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COVID-19 has caused global health problems, and so rapid diagnosis is crucial to slow spread of the disease. Herein, a novel lab-on-paper screening method for SARS-CoV-2 Omicron BA.2 variant was developed using a gold nanoparticle-based colorimetric biosensor along with sensitive detection of SARS-CoV-2 antigen using laser desorption ionization-mass spectrometry (LDI-MS). As a result of antigen–antibody interaction, in the presence of SARS-CoV-2 antigen the gold nanoparticles undergo aggregation and change color from red to light purple, allowing for rapid determination of SARS-CoV-2 antigen with the naked eye. Furthermore, the lab-on-paper method can be directly applied as a substrate for sensitive quantitation of SARS-CoV-2 antigen in saliva using LDI-MS without the use of a conventional organic matrix and sample preparation. LDI-MS offers early diagnosis with high sensitivity, rapidity without sample preparation and lower cost per test compared with reverse transcriptase-PCR, which is crucial for preventing mortality in patients with underlying conditions. This method showed linearity over 0.01–1 μg mL−1 covering the cut-off value of 0.048 μg mL−1 for COVID-19 detection in human saliva. Moreover, a colorimetric sensor for urea was also fabricated in-parallel, for prediction of COVID-19 severity in patients with chronic kidney disease. The color change upon increasing urea concentration directly reflected kidney damage, which is related to increasing risk of mortality among patients with COVID-19. Hence, this platform might be a potential device for non-invasive diagnosis of SARS-CoV-2 Omicron BA.2 variant, which is the variant of most concern because it is transmitted more rapidly than the original SARS-CoV-2 virus and the Delta variant. [ABSTRACT FROM AUTHOR]

Pesticide residues are a serious problem towards agriculture, environment and food safety, so it is highly desirable to develop a swift, efficient and portable pesticide detection method. A fluorescence visual sensing method for glyphosine based on a nitrogen-doped biomass carbon quantum dot (N-CQD) paper-based sensor was developed. The fluorescence signal was quenched by Fe3+ in a static quenching process, and then the fluorescence of N-CQDs was recovered after adding glyphosine. Under the optimal experimental conditions and when tested with a fluorescence spectrofluorometer, the detection of glyphosine showed a two-stage linear pattern in the range of 0.1–0.6 μM and 0.6–1.6 μM with a detection limit of 0.075 μM. Then, the RGB values of different concentrations of glyphosine on the filter paper chip were detected by the software of the smartphone-color identifier. The logarithm of the glyphosine concentration was linearly related to the G value of RGB in the range of 0.25–10.00 mM and with a detection limit of 0.15 mM. The method was applied to measuring glyphosine-spiked juice and flour samples, and the recovery rates were 87.60–112.69% and 93.27–105.83%, respectively. The proposed N-CQDs/Fe3+ system had wide applications, and it was expected to be fast and effective at detecting pesticide residues. [ABSTRACT FROM AUTHOR]

A new fluorescent probe (T2) containing pyrene-hydrazone furan moieties was developed and synthesized through a two-step process and then coated onto filter paper to form a paper-based sensor for TNT detection. The T2 sensor uses photoinduced electron transfer (PET) induced fluorescence quenching to detect TNT. The sensor properties were studied using fluorescence spectra, 1H-NMR titration and density functional theory (DFT) calculations. The reaction time of the T2 paper-based sensor for TNT detection was only five minutes. A smartphone was used as an alternative instrument to detect fluorescence signals and a typical image J-processing application was employed to evaluate the grayscale values of the smartphone-captured photographs. The sensor showed a linear concentration range for TNT detection of between 30–500 μM and a detection limit of 30 μM. The T2 paper-based sensor was found to have high selectivity and sensitivity, and it can successfully detect and image TNT in actual samples. This research demonstrates that a T2 paper-based sensor is a promising alternative for TNT detection owing to its short reaction time, high selectivity, sensitivity, and easy applicability. [ABSTRACT FROM AUTHOR]

Paper-based analytical devices (PADs) offer a low-cost, user-friendly platform for rapid point-of-use testing. Without scalable fabrication methods, however, few PADs make it out of the academic laboratory and into the hands of end users. Previously, wax printing was considered an ideal PAD fabrication method, but given that wax printers are no longer commercially available, alternatives are needed. Here, we present one such alternative: the air-gap PAD. Air-gap PADs consist of hydrophilic paper test zones, separated by "air gaps" and affixed to a hydrophobic backing with double-sided adhesive. The primary appeal of this design is its compatibility with roll-to-roll equipment for large-scale manufacturing. In this study, we examine design considerations for air-gap PADs, compare the performance of wax-printed and air-gap PADs, and report on a pilot-scale roll-to-roll production run of air-gap PADs in partnership with a commercial test-strip manufacturer. Air-gap devices performed comparably to their wax-printed counterparts in Washburn flow experiments, a paper-based titration, and a 12-lane pharmaceutical screening device. Using roll-to-roll manufacturing, we produced 2700 feet of air-gap PADs for as little as $0.03 per PAD. [ABSTRACT FROM AUTHOR]

The achievement of high-throughput separation and high-sensitivity detection of complex samples has been one of the most challenging issues in the field of analytical science. The application of a single technology alone could not satisfy the above requirements. The combination of technologies with the capability of high-efficiency separation and high-sensitivity structural-recognition is highly desired to meet the technical requirements. Herein, an automatic high-performance liquid chromatography (HPLC)-surface enhanced Raman spectroscopy (SERS) hyphenated system using paper substrates as the "interface" was constructed to achieve efficient separation and real-time detection. A homogeneous Au nanoparticle was printed on the hydrophobic filter paper with the inkjet technology. The prepared substrates served as a linkage for the continuous realization of HPLC and SERS functions. The complex system was separated by HPLC, and the effluents were loaded onto automatically and continuously replaceable paper substrates for real time SERS measurements. The continuous rapid separation and real-time detection of various two-component mixtures were achieved with the separation efficiency and detection sensitivity of each technology. The results demonstrated that the HPLC-SERS hyphenated system exhibited the complementary capability of the on-line separation and continuous structural identification of illegal additives in real samples. The detection sensitivity was increased by an order of magnitude to reach 10−5 mol dm−3, and the efficiency and accuracy for the separation and identification on the multi-components samples were higher than those of the individual HPLC or SERS technology. It is believed that the continuous paper substrate-based HPLC-SERS hyphenated system would be developed as a promising technique for the separation and identification of multi-components mixtures with high throughput. [ABSTRACT FROM AUTHOR]

Metabolic alkalosis, the most common acid–base disorder, is related to significantly increased mortality in hospitalized patients. Hunting for pH sensors lying in the neutral to alkaline pH range still remains challenging and in demand. Herein, we engineered a colorimetric/fluorescent method for monitoring alkalic pH based on a phenylboronic acid-containing probe (DDPB). In this approach, the dicyanoisophorone group of DDPB acted as an optical signal moiety, while the boronic acid acted as the latent pH response site. It was exactly deciphered that the reversible pH monitoring principle is based on the deprotonation/protonation mechanism and intramolecular charge transfer (ICT) strategy via1H NMR and DFT calculations. This approach presented a pH-sensitive response over pH values ranging from 7.00 to 10.23 (pKa = 9.33) with excellent reversibility. We further explored its application in sensing pH on a paper substrate for visual and rapid detection. In addition, it was successfully applied to measure pH variations in HK-2 cells when the cells underwent alkalosis. This work extends the application of optical probes based on boronic acid under alkaline pH conditions, and provides a new strategy for the design of alkaline pH probes. [ABSTRACT FROM AUTHOR]

Cellular viability measurements quantify decreased proliferation or increased cytotoxicity caused by drug candidates or potential environmental toxins. Direct viability measures count each cell to provide an accurate readout. This approach can prove analytically challenging and time-consuming when cells are maintained in 3D structures akin to tissues or solid tumors. While less labor-intensive, indirect viability measures can be less accurate due to the heterogeneous structural and chemical microenvironment that arises when cells are maintained in tissue-like architectures and in contact with extracellular matrices. Here we determine the analytical figures of merit of five indirect viability assays in the paper-based cell culture platform we continue to develop in our laboratory: calcein-AM staining, the CellTiter-Glo assay, imaging fluorescent protein expression, propidium iodide staining, and the resazurin assay. We also determined the compatibility of each indirect assay with hypoxic conditions, intra-experimental repeatability, inter-experimental reproducibility, and ability to predict a potency value for a known antineoplastic drug. Our results show that each assay has benefits and drawbacks to consider when choosing the appropriate readout to answer a particular research question. We also highlight that only one indirect readout is unaffected by hypoxia, a commonly overlooked variable in cell culture that likely yields inaccurate viability measures. [ABSTRACT FROM AUTHOR]

Deterministic lateral displacement (DLD) is a passive separation method that separates particles by hydrodynamic size. This label-free method is a promising technique for cell separation because of its high size resolution and insensitivity to flow rate. Development of capillary-driven microfluidic technologies allows microfluidic devices to be operated without any external power for fluid pumping, lowering their total cost and complexity. Herein, we develop and test a DLD-based particle and cell sorting method that is driven entirely by capillary pressure. We show microchip self-filling, flow focusing, flow stability, and capture of separated particles. We achieve separation efficiency of 92% for particle–particle separation and more than 99% efficiency for cell–particle separation. The high performance of driven flow and separation along with simplicity of the operation and setup make it a valuable candidate for point-of-care devices. [ABSTRACT FROM AUTHOR]

Sweat, as a sample that includes a lot of biochemical information, is good for non-invasive monitoring. In recent years, there have been an increasing number of studies on in situ monitoring of sweat. However, there are still some challenges for the continuous analysis of samples. As a hydrophilic, easy-to-process, environmentally friendly, inexpensive and easily accessible material, paper is an ideal substrate material for making in situ sweat analysis microfluidics. This review introduces the development of paper as a sweat analysis microfluidic substrate material, focusing on the advantages of the structural characteristics of paper, trench design and equipment integration applications to expand the design and research ideas for the development of in situ sweat detection technology. [ABSTRACT FROM AUTHOR]

From HIV and influenza to emerging pathogens like COVID-19, each new infectious disease outbreak has highlighted the need for massively-scalable testing that can be performed outside centralized laboratory settings at the point-of-care (POC) in order to prevent, track, and monitor endemic and pandemic threats. Nucleic acid amplification tests (NAATs) are highly sensitive and can be developed and scaled within weeks while protein-based rapid tests require months for production. Combining NAATs with paper-based detection platforms are promising due to the manufacturability, scalability, and simplicity of each of these components. Typically, paper-based NAATs consist of three sequential steps: sample collection and preparation, amplification of DNA or RNA from pathogens of interest, and detection. However, these exist within a larger ecosystem of sample collection and interpretation workflow, usability, and manufacturability which can be vastly perturbed during a pandemic emergence. This review aims to explore the challenges of paper-based NAATs covering sample-to-answer procedures along with three main types of clinical samples; blood, urine, and saliva, as well as broader operational, scale up, and regulatory aspects of device development and implementation. To fill the technological gaps in paper-based NAATs, a sample-in-result-out system that incorporates the integrated sample collection, sample preparation, and integrated internal amplification control while also balancing needs of users and manufacturability upfront in the early design process is required. [ABSTRACT FROM AUTHOR]

Paper-based microfluidics is an emerging analysis tool used in various applications, especially in point-of-care (PoC) diagnostic applications, due to its advantages over other types of microfluidic devices in terms of simplicity in both production and operation, cost-effectiveness, rapid response time, low sample consumption, biocompatibility, and ease of disposal. Recently, various techniques have been developed and utilized for the fabrication of paper-based microfluidics, such as photolithography, micro-embossing, wax and PDMS printing, etc. In this study, we offer a fabrication methodology for a microfluidic paper-based immunosorbent assay (μPISA) platform and the detection of Hepatitis C Virus (HCV) was carried out to validate this platform. A laser ablation technique was utilized to form hydrophobic barriers easily and rapidly, which was the major advantage of the developed fabrication methodology. The characterization of the μPISA platform was performed in terms of micro-channel properties using bright-field (BF) microscopy, and surface properties using scanning electron microscopy (SEM). At the same time, sample volume and liquid handling capacity were analyzed quantitatively. Ablation speed (S) and laser power (P) were optimized, and it was shown that one combination (10P60S) provided minimal deviation in micro-channel dimensions and prevented deterioration of hydrophobic barriers. Also, the minimum hydrophobic barrier width, which prevents cross-barrier bleeding, was determined to be 255.92 ± 10.01 μm. Furthermore, colorimetric HCV NS3 detection was implemented to optimize and validate the μPISA platform. Here, HCV NS3 in both PBS and human blood plasma was successfully detected by the naked eye at concentrations as low as 1 ng mL−1 and 10 ng mL−1, respectively. Moreover, the limit of detection (LoD) values for HCV NS3 were acquired as 0.796 ng mL−1 in PBS and 2.203 ng mL−1 in human blood plasma with a turnaround time of 90 min. In comparison with conventional ELISA, highly sensitive and rapid HCV NS3 detection was accomplished colorimetrically on the developed μPISA platform. [ABSTRACT FROM AUTHOR]

Cervical cancer is a leading cause of cancer death for women in low-resource settings. The World Health Organization recommends that cervical cancer screening programs incorporate HPV DNA testing, but available tests are expensive, require laboratory infrastructure, and cannot be performed at the point-of-care. We developed a two-dimensional paper network (2DPN), hybrid-capture, signal amplification assay and a point-of-care sample preparation protocol to detect high-risk HPV DNA from exfoliated cervical cells within an hour. The test does not require expensive equipment and has an estimated cost of <$3 per test without the need for batching. We evaluated performance of the paper HPV DNA assay with short synthetic and genomic HPV DNA targets, HPV positive and negative cellular samples, and two sets of clinical samples. The first set of clinical samples consisted of 16 biobanked, provider-collected cervical samples from a study in El Salvador previously tested with careHPV and subsequently tested in a controlled laboratory environment. The paper HPV DNA test correctly identified eight of eight HPV-negative clinical samples and seven of eight HPV-positive clinical samples. We then performed a field evaluation of the paper HPV DNA test in a hospital laboratory in Mozambique. Cellular controls generated expected results throughout field testing with fully lyophilized sample preparation and 2DPN reagents. When evaluated with 16 residual self-collected cervicovaginal samples previously tested by the GeneXpert HPV assay ("Xpert"), the accuracy of the HPV DNA paper test in the field was reduced compared to testing in the controlled laboratory environment, with positive results obtained for all eight HPV-positive samples as well as seven of eight HPV-negative samples. Further evaluation showed reduction in performance was likely due in part to increased concentration of exfoliated cells in the self-collected clinical samples from Mozambique compared with provider-collected samples from El Salvador. Finally, a formal usability assessment was conducted with users in El Salvador and Mozambique; the assay was rated as acceptable to perform after minimal training. With additional optimization for higher cell concentrations and inclusion of an internal cellular control, the paper HPV DNA assay offers promise as a low-cost, point-of-care cervical cancer screening test in low-resource settings. [ABSTRACT FROM AUTHOR]

We report a highly accurate single-step label-free testing technology for simultaneous and independent hematocrit (Hct) and hemoglobin (Hb) level detection from a drop of whole blood by employing a disposable paper strip sensor interfaced with a portable impedimetric device. The paper strip is fabricated by in situ automated printing of a customized electrode template on the non-glossy side of a commercially available photo paper substrate followed by graphite deposition. The integrated platform device technology additionally includes a compact detection cum readout unit comprising a high precision impedance converter system that combines an on-board frequency generator with an analog-to-digital converter evaluation board, collectively interfaced with a central processor, calibration circuit, and smartphone. Employing a dispensed blood sample volume of 25 μL, the device is shown to have a sensitivity of 92 Ω/Hct and 287 Ω/Hb at an optimal frequency of 57 kHz. The respective linear response regimes appear to be wide enough to cover physiologically relevant limits, with excellent stability and reproducibility. Validation with clinical samples reveals limits of detection of Hct and Hb levels as low as 4.66% and 1.89 g dL−1, respectively, which are beyond the quantitative capability of commonly used affordable point of care test kits. The envisaged paradigm of rapid, robust, highly accurate, energy-efficient, simple, user-friendly, multiplex portable detection, obviating any possible ambiguities in interpretation due to common artefacts of colorimetric detection technologies such as optical interference with the image analytical procedure due to the inherent redness of blood samples and background illumination, renders this ideal for deployment in resource-limited settings. [ABSTRACT FROM AUTHOR]

Electrochemical oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) has received increasing attention as it is an eco-friendly strategy for synthesizing a key monomer for the production of bio-based plastics. Developing efficient, low-cost and stable electrocatalysts is crucial for this electrochemical reaction. In this work, we have reported a facile process for the synthesis of hybrid nanosheet-structured NiCo2O4 on carbon fiber paper (NiCo2O4-CFP) for the efficient electrochemical conversion of HMF into FDCA. As a non-noble binary metal-based catalyst, NiCo2O4-CFP featured a nanosheet network and 3D nanosheet flower-like microspheres, showing 94.3% selectivity and 89.6% faradaic efficiency (FE) for FDCA, which outperformed its single component metal oxides NiO-CFP and Co3O4-CFP. And it also exhibited relatively high stability by maintaining over 80% FE after four successive cycles. The proposed mechanism suggested that the synergistic effect of Ni and Co elements in NiCo2O4 could facilitate HMF oxidation. [ABSTRACT FROM AUTHOR]

Microfluidic paper-based analytical devices (microPADs) are emerging as simple-to-use, low-cost point-of-care testing platforms. Such devices are mostly fabricated at present by creating hydrophobic barriers using wax or photoresist patterning on porous paper sheets. Even though devices fabricated using these methods are used and tested with a wide variety of analytes, still they pose many serious practical limitations for low-cost automated mass fabrication for their widespread applicability. We present an affordable and simple two-step process – cut and heat (CH-microPADs) – for the selective fabrication of hydrophilic channels and reservoirs on a wide variety of porous media such as tissue/printing/filter paper and cloth types, such as cotton and polyester, by a lamination process. The technique presents many advantages as compared to existing commonly used methods. The devices possess excellent mechanical strength against bending, folding and twisting, making them virtually unbreakable. They are structurally flexible and show good chemical resistance to various solvents, acids and bases, presenting widespread applicability in areas such as clinical diagnostics, biological sensing applications, food processing, and the chemical industry. Fabricated paper media 96 well-plate CH-microPAD configurations were tested for cell culture applications using mice embryonic fibroblasts and detection of proteins and enzymes using ELISA. With a simple two-step process and minimal human intervention, the technique presents a promising step towards mass fabrication of inexpensive disposable diagnostic devices for both resource-limited and developed regions. [ABSTRACT FROM AUTHOR]

Multilayer graphene (MLG) is in situ formed in a matrix of amorphous carbon prepared from carbonized waste paper at 750 °C. The resulting samples are systematically characterized by morphology, spectroscopy, diffractometry, nitrogen adsorption–desorption and electrochemistry. The carbon structure with six layered graphene can be formed in a matrix of amorphous carbon at such a low temperature. The resulting sample displays a specific surface area of 862 m2 g−1, a meso-pore volume of 0.55 cm3 g−1 and a capacitance of 214 F g−1, which are correspondingly 2.16, 2.29 and 2.14 times higher than those of the sample prepared directly from carbonized waste paper. Although the sample displays the basic characteristics of amorphous carbon, MLG is mostly found to be formed around the regular nickel crystal face in the amorphous carbon matrix. It is also found that the formation of MLG can be affected by the coexistence of nickel crystals and sodium metal. The optimized porous structural characteristics, including the specific surface area, and the micro- and meso-pore volumes, result from the rearrangement of graphite microcrystallites, giving an improved capacitive performance. [ABSTRACT FROM AUTHOR]

Bacterial meningitis, an infection of the membranes (meninges) and cerebrospinal fluid (CSF) surrounding the brain and spinal cord, is one of the major causes of death and disability worldwide. Higher case-fatality rates and short survival times have been reported in developing countries. Hence, a quick, straightforward, and low-cost approach is in great demand for the diagnosis of meningitis. In this research, a microfluidic fully paper-based analytical device (μFPAD) integrated with loop-mediated isothermal amplification (LAMP) and ssDNA-functionalized graphene oxide (GO) nano-biosensors was developed for the first time for a simple, rapid, low-cost, and quantitative detection of the main meningitis-causing bacteria, Neisseria meningitidis (N. meningitidis). The results can be successfully read within 1 hour with the limit of detection (LOD) of 6 DNA copies per detection zone. This paper device also offers versatile functions by providing a qualitative diagnostic analysis (i.e., a yes or no answer), confirmatory testing, and quantitative analysis. These features make the presented μFPAD capable of a simple, highly sensitive, and specific diagnosis of N. meningitis. Furthermore, this microfluidic approach has great potential in the rapid detection of a wide variety of different other pathogens in low-resource settings. [ABSTRACT FROM AUTHOR]

We demonstrated an instrument-free miniaturized adaptation of the laboratory gold standard methodology for the direct estimation of plasma glucose from a drop of whole blood using a low-cost single-user-step paper-strip sensor interfaced with a smartphone. Unlike a majority of the existing glucose meters that use whole blood-based indirect sensing technologies, our direct adaptation of the gold-standard laboratory benchmark could eliminate the possibilities of cross interference with other analytes present in the whole blood by facilitating an in situ plasma separation, capillary flow and colorimetric reaction occurring concomitantly, without incurring additional device complexity or embodiment. The test reagents were dispensed in lyophilized form, and the resulting paper strips were found to be stable over three months stored in a normal freezer, rendering easy adaptability commensurate with the constrained supply chains in extreme resource-poor settings. Quantitative results could be arrived at via a completely-automated mobile-app-based image analytics interface developed using dynamic machine learning, obviating manual interpretation. The tests were demonstrated to be of high efficacy, even when executed by minimally trained frontline personnel having no special skill of drawing precise volume of blood, on deployment at under-resourced community centres having no in-built or accessible healthcare infrastructure. Clinical validation using 220 numbers of human blood samples in a double-blinded manner evidenced sensitivity and specificity of 98.11% and 96.7%, respectively, as compared to the results obtained from a laboratory-benchmarked biochemistry analyser, establishing its efficacy for public health and community disease management in resource-limited settings without any quality compromise of the test outcome. [ABSTRACT FROM AUTHOR]

We leverage electroosmotic-flow generation in porous media in combination with a hydrophobic air gap to create a controllable valve capable of operating in either finite dosing or continuous flow mode, enabling the implementation of multi-step assays on paper-based devices. The hydrophobic air gap between two paper pads creates a barrier keeping the valve nominally closed. Electroosmotic actuation, implemented using a pair of electrodes under the upstream pad, generates sufficient pressure to overcome the barrier and connect the two pads. We present a model describing the flow and governing parameters, including the electric potentials required to open and close the valve and the threshold potential for switching between the modes of operation. We construct the air gap using a hierarchical superhydrophobic surface and study the stability of the closed valve under strenuous conditions and find good agreement between our model and experimental results, as well as stable working conditions for practical applications. We present a straightforward design for a compact and automated device based on paper pads placed on top of printed circuit boards (PCB), equipped with heating and actuation electrodes and additional power and logic capabilities. Finally, we demonstrate the use of the device for amplification of SARS-CoV-2 sequences directly from raw saliva samples, using a loop-mediated isothermal amplification (LAMP) protocol requiring sample lysis followed by enzymatic deactivation and delivery to multiple amplification sites. Since PCB costs scale favorably with mass-production, we believe that this approach could lead to a low-cost diagnostic device that offers the sensitivity of amplification methods. [ABSTRACT FROM AUTHOR]

Sodium thiocyanate (NaSCN) is a naturally antibacterial component in milk, but excessive consumption of thiocyanate may cause potential risks to human health. Currently available methods for the detection of thiocyanate have some disadvantages such as poor sensitivity and high price. Here, we report a robust and cost-effective method to detect NaSCN based on paper substrates deposited with in situ reduced Ag nanoparticles by surface-enhanced Raman spectroscopy (SERS). Densely packed multilayer AgNPs provide uniform narrow nanogaps, which exponentially enhance the Raman signals. Moreover, these homogeneous narrow hotspots ensure that this method has high sensitivity (the limit of detection is 10−12 mol L−1), a wide linear range (from 10−9 mol L−1 to 10−4 mol L−1), and remarkable reproducibility (the coefficient of variation within a SERS sensor is 6.5%). Spiked milk samples were detected and the recovery rates of NaSCN were in the range of 95.1%–108.0%. This paper-based SERS sensor offers great potential for sensitive NaSCN detection and milk analysis. [ABSTRACT FROM AUTHOR]

Herein, a unique electrochemiluminescence (ECL) sensor combined with a paper electrode was proposed for the detection of phenylalanine (L -Phe) in blood samples. The L -Phe detection was performed by converting L -Phe into ammonia using phenylalanine ammonia-lyase (PAL) enzyme and the ECL signal of Ru(bpy)32+ was produced in combination with ammonia as a co-reactant. In this report, we used AuNP decorated paper electrodes to obtain the ECL signal of Ru-(bpy)32+ in the presence of NH3. The produced ammonia molecules were carried to the working electrode and their contact with the sample was cut off. Since there was no contact between the sample matrix and the electrode, the developed method achieved excellent selectivity. According to experimental data, a linear increase of the ECL signals with the logarithms of varying L -Phe concentrations between 1.5 × 10−2 and 1.211 mM was observed with a correlation coefficient (R2) of 0.9898 and a limit of detection (LOD) of 8.4 × 10−3 mM. The proposed method was efficiently applied for L -Phe detection in reference blood samples and the average recovery was calculated as 96.8%. Furthermore, the HPLC-UV method as a comparison verified that the recovery values provided by the proposed method were acceptable with a similarity of 95.1% for L -Phe detection in a reference blood sample. The results showed that the developed ECL sensor combined with the paper electrode can be considered as a promising unique and powerful technique for a point-of-care diagnosis of PKU. [ABSTRACT FROM AUTHOR]

Amino acids are closely related to human health, and their rapid determination is important for the rapid diagnosis, timely treatment, and assessment of serious diseases. In this work, we propose a novel paper-based sample-processing device combined with isotope-dilution MS for the fast analysis of 11 amino acids from blood samples. By using an isoelectric focusing electrokinetic separation method, without the aid of carrier ampholytes and the addition of inhibitors, this approach uses only the characteristic of the isoelectric point of the target amino acids to achieve separation and purification from other coexisting components in the medium; it can meet the requirements for mass spectrometry detection. Driven by a DC voltage, a stable and sharp pH gradient (pH 3–10.5 over 5 mm) can be established in a glass-fiber paper-based fluidic channel with a MS-friendly electrolyte. Amphoteric species can be well separated from the complex blood matrix and concentrated into a narrow band in the channel within 2 min, which is 20 times faster than a commercial kit method. The method can be applied to both liquid and dry spot samples, and the cleaned sample band can be simply dissolved for direct IDMS detection in ESI MRM mode. This method is a promising strategy for the rapid MS-based detection of amino acids from serum without pre-separation via liquid chromatography. [ABSTRACT FROM AUTHOR]

Paper-based microfluidic solution sampling is a viable option for potentiometric sensors to be used for the determination of analytes in samples with high solid-to-liquid ratios. Unfortunately, heavy metal sensitive electrodes cannot be easily integrated with paper-based solution sampling as heavy metals have strong physicochemical adsorption affinity towards paper substrates. In this work, paper substrates were modified with an ion-selective membrane (ISM) cocktail (used for the preparation of Pb2+-ion-selective electrodes (ISEs)) and coupled with model heavy metal Pb2+-ISEs. It was found that the super-Nernstian response of Pb2+-ISEs was eliminated when 10 to 50 mg ml−1 of the ISM cocktail was used for the modification of paper substrates. The modification of the paper substrates by Pb2+-ISM allowed the elimination of adsorption sites. In addition, it resulted in an improvement of sensor performance in terms of their detection limits to be similar to those for conditioned electrodes in standard beaker-based measurements. It is believed that the elimination of super-Nernstian response of the electrodes and improving the potentiometric responses and detection limits of ISEs were attributed to the compatibility improvement of the paper substrates and Pb2+-ISEs to the same type of ISM. [ABSTRACT FROM AUTHOR]

Petroleum-based plastics are useful, but they pose a huge threat to the environment and human health. The development of sustainable cellulose paper materials with excellent mechanical and water-resistance properties to replace plastics is highly desirable but also challenging. Herein, we report a new kind of rosin-based modifier synthesized from fully hydrogenated rosin and (3-glycidoxypropyl)triethoxysilane, which can covalently bind with cellulose fiber networks to improve the hydrophobicity and weaken the capillarity of cellulose paper. The rosin-grafted cellulose composite paper shows a unique combination of water resistance (water absorption of 19.2% and 37.9% in 25 and 90 °C water, respectively) and high strength (tensile strength of 47.9 MPa and Young's modulus of 2.32 GPa). Moreover, the rosin-grafted cellulose composite paper can be completely degraded when buried in soil for up to 100 days, and it can be recycled when treated with an alkali. These impressive performances make rosin-grafted cellulose composite paper a promising eco-friendly alternative material to replace plastics in straws, boxes, cups, bags and so on. [ABSTRACT FROM AUTHOR]

In 2022, the outbreak of the monkeypox virus occurred in many non-endemic countries, and the World Health Organization (WHO) assessed that this outbreak was "atypical". The establishment of a rapid and effective assay that can be used for the early diagnosis of monkeypox virus infection is crucial for outbreak prevention and control. In this study, the monkeypox virus A29 protein and the homologous vaccinia virus A27 protein and cowpox virus 162 protein were expressed in Escherichia coli BL21 for screening. We synthesized the monkeypox virus A2917–49 peptide as the immunogen and obtained 25 monoclonal antibodies (mAbs) against the A29 protein using mouse hybridoma techniques. Then an immunochromatographic test strip method for detecting A29 was established. The strips utilizing mAb-7C5 and 5D8 showed the best sensitivity and lowest limit of detection: 50 pg mL−1 for purified A29 and specificity tests showed that the strips did not cross-react with other orthopox viruses (vaccinia virus or cowpox virus) as well as common respiratory pathogens (SARS-CoV-2, influenza A and influenza B). Therefore, this method can be used for early and rapid diagnosis of monkeypox virus infection by antigen detection. [ABSTRACT FROM AUTHOR]

A series of Ti-doped W18O49 samples were prepared using a convenient solvothermal route. Due to the synergistic effect of doped Ti and oxygen vacancies, the samples showed excellent visible-light photochromic properties. Their performances as light-printable rewritable paper and smart windows showed great application value and promotion value. [ABSTRACT FROM AUTHOR]

As a part of our ongoing research, we have synthesized a new fluorescence probe, p-C4A, based on a calix[4]arene substituted with 4-aminoquinoline moieties with amide linkages. p-C4A can selectively recognize Li+ and PO43− ions and has been characterized via an emission study, an absorption study, ESI-MS spectroscopy, a 1H NMR study and cyclic voltammetry. The fluorescence sensor p-C4A can operate over a concentration range of 5–170 nM for Li+ sensing and 5–80 nM for PO43− sensing. The R2 values obtained for the sensing of Li+ and PO43− ions are 0.9962 and 0.9911, respectively. p-C4A demonstrates a minimum detection limit of 6.15 nM for Li+ and 9.0 nM for PO43−. The quantum yields of p-C4A as its Li+ and PO43− ion complexes were found to be 0.014 and 0.27, respectively. Herein, we report an easy-to-use, low-cost, disposable, paper-based, fluorescent, wax-printed device for the rapid chemical screening of Li+ and PO43−. This device can be used as a quick, portable, multiple-test panel that is simple, lightweight, and disposable. Moreover, in order to assess its analytical applicability, the prepared sensor was successfully used for the determination of Li+ and PO43− from wastewater samples, validating the proposed ion recovery method with 96–99% recovery rates. [ABSTRACT FROM AUTHOR]

Bimodal NiCo2O4·MnO2 (NCM) nanorods were grown on carbon fiber paper (CFP) using a hydrothermal process. The structural and morphological studies were performed via powder X-ray diffraction and field-emission scanning electron microscopy, respectively. The aspect ratio of the developed electrode significantly improved up to a threshold concentration of manganese in the Ni/Co binary oxide, and thereafter decreased. The capacitive performance and electrochemical parameters of the developed NCM nanorods were analyzed using cyclic voltammetry, galvanostatic charge–discharge, and impedance spectroscopy. The maximum specific capacitance of the developed NCM nanorods was found to be 2575 F g−1 (305 mA h g−1) at a current density of 5 A g−1. Additionally, the excellent cyclic retention of nearly 92.5% was achieved for the NCM nanocomposite even after 5000 cycles. Also, the response time (τo) calculated from the Bode plot was found to be ∼22 s, which validated the fast charging of the developed electrode material. Furthermore, an asymmetric solid-state supercapacitor (ASC) device was successfully assembled utilizing NCM (1 : 2 : 2) nanorods and activated carbon as positive and negative electrodes, respectively. The developed device achieved a capacitance of 130 F g−1 (176.1 mA h g−1) with an energy density and power density of 138 W h kg−1 and 722 W kg−1, respectively, which could illuminate an LED bulb (1.8 V) for 50 min. [ABSTRACT FROM AUTHOR]

This work demonstrated a quantitative determination of Cu and Zn in tree rings using laser ablation-ICP-MS and the use of quantitative filter paper as a solid support for constructing the calibration curve using aqueous standards. After cleaning the filter paper using 10% v/v HNO3 for 30 min and drying it, 4 μL of standards is delivered on the filter surface and the results are attained with no normalized data. The analytical curves ranged from 0.5 to 10.0 μg g−1 and 5.0 to 100.0 μg g−1 for Cu and Zn, respectively, and the accuracy of the results was checked not only through Certified Reference Materials (NIST 1573a, tomato leaves and 1575a, pine needles) but also using ICP-MS (Inductively Coupled Plasma Mass Spectrometry) as a reference technique. Then, using such minimalist strategies, this method was applied for evaluating the mass fractions of Zn and Cu directly in tree rings. Three parallel ablation lines were drawn with a 220 μm distance between each one, with the same size of the tree ring samples. The average mass fractions for each tree ring and between the 3 ablated lines were at most ca. 18 and 13 μg g−1 for Cu and Zn, respectively, in Hymenaea courbaril, ca. 4 and 9 μg g−1 for Cu and Zn, respectively, in Tipuana tipu, and ca. 160 μg g−1 and

It is significant to develop low-cost and highly efficient electrocatalysts for the hydrogen evolution reaction (HER) via electrochemical water splitting. Herein, we constructed P-doped NiCo2S4 nanowire arrays on carbon fiber paper (NiCo2S4−xPx/CFP) as a HER electrocatalyst in both acidic and alkaline media. Benefitting from P doping into NiCo2S4, the as-prepared NiCo2S4−xPx/CFP exhibits low HER overpotentials of 80 and 132 mV in acidic and alkaline media at a cathodic current density of 10 mA cm−2, respectively, which are far superior to counterparts of NiCo2S4 nanowire arrays on the carbon fiber paper (NiCo2S4/CFP). Meanwhile, the NiCo2S4−xPx/CFP presents excellent HER stability of 20 hours in acidic and alkaline media. From the results of density functional theory calculations, P doping can not only optimize the hydrogen adsorption energetics on each kind of atomic site of catalysts, but also strengthen the H2O molecule binding ability on the catalyst surface for the alkaline HER and favor kinetics of hydrogen adsorption and H2 formation on the catalyst surface for the acidic HER, eventually improving overall HER performances. The investigation of the HER mechanism modulated by P doping in our work offers novel inspiration to develop highly efficient ternary metal sulfides for the HER. [ABSTRACT FROM AUTHOR]

The combination of electron-deficient viologen ligands with electron-rich POMs is a typical acceptor–donor system that has recently received much attention. Under solvothermal and hydrothermal conditions, by introducing three symmetric viologen ligands into POM-based hybrid materials, we successfully constructed four POMs–viologen inorganic–organic hybrid compounds, namely (1,3-bcbpy)2·(δ-Mo8O26) (1) (1,3-bcbpy·2Cl = 1,1′-bis(3-carboxybenzyl)-4,4′-bipyridine dichloride), {CoII(1,4-bcbpy)2(H2O)2[H2(β-Mo8O26)]}·2H2O·2CH2O (2), (1,4-bcbpy)2·(δ-Mo8O26)·2H2O (3) (1,4-bcbpy·2Cl = 1,1′-bis(4-carboxybenzyl)-4,4′-bipyridine dichloride, CH2O = formaldehyde), and {CuII(1,1-pmbby)2(H2O)[H2(β-Mo8O26)2]}·5H2O·C2H7N (4) (1,1-pmbby·2Cl = 1,1′-[1,4-phenylbis(methylene)]bis-(4,4′-bipyridine)dichloride, C2H7N = dimethylamine). These four compounds exhibit different fascinating structures, especially compound 4 is a typical metal–organic framework. Compounds 1–4 exhibit good discoloration behaviors under various external stimuli. For example, compounds 1–4 showed a positive response to the irradiation from a 300 W Xe lamp. When a positive voltage was applied to the ECD based on compounds 1–4, 1/2/3/4-ECD underwent a significant color conversion. What's more, compound 4 also showed obvious discoloration results after heating. In a word, 1–4 are multifunctional discoloration materials under different external stimuli. In addition, the coated filter paper prepared based on compound 3 can be used as a new printing material medium and can be successfully applied in erasable inkless printing and dual anti-counterfeiting. [ABSTRACT FROM AUTHOR]

Waterproof coating is necessary for paper-based packaging materials, especially as a plastic substitute in single-use applications. Currently, most paper-based packaging employs hazardous fluorocarbon coatings or other petroleum-based additives, which has caused a lot of concerns over safety. Herein, a novel edible waterproof coating was fabricated by a beeswax-in-water Pickering emulsion using hemicellulose-grafted-lauric acid (H-LA) micelles as nano-stabilizers. The fully biomass-based waterproof coating agent presented a uniform and stable water dispersion with a droplet size of around 1 μm. And compared with conventional surfactants, H-LA micelles stabilized at the oil–water interfaces and formed Pickering emulsions with enhanced stability. The Pickering emulsion was then applied as a coating of paper. The coated paper exhibited excellent water-resistance with a water contact angle of 130 ± 2.89° and an effective waterproof time of up to 6 h. The coated paper also showed good moisture barrier properties; the water vapor transmission rate was lower than 5.05 g mm m−2 day−1. Moreover, the waterproof coating was non-toxic, environmentally friendly and biocompatible, and could completely biodegrade in soil within 2 months. This work may provide an alternative solution for safe, cost-effective and sustainable paper-based packaging materials to replace traditional disposable plastics. [ABSTRACT FROM AUTHOR]

Bioelectrochemical technologies have attracted significant scientific interest because the effective bacterial electron exchange with external electrodes can provide a sustainable solution that joins environmental remediation and energy recovery. Multispecies electroactive bacterial biofilms are catalysts that will drive the operation of bioelectrochemical devices. Unfortunately, there is a lack of understanding of key mechanisms determining their electron-generating capabilities and syntrophic relations within microbial communities in biofilms. This is because there are no universally standardized models for simple, rapid, reliable, and cost-effective fabrication and characterization of electroactive multispecies biofilms. The heterogeneous and long-term nature of biofilm formation has hampered the development of those models. This work develops novel biofabrication and analysis platforms by creating innovative, paper-based 3-D systems that accurately recapitulate the structure, function, and physiology of living multispecies biofilms. Multiple layers of paper containing bacterial cells were stacked to simulate different layered 3-D biofilm models with defined cellular compositions and microenvironments. Overall bacterial electrogenic capabilities through the biofilm structures were characterized by thoroughly monitoring collective electron flows through different external resistors. Changes in the type of species and order of stacking created biofilm modeling which allowed for the study of their electrogenic performance via variation in electron flow rate output. Furthermore, multi-laminate structures allowed for straightforward de-stacking and layer-by-layer separation for analyses of pH distribution and cellular viability. Our multi-laminate structures provide a new strategy for (i) controlling the biofilm geometry of 3-D bacterial cultures, (ii) monitoring the microbial electoral properties, and (iii) constructing an artificial biofilm layer by layer. [ABSTRACT FROM AUTHOR]

Exosomes are vesicles released by healthy and cancer cells into the extracellular matrix and bodily fluid. Cancer cell-derived exosomes have attracted much attention in early-stage detection and prognostication of treatment response. Thus, detecting exosomes is of great interest to biology and medicine. However, many conventional detection methods require high-cost equipment and centralized laboratory facilities, making diagnostics inaccessible in limited-resource settings. This study reports a proof-of-concept low-cost electrochemical paper-based analytical device to quantify both the total bulk and cancer cell-derived exosomes in cell culture media. The device employs a sandwich immune assay design, where exosomes are initially captured using the electrode-bound generic antibodies (i.e. CD9) and subsequently detected via ovarian cancer-specific CA125 antibodies. Our proposed device quantifies the total bulk exosome concentration with a detection limit of 9.3 × 107 exosomes per mL and ovarian cancer cell-derived exosomes with a detection limit of 7.1 × 108 exosomes per mL, with a relative standard deviation of <10% (n = 3). We suggest that this low-cost and simple electrochemical paper-based device could be an alternative tool for detecting disease-specific exosomes in biological samples with the potential to be further developed for point-of-care diagnosis. [ABSTRACT FROM AUTHOR]

Paper-fluidic devices are a popular platform for point-of-care diagnostics due to their low cost, ease of use, and equipment-free detection of target molecules. They are limited, however, by their lack of sensitivity and inability to incorporate more complex processes, such as nucleic acid amplification or enzymatic signal enhancement. To address these limitations, various valves have previously been implemented in paper-fluidic devices to control fluid obstruction and release. However, incorporation of valves into new devices is a highly iterative, time-intensive process due to limited experimental data describing the microscale flow that drives the biophysical reactions in the assay. In this paper, we tested and modeled different geometries of thermally actuated valves to investigate how they can be more easily implemented in an LFIA with precise control of actuation time, flow rate, and flow pattern. We demonstrate that bulk flow measurements alone cannot estimate the highly variable microscale properties and effects on LFIA signal development. To further quantify the microfluidic properties of paper-fluidic devices, micro-particle image velocimetry was used to quantify fluorescent nanoparticle flow through the membranes and demonstrated divergent properties from bulk flow that may explain additional variability in LFIA signal generation. Altogether, we demonstrate that a more robust characterization of paper-fluidic devices can permit fine-tuning of parameters for precise automation of multi-step assays and inform analytical models for more efficient design. [ABSTRACT FROM AUTHOR]

A direct mass spectrometry method utilizing reactive paper spray ionization was developed for sensitive cannabinoid quantitation in biofluid matrices. The ca. 2-minute sample measurements used on-paper derivatization to significantly increase paper spray mass spectrometry (PS-MS) positive ion mode sensitivity while minimizing sample preparation steps. Calibrations demonstrate high linearity, with R2 > 0.99 for (−)-trans-Δ9-tetrahydrocannabinol (THC) in oral fluid and 11-nor-9-carboxy-Δ9-tetrahydrocannabinol (THC-COOH) in urine. The limit of detection and lower limit of quantitation were 0.78 and 10 ng mL−1 for THC in oral fluid and 1.3 and 10 ng mL−1 for THC-COOH in urine, respectively. THC-COOH levels measured by reactive PS-MS in seven spiked human urine samples showed bias of −9.4 to 5.9%, and percent difference values of −16.8 to 9.8% in comparison with a reference LC-MS method. Based upon the method simplicity, validation experiments, sensitivity, and rapidity, we conclude that reactive PS-MS has potential applications for rapid cannabinoid drug testing in urine and oral fluid. [ABSTRACT FROM AUTHOR]

In this work, Au nanoparticle (AuNP)-modified filter paper as a highly sensitive mercury extractant was successfully prepared in situ and applied in the head-space solid phase extraction (HS-SPE) of Hg(II) in water. The microstructure of the modified filter paper was characterized by using X-ray diffraction and scanning electron microscopy (XRD/SEM), and the results showed that AuNPs were well distributed on the fiber surface of the filter paper. Combined with portable Zeeman atomic absorption spectroscopy (ZAAS), the modified filter paper was successfully applied to Hg detection in water samples. Specifically, it can easily achieve in situ sample collection and detection under negative pressure in the field, which was reported for the first time. Several influencing factors such as extraction temperature, time, stirring speed, pH value, reductants, inorganic ions, and organic interfering and complexing agents were all investigated thoroughly. The limit of detection (LOD) for Hg(II) was 0.09 μg L−1, with linearity ranging from 0.09 to 50 μg L−1. Good recoveries were also obtained between 82 and 106% with RSDs below 7% in real water samples. The established method provided a convenient route for mercury detection in environmental water with a low amount of sample required (1 mL) and good detection performance, which is comparable to that of ICP-MS. [ABSTRACT FROM AUTHOR]

A chromone-based symmetrical dipodal Schiff base probe L was designed and synthesized for multi-analyte detection in both aqueous and organic media. L displayed a prominent 'turn-on' fluorescence response with Al3+ (LOD = 6.9 μM) via the chelation-enhanced fluorescence (CHEF) process in a fully aqueous medium based on the inhibition of the photoinduced electron transfer (PET) process. Moreover, the in situ generated [L-Al3+] system was able to detect pyrophosphate (PPi) under identical experimental conditions. The proposed sensing pathway is believed to be the complexation with aluminium, followed by the subsequent decomplexation of the system by PPi. Furthermore, as the probe was decorated with –NH functionalities, it attained fluorescence indications upon binding with a basic anion. The detection ability of the probe for fluoride ions (LOD = 6.8 × 10−8 M) in the organic medium was studied using the 'turn-off' emission change based on the formation of a N–H⋯F hydrogen bond and subsequent deprotonation, as well as a visual change in color from yellow to reddish-yellow under UV light. The in situ prepared [L-F−] adducts could potentially sense Zn2+ ions with a 'turn-on' response via the metal-induced release of the free probe. All of the spectroscopic analyses were recorded to support the recognition mechanism of the aforementioned analytes by the reported probe molecule L. The probe also found applications in testing real water samples. [ABSTRACT FROM AUTHOR]

Herein, Cu-doped Co-ZIF nanoplate arrays are uniformly grown on a commercial paper towel substrate first. After a subsequent annealing treatment, well-defined Cu-doped Co/CoO nanoparticles embedded in N-doped carbon hybrid nanoplate arrays supported on the carbon paper substrate (denoted as Cu-doped Co/CoO/NC NPAs@CP) are obtained, which exhibit excellent performance as a low-cost, lightweight and binder-free anode for lithium ion storage. [ABSTRACT FROM AUTHOR]

The current open-loop practices employed to render paper substrates water- and oil-repellent for packaging and non-packaging applications have generated ocean pollution and have placed daunting burdens on landfills. In this study, we report a green, unique and facile approach for the fabrication of grease- and water-resistant paper products with 100% recyclability of the paper pulp. Low surface energy polydimethylsiloxane (PDMS) was grafted onto a biobased chitosan polymer via urea linkages to prepare the graft copolymer chitosan-graft-polydimethylsiloxane (chitosan-g-PDMS). Chitosan-g-PDMS was then applied as a coating onto an unbleached Kraft paper substrate from an aqueous solution. The coated paper substrates exhibited good hydrophobic properties with a water contact angle of 120.53 ± 0.96° and a Cobb 60 value of 9.89 ± 0.32 g m−2. The coated paper substrates also showed good oil-resistance as evident from the kit rating value of 11.7/12. The tensile strength, crushing resistance, bending stiffness, and internal tearing resistance of the paper before and after coating treatment was determined. Scanning electron microscopy (SEM) analysis was used to characterize changes in the porosity of the paper before and after the coating. The pulp recyclability of the coated paper was validated by subjecting the coated paper samples to repulping and washing treatment. This novel and practical approach can provide significant environmental benefits by offering plastic-free, fluorine-free and fully-recyclable water- and grease-resistant paper; thus promoting sustainability due to its unique closed-loop nature. [ABSTRACT FROM AUTHOR]

Paper devices have attracted great attention for their rapid development in multiple fields, such as life sciences, biochemistry, and materials science. When manufacturing paper chips, flexible materials, such as cellulose paper or other porous flexible membranes, can offer several advantages in terms of their flexibility, lightweight, low cost, safety and wearability. However, traditional cellulose paper sheets with chaotic cellulose fiber constitutions do not have special structures and optical characteristics, leading to poor repeatability and low sensitivity during biochemical sensing, limiting their wide application. Recent evidence showed that the addition of ordered structure provides a promising method for manufacturing intelligent flexible devices, making traditional flexible devices with multiple functions (microfluidics, motion detection and optical display). There is an urgent need for an overall summary of the evolution of paper devices so that readers can fully understand the field. Hence, in this review, we summarized the latest developments in intelligent paper devices, starting with the fabrication of paper and smart flexible paper devices, in the fields of biology, chemistry, electronics, etc. First, we outlined the manufacturing methods and applications of both traditional cellulose paper devices and modern smart devices based on pseudopaper (order paper). Then, considering different materials, such as cellulose, nitrocellulose, nature sourced photonic crystals (photonic crystals sourced from nature directly) and artificial photonic crystals, we summarized a new type of smart flexible device containing an ordered structure. Next, the applications of paper devices in biochemical sensing, wearable sensing, and cross-scale sensing were discussed. Finally, we summarized the development direction of this field. The aim of this review is to take an integral cognition approach to the development of smart flexible paper devices in multiple fields and promote communications between materials science, biology, chemistry and electrical science. [ABSTRACT FROM AUTHOR]

A portable paper-based electrochemical sensor has been developed to determine 5-hydroxymethylfurfural (5-HMF). A screen-printed carbon electrode (SPCE) was facilely fabricated for the first time on poster paper which showed a very satisfactory electrochemical response. The analytical performance of the electrode was enhanced by electrochemical deposition of silver microdendrites (AgMDs). The cathodic peak of 5-HMF occurred at approximately −1.48 V, lower than that obtained from the bare poster-SPCE. Moreover, the modified electrode showed a higher current response than the bare electrode, revealing that the AgMDs not only exhibited highlighted electrocatalytic features but also improved the electrical conductivity and increased the electrode surface area. Afterward, some influencing conditions were optimized, including scan rate and the number of scan cycles for AgMD deposition, pH, temperature, and square wave voltammetric parameters. Under the optimal conditions, the analytical characteristics of the proposed sensor were evaluated. The cathodic peak current increased linearly according to 5-HMF concentration over the range of 3–100 ppm, and the detection limit was 1.0 ppm. This low-cost, disposable electrochemical sensor provided environmentally friendly, simple and rapid detection, acceptable precision, good stability, and high selectivity. Additionally, this method can be applied to quantify 5-HMF in honey samples with satisfying accuracy. [ABSTRACT FROM AUTHOR]

The sustainable goal of technological advancement is to go from lab to site through the development of a sensitive, specific and portable sensor for pollution monitoring. Herein, we report a completely portable colorimetric prototype device for the selective monitoring of lead (Pb) pollution, mainly in air, which relies on a new aspect of analysing the colorimetric assays on paper strips by the direct measurement of the retroreflective information, other than the available tedious image analysis methods. Our indigenously developed citrate-functionalized silver nanoparticles (AgNPs) embedded in cellulose paper strips showed significant localized surface plasmonic resonance (LSPR) peaks in the blue region and with the increase in the Pb concentration, the LSPR band in the blue region decreased and a new peak appeared in the green region of the electromagnetic spectrum due to the formation of larger aggregates. The prototype device monitored these spectral changes and accordingly gave the Pb content present in the sample. In this work, we made the sample under study by the acid digestion of one of the widely present air-suspended particulates, i.e., PbO2. The prototype device is a suitable fielddeployable technique for environmental Pb sensing and will open up new perspectives for future advancement in low-cost paper-based sensing. [ABSTRACT FROM AUTHOR]

The integration of smartphones with visual-based paper strips has gained great attention because of the rapid, low-cost, and relible analysis. Herein, we report on the synthesis of a red luminescent europiumbased metal organic framework (Eu-MOF) for the detection of folic acid in pharmaceutical formulations. The Eu-MOF showed strong and stable red emission fluorescence (excited at 270 nm), and the emission was significantly quenched upon exposure to folic acid due to the inner filter effect. A fluorometric assay in solution and visual detection based on fluorescence on a paper strip were used independently to quantify folic acid. The paper strips were prepared using chromatography paper and with the aid of a smartphone, folic acid was visually detected. In solution, the calculated LOD was 0.3 mM with a dynamic linearity range from 1.0 to 12.50 mM. Meanwhile, in the visual detection based on a smartphone integrated with a paper test strip, the linearity was from 1.0 to 9.0 mM with 0.12 mM as the LOD. Color analysis, from the photographs taken with a smartphone, was performed via analyzing the RGB coordinates using the Image-J program. The luminescent probe was applicable to detect folic acid in various drug tablets with recovery data ranging from 95 to 103%. The application of smartphones and fluorescent paper strips provides reliable detection of folic acid for on-site analysis, particularly in remote rural areas. [ABSTRACT FROM AUTHOR]

Surveillance of SARS-CoV-2 infection is critical for controlling the current pandemic. Antigen rapid tests (ARTs) provide a means for surveillance. Available lateral flow assay format ARTs rely heavily on nitrocellulose paper, raising challenges in supply shortage. Vertical flow assay (VFA) with cellulose paper as test material attracts much attention as a complementary test approach. However, current reported VFAs are facing challenges in reading the test signal from the bottom face of the test cassette, complicating the test workflow and hindering translation into rapid test application. Here, we address this gap with an enhanced VFA against SARS-CoV-2 N protein that adapts a cellulose pull-down test format allowing (1) one-step sample application at the top of the test cassette and (2) readout of the test signal from the top. We also demonstrate the feasibility of translating the enhanced VFA into a point-of-care application that can help in SARS-CoV-2 surveillance. [ABSTRACT FROM AUTHOR]

Chronic obstructive pulmonary disease (COPD) has become the third leading cause of global death. Insufficiency in early diagnosis and treatment of COPD, especially COPD exacerbations, leads to a tremendous economic burden and medical costs. A cost-effective and timely prevention requires decentralized point-of-care diagnostics at patients' residences at affordable prices. Advances in point-of-care (POC) diagnostics may offer new solutions to reduce medical expenditures by measuring salivary and blood biomarkers. Among them, paper-based analytical devices have been the most promising candidates due to their advantages of being affordable, biocompatible, disposable, scalable, and easy to modify. In this review, we present salivary and blood biomarkers related to COPD endotypes and exacerbations, summarize current technologies to collect human whole saliva and whole blood samples, evaluate state-of-the-art paper-based analytical devices that detect COPD biomarkers in saliva and blood, and discuss existing challenges with outlooks on future paper-based POC systems for COPD diagnosis and management. [ABSTRACT FROM AUTHOR]

Surface-enhanced Raman spectroscopy (SERS) is an emerging analytical technique for chemical analysis, which is favourable due to its combination of short measurement time, high sensitivity and molecular specificity. However, the application of SERS is still limited, largely because in real samples the analyte is often present in a complex matrix that contains micro/macro particles that block the probe laser, as well as molecular contaminants that compete for the enhancing surface. Here, we show a simple and scalable spray-deposition technique to fabricate SERS-active paper substrates which combine sample filtration and enhancement in a single material. Unlike previous spray-deposition methods, in which simple colloidal nanoparticles were sprayed onto solid surfaces, here the colloidal nanoparticles are mixed with hydroxyethyl cellulose (HEC) polymer before application. This leads to significantly improved uniformity in the distribution of enhancing particles as the film dries on the substrate surface. Importantly, the polymer matrix also protects the enhancing particles from air-oxidation during storage but releases them to provide SERS enhancement when the film is rehydrated. These SERS-paper substrates are highly active and a model analyte, crystal violet, was detected down to 4 ng in 10 μL of sample with less than 20% point-by-point signal deviation. The filter paper and HEC effectively filter out both interfering micro/macro particles and molecular (protein) contaminants, allowing the SERS-paper substrates to be used for SERS detection of thiram in mud and melamine in the presence of protein down to nanogram levels without sample pre-treatment or purification. [ABSTRACT FROM AUTHOR]

Quantitative nucleic acid amplification tests (qNAATs) are critical in treating infectious diseases, such as in HIV viral load monitoring or SARS-CoV-2 testing, in which viral load indicates viral suppression or infectivity. Quantitative PCR is the gold standard tool for qNAATs; however, there is a need to develop point-of-care (POC) qNAATs to manage infectious diseases in outpatient clinics, low- and middle-income countries, and the home. Isothermal amplification methods are an emerging tool for POC NAATs as an alternative to traditional PCR-based workflows. Previous works have focused on relating isothermal amplification bulk fluorescence signals to input copies of target nucleic acids for sample quantification with limited success. In this work, we show that recombinase polymerase amplification (RPA) reactions on paper membranes exhibit discrete fluorescent amplification nucleation sites. We demonstrate that the number of nucleation sites can be used to quantify HIV-1 DNA and viral RNA in less than 20 minutes. An image-analysis algorithm quantifies nucleation sites and determines the input nucleic acid copies in the range of 67–3000 copies per reaction. We demonstrate a mobile phone-based system for image capture and onboard processing, illustrating that this method may be used at the point-of-care for qNAATs with minimal instrumentation. [ABSTRACT FROM AUTHOR]

The evaluation of the leaching of metals is important in the study of metal-catalyzed reactions. However, analytical methods for the determination of trace metals in organic reaction solution require high purity reagents and time-consuming digestion processes. We present a rapid and sensitive method for the determination of platinum group elements (PGEs) in an organic reaction solution using LA-ICP-MS. Novel sample preparation for the dried solution spot and linear scanning ablation method was developed for the total sampling technique. For a 0.1 μl solution sample, the detection limits of PGEs were 0.034 to 1 ng ml−1 and the detection efficiency of sampling of the detector was 1.5 × 10−5 to 3.3 × 10−4. The proposed method does not require pre-treatment such as digestion, dilution and addition of internal standards to the sample and can be completed within about 5 minutes including sample preparation. To demonstrate the adaptability to organic reaction solution, the quantitative analysis of Pt leaching in continuous-flow hydrogenation reactions with Pt/C as a fixed bed catalyst was performed by the proposed method and compared with the conventional microwave-assisted acid digestion/ICP-MS and isopropanol dilution/ICP-MS methods. The determined concentration showed good agreement with the concentration determined by the conventional methods. The relative deviations of the measured value by LA-ICP-MS were −4.1% from the value obtained by MW/ICP-MS and −3.6% from the value obtained by IPA-dilution/ICP-MS, confirming the accuracy of the proposed method. This method will be a powerful tool for the evaluation of metal leaching and for the analysis of trace metals in organic reaction solutions. [ABSTRACT FROM AUTHOR]