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Deoxyribonuclease I (DNase I) is a biomarker which has important applications in various biological processes. Thus, it is highly important to develop a user-friendly method for the detection of DNase I. Here, we present a paper-based distance sensor for the rapid detection of DNase I based on changes in the viscosity of DNA mucus. The viscosity of DNA mucus varies with different concentrations of DNase I, showing different water flow lengths on the pH test papers, this makes the quantification of DNase I possible. This method has a wide linear range (0.01–10 U/mL), excellent sensitivity, remarkable specificity and excellent reproducibility. The detection limit reaches 0.003 U/mL. Additionally, it can be well applied to detection of DNase I inhibitors, assay of DNase I in human serum and quality evaluation of nucleic acid scavengers. In general, this study offers a brief, convenient, label-free, and economical method to construct paper-based distance sensors using DNA mucus, which is very promising in the detection of DNase I in various applications. [Display omitted] • The paper-based sensor detects DNase I by distance signal. • The new method for detecting DNase I based on viscosity changes. • The detection limit for DNase I is 0.003 U/mL. • The sensor shows excellent specificity, remarkable practicality and portability. [ABSTRACT FROM AUTHOR]

Paper spray mass spectrometry (PSMS) is currently used in different analytical fields, but less effort has been made so far to use PSMS for highly polar compounds. Such analytes usually show poor performance in PSMS due to their high affinity for common paper substrates in addition to high matrix effects. In this study, strategies for hydrophobic modifications of commercially available paper substrates using ten different organosilanes were developed. The modified substrates were generated, characterized, and applied for PSMS analysis of polar toxins. By using the modified paper, PSMS performance of some of the toxins could be considerably increased, especially for orellanine, showing a more than 80-fold signal enhancement when substrates modified with chlorotrimethylsilane were used. For other toxins like ricinine, only small beneficial effects could be shown on PSMS performance when using modified substrates. Statistical equivalence tests showed sufficient ruggedness of the developed procedures also compared to conventional substrates. Thus, further systematic development of paper substrates modified with organosilane derivatives based on the presented study for application in PSMS should be encouraged. Image 1 • Comprehensive study using 10 different mono-/trichlorosilanes for paper modification. • Optimization of modification methods and characterization of modified substrates. • Improvements for paper spray MS performance were achieved for many polar toxins. • Equivalence tests proved robustness of paper spray MS performance using modified substrates. [ABSTRACT FROM AUTHOR]

Abstract Patterned paper sensors such as letter- and barcode-shaped sensors have become a subject of growing interest due to the potential in information embedding and data interpretation, which brings a requirement on easily fabricating these paper-based analytical devices. The answer, in part, may lie in the influence of paper structure on the performance of paper-based analytical devices. After investigating the effect of physical properties of paper on precipitation and non-precipitation assays for detecting Fe(II), here we propose a simple and promising approach for barrier-free paper patterning. Without building hydrophobic boundaries, the precipitates of sensing reactions on low-bulk and medium-thick paper substrates allow patterned signal readout directly. As a proof of concept, barrier-free patterned paper sensors for detecting heavy metals were fabricated, with detection limits of 0.25 ppm for Fe(II), 0.4 ppm for Ni(II), and 0.5 ppm for Cu(II). Our work provides a valuable perspective on fabrication of patterned paper sensors. Graphical abstract fx1 Highlights • Skipping the hydrophobic treatment in fabrication of patterned paper sensors. • Providing a versatile platform for facile preparation of patterned paper sensors. • Low-bulk and medium-thick paper substrate holds the key to barrier-free fabrication. [ABSTRACT FROM AUTHOR]

Due to the serious risks of lead pollution to human health, it plays a great role in constructing a simple, inexpensive, portable, and user-friendly strategy for Pb2+ detection in environmental samples. Herein, a paper-based distance sensor is developed to detect Pb2+ assisted with the target-responsive DNA hydrogel. Pb2+ can activate DNAzyme to cleave its substrate strand, which results in the hydrolysis of the DNA hydrogel. The released water molecules trapped in the hydrogel can flow along the patterned pH paper due to the capillary force. The water flow distance (WFD) is significantly influenced by the amount of water released from the collapsed DNA hydrogel triggered by the addition of various Pb2+ concentrations. In this way, Pb2+ can be quantitatively detected without using specialized instruments and labeled molecules, and the limit of detection (LOD) of Pb2+ is 3.0 nM. Additionally, the Pb2+ sensor works well in lake water and tap water. Overall, this simple, inexpensive, portable, and user-friendly method is very promising for quantitative and in-field detection of Pb2+ with excellent sensitivity and selectivity. [Display omitted] • A novel paper-based distance sensor assisted with DNA hydrogel is developed. • The hydrolysis of the DNA hydrogel by Pb2+ triggers release of the water. • The water flow distance is used to assess the level of Pb2+. • The detection of Pb2+ is successfully demonstrated in lake water and tap water. [ABSTRACT FROM AUTHOR]

Widening the methodology of chromophore analysis in pulp and paper science, a sensitive gas-chromatographic approach with electron-capture detection is presented and applied to model samples and real-world historic paper material. Trifluoroacetic anhydride was used for derivatization of the chromophore target compounds. The derivative formation was confirmed by NMR and accurate mass analysis. The method successfully detects and quantifies hydroxyquinones which are key chromophores in cellulosic matrices. The analytical figures of merit appeared to be in an acceptable range with an LOD down to approx. 60 ng/g for each key chromophore, which allows for their successful detection in historic sample material. [ABSTRACT FROM AUTHOR]

The utility of strikingly simple and cheap optoelectronic detectors operating according to a Paired-Emitter-Detector-Diode (PEDD) principle for microfluidic paper-based analytical devices (μPAD) has been experimentally confirmed. The prototypes of these compact detectors have been made of only two customary light emitting diodes without any additional optical parts like lens, filters, fibers etc. Moreover, for their operation economic and portable equipment is required (low-power circuit and ordinary voltmeter). Photometric and fluorometric PEDDs for paper devices are developed. In both cases the possibility of their applicability in transmittance and reflectance modes of measurements are presented. In these investigations as model analytes some coloured and fluorescence substances have been handled, but the utility of several developed systems for real chemical analysis has also been demonstrated. The results of photometric determination of hemoglobin in human blood, as well as fluorometric determination of quinine in tonics and calcium ions in mineral waters using various PEDD-μPAD systems have been shown. [ABSTRACT FROM AUTHOR]

A cost-effective assay for antioxidant using simple cotton thread combining paper based device with mobile phone detection has been investigated. Standard and sample solutions flow along a bunch of cotton thread treated with sodium hydroxide via microfluidic behaviors without external pumping. The analyte solution reacts with the reagents that have been immobilized on the paper strip fixed at the end of the cotton bunch. The developed platforms were used for the assays of total phenolic content and antioxidant capacity by employing Folin-Ciocalteu and 2, 2-diphenyl-1-picryhydrazyl (DPPH) respectively. Simple detection can be made by employing a mobile phone camera (iPhone 4S) with Image J or Photoshop for image processing and evaluation. Gallic acid was used as a reference standard in this work, as its polyphenol structures can be found in many plants. The total phenolic content is expressed as gallic acid equivalents (GAE) (mg/g material). Inhibition capacity is calculated by the equation: % I = [(I o – I s )/ I o ] × 100, where I s is the relative magenta intensity (CMYK mode) of sample, and I o the relative magenta intensity of DPPH•. IC 50 inhibition can be estimated from the graph and can be used for the antioxidant capacity consideration. Applications to the assay green tea samples were demonstrated. The total phenolic contents in the green tea samples were found to be 48–105 mg/g, with %RSD of less than 10 for that of higher 50 GAE mg/g and IC 50 values of the samples studied were 25–50 mg/L. The results obtained by the developed methods agree with that of the standard methods. [ABSTRACT FROM AUTHOR]

The possibility of using pyrolyzed paper as disposable working electrodes for trace metals determination is reported for the first time. A small piece of pyrolyzed paper (0.7×0.7 cm) was positioned at the bottom side of the electrochemical cell using a rubber O-ring, which defined the electrode area (0.48 cm; 0.18 cm 2 ). A large number of electrodes can be obtained from a single piece of standard dimensions (2.5 cm×7.5 cm) of paper, therefore minimizing the cost per unit. The electrochemical performance of the pyrolyzed paper was demonstrated by cyclic voltammetry, electrochemical impedance spectroscopy and by the determination of Zn, Cd, and Pb by square-wave anodic stripping voltammetry. The unmodified pyrolyzed paper showed excellent performance for Pb and Cd detection (LOD =0.19 and 0.16 ppb, respectively). In the presence of Bi 3+ (in-situ film formation), the simultaneous determination of Zn, Cd and Pb was also possible (LOD=0.26, 0.25, and 0.39 ppb, respectively). [ABSTRACT FROM AUTHOR]

A new sensitive non-invasive gold nanoparticle-based sensor that enables to detect thiols in the human skin has been developed. The detection procedure implied the assessment of the color change of a paper sensor resulting from aggregation of gold nanoparticles caused by thiols. The ratio of the intensity of the photo image blue channel vs the red one (in units of RGB coloration) served as analytical response. The main thiol in the skin is glutathione, therefore, it was used as model biothiol and spiking substance. The range of linearity for glutathione was 8–75 µM, the detection limit was 6.9 µM. RSD≤7% is for inter-day determination of 10 μM glutathione and RSD≤12% is the intra-day value. The recovery of 5 µM and 10 µM of glutathione was evaluated by applying solution, containing thiol-spikes, on skin. The results varied in the range 77–138%. A hundred-fold excess of serine, alanine, histidine, threonine, creatinine, urea, and ammonia; a ten-fold excess of glycine, proline, leucine, isoleucine, phenylalanine, asparagine; and a five-fold excess of valine, tryptophan, tyrosine, and uric acid, which can be extracted from the skin and is contained in the test matrix, have no significant effect on 10 µM glutathione signal. Thiols level in the skin of volunteers (21–65 years old, men and women) detected with the use of a proposed non-invasive sensor was 11.6–47.5 µM. [ABSTRACT FROM AUTHOR]

Herein, we have developed a simple, sensitive and paper-based colorimetric sensor for the selective detection of Chromium (Ⅵ) ions (Cr (VI)). Silanization-titanium dioxide modified filter paper (STCP) was used to trap bovine serum albumin capped gold nanoparticles (BSA-Au NPs), leading to the fabrication of BSA-Au NPs decorated membrane (BSA-Au NPs/STCP). The BSA-Au NPs/STCP operated on the principle that BSA-Au NPs anchored on the STCP were gradually etched by Cr (VI) as the leaching process of gold in the presence of hydrobromic acid (HBr) and hence induced a visible color change. Under optimum conditions, the paper-based colorimetric sensor showed clear color change after reaction with Cr (VI) as well as with favorable selectivity to a variety of possible interfering counterparts. The amount-dependent colorimetric response was linearly correlated with the Cr (VI) concentrations ranging from 0.5 µM to 50.0 µM with a detection limit down to 280 nM. Moreover, the developed cost-effective colorimetric sensor has been successfully applied to real environmental samples which demonstrated the potential for field applications. [ABSTRACT FROM AUTHOR]

This manuscript describes the development and clinical testing of a paper-based, metabolic assay designed for rapid, semi-quantitative measurement of organophosphate poisoning. Paper-based platforms, including point-of-care devices and 96-well plates, provided semi-quantitative information regarding the concentration of AchE (a biomarker for organophosphate poisoning). The paper-based 96-well-plate developed and implemented in this study was used to measure the level of organophosphate poisoning in three different clinical patients. Results were comparable to those obtained using conventional hospital methods currently considered the “gold standard”. This diagnostic device offers several advantages over conventional methods, including short operating time (twice as fast as conventional methods), procedure simplicity, and reduced fabrication cost. With further commercialization efforts, the methods described in this manuscript could be applied to a wide range of potential diagnostic applications in the field. [ABSTRACT FROM AUTHOR]

Here we present a new and rapid immunofiltration assay for simultaneous detection of HIV p24 and hepatitis B virus antigens. The assay platform is composed of a 13 mm nitrocellulose filter spotted with capturing bioprobes and inserted in a Swinnex ® syringe filter holder. Samples and reagents are flown through the nitrocellulose filter by manual pressure on the syringe. A colorimetric detection allows for naked eye results interpretation. The assay provides sensitivity in the picomolar range in just 5 min, even using low volumes of sample in complex matrix. Probe deposition by spotting allows for flexible combinations of different capturing agents and multiple diagnoses; furthermore, the very simple and inexpensive set-up makes the syringe-based immunoassay on paper microarray a suitable diagnostic system for resource-limited settings. [ABSTRACT FROM AUTHOR]

Contact with thermal printing paper is a relevant source of dermal exposure to unbonded bisphenol A (BPA). In order to limit this exposure route, the European Union has introduced a drastic reduction in the maximum allowed concentration of BPA in thermal paper produced after beginning of year 2020. This study investigates the suitability of direct analysis in real time (DART), combined with accurate mass spectrometry, as a faster alternative to chromatography-based methods for the quantitative determination of BPA, and three analogues species, in receipts and tickets usually printed on thermal paper. The ionization efficiency of these compounds is evaluated under different conditions, and the effect of instrumental parameters of the DART source in the observed responses is discussed. The yield of the DART desorption-ionization process was greatly improved when compounds are previously converted into their acetyl derivatives; thereafter, the temperature of electronically excited helium atoms was the most relevant of the evaluated instrumental parameters. Under optimized conditions, the reported method provided recoveries in the range from 90 to 110%, a limit of quantification of 0.004% (w:w), well below the maximum concentration established after 2020 for BPA (0.02%, w:w), and permitted to perform duplicate determinations of each sample extract with a response time around 1 min. The accuracy of BPA levels found in non-spiked samples was confirmed using GC-EI-MS as reference technique. BPA was systematically noticed in the processed samples with concentrations ranging from 0.005% to more than 6%. Image 1 • Rapid determination of bisphenol A in thermal printing paper by DART accurate MS. • Acetylation greatly enhances the yield of DART desorption-ionization. • Procedural LOQs below limits set for bisphenol A in thermal paper. • Good correlation between DART-MS and GC-EI-MS values in thermal paper samples. [ABSTRACT FROM AUTHOR]