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.

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.

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.

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.

A Smartphone-assisted Paper-based Analytical Device for Fluorescence Assay of Hg2+

Rapid,efficiency and portable detection systems in low-resource settings with limited laboratory equipment and technical expertise are urgently needed.Herein,an integrated platform composed of a paper-based analytical device and a smartphone detection system for Hg^2+ onsite testing was developed.Nitrogen-doped carbon dots(N-CDs)were synthesized by a simple hydrothermal method using citric acid as the carbon source and ethanediamine as the nitrogen source,which gave out bright blue fluorescence under the excitation at 350 nm UV light and the absolute fluorescence quantum yield was 17.1%.The fluorescence of the prepared N-CDs can be effectively quenched by Hg^2+.In addition,an external attachment of smartphone for illumination and external light interference was designed to trace the fluorescence signals,and a software application of Android system with simple operation program was developed to perform snapshot and image processing.The smartphone-assisted detection system was combined with the N-CDs decorated paper chip to achieve the sensitive detection of Hg^2+ in water samples.This integrated method for reliable sensing of Hg^2+ shows a good linear detection range of 10–800μmol/L(R2=0.9595)with detection limit of 1.07×10^?8 mol/L.

Paper-based fluorescent devices for multifunctional assays:Biomarkers detection,inhibitors screening and chiral recognition

The development of a single analytical platform with different functions is highly desirable but remains a challenge at present.Here,a paper-based device based on fluorescent carbon dots(CDs)functionalized paper/MnO_(2)nanosheets(MnO_(2)NS)hybrid devices(PCD/NS)was proposed for single-device multi-function applications.MnO_(2)NS functioned as a fluorescence quencher of CDs and recognizer of H_(2)O_(2)released from the oxidase catalyzed system.Fluorescence recovery would occur after the decomposition of MnO_(2)NS induced by H_(2)O_(2),by which a simple and effective strategy could be developed for fluorescence monitoring multiplex biological events.Xanthine(XA)sensing,xanthine oxidase(XOD)inhibitors screening analysis and chiral recognition of glucose enantiomers were performed on PCD/NS to investigate the multifunctional application of the paper-based device.By means of PCD/NS,XA could be determined in the range of 0.1–40μmol/L with a low detection of limit of 0.06μmol/L.The IC_(50)value of allopurinol,the model inhibitor of XOD,was sensitively detected to be 7.4μmol/L.Glucose enantiomers were also recognized in terms of the specific fluorescence response to d-glucose.This work firstly presented a paper-based device capable of biomarkers detection,inhibitors screening and chiral recognition,which enlightened a promising strategy for the construction of multifunctional devices and hold the great potential application in clinical diagnosis and drug discovery.

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）.

An All‑In‑One Multifunctional Touch Sensor with Carbon‑Based Gradient Resistance Elements

Human–machine interactions using deep-learning methods are important in the research of virtual reality,augmented reality,and metaverse.Such research remains challenging as current interactive sensing interfaces for single-point or multipoint touch input are trapped by massive crossover electrodes,signal crosstalk,propagation delay,and demanding configuration requirements.Here,an all-inone multipoint touch sensor(AIOM touch sensor)with only two electrodes is reported.The AIOM touch sensor is efficiently constructed by gradient resistance elements,which can highly adapt to diverse application-dependent configurations.Combined with deep learning method,the AIOM touch sensor can be utilized to recognize,learn,and memorize human–machine interactions.A biometric verification system is built based on the AIOM touch sensor,which achieves a high identification accuracy of over 98%and offers a promising hybrid cyber security against password leaking.Diversiform human–machine interactions,including freely playing piano music and programmatically controlling a drone,demonstrate the high stability,rapid response time,and excellent spatiotemporally dynamic resolution of the AIOM touch sensor,which will promote significant development of interactive sensing interfaces between fingertips and virtual objects.

Functional poly(carboxybetaine methacrylate)coated paper sensor for high efficient and multiple detection of nutrients in fruit

Rapid and simultaneous in situ detection of multi-components is extremely crucial for the real-time monitoring of nutrients in fruits.Herein,a facile and user-friendly poly(carboxybetaine methacrylate)-coated paper-based microfluidic device(pCBMA-μPAD)has been exploited to synchronously identify and semi-quantify vitamin C.glucose,sucro se and fructose in fruits.The pCBMA was successfully grafted from the surface of paper sensor using a co nvenient and robust method,which was confirmed by Fourier transform infrared spectroscopy(FT-IR)and X-ray photoelectron spectrometry(XPS).The superior hydrophilicity and ultra-low fouling of pCBMA endowed the pCBMA-μPAD with remarkably rapid response(3 min),high sensitivity,good linear relationship and low detection limit(LOD)(vitamin C:y=33.809+5.175 x,R^2=0.993,LOD=0.179 mmol/L;glucose:y=-0.113+30.0661 g(x),R^2=0.988,LOD=0.095 mmol/L;sucrose:y--5.334+34.858 lg(x),R^2=0.996,LOD=0.097 mmol/L;fructose:y=4.996+23.325 lg(x),R^2=0.994,LOD=0.140 mmol/L).Furthermore,satisfactory results were yielded in the detection of these nutrients in 9 fruits,which were much agreed well with those obtained by spectrophotometry.Such a portable and versatile pCBMA-μPAD will pro foundly shape the future of food analysis,especially for the assessment of food quality and nutrition in the process of agricultural production and marketing.