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Environmental toxic pollutants and pathogens that enter the ecosystem are major global issues. Detection of these toxic chemicals/pollutants and the diagnosis of a disease is a first step in efficiently controlling their contamination and spread, respectively. Various analytical techniques are available to detect and determine toxic chemicals/pathogens, including liquid chromatography, HPLC, mass spectroscopy, and enzyme-linked immunosorbent assays. However, these sensing strategies have some drawbacks such as tedious sample pretreatment and preparation, the requirement for skilled technicians, and dependence on large laboratory-based instruments. Alternatively, biosensors, especially paper-based sensors, could be used extensively and are a cost-effective alternative to conventional laboratory testing. They can improve accessibility to testing to identify chemicals and pollutants, especially in developing countries. Due to its low cost, abundance, easy disposal (by incineration, for example) and biocompatible nature, paper is considered a versatile material for the development of environmentally friendly electrochemical/optical (bio) sensor devices. This review presents an overview of sensing platforms constructed from paper, pointing out the main merits and demerits of paper-based sensing systems, their fabrication techniques, and the different optical/electrochemical detection techniques that they exploit.

Rapid, simple, and sensitive analysis of relevant proteins is crucial in many research areas, such as clinical diagnosis and biomarker detection. In particular, clinical data on cancer biomarkers show great promise in forming reliable predictions for early cancer diagnostics, although the current analytical systems are difficult to implement in regions of limited recourses. Paper-based biosensors, in particular, have recently received great interest because they meet the criteria for point-of-care (PoC) devices; the main drawbacks with these devices are the low sensitivity and efficiency in performing quantitative measurements. In this work, we design a low-cost paper-based nanosensor through plasmonic calligraphy by directly drawing individual plasmonic lines on filter paper using a ballpoint pen filled with gold nanorods (AuNR) as the colloidal ink. The plasmonic arrays were further successively coated with negatively and positively charged polyelectrolyte layers employed as dielectric spacers to promote the enhancement of the emission of carboxyl-functionalized quantum dots (QD)—previously conjugated with specific antibodies—for indirect detection of the carcinoembryonic antigen-related cell adhesion molecule 5 (CEACAM5). The efficiency, sensitivity, as well as the specificity of our portable nanosensor were validated by recording the luminescence of the QD@Ab complex when different concentrations of CEACAM5 were added dropwise onto the calligraphed plasmonic arrays. [ABSTRACT FROM AUTHOR]

Deoxyribonuclease I (DNase I) is a biomarker which has important applications in various biological processes. Thus, it is highly important to develop a user-friendly method for the detection of DNase I. Here, we present a paper-based distance sensor for the rapid detection of DNase I based on changes in the viscosity of DNA mucus. The viscosity of DNA mucus varies with different concentrations of DNase I, showing different water flow lengths on the pH test papers, this makes the quantification of DNase I possible. This method has a wide linear range (0.01–10 U/mL), excellent sensitivity, remarkable specificity and excellent reproducibility. The detection limit reaches 0.003 U/mL. Additionally, it can be well applied to detection of DNase I inhibitors, assay of DNase I in human serum and quality evaluation of nucleic acid scavengers. In general, this study offers a brief, convenient, label-free, and economical method to construct paper-based distance sensors using DNA mucus, which is very promising in the detection of DNase I in various applications. [Display omitted] • The paper-based sensor detects DNase I by distance signal. • The new method for detecting DNase I based on viscosity changes. • The detection limit for DNase I is 0.003 U/mL. • The sensor shows excellent specificity, remarkable practicality and portability. [ABSTRACT FROM AUTHOR]

In the past few years, point-of-care testing (POCT) technology has crossed the boundaries of laboratory determination and entered the stage of practical applications. Herein, the latest advances and principal issues in the design and fabrication of paper-based bipolar electrode electrochemiluminescence (BPE-ECL) sensors, which are widely used in the POCT field, are highlighted. After introducing the attractive physical and chemical properties of cellulose paper, various approaches aimed at enhancing the functions of the paper, and their underlying principles are described. The materials typically employed for fabricating paper-based BPE are also discussed in detail. Subsequently, the universal method of enhancing BPE-ECL signal and improving detection accuracy is put forward, and the ECL detector widely used is introduced. Furthermore, the application of paper-based BPE-ECL sensors in biomedical, food, environmental and other fields are displayed. Finally, future opportunities and the remaining challenges are analyzed. It is expected that more design concepts and working principles for paper-based BPE-ECL sensors will be developed in the near future, paving the way for the development and application of paper-based BPE-ECL sensors in the POCT field and providing certain guarantee for the development of human health. • Preparation and application prospect of paper-based BPE-ECL sensor are discussed. • Approaches to boost functionalization of paper and existing limitations are described. • Fabricating BPE from classical electrode materials are introduced exhaustively. • Strategies of enhancing ECL signal to improve device sensitivity are displayed. [ABSTRACT FROM AUTHOR]

Signal amplification in colorimetric biosensors usually requires labile reagents and/or additional steps, which are not ideal for in-field measurements. Here we show that the limit of detection of a gold nanoparticle-labeled colorimetric immunosensor can be decreased 10-fold by performing the assay on a folded piece of paper. In this approach, the intrinsic porosity of the substrate enables generating multiple signals with a single drop of reagent. This yields combined signals with higher optical density thanks to the semitransparent nature of the wet material. It will be shown that this method can decrease the limit of detection 10 times in a model immunosensor for the detection of immunoglobulins. The procedure is so straightforward that it could be easily implemented to decrease the limit of detection of microfluidic paper-based analytical devices with colorimetric readouts. [ABSTRACT FROM AUTHOR]

Abstract Nowadays, point-of-care testing (POCT) techniques have achieved flourishing development in human health monitoring, where paper-based POCT platforms have exhibited superior properties of low cost, easy accessibility and eco-friendliness. For fabrication of paper-based POCT platforms, the pen-on-paper (PoP) strategies through directly writing desired functional materials on paper have been creatively developed in recent years. The PoP strategies are characterized by simplicity, rapid prototyping and do-it-yourself capability, and are also likely to realize scalable manufacturing through integration with software-controlled plotter. In this review, we firstly introduce various kinds of papers and pens employed in the PoP strategies, and then summarize the state-of-art advances of PoP strategies for making paper-based POCT platforms. Subsequently, we discuss the representative applications of PoP strategies for human health monitoring. Conclusions, current challenges and future perspectives of the PoP strategies for human health related POCT uses are finally given. Highlights • A variety of pens and papers involved in pen-on-paper (PoP) strategies are summarized. • The state-of-art of PoP strategies in realizing key steps involved in construction of POCT platforms are reviewed. • Representative applications of PoP strategies in human health monitoring are discussed. • Possible roadmaps can be oriented to move PoP strategies a giant step forward for human health. [ABSTRACT FROM AUTHOR]

In this work, a microfluidic paper-based fluorescent sensor device was constructed for quantitative detection of microRNA (miRNA) and determination of the expression of folate receptor (FR) on the cell surface. It is worth pointing out that simultaneous detection of two biomarkers in cancer was achieved through dynamic self-assembly of T-shaped duplex structure. T-shaped duplex structure can respond to specific triggers and convert to an output due to the conformation changes, it is meaningful to fabricate T-shaped duplex structure into powerful biosensors that can monitor chemical stimuli. Moreover, lamellar MnO 2 nanosheets were synthesized, which exhibited excellent quenching ability via adsorbed fluorophore-labeled ssDNA, but the adsorption of the dsDNA was significantly lower than ssDNA because of the shielding of nucleobase pairs by the phosphate groups. This newly designed biosensor provided a sensitive detection of miR-21 from 0.01 to 5.0 fM with a relatively low detection limit of 0.0033 fM. Besides, the present sensing system has a detection of FR in the range from 2.0 to 30.0 ng/mL with the detection limit of 0.667 ng/mL. As biological markers for disease diagnosis, the detection of FR and miRNA will provide a new approach and therapeutic tool for early clinical diagnosis. [ABSTRACT FROM AUTHOR]

Abstract: Paper, one of the oldest materials for storage and exchange of human's information, has been reinvented as a building component of electronic and optoelectronic devices over the past decades with successful demonstration of paper‐based or paper‐using devices. These recent achievements can meet the demand for lightweight, cost‐effective, and/or flexible electronic and optoelectronic devices with advanced functionality and reduced manufacturing costs. This article provides a review of electronic and optoelectronic devices relying on or making use of the unique properties achievable with paper‐based materials. Basic scientific/technical principles, quantitative comparisons of material, electronic and/or optical properties, and benefits for each paper‐based application are given. Application‐specific research challenges, future design considerations, and development directions are also discussed. [ABSTRACT FROM AUTHOR]

The attractive structural and mechanical properties of cellulose substrates (paper, cloth, and thread), including passive fluid transport, biocompatibility, durability, and flexibility, have attracted researchers in the past few decades to explore them as alternative microfluidic platforms. The incorporation of electrochemical (EC) sensing broadened their use for applications such as clinical diagnosis, pharmaceutical chemical analyses, food quality, and environmental monitoring. This article provides a review on the microfluidic devices constructed on paper, cloth, and thread substrates. It begins with an overview on paper-based microfluidic devices, followed by an in-depth review on the various applications of EC detection incorporated on paper-based microfluidic devices reported to date. The review on paper-based microfluidic devices attempts to convey a few perspective directions that cloth- and thread-based microfluidic devices may take in its development. Finally, the research efforts on the development and evaluation, as well as current limitations of cloth- and thread-based microfluidic devices are discussed. Microfluidic devices constructed on paper, cloth, and thread substrates are still at an early development stage (prototype) requiring several improvements in terms of fabrication, analytical techniques, and performance to become mature platforms that can be adapted and commercialized as real world products. However, they hold a promising potential as wearable devices. [ABSTRACT FROM AUTHOR]

Paper based microfluidic devices have emerged as a simple and low cost platform for efficient clinical diagnostics. An effort has been made in the present work to develop a microfluidic cholesterol biosensor using paper based platform. Microfluidic channels have been fabricated by patterning filter paper (Whatman 1) using photolithography. SU 8 photoresist formed a hydrophobic barrier on the paper with microchannels of dimensions 1000 μm(w)×100 μm(t). A three electrode system was fabricated by simple mask printing of graphite as the working, as well as the counter electrodes, and silver as the reference electrode. The working electrode was modified using nickel oxide nanoparticles prepared using co-precipitation method. Cholesterol oxidase enzyme is spotted on the test zone and chronoamperometric measurements are taken for different concentrations of cholesterol in the range of 0.12-10.23 mM, giving a quick and sensitive detection with a sensitivity of 24 µA mM−1 cm−2. [ABSTRACT FROM AUTHOR]

There is a need in the field of microfluidics for integration of analytical detection methods onto small fluidic chips. Electrogenerated chemiluminescence (ECL) is an effective method for detecting a wide range of analytes, including small molecules, metal ions and bacteria. This Minireview discusses recent applications of ECL-based detection methods to inexpensive microfluidic devices. We discuss various paper and cloth based devices, including 3D-origami devices and devices utilizing bipolar electrodes. We also discuss novel devices that have replaced traditional instrumentation with inexpensive and portable equipment, such as mobile phones. [ABSTRACT FROM AUTHOR]

A multi-amplified paper-based electrochemical strategy using Pb 2+ dependent DNAzyme as the recognition unit for Pb 2+ detection was developed. In this work, flower-like reduced graphene (FrGO) was prepared utilizing flower-like ZnO as template, which was first one step grown on the gold nanoparticles modified paper working electrode (Au-PWE). After being treated with acid and then modified with Au, a novel sensor platform named Au/FrGO/Au-PWE with large specific surface area and good electrical conductivity was fabricated. The Mn 2 O 3 nanoparticle-assembled hierarchical hollow spheres (H-Mn 2 O 3 ) was served as nanocarrier to immobilize GOx, HRP and signal strand (S3), resulting to the formation of S3/H-Mn 2 O 3 /HRP/GOx bioconjugations. In the presence of Pb 2+ , the DNAzyme (S1) was activated and the substrate strand (S2) was cleaved. After the incubation with S3/H-Mn 2 O 3 /HRP/GOx in 0.1 M HAc–NaAc solution (pH 4.3) containing 30 mM aniline and 15 mM glucose, a readily measurable “turn-on” electrochemical signal could be measured. On the basis of the signal amplification strategy of Au/FrGO/Au-PWE sensing platform and S3/H-Mn 2 O 3 /HRP/GOx bioconjugations, the developed biosensor exhibited a good linear response toward over a wide range of concentration from 0.005 to 2000 nM. [ABSTRACT FROM AUTHOR]

We report the fabrication of a paper-sensor for quantitative detection of α -amylase activity in human blood serum. Pieces of filter papers were coated with starch–iodine solution leading to an intense blue coloration on the surface. Dispensing α- amylase solution on the starch–iodine coated paper reduced the intensity of the color because of starch-hydrolysis catalyzed by amylase. The variation in the intensity of the color with the concentration of amylase was estimated in three stages: (i) initially, the paper-surface was illuminated with a light emitting diode, (ii) then, the transmitted (reflected) rays emitted through (from) the paper were collected on a photoresistor, and (iii) the variations in the electrical resistance of the photoresistor were correlated with the amylase concentration in analyte. The resistance of photoresistor decreased monotonically with an increase in amylase concentration because the intensity of the reflected (transmitted) rays collected from (through) the paper increased with reduction in the color intensity on the paper surface. Since a specific bio-reaction was employed to detect the activity of amylase, the sensor was found to be equally efficient in detecting unknown quantities of amylase in human blood serum. The reported sensor has shown the potential to graduate into a point-of-care detection tool for α- amylase. [ABSTRACT FROM AUTHOR]

This article details the study of electrochemical behavior of new carbon electrodes based on pyrolysis of different paper sources to be used in biosensor applications. The resistivity of the pyrolyzed papers was initially used as screening parameters to select the best three paper samples (imaging card paper, multipurpose printing paper, and 3MM chromatography paper) and assemble working electrodes that were further characterized by a combination of microscopy, electrochemistry, and spectroscopy. Although slight differences in performance were observed, all carbon substrates fabricated from pyrolysis of paper allowed the development of competitive biosensors for uric acid. The presented results demonstrate the potential of these electrodes for sensing applications and highlight the potential advantages of 3MM chromatography paper as a substrate to fabricate electrodes by pyrolysis. [ABSTRACT FROM AUTHOR]

We report on a paper device capable of carrying out target-induced rolling circle amplification (RCA) to produce massive DNA amplicons that can be easily visualized. Interestingly, we observed that RCA was more proficient on paper than in solution, which we attribute to a significantly higher localized concentration of immobilized DNA. Furthermore, we have successfully engineered a fully functional paper device for sensitive DNA or microRNA detection via printing of all RCA-enabling molecules within a polymeric sugar film formed from pullulan, which was integrated with the paper device. This encapsulation not only stabilizes the entrapped reagents at room temperature but also enables colorimetric bioassays with minimal steps. [ABSTRACT FROM AUTHOR]

There is growing interest in developing printable paper sensors to enable rapid testing of analytes for environmental, food safety, and clinical applications. A major challenge is to find suitable bioinks that are amenable to high-speed printing and remain functional after printing. We report on a simple and effective approach wherein an aqueous ink composed of megadalton-sized tandem repeating structure-switching DNA aptamers (concatemeric aptamers) is used to rapidly create patterned paper sensors on filter paper by inkjet printing. These concatemeric aptamer reporters remain immobilized at the point of printing through strong adsorption but retain sufficient segmental mobility to undergo structure switching and fluorescence signaling to provide both qualitative and quantitative detection of small molecules and protein targets. The convenience of inkjet printing allows for the patterning of internally referenced sensors with multiplexed detection, and provides a generic platform for on-demand printing of sensors even in remote locations. [ABSTRACT FROM AUTHOR]

In this paper, we report a multianode paper-based microbial fuel cell (MFC) capable of generating a power density of 28.4 μW/cm2. This MFC features: 1) flexible multilayered carbon cloth anodes for bacterial attachment and 2) paper reservoirs for holding the anolyte and catholyte for an extended period of time. The hydrophobic barriers in the anodes and paper-based reservoirs were patterned by impregnating and selectively polymerizing photoresist through UV lithography. Upon inoculum/catholyte introduction, a current of 211 μA/cm2 was immediately generated. By using the multianode MFC, the power and current densities increased by 5× and 3×, respectively, compared with a single anode one. The paper-based MFC is expected to be a simple and easy-to-use power source for single-use diagnostic biosensors because even sewage or soiled water in a puddle can become an excellent source for operating MFCs and harvesting electricity through bacterial metabolism. [ABSTRACT FROM PUBLISHER]

Highlights: [•] We present nanoparticle-based lateral-flow test-strip devices. [•] We review nanomaterial-based paper biosensors. [•] We discuss future opportunities for nanomaterial-based paper biosensors. [ABSTRACT FROM AUTHOR]

Abstract: Paper based colorimetric biosensing platform utilizing cross-linked siloxane 3-aminopropyltriethoxysilane (APTMS) as probe was developed for the detection of a broad range of targets including H2O2, glucose and protein biomarker. APTMS was extensively used for the modification of filter papers to develop paper based analytical devices. We discovered when APTMS was cross-linked with glutaraldehyde (GA), the resulting complex (APTMS–GA) displays brick-red color, and a visual color change was observed when the complex reacted with H2O2. By integrating the APTMS–GA complex with filter paper, the modified paper enables quantitative detection of H2O2 through the monitoring of the color intensity change of the paper via software Image J. Then, with the immobilization of glucose oxidase (GOx) onto the modified paper, glucose can be detected through the detection of enzymatically generated H2O2. For protein biomarker prostate specific antigen (PSA) assay, we immobilized capture, not captured anti-PSA antibody (Ab1) onto the paper surface and using GOx modified gold nanorod (GNR) as detection anti-PSA antibody (Ab2) label. The detection of PSA was also achieved via the liberated H2O2 when the GOx label reacted with glucose. The results demonstrated the possibility of this paper based sensor for the detection of different analytes with wide linear range. The low cost and simplicity of this paper based sensor could be developed for “point-of-care” analysis and find wide application in different areas. [Copyright &y& Elsevier]

Abstract: A novel strategy was reported for the preparation of TiO2 nanobelts by the acid-assisted hydrothermal method. Complex nanopaper based on the TiO2 nanobelts and graphene was fabricated via a modified paper-making process. The as-prepared TiO2–graphene structure inherited the excellent electron transport of graphene and facilitated the spatial separation of photo-generated charge carrier, therefore resulting in the enhanced photocurrent, and making it a promising candidate for developing photoelectrochemical (PEC) biosensors. Thus, an advanced PEC biosensing platform for the detection of carcinoembryonic antigen was proposed at relatively low applied potential on screen-printed working paper-electrode using the as-prepared TiO2–graphene complex nanopaper. The complex nanopaper with good biocompatibility showed high PEC intensity and satisfactory stability, all of which held great promise for the fabrication of PEC biosensors with improved sensitivity. Furthermore, the TiO2–graphene complex nanopaper based PEC biosensor in this study was anticipated to provide the chance for the design of high-performance PEC biosensors for the detection of other enzymes and biomolecules. [Copyright &y& Elsevier]

Inkjet-printed paper-based volatile organic compound (VOC) sensor strips imaged with polydiacetylenes (PDAs) are developed. A microemulsion ink containing bisurethane-substituted diacetylene (DA) monomers, 4BCMU, was inkjet printed onto paper using a conventional inkjet office printer. UV irradiation of the printed image allowed fabrication of blue-colored poly-4BCMU on the paper and the polymer was found to display colorimetric responses to VOCs. Interestingly, a blue-to-yellow color change was observed when the strip was exposed to chloroform vapor, which was accompanied by the generation of green fluorescence. The principal component analysis plot of the color and fluorescence images of the VOC-exposed polymers allowed a more precise discrimination of VOC vapors. [ABSTRACT FROM AUTHOR]

Research into paper-based sensors or functional materials that can perform analytical functions with active recognition capabilities is rapidly expanding, and significant research effort has been made into the design and fabrication of bioactive paper at the biosensor level to detect potential health hazards. A key step in the fabrication of bioactive paper is the design of the experimental and operational procedures for the immobilization of biomolecules such as antibodies, enzymes, phages, cells, proteins, synthetic polymers and DNA aptamers on a suitably prepared paper membrane. The immobilization methods are concisely categorized into physical absorption, bioactive ink entrapment, bioaffinity attachment and covalent chemical bonding immobilization. Each method has individual immobilization characteristics. Although every biomolecule-paper combination has to be optimized before use, the bioactive ink entrapment method is the most commonly used approach owing to its general applicability and biocompatibility. Currently, there are four common applications of bioactive paper: (1) paper-based bioassay or paper-based analytical devices for sample conditioning; (2) counterfeiting and countertempering in the packaging and construction industries; (3) pathogen detection for food and water quality monitoring; and (4) deactivation of pathogenic bacteria using antimicrobial paper. This article reviews and compares the different biomolecule immobilization techniques and discusses current trends. Current, emerging and future applications of bioactive paper are also discussed. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Abstract: Paper supports were used to develop a simple, inexpensive, fast and sensitive electrochemical immunosensor for the analysis of antibiotic residues in milk samples, where single-walled carbon nanotubes (SWNTs) and a simple dip–dry coating method were employed to prepare the highly sensitive biosensor. Well-dispersed SWNTs were impregnated with an antibody against neomycin to obtain a composite coating solution, followed by dipping the filtration paper in the solution to fabricate the sensitive biosensor which had high electrical conductivity. Based on the impedance change in the entire paper supported biosensor with increased concentrations of neomycin, the limit detection of the optimized method was 0.04ngmL−1 and a linear detection range from 0.2 to 125ngmL−1, well below the European Union regulations for neomycin in this matrix. This paper supported biosensor was applied to determine neomycin in milk samples after a simple sample treatment, with spiked recoveries which ranged from 93.25 to 110.47%. A variety of antibiotic residues in milk samples could be determined following similar sensor preparation. [Copyright &y& Elsevier]

Well-ordered two-dimensional functional nanostructure arrays have a broad range of potential applications in molecular electronics, ultra-high density data storage, biosensors, single-electron, single-photon and quantum computation devices. Various surface nanotemplates that are naturally or artificially patterned at the nanometre scale have been used to guide the formation of highly periodic nanostructure arrays. In this paper, we review recent progress in the development of various surface nanotemplates as well as the self-assembly of nanostructures on them, with particular emphasis on the unique SiC nanomesh template. The formation mechanism of this nanomesh template is attributed to the self-assembly of accumulated carbon atoms into well-ordered honeycomb superstructures at the nanometre scale on the 6H-SiC(0 0 0 1) surface. The size and spacing of unit cells of the SiC nanomesh can be tailored in the 2-2.5 nm range by adjusting the annealing time. This nanomesh is demonstrated to be an effective template for the formation of well-ordered molecular arrays of copper(II) phthalocyanine (CuPc). The growth of C60 on the nanomesh follows a typical Stranski-Krastanov mode, and a complete C60 wetting monolayer can be epitaxially grown on this nanotemplate. It is effective in isolating metal nanoclusters, resulting in the formation of monodispersed Co nanoclusters with a narrow size distribution. The adsorption and desorption of Co nanoclusters and C60 do not change its atomic structure, making it a chemically and thermally stable nanotemplate for the formation of well-ordered nanostructures arrays as well as monodispersed metal nanoclusters. [ABSTRACT FROM AUTHOR]

From the first investigations on peptide nucleic acids (PNA), peculiar features have been described as intrinsic of the singular chemical nature of these biomolecules. Relevant applications in the development of biosensors occurred in the last decades, exploiting them as bioreceptors. Their outstanding chemical and thermal stability as well as highly sensitive towards both complementary and non-complementary sequences, promoted them in the Olympus of biocomponents for applications in diagnostics. The intent of this review (85 ref) is to describe the last trends on the astonishing PNA technology in the biosensing field, in the view of the positive contamination with vanguard technologies including rational design and nanotechnology. In particular, electrochemical and optical biosensors exploiting PNA were reported from the literature, as well as nanostructured and paper-based biosensors for the design of microfluidics and lab-on-chip tools. • PNAs mimic DNA in binding oligonucleotide sequences through Hoogsteen base pairing in the major groove. • PNAs show outstanding stability and sensitivity towards both complementary and non-complementary sequences. • Vanguard technologies as rational design, nanotechnology, and microfluidics boost PNA use as smart bioreceptors for biosing. [ABSTRACT FROM AUTHOR]

Screen-printing technology has revolutionized many fields, including that of electrochemical biosensing. Due to their current relevance, this review, unlike other papers, discusses the relevant aspects of electrochemical biosensors manufactured using this technology in connection to both paper substrates and wearable formats. The main trends, advances, and opportunities provided by these types of devices, with particular attention to the environmental and biomedical fields, are addressed along with illustrative fundamentals and applications of selected representative approaches from the recent literature. The main challenges and future directions to tackle in this research area are also pointed out. [ABSTRACT FROM AUTHOR]

Abnormal expression of MicroRNA-21 (miRNA-21) is considered to be a reliable biomarker for the early diagnosis of cancer. In this work, a novel paper based biosensor was fabricated to detect sub-micro molar concentrations of miRNA-21 based on peroxidase mimetic activity of DNA-templated Ag/Pt nanoclusters (DNA-Ag/Pt NCs), which could catalyze the reaction of hydrogen peroxide and 3,3′,5,5′ tetramethylbenzidine (TMB), to produce a blue color. The Mechanism of reaction was based on the inhibition effect of miRNA-21 on peroxidase-like activity of nanosensor which resulted to quantitative determination of miRNA-21 concentration. It was found that miRNA-21 could be linearly detected in the range from 1-700 pM (A 652 = 0.16x-0.96, R2 = 0.99; x = -log [miRNA-21]) with a detection limit of 0.6 pM. Moreover, a paper assay was carried out on a Y-shaped paper-based microfluidic device in order to use the distinctive features of micro-channels such as short response time, very low reagent volume, low fabrication cost, etc. After performing paper based assay, a good linear range was observed between 10-1000 pM (y = 0.06x+147.48, R2 = 0.99; x = [miRNA-21]) with detection limit of 4.1 pM. The practical application of proposed method for detection of miRNA-21 in real sample was assayed in the human urine sample and indicated the colorimetric method had acceptable accuracy. Image 1 • A novel paper-based microfluidic sensor was designed for detection of miRNA-21. • The miRNA-21 detection mechanism is based on peroxidase mimetic activity of DNA-Ag/Pt NCs. • The color change was obvioused in different concentration of miRNA-21. • This strategy shows excellent selectivity toward miR-21. [ABSTRACT FROM AUTHOR]

In article number 1804798, Max Grell, Firat Guder, and co‐workers describe a method for depositing a wide range of metals inside fabrics which they call Si ink‐enabled autocatalytic metallization. Without requiring surface modification, the method provides access to devices as diverse as antennas, batteries, biosensors, or Raman spectroscopy substrates. Future research might bring many more applications for this highly adaptable method. [ABSTRACT FROM AUTHOR]

Commercially available metal inks are mainly designed for planar substrates (for example, polyethylene terephthalate foils or ceramics), and they contain hydrophobic polymer binders that fill the pores in fabrics when printed, thus resulting in hydrophobic electrodes. Here, a low‐cost binder‐free method for the metallization of woven and nonwoven fabrics is presented that preserves the 3D structure and hydrophilicity of the substrate. Metals such as Au, Ag, and Pt are grown autocatalytically, using metal salts, inside the fibrous network of fabrics at room temperature in a two‐step process, with a water‐based silicon particle ink acting as precursor. Using this method, (patterned) metallized fabrics are being enabled to be produced with low electrical resistance (less than 3.5 Ω sq−1). In addition to fabrics, the method is also compatible with other 3D hydrophilic substrates such as nitrocellulose membranes. The versatility of this method is demonstrated by producing coil antennas for wireless energy harvesting, Ag–Zn batteries for energy storage, electrochemical biosensors for the detection of DNA/proteins, and as a substrate for optical sensing by surface enhanced Raman spectroscopy. In the future, this method of metallization may pave the way for new classes of high‐performance devices using low‐cost fabrics. Hydrophilic metallization on fabrics for new high‐performance devices is demonstrated. A wide range of metals are deposited inside fabrics (paper, cotton) and nitrocellulose membranes, without modifying the surface. Coil antennas are then demonstrated for wireless energy harvesting, Ag–Zn batteries for energy storage, electrochemical biosensors for DNA/protein detection, and a substrate for surface enhanced Raman spectroscopy. [ABSTRACT FROM AUTHOR]