Currently, portable, low-cost, and easy to operate on-chip analytical units are urgently demanded to meet the requirement for point-of-care testing in resource-limited regions. Herein, a dual-mode lab-on-paper platform is presented, which integrates distance-based visualized readout with ratiometric electrochemiluminescence (ECL) assay in one device. The distance-based measurement is based on a brown visualized strip generated from the oxidation reaction of 3,3′-diaminobenzidine in the presence of H2O2 initiated by horseradish peroxidase (HRP). Notably, visualized semiquantitative results are displayed as the length of a brown bar chart directly on the devicewithout the need for any data processing or plotting steps, thus avoiding the error caused by the naked eye for distinguishing the color depth. On the contrary, a ratiometric ECL technique was employed for accurate analysis based on the specific biorecognition between Pb2+-dependent DNAzymes and targets. Concretely, upon addition of Pb2+ into the fabricated device, cleaved oligonucleotide fragments connected with HRP functionalized Au nanocubes could permeate through the cellulose on account of their size that is smaller than paper pores, quench the ECL signal of the CdS quantum dots because of resonance energy transfer, and synchronously boost the ECL intensity generated from luminol by catalyzing H2O2. As a consequence, satisfied prediction and accurate monitoring performance was obtained in the range 0.1–2000 nM and 0.01–2000 nM by measuring the length of colored product and the ratio of ECL intensity, respectively. The beneficial advantages of low cost, high efficiency, and the capacity to perform dual-mode assay qualify this innovative device for use with diverse applications.

Herein, a hand-drawing paper-based bipolar electrode (BPE) electrochemiluminescence (ECL) platform for M.SssI methyltransferase (M.SssI MTase) assay was proposed via employing high electrocatalytic Pt@CeO2 as an ECL co-reaction accelerator and pencil-drawing graphite electric circuits as wires and electrodes. Notably, the introduction of pencil-drawing trace not only simplified the manufacturing process but also reduced the cost and saved fabricating time. Meanwhile, Pt@CeO2 with good electrocatalytic activity and satisfactory chemical stability was used at the anode of the closed BPE-ECL device to accelerate the oxidation rate of uric acid. Due to the balanced charges of the bipolar electrode, the ECL response of the MnS: CdS@ZnS/S2O8 2– system emitted on the cathode was enhanced. In situ growth of gold nanoparticles in the two electrode areas was convenient for DNA immobilization. With the above points in mind, the specific DNA double strands functionalized via Pt@CeO2 were employed to identify M.SssI MTase. The unmethylated DNA double strands were cut by HpaII endonuclease, resulting in the quenching of the ECL signal. Under the optimal conditions, sensitive detection of M.SssI MTase in a wide linear range of 0.01–100 U·mL–1 with a satisfactory detection limit of 0.008 U·mL–1 was realized. The reliable and versatile BPE-ECL tool for the determination of M.SssI MTase with easy-to-operate pencil-drawing traces and independent solution systems provides a new opportunity to develop paper-based devices applied in early disease diagnosis and pathogenesis research.

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