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Multiple protocols have been reported to fabricate paper-based analytical devices (PADs). However, some of these techniques must be revised because of the instrumentation required. This paper describes a versatile and globally affordable method to fabricate PADs using office paper as a substrate and a laser printing technique to define hydrophobic barriers on paper surfaces. To demonstrate the feasibility of the alternatives proposed in this study, the fabrication of devices for three types of detection commonly associated with using PADs was demonstrated: colorimetric detection, electrochemical detection, and mass spectrometry associated with a paper-spray ionization (PSI-MS) technique. Besides that, an evaluation of the type of paper used and chemical modifications required on the substrate surface are also presented in this report. Overall, the developed protocol was suitable for using office paper as a substrate, and the laser printing technique as an efficient fabrication method when using this substrate is accessible at a resource-limited point-of-need. Target analytes were used as a proof of concept for these detection techniques. Colorimetric detection was carried out for acetaminophen, iron, nitrate, and nitrite with limits of detection of 0.04 μg, 4.5 mg mL−1, 2.7 μmol L−1, and 6.8 μmol L−1, respectively. A limit of detection of 0.048 fg mL−1 was obtained for the electrochemical analysis of prostate-specific antigen. Colorimetric and electrochemical devices revealed satisfactory performance when office paper with a grammage of 90 g m−2 was employed. Methyldopa analysis was also carried out using PSI-MS, which showed a good response in the same paper weight and behavior compared to chromatographic paper. [ABSTRACT FROM AUTHOR]

Hydrogen peroxide (H2O2) is an essential analyte for detecting neurodegenerative diseases and inflammatory processes and plays a crucial role in pharmaceuticals, the food industry, and environmental monitoring. However, conventional H2O2 detection methods have drawbacks such as lengthy analysis times, high costs, and bulky equipment. Non-enzymatic sensors have emerged as promising alternatives to overcome these limitations. In this research, we introduce a simple, portable, and cost-effective non-enzymatic sensor that uses carbon black (CB) and silver nanoparticle-modified δ-FeOOH (Ag/δ-FeOOH) integrated into a disposable electrochemical cell (DCell). Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and electrochemical impedance spectroscopy (EIS) confirmed successful CB and Ag/δ-FeOOH immobilization on the DCell working electrode. Electrochemical investigations revealed that the DCell-CB//Ag/δ-FeOOH sensor exhibited an approximately twofold higher apparent heterogeneous electron transfer rate constant than the DCell-Ag/δ-FeOOH sensor, capitalizing on CB's advantages. Moreover, the sensor displayed an excellent electrochemical response for H2O2 reduction, boasting a low detection limit of 22 µM and a high analytical sensitivity of 214 μA mM−1 cm−2. Notably, the DCell-CB//Ag/δ-FeOOH sensor exhibited outstanding selectivity for H2O2 detection, even in potential interferents such as dopamine, uric acid, and ascorbic acid. Furthermore, the sensor has the right qualities for monitoring H2O2 in complex biological samples, as evidenced by H2O2 recoveries ranging from 92% to 103% in 10% fetal bovine serum. These findings underscore the considerable potential of the DCell-CB//Ag/δ-FeOOH sensor for precise and reliable H2O2 monitoring in various biomedical and environmental applications. [ABSTRACT FROM AUTHOR]

In this paper we report on a modular design that allows one to fabricate electrochemical sensors upon combining 3D printing and screen printing. The usefulness of the design is showcased with graphene paste electrodes (GPE) coated with magnetic microspheres used to detect the drug nimesulide (NIM), biomarkers dopamine (DOP) and uric acid (UA). Under optimized conditions, the limit of detection was 0.0023 μmol L−1 in the range from 0.5 to 9 μmol L−1, 0.01 μmol L−1 within the range from 0.8 to 6 μmol L−1, and 0.0034 μmol L−1 from 0.7 to 10 μmol L−1 for dopamine, nimesulide, and uric acid, respectively. The three analytes could also be detected in blood serum and artificial urine samples within approximately 20 s, which is promising for clinical applications. With the modular design, the paste can be prepared with a variety of nanomaterials, functionalized with biomolecules and magnetic particles, and then stored for later use. The working electrode may also be polished to allow for reuse. Furthermore, in contrast to standard sensors made with carbon pastes, the electrochemical sensor proposed here requires small volumes (20–200 μL), which is crucial for drug monitoring and other biomedical applications. [ABSTRACT FROM AUTHOR]

A non‐enzymatic sensor for hydrogen peroxide (H2O2) determination based on Ag/δ‐FeOOH nanocomposite immobilized on an all‐plastic disposable carbon‐based electrochemical cell (DCell) is constructed by a rapid prototyping technique. Ag/δ‐FeOOH is synthesized by a simple and reproducible method and its structural and morphological properties characterized by X‐ray diffraction (XRD), Fourier transform‐infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The Ag/δ‐FeOOH is successfully immobilized on the DCell, as revealed by SEM images. The electrochemical investigation indicates that the Ag/δ‐FeOOH/DCell has a good electrocatalytic response for the H2O2 reduction, showing detection limit of 71 μmol L−1 H2O2 at a signal‐to‐noise ratio of 3 and analytical sensitivity of 215.4 μA mM−1 cm−2. Moreover, Ag/δ‐FeOOH/DCell can be used to selectively detect H2O2 in the presence of dopamine (DA), uric acid (UA), and ascorbic acid (AA). Finally, Ag/δ‐FeOOH/DCell can be used to determine H2O2 in fetal bovine serum. The achieved results indicate that the non‐enzymatic Ag/δ‐FeOOH/DCell is a cost‐effective alternative for the determination of H2O2. [ABSTRACT FROM AUTHOR]

Herein, we reported the detection of dopamine (DA) based on use of a cathodically pretreated polyaniline (PANI) modified electrode. The PANI electrode presents a remarkable change in their electrocatalytic properties after a simple cathodic pretreatment, which consisted in applying a potential of −0.7 V for 3 s. While the as‐prepared PANI shows no electrochemical response for DA, the cathodically pretreated PANI presented reversible electrochemical responses with well‐defined anodic and cathodic peaks. The electrochemical behavior of DA at the PANI electrode was investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Under the optimized experimental conditions, the anodic peak currents increased proportionally to the DA concentration, displaying a linear relationship in the concentration range of 0.11 to 1.75×10−4 M with a detection limit of 13.7 μM (3 σ/slope). Recovery studies in pharmaceutical formulations presented values between 98 % and 104 %. The cathodically pretreated PANI electrode was successfully applied for DA detection in real samples of pharmaceutical formulation showing good agreement with spectrometric comparative method. The unexpected easily capability of modulate the electrocatalytic properties of the electropolymerized PANI film using a simple pretreatement was successfully demonstrated. The cathodically pretreatment PANI electrode showed electrochemical responses for DA with excellent selectivity, sensitivity, and high stability. [ABSTRACT FROM AUTHOR]

ArtinM, a D-mannose-binding lectin from Artocarpus heterophyllus (jackfruit), interacts with N-glycosylated receptors on the surface of several cells of hematopoietic origin, triggering cell migration, degranulation, and cytokine release. Because malignant transformation is often associated with altered expression of cell surface glycans, we evaluated the interaction of ArtinM with human myelocytic leukemia cells by Quartz Cristal Microbalance (QCM) and cross compared this investigation with cellular responses (cytotoxicity) to lectin binding by the colorimetric assay MTT, which is a standard method in biology. QCM analysis was able to provide additional information (not possible to be obtained by MTT) that impact on the knowledge of medical biology related to leukemic cells. For instance, it was shown that association rate constant of ArtinM and cellular membranes (obtained from QCM) of leukemia cell varies across the myeloid leukemia cell lines, decreasing as cytotoxic effect increases. Meanwhile no differences were observed for dissociation rate constants so that the equilibrium binding affinity constant was observed to be a direct function of the association rate event. It was supposed that ArtinM cytotoxicity is affected by the association time with glycans on the cellular membranes of leukemia cells in a way that the higher it is the association time (the lower was the association rate constant) the higher is the ArtinM cytotoxicity over the leukemia cell lines. [ABSTRACT FROM AUTHOR]

A high throughput electrochemiluminescent (ECL) chip was fabricated and integrated into a fluidic system for screening toxicity-related chemistry of drug and pollutant metabolites. The chip base is conductive pyrolytic graphite onto which are printed 64 microwells capable of holding one-μL droplets. Films combining DNA, metabolic enzymes and an ECL-generating ruthenium metallopolymer (RuIIPVP) are fabricated in these microwells. The system runs metabolic enzyme reactions, and subsequently detects DNA damage caused by reactive metabolites. The performance of the chip was tested by measuring DNA damage caused by metabolites of the well-known procarcinogen benzo[a]pyrene (B[a]P). Liver microsomes and cytochrome P450 (cyt P450) enzymes were used with and without epoxide hydrolase (EH), a conjugative enzyme required for multi-enzyme bioactivation of B[a]P. DNA adduct formation was confirmed by determining specific DNA-metabolite adducts using similar films of DNA/enzyme on magnetic bead biocolloid reactors, hydrolyzing the DNA, and analyzing by capillary liquid chromatography-mass spectrometry (CapLC-MS/MS). The fluidic chip was also used to measure IC50-values of inhibitors of cyt P450s. All results show good correlation with reported enzyme activity and inhibition assays. [ABSTRACT FROM AUTHOR]

A multiplexed, microfluidic platform to detect reactive metabolites is described, and its performance is illustrated for compounds metabolized by oxidative and bioconjugation enzymes in multi-enzyme pathways to mimic natural human drug metabolism. The device features four 8-electrode screen printed carbon arrays coated with thin films of DNA, a ruthenium-polyvinylpyridine (RuPVP) catalyst, and multiple enzyme sources including human liver microsomes (HLM), cytochrome P450 (cyt P450) 1B1 supersomes, microsomal epoxide hydrolase (EH), human S9 liver fractions (Hs9) and N-acetyltransferase (NAT). Arrays are arranged in parallel to facilitate multiple compound screening, enabling up to 32 enzyme reactions and measurements in 20–30 min. In the first step of the assay, metabolic reactions are achieved under constant flow of oxygenated reactant solutions by electrode driven natural catalytic cycles of cyt P450s and cofactor-supported bioconjugation enzymes. Reactive metabolites formed in the enzyme reactions can react with DNA. Relative DNA damage is measured in the second assay step using square wave voltammetry (SWV) with RuPVP as catalyst. Studies were done on chemicals known to require metabolic activation to induce genotoxicity, and results reproduced known features of metabolite DNA-reactivity for the test compounds. Metabolism of benzo[a]pyrene (B[a]P) by cyt P450s and epoxide hydrolase showed an enhanced relative DNA damage rate for DNA compared to cyt P450s alone. DNA damage rates for arylamines by pathways featuring both oxidative and conjugative enzymes at pH 7.4 gave better correlation with rodent genotoxicity metric TD50. Results illustrate the broad utility of the reactive metabolite screening device. [ABSTRACT FROM AUTHOR]

The natural catalytic cycle of cytochrome (cyt) P450 enzymes in human liver microsome (HLM) films was activated electrochemically via the electron transfer sequence electrode→cyt P450 reductase (CPR)→cyt P450. Cyclic voltammograms for HLM films had midpoint potentials of −0.50 V vs. SCE at pH 7.4 characteristic of CPR, not cyt P450s. HLM and CPR microsomes without cyt P450s did not electrocatalytically reduce H2O2, and did not shift midpoint potential when CO was added, also indicating that the peaks do not correspond to iron heme cyt P450 enzymes. Electrochemical activation of the natural cyt P450 cycle for substrate conversion via CPR in HLM films was confirmed by catalytic electrolysis in an electrochemical microfluidic array designed to generate and detect reactive metabolites by measuring their reactivity with DNA. [ABSTRACT FROM AUTHOR]

The paper reports on the successful use of the quartz crystal microbalance technique to assess accurate kinetics and equilibrium parameters regarding the investigation of in situ adsorption of nanosized cobalt ferrite particles (CoFe2O4―10.5 nm-diameter) onto two different surfaces. Firstly, a single layer of nanoparticles was deposited onto the surface provided by the gold-coated quartz resonator functionalized with sodium 3-mercapto propanesulfonate (3-MPS). Secondly, the layer-by-layer (LbL) technique was used to build multilayers in which the CoFe2O4 nanoparticle-based layer alternates with the sodium sulfonated polystyrene (PSS) layer. The adsorption experiments were conducted by modulating the number of adsorbed CoFe2O4/PSS bilayers (n) and/or by changing the CoFe2O4 nanoparticle concentration while suspended as a stable colloidal dispersion. Adsorption of CoFe2O4 nanoparticles onto the 3-MPS-functionalized surface follows perfectly a first order kinetic process in a wide range (two orders of magnitude) of nanoparticle concentrations. These data were used to assess the equilibrium constant and the adsorption free energy. Alternatively, the Langmuir adsorption constant was obtained while analyzing the isotherm data at the equilibrium. Adsorption of CoFe2O4 nanoparticles while growing multilayers of CoFe2O4/PSS was conducted using colloidal suspensions with CoFe2O4 concentration in the range of 10−8 to 10−6 (moles of cobalt ferrite per litre) and for different numbers of cycles n = 1, 3, 5, and 10. We found the adsorption of CoFe2O4 nanoparticles within the CoFe2O4/PSS bilayers perfectly following a first order kinetic process, with the characteristic rate constant growing with the increase of CoFe2O4 nanoparticle concentration and decreasing with the rise of the number of LbL cycles (n). Additionally, atomic force microscopy was employed for assessing the LbL film roughness and thickness. We found the film thickness increasing from about 20 to 120 nm while shifting from 3 to 10 CoFe2O4/PSS bilayers, using the 8.9 × 10−6 (moles of cobalt ferrite per litre) suspension. [ABSTRACT FROM AUTHOR]

Abstract: Graphene is a material that has attracted attention with regard to sensing and biosensing applications in recent years. Here, we report a novel treatment (using ultrasonic bath and ultrasonic tip) to obtain graphene oxide (GO) and a new stable conducting film using reduced graphene oxide (RGO) and dihexadecylphosphate film (DHP). The GO was obtained by chemical exfoliation and it was reduced using NaBH4. Subsequently, RGO–DHP dispersion was prepared and it was dropped onto a glassy carbon electrode by casting technique. The electrode was characterized by cyclic voltammetry and electrochemical spectroscopy impedance. The voltammetric behavior of the RGO–DHP/GC electrode in the presence of estradiol was studied, and the results reported an irreversible oxidation peak current at 0.6V. Under the optimal experimental conditions, using linear sweep adsorptive stripping voltammetry, the detection limit obtained for this hormone was 7.7×10−8 molL−1 . The proposed electrode can be attractive for applications as electrochemical sensors and biosensors. [Copyright &y& Elsevier]

Herein we report a low cost, sensitive, supercapacitor-powered electrochemiluminescent (ECL) protein immunoarray fabricated by an inexpensive 3-dimensional (3D) printer. The immunosensor detects three cancer biomarker proteins in serum within 35 min. The 3D-printed device employs hand screen printed carbon sensors with gravity flow for sample/reagent delivery and washing. Prostate cancer biomarker proteins, prostate specific antigen (PSA), prostate specific membrane antigen (PSMA) and platelet factor-4 (PF-4) in serum were captured on the antibody-coated carbon sensors followed by delivery of detection-antibody-coated Ru(bpy) 3 2+ (RuBPY)-doped silica nanoparticles in a sandwich immunoassay. ECL light was initiated from RuBPY in the silica nanoparticles by electrochemical oxidation with tripropylamine (TPrA) co-reactant using supercapacitor power and ECL was captured with a CCD camera. The supercapacitor was rapidly photo-recharged between assays using an inexpensive solar cell. Detection limits were 300–500 fg mL −1 for the 3 proteins in undiluted calf serum. Assays of 6 prostate cancer patient serum samples gave good correlation with conventional single protein ELISAs. This technology could provide sensitive onsite cancer diagnostic tests in resource-limited settings with the need for only moderate-level training. [ABSTRACT FROM AUTHOR]

Abstract: Xylella fastidiosa is a gram-negative bacterium that causes serious diseases in economically important crops, including grapevine, coffee, and citrus fruits. X. fastidiosa colonizes the xylem vessels of the infected plants, thereby blocking water and nutrient transport. The genome sequence of X. fastidiosa has revealed an operon containing nine genes possibly involved in the synthesis of an exopolisaccharide (EPS) named fastidian gum that can be related with the pathogenicity of this bacterium. The α-1,3-mannosyltransferase (GumH) enzyme from X. fastidiosa is involved in fastidian gum production. GumH is responsible for the transfer of mannose from guanosine diphosphate mannose (GDP-man) to the cellobiose–pyrophosphate–polyprenol carrier lipid (CPP-Lip) during the assembly and biosynthesis of EPS. In this work, a method for real-time detection of recombinant GumH enzymatic activity was successfully developed using a Quartz Crystal Microbalance with dissipation monitoring (QCM-D). The QCM-D transducer was strategically modified with CPP-Lip by using a solid-supported lipid bilayer that makes use of a self-assembled monolayer of 1-undecanethiol. Monitoring the real-time CPP-Lip QCM-D transducer in the presence of GDP-man and GumH enzyme shows a mass increase, indicating the transfer of mannose. The real-time QCM-D determination of mannosyltransferase function was validated by a High Performance Liquid Chromatography (LC) method developed for determination of GDP produced by enzymatic reaction. LC results confirmed the activity of recombinant GumH protein, which is the first enzyme involved in the biosynthesis of the EPS from X. fastidiosa enzymatically characterized. [Copyright &y& Elsevier]

Glutathione-s-transferase is believed to be involved in the resistance to chemotherapeutic drugs, which depends on the interaction with the cell membranes. In this study, we employed Langmuir monolayers of a mixture of phospholipids and cholesterol (MIX) as models for tumor cell membranes and investigated their interaction with the anticancer drugs cisplatin (CDDP) and doxorubicin (DOX). We found that both DOX and CDDP expand and affect the elasticity of MIX monolayers, but these effects are hindered when glutathione-s-transferase (GST) and its cofactor glutathione (GSH) are incorporated. Changes are induced by DOX or CDDP on the polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS) data for MIX/GST/GSH monolayers, thus denoting some degree of interaction that is not sufficient to alter the monolayer mechanical properties. Overall, the results presented here give support to the hypothesis of the inactivation of DOX and CDDP by GST and point to possible directions to detect and fight drug resistance. [Display omitted] • Langmuir monolayers as models for tumor cell membranes. • Studies with the anticancer drugs cisplatin (CDDP) and doxorubicin (DOX). • DOX and CDDP expand and affect the elasticity of Langmuir monolayers. • Our results give support to the hypothesis of inactivation of DOX and CDDP by GST. [ABSTRACT FROM AUTHOR]

• The interaction of gemcitabine (GEM) with Langmuir films that mimic healthy and cancerous cell membranes. • The SM concentration (40 mol%) could be useful for the design of drug delivery systems. • Molecular dynamics simulations indicated how GEM approaches the membrane. The fight against drug resistance in chemotherapy requires a molecular-level understanding of the drug interaction with cell membranes, which today is feasible with membrane models. In this study, we report on the interaction of gemcitabine (GEM), a pyrimidine nucleoside antimetabolite used to treat pancreatic cancer, with Langmuir films that mimic healthy and cancerous cell membranes. The cell membrane models were made with eight compositions of a quaternary mixture containing 1,2-dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC), 1,2-dipalmitoyl-sn-glycero-3-phosphoserine (DPPS), sphingomyelin (SM), and cholesterol (CHOL). The relative concentration of SM was increased so that four of these compositions represented cancerous cells. GEM was found to increase the mean molecular area, also increasing their surface elasticity, with stronger interactions being observed for membranes corresponding to cancerous cells. More specifically, GEM penetrated deepest in the membrane with the highest SM concentration (40 mol%), as inferred from polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS). This finding was confirmed with molecular dynamics simulations that also indicated how GEM approaches the membrane, which could be useful for guiding the design of drug delivery systems. The experimental and simulation results are consistent with the preferential attachment of GEM onto cancerous cells and highlight the role of SM on drug-cell interactions. [ABSTRACT FROM AUTHOR]

Alzheimer's disease (AD) is a neurodegenerative condition that affects a large number of elderly people worldwide and has a high social and economic impact. The diagnosis of AD in early stage can significantly improve the evolution and prognosis of the disease. We report the use of A Disintegrin And Metalloprotease 10 (ADAM10) as a blood biomarker for the early diagnosis of AD. A simple, low-cost, sensitive, and disposable microfluidic platform (DμP) was developed for ADAM10 detection in plasma and cerebrospinal fluid based on electrochemical immunosensors. The assay was designed to accurately detect ADAM10 in serum, with a limit of detection of 0.35 fg/mL. ADAM10 was detected in subjects divided into cognitively healthy subjects, subjects with mild cognitive impairment, and AD patients in different disease stages. An increase in protein levels was found throughout the disease, and good DμP accuracy in differentiating individuals was observed. The DμP provided significantly better sensitivity than the well-established enzyme-linked immunosorbent assay test. ADAM10 and its detection using the DμP were proven to be an alternative tool for the early diagnosis and monitoring of AD, bringing new exciting possibilities to improve the quality of life of AD patients.

Diagnosis of cancer using electroanalytical methods can be achieved at low cost and in rapid assays, but this may require the combination with data treatment for determining biomarkers in real samples. In this paper, we report an immunomagnetic nanoparticle-based microfluidic sensor (INμ-SPCE) for the amperometric detection of the prostate-specific antigen (PSA) biomarker, the data of which were treated with information visualization methods. The INμ-SPCE consists of eight working electrodes, reference and counter electrodes. On the working electrodes, magnetic nanoparticles with secondary antibodies with the enzyme horseradish peroxidase were immobilized for the indirect detection of PSA in a sandwich-type procedure. Under optimal conditions, the immunosensor could operate within a wide range from 12.5 to 1111 fg·L -1 , with a low detection limit of 0.062 fg·L -1 . Multidimensional projections combined with feature selection allowed for the distinction of cell lysates with different levels of PSA, in agreement with results from the traditional enzyme-linked immunosorbent assay. The approaches for immunoassays and data processing are generic, and therefore the strategies described here may provide a simple platform for clinical diagnosis of cancers and other types of diseases., (Copyright © 2019, Proença et al.; licensee Beilstein-Institut.)