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Pencil drawing is one of the simplest and most cost-effective ways of fabricating miniaturized electrodes on a paper substrate. However, it is limited by the lack of reproducibility regarding the electrode drawing process. A 3D-printed pencil holder (3DPH) is proposed here for simple, reproducible, and low-cost hand-drawn fabrication of paper-based electrochemical devices. 3DPH was designed to keep pressure and angulation of the graphite mine constant on the paper substrate using a micromechanical pencil regardless of the user/operator. This approach significantly improved the reproducibility and cost of making reliable pencil-drawn electrodes. The results showed high reproducibility and accuracy of the 3DPH-assisted electrodes prepared by 4 different operators in terms of sheet resistance and electrochemical behavior. Cyclic voltammetric (CV) curves in the presence of [Fe(CN) 6 ] 3-/4- redox probe showed only 3.9% variation for the anodic peak currents of different electrodes prepared by different operators when compared with electrodes prepared without the 3D-printed support. SEM analyses revealed a more uniform graphite deposition/design of the electrodes prepared with 3DPH, which corroborates the results obtained by CV. As a proof of concept, 3DPH-assisted pencil-drawn graphite electrodes were employed for dopamine detection in synthetic saliva, showing a proportional increase in anodic peak current at 0.12 V vs. carbon pRE with increasing dopamine (DA) concentration, with a detection limit of 0.39μmol L -1 . Moreover recovery was in the range 93-104% of DA (4-7% RSD) in synthetic saliva for three different concentrations, demonstrating the reliability of the approach. Finally, we believe this approach can make pencil-drawn technology more robust, accessible, reliable, and inexpensive for real on-site applications, especially in hard-to-reach locations or research centers with little investment., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

Paper-based electrochemical analytical devices (ePADs) have gained significant interest as promising analytical units in recent years because they can be fabricated in simple ways, are low-cost, portable, and disposable platforms that can be applied in various fields. In this sense, paper-based electrochemical biosensors are attractive analytical devices since they can promote diagnose several diseases and potentially allow decentralized analysis. Electrochemical biosensors are versatile, as the measured signal can be improved by using mainly molecular technologies and nanomaterials to attach biomolecules, resulting in an increase in their sensitivity and selectivity. Additionally, they can be implemented in microfluidic devices that drive and control the flow without external pumping and store reagents, and improve the mass transport of analytes, increasing sensor sensitivity. In this review, we focus on the recent developments in electrochemical paper-based devices for viruses' detection, including COVID-19, Dengue, Zika, Hepatitis, Ebola, AIDS, and Influenza, among others, which have caused impacts on people's health, especially in places with scarce resources. Also, we discuss the advantages and disadvantages of the main electrode's fabrication methods, device designs, and biomolecule immobilization strategies. Finally, the perspectives and challenges that need to be overcome to further advance paper-based electrochemical biosensors' applications are critically presented., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

A new concept of paper-based device has been developed combining the advantages of cellulose supports and the rich surface chemistry of metal-organic frameworks (MOFs). The composite, named as NH 2 -UiO-66@paper, has been developed for the isolation of synthetic cannabinoid receptor agonists (SCRAs) in oral fluids, trying to mimic the interactions of those compounds with the human CB1R and CB2R receptors, mainly governed by hydrogen bonding and π-interactions with serine and histidine residues. MOF selection (UiO-66) and functionalization of the ligand (2-aminoterephthalic acid) has been done according to the following criteria: (i) water stability of the selected MOF, and (ii) promoting appropriate interactions with SCRAs due to the MOF nature. NH 2 -UiO-66@paper composite has been characterized in depth and the results confirmed that the material is stable at the temperature selected for thermal desorption (230 °C). Furthermore, the developed method provided appropriate precision values (RSD < 12%) and a limit of detection as low as 10 ng using ion mobility spectrometry as analytical technique. Lastly, the method has been successfully applied to the isolation of several synthetic cannabinoids from oral fluids. This method claims to be an interesting approach for expanding the combination of MOFs with sustainable support and represents a promising alternative to sophisticated and non-portable systems due to the negligible sample treatment required and the simplicity of the operation, which can be applied with screening purposes., (© 2023. The Author(s).)

The detection of biogenic amines released from degraded meats is an effective method for evaluating meat freshness. However, existing traditional methods like titration are deemed tedious, while the use of sophisticated analytical instruments is not amenable to field testing. Herein, a cyanostilbene-based fluorescent array was rapidly fabricated using macroarray synthesis on a cellulose paper surface to detect amines liberated from spoiled beef, fish, and chicken. The fluorescence changes of immobilized molecules from the interaction with gaseous amines were used to monitor changes in freshness levels. Thanks to the high-throughput nature of macroarray synthesis, a set of highly responsive molecules such as pyridinium and dicyanovinyl moieties were quickly revealed. Importantly, this method offers flexibility in sensing applications including (1) sensing by individual sensor molecules, where the fluorescence response correlated well with established titration methods, and (2) collective sensing whereby chemometric analysis was used to provide a cutoff of freshness with 73-100% accuracy depending on meat types. Overall, this study paves the way for a robust and cost-effective tool for monitoring meat freshness., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

Bacillus cereus is one of the most common foodborne pathogens found in various kinds of staple foods such as rice and wheat. A rapid and accurate detection method for this pathogen is highly desirable for the sustainable production of relevant food products. While several classical and molecular-based detection methods are available for the identification of B. cereus, they suffered one or more limitations such as the requirement for a tedious and time-consuming process, less than ideal specificity, and the lack of portability. Herein, we developed the first paper-based sensing device that exhibits high species specificity with sufficiently low limit of detection for the visual detection of specific DNA sequences of B. cereus. The success is attributed to the strategic planning of fabrication in various dimensions including thorough bioinformatics search for highly specific genes, the use of the pyrrolidinyl peptide nucleic acid (PNA) probe whose selectivity advantage is well documented, and an effective PNA immobilization and DNA-binding visualization method with an internal cross-checking system for validating the results. Testing in rice matrices indicates that the sensor is capable of detecting and distinguishing B. cereus from other bacterial species. Hence, this paper-based sensor has potential to be adopted as a practical means to detect B. cereus in food industries., (© 2021. Springer-Verlag GmbH Germany, part of Springer Nature.)

The oxidation of paper by periodate was investigated and systematically characterized by Fourier-transform infrared (FTIR) spectroscopy, scanning electron microscopy, X-ray diffraction, goniometry, and dynamic mechanical analysis. For the first time, in situ FTIR microscopy analysis was performed, yielding chemical images of carbonyl groups on the cellulose fibers. The enhancement of protein immobilization on oxidized paper was quantified by a colorimetric assay with Ponceau dye, demonstrating that 0.5-h oxidation suffices to functionalize the paper-based devices. The oxidized paper was applied as a sensor for protein quantification in urine, a test able to detect levels of proteinuria and even microalbuminuria. The quantification was based on the capture of proteins through covalent bonds formed with the carbonyl groups on the oxidized paper followed by the staining of the region with Ponceau dye. There is a linear dependency between human serum albumin (HSA) concentration and the length of the stained blot from 0.1 to 3 mg mL -1 . This method correlated linearly with a reference method showing a higher sensitivity (0.866 cm mL mg -1 ) than the latter. The limit of quantification was 0.1 mg mL -1 , three times lower than that of the commercial strip. Graphical abstract Paper oxidation with periodate and extensive characterization, including microspectroscopy. The conversion of cellulose hydroxyl groups to aldehyde enhances covalent immobilization of protein on paper for application as analytical device. The oxidized paper determined protein in urine, suitable for proteinuria diagnosis.

Paper-based immunoassays are effective methods that employ microfluidic paper-based analytical devices (μPADs) for the rapid, simple, and accurate quantification of analytes in point-of-care diagnosis. In this study, we developed a wax-printed multilayered μPAD for the colorimetric detection of carcinoembryonic antigen (CEA), where the device contained a movable and rotatable detection layer to allow the μPAD to switch the state of the sample solutions, i.e., flowing or storing in the sensing zones. A smartphone with a custom-developed program served as an automated colorimetric reader to capture and analyze images from the μPAD, before calculating and displaying the test results. After optimizing the crucial conditions for the assay, the proposed method exhibited a wide linear dynamic range from 0.5 to 70 ng/mL, with a low CEA detection limit of 0.015 ng/mL. The clinical performance of this method was successfully validated using 50 positive and 40 negative human serum samples, thereby demonstrating the high sensitivity of 98.0% and specificity of 97.5% in the detection of CEA. The proposed method is greatly simplified compared with the cumbersome steps required for traditional immunoassays, but without any loss of accuracy and stability, as well as reducing the time needed to detect CEA. Complex and bulky instruments are replaced with a smartphone. The proposed detection platform could potentially be applied in point-of-care testing. Graphical abstract.

We report a smartphone-paper-based sensor impregnated with cetyltrimethylammonium bromide modified silver nanoparticles (AgNPs/CTAB) for determination of Fe 3+ in water and blood plasma samples. The methodology for determination of Fe 3+ is based on the change in signal intensity of AgNPs/CTAB fabricated on a paper substrate after the deposition of analyte, using a smartphone followed by processing with ImageJ software. The mechanism of sensing for detection and determination of Fe 3+ is based on the discoloration of AgNPs which impregnated the paper substrate. The discoloration is attributed to the electron transfer reaction taking place on the surface of NPs in the presence of CTAB. Fe 3+ was determined when the paper was impregnated with 1 mM AgNPs for 5 min of reaction time and the substrate was kept under acidic conditions. The linear range for determination of total iron in terms of Fe 3+ was 50-900 μg L -1 with a limit of determination (LOD) of 20 μg L -1 and coefficient of variation (CV) of 3.2%. The good relative recovery of 91.3-95.0% and interference studies showed the selectivity of the method for determination of total iron in water and blood plasma samples. Smartphone-paper-based sensors have advantages of simplicity, rapidity, user-friendliness, low cost, and miniaturization of the method for on-site determination of total iron compared to methods that require sophisticated analytical instruments. Graphical abstract Smartphone-paper-based sensor with cetyltrimethylammonium bromide modified silver nanoparticles for determination of Fe 3+ in water and blood plasma samples.

Purpose: To study respiratory effects of exposure to soft paper dust exposure, a relationship that is rarely studied., Methods: Soft tissue paper mill workers at a Swedish paper mill were investigated using a questionnaire and lung function and atopy screening. Spirometry without bronchodilation was performed with a dry wedge spirometer, and forced vital capacity (FVC) and forced expiratory volume in 1 s (FEV 1 ) were obtained and expressed as percent predicted. Exposure to soft paper dust was assessed from historical stationary and personal measurements of total dust, in addition to historical information about the work, department, and production. The impact of high exposure to soft paper dust (> 5 mg/m 3 ) vs. lower exposure ≤ 5 mg/m 3 , as well as cumulative exposure, was analyzed using multiple linear regression models. Multivariate models were adjusted for smoking, atopy, gender, and body mass index., Results: One hundred ninety-eight current workers (124 male and 74 female) were included. There were significant associations between both cumulative exposure and years of high exposure to soft paper dust and impaired lung function. Each year of high exposure to soft paper dust was associated with a 0.87% decrease in FEV 1 [95% confidence interval (CI) - 1.39 to - 0.35] and decreased FVC (- 0.54%, 95% CI - 1.00 to - 0.08) compared to the lower exposed workers., Conclusions: The present study shows that occupational exposure to soft paper dust (years exceeding 5 mg/m 3 total dust) is associated with lung function impairment and increased prevalence of obstructive lung function impairment.

In the current study, pretreatment of sugarcane bagasse has been carried out with ultrafiltered xylano-pectinolytic enzymes, before conventional chemical bleaching process. Optimized enzymatic dose (4 IU xylanase and 1.2 IU pectinase per g of oven dried pulp) and retention time (180 min) were determined on the basis of maximum decrement in kappa number (from 20.93 to 15.32), release of maximum sugars (7.4 mg/g) as well as attainment of maximum brightness (25.1% ISO), whiteness (from - 57.3 to - 41.9) and minimum yellowness (from 48.7 to 35.3) of the pulp samples. Enzymatically treated samples also showed release of phenolic, lignin and hydrophobic compounds in their filtrates. Nearly 30% decrement in the exhaustion of bleaching chemical dose was detected as compared to control samples. The physical properties such as tear index, burst index, double fold number, breaking length, gurley porosity and viscosity of enzymo-chemically treated bagasse pulp samples were improved by 6.68%, 33.86%, 22.92%, 13.43%, 17.5% and 9.64%, respectively. Additionally, a decrement of 36.75% and 28.29% in the values of BOD and COD of the effluents was also noted, which demonstrated the fact that, inclusion of enzymes in chemical based protocols of paper and pulp industries could be a highly beneficial and eco-friendly approach in upcoming decades. This is the first report mentioning the effect of ultrafiltered xylano-pectinolytic enzymes concoction on sugarcane bagasse pulp., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

A paper-based colorimetric assay for the determination of bilirubin has been developed. The method is based on the in-situ reduction of chloroauric acid to form gold nanoparticles. A chromatographic paper was patterned using a wax printer. Chloroauric acid was drop-cast onto the reagent zone. In the presence of bilirubin, gold(III) ions are reduced and form gold nanoparticles. This leads to a color change from yellow to purple. The intensity of the purple color (peak at 530 nm) increases with bilirubin concentration in the 5.0 to 1000 mg L -1 range. The detection limit is 1.0 mg L -1 . For the quantification of bilirubin, images were captured using a digital camera, and data were processed with the help of machine learning-based supervised prediction using Random Forest classification. The method was applied to the determination of bilirubin in urine samples. The spiked urine samples exhibit more than 95% recovery. Graphical abstractSchematic representation of the paper-based colorimetric assay for the detection of bilirubin based on the in-situ formation of gold nanoparticles. A color band is generated for visual interpretation and used for the testing of bilirubin in urine.

The copper(II) ion (Cu 2+ ) has played an indispensable role in diverse kinds of functional physiological processes of organisms, which has become of growing interest. Despite the fact that numerous Cu 2+ test papers using fluorescent probes have been fabricated, sensors featuring the ratiometric property that integrates quenched probes and an inner standard dye are rarely reported. Herein, a two-component ratiometric sensor in a paper-based device is proposed to realize highly selective Cu 2+ detection. To overcome shortcomings such as low signal-to-noise ratio and incorrect response of the quenching probe, a novel BODIPY-based turn-off probe (P2017) is designed and introduced into the paper-based device with better water solubility and selectivity for Cu 2+ detection. Furthermore, a reference dye (B001), exhibiting an emission at 690 nm when the excitation wavelength is 480 nm, is also introduced into the paper-based device. These two components can enhance the quality of the signal as P2017 is sensitively quenched by Cu 2+ , while B001 with a photostable property, serving as an internal benchmark, is unable to react with Cu 2+ . The results indicated that the two components provided a new concept for optimizing paper-based device fabrication and developing accurate, simple, and inexpensive Cu 2+ detection methods, which could be potentially applied to monitor human health and the environment in remote areas. Graphical abstract.

A rapid and accurate detection of pathogens is essential for bedside or on-site diagnosis. Filter paper is an ideal diagnostic tool as it requires no equipment, possesses a high surface-area-to-volume ratio and a high capacity of capillary force. The functionalization of the surface of cellulose filter paper was explored by using glutaric anhydride, N-hydroxysuccinimide, and N,N'-dicyclohexylcarbodiimide. The activated surface systems enable aminated DNA to be immobilized on the surface of filter paper. Both synthetic oligonucleotides and bacterial genomic DNA of Staphylococcus aureus, Escherichia coli, and Campylobacter jejuni were detected successfully. The system produces a clear, consistent and highly visible brown signal within 1-5 min. The digital image can also be analyzed quantitatively due to the brown color resulting from the presence of magnetic beads. Bacterial DNA detection was accomplished by using 16S rDNA probe on the activated paper surface for universal bacterial diagnosis. The method is stable and repeatable. It can detect at least 0.5 pmol of a 120-base synthetic oligonucleotide per assay and 5-10 ng of bacterial DNA per assay. Graphical abstract Schematic representation of the method: a. functionalization of cellulose filter paper, b. printing of aminated probes, c. incubation, d. blocking of unreacted functional groups (as dots shown), e. a visual detection of targets, f. quantitative analysis of image.

Paper spray high-resolution accurate mass spectrometry is a fast and versatile analysis method. This ambient ionization technique enables the quantitation of xenobiotics in complex biological matrices without chromatography or conventional sample extraction. The simplicity, rapidity, and affordability of the paper spray mass spectrometry (PS-MS) method make the technique especially attractive for clinical investigations where fast and affordable sample analysis is crucial. A new PS-MS method for the quantitation of voriconazole in equine tears was developed and validated. For a concentration range of 10 to 1000 ng/mL, good linearity (R 2  > 0.99), inter- and intra-run precision (coefficient of variation (CV) max. 11.9%), accuracy (bias of the nominal concentration ± 13.9%), and selectivity (signal areas of the double blanks represent 0.13 ± 0.05% of the lower limit of quantitation (LLOQ) signal in equine tears) were observed. The quantitation of voriconazole was based on three product ions and calculated relative to the isotope-labeled internal standard, voriconazole-d 3 , which had a final concentration of 250 ng/mL in the standards and samples. The matrix effect of the method showed an ionization suppression by reduction of the voriconazole response to 63.6%, 70.2%, and 81.9% for 30 ng/mL, 450 ng/mL, and 900 ng/mL in equine tears compared with voriconazole in solvent (methanol:water, 50:50, v:v). The method was used to analyze 126 study samples collected for a pharmacokinetic study investigating a novel approach for treatment of fungal keratitis in horses. Therefore, the integrity of the sample dilution (n = 6, CV 6.90%, and bias of nominal concentration + 8.40%) and the carryover effect (increase from 0.33 ± 0.21% to 1.33 ± 0.89% of the signal of the LLOQ) was further investigated. To our knowledge, this method is the first application of PS-MS for quantitation of drug concentrations in tears from any species.

Isoelectric focusing (IEF), a powerful technique for protein separation and enrichment, was successfully integrated into microfluidic paper-based analytical devices (μPADs) in this work. The μPADs for isoelectric focusing were fabricated by octadecyltrichlorosilane (OTS) silanization and subsequent region-selective plasma treatment. The system of IEF on μPADs could be easily assembled. And a series of conditions of the system were investigated, including the suitable concentration of ampholyte to create good pH gradient, the effect of polyvinylpyrrolidone (PVP) on electroosmotic flow (EOF) suppression, and focusing voltage applied on the paper channel. After optimization, simultaneous separation and enrichment of protein sample containing myoglobin and cytochrome C was successfully demonstrated. Besides, parallel IEF on multichannels were also achieved for the separation of multiple protein samples on one single chip, and their performance was compared with that of the conventional gel-IEF system. The developed IEF on μPADs exhibits appealing features such as low cost, simplicity, and disposability and are believed to have great application potentials.

Rapid, low-cost, and sensitive nucleic acid detection and quantification assays enabled by microfluidic paper-based analytical devices (μPADs) hold great promise for point-of-care disease diagnostics and field-based molecular tests. Through the capillary action in μPAD, flexible manipulation of nucleic acid samples can be achieved without the need for external pumps or power supplies, making it possible to fabricate highly integrated sample-to-answer devices that streamline the nucleic acid extraction, separation, concentration, amplification, and detection. To detect minute amounts of genetic materials from clinical and biological samples, it is also critical to develop sensitive signal readouts that generate physically detectable signals for in-device nucleic acid detection and/or quantification. In this review, we will focus on μPAD approaches for the facile manipulation of nucleic acids and emerging signal transduction strategies allowing sensitive and specific nucleic acid detection in μPAD. Graphical abstract ᅟ.

Analytical strategies to ensure the quality and safety of food products without the need for skilled personnel are highly required. The simplicity of glucose strips for diabetes monitoring should be translated to the agri-food sector, ensuring easy evaluation of certain molecules and/or the freshness of a beverage/foodstuff. In addition to the well-known advantages that are characteristic of electroanalytical methods over other methods, paper-based materials are being used to further reduce the gap between complex laboratory testing and simple point-of-need testing. This article highlights some of the most recent advances in the development of paper-based electrochemical approaches for food surveillance, specifically focusing on the use of novel paper-based materials. Two examples are discussed: the development of a miniaturized biosensor realized on copy paper for the quantification of ethanol in commercial beers, and the measurement of ascorbic acid in food supplements within printed electronics supports. Paper-based materials have the potential to lower economic costs, simplify the operative tasks, and most importantly reduce waste generation. The continued combination of manufacturing methods and functional (smart) materials will facilitate the implementation of food analysis at the point of need.

Genome-wide association studies have demonstrated that combinations of single nucleotide polymorphisms (SNPs), rather than individual SNPs, represent genetic signatures that correlate with heterogeneous and complex diseases. In this context, we developed a paper-based device that provides visual detection of a 10-SNP panel as a genetic signature associated with the risk for breast cancer. The method involves multiplex PCR amplification, multiplex extension reaction of allele-specific primers, without prior purification of the amplified sequences, and, finally, capture and visualization of the extension products within minutes on the device. Detection and monitoring are accomplished either by naked eye or by scanning with a common flatbed scanner. The total assay time is ∼ 2 h. The method was evaluated by using 21 clinical samples of known genotypes. The results were fully concordant with the reference method (sequencing). The proposed method is accurate, simple, rapid, and cost-effective. Visual detection does not require specialized instrumentation or highly trained technical personnel. We anticipate that the proposed device will become a useful analytical tool for precision medicine of breast cancer.

The Jatropha curcas plant (Jatropha) has been proposed as a source of biodiesel fuel, as it yields crude glycerol as an abundant by-product. Its by-products could serve as a starting material in making glycerol for FDA-regulated products. Jatropha is not regarded as a source of edible vegetable oil since it contains phorbol esters (PEs). PEs, even at very low exposure concentrations, demonstrate various toxicities in humans and animals, but may not be detected by routine impurity analyses. Here, we demonstrate the development of a rapid and simplified method for the detection and quantification of Jatropha-derived PE toxins using ambient ionization mass spectrometry. To do this, we successfully coupled a paper spray ambient ionization source with an ion trap portable mass spectrometer. The paper spray source was assembled using chromatography papers, and analyte ions were generated by applying a high voltage to a wetted paper triangle loaded with PE standards. For method development, we used commercially available PE standards on an ion trap portable mass spectrometer. Standard solutions were prepared using ethanol with PE concentrations ranging from 1.0 to 0.0001 mg mL -1 . Spike and recovery experiments were performed using USP grade and commercially available glycerol. To discern chemical differences between samples, we applied multivariate data analysis. Based on the results obtained, paper spray coupled with a portable mass spectrometric method can be successfully adopted for the analysis of toxic contaminants present in glycerol-based consumer products with LOD and LOQ of 0.175 μg mL -1 and 0.3 μg mL -1 respectively. This direct, simple design, and low-cost sampling and ionization method enables fast screening with high sensitivity in non-laboratory settings.

Synthetic cannabinoids are one of the many substances of abuse widely spreading in modern society. Medical practitioners and law enforcement alike highly seek portable, efficient, and reliable tools for on-site detection and diagnostics. Here, we propose a colorimetric lateral flow assay (LFA) combined with dye-loaded polymersome to detect the synthetic cannabinoid JWH-073 efficiently. Rhodamine B-loaded polymersome was conjugated to antibodies and fully characterized. Two LFA were proposed (sandwich and competitive), showing a high level of sensitivity with a limit of detection (LOD) reaching 0.53 and 0.31 ng/mL, respectively. The competitive assay was further analyzed by fluorescence, where the LOD reached 0.16 ng/mL. The application of the LFA over spiked synthetic saliva or real human saliva demonstrated an overall response of 94% for the sandwich assay and 97% for the competitive LFA. The selectivity of the system was assessed in the presence of various interferents. The analytical performance of the LFA system showed a coefficient of variation below 6%. The current LFA system appears as a plausible system for non-invasive detection of substance abuse and shows promise for synthetic cannabinoid on-site sensing., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

The production processes of the pulp and paper industry often run in campaigns, leading to large variations in the composition of wastewaters and waste sludges. During anaerobic digestion (AD) of these wastes, the viscosity or the production of extracellular polymeric substances (EPS) and soluble microbial products (SMP) may be affected, with the risk of foam formation, inefficient digester mixing or poor sludge dewaterability. The aim of this study was to investigate how viscosity and production of EPS and SMP during long-term AD of pulp and paper mill sludge is affected by changes in organic loading rate (OLR) and hydraulic retention time (HRT). Two mesophilic lab-scale continuous stirred tank reactors (CSTRs) were operated for 800 days (R1 and R2), initially digesting only fibre sludge, then co-digesting fibre sludge and activated sludge. The HRT was lowered, followed by an increase in the OLR. Reactor fluids were sampled once a month for rheological characterization and analysis of EPS and SMP. The production of the protein fraction of SMP was positively correlated to the OLR, implicating reduced effluent qualities at high OLR. EPS formation correlated with the magnesium content, and during sulphate deficiency, the production of EPS and SMP increased. At high levels of EPS and SMP, there was an increase in viscosity of the anaerobic sludges, and dewatering efficiency was reduced. In addition, increased viscosity and/or the production of EPS and SMP were important factors in sludge bulking and foam formation in the CSTRs. Sludge bulking was avoided by more frequent stirring.

Despite the green energy generation with low cost compared to conventional fuel cells, microbial fuel cells (MFCs) still suffer with anode related constraints including laborious pretreatment and modification process of conventional electrodes, limited bacterial loading capacity, and inferior extracellular electron transfer efficiency. Accordingly, this investigation explores the waste tissue paper derived three dimensional (3D) carbon aerogel (CA) integrated with cerium dioxide (CeO 2 ) nanotubes decorated nitrogen-doped reduced graphene oxide nanosheets (NRGO) as a competent anode to address these technical complements. The direct growth of NRGO and CeO 2 over CA in the form of freestanding and binder-free NRGO/CeO 2 (1:2)/CA alleviates the significant constrains of conventional anode fabrication. The 3D hierarchical architectures of CA with open porous structure provide easy access of bacteria, thus increases the bacterial colonies per unit volume. Furthermore, the hydrogen bonding between the interfacial oxygen atoms of CeO 2 and lysine residues of the cytochrome c in bacteria yields excellent extracellular electron transfer efficiency. The electrostatic interaction between the NRGO and bacteria cells improves the bacterial adhesion and biofilm formation, leading to the compact biofilm formation for the improved direct electron transference. With the profits of above, the MFC with NRGO/CeO 2 (1:2)/CA demonstrates a maximum power output and good lifespan performances. The present exploration facts thus access advanced avenues to converting waste matters of tissue paper, human urine, and wastewater into profitable constituents for the development of efficient and durable power producing systems.

Infections caused by foodborne microorganisms are a great threat to the global environment and public healthcare today. Thus, rapid, portable and sensitive assays that can realize the identification of foodborne bacteria are highly desired. In this study, a smart fluorescent and colorimetric dual-readout sensing system has been established for simple and rapid E. coli determination by utilizing the Cu 2+ -triggered oxidation of o-phenylenediamine (OPD). Initially, Cu 2+ can oxidize OPD to OPDox, resulting in an orange-yellow fluorescence and visible pale-yellow color. However, E. coli can effectively reduce Cu 2+ into Cu + , inhibiting the Cu 2+ -triggered oxidation of OPD to OPDox. Consequently, the introduction of E. coli can turn off both the fluorescence and the UV-vis absorbance signals of the OPD-Cu 2+ system, illustrating an original mechanism for fluorescent and colorimetric dual-channel detection of E. coli. Moreover, a filter paper-based visual sensor was built and coupled with OPD-Cu 2+ solution under the assistance of a UV lamp. The as-prepared sensor can detect E. coli quantitatively with the help of a typical smartphone color-scanning application (APP). Thus, this study offers a valid dual-mode assay for sensitive and on-site visible detection of E. coli, guaranteeing the reliability of the results and is more attractive for practical use. Graphical Abstract Schematic illustration of the smartphone-integrated sensing system for fluorescent and colorimetric dual-channel detection of E. coli based on the Cu 2+ -OPD system.

The potential reach of point-of-care (POC) diagnostics into daily routines for exposure to reactive oxygen species (ROS) and Cu in aerosolized particulate matter (PM) demands that microfluidic paper-based analytical devices (μPADs) take into consideration the simple detection of these toxic PM components. Here, we propose μPADs with a dual-detection system for simultaneous ROS and Cu(II) detection. For colorimetric ROS detection, the glutathione (GSH) assay with a folding design to delay the reaction yielded complete ROS and GSH oxidation, and improved homogeneity of color development relative to using the lateral flow pattern. For electrochemical Cu(II) determination, 1,10-phenanthroline/Nafion modified graphene screen-printed electrodes showed ability to detect Cu(II) down to pg level being low enough to be applied to PM analysis. No intra- and inter-interference affecting both systems were found. The proposed μPADs obtained LODs for 1,4-naphthoquinone (1,4-NQ), used as the ROS representative, and Cu(II) of 8.3 ng and 3.6 pg, respectively and linear working ranges of 20 to 500 ng for ROS and 1 × 10 -2 to 2 × 10 2 ng for Cu(II). Recovery of the method was between 81.4 and 108.3% for ROS and 80.5-105.3% for Cu(II). Finally, the sensors were utilized for simultaneous ROS and Cu(II) determination in PM samples and the results statistically agreed with those using the conventional methods at 95% confidence., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

Objective: To elucidate whether occupational noise exposure increases the mortality from ischemic heart disease (IHD) and stroke, and if exposure to paper dust modified the risks., Methods: We studied 6686 workers from soft paper mills, with occupational noise exposure, < 85 dBA, 85-90 dBA and > 90 dBA, and high (> 5 mg/m 3 ) exposure to paper dust. Person-years 1960-2019 were stratified according to gender, age, and calendar-year. Expected numbers of deaths were calculated using the Swedish population as the reference and standardized mortality ratios (SMR) with 95% confidence intervals (95% CI) were assessed., Results: SMR for IHD was 1.12 (95% CI 0.88-1.41) for noise < 85 dBA, 1.18 (95% CI 0.90-1.55) for 85-90 dBA, and 1.27 (95% CI 1.10-1.47) among workers exposed > 90 dBA. Joint exposure to high noise exposure and high exposure to paper dust resulted in slightly higher IHD mortality (SMR 1.39, 95% CI 1.15-1.67). SMR for ischemic stroke was 0.90 (95% CI 0.37-2.15) for noise < 85 dBA, 1.08 (95% CI 0.45-2.59) for 85-90 dBA, and 1.48 (95% CI 0.99-2.00) among workers exposed > 90 dBA. High noise exposure and high exposure to paper dust resulted in higher ischemic stroke mortality (SMR 1.83, 95% CI 1.12-2.98)., Conclusion: Noise levels > 90 dBA was associated with increased IHD mortality. Combined exposures of noise and paper dust may further increase the risks. Our results do not provide support for a causal relationship for ischemic stroke. Residual confounding from smoking has to be considered. Workers need to be protected from occupational noise levels exceeding 90 dBA., (© 2023. The Author(s).)

Molecularly imprinted polymers are efficient and selective adsorbents which act as artificial receptors for desired compounds with the ability to recognize the size, shape, and functional groups of the compounds simultaneously. A molecularly imprinted polymer is prepared by the polymerization of functional monomers around a template (analyte) molecule. Afterward, the removal of the template from the polymer matrix leaves a selective cavity behind. The fabrication and development of molecularly imprinted polymers grew rapidly, due to their low cost, simple preparation, selectivity, sensitivity, and stable physicochemical properties. Traditionally, molecularly imprinted polymers can be synthesized using two main methods, namely bulk and surface imprinting. For more efficient use of the latter method, researchers have developed molecularly imprinted polymers grafted on the solid-phase matrix (substrate). This grafting technique would be particularly useful for surface imprinting of macromolecules, such as proteins. Cellulose fibers of papers with unique properties such as being abundant, retaining a porous structure, having good adsorption properties, and possessing hydroxyl groups naturally have gained much attention as substrate. The goal of this review is to introduce molecularly imprinted polymer-grafted or molecularly imprinted polymer-coated paper, as an interesting, simple, and efficient method in the detection and separation of small and large molecules. Therefore, in the present paper, several recent preparation techniques and applications of molecularly imprinted polymer-grafted paper are reviewed and discussed in detail. Green, cost-effective, selective, and sensitive paper-based sensor prepared via grafting molecularly imprinted polymer on paper surface with the potential use for online detection trace of analytes in the point-of-care testing., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

Simple and visual quantitative detection of foodborne pathogens can effectively reduce the outbreaks of foodborne diseases. Herein, we developed a simple and sensitive quantum dot (QD)-based paper device for visual and quantitative detection of Escherichia coli (E. coli) O157:H7 based on immunomagnetic separation and nanoparticle dissolution-triggered signal amplification. In this study, E. coli O157:H7 was magnetically separated and labeled with silver nanoparticles (AgNPs), and the AgNP labels can be converted into millions of Ag ions, which subsequently quench the fluorescence of QDs in the paper strip, which along with the readout can be visualized and quantified by the change in length of fluorescent quenched band. Owing to the high capture efficiency and effective signal amplification, as low as 500 cfu mL -1 of E. coli O157:H7 could be easily detected by naked eyes. Furthermore, this novel platform was successfully applied to detect E. coli O157:H7 in spiked milk samples with good accuracy, indicating its potential in the detection of foodborne pathogens in real samples.

We develop a capillary-paper spray (CPS) ion source which allows for sample separation in the capillary and enables rapid and sensitive paper spray (PS) mass spectrometry (MS) analysis of biofluids. The CPS employs a glass capillary to load liquid analytes, vertically standing at the rear of the PS. To further reduce the matrix effect, a nitrocellulose filter membrane is placed between the glass tube and chromatography paper to absorb proteins and other macromolecules, which is beneficial for the detection of the small molecules. Compared with the normal PS method, the CPS method markedly improves spray stability and prolongs analysis duration, and also generates significantly better signal intensities during the analysis of drugs, thus indicating its potential for clinical use. As a proof of concept, quantitative analysis of drugs (metformin hydrochloride and berberine hydrochloride) in serum is performed.

Paper-based analytical devices (PADs) are powerful platforms for point-of-need testing since they are inexpensive devices fabricated in different shapes and miniaturized sizes, ensuring better portability. Additionally, the readout and detection systems can be accomplished with portable devices, allying with the features of both systems. These devices have been introduced as promising analytical platforms to meet critical demands involving rapid, reliable, and simple testing. They have been applied to monitor species related to environmental, health, and food issues. Herein, an outline of chronological events involving PADs is first reported. This work also introduces insights into fundamental parameters to engineer new analytical platforms, including the paper type and device operation. The discussions involve the main analytical techniques used as detection systems, such as colorimetry, fluorescence, and electrochemistry. It also showed recent advances involving PADs, especially combining optical and electrochemical detection into a single device. Dual/combined detection systems can overcome individual barriers of the analytical techniques, making possible simultaneous determinations, or enhancing the devices' sensitivity and/or selectivity. In addition, this review reports on distance-based detection, which is also considered a trend in analytical chemistry. Distance-based detection offers instrument-free analyses and avoids user interpretation errors, which are outstanding features for analyses at the point of need, especially for resource-limited regions. Finally, this review provides a critical overview of the practical specifications of the recent analytical platforms involving PADs, demonstrating their challenges. Therefore, this work can be a highly useful reference for new research and innovation., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

A turn-on fluorescent aptasensor based on a paper-based microfluidic chip was developed to detect arsenite via aptamer competition strategy and smartphone imaging. The chip was prepared by wax-printing hydrophilic channels on filter paper. It is portable, low-cost, and environmentally friendly. Double-stranded DNA consisting of aptamer and fluorescence-labeled complementary strands was immobilized on the reaction zone of the paper chip. Due to the specific strong binding between aptamer and arsenite, the fluorescent complementary strand was squeezed out and driven by capillary force to the detection area of the paper chip, so that the fluorescent signal arose in the detection area under the excitation wavelength of 488 nm. Arsenite can be quantified by using smartphone imaging and RGB image analysis. Under the optimal conditions, the paper-based microfluidic aptasensor exhibited excellent linear response over a wide range of 1 to 1000 nM, with a detection limit as low as 0.96 nM (3σ)., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

The fast-growing healthcare demand for user-friendly and affordable analytical tools is driving the efforts to develop reliable platforms for the customization of therapy based on individual health conditions. In this overall scenario, we developed a paper-based electrochemical sensor for the quantification of iron ions in serum as a cost-effective sensing tool for the correct supplement administration. In detail, the working electrode of the screen-printed device has been modified with a nanocomposite constituted of carbon black and gold nanoparticles with a drop-casting procedure. Square wave voltammetry has been adopted as an electrochemical technique. This sensor was further modified with Nafion for iron quantification in serum after sample treatment with trifluoroacetic acid. Under optimized conditions, iron ions have been detected with a LOD down to 0.05 mg/L and a linearity up to 10 mg/L in standard solution. The obtained results have been compared with reference methods namely commercial colorimetric assay and atomic absorption spectroscopy, obtaining a good correlation within the experimental errors. These results demonstrated the suitability of the developed paper-based sensor for future applications in precision medicine of iron-deficiency diseases., (© 2023. Springer-Verlag GmbH Germany, part of Springer Nature.)

A highly stable and luminescent lead-free manganese(II) halide hybrid MnBr 4 (TMN) 2 (C 34 H 42 Br 4 MnN 4 ) was designed and synthesized by introducing a large cationic organic spacer. The MnBr 4 (TMN) 2 displays high luminescence with quantum yields up to 77% and possesses turn-off fluorescence behavior (E x /E m =365/546 nm) for water. These properties make the MnBr 4 (TMN) 2 a promising candidate as an alternative indicator for the detection of water with potential applications for the fabrication of LEDs. Herein, a paper-based sensor based on MnBr 4 (TMN) 2 is described for the determination of water content in organic solvents. The mechanism of water sensing can be tentatively explained by fluorescence quenching originating from the destruction of water due to the Mn-Br bonds of MnBr 4 (TMN) 2 . The MnBr 4 (TMN) 2 -based paper sensor exhibits an excellent discrimination ability of water content in the range 0-25.0% with a detection limit of 0.27%. Satisfactory recoveries (94.91±4.09% to 103.23±2.38%) are obtained in spiked ethanol solvent samples, which demonstrate that the MnBr 4 (TMN) 2 -based paper sensor is capable of detecting water content in real ethanol solvent samples., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

Biofuel cells (BFCs) based on anodic oxidation and cathodic oxygen reduction represent an attractive alternative to self-powered devices. A glucose/oxygen BFC is described for monitoring glucose. It is making use of a piece of paper carrying a glucose oxidase (GOx) based bioanode, and a bilirubin oxidase (BilOx) based biocathode. The performance of the BFC is affected by the generation of H 2 O 2 , a byproduct of enzymatic glucose oxidation. Therefore, the removal of H 2 O 2 is a crucial step in terms of BFC performance and stability. In addition, direct, unambiguous visual read-out is an ideal way to provide quantitative information. The colorimetric readout system described here is based on the consumption of undesired H 2 O 2 and to convert the extent of energy generation into recognizable variations in color. As the H 2 O 2 travels along the hydrophilic channel by capillary action, the formation of red gold nanoparticles from AuCl 4 leads to the appearance of a red bar that provides distance-based information that can be read visually. The multiply readable information (maximum power density of BFC or visible distance) provides further choices for quantification. It also enhances reliability. The self-powered system based on the BFC exhibits excellent performance. Glucose can be determined by this method in the 1 to 50 mM concentration range. Graphical abstract Schematic presentation of a paper-supported biofuel cell equipped with a visual distance readout to display the level of energy generation in biofuel cells, and its application in sensing of glucose.- leads to the appearance of a red bar that provides distance-based information that can be read visually. The multiply readable information (maximum power density of BFC or visible distance) provides further choices for quantification. It also enhances reliability. The self-powered system based on the BFC exhibits excellent performance. Glucose can be determined by this method in the 1 to 50 mM concentration range. Graphical abstract Schematic presentation of a paper-supported biofuel cell equipped with a visual distance readout to display the level of energy generation in biofuel cells, and its application in sensing of glucose.

Mitigation of the peroxide explosive threat, specifically triacetone triperoxide (TATP) and hexamethylene triperoxide diamine (HMTD), is a priority among the law enforcement community, as scientists and canine (K9) units are constantly working to improve detection. We propose the use of paper spray ionization-high-resolution mass spectrometry (PSI-HRMS) for detection of peroxide explosives in biological matrices. Occurrence of peroxide explosives and/or their metabolites in biological samples, obtained from urine or blood tests, give scientific evidence of peroxide explosives exposure. PSI-HRMS promote analysis of samples in situ by eliminating laborious sample preparation steps. However, it increases matrix background issues, which were overcome by the formation of multiple alkali metal adducts with the peroxide explosives. Multiple ion formation increases confidence when identifying these peroxide explosives in direct sample analysis. Our previous work examined aspects of TATP metabolism. Herein, we investigate the excretion of a TATP glucuronide conjugate in the urine of bomb-sniffing dogs and demonstrate its detection using PSI from the in vivo sample.

A colorimetric paper-based enzyme-coupled antimony tin oxide nanoparticle (ATONP) nanobiosensor for selective detection of Cd 2+ ions in clams and mussels is presented. Alkaline phosphatase (ALP) was immobilized on ATONPs via 16-phosphonohexadecanoic acid (16-PHA) to develop ATONP-ALP nanobiosensor. The biosensor was characterized using XPS, Raman spectroscopy, SEM, and EDX. ATONP-ALP nanobiosensor exhibited high selectivity towards detection of Cd 2+ ion with a LOD 0.006 μg L -1 and linear range of detection 0.005-1 μg L -1 . The developed biosensor was further integrated into a low-cost paper-based format. A visual color change was obtained for Cd 2+ ion in the range 0.1-10 μg L -1 . The developed biosensor was successfully demonstrated for the analysis of Cd 2+ ions in clams with recoveries 101-104%. The ATONP-ALP nanobiosensor was validated using mussel tissue (BCR-668) and the conventional ICP-OES and ICP-MS techniques.

A molecularly imprinted paper-based analytical device (MIP-μPAD) was developed for the sensing of bisphenol A (BPA). The platform was screen-printed onto a filter paper support, where the electrodes and the fluorescence μPADs were designed. Owing to its dual electrochemical and fluorescence responses, molecularly imprinted curcumin nanoparticles were used to sense BPA. The μPAD design was characterized by transmission electron microscopy, scanning electron microscopy, fluorescence spectroscopy, and electrochemical techniques. The sensor design comprised a wide linear range from 1 to 200 μg L -1 with limits of detection of 0.47 ± 0.2 and 0.62 ± 0.3 μg L -1 (LOD, S/N = 3) for electrochemical and fluorescence sensing, respectively. Furthermore, the system showed good analytical performance such as selectivity, stability, and reproducibility. The feasibility of the MIP-μPAD was demonstrated for the sensing of BPA in seawater, foods, and polycarbonate plastic packaged water with recovery values of 97.2 and 101.8%.

A colorimetric assay is presented for the detection of Stachybotrys chartarum proteases as biomarkers. The assay comprises a gold film acting as solid support and carrying an immobilized peptide substrate that is specific for S. chartarum protease. The substrate was conjugated to black magnetic nanoparticles (MNPs) to form a monolayer on the gold film. Hence, detection nanoprobe is black. If, however, the peptide-MNP fragments are cleaved by S. chartarum proteases present in a sample, the golden color of the detecting nanoprobe becomes apparent so that positive visual readout is enabled. The method was applied to the determination of S. chartarum in (spiked) environmental samples. The limit of detection ranges from 10 to 100 spores·mL -1 depending on the kind of sample (culture, dust, mold and soil). Assay specificity was examined for Aspergillus flavus, Fusarium solani. Penicillin chrysogenum, and Saccharomyces cerevisiae, and negative readouts were observed visually for all samples, except for those also containing S. chartarum. Graphical abstract Schematic presentation of S. chartarum colorimetric nanoprobe.

Production of laccase from Ganoderma lucidum RCK 2011 under solid-state fermentation (SSF) conditions was optimized using response surface methodology, resulting in an approximate eightfold increase compared to that in the unoptimized media. Further, the enzyme produced under SSF as whole fermented substrate (in situ SSF laccase) was found to be more stable than the in vitro enzyme (harvested by downstreaming processing of fermented wheat bran). Interestingly, the biobleaching potentials of both in situ and in vitro SSF laccases were comparable, saving 25% chlorine dioxide for achieving similar pulp brightness as obtained in the pulp treated chemically. The reduction in the demand of chlorine dioxide in the pulp bleaching sequence subsequently decreased the levels of adsorbable organic halogen (AOX) in the resulting effluents of the process by 20% compared to the effluents obtained from chemical bleaching sequence. Therefore, direct application of in situ SSF laccase in pulp biobleaching will be environmentally friendly as well as economical and viable for implementation in paper mills.

A method is described for simultaneous fluorometric determination of the biomarkers carcinoembryonic antigen (CEA) and prostate specific antigen (PSA) on the same zone of a paper-based immunodevice. Two kinds of CdTe quantum dots, with respective emission peaks at 525 nm and 605 nm under a single excitation wavelength of 272 nm, were used to label the antibodies against CEA and PSA. Then the capture antibodies of CEA and PSA were immobilized on the same zone of the paper-based device. With the difference of the colors of the quantum dot fluorescence (green and orange), CEA and PSA can be detected on the same zone of the paper-based device. By using of sandwich immunoassay format, CEA and PSA can be simultaneously detected in human serum samples with a linear response in the 1.0-40 ng·mL -1 concentration range for both. The recovery rates of the serum sample were in the range of 95-105%. The method has the potential of being applied to the simultaneous determination of various other kinds of substances on a single multichannel paper-based chip. Graphical abstract Schematic presentation of the simultaneous fluorometric detection of two cancer biomarkers on the same zone of the paper-based immunodevice is provided. Two kinds of CdTe quantum dots with different emission peaks under the same excitation wavelength are labeled on different detection antibodies.

Rapid and reliable identification of bacteria is an important issue in food, medical, forensic, and environmental sciences; however, conventional procedures are time-consuming and often require extensive financial and human resources. Herein, we present a label-free method for bacterial discrimination using surface-enhanced Raman spectroscopy (SERS) and partial least squares discriminant analysis (PLS-DA). Filter paper decorated with gold nanoparticles was fabricated by the dip-coating method and it was utilized as a flexible and highly efficient SERS substrate. Suspensions of bacterial samples from three genera and six species were directly deposited on the filter paper-based SERS substrates before measurements. PLS-DA was successfully employed as a multivariate supervised model to classify and identify bacteria with efficiency, sensitivity, and specificity rates of 100% for all test samples. Variable importance in projection was associated with the presence/absence of some purine metabolites, whereas confidence intervals for each sample in the PLS-DA model were calculated using a resampling bootstrap procedure. Additionally, a potential new species of bacteria was analyzed by the proposed method and the result was in agreement with that obtained via 16S rRNA gene sequence analysis, thereby indicating that the SERS/PLS-DA approach has the potential to be a valuable tool for the discovery of novel bacteria. Graphical abstract This paper describes the discrimination of bacteria at the genus and species levels, after minimal sample preparation, using paper-based SERS substrates and PLS-DA with uncertainty estimation.

An electrochemical paper-based sensor was developed for the detection of bacterial infection (BI)-specific biomarker procalcitonin (PCT). Reduced graphene oxide-gold nanoparticles (rGO-AuNP) and poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) were synthesized and were fabricated to a disposable, portable, and inexpensive cellulose fiber paper (CFP) substrate. rGO-AuNP-PEDOT:PSS nanocomposite-modified conductive paper-based biosensing platform was efficaciously fabricated by a constant and simple coating procedure. rGO-AuNP-PEDOT:PSS nanocomposite-modified conductive paper electrode was found to provide a sensitive and conductive substrate for PCT detection. The presence of rGO-AuNP-PEDOT:PSS nanocomposite on CFP substate was investigated by Fourier transform infrared spectrometry, field emission scanning electron microscopy, ultraviolet-visible spectroscopy, and X-ray diffraction studies. The electrochemical behavior of rGO-AuNP-PEDOT:PSS @CFP surface was studied with impedance spectroscopy, cyclic voltammetry, and chronoamperometry techniques. This low-cost paper-based biosensor has a linear range for PCT of 1 × 10 3 to 6 × 10 7  fg mL -1 . This developed sensor exhibited good reproducibility with a relative standard deviation (RSD) of about 3.7%. The proposed CFP-based biosensor has been proven as an accelerated simple point-of-care (POC) exploratory approach for early PCT diagnosis in inadequate areas with limited production facilities, computational techniques, and highly skilled experts., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

One of the problems in the distance-based microfluidic paper-based analytical device (DB-µPAD) that limits the detection resolution is the mixing of reagents from the detection to the sampling zone or vice versa due to spreading by capillary action. In the present paper, to overcome mixing of the reagents in the zones, a multi-functional connector using a three-dimensional (3D) design has been developed externally to connect the two zones. Using such a novel design, it is acertained that there is no any mixing due to the dispersion of the reagents in the two zones. Interestingly, the simple 3D connector has other functions, such as its potential to be used as a masking zone and/or reaction zone whenever is needed. Based on this proposed 3D connector-based DB-µPAD, three parallel microchannels were built as detection zones with one sampling zone for multiplex analysis for the detection of Fe 2+ , Ni 2+ , and hardness of water. In the Ni 2+ channel, the connector piece worked as both masking part and connection part. In the Fe 2+ line, the connector served as the connector and reducing pad (Fe 3+ to Fe 2+ ions). While in the third channel, the connector has connection function only. Satisfactory limit of detection (LoD), accuracy, and precision were obtained using this design. The LODs obtained with the proposed design were 1.13, 0.62, and 1.87 mg.L -1 for total hardness, Fe 2+ , and Ni 2+ , respectively., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

A paper-based analytical device (PAD) is presented with colorimetric/electrochemical dual readouts for the simultaneous sensing of total chromium (Cr) and hexavalent chromium (Cr(VI)). This device consists of a homemade three-electrode system and a patterned paper chip, integrating multiple functions including electrochemical detection, fluid driving, online oxidation, and colorimetric detection. The fiberglass filter paper with a hydrophilic microchannel was used to achieve self-driving fluidics without external equipment. One end of the microchannel was integrated with a homemade three-electrode system to achieve sample loading and electrochemical detection. The middle region on the microchannel was modified with oxidizing reagents to perform online pretreatment, and the yield of Cr(III) oxidation can reach 97.9%, ensuring reliable colorimetric detection of total Cr at another end of the microchannel modified with chromogenic agents. With this device, the signals of Cr(VI) (the signal peak at 0.29 V vs. Ag/AgCl) and total Cr can be obtained in one single injection. After optimization, the limit of detection (LOD) of Cr(VI) and total Cr were 0.01 mg L -1 and 0.06 mg L -1 and the linear ranges were 0.05-3.0 mg L -1 and 0.2-3.0 mg L -1 , respectively. The relative standard deviations (RSD) of the electrochemical testing of Cr(VI) results were in a range 1.3%-8.7% (n = 3), and the RSD values of the colorimetric testing of total Cr were between 0.7-9.2% (n = 3). The device's reliability was demonstrated by performing the practical speciation of Cr in tap water, river water, and electroplating wastewater while the recoveries obtained using the present method were in the range 93.5-106%. Overall, the proposed device provides high application prospect in the on-site rapid Cr speciation., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

SARS-CoV-2 has mutated many times since the onset of the COVID-19 pandemic, and the omicron is currently the most dominant variant. Determining the specific strain of the virus is beneficial in providing proper care and containment of the disease. We have previously reported a novel method of counting the number of particle immunoagglutination on a paper microfluidic chip using a smartphone-based fluorescence microscope. A single-copy-level detection was demonstrated from clinical saline gargle samples. In this work, we further evaluated two different SARS-CoV-2 monoclonal antibodies to spike vs. nucleocapsid antigens for detecting omicron vs. delta and spike vs. nucleocapsid proteins. The SARS-CoV-2 monoclonal antibody to nucleocapsid proteins could distinguish omicron from delta variants and nucleocapsid from spike proteins. However, such distinction could not be found with the monoclonal antibody to spike proteins, despite the numerous mutations found in spike proteins among variants. This result may suggest a clue to the role of nucleocapsid proteins in recognizing different variants., (© 2022. Springer-Verlag GmbH Germany, part of Springer Nature.)

We developed a paper-based colorimetric sensor for facile and cost-effective detection of Pb 2+ in drinking and environmental water samples. The Pb 2+ ion-selective optodes are fabricated by inkjet printing of ionophore, chromoionophore, and ion exchanger on cellulose paper. Pb 2+ in water samples induces deprotonation of the pH chromoionophore and changes the optode color, which is acquired and analyzed by a smartphone. The paper-based optode without any plasticizer or polymer has a dynamic range and selectivity comparable to those of traditional optodes using PVC polymer and/or plasticizer. Furthermore, the response time of the plasticizer/polymer-free paper-based optode is much shorter than those of plasticized PVC-based optodes on paper and glass (5 min vs. 15 and 50 min). Moreover, the plasticizer/polymer-free optode preserves the water-wicking capability of porous cellulose paper, allowing for the design of pump-free microfluidic devices. Chloramine, a widely used disinfectant in drinking water, was found to be a strong and generic interference species for heavy metal ion detection via ion-selective optodes. A fully inkjet-printed lateral-flow paper-based device consisting of a sodium thiosulfate-based chloramine elimination zone and a plasticizer/polymer-free sensing zone was designed for Pb 2+ detection in tap water disinfected by chloramine. The dynamic range of the Pb 2+ sensor may be shifted from the current 10 -6 to 10 -5  M to lower concentrations by using stronger ionophores, but this work lays a foundation for the design of paper-based heavy metal ion sensors without detrimental interference from disinfectants., (© 2022. Springer-Verlag GmbH Germany, part of Springer Nature.)