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This paper introduces a novel potential-resolved paper-based biosensor for simultaneous detection of multiple microRNAs (miRNAs) (taking miRNA-155 and miRNA-126 as examples) based on the bipolar electrode (BPE) electrochemiluminescence (ECL) strategy. The proposed multiple-channel paper-based sensing microfluidic platform was prepared by wax-printing technology, screen-printing method, and in situ Au nanoparticles (AuNPs) growth to form hydrophilic areas, hydrophobic boundaries, waterproof electronic bridge, driving electrode regions, and parallel bipolar electrode regions. CdTe quantum dots (QDs)-H2 and Au@g-C3N4 nanosheets (NSs)-DNA1 were used as dual electrochemiluminescence signal probes, and carboxylated Fe3O4 magnetic nanoparticles existed as carriers. CdTe QDs-H2/S2O82- and Au@g-C3N4 NSs-DNA1/S2O82- could exhibit two strong and stable ECL emissions at a drive voltage of 9 and 12 V, respectively, which can be used as effective potential-resolved signal tags. In addition, the proposed three-dimensional (3D) DNA nanomachine model and the target miRNA cycle strategy were used to achieve double amplification of electrochemiluminescence intensity. More importantly, the combination of the bipolar electrode system and the potential-resolved multitarget electrochemiluminescence method can greatly reduce the spatial interference between substances. The prepared ECL biosensor showed a favorable linear response for the detection of miRNA-155 and miRNA-126 with relatively low detection limits of 5.7 and 4.2 fM, respectively. With excellent sensitivity, the strategy may provide an efficient method for clinical application, especially in detection of trace multiple targets.

Exploring efficient luminophores in the electrochemiluminescence (ECL) system is highly desired to pursue a sensitive ECL sensing platform. Herein, the black phosphorus nanosheets (BP NSs) with excellent ECL properties are investigated and serve as the luminophore with the coreactant of peroxydisulfate (S2O82-) solution. Moreover, owing to the overlapping of emission and absorbance spectra, effective resonance energy transfer (RET) is realized between the BP NSs and the introduced Au nanoparticles. In order to achieve the portable and miniaturized developing trends for the paper-based ECL sensing platform, a paper-based perovskite solar cell (PSC) device is designed to act as the power source to replace the commonly utilized expensive and cumbersome electrochemical workstation. Benefiting from that, a PSC driven paper-based constant potential ECL-RET sensing platform is constructed, thereby realizing sensitive microRNAs (miRNAs) detection. What's more, to attain the preferable analytical performance, the duplex-specific nuclease (DSN) is also introduced to assist the target recycling signal amplification strategy. Based on this, highly sensitive detection of miRNA-107 with a range from 0.1 pM to 15 nM is achieved by this designed sensing platform. Most importantly, this work not only pioneers a precedent for developing a high-sensitivity PSC triggered ECL sensing platform but also explores the application prospect of BP nanomaterial in the field of bioanalysis.

In this work, a novel dual photoelectrochemical/colorimetric cyto-analysis format was first introduced into a microfluidic paper-based analytical device (μ-PAD) for synchronous sensitive and visual detection of H2O2 released from tumor cells based on an in situ hydroxyl radicals ((•)OH) cleaving DNA approach. The resulted μ-PAD offered an excellent platform for high-performance biosensing applications, which was constructed by a layer-by-layer modification of concanavalin A, graphene quantum dots (GQDs) labeled flower-like Au@Pd alloy nanoparticles (NPs) probe, and tumor cells on the surface of the vertically aligned bamboo like ZnO, which grows on a pyknotic Pt NPs modified paper working electrode (ZnO/Pt-PWE). It was the effective matching of energy levels between GQDs and ZnO levels that lead to the enhancement of the photocurrent response compared with the bare ZnO/Pt-PWE. After releasing H2O2, the DNA strand was cleaved by (•)OH generated under the synergistic catalysis of GQDs and Au@Pd alloy NPs and thus, reduced the photocurrent, resulting in a high sensitivity to H2O2 in aqueous solutions with a detection limit of 0.05 nmol observed, much lower than that in the previously reported method. The disengaged probe can result in catalytic chromogenic reaction of substrates, resulting in real-time imaging of H2O2 biological processes. Therefore, this work provided a truly low-cost, simple, and disposable μ-PAD for precise and visual detection of cellular H2O2, which had potential utility to cellular biology and pathophysiology.

We report the first portable upconversion nanoparticles (UCNPs)-based paper device for road-side field testing of cocaine. Upon the recognition of cocaine by two pieces of rationally designed aptamer fragments, the luminescence of UCNPs immobilized on the paper is quenched by Au nanoparticles (AuNPs), which indicates the cocaine concentration. This device can give quantitative results in a short time with high sensitivity using only a smartphone as the apparatus. Moreover, this device is applicable in human saliva samples, and it also can be used to monitor the cocaine content change in blood samples. The results of this work demonstrate the prospect of developing UCNPs-based paper devices for field testing of drug abuse.

Viral pathogens are a serious health threat around the world, particularly in resource limited settings, where current sensing approaches are often insufficient and slow, compounding the spread and burden of these pathogens. Here, we describe a label-free, point-of-care approach toward detection of virus particles, based on a microfluidic paper-based analytical device with integrated microwire Au electrodes. The device is initially characterized through capturing of streptavidin modified nanoparticles by biotin-modified microwires. An order of magnitude improvement in detection limits is achieved through use of a microfluidic device over a classical static paper-based device, due to enhanced mass transport and capturing of particles on the modified electrodes. Electrochemical impedance spectroscopy detection or West Nile virus particles was carried out using antibody runctionalized Au microwires, achieving a detection limit of 10.2 particles in 50 μL of cell culture media. No increase in signal is found on addition of an excess of a nonspecific target (Sindbis). This detection motif is significantly cheaper (~$1 per test) and faster (~30 min) than current methods, while achieving the desired selectivity and sensitivity. This sensing motif represents a general platform for trace detection of a wide range of biological pathogens.

We introduce a surface-enhanced Raman scattering (SERS)-functionalized, gold nanoparticle (GNP)-deposited paper strip capable of label-free biofluid sensing for the early detection of infectious eye diseases. The GNP biosensing paper strip was fabricated by the direct synthesis and deposition of GNPs on wax-divided hydrophilic areas of a permeable porous substrate through a facile, power-free synthesizable, and highly reproducible successive ionic layer absorption and reaction (SILAR) technique. To maximize localized surface plasmon resonance-generated SERS activity, the concentration of the reactive solution and number of SILAR cycles were optimized by controlling the size and gap distance of GNPs and verified by computational modeling with geometrical hypotheses of Gaussian-estimated metallic nanoparticles. The responses of our SERS-functionalized GNP paper strip to Raman intensities exhibited an enhancement factor of 7.8 × 10(8), high reproducibility (relative standard deviation of 7.5%), and 1 pM 2-naphthalenethiol highly sensitive detection limit with a correlation coefficient of 0.99, achieved by optimized SILAR conditions including a 10/10 mM/mM HAuCl4/NaBH4 concentration and six SILAR cycles. The SERS-functionalized GNP paper is supported by a multivariate statistics-preprocessed machine learning-judged bioclassification system to provide excellent label-free chemical structure sensitivity for identifying infectious keratoconjunctivitis. The power-free synthesizable fabrication, label-free, rapid analysis, and high sensitivity feature of the SILAR-fabricated SERS-functionalized GNP biosensing paper strip makes it an excellent alternative in point-of-care applications for the early detection of various infectious diseases.

Convenient, rapid, and accurate detection of chemical and biomolecules would be a great benefit to medical, pharmaceutical, and environmental sciences. Many chemical and biosensors based on metal nanoparticles (NPs) have been developed. However, as a result of the inconvenience and complexity of most of the current preparation techniques, surface plasmon-based test papers are not as common as, for example, litmus paper, which finds daily use. In this paper, we propose a convenient and practical technique, based on the photothermal effect, to fabricate the plasmonic test paper. This technique is superior to other reported methods for its rapid fabrication time (a few seconds), large-area throughput, selectivity in the positioning of the NPs, and the capability of preparing NP arrays in high density on various paper substrates. In addition to their low cost, portability, flexibility, and biodegradability, plasmonic test paper can be burned after detecting contagious biomolecules, making them safe and eco-friendly.

This paper describes a colorimetric sensor array for the discrimination of volatile amines. Analyte discrimination is achieved by combining two functional elements: (1) a "chemical class-selective" single chromogenic sensing dye with selectivity for amines in general, encapsulated into (2) polymer nanoparticles with different polarities. The resulting array has the ability to distinguish one closely related amine from another, relying on a polarity-based approach. In order to achieve reproducible, cost efficient, and flexible sensor array fabrication with the potential for mass production, inkjet-printing technology combined with standard copy paper as a sensor substrate is applied. Printing of 6 types of inks, which are prepared by mixing two dye encapsulating nanoparticles of different polarity in different mixture ratios, results in a colorimetric sensor array with a polarity gradient. Seven primary amines with increasing alkyl chain lengths have been selected to demonstrate the performance of the sensor array. The RGB color differences (ΔR, ΔG, ΔB) of the sensor array spots before and after gas exposure were analyzed by principal component analysis (PCA) and agglomerative hierarchical clustering (AHC) analysis. Under the selected measurement conditions, results of PCA and AHC analysis indicated high discrimination ability with high reproducibility of the sensor array down to amine concentrations of 50 ppm. The discrimination ability was maintained at relative humidities between 10% and 80%. Furthermore, the sensor array showed no significant response to common volatile organic compounds, confirming the high selectivity toward amines. This is, to the best of our knowledge, the first report of a colorimetric sensor array with selectivity for a specific chemical class of analytes and the ability to discriminate compounds of the same class, which is obtained by simply mixing two types of single dye-encapsulating polymer nanoparticles.

The majority of bioassays utilize thermosensitive reagents (e.g., biomolecules) and laboratory conditions for analysis. The developing world, however, requires inexpensive, simple-to-perform tests that do not require refrigeration or access to highly trained technicians. To address this need, paper-based bioassays using gold nanoparticle (AuNP) colorimetric probes have been developed. In the two prototype DNase I and adenosine-sensing assays, blue (or black)-colored DNA-cross-linked AuNP aggregates were spotted on paper substrates. The addition of target DNase I (or adenosine) solution dissociated the gold aggregates into dispersed AuNPs, which generated an intense red color on paper within one minute. Both hydrophobic and (poly(vinyl alcohol)-coated) hydrophilic paper substrates were suitable for this biosensing platform; by contrast, uncoated hydrophilic paper caused "bleeding" and premature cessation of the assay due to surface drying. The assays are surprisingly thermally stable. During preparation, AuNP aggregate-coated papers can be dried at elevated temperatures (e.g., 90 degrees C) without significant loss of biosensing performance, which suggests the paper substrate protects AuNP aggregate probes from external nonspecific stimuli (e.g., heat). Moreover, the dried AuNP aggregate-coated papers can be stored for at least several weeks without loss of the biosensing function. The combination of paper substrates and AuNP colorimetric probes makes the final products inexpensive, low-volume, portable, disposable, and easy-to-use. We believe this simple, practical bioassay platform will be of interest for use in areas such as disease diagnostics, pathogen detection, and quality monitoring of food and water.