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.

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.

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.

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.