•An approach for direct detection of free IAA and SA in tiny plant sample were proposed.•The tiny plant sample was put on the surface of the working electrodes in PADS.•The low sample volume of ∼10 μL allowed detection of IAA and SA at the level of ng.•The obtained results were comparable to previous indirect detection approaches.•The IAA and SA in different location of pea seedlings were useful for further study.It is not easy to directly obtain concentrations of auxin (mainly indole-3-acetic acid, or IAA) and other phytohormones in different locations of individual plants although such information is critical for the study of their functions. Here we developed a paper-based analytical device consisting of a disposable working electrode to provide a platform for direct and simultaneous detection of free IAA and salicylic acid (SA) in different parts of pea seedlings with the weights of several milligrams. The double sided conductive carbon tape modified with carbon nanotube was used as the disposable working electrodes after they were treated with oxygen plasma. Different parts of pea seedlings were applied on the surface of working electrodes for direct electrochemical detection of free IAA and SA in paper-based analytical devices. The requirement of solution volumes with only 10 microliters made it possible to quantify free IAA and SA at the level of ng. Our results suggested that large amounts of inherent IAA and SA could be lost because of complicated and time-consuming preparation of samples in traditional gas/liquid chromatography-mass spectrometry methods Our approach not only avoids such steps but also provides concentrations of IAA and SA in different zones of individual pea seedlings. The obtained results could be applied for the study of individual differences and interactions between IAA and SA in development of peas. This strategy not only paved the foundation for further investigation of regulating mechanisms of free IAA and its interaction with other phytohormones but also might provide an alternative approach for detection of free electroactive biomolecules in other living organs.

Fabrication of disposable gold working electrodes in bulk is desirable for their extensive application in electrochemical detection. In this paper the gold film electrodes were prepared by sputtering the gold film with the thickness of ∼12 nm on the double sided conductive carbon tape. The gold film coated carbon tape could be used like stickers with small square pieces and attached on ITO glass for fabrication of disposable gold film electrodes. The electrochemical responses of the gold film modified electrodes on Cr(VI) in acidic solutions were similar to previous gold electrodes, suggesting the similar mechanism as before. Cr(VI) could be determined by the amperometric method with the detection limit of 0.7 μg L−1 (0.013 μM), which was significantly improved compared with previously reported disposable gold-based electrodes. The batch-by-batch (n = 20) reproducibility of the fabricated electrodes was 7.3% at 50 μg L−1 and 3.8% at 5.0 mg L−1, respectively. The disposable electrodes could be applied to quantify Cr(VI) in real samples including plastics, tap water and lake water with results in agreement with those obtained with HPLC-ICP-MS. This study provides a simple and effective alternative for preparation of disposable gold film electrodes.

•Paper could physically trap red blood cells on the surface of working electrodes.•The permeability of paper allows oxygen or nitrogen to reach cells without disturbance.•The breathing process of red blood cells could be electrochemically studied.•Electrochemical responses might be ascribed to reduction of oxyhemoglobin.Herein we utilized the filter paper to physically trap red blood cells (RBC) to observe the breathing process of red blood cells based on the permeability of the filter paper. By integrating double-sided conductive carbon tape as the working electrodes, the device could be applied to monitor electrochemical responses of RBC for up to hundreds of minutes. The differential pulse voltammetry (DPV) peak currents increased under oxygen while decreased under nitrogen, indicating that RBC could take in and release oxygen. Further studies demonstrated that the RBC suspension could more effectively take in oxygen than the solution of hemoglobin and the supernatant of RBC, suggesting the natural advantage of RBC on oxygen transportation. This study implied that simple paper-based analytical devices might be effectively applied in the study of gas-participating reactions and biochemical detections.

Stable and sensitive electrochemiluminescence (ECL) detection relies on successful immobilization of quantum dots (QDs) on working electrodes. Herein, we report a new technique to apply double-sided carbon adhesive tape as the working electrode to improve the stability and reproducibility of QD-based ECL emission. CdS QD-modified electrodes were prepared by dropping and drying CdS QD suspension on the carbon adhesive tape supported by indium tin oxide (ITO) glass. The ECL detection was performed with the prepared electrode on a paper-based platform. We tested our system using H2O2 of various concentrations and demonstrated that consistent ECL emission could be obtained. We attribute stable and reproducible ECL emission to the robust attachment of CdS QDs on the carbon adhesive tape. The proposed method could be used to quantify the concentration of dopamine from 1 μM to 10 mM based on the quenching effect of dopamine on ECL emission of CdS QD system using H2O2 as the coreactant. Our approach addressed the problem in the integration of stable QD-based ECL detection with portable paper-based analytical devices. The similar design offers great potential for low-cost electrochemical and ECL analytical instruments.