Recent Research Progress of Paper-Based Supercapacitors Based on Cellulose

In recent years,paper-based functional materials have received extensive attention in the field of energy storage due to their advantages of rich and adjustable porous network structure and good flexibility.As an important energy storage device,paper-based supercapacitors have important application prospects in many fields and have also received extensive attention from researchers in recent years.At present,researchers have modified and regulated paper-based materials by different means such as structural design and material composition to enhance their electrochemical storage capacity.The development of paper-based supercapacitors provides an important direction for the development of green and sustainable energy.Therefore,it is of great significance to summarize the relevant work of paper-based supercapacitors for their rapid development and application.In this review,the recent research progress of paper-based supercapacitors based on cellulose was summarized in terms of various cellulose-based composites,preparation skills,and electrochemical performance.Finally,some opinions on the problems in the development of this field and the future development trend were proposed.It is hoped that this review can provide valuable references and ideas for the rapid development of paper-based energy storage devices.

Rapid fabrication of modular 3D paper-basedmicrofluidic chips using projection-based 3D printing

Paper-based microchips have different advantages,such as better biocompatibility,simple production,and easy handling,making them promising candidates for clinical diagnosis and other fields.This study describes amethod developed to fabricate modular three-dimensional(3D)paper-based microfluidic chips based on projection-based 3D printing(PBP)technology.A series of two-dimensional(2D)paper-based microfluidic modules was designed and fabricated.After evaluating the effect of exposure time on the accuracy of the flow channel,the resolution of this channel was experimentally analyzed.Furthermore,several 3D paper-based microfluidic chips were assembled based on the 2D ones using different methods,with good channel connectivity.Scaffold-based 2D and hydrogel-based 3D cell culture systems based on 3D paper-based microfluidic chips were verified to be feasible.Furthermore,by combining extrusion 3D bioprinting technology and the proposed 3D paper-based microfluidic chips,multiorgan microfluidic chips were established by directly printing 3D hydrogel structures on 3D paperbased microfluidic chips,confirming that the prepared modular 3D paper-based microfluidic chip is potentially applicable in various biomedical applications.

Fiber swelling to improve cycle performance of paper-based separator for lithium-ion batteries application

It is well established that paper-based separators display short-circuit risk in lithium-ion batteries due to their intrinsic micron-sized pores.In this research,we have adjusted pore structure of paper by fiber swelling in liquid electrolyte.Specifically,the paper-based separator is prepared by propionylated sisal fibers through a wet papermaking process.Scanning electron microscope(SEM)and multi-range X-ray nano-computed tomography(CT)images display strong swelling of modified fibers after electrolyte absorption,which can effectively decrease the pore size of separator.Due to the high electrolyte uptake(817 wt%),paper-based separator exhibits ionic conductivity of 2.93 mS cm^(-1).^(7)Li solid-state NMR spectroscopy and Gaussian simulation reveal that the formation of local high Li^(+)ion concentration in the separator and its low absorption energy with Li^(+) ion(62.2 kcal mol^(-1))is conducive to the ionic transportation.In particular,the assembled Li/separator/LiFePO_(4) cell displays wide electrochemical stability window(5.2 V)and excellent cycle performance(capacity retention of 96.6%after 100 cycles at 0.5C)due to the reduced side reactions as well as enhanced electrolyte absorption and retention capacity by propionylation.Our proposed strategy will provide a novel perspective to design high-performance biobased separators to boost the development of clean and sustainable energy economy.

In Situ Directional Polymerization of Poly(1,3-dioxolane)Solid Electrolyte Induced by Cellulose Paper-Based Composite Separator for Lithium Metal Batteries

In traditional in situ polymerization preparation for solid-state electrolytes,initiators are directly added to the liquid precursor.In this article,a novel cellulose paper-based composite separator is fabricated,which employs alumina as the inorganic reinforcing material and is loaded with polymerization initiator aluminum trifluoromethanesulfonate.Based upon this,a separator-induced in situ directional polymerization technique is demonstrated,and the extra addition of initiators into liquid precursors is no longer required.The polymerization starts from the surface and interior of the separator and extends outward with the gradually dissolving of initiators into the precursor.Compared with its traditional counterpart,the separator-induced poly(1,3-dioxolane)electrolyte shows improved interfacial contact as well as appropriately mitigated polymerization rate,which are conducive to practical applications.Electrochemical measurement results show that the prepared poly(1,3-dioxolane)solid electrolyte possesses an oxidation potential up to 4.4 V and a high Li+transference number of 0.72.After 1000 cycles at 2 C rate(340 mA g^(−1)),the assembled Li||LiFePO_(4)solid battery possesses a 106.8 mAh g^(−1)discharge capacity retention and 83.5%capacity retention ratio,with high average Coulombic efficiency of 99.5%achieved.Our work may provide new ideas for the design and application of in situ polymerization technique for solid electrolytes and solid batteries.

A MXene-functionalized paper-based electrochemical immunosensor for label-free detection of cardiac troponin I

Convenient,rapid,and accurate detection of cardiac troponin I(cTnI)is crucial in early diagnosis of acute myocardial infarction(AMI).A paper-based electrochemical immunosensor is a promising choice in this field,because of the flexibility,porosity,and cost-efficacy of the paper.However,paper is poor in electronic conductivity and surface functionality.Herein,we report a paper-based electrochemical immunosensor for the label-free detection of cTnI with the working electrode modified by MXene(Ti_(3)C_(2))nanosheets.In order to immobilize the bio-receptor(anti-cTnI)on the MXene-modified working electrode,the MXene nanosheets were functionalized by aminosilane,and the functionalized MXene was immobilized onto the surface of the working electrode through Nafion.The large surface area of the MXene nanosheets facilitates the immobilization of antibodies,and the excellent conductivity facilitates the electron transfer between the electrochemical species and the underlying electrode surface.As a result,the paper-based immunosensor could detect cTnI within a wide range of 5-100 ng/mL with a detection limit of 0.58 ng/mL.The immunosensor also shows outstanding selectivity and good repeatability.Our MXene-modified paper-based electrochemical immunosensor enables fast and sensitive detection of cTnI,which may be used in real-time and cost-efficient monitoring of AMI diseases in clinics.

Fabrication of paper-based devices for in vitro tissue modeling

Paper devices have recently attracted considerable attention as a class of cost-effective cell culture substrates for various biomedical applications.The paper biomaterial can be used to partially mimic the in vivo cell microenvironments mainly due to its natural three-dimensional characteristic.The paper-based devices provide precise control over their structures as well as cell distributions,allowing recapitulation of certain interactions between the cells and the extracellular matrix.These features have shown great potential for the development of normal and diseased human tissue models.In this review,we discuss the fabrication of paper-based devices for in vitro tissue modeling,as well as the applications of these devices toward drug screening and personalized medicine.It is believed that paper as a biomaterial will play an essential role in the field of tissue model engineering due to its unique performances,such as good biocompatibility,eco-friendliness,cost-effectiveness,and amenability to various biodesign and manufacturing needs.

Facile Fabrication of Cellulosic Paper-based Composites with Temperature-controlled Hydrophobicity and Excellent Mechanical Strength

In this paper,we presented a novel strategy to employ a plantderived carbohydrate polymer,i.e.,cellulose,to prepare a hydrophobic composite.Cellulose was used as a scaffold,and ethylene-propylene side by side(ES)fiber was thermally melted and then coated on the cellulose surface to achieve hydrophobicity.Experimental results revealed that the thermocoating ES fibers greatly increased the water contact angle of the cellulose scaffold from 25°to 153°while simultaneously enhanced the wet tensile strength of the composite approximately 6.7-fold(drying temperature of 170℃)compared with the pure cellulose paper.In particular,compared with other related research,the prepared cellulose-based composite possessed excellent hydrophobicity and superior mechanical strength,which introduces a new chemical engineering approach to prepare hydrophobic cellulose-based functional materials.

Highly Improved Microstructure and Properties of Poly(p-phenylene terephthalamide) Paper-based Materials via Hot Calendering Process

In this study,the effect of hot calendering process on the microstructure and properties of poly(p-phenylene terephthalamide)(PPTA) paper-based materials was investigated.The microstructures of the fracture surface,crystalline structure,and single fiber strength of the PPTA paperbased materials as well as the different bonding behaviors between the PPTA fibers and PPTA fibrids obtained before and after the hot calendering process were examined.The results indicated that a high linear pressure would result in a limited improvement of the strength owing to the unimproved paper structure.The optimal values of tensile index and dielectric strength of 56.6 N·m/g and 27.6 kV/mm,respectively,could only be achieved with a synergistic effects of hot calendering temperature and linear pressure(240℃ and 110 k N/m,respectively).This result suggested it was possible to achieve a significant reinforcement and improvement in the interfacial bonding of functional PPTA paper-based materials,and avoid the formation of unexpected pleats and cracks in PPTA paper-based materials during the hot calendering process.

Determination of inhibitory activity of Salvia miltiorrhiza extracts on xanthine oxidase with a paper-based analytical device

A novel paper-based analytical device(PAD)was prepared and applied to determine the xanthine oxidase(XOD)inhibitory activity of Salvia miltiorrhiza extracts(SME).First,polycaprolactone was 3D printed on filter paper and heated to form hydrophobic barriers.Then the modified paper was cut according to the specific design.Necessary reagents including XOD for the colorimetric assay were immobilized on two separate pieces of paper.By simply adding phosphate buffer,the reaction was performed on the double-layer PAD.Quantitative results were obtained by analyzing the color intensity with the specialized device system(consisting of a smartphone,a detection box and sandwich plates).The 3Dprinted detection box was small,with a size of 9.0 cm×7.0 cm×11.5 cm.Color component G performed well in terms of linearity and detection limits and thus was identified as the index.The reaction conditions were optimized using a definitive screening design.Moreover,a 10%glycerol solution was found to be a suitable stabilizer.When the stabilizer was added,the activity of XOD could be maintained for at least 15 days under 4℃ or-20℃ storage conditions.The inhibitory activity of SME was investigated and compared to that of allopurinol.The results obtained with the PAD showed agreement with those obtained with the microplate method.In conclusion,the proposed PAD method is simple,accurate and has a potential for point-of-care testing.It also holds promise for use in rapid quality testing of medicinal herbs,intermediate products,and preparations of traditional Chinese medicines.

A flow chemiluminescence paper-based microfuidic device for detection of chromium(Ⅲ)in water

In this work,a solely gravity and capillary force-driven flow chemiluminescence(GCF-CL)paper-based microfuidic device has been proved for the first time as a new platforn for inex-pensive,usable,mini mally instrumented dynamic chemiluninescence(CL)detection of chromium(Ⅲ)[Cr(Ⅲ)],where an appropriate angle of inclination between the loading and detection zones on the paper produces a rapid flow of CL prompt solution through the paper charnel.For this study,we use a cost-effective paper device that is manufactured by a simple wax screen-printing method,while the signal generated from the Cr(Ⅲ)-catalyzed oxidation of luminol by H_(2)O_(2) is recorded by a low-cost and luggable CCD camera.A series of GCF-CL affecting factors have been evaluated carefully.At optimal conditions,two linear relationships between GCF-CL intensities and the logarithms of Cr(Ⅲ)concentrations are obtained in the concentration mnges of 0.025-35 mg/L and 50-500 mg/L separately,with the detection limit of 0.0245mg/L for a les than 30s assay,and relative standard deviations(RSDs)of 38%,4.5%and 2.3%for 0.75,5 and 50 mg/L of Cr(Ⅲ)(n=8).The above results indicate that the GCF-CL paper-based microfluidic device possesses a receivable sensitivity,dynamic range,storage stability and reproducibility.Finally,the developed GCF-CL is utilized for Cr(Ⅲ)detection in real water samples.

Literature Review of the Use of Zinc and Zinc Compounds in Paper-Based Microfluidic Devices

Zinc and its compounds, alloys and composites play an important role in the modern day world and find application in almost every aspect that can improve the quality of our lives. This ranges from supplements and pharmaceuticals that are meant to improve our health and wellbeing to additives meant to guard or reduce corrosion in metals. However, over the past several years, a new area of technology has been garnering a great deal of attention and has made use of zinc and its compounds. This is with reference to paper-based microfluidic technology that offers several advantages and that keeps expanding in the amount of applications it covers. In this paper, a review is offered for the applications that have used zinc or zinc compounds in paper-based microfluidic devices.

Flexible Paper-Based Li-ion Batteries: A Review

Lithium-ion (Li-ion) batteries have been fabricated in various ways to improve flexibility. Flexibility could be enhanced via active materials, separators, electrodes, and electrolytes, which could then be integrated to form flexible electronic devices with promising electrochemical properties compared to traditional non-flexible Li-ion batteries. Recent progress towards flexible Li- ion batteries fabrication, materials, and their electrochemical properties are investigated in this review. Additionally, recent developments in electronic devices utilizing flexible batteries and their future applications are explored. Portable and wearable electronics, as the primary beneficiaries of the flexible, rechargeable, and high-performance Li-ion batteries, are examined. In the end, various applications and challenges of flexible batteries in healthcare and various energy storage systems, considering practical implementation, are argued.

Reconfigurable paper-based metamaterial antenna: Structural transition from 2D to 3D

Paper-based electronics offer a simple and cost-effective means to fabricate reconfigurable devices. In response to the problem of fixed shape and single function of most antennas, which limits their applications, a reconfigurable paper-based metamaterial antenna with 2D and 3D forms is presented for tunable operating frequency. The proposed antenna consists of two square split resonant rings fed by a coplanar waveguide. The working frequency of the 2D antenna is adjusted by the length, width, and opening size of the internal open resonant ring. While the folding angle of the antenna turns from 0° to 90°, the operating frequency of the paper-based metamaterial antenna changes from 2.759 to 4.223 GHz. In terms of 3D form, an additional resonant peak is generated by bending the paper-based metamaterial antenna, thus further realizing dual-band antenna design.After a simple process flow, a series of proposed antennas are fabricated and evaluated. The simulated and measured results both demonstrate that the proposed antenna has a good performance in turning the working band. The environment-friendly nature and pliability of paper, as well as simple fabrication procedures, make paper-based metamaterial promising candidates for future green electronics.

Paper-based biosensors based on multiple recognition modes for visual detection of microbially contaminated food

Microbially contaminated food can cause serious health hazards and economic losses,therefore sensitive,rapid,and highly specific visual detection is called for.Traditional detection of microorganisms is complex and time-consuming,which cannot meet current testing demands.The emergence of paper-based biosensors provided an effective method for efficient and visual detection of microorganisms,due to its high speed,all-in-one device,low cost,and convenience.This review focused on 5 biomarkers,namely nucleic acids,proteins,lipopolysaccharides.metabolites,and the whole microorganism of microorganisms.Besides,the recognition methods were summed up in 5 forms,including immunological recognition,aptamer recognition,nucleic acid amplification-mediated recognition.DNAzyme recognition and clustered regularly interspaced short palindromic repeats mediated recognition.In addition,we summarized the applications of paper-based biosensors in the detection of microorganisms thoroughly.Through the exploration of different biomarkers,identification methods,and applications,we hope to provide a reference for the development of paper-based biosensors and their application in safeguarding the food chain.

Transparent paper-based triboelectric nanogenerator as a page mark and anti-theft sensor

The triboelectric nanogenerator （TENG）, based on the well-known triboelectric effect and electrostatic induction effect, has been proven to be a simple, cost effective approach for self-powered systems to convert ambient mechanical energy into electricity. We report a flexible and transparent paper-based triboelectric nanogenerator （PTENG） consisting of an indium tin oxide （ITO） film and a polyethylene terephthalate （PET） film as the triboelectric surfaces, which not only acts as an energy supply but also as a self-powered active sensor. It can harvest kinetic energy when the sheets of paper come into contact, bend or slide relative to one another by a combination of vertical contact-separation mode and lateral sliding mode. In addition, we also integrate grating-structured PTENGs into a book as a self-powered anti-theft sensor. The mechanical agitation during handling the book pages can be effectively converted into an electrical output to either drive a commercial electronic device or trigger a warning buzzer. Furthermore, different grating-structures on each page produce different numbers of output peaks by sliding relative to one another, which can accurately act as a page mark and record the number of pages turned. This work is a significant step forward in self-powered paper-based devices.

A paper-based microfluidic biosensor integrating zinc oxide nanowires for electrochemical glucose detection

This paper reports an electrochemical microfluidic paper-based analytical device(EμPAD)for glucose detection,featuring a highly sensitive working electrode(WE)decorated with zinc oxide nanowires(ZnO NWs).In addition to the common features ofμPADs,such as their low costs,high portability/disposability,and ease of operation,the reported EμPAD has three further advantages.(i)It provides higher sensitivity and a lower limit of detection(LOD)than previously reportedμPADs because of the high surface-to-volume ratio and high enzyme-capturing efficiency of the ZnO NWs.(ii)It does not need any light-sensitive electron mediator(as is usually required in enzymatic glucose sensing),which leads to enhanced biosensing stability.(iii)The ZnO NWs are directly synthesized on the paper substrate via low-temperature hydrothermal growth,representing a simple,low-cost,consistent,and mass-producible process.To achieve superior analytical performance,the on-chip stored enzyme(glucose oxidase)dose and the assay incubation time are tuned.More importantly,the critical design parameters of the EμPAD,including the WE area and the ZnO-NW growth level,are adjusted to yield tunable ranges for the assay sensitivity and LOD.The highest sensitivity that we have achieved is 8.24μA·mM^(−1)·cm^(−2),with a corresponding LOD of 59.5μM.By choosing the right combination of design parameters,we constructed EμPADs that cover the range of clinically relevant glucose concentrations(0−15 mM)and fully calibrated these devices using spiked phosphate-buffered saline and human serum.We believe that the reported approach for integrating ZnO NWs on EμPADs could be well utilized in many other designs of EμPADs and provides a facile and inexpensive paradigm for further enhancing the device performance.

Screen printing fabricating patterned and customized full paper-based energy storage devices with excellent photothermal,self-healing,high energy density and good electromagnetic shielding performances

Supercapacitors are favored by researchers because of their high power density,especially with the acceleration of people’s life rhythm.However,their energy density,especially from the point of view of the whole energy storage device,is far lower than that of commercial batteries.In this work,a kind of customizable full paper-based supercapacitor device with excellent self-healing ability is fabricated by simple and low-cost screen printing,electropolymerization and dip coating methods.The resultant separatorfree supercapacitor device exhibits both ultrahigh gravimetric and areal specific energy(power)densities of 39 Wh kg^(-1)(69 k W kg^(-1))and 692μWh cm^(-2)(236 m W cm^(-2)),achieving excellent supercapacitor performance.Notably,the addition of vitrimers endows the whole device with outstanding self-healing properties,which is helpful for enhancing the adaptability of the device to the environment.In addition,this kind of paper-based device also displays good photothermal and electromagnetic shielding performances.These striking features make paper matrix composites attractive in the fields of supercapacitors,medical photothermal treatment and electromagnetic shielding.

Recent Advances and Applications in Paper-Based Devices for Point-of-Care Testing

Point-of-care testing(POCT),as a portable and user-friendly technology,can obtain accurate test results immediately at the sampling point.Nowadays,microfluidic paper-based analysis devices(μPads)have attracted the eye of the public and accelerated the development of POCT.A variety of detection methods are combined withμPads to realize precise,rapid and sensitive POCT.This article mainly introduced the development of electrochemistry and optical detection methods onμPads for POCT and their applications on disease analysis,environmental monitoring and food control in the past 5 years.Finally,the challenges and future development prospects ofμPads for POCT were discussed.

An ultra-sensitive and wide measuring range pressure sensor with paper-based CNT film/interdigitated structure

Flexible pressure sensors have attracted great attention due to their potential in the wearable devices market and in particular in human-machine interactive interfaces.Pressure sensors with high sensitivity,wide measurement range,and low-cost are now highly desired for such practical applications.In the present investigation,an ultrasensitive pressure sensor with wide measurement range has been successfully fabricated.Carbon nanotubes(CNTs)(uniformly sprayed on the surface of paper)comprise the sensitivity material,while lithographed interdigital electrodes comprise the substrate.Due to the synergistic effects of CNT’s high specific surface area,paper’s porous structure,interdigital electrodes’efficient contact with CNT,our pressure sensor realizes a wide measurement range from 0 to 140 kPa and exhibits excellent stability through 15,000 cycles of testing.For the paper-based CNT film/interdigitated structure(PCI)pressure sensor,the connection area between the sensitive material and interdigital electrodes dominates in the lowpressure region,while internal change within the sensitive materials plays the leading role in the high-pressure region.Additionally,the PCI pressure sensor not only displays a high sensitivity of 2.72 kPa–1(up to 35 kPa)but also can detect low pressures,such as that exerted by a resting mung bean(about 8 Pa).When attached to the surface of a human body,the pressure sensor can monitor physiological signals,such as wrist movement,pulse beats,or movement of throat muscles.Furthermore,the pressure sensor array can identify the spatial pressure distribution,with promising applications in humanmachine interactive interfaces.

Disposable paper-based bipolar electrode array for multiplexed electrochemiluminescence detection of pathogenic DNAs

A novel disposable paper-based bipolar electrode （BPE） array is fabricated for multiplexed electrochemiluminescence （ECL） detection of pathogenic DNAs. This proposed BPE array device consists of 15 units, each consisting of six sensing cells and two reporting cells patterned using hydrophobic wax. A hairpin structure DNA assembled on the cathodes of BPEs hybridizes with Pt nanoparticles （NPs） labeled probe DNA in the presence of complementary target DNA. The introduction of Pt NPs catalyzes the reduction of dissolved 02 at cathodes and induces an enhanced ECL signal from Ru（bpy）32＋/tripropylamine （TPrA） at the anodes of BPEs. The dissolved 02 lost in reduction reaction could be promptly replenished due to the relatively large contact area of the paper-based cells with air, which ensures the stability of ECL signal. This obtained paper-based BPE array sensor showed excellent performances for the multiplexed analysis of the syphilis （Treponema pallidum） gene, the immunodeficiency virus gene （HIV） and hepatitis B virus gene （HBV）.