Search

Jaundice continues to be a serious health concern and is among the leading causes of deaths during the first days of newborn babies’ lives. Serum bilirubin is currently being exploited in the clinic as a key biomarker for the diagnosis and management of neonatal jaundice. The commonly used methods for serum bilirubin determination in clinical settings are direct spectroscopic measurement and the diazo reaction method. These methods have drawbacks such as low sensitivity, matrix interference, poor stability, high-cost, professional training, less specificity and tedious sample preparation. Thus, it is very urgent to develop a rapid and economical route for sensitive and specific detection of free bilirubin directly in human serum. Surface-enhanced Raman scattering (SERS) has emerged as a powerful analytical technique for biosensing applications with high sensitivity, molecular specificity, powerful multiplex detection capability, and excellent photostability. This talk will present our recent study on the development of a paper-based SERS biosensor for label-free detection of bilirubin in serum. This biosensor comprises multifunctional graphene oxide-gold nanostar (GO-GNS) hybrids decorated on the filter paper. This biosensor combines the enrichment for serum bilirubin and plasmonic enhancement for Raman signals of bilirubin for boosting the label-free detection sensitivity directly in blood serum without the need for additional sample preparation. Our results demonstrated the excellent detection performance for detection of bilirubin directly in serum in a label-free manner, and the detection results were compared with the commercial diazo reaction method, which justifies the clinical effectiveness and suitability of the present paper-based SERS biosensor. We believe that the present paper-based SERS biosensor has great potential for clinical translation in accurate diagnosis of jaundice and other related diseases. Reference: Xiang Pan, Linhu Li, Hangduo Lin, Jiayi Tan, Haitao Wang, Mengling Liao, Caiju Chen, Beibei Shan, Yingfan Chen, Ming Li, A graphene oxide-gold nanostar hybrid based-paper biosensor for label-free SERS detection of serum bilirubin for diagnosis of jaundice, Biosensors and Bioelectronics, 2019, 145, 111713.

Point-of-care testing (POCT) of proteins is crucial for on-site and rapid diagnosis of diseases in community and family medicine. Microfluidic paper-based analytical devices (µPADs) have attracted growing attention in POCT of proteins, while the practical applications of µPADs in the analysis of proteins in physiological samples is still limited as physiological samples are usually high-salt and complex. Herein, we developed a three-dimensional (3D) paper-based isoelectric focusing (IEF) platform, which is composed of power supply, reservoirs and separation channel make by origami and stacking of cellulose acetate membrane, to simultaneously separate and enrich proteins in both low-salt samples and high-salt samples, especially for directly pretreating and analyzing proteins in physiological samples. Under the optimized experimental conditions, standard proteins (Phy and BHb) were separated in 18 min under a 36.0 V power supply and obtained 10-fold enrichment using the 3D paper-based IEF platform. Then, the capability of the 3D paper-based IEF platform with using a 12.0 V battery as power supply for direct pre-treatment of high-salt samples was proven through separating three standard proteins in saline (0.9 % NaCl) with separation resolution (SR) >1.29. Through further coupling with colorimetric and lateral flow strip measurements, the 3D paper-based IEF platform was applied to directly pre-treat and quantitatively analyze the two disease biomarkers, i.e., microalbuminuria and C-reactive proteins in clinical human serum. The analytical results had the relative deviations of References [1] J. C. Niu, T. Zhou, L. L. Niu, Z. S. Xie, F. Fang, F. Q. Yang, Z. Y. Wu, Simultaneous Pre-concentration and Separation on Simple Paper-based Analytical Device for Protein Analysis, Analytical and Bioanalytical Chemistry 410.6 (2018): 1689-1695. [2] J. C. Niu, H. X. Shi, H. G. Wei, B. Gao, J. X. Li, F. Xu, X. G. Li, F. Li, Liquid Plasticine Integrated with Isoelectric Focusing for Miniaturized Protein Analysis, Analytical Chemistry 92.13 (2020): 9048–9056.

In this work, by utilizing carbon paper having cress-crossing fibrous network structure as a template, high porosity crystalline V2O5 film electrode is synthesized using a simple sol precursor dip-dry-anneal method. Detailed cyclic voltammetry (CV), charge-discharge (CD) and impedance measurements were carried out in acetonitrile +LiClO4 electrolyte. CV data identify V5+/V4+ and V4+ /V3+ redox peaks which yield high specific capacitance of 800 Fg-1. These values are significantly higher compared with the similarly processed V2O5 over flat stainless steel (SS) foil substrate which proves the efficacy of carbon fiber paper for structuring V2O5 and in enhancing its specific capacitance. The CD data show high (>92%) Coulomb efficiency highly reversible redox reactions compared to the V2O5 film over SS. The major contributing factor was multifaceted access to electrolyte ions which enhances redox rates via charge transfer in response to electron injection or extraction via carbon fiber network.

A helium (He) atmospheric-pressure dielectric barrier discharge jet (DBDjet) is used to pattern 1H, 1H, 2H, 2H-perfluorodecyltrichlorosilane (PFDTS)-coated cellulose paper with a shadow mask. DBDjet processing under appropriate conditions can be used to form hydrophilic patterns. The properties of the DBDjet-patterned PFDTS-coated paper are investigated through water contact angle measurement, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS), and the results indicate the successful deposition and removal of PFDTS before/after DBDjet treatment. The successful routing and mixing of liquid in the hydrophilic stripes are demonstrated, and a glucose concentration colorimetric test is demonstrated using this DBDjet-patterned PFDTS-coated paper.

In this study, we have developed a paper-based electrochemical biosensor for dopamine (DA) detection. For this purpose, a screen-printed graphene electrode (SPGNE) was printed on a paper substrate, and the electrode surface was modified with PEDOT:PSS/RGO. The fabricated sensor was characterized by analyzing the capacitance, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) measurements. Differential pulse voltammetry (DPV) was employed for the quantitative detection of dopamine. The paper-based SPGNE biosensor developed in this study could detect dopamine in a linear range from 0.0125 to 0.1 mM with a sensitivity of 24.9 μA mM−1. The reliability of the developed biosensor for dopamine detection was assessed by using normal serum samples. The paper-based graphene biosensor proposed in this study could be low-cost and eco-friendly, and its ability to determine the dopamine from real serum samples showed promising results. The developed SPGNE dopamine-sensing biosensor could be potentially applied for the early-stage diagnosis of various neurological diseases/disorders.

Development of highly active catalyst for hydrogen evolution reaction (HER) is an urgent research to realize the energy consumption transformation from fossil flue to clean and renewable hydrogen energy and alleviate the energy crisis and. Electrochemical water splitting offers an ideal approach for hydrogen production with ultrahigh purity, which need a cost-effective electrocatalyst to drive the HER. Until now, Pt-group metals have been proved to be the best electrocatalysts for HER due to the extraordinary low overpotential near the thermodynamic potential of HER, but their widespread commercial application on a large scale is hampered by the prohibitive cost and scarcity. In this study, we reported amorphous Co-Ni-S catalysts fabricated on carbon paper by a simple one-step electrodeposition. By varying the deposition potential/time and concentration of sulfur source, the morphologies and compositions of Co-Ni-S were controlled, and optimal condition for synthesis was obtained. The structure, surface morphology and composition of deposits were characterized in detail. And the electrochemical performance and stability of catalysts were tested in alkaline media by directly using the as obtained Co-Ni-S/Carbon Paper as a cathode. The characterization results showed Co-Ni-S was amorphous and uniformly deposited on carbon paper. And the electrochemical test indicated that Co-Ni-S/Carbon Paper has acceptable performance with low overpotentials of 99mV at 10mA/cm2, Tafel slop of 85mV/dec and long-tern durability. Moreover, the double-layer capacitance (Cdl) result indicated that Ni−Co−S catalyst possesses high electrochemical surface area (ECSA), which could provide abundant active sites for electrocatalytic reaction

We have developed paper-based screen-printed biofuel cells using MgO-templated carbon (MgOC) as an electrode material1) in which a mediator and an enzyme were immobilized by dropping the solutions on the MgOC surface. However, the immobilization scheme should be shortened for practical applications. In this study, we newly prepare an enzyme-modified carbon ink using chitosan, which has high bio-affinity as a binder. By preparing chitosan-based enzyme ink, it becomes possible to immobilize the enzyme on the electrode by a simple printing process. A paper-based glucose/O2 biofuel cell was fabricated by screen printing with the enzyme-modified carbon inks. In this abstract, we describe the results of the glucose anode. Firstly, a glucose oxidase (GOx) and 1,2-naphthoquinone (1,2-NQ) were physically adsorbed in the pores of the MgOC. Then a chitosan-based enzyme ink was prepared by mixing the GOD and 1,2-NQ immobilized MgOCwith chitosan, and then cross-linked with genipin. A commercially available carbon ink and the as-prepared chitosan-based enzyme ink were successively printed on a water-repellent Japanese paper and dried overnight in a refrigerator to prepare a bioanode. In this study, we used two kinds of carbon. One is an untreated MgOC (normal MgOC). Another is a “washed MgOC”, which were washed with 0.25M NaOH and pure water before the chitosan-based enzyme ink was prepared. Anodes prepared with chitosan-based enzyme inks using normal MgOC and washed MgOC were evaluated by chronoamperometry (measurement potential: 0.2 V) in phosphate buffer containing 100 mM glucose (Fig.1 (a)). The catalytic oxidation reaction was not observed in the anode using normal MgOC, whereas the catalytic oxidation current of about 0.5 mA/cm2 was obtained after 500 seconds in the anode using the washed MgOC. From the SEM (accelerating voltage: 15.0 kV) of the anode using washed MgOC, a structure with many macroporesof about 5 to 10 µm was observed clearly. (Fig. 1(b)). On the other hand, no such macropores were observed in the anode using normal MgOC. The surface of normal MgOC has many functional groups such as -COOH, and it shows acidity when mixed with water. The cross-linking reaction does not occur sufficiently in between genipin and chitosan under acidic condition. On the other hand, in the neutral condiiton, the cross-linking reaction that accompanies the self-polymerization of genipin proceeds enough to form long and flexible chains 2). Therefore, the neutralization of the MgOC surface by the washing treatment forms an electrode with macropores between carbons, resulting in increase of glucose supply to the GOD immobilized in the mesopore of MgOC. References 1) Isao Shitanda et al., J. Electrochem. Soc, 166(12) (2019) B1063-B1068. 2) Elí Emanuel Esparza Floreset et al., Process Biochemistry, 84, (2019) 73-80. Acknowledgements This work was partially supported by JST-ASTEP Grant Number JPMJTS1513, JSPS Grant Number 17H02162 and Private University Research Branding Project (2017-2019) from Ministry of Education, Culture, Sports, Science and Technology, and Tokyo University of Science Grant for President's Research Promotion． Figure 1

Biomarkers indicate human health conditions and diseases. For example, viral RNA and antigens are used for COVID-19 screening. Currently enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR) are the gold standard methods for measuring protein and nucleic acid biomarkers, respectively. Both PCR and ELISA require professionals to operate in a centralized laboratory for several hours. Therefore, this presentation shows our effort to develop paper-based lateral flow strips as point-of-care testing (POCT) devices for rapid and in-field detection of proteins and nucleic acids by laypersons at clinics, home, and remote areas. Plasmonic nanostructures have been developed to enhance fluorescence or surface-enhanced Raman scattering (SERS) to improve sensitivity. Such optical sensors have been integrated with paper-based microfluidic strips to achieve automation and miniaturization. The integrated paper-based lateral flow strips have been used for detection of viruses and biomarkers of several human diseases such as traumatic brain injury and cancers.

A high-performance paper electrode is fabricated through coating polypyrrole (PPy) on ordinary laboratory filter paper via a traditional interfacial polymerization method with perchloric acid (HClO4) as a dopant. Owing to the superior mechanical flexibility and environmental stability of the free standing PPy paper, the robust electrode displays an ultrahigh capacitance of 1650 mF cm−2 and remarkable cyclic stability of losing 11.66% after cycling for 10000 times in a three-electrode system. More importantly, the areal specific capacitance has only decreased by 0.08% after five months. Furthermore, by employing the synthesized PPy papers as electrodes and the PVA-H2SO4 gel as electrolyte, the assembled all-solid-state supercapacitor with an areal specific capacitance of 566.5 mF cm−2 is achieved, corresponding to an areal energy density of 38.55 μW h cm−2 and power density of 0.17 mW cm−2. These results suggest that the simple synthesis of PPy paper electrode pave a promising way to exploit flexible and durable energy storage applications.

Cardiovascular diseases (CVDs) are reported to be the leading cause of death worldwide by World Health Organization (WHO) with an approximate of 31% of global deaths. Consequently, it has been noted that the largest sector of population which experiences coagulation or hemostatic imbalances or undergo oral anticoagulation therapy (OAT) are the major sector susceptible to the risk of mortality due to cardiovascular ailments such as atherosclerosis, deep vein thrombosis (DVT), stroke etc. These candidates are prescribed or administered using oral anticoagulation therapy (OAT) and are advised to take the Prothrombin Time (PT) test respectively. Prothrombin Time (PT) analyzers are the type of haemostasis analyzer mainly catering to the coagulation following the extrinsic pathways. Additionally, the candidates under OAT requires routine administration of the coagulation status for proper dosage of warfarin or its derivatives which shares a very narrow therapeutic window. A slight amount of imbalance in the coagulation chemistry can disrupt the cardiovascular functioning, hence a routine monitoring is strongly mandated by cardiac surgeons. It is important to realize a simplified hand held, low cost point of care solution for diagnosing hemostasis or coagulation status to cater both the rural and urban sectors resulting in lower casualties due to coagulation imbalance. The respective work proposes a handheld point of care PT sensing paper sensor using very inexpensive pencil and correction pen and Whattman filter paper. In addition the sensor has enhanced capability of carrying our sensitive detection of coagulation status compared to the existing complex and expensive sensors developed through a variety of methods like screen printing, lithography, flexography printing, wax printing, PDMS printing, stamping etc. The proposed device consists of two pencil marks as electrodes. The device is illustrated in Figure 1. The sensor monitors a change in impedance (resistance) w.r.t time. Blood being an ionic fluid whose chemistry changes with the ionic interactions during the process of coagulation results in a direct correlation of the coagulation process to the respective impedimetric signatures. The synthetic coagulation behavior and the response of the device has been measure using nail paint as an analyte. The points of maximum changes in resistance (first and second) denotes the application of the analyte to the sensor and initiation of coagulation or solidification respectively (shown in Figure 2) from which the coagulation time is further derived. Lab View has been used as an interfacing platform for processing the respective resistive data and generating corresponding coagulation status. Thus, the particular PDE-PAD (pencil drawn electrodes- paper-based analytical devices) can be considered as a promising future device for low cost sensitive detection platform for a point of care PT diagnosis. Figure 1

Microfluidic electrochemical paper-based devices (ePADS) are a promising platform for point of care (PoC) diagnostics. In this work, we present a microfluidic device for home-based detection of the neurotransmitter dopamine, which is crucial for further understanding of nervous system disorders such as Parkinson’s disease and other chronic mental illnesses including schizophrenia. Our device features a 3-electrode ePAD, where the electrodes are aligned along a wax-defined microfluidic channel, in a capillary flow device which uses Whatman filter paper as the porous wicking substrate. The working electrode was embedded directly into the Whatman filter-paper by using the paper as a precursor for laser-induced-graphene (LIG). To obtain LIG, we treat the Whatman filter in commercial flame-retardant spray and then treat with a CO2 infrared laser, this treatment produces a highly conductive, 3D porous graphene network with high surface area and electrical conductivity, directly in the paper matrix. The working and counter LIG electrodes are patterned by laser alongside the wax-defined microfluidic channel as shown in figure 1a, and a third reference electrode was defined in inkjet-printed silver (Dimatix DMP-2831) and then treated in commercial bleach to obtain an Ag/AgCl pseudo-reference electrode. The charge-transfer kinetics of the LIG surface was obtained by cyclic voltammetry (figure 1b) of the LIG electrode in a 3-electrode setup (platinum counter electrode and Ag/AgCl reference electrode in 3.0 M KCl). The LIG electrode was cycled in 0.1 M aqueous solution of KCl consisting of 5mM ferro-ferricyanide redox couple. The Randles–Sevcik analysis was used to obtain an electroactive surface area of 1.97 mm2 (2.5 times higher than the geometrical surface area) and the analysis also showed a rapid electron transport kinetic. The working electrode was modified from the pristine LIG by initially (i) chemical activation in 2 molar urea solution to introduce nitrogen-functional groups on the LIG and (ii) electrodeposition of MnO2 nanoparticles over the N-functionalised graphene to produce a sensing electrode with low background current and rapid electron transfer characteristics. Crucially for microfluidic devices to be used as a real PoC device, the patient needs to be able to simply deposit the biomarker. For neurotransmitter analysis, blood/plasma from a finger-prick enables a plausible route for sampling. Here, we show a novel blood sampling design of the ePAD cassette (holder) which enables rapid and low volume blood sampling, which is shown in figure 1c. The holder includes a hydrophilic microfluidic channel which rapidly samples 5 μL blood from a finger-prick droplet. An air vent at the channel end enables the channel to be filled to exactly 5.0 μL but not over-filled. The blood is prevented from entering the ePAD by a removable adhesive tab, which also covers a reservoir filled with running buffer (RB), (TBS + 0.05% Tween + 0.5% BSA). When the channel is filled with blood, the removal of the adhesive tab enables release of the defined volume of blood and RB into (i) a Pall Cytosep 1668 blood filtration membrane and then (ii) into the wax-patterned lateral flow channel of the ePAD device for rapid electrochemical detection of dopamine, creatinine and uric acid by square wave anodic stripping voltammetry. Figure 1

Graphene oxide (GO) derives from graphite through oxidation, with subsequent dispersion and exfoliation in suitable solvents [1]. GO contains various oxygen-containing functional groups, mainly including hydroxyl, carboxyl, carbonyl and epoxy groups [2]. These oxygen-containing groups make GO highly hydrophilic and can form stable aqueous colloids to assemble paper-like materials by simple and inexpensive solution processes [3]. A monolayer GO nanosheet has high Young’s modulus (207.6 GPa [4]) and ultimate strength (63 GPa [5]). However when individual GO nanosheets are assembled into mesoscopic sheets or “paper”, these mechanical properties decrease significantly because GO sheets are only weakly connected by hydrogen bonds and van der Waals interactions [6]. GO paper also has low plasticity due to the limited movement of dislocation dipoles in a hexagonal lattice [7-8], so it is very brittle and cannot form complex 3D structures. The fabrication of GO paper thus needs to be optimized to achieve better mechanical properties and wider applications. In this study we fabricated ultra-stiff and strong GO paper with controlled thicknesses by directed-flow vacuum filtration. Young’s modulus and ultimate strength were improved by three methods: (i) borax cross-linking, to form a combined hydrogen and covalent bonding system; (ii) thermal annealing, to evaporate inter-sheet water to make GO paper more compact; (iii) sonication, to disperse GO nanosheet more uniformly before filtration. Mechanical tests were performed by both flexion (three-point bending) and uniaxial tension. We found that the flexural modulus of GO paper is significantly lower than the tensile modulus because of interlayer shearing, micro-buckling and delamination during flexural deformation. The stiffest material we made has a tensile modulus of 109.9 GPa and a flexural modulus of 45.7 GPa, which is among the strongest and stiffest GO papers in the open literature (Fig.1) [9]. Another challenge is to make GO paper plastically deformable, a requirement to form 3D structures from flat paper-like materials. Here we developed a low-cost and eco-friendly method to “plasticize” GO paper by the addition of a slurry of cellulose fibers. After mixing 25 wt.% cellulose slurry with GO suspension, the filtrated composite paper can retain 85% of Young’s modulus but shows around three times larger fracture strain than pure GO paper. Using the GO paper reinforced by office paper slurry, we successfully formed semi-spheres with smooth and compact surfaces using an embossing method. The stiffness of the deformed structure was further improved by immersion cross-linking in borax solution. The stiff and lightweight semi-spheres can be used as mechanical structures such as acoustic diaphragms and protective layers. After reduction either by chemical or thermal method, the application can be further expanded to supercapacitors, actuators and electrode materials. References [1] Dreyer D.R.; Park S.; Bielawski C.W.; Ruoff R.S. The chemistry of graphene oxide. Chemical Society Reviews 2010, 39, 228-240. [2] Eda, G.; Chhowalla, M. Chemically derived graphene oxide: towards large-area thin-film electronics and optoelectronics. Advanced Materials 2010, 22, 2392-2415. [3] Pei S.; Cheng H.M. The reduction of graphene oxide. Carbon 2012, 50, (9), 3210-3228. [4] Suk J.W.; Piner R.D.; An J.; Ruoff R.S. Mechanical properties of monolayer graphene oxide. ACS Nano 2010, 4, (11), 6557-6564. [5] Paci J.T.; Belytschko T.; Schatz G.C. Computational studies of the structure, behavior upon heating, and mechanical properties of graphite oxide. The Journal of Physical Chemistry C 2007, 111, (49), 18099-18111. [6] Medhekar N.V.; Ramasubramaniam A.; Ruoff R.S.; Shenoy V.B. Hydrogen bond networks in graphene oxide composite paper: structure and mechanical properties. ACS Nano 2010, 4, (4), 2300-2306. [7] Chen S.; Chrzan D.C. Continuum theory of dislocations and buckling in graphene. Physical Review B 2011, 84, 214103(1-5). [8] Warner J.H.; Margine E.R.; Mukai M.; Robertson A.W.; Giustino F.; Kirkland A.I. Dislocation-driven deformations in graphene. Science 2012, 337, 209-212. [9] Liu S.; Hu K.; Cerruti M.; Barthelat F. Ultra-stiff graphene oxide paper prepared by directed-flow vacuum filtration. Carbon. In press. DOI: 10.1016/j.carbon.2019.11.007. Figure 1

This study aims at an electrochemical paper-based device for the selective and sensitive detection of exosomes as an economic and flexible platform. Using a laser cutter, a three-electrode platform was patterned on a hydrophobic paper, and then synthetic carbon and silver ink were screen-printed on the paper. Anti-human CD9 antibody was covalently attached to the surface of a carbon ink electrode enriched with graphene oxide aerogel/CoFe2O4@chitosan nanocomposite. The immobilization, incubation and binding time of the capture antibody were investigated as effective parameters. Under optimum conditions, the differential pulse voltammetry (DPV) was used to establish a calibration plot that covered 500 to 5 × 106 exosoms μl−1 with a detection limit of 100 exosome μl−1. This method was implemented successfully for the detection of exosomes in a serum sample. As the results show, the fabricated biosensor is capable of detecting exosomes for the early diagnosis of cancers.

This paper describes the design, fabrication, and validation of a paper-based diagnostic device for the rapid diagnosis of hypocalcemia in dairy cattle at the point-of-care (POC). The device incorporates a 3D printed calcium ion-selective membrane (ISM) as the sensing element for free—unbound—calcium in real bovine whole blood samples. With a linear response range of 100 mM to 97.7 μM, the sensor covers the clinically relevant concentrations of Ca2+ associated with both healthy cattle as well as those suffering from hypocalcemia. The components of the Ca2+ ion-selective electrodes were successfully translated to a paper-based device to provide a sensing platform that is simple to use, disposable, and low-cost, and is therefore well-situated for applications at the POC. The paper-based calcium sensor showed a Nernstian response between 10 mM and 100 μM and required only 12 μl of sample to perform a measurement, which can be accomplished in less than two minutes without the need for time-consuming separation steps. The performance of the paper-based Ca2+ sensor was validated using the commercially available epoc® Blood Analysis System, which provided results within 5% of the data obtained with 3D printed Ca2+-ISM integrated paper-based device.

As a renewable energy source to replace traditional fossil fuels, hydrogen is a promising sustainable energy carrier due to its eco-friendly nature and high energy density. Although Pt-based materials are widely used as catalysts for generating hydrogen through water electrolysis because of their high catalytic activity, Pt is expensive, and its scarcity hinders the commercialization of large-scale hydrogen production. The development of alternative low-cost materials with low hydrogen evolution reaction (HER) overpotential is the key to achieve low price and highly efficient hydrogen generators such as proton-exchange membrane water electrolysis (PEMWE). Among the numerous candidates of earth-abundant materials, transition metal-based phosphides (TMPs) are suitable for HER applications due to their low toxicity, high electrical conductivity, and catalytic activity. Especially, FeP is in the spotlight as a HER catalyst due to its high catalytic activity in solutions with a wide pH range, and this is a competitive material for large-scale commercial production of hydrogen, since Fe is one of the most abundant elements on earth. In this study, we synthesized the colloidal FeP nanoparticles (NPs) via a hot injection process, so that the pre-synthesized Fe NPs can be converted to FeP NPs through the phosphorization reactions by various phosphorus sources (trioctylphosphine, triphenylphosphite (TPP), tris(diethylamino)phosphine, and tri-n-butylphosphine). Different HER activities were induced by the phase transformation of NPs over the controlled reaction time for the NP samples synthesized with each phosphorus precursor. The FeP synthesized using TPP achieved excellent HER activity with an overpotential of 76 mV at 10 mA cm-2 in 0.5 M H2SO4 as measured by drop casting the catalyst on Ti foil. In terms of the fabrication for the efficient HER electrode, the prepared FeP NPs were deposited on the carbon paper (CP) via electrophoretic deposition (EPD), which is a suitable method for the fabrication of NP films that can be used for various electronic applications. Different morphologies and catalytic activities of the FeP/CP samples were derived by controlling EPD parameters such as mixing ratio of solvents, NP concentration, and deposition voltage. The optimized EPD process lead to excellent HER activity of the FeP/CP with an overpotential of 38 mV and 91 mV at 10 mA cm-2 in 0.5 M H2SO4 and 1 M KOH, respectively. The maximum activity of the catalyst was mainly attributed to the large active surface area and low charge transfer resistance due to the strong contact between the NPs and CP. A PEMWE single cell with the FeP/CP cathode achieved 1.2 A cm-2 at cell voltage of 2.0 V. This study of the EPD procedure for fabricating the NP film from the colloidal NP catalysts contributes to advance manufacturing of HER electrodes for efficient hydrogen generation through water electrolysis.

Rapid and accurate detection of protein and small molecule biomarkers in human blood and saliva are incredibly valuable for clinical applications. However, biomarkers are typically detected using time-consuming and expensive methods such as enzyme-linked immunosorbent assay (ELISA), Western blot, and other centralized laboratory instrumentation, so these tools cannot be used in the point-of-care setting. In this work, a paper-based lateral flow strip (PLFS) has been developed as a rapid, low-cost, point-of-care device for detecting biomarkers in whole blood and saliva. Typically, PLFSs operate using colorimetric detection and suffer from poor sensitivity and high background interference from the biological matrix. To overcome these challenges, surface-enhanced Raman scattering (SERS) and near-infrared fluorescence were applied in a PLFS as the signal transducers to improve device sensitivity and overcome biological interference. These advantages are attributed to the optical excitation in the near-infrared biological transparency window and plasmonic nanostructure enhancement. The PLFS is designed using a plasmonic nanostructures and a blood plasma separation unit for highly sensitive biomarker detection.

The construction of conductive graphite channels on paper using the pencil drawing method for supercapacitors and sensors has been reported, but its performance needs to be improved to meet practical applications. In this, we develop green and efficient method to prepare high-performance supercapacitor electrodes. After pencil drawing, the polypyrrole graphite active material (PPy-G) is prepared via interfacial polymerization. The graphite layer not only provides an efficient electron transport path but also greatly increases the electrical capacity of electrodes with a good combination of PPy. The prepared electrodes exhibit an excellent area specific capacitance (1654 mF cm−2) and good cycling stability (at 95.3% after 10,000 cycles). Furthermore, the symmetric supercapacitor is prepared using the dual electrodes exhibit a good energy density of 159.6 μWh cm−2 at a power density of 0.8 mW cm−2. The kinetic processes for the electrodes are also further investigated.

A high costing screen-printed electrode, the electrochemical software required, and a electrochemistry laboratory are all needed to conduct a electrochemical test. The need for this type of technology on the Navajo Nation is important because it would allow them to have real-time, on-site detection that is cost effective. This would allow the Navajo Nation to detect and analyze compounds that may cause severe health issues. The materials that are required to fabricate these paper-based electrodes are chromatography paper, a wax printer, electrochemically active and conductive ink, electrochemistry equipment, buffer solution, and the compound that is being tested. First we would get chromatography paper and print the electrode outline, designed at Navajo Technical University, using the wax printer. The next step is to coat the electrodes with the conductive ink and add gold or copper nano-particles, which will act as our catalyst. Then we get our compound, which is Glucose in this case, and test multiple different concentrations. With the electrochemical software we are able to use different types of techniques like Differential pulse voltammetry (DPV) and Cyclic voltammetry (CV) to test Glucose. We hope to continue testing with these electrodes to improve our techniques and ensure that we are able to test paper-based electrodes on multiple different compounds. Another goal of our project is to develop a way to conduct these tests while in the field.

The history of mining and mineral extraction across the Navajo Nation has resulted in considerable contamination of the land and the groundwater resources, which is a significant environmental concern. Through a partnership between Navajo Technical University and Harvard University, we have designed and fabricated flexible, paper-based sensors in tandem with electrochemical techniques such as cyclic voltammetry, differential pulse voltammetry, and anodic stripping voltammetry to determine heavy metal concentrations in test samples. We have selected to fabricate paper-based electrochemical sensors because; they are low-cost, easy to make, environmentally friendly, and can be deployed for field testing across the Navajo Nation. We have demonstrated that our electrodes have successfully oxidized lead and arsenic oxide using the techniques stated above. The performance of our electrode is comparable to commercially available electrochemical sensors. Furthermore, the linear electrochemical response and sensitivity of our electrodes, for detecting heavy metals, makes them well suited for real-time sensors in field-testing applications.

Bisphenol (BP) is a chemical additive that strengthens polycarbonate plastics and epoxy resins. Bisphenol, however, is a known toxicant often categorized as an endocrine-disrupting chemical (EDC). Bisphenol absorption in the body has been implicated in contributing to metabolic disorders such as type-2 diabetes, obesity, immune toxicity, and other serious diseases. Approximately 90% of humans accumulate BP levels through exposure to food containers, plastic bottles, thermal printing papers, and other everyday plastic products. This accumulation is of special concern on the Navajo Reservation, which has a high rate of diabetes and obesity. We report the development of low-cost, flexible paper-based electrodes for the electrochemical detection of BP compounds. We fabricated paper-based electrodes using conductive carbon paste in a three-electrode system. We demonstrate that our paper-based electrodes can detect BP at 0.1mM, 0.3mM, 0.5mM, and 1mM in the laboratory at physiological pH conditions. These results demonstrate that the sensitivity of these electrodes and their linear electrochemical response make them well suited for real-time applications and point detections.

This research explores the use of interdigitated electrode arrays (IDE) screen-printed on paper substrate for electrochemical measurements in steady state. Since the steady state is strongly related to IDE dimensions, the accuracy and reproducibility of the fabrication process were assessed for stencils of 120- and 200-mesh. Simulations were used to predict the limiting current and time response, and as a benchmark for comparison with the experimental results. For accurate an comparison, evaporation was prevented by using a homemade humidity box, which enabled measurements for periods as long as 30 min. Although cyclic voltammetry measurements in steady state were possible, this required at least 15 min per cycle when using the smallest electrodes (band width of 0.205 mm). Chronoamperometric measurements reaching steady state were also possible, requiring nearly 5 min for the largest electrodes (band width of 0.376 mm). Regarding the reproducibility of measurements, the relative standard deviations (RSD) of current and response time were near 12% and 26%, respectively. We attribute this mainly to the reproducibility of IDE fabrication (8% RSD). Experimental currents were approximately 30% to 34% of their simulated counterparts. Conversely, the simulated response times were about 30% to 50% of their experimental counterparts. We ascribe these discrepancies to the porosity of the paper (Whatman 2 CHR), estimated to be near 31% under wet conditions. This suggests that fibers inside the paper substrate block the passage of electrochemical species, thereby delaying their diffusion and decreasing the current.