Electrochemical Aptasensor with Antifouling Properties for Label-Free Detection of Oxytetracycline.

Oxytetracycline (OTC) is a widely employed antibiotic in veterinary treatment and in the prevention of infections, potentially leaving residues in animal-derived food products, such as milk, that are consumed by humans. Given the detrimental effects of prolonged human exposure to antibiotics, it has become imperative to develop precise and sensitive methods for monitoring the presence of OTC in food. Herein, we describe the development and results of a preliminary label-free electrochemical aptasensor with antifouling properties designed to detect OTC in milk samples. The sensor was realized by modifying a gold screen-printed electrode with α-lipoic acid-NHS and an amine-terminated aptamer. Different electrochemical techniques were used to study the steps of the fabrication process and to quantify OTC in the presence of the Fe(CN)64-/Fe(CN)63- redox couple The detectable range of concentrations satisfy the maximum residue limits set by the European Union, with an limit of detection (LOD) of 14 ng/mL in phosphate buffer (BP) and 10 ng/mL in the milk matrix, and a dynamic range of up to 500 ng/mL This study is a steppingstone towards the implementation of a sensitive monitoring method for OTC in dairy products.

Photonic Dipstick Immunosensor to Detect Adulteration of Ewe, Goat, and Donkey Milk with Cow Milk through Bovine κ-Casein Detection.

The quality and authenticity of milk are of paramount importance. Cow milk is more allergenic and less nutritious than ewe, goat, or donkey milk, which are often adulterated with cow milk due to their seasonal availability and higher prices. In this work, a silicon photonic dipstick sensor accommodating two U-shaped Mach-Zehnder Interferometers (MZIs) was employed for the label-free detection of the adulteration of ewe, goat, and donkey milk with cow milk. One of the two MZIs of the chip was modified with bovine κ-casein, while the other was modified with bovine serum albumin to serve as a blank. All assay steps were performed by immersion of the chip side where the MZIs are positioned into the reagent solutions, leading to a photonic dipstick immunosensor. Thus, the chip was first immersed in a mixture of milk with anti-bovine κ-casein antibody and then in a secondary antibody solution for signal enhancement. A limit of detection of 0.05% v/v cow milk in ewe, goat, or donkey milk was achieved in 12 min using a 50-times diluted sample. This fast, sensitive, and simple assay, without the need for sample pre-processing, microfluidics, or pumps, makes the developed sensor ideal for the detection of milk adulteration at the point of need.

Multiplexed colorimetric assay of antioxidants in wines with paper-based sensors fabricated by pen plotting.

This work reports the development of low-cost and rapid multiplexed colorimetric assay of antioxidants (total phenolics, antioxidant capacity, flavonoids and anthocyanins) in wines at daisy-shaped fluidic paper-based analytical devices (PADs). The desired fluidic patterns were formed on paper by pen drawing and colorimetric reagents were immobilized at the 6 peripheral test zones. The sample was added at the central sample zone, migrated to the test zones and reacted with the immobilized reagents producing characteristic colors that were captured and analyzed. The paper-based approach was applied to the analysis of several wine samples and the results were statistically correlated to standard solution-based colorimetric assays, indicating that it could be reliably used for ranking wines according to their antioxidants content. In addition, the paper-based analytical methodology is simple, instrument-free, portable, cost-effective, rapid and environment friendly.

A simplified lateral flow immunosensor for the assay of carcinoembryonic antigen in low-resource settings.

Carcinoembryonic antigen (CEA) is a glycoprotein widely used as a tumor marker. In this work, a colorimetric lateral flow immunosensor is developed for rapid and low-cost quantification of CEA in human blood serum. The immunosensor consists of a glass fiber sample/conjugation pad, a nitrocellulose detection pad and a cellulose absorption pad. The detection is based on a sandwich immunoreaction: the sample/conjugation pad is modified with gold nanoparticles (GNPs)-labeled anti-CEA conjugate probes which bind to the CEA target molecules in the sample and the complexes are captured at capture anti-CEA immobilized at the test line. The color intensity of the test line, measured from a scanned image of the strip, is related to the CEA concentration in the sample. The different assay parameters are studied in detail. The linearity holds from 1.25 to 640 ng mL-1 of CEA, the instrumental and visual limits of detection are 0.45 and 0.63 ng mL-1, respectively, and the total assay time is 15 min. The specificity of the immunoassay versus other cancer biomarkers is satisfactory. The recovery in samples of human serum spiked with CEA is in the range of 81-118% and the coefficient of variation of the method is ≤10%. Results obtained with the lateral flow immunosensor correlated well with a reference radioimmunoassay method (R2 = 0.99). This immunosensor can be readily applied to CEA monitoring at the point-of-care (POC) or in resource-limited settings thanks to its low-cost and simplicity.

Effect of in vivo aging on the surface and electrochemical properties of magnetic attachments used in facial prostheses: A retrieval analysis study.

STATEMENT OF PROBLEM: Reasons associated with the failure of facial prosthesis are of major concern and may be associated with deterioration of both elastomeric materials and magnetic attachments. However, the extent of deterioration of these components is unclear. PURPOSE: The purpose of this in vitro study was to evaluate selected retrieved facial prostheses and provide information regarding the electrochemical characterization of the recovered magnetic attachments. MATERIAL AND METHODS: Five facial prostheses (RP1, RP2, RP3, RP4, RP5) fabricated at the University of Texas, M.D. Anderson Cancer Center were retrieved following clinical use. The intaglio and external surfaces of the prostheses along with the incorporated magnetic attachments were photographed. The areas with the detected failures on the retrieved prostheses, as well as the recovered magnetic attachments, were evaluated under a reflected light stereomicroscope at ×16 nominal magnification and photographed with a digital camera. Five magnetic attachments recovered from the prostheses (retrieved group RT) were evaluated for degradation of their corrosion resistance after electrochemical testing in artificial sweat solution and were compared with 5 unused magnetic attachments (control group, CT). To identify the elemental composition of the intact magnet surface, 1 specimen from the control group was investigated by X-ray energy dispersive spectroscopy (EDS). Means and standard deviations of the open circuit potential (EOCP), the zero-circuit potential (Ecorr), and Icorr were calculated and statistically analyzed by a t test (α=.05 for all tests). RESULTS: The main reasons of failure were discoloration, degradation and rupture of the silicone elastomer, marginal misfit, and delamination of the polyurethane sheet. Additional findings were tarnish and discoloration of the magnetic attachments accompanied by considerable smear build-up. EDS results verified the Ni plating of tested magnets. Electrochemical testing revealed that retrieved magnets showed significantly lower OCP (P<.001) and Ecorr (P<.001) but similar Icorr (P=0.083) while the pseudopassivity region of unused magnets vanished in the retrieved group, denoting a degradation of electrochemical properties after clinical use. CONCLUSIONS: In vivo aging exerts extended degradation on the elastomer part of facial prostheses as well as deterioration of their surface integrity and electrochemical properties.

An Aptamer-Based Lateral Flow Biosensor for Low-Cost, Rapid and Instrument-Free Detection of Ochratoxin A in Food Samples.

In this work, a simple and cost-efficient aptasensor strip is developed for the rapid detection of OTA in food samples. The biosensor is based on the lateral flow assay concept using an OTA-specific aptamer for biorecognition of the target analyte. The strip consists of a sample pad, a conjugate pad, a nitrocellulose membrane (NC) and an absorbent pad. The conjugate pad is loaded with the OTA-specific aptamer conjugated with gold nanoparticles (AuNPs). The test line of the NC membrane is loaded with a specific OTA-aptamer probe and the control line is loaded with a control probe. The assay is based on a competitive format, where the OTA present in the sample combines with the OTA aptamer-AuNP conjugate and prevents the interaction between the specific probe immobilized on the test line and the OTA aptamer-AuNP conjugates; therefore, the color intensity of the test line decreases as the concentration of OTA in the sample increases. Qualitative detection of OTA is performed visually, while quantification is performed by reflectance colorimetry using a commercial scanner and image analysis. All the parameters of the assay are investigated in detail and the analytical features are established. The visual limit of detection (LOD) of the strip is 0.05 ng mL-1, while the LOD for semi-quantitative detection using reflectance colorimetry is 0.02 ng mL-1. The lateral flow strip aptasensor is applied to the detection of OTA in wine, beer, apple juice and milk samples with recoveries in the range from 91 to 114%. The assay exhibits a satisfactory selectivity for OTA with respect to other mycotoxins and lasts 20 min. Therefore, the lateral flow strip aptasensor could be useful for the rapid, low-cost and fit-for-purpose on-site detection of OTA in food samples.

Cancer Marker Immunosensing through Surface-Enhanced Photoluminescence on Nanostructured Silver Substrates.

Nanostructured noble metal surfaces enhance the photoluminescence emitted by fluorescent molecules, permitting the development of highly sensitive fluorescence immunoassays. To this end, surfaces with silicon nanowires decorated with silver nanoparticles in the form of dendrites or aggregates were evaluated as substrates for the immunochemical detection of two ovarian cancer indicators, carbohydrate antigen 125 (CA125) and human epididymis protein 4 (HE4). The substrates were prepared by metal-enhanced chemical etching of silicon wafers to create, in one step, silicon nanowires and silver nanoparticles on top of them. For both analytes, non-competitive immunoassays were developed using pairs of highly specific monoclonal antibodies, one for analyte capture on the substrate and the other for detection. In order to facilitate the identification of the immunocomplexes through a reaction with streptavidin labeled with Rhodamine Red-X, the detection antibodies were biotinylated. An in-house-developed optical set-up was used for photoluminescence signal measurements after assay completion. The detection limits achieved were 2.5 U/mL and 3.12 pM for CA125 and HE4, respectively, with linear dynamic ranges extending up to 500 U/mL for CA125 and up to 500 pM for HE4, covering the concentration ranges of both healthy and ovarian cancer patients. Thus, the proposed method could be implemented for the early diagnosis and/or prognosis and monitoring of ovarian cancer.

Paper-Based Aptasensors: Working Principles, Detection Modes, and Applications.

Aptamers are short oligonucleotides designed to possess high binding affinity towards specific target compounds (ions, molecules, or cells). Due to their function and unique advantages, aptamers are considered viable alternatives to antibodies as biorecognition elements in bioassays and biosensors. On the other hand, paper-based devices (PADs) have emerged as a promising and powerful technology for the fabrication of low-cost analytical tools, mainly intended for on-site and point-of-care applications. The present work aims to provide a comprehensive overview of paper-based aptasensors. The review describes the fabrication methods and working principles of paper-based devices, the properties of aptamers as bioreceptors, the different modes of detection used in conjunction with aptasensing PADs, and representative applications for the detection of ions, small molecules, proteins, and cells. The future challenges and prospects of these devices are also discussed.

Eco-friendly voltammetric platform for trace metal determination using a conductive polymer sensor modified with bismuth nanoparticles generated by spark discharge.

The fabrication of a low-cost eco-friendly sensor platform for the voltammetric determination of trace metals by electrochemical stripping analysis is reported. Plastic conductive electrodes were manufactured via injection moulding from polysterene reinforced with carbon fibres. The platform comprises a carbon counter electrode, a working electrode modified with bismuth nanoparticles generated by spark discharge and a reference electrode coated with AgCl. The sensor fabrication and modification procedures are simple, cost-effective and fast while the materials used are environment-friendly. The utility of the voltammetric platform is demonstrated for stripping analysis of Cd(II) and Pb(II); the limits of detection are 0.7 µg L-1 and 0.6 µg L-1, respectively (with a deposition time of 240 s) which are comparable to conventional Bi-modified sensors and are sufficient to determine the target metals in water and food samples. The scope of the analytical platform for multi-element assays and for the determination of other trace metals is discussed with representative examples. Therefore, this sustainable and economical platform holds great potential for electrochemical sensing of trace metals.

Electrochemical Determination of the Drug Colchicine in Pharmaceutical and Βiological Samples Using a 3D-Printed Device.

In this work, a simple, fast, and sensitive voltammetric method for the trace determination of the alkaloid drug colchicine (Colc) using a 3D-printed device is described. The electrochemical method was based on the adsorptive accumulation of the drug at a carbon-black polylactic acid (CB/PLA) working electrode, followed by voltammetric determination of the accumulated species. The plastic sensor was printed in a single step by a low-cost dual extruder 3D-printer and featured three CB/PLA electrodes (serving as working, reference, and counter electrodes) and a holder, printed from a non-conductive PLA filament. The electrochemical parameters that affected the response of the device towards Colc determination, such as accumulation time and potential, solution pH, and other variables, were optimized. Under the selected conditions, the oxidation current of Colc was proportional to the concentration of Colc, and its quantification was conducted in the concentration range of 0.6-2.2 µmol L-1 with a limit of detection of 0.11 µmol L-1 in phosphate buffer (pH 7.0). Both within-device and between-device reproducibility were lower than 9%, revealing satisfactory operational and fabrication reproducibility. Furthermore, the 3D-printed device was employed for the voltammetric determination of Colc in pharmaceutical tablets and in human urine with satisfactory results, justifying its suitability for low-cost routine analysis of Colc.

Mach-Zehnder Interferometric Immunosensor for Detection of Aflatoxin M1 in Milk, Chocolate Milk, and Yogurt.

Aflatoxin M1 (AFM1) is detected in the milk of animals after ingestion of aflatoxin B1-contaminated food; since 2002, it has been categorized as a group I carcinogen. In this work, a silicon-based optoelectronic immunosensor for the detection of AFM1 in milk, chocolate milk, and yogurt has been developed. The immunosensor consists of ten Mach-Zehnder silicon nitride waveguide interferometers (MZIs) integrated on the same chip with the respective light sources, and an external spectrophotometer for transmission spectra collection. The sensing arm windows of MZIs are bio-functionalized after chip activation with aminosilane by spotting an AFM1 conjugate with bovine serum albumin. For AFM1 detection, a three-step competitive immunoassay is employed, including the primary reaction with a rabbit polyclonal anti-AFM1 antibody, followed by biotinylated donkey polyclonal anti-rabbit IgG antibody and streptavidin. The assay duration was 15 min with limits of detection of 0.005 ng/mL in both full-fat and chocolate milk, and 0.01 ng/mL in yogurt, which are lower than the maximum allowable concentration of 0.05 ng/mL set by the European Union. The assay is accurate (% recovery values 86.7-115) and repeatable (inter- and intra-assay variation coefficients <8%). The excellent analytical performance of the proposed immunosensor paves the way for accurate on-site AFM1 determination in milk.

3D-printed electrochemical glucose device with integrated Fe(II)-MOF nanozyme.

Estimation of glucose (GLU) levels in the human organism is very important in the diagnosis and monitoring of diabetes. Scientific advances in nanomaterials have led to the construction of new generations of enzymatic-free GLU sensors. In this work, an innovative 3D-printed device modified with a water-stable and non-toxic metal-organic framework of iron (Fe(II)-MOF), which serves as a nanozyme, has been developed for the voltammetric determination of GLU in artificial sweat. In contrast to existing MOF-based GLU sensors which exhibit electrocatalytic activity for the oxidation of GLU in alkaline media, the nanozyme Fe(II)-MOF/3D-printed device can operate in the acidic epidermal sweat environment. The enzymatic-free GLU sensor is composed of a 3-electrode 3D-printed device with the MOF nanozyme immobilized on the surface of the working electrode. GLU sensing is conducted by differential pulse voltammetry without interference from other co-existing metabolites in artificial sweat. The response is based on the oxidation of glucose to gluconolactone, induced by the redox activity of the Fe-centers of the MOF. GLU gives rise to an easily detectable and well-defined voltammetric peak at about - 1.2 V and the limit of detection is 17.6 µmol L-1. The synergy of a nanozyme with 3D printing technology results in an advanced, sensitive, and low-cost sensor, paving the way for on-skin applications.

Gold nanoparticle-modified sustainable plastic sensor chip for voltammetric monitoring of Hg(II).

Mercury is a toxic environmental contaminant that can cause serious health problems. This work describes a new type of eco-friendly three-electrode plastic sensor chip for the determination of trace Hg(II) by means of anodic stripping voltammetry (ASV). The sensor chip is entirely fabricated by injection moulding, which is a sustainable manufacturing method, and consists of three conductive carbon-based electrodes embedded in a plastic holder while the reference electrode is coated with Ag using e-beam evaporation. The sample is spiked with Au(III) which deposits on the working electrode in the form of gold nanoparicles during the analysis; the target Hg(II) co-deposits on the gold nanoparticles forming a Au(Hg) amalgam in situ. The accumulated Hg is stripped off the electrode and quantified by an anodic square wave potential scan. The relevant conditions and the potential interferences are investigated. The limit of detection for Hg(II) is 0.4 µg L-1 and the repeatability at the 20 µg L-1 Hg(III) level (n = 10) is 5.3%. The sensor is applied to water, honey, fish oil and mussel samples with recoveries between 98 and 107%.

Wooden Tongue Depressor Multiplex Saliva Biosensor Fabricated via Diode Laser Engraving.

Since wood is a renewable, biodegradable naturally occurring material, the development of conductive patterns on wood substrates is a new and innovative chapter in sustainable electronics and sensors. Herein, we describe the first wooden (bio)sensing device fabricated via diode laser-induced graphitization. For this purpose, a wooden tongue depressor (WTD) is laser-treated and converted to an electrochemical multiplex biosensing device for oral fluid analysis. A low-cost laser engraver, equipped with a low-power (0.5 W) diode laser, programmably irradiates the surface of the WTD, forming two mini electrochemical cells (e-cells). The two e-cells consist of four graphite electrodes: two working electrodes, a common counter, and a common reference electrode. The two e-cells are spatially separated via programmable pen-plotting, using a commercial hydrophobic marker pen. Proof-of-principle for biosensing is demonstrated for the simultaneous determination of glucose and nitrite in artificial saliva. This wooden electrochemical biodevice is an easy-to-fabricate disposable point-of-care chip with a wide scope of applicability to other bioassays, while it paves the way for the low-cost and straightforward production of wooden electrochemical platforms.

3D Printed Voltammetric Sensor Modified with an Fe(III)-Cluster for the Enzyme-Free Determination of Glucose in Sweat.

In this work, a 3D printed sensor modified with a water-stable complex of Fe(III) basic benzoate is presented for the voltammetric detection of glucose (GLU) in acidic epidermal skin conditions. The GLU sensor was produced by the drop-casting of Fe(III)-cluster ethanolic mixture on the surface of a 3D printed electrode fabricated by a carbon black loaded polylactic acid filament. The oxidation of GLU was electrocatalyzed by Fe(III), which was electrochemically generated in-situ by the Fe(III)-cluster precursor. The GLU determination was carried out by differential pulse voltammetry without the interference from common electroactive metabolites presented in sweat (such as urea, uric acid, and lactic acid), offering a limit of detection of 4.3 µmol L-1. The exceptional electrochemical performance of [Fe3O(PhCO2)6(H2O)3]∙PhCO2 combined with 3D printing technology forms an innovative and low-cost enzyme-free sensor suitable for noninvasive applications, opening the way for integrated 3D printed wearable biodevices.

Mechanical and electrochemical characterization of 3D printed orthodontic metallic appliances after in vivo ageing.

OBJECTIVES: Three-dimensional (3D) printing technology is a promising technique for fabricating custom orthodontic metallic appliances. Aim of this study was to assess the effect of intraoral aging on the mechanical / electrochemical properties of 3D-printed orthodontic metallic appliances. METHODS: Twelve molar orthodontic distalization appliances 3D-printed from cobalt chromium (Co-Cr) alloy were retrieved after intraoral use and twenty blocks fabricated under similar conditions were used as control. The samples' microstructural / elemental composition assessment was assessed with SEM/EDS, while their mechanical properties (modulus of elasticity [EIT], Martens hardness [HM] and the elastic index [ηIT]) were measured by instrumented indentation testing. Finally, the samples' electrochemical features were assessed with a potentiostat-connected cell arrangement in terms of open circuit potential (OCP), corrosion potential (Ez), current density (I300) and breaking potential (Epit). Results were analyzed by t-test / Mann-Whitney test (α = 0.05). RESULTS: The used Co-Cr alloy was found to have a highly homogenous structure with no significant differences between retrieved and new specimens in HM (4037.7 ± 215.6 vs 4090.9 ± 259.8 N/mm2), EIT (120.0 ± 13.2 vs 123.8 ± 12.9 GPa), or nIT (28.4 ± 2.6 vs 28.6 ± 2.9 %) (P > 0.05 in all instances). Metallic surfaces retained the same oxidation tendency and oxide dissolution rate in passive region in both groups (P > 0.05 for OCP, Ez, and I300). However, intraorally-aged specimens had a significantly lower breakdown potential due to degraded protection efficacy of surface oxide (P = 0.003 for Epit). SIGNIFICANCE: The tested 3D-printed Co-Cr orthodontic appliances present clinically-acceptable mechanical properties that remained unaffected by intraoral ageing, which however degraded the protection of surface oxide against pitting corrosion.

Electrochemical characterization of three types of Co-Cr based alloys manufactured by casting and selective laser melting according to ISO 10271.

OBJECTIVE: To characterize the effect of elemental composition and manufacturing process on the electrochemical properties of Co-Cr-Mo, Co-Cr-W and Co-Cr-Mo-W alloys. METHODS: Six Co-Cr based alloys were included in this study. All alloys are Co-Cr based alloys, classified in three different types according to their elemental composition. The first group has Mo as the third alloying element while the second one has W instead of Mo. The third one has both alloying elements. The groups are further divided by the manufacturing process (casting or Selective Laser Melting(SLM)). All groups were subjected to static immersion, open circuit potential, anodic scan, SEM/EDX analysis, static and cyclic tarnish testing according to ISO 10271 requirements. The ionic release was evaluated by inductively coupled plasma mass spectrometry and the results were statistically analyzed by two way ANOVA and Tukey test (a=0.05). RESULTS: No statistical differences were identified for Co-Cr-Mo alloy for all elements and their total ionic release between casting and SLM manufacturing processes, in contrast to significantly lower values for SLM groups for the other two groups. All groups tested demonstrated similar performance in OCP and AS testing while no gross elemental changes before and after AS were identified following EDX analysis. All alloys fulfilled the requirements of tarnish resistance CONCLUSIONS: The ionic release is dependent on alloy type and manufacturing process while all groups were found to fulfill the requirements of international standards for ionic release, corrosion and tarnish resistance and thus an acceptable clinical performance is anticipated.

Plot-on-demand integrated paper-based sensors for drop-volume voltammetric monitoring of Pb(II) and Cd(II) using a bismuth nanoparticle-modified electrode.

The fabrication of fully ink-drawn fluidic electrochemical paper-based analytical devices (ePADs) is reported for the determination of trace Pb(II) and Cd(II) by differential pulse anodic stripping voltammetry (DPASV). The fluidic pattern was formed on the paper substrate using an inexpensive computer-controlled x-y plotter and a commercial hydrophobic marker pen. Then, electrodes were deposited on the devices using a second x-y plotting step with a commercial technical pen filled with a graphite-based conductive ink prepared in house. The fabrication parameters of the ePADs were studied by cyclic voltammetry using the ferro/ferri couple as a probe and by scanning electron microscopy. The ePADs, featuring a bismuth nanoparticle-modified working electrode, were applied to the determination of Pb(II) and Cd(II) by DPASV. The chemical and instrumental conditions were studied. The limits of detection were 3.1 µg L-1 for Cd(II) and 4.5 µg L-1 for Pb(II) whereas the between-device reproducibility (expressed as the % relative standard deviation of the response at 6 different ePADs) was < 14%. Each ePAD requires 120 s to fabricate and costs less than 0.15 € in terms of consumables. The ePADs are suitable for the on-site determination of Pb(II) and Cd(II) in environmental and food samples.

Wearable Electronic Finger for Date Rape Drugs Screening: From "Do-It-Yourself" Fabrication to Self-Testing.

In-house digital fabrication of low-cost sensors that can on-site and rapidly detect adulteration of alcoholic beverages with sedation drugs (known as date rape drugs, (DRDs)) and analgesics is of great importance for everyday consumers and supervisory authorities. DRDs and analgesics are administrated in spirits for "drug-facilitated sexual assault" crimes and for the reduction of the following day hangover caused by low-quality spirits, respectively. This work describes, a novel "do-it-yourself" wearable 3D printed electrochemical finger (e-finger), which enables direct, rapid, and multianalyte self-testing of the main DRDs (flunitrazepam, scopolamine, ketamine) and paracetamol via direct immersing into a spirit shot. The oxygen interference on flunitrazepam detection was alleviated by dissolving an effervescent tablet of vitamin C in the spirit shot, as ascorbic acid serves as a scavenger for dissolved oxygen. The e-finger can be printed in-house at any size by anyone with access to a low-cost domestic 3D printer using a simple, fast, and low-cost printing procedure. The e-finger is addressed by a smartphone-based miniature potentiostat and allows on-the-spot self-checking of the quality and safety of alcoholic spirits, via a single calibration-free voltammetric measurement, readily performed even by untrained end users. The e-finger is a new powerful screening tool in the hands of supervisory authorities to conduct on-site forensic investigations. More importantly, it paves the way toward in-house e-production of "ready-to-use" reliable self-testing devices.

Single-Use Fluidic Electrochemical Paper-Based Analytical Devices Fabricated by Pen Plotting and Screen-Printing for On-Site Rapid Voltammetric Monitoring of Pb(II) and Cd(II).

This work reports the fabrication of integrated electrochemical fluidic paper-based analytical devices (ePADs) using a marker pen drawing and screen-printing. Electrodes were deposited on paper using screen-printing with conductive carbon ink. Then, the desired fluidic patterns were formed on the paper substrate by drawing with a commercial hydrophobic marker pen using an inexpensive computer-controlled x-y plotter. The working electrode was characterized by cyclic voltammetry and scanning electron microscopy. The analytical utility of the electrochemical PADs is demonstrated through electrochemical determination of Pb(II) and Cd(II) by anodic stripping voltammetry. For this purpose, the sample was mixed with a buffer solution and a Bi(III) solution, applied to the test zone of the PAD, the metals were preconcentrated as a bismuth alloy on the electrode surface and oxidized by applying an anodic potential scan. The proposed manufacturing approach enables the large-scale fabrication of fit-for-purpose disposable PADs at low cost which can be used for rapid on-site environmental monitoring.