DNAzyme-Triggered Visual and Ratiometric Electrochemiluminescence Dual-Readout Assay for Pb(II) Based on an Assembled Paper Device.

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.

Colorimetric and Electrochemiluminescence Dual-Mode Sensing of Lead Ion Based on Integrated Lab-on-Paper Device.

A highly selective two-point separation strategy was designed based on a cross-like all-in-one lab-on-paper analytical device. The stable and cleavable enzyme-coated reduced graphene oxide (rGO)-PdAu probe was fabricated as the signal reporter to enable the visualization and electrochemiluminescence (ECL) dual-mode sensing of Pb2+. Concretely, the experimental workflow consists of the following process: (i) fabrication of the lab-on-paper device and growth of Au nanoparticles on ECL detection zone, (ii) immobilization of Pb2+-specific DNAzyme, and (iii) hybridization between DNAzyme and rGO-PdAu-glucose oxidase (GOx) labeled oligonucleotide to form the double-stranded DNA. Upon addition of Pb2+ into the prepared system, the double-helix structure of the DNA was destroyed, resulting in the release of cleaved rGO-PdAu-GOx probe to visualization bar to promote the effective oxidation and color change of 3,3',5,5'-tetramethylbenzidine. As a consequence, the color change can be recognized by naked eye, meanwhile GOx on an uncleaved signal probe can oxidize glucose along with the H2O2 production. As a co-reaction reagent for luminol ECL system, the concentration of H2O2 is proportional to the ECL intensity, which constitutes a new mechanism for colorimetric and ECL dual mode to detect Pb2+. With the method developed here, the concentration of Pb2+ could be easily determined by the naked eye within a linear range from 5 to 2000 nM, as well as by monitoring the decreased ECL intensity of luminol in a linear range of 0.5-2000 nM. This work not only constructs a simple and versatile platform for on-site visible monitoring of Pb2+ in tap water and river water but also furnishes a strategy for designing a dual-mode sensing toward different heavy metal ions based on specific DNAzyme in the fields of environmental monitoring-related technologies.

Growth of gold-manganese oxide nanostructures on a 3D origami device for glucose-oxidase label based electrochemical immunosensor.

Flexible biosensors are of considerable current interest for the development of portable point-of-care medical products, minimally invasive implantable devices, and compact diagnostic platforms. Here, we reported an electrochemical paper based analytical device fabricated (EPADs) by sequentially growing gold nanoparticles (AuNPs) and manganese oxide (MnO2) nanowires networks on a freestanding three dimensional (3D) origami device. This fabricated through the growth of an AuNPs layer on the surfaces of cellulose fibers in the screen-printed paper working electrode (PWE), and thus developed a gold paper working electrode (Au-PWE). Subsequently, MnO2 nanowires were successfully electrodeposited on Au-PWE to form a 3D network with large surface areas. Based on this novel EPADs and the principle of origami, we presented herein a simple immunosensing scheme using glucose oxidase (GOx) as an enzyme label, 3,3',5,5'-tetramethylbenzidine (TMB) as a redox terminator, and glucose as an enzyme substrate. The electrochemical enzymatic redox cycling was applied to the detection of prostate protein antigen (PSA), a biomarker of prostatic cancer. The proposed method successfully fulfilled the highly sensitive detection of PSA with a linear range of 0.005 ng mL(-1)-100 ng mL(-1) with a detection limit of 0.0012 ng mL(-1). This EPADs exhibited high sensitivity, specificity and excellent performance in real human serum assay, and could be applied in point-of-care testing of other tumor markers for remote regions and developing countries.

Hand-drawn&written pen-on-paper electrochemiluminescence immunodevice powered by rechargeable battery for low-cost point-of-care testing.

In this paper, a pen-on-paper electrochemiluminescence (PoP-ECL) device was entirely hand drawn and written in commercially available crayon and pencil in turn for the first time, and a constant potential-triggered sandwich-type immunosensor was introduced into the PoP-ECL device to form a low-cost ECL immunodevice proof. Each PoP-ECL device contained a hydrophilic paper channel and two PoP electrodes, and the PoP-ECL device was produced as follows: crayon was firstly used to draw hydrophobic regions on pure cellulose paper to create the hydrophilic paper channels followed with a baking treatment, and then a 6B-type black pencil with low resistivity was applied for precision writing, as the PoP electrodes, across the hydrophilic paper channel. For further point-of-care testing, a portable, low-cost rechargeable battery was employed as the power source to provide constant potential to the PoP electrodes to trigger the ECL. Using Carbohydrate antigen 199 as model analyte, this PoP-ECL immunodevice showed a good linear response range from 0.01-200 U mL(-1) with a detection limit of 0.0055 U mL(-1), a high sensitivity and stability. The proposed PoP-ECL immunodevice could be used in point-of-care testing of other tumor markers for remote regions and developing countries.

A chemiluminescence excited photoelectrochemistry aptamer-device equipped with a tin dioxide quantum dot/reduced graphene oxide nanocomposite modified porous Au-paper electrode.

In this work, a paper-based chemiluminescence excited photoelectrochemical aptamer device (PPECD) was developed for adenosine triphosphate (ATP) measurement based on a porous Au-paper electrode modified with a tin dioxide quantum dot/reduced graphene oxide nanocomposite (SnO2 QD/RGO) integrated with an all-solid-state paper supercapacitor (PSC) amplifier and a digital multi-meter (DMM). The Au-paper electrode was constructed through the growth of a gold nanoparticle (AuNP) layer on the back of the paper working electrode to improve the electron conduction. Fe3O4@AuNP nanocomposites were used as labels of luminol, glucose oxidase (GOx) and signal aptamer which greatly enhanced the chemiluminescence emission and provided a simple magnetic separation approach to attain interference-free measurement for real detection. GOx was used for the oxidation of glucose to produce H2O2 which was not only used as the co-reactant in the CL system, but also as the electron donors to suppress the corrosion of SnO2 QDs under illumination as well as to facilitate the generation of stable photocurrent. A PSC was constructed and integrated into a PPECD as an effective electrical energy storage unit to collect and store the photocurrents. The stored electrical energy could be released instantaneously through a low cost, portable, and simple DMM to obtain an amplified current for the quantification of ATP.