assisted Target Recycling.

In this study, we proposed a nanopore-based electrochemiluminescence (ECL) sensor combined with duplex-specific nuclease (DSN)-assisted target recycling amplification to detect microRNAs. Because of the synergetic effect of electrostatic repulsion and volume exclusion of gold nanoparticle-labeled DNA capture (DNA-Au NPs) to the negatively charged luminol anion probe, the DNA-Au NP-modified anodized aluminum oxide (AAO) nanopore electrode exhibited high ECL decline in comparison with the bare AAO electrode. Upon the introduction of DSN and target microRNA, the specific DNA-RNA binding and enzyme cleaving could trigger the detachment of capture DNA from the membrane surface, resulting in uncapping of AAO and an increased ECL signal. For comparison, positively charged Ru(bpy)32+ was used as the ECL probe instead of luminol. Because the electrostatic attraction effect between DNA and Ru(bpy)32+ is partially offset by the volume exclusion effect of Au NPs, the AAO electrode modified with only DNA capture is more suitable for the Ru(bpy)32+ case. In our experiment, the case of negatively charged luminol combined with the synergetic effect of electrostatic repulsion and volume exclusion of DNA-Au NPs provides a quantitative readout proportional to the target microRNA concentration in the range of 1.0 fM to 1.0 nM, with a lower detection limit of 1 fM.