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A simple and rapid distance paper-based analytical device (dPAD) for the detection of lead (Pb) in foods is proposed herein. The assay principle is based on competitive binding between carminic acid (CA) and polyethyleneimine (PEI) to Pb in a food sample. The paper channels were pre-immobilized with PEI, before reacting with a mixture of the sample and CA. Pb can strongly bind to the CA; hence, the length of the red color deposition on the flow channel decreased as a lower amount of free CA bound to PEI. The dPAD exhibited good linear correlation, with ranges of 5-100 µg·mL -1 ( R 2 = 0.974) of Pb. Although, the limit of detection (LOD) of this platform was rather high, at 12.3 µg·mL -1 , a series of standard additions (8.0, 9.0, and 10.0 µg·mL -1 ) can be used to interpret the cutoff of Pb concentrations at higher or lower than 2 µg·mL -1 . The presence of common metal ions such as calcium, magnesium, nickel, and zinc did not interfere with the color distance readout. The validity of the developed dPAD was demonstrated by its applicability to screen the contamination of Pb in century egg samples. The results obtained from the dPAD are in accordance with the concentration measured by atomic absorption spectroscopy (AAS) ( n = 9). In conclusion, this proposed dPAD, combined with the standard addition method, could be applied for screening Pb contamination in food matrices. This platform is, therefore, potentially applicable for field measurements of Pb in developing countries, because it is cheap and rapid, and it requires no significant laborious instruments.

A paper-based microfluidic device based on unconventional principle was developed and used to detect lead ions through a two-step process including heated incubation and subsequent mixing. The device was made by generating a superhydrophobic pattern, which defines channel and reservoir barriers, on a water-impermeable paper substrate, followed by loading and drying the reagents in the defined reservoirs. Different from the conventional paper-based devices that are made of water-permeable paper, the as-prepared device holds water drops in discrete reservoirs, and the water drops will not move unless the device is titled along the direction of the predefined channels. In this way, the liquid samples applied onto the device are handled as individual drops and could be stored, transported, and mixed on demand. Different from the conventional paper-based devices that use capillary force to drive liquid, our new device uses wetting and gravity as driving force. We name this operation principle suspending-droplet mode paper-based device (SD-μPAD). The use of a Teflon contact-printing stamp makes the production of such devices rapid, cost efficient, and mass productive. Utilizing a G-quadruplex-based luminescence switch-on assay, we demonstrated rapid, convenient, highly sensitive, and low cost detection of lead(II) ions in water samples, using a custom made battery-powered portable device, and a smart phone as the detector., (Copyright © 2017 Elsevier B.V. All rights reserved.)

A highly sensitive electrochemical (EC) biosensor combined with a 3D origami device for detection of Pb 2+ was developed based on novel Au nanoparticles modified paper working electrode (Au-PWE) as sensor platform and DNA functionalized iron-porphyrinic metal-organic framework ((Fe-P)n-MOF-Au-GR) hybrids as signal probes. In the presence of Pb 2+ , GR could be specifically cleaved at the ribonucleotide (rA) site, which produced the short (Fe-P) n -MOF-linked oligonucleotide fragment to hybridize with hairpin DNA immobilized on the surface of Au-PWE. Because of the mimic peroxidase property of (Fe-P) n -MOF, enzymatically amplified electrochemical signal was obtained to offer the sensitive detection of Pb 2+ . In addition, benefiting from the Pb 2+ dependent GR, the proposed assay could selectively detect Pb 2+ in the presence of other metal ions. This method showed a good linear relationship between the current response and the Pb 2+ concentration ranging from 0.03 to 1000nmolL -1 with a detection limit of 0.02nmolL -1 . The Au-PWE based electrochemical sensor along with the (Fe-P) n -MOF-Au-GR probe exhibited the advantages of low-cost, simple fabrication, high sensitivity and selectivity, providing potential application of real-time Pb 2+ detection both in environmental and biological samples., (Copyright © 2016 Elsevier B.V. All rights reserved.)

A multi-amplified paper-based electrochemical strategy using Pb(2+) dependent DNAzyme as the recognition unit for Pb(2+) detection was developed. In this work, flower-like reduced graphene (FrGO) was prepared utilizing flower-like ZnO as template, which was first one step grown on the gold nanoparticles modified paper working electrode (Au-PWE). After being treated with acid and then modified with Au, a novel sensor platform named Au/FrGO/Au-PWE with large specific surface area and good electrical conductivity was fabricated. The Mn2O3 nanoparticle-assembled hierarchical hollow spheres (H-Mn2O3) was served as nanocarrier to immobilize GOx, HRP and signal strand (S3), resulting to the formation of S3/H-Mn2O3/HRP/GOx bioconjugations. In the presence of Pb(2+), the DNAzyme (S1) was activated and the substrate strand (S2) was cleaved. After the incubation with S3/H-Mn2O3/HRP/GOx in 0.1M HAc-NaAc solution (pH 4.3) containing 30 mM aniline and 15 mM glucose, a readily measurable "turn-on" electrochemical signal could be measured. On the basis of the signal amplification strategy of Au/FrGO/Au-PWE sensing platform and S3/H-Mn2O3/HRP/GOx bioconjugations, the developed biosensor exhibited a good linear response toward over a wide range of concentration from 0.005 to 2000 nM., (Copyright © 2016 Elsevier B.V. All rights reserved.)

A disposable electrochemical lateral flow paper-based sensing device for heavy metal detection is proposed. The quantification of lead and cadmium in aqueous samples is demonstrated in a range from 10 to 100 ppb with a limit of detection of 7 and 11 ppb respectively. Moreover, the platform itself, which is made of paper, served as a sample pretreatment material due to its filtering properties. Real samples, especially in which the matrix is usually turbid and would in principle need a previous filtration, are successfully analyzed. This lab-on-paper device is simple, low cost, easy to fabricate, and portable, being a promising tool for new point-of-care applications in environmental monitoring, public health, and food safety.

The main aim of this work was to study the removal efficiency of Pb from synthetic and industrial wastewaters by using biomass fly ashes. The biomass fly ashes were produced in a biomass boiler of a pulp and paper industry. Three concentrations of Pb(2+) were tested in the synthetic wastewater (1, 10 and 1000 mg Pb/L). Moreover, two different wastewaters were collected in an industrial wastewater treatment plant (IWWTP) of an industry of lead-acid batteries: (i) wastewater of the equalization tank, and (ii) IWWTP effluent. All the wastewaters were submitted to coagulation-flocculation tests with a wide range of biomass fly ashes dosage (expressed as Solid/Liquid - S/L - ratios). All supernatants were characterized for chemical and ecotoxicological parameters. The use of biomass fly ashes has reduced significantly the Pb concentration in the synthetic wastewater and in the wastewaters collected in the IWWTP. For example, the definitive coagulation-flocculation assays performed over the IWWTP effluent presented a very low concentration of Pb (0.35 mg/L) for the S/L ratio of 1.23 g/L. Globally, the ecotoxicological characterization of the supernatants resulting from the coagulation-flocculation assays of all wastewaters has indicated an overall reduction on the ecotoxicity of the crude wastewaters, due to the removal of Pb., (Copyright © 2014 Elsevier Inc. All rights reserved.)

A revised procedure for processing a capillary blood sample collected on filter paper (FP) for analysis by graphite furnace atomic absorption spectrometry (GFAAS) is described. A 1/4-in. diameter disk of the dried FP sample was used, and a correlation of 0.975 with a false-positive rate of 0.8% and a false-negative rate of 1.7% was found when the results from the FP sample and its corresponding venous sample were compared. Several analytical variables were investigated, and the following was found: blood samples with hematocrit values of 30-39% did not show any significant differences between the paired FP and venous lead results; filter paper blank values were < 2 micrograms/dl with the use of aqueous standards without correction and 0.1 microgram/dl with paper blank correction; and during the collection of 163 samples from 6 different urban sites over a period of 1 year, no environmental lead contamination was encountered based upon the good agreement between all of the paired FP and venous lead results. The method described is easier to perform than an earlier version. All indications suggest that a fingerstick capillary blood sample collected on filter paper is suitable for lead screening. Proper precautions must always be taken to guard against contamination.

A series of 15 blood samples with haemoglobin levels ranging from 4-6--16-1 g/dl were spotted on to Whatman No. 4 filter paper. Blood samples with low haemoglobin concentrations spread over a greater area of the filter paper than did those with high haemoglobin concentrations. This was further investigated by studying the performance of laboratory-prepared samples, and any effect on the estimation of blood lead value. Blood lead values assayed by the punched disc method on blood samples with low haemoglobin values were unreliable unless the estimated value was adjusted with respect to the area over which the blood had spread.