Kang Cui

Flexible Electronics Based on Micro/Nanostructured Paper

Over the past several years, a new surge of interest in paper electronics has arisen due to the numerous merits of simple micro/nanostructured substrates. Herein, the latest advances and principal issues in the design and fabrication of paper-based flexible electronics are highlighted. Following an introduction of the fascinating properties of paper matrixes, the construction of paper substrates from diverse functional materials for flexible electronics and their underlying principles are described. Then, notable progress related to the development of versatile electronic devices is discussed. Finally, future opportunities and the remaining challenges are examined. It is envisioned that more design concepts, working principles, and advanced papermaking techniques will be developed in the near future for the advanced functionalization of paper, paving the way for the mass production and commercial applications of flexible paper-based electronic devices.

Polyhedral-AuPd nanoparticles-based dual-mode cytosensor with turn on enable signal for highly sensitive cell evalution on lab-on-paper device

A novel dual-mode cytosensor based on polyhedral AuPd alloy nanoparticles (PH-AuPd NPs) and three-dimentional reduced graphene oxide (3D-rGO) was constructed for highly sensitive detection of MCF-7 cells. The 3D-rGO was in situ synthesized on the paper working electrode (PWE) by a pollution-free hydrothermal method, increasing the specific surface area and further facilitating the modification of Au nanoparticles (AuNPs). After modified with AuNPs, the Au@u202f3D-rGO/PWE was then functionalized by aptamer H1 to trap MCF-7 cells. To construct the cytosensor, PH-AuPd NPs was prepared as a novel catalytic material, and further modified with aptamer H2 for recognizing MCF-7 cells. With the occurrence of efficient recognition of MCF-7 cells, PH-AuPd NPs were bound onto the surface of the cells, and could catalyze H2O2 to generate •OH, leading to an amplified electrochemical signal. Meanwhile, as the electrolyte solution flowed, the •OH are transferred outward to the colorimetric detection zone, and catalyzed a chromogenic substrate TMB forms a colored product. The electrical signal measurement and colorimetric detection were carried out on a compatibly designed lab-on-paper device (LPD), realizing a dual-mode signal readout. This paper-based dual-mode cytosensor provided a relatively low detection limit of 20 cells mL-1 and a sensitive detection from 50 cells mL-1 to 107 cells mL-1 for MCF-7 cells, providing a reliable pathway of sensitively detecting cancer cells in clinical applications.

Stackable Lab-on-Paper Device with All-in-One Au Electrode for High-Efficiency Photoelectrochemical Cyto-Sensing

Highly conductive, robust, and multifunctional integrated paper-supported electrodes are requisite to fulfill the promise of paper-based analytical application. Herein, an all-in-one Au electrode comprising of detection zone, waterproof electronic bridge, and signal output contactor was engineered via combining the double-sided growth method with the secondary wax-printing. Benefiting from the strongly omnidirectional conductivity and desirably mechanical robustness of the as-prepared electrode, a stackable lab-on-paper cyto-device integrated with high-efficiency photoelectrochemical strategy was developed for the MCF-7 cells assay. Specifically, the detection zone of the electrode, serving as the signal generator, was functionalized with a low-toxic cosensitized structure composed of corn-like ZnO nanorods, graphene quantum dots (GQDs), and Ag2Se QDs. With the proximity control of DNA hairpin-based aptamer probe (DHAP), a strong photocurrent could be promoted by the activated cosensitization effect and collected on the signal output contactor via the electron transport of waterproof electronic bridge. Upon the MCF-7 cells recognition, the DHAP switched from closed to open state with the formation of DNA-cell bioconjugates and the spatial separation of Ag2Se QDs linked on the terminal of DHAP from the electrode surface. The photocurrent was noticeably decreased due to the double inhibition of steric hindrance effect and vanished cosensitization effect. Based on the target-triggered photocurrent attenuation, the sensitive detection of target cells was achieved. This work not only provided a unique method for paper-based electrode preparation but also offered a powerful platform for the highly sensitive photoelectrochemical bioanalysis.

“On–Off–On” Photoelectrochemical/Visual Lab-on-Paper Sensing via Signal Amplification of CdS Quantum Dots@Leaf-Shape ZnO and Quenching of Au-Modified Prism-Anchored Octahedral CeO2 Nanoparticles

An effectivexa0on-off-on photoelectrochemical (PEC)/visual sensing system based on cleaning-switchable lab-on-paper device was designed to achieve ultrasensitive detection of analytes. The first amplified signal-on PEC state was gained by CdS quantum dots sensitized leaf-shape ZnO (CdS QDs/leaf-shape ZnO) structure, which was assembled on reduced graphene oxide (rGO) modified paper electrode. Then Au-modified prism-anchored octahedral CeO2 nanoparticles (Au@PO-CeO2 NPs), as an efficient signal quencher, were immobilized on the CdS QDs/leaf-shape ZnO with the assistance of DNA hybridization, resulting in a noticeable photocurrent response decrement with the signal-off PEC state. With the addition of analytes, the quencher Au@PO-CeO2 NPs were immediately released from the sensing surface and robust PEC response was recovered to the signal-on state again. Meanwhile, the disengaged quencher in electrolyte solution flowed to the colorimetric detection area of lab-on-paper device and catalyzed oxidation of the chromogenic substrate 3,3,5,5-tetramethylbenzidine in the presence of H2O2 to form the colored product, making the analytes detection more convincing with the visual discrimination. Under optimal conditions, the proposed PEC/visual lab-on-paper device possessed the detection limits toward adenosine and potassium ion as low as 0.15 and 0.06 nM, respectively. With ingenious design of actuating conversion process between hydrophilicity and hydrophobicity by slipping paper tab to solve cleaning issue in the assay procedures, the cleaning-switchable lab-on-paper device was constructed for high-performance biosensing applications. It provides an unambiguous simplicity and portable operation for exploring high reliability and sensitivity of novel point-of-care diagnostic tool with dual-signal readout.

Hierarchical hematite/TiO 2 nanorod arrays coupled with responsive mesoporous silica nanomaterial for highly sensitive photoelectrochemical sensing

The photoelectrochemical (PEC) technique has resulted in substantial progress in chemical sensing applications. However the complicated photoelectrode modification procedures would enable undesired background noise and decreasing sensitivity. Hence, it is important to explore a new approach alternative to inconvenient substrate modification. Herein, inspired by the stimuli-responsive drug delivery systems, an innovative PEC system is developed for efficiently microRNA-21 (miRNA-21) tracing. Hierarchical nanocomposites based on hematite (α-Fe2O3) coated self-ordered titanium dioxide nanorod arrays (TiO2 NRAs) exhibited enhanced response to solar light, promoted charge carrier separation and transfer efficiency was adopted as photoelectrode directly. Functional mesoporous silica nanomaterial (MSN) is prepared as nanocarriers for efficient loading of Cu2+, further capped with miRNA-21 responsive capture RNA probe. Thereafter, the capture RNA probe endows the functional MSN with responsiveness to miRNA-21. With the presence of miRNA-21, this system is thus triggered and a quickly release of capped Cu2+ occurs due to the dissociation of capture RNA probe presented on the MSN surface via base-pair hybridization. The released Cu2+ was then served as electron acceptor reduced to Cu° at the counter electrode to enhance electron-hole pair separation efficiency, leading to a promoted photocurrent response. Consequently, the miRNA-21 can be accurately quantified. Taking advantage of its sensitivity and specificity, this versatile strategy demonstrates a new route for the design PEC sensing approach without any photoelectrode modification procedure, and holds great potential for biosensing and clinical diagnosis.

Ultrasensitive Enzyme-free Biosensor by Coupling Cyclodextrin Functionalized Au Nanoparticles and High-Performance Au-Paper Electrode

Microfluidic paper-based analytical device (μPAD), originally developed for improving healthcare in developing countries, presents a simple yet powerful platform for performing low-cost and portable diagnostic devices. Here, we report an enzyme-free μPAD for the detection of two tumor markers. First, a porous structure of gold nanoparticle (AuNP)-modified paper working electrode (Au-PWE), with a feature of all-round conductivity and plenty of active sites favoring biological ligand attachment, was fabricated as a sensor substrate. Next, cyclodextrin functionalized AuNPs (CD@AuNPs) as dual mimicking enzyme were prepared to load secondary antibodies or peptide. On one sample zone, in the presence of carcinoembryonic antigen (CEA), CD@AuNPs could be introduced into the Au-PWE through a sandwich immunoreaction, boosting the electrochemical signal of o-phenylenediamine (o-PD) via the trigger of a cascade catalysis reaction toward glucose and o-PD, eventually resulting in the sensitive detection of CEA. On another working zone, with the introduction of another target prostate-specific antigen (PSA), peptide cleavage took place, which further led to CD@AuNPs being released from Au-PWE, and then, the variation of electrochemical signals was recorded for the detection of PSA. We demonstrated, using the device, that the detection of CEA and PSA clinically had high sensitivity, wide linear ranges, and low detection limits. We believe that our work provides a promising platform for point-of-care testing, especially in resource-limited regions.

A single-interface photoelectrochemical sensor based on branched TiO2 nanorods@strontium titanate for the detection of two biomarkers

In this study, a single-interface photoelectrochemical (PEC) sensor for detecting two antigens, alpha fetoprotein (AFP) and cancer antigen 153 (CA 153), was achieved based on the heterostructure of branched titanium dioxide nanorods (B-TiO2 NRs)@strontium titanate (SrTiO3) heterostructures. The B-TiO2 NRs@SrTiO3 heterostructure, prepared by a facile hydrothermal method with the feature of enhanced photogenerated charge carrier separation properties, was first employed as a photoactive substrate for anchored analyst. In order to achieve the goal of successfully detecting two biomarkers at a single interface, the two specific enzyme tags β-galactosidase and acetylcholine esterase linked with a secondary detection antibody were utilized to catalytically hydrolyze p-aminophenyl galactopyranoside and acetylthiocholine to p-aminophenol and thiocholine, respectively. Based on the above enzyme-catalyzed reactions to produce sacrificial electron donors, the photocurrent signals generated from different analytes could be distinguished at a single interface. The results demonstrate that this single-interface PEC sensor not only provides a method for the early detection of AFP and CA 153 but also provides new insight into designing a novel PEC sensor for the detection of two biomarkers with high efficiency and a simple method of operation.

Highly conductive and bendable gold networks attached on intertwined cellulose fibers for output controllable power paper

On-chip energy units are urgently required for the rapid development of the Internet of Things and flexible electronics. Herein, a flexible integrated platform by incorporating paper microfluidic technology with a pencil-drawing approach is presented for self-charging/recharging, self-powered electropolymerization and sensing. By adopting a double bottom-up growth strategy based on paper microfluidics and a wax printing process, gold networks attached on intertwined cellulose fibers with extremely low horizontal sheet resistance (1.6 Ω sq−1) and good vertical conductivity (44.58 S cm−1) were achieved. Then, a low-cost pencil-drawing method based on the porosity of the paper substrate was introduced to overcome the key technical issue of reversible control for fluid and current. Utilizing the unique platform produced, a flexible power paper with a magnesium anode and a Prussian blue cathode was explored. The obtained output controllable power device was applied to drive the electropolymerization of polypyrrole film and a polyaniline network, and electrochemiluminescence images with competitive performance. It is believed that this work offers new insights into the formation of flexible green power and may be instructive for the future design of integrated platforms.

Addressable TiO2 Nanotubes Functionalized Paper-Based Cyto-Sensor with Photocontrollable Switch for Highly-Efficient Evaluating Surface Protein Expressions of Cancer Cells

Inspired by the well-known Wheel of Fortune, a rotatable paper-photocontrollable switch (RPPS) was designed to form an addressable paper-based photoelectrochemical (PEC) cyto-sensor for ultrasensitive detection of a cell-surface protein. By simply rotating the RPPS, a light source can selectively activate the desired working zones of the cyto-sensor. To realize the high-performance paper-based PEC cyto-sensor, a cascaded photoactive interface consisting of neat TiO2 nanotubes arrays, Pt nanoparticles (NPs), and nitrogen-carbon dots was introduced into paper fibers, gaining signal-on PEC state (NTPP for short). Then the NTPP fixed with a hairpin probe H1 allowed the hybridization chain reaction (HCR) to happen with CuS NPs-labeled hairpin probe H2 by the free primer strand (PS) triggering; hence, the CuS NPs as the emulative sensitizers were introduced onto the NTPP with the photocurrent intensity decrement for signal-off PEC state. During this process, the PS carefully designed with specific sequences can recognize the target strand (TS) of MCF-7 cells and stimulate HCR by its trigger zone. The presence of MCF-7 cells destroyed the interaction between PS and ZnFe2O4 functionalized TS, causing the PS release from the mixture of PS and TS under the help of a magnet. Then, the released PS, acting as a primer probe, realized ultrasensitive detection of a cell-surface protein. On the basis of this novel protocol, multiple-signal amplification was skillfully imported into the addressable paper PEC chip, resulting in ultrasensitive quantification of carcinoembryonic antigen in the surface of MCF-7 cells. Given the fascinating analytical performances of the developed cyto-sensor, ultralow expression of antigens for MCF-7, A549, and PC 3 cells was discriminated effectively.