A sandwich-type electrochemical immunosensor based on Au-rGO composite for CA15-3 tumor marker detection.

A sensitive detection of carbohydrate antigen 15-3 (CA15-3) levels may allow for early diagnosis and monitoring the treatment of breast cancer, but this can only be made in routine clinical practice if low-cost immunosensors are available. In this work, we developed a sandwich-type electrochemical immunosensor capable of rapid detection of CA15-3 with an ultra-low limit of detection (LOD) of 0.08 fg mL-1 within a wide linear concentration range from 0.1 fg mL-1 to 1 µg mL-1. The immunosensor had a matrix of a layer-by-layer film of Au nanoparticles and reduced graphene oxide (Au-rGO) co-electrodeposited on screen-printed carbon electrodes (SPCE). The high sensitivity was achieved by using secondary antibodies (Ab2) labeled with horseradish peroxidase (HRP) in the presence of hydrogen peroxide (H2O2) as signal amplifiers, and hydroquinone (HQ) was used as an electron mediator. The immunosensor was selective for CA15-3 in human serum and artificial saliva samples, robust, and stable to permit storage at 4 °C for more than 30 days. With its high performance, the immunosensor may be incorporated into future point-of-care (POC) devices to determine CA15-3 in distinct biological fluids, including in blood and saliva samples.

Flexible and integrated dual carbon sensor for multiplexed detection of nonylphenol and paroxetine in tap water samples.

Multiplex detection of emerging pollutants is essential to improve quality control of water treatment plants, which requires portable systems capable of real-time monitoring. In this paper we describe a flexible, dual electrochemical sensing device that detects nonylphenol and paroxetine in tap water samples. The platform contains two voltammetric sensors, with different working electrodes that were either pretreated or functionalized. Each working electrode was judiciously tailored to cover the concentration range of interest for nonylphenol and paroxetine, and square wave voltammetry was used for detection. An electrochemical pretreatment with sulfuric acid on the printed electrode enabled a selective detection of nonylphenol in 1.0-10 × 10-6 mol L-1 range with a limit of detection of 8.0 × 10-7 mol L-1. Paroxetine was detected in the same range with a limit of detection of 6.7 × 10-7 mol L-1 using the printed electrode coated with a layer of carbon spherical shells. Simultaneous detection of the two analytes was achieved in tap water samples within 1 min, with no fouling and no interference effects. The long-term monitoring capability of the dual sensor was demonstrated in phosphate buffer for 45 days. This performance is statistically equivalent to that of high-performance liquid chromatography (HPLC) for water analysis. The dual-sensor platform is generic and may be extended to other water pollutants and clinical biomarkers in real-time monitoring of the environment and health conditions. Silver pseudo-reference electrodes for paroxetine (REP) and nonylphenol (REN), working electrodes for paroxetine (WP) and nonylphenol (WN), and auxiliary electrode (AE). USP refers to the University of Sao Paulo. "Red" is reduced form and "Oxi" is oxidized form of analytes.

Adsorption according to the Langmuir-Freundlich model is the detection mechanism of the antigen p53 for early diagnosis of cancer.

Biosensors for early detection of cancer biomarkers normally depend on specific interactions between such biomarkers and immobilized biomolecules in the sensing units. Though these interactions are expected to yield specific, irreversible adsorption, the underlying mechanism appears not to have been studied in detail. In this paper, we show that adsorption explained with the Langmuir-Freundlich model is responsible for detection of the antigen p53 associated with various types of cancers. Irreversible adsorption was proven between anti-p53 antibodies immobilized on the biosensors and the antigen p53, with the adequacy of the Langmuir-Freundlich model being confirmed with three independent experimental methods, viz. polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS), nanogravimetry using a quartz crystal microbalance and electrochemical impedance spectroscopy. The method based on this irreversible adsorption was sufficiently sensitive (limit of detection of 1.4 pg mL(-1)) for early diagnosis of Hodgkin lymphoma, pancreatic and colon carcinomas, and bladder, ovarian and lung cancers, and could distinguish between MCF7 cells containing the antigen p53 from Saos-2 cells that do not contain it.

Simultaneous determination of epinephrine and dopamine by electrochemical reduction on the hybrid material SiO2/graphene oxide decorated with Ag nanoparticles.

This paper describes the synthesis, characterization and applications of a new hybrid material composed of mesoporous silica (SiO2) modified with graphene oxide (GO), SiO2/GO, obtained by the sol-gel process using HF as the catalyst. The hybrid material, SiO2/GO, was decorated with silver nanoparticles (AgNPs) with a size of less than 20 nanometres, prepared directly on the surface of the material using N,N-dimethylformamide (DMF) as the reducing agent. The resulting material was designated as AgNP/SiO2/GO. The Ag/SiO2/GO material was characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) and high-resolution transmission electron microscopy (HR-TEM). A glassy carbon electrode modified with AgNP/SiO2/GO was used in the development of a sensitive electrochemical sensor for the simultaneous determination of epinephrine and dopamine employing electrocatalytic reduction using squarewave voltammetry. Well-defined and separate reduction peaks were observed in PBS buffer at pH 7. No significant interference was seen for primarily biological interferents such as uric acid and ascorbic acid in the detection of dopamine and epinephrine. Our study demonstrated that the resultant AgNP/SiO2/GO-modified electrode is highly sensitive for the simultaneous determination of dopamine and epinephrine, with the limits of detection being 0.26 and 0.27 µmol L(-1), respectively. The AgNP/SiO2/GO-modified electrode is highly selective and can be used to detect dopamine and epinephrine in a human urine sample.

Core-Shell Nanocables Decorated with Carbon Spherical Shells and Silver Nanoparticles for Sensing Ethinylestradiol Hormone in Water Sources and Pills.

The selective, rapid detection of low levels of hormones in drinking water and foodstuffs requires materials suitable for inexpensive sensing platforms. We report on core-shell Ag@C nanocables (NCs) decorated with carbon spherical shells (CSSs) and silver nanoparticles (AgNPs) by using a hydrothermal green approach. Sensors were fabricated with homogeneous, porous films on screen-printed electrodes, which comprised a 115 nm silver core covered by a 122 nm thick carbon layer and CSSs with 168 nm in diameter. NCs and CSSs were also decorated with 10-25 nm AgNPs. The NC/CSS/AgNP sensor was used to detect ethinylestradiol using square wave voltammetry in 0.1 M phosphate buffer (pH 7.0) over the 1.0-10.0 µM linear range with a detection limit of 0.76 µM. The sensor was then applied to detect ethinylestradiol in tap water samples and a contraceptive pill with recovery percentages between 93 and 101%. The high performance in terms of sensitivity and selectivity for hormones is attributed to the synergy between the carbon nanomaterials and AgNPs, which not only increased the sensor surface area and provided sites for electron exchange but also imparted an increased surface area.

Comparing atrazine and cyanuric acid electro-oxidation on mixed oxide and boron-doped diamond electrodes.

The breakdown of pesticides has been promoted by many methods for clean up of contaminated soil and wastewaters. The main goal is to decrease the toxicity of the parent compound to achieve non-toxic compounds or even, when complete mineralization occurs, carbon dioxide and water. Therefore, electrochemical degradation (potentiostatic and galvanostatic) of both the pesticide atrazine and cyanuric acid (CA) at boron-doped diamond (BDD) and Ti/Ru0.3Ti0.7O2 dimensionally stable anode (DSA) electrodes, in different supporting electrolytes (NaCl and Na2SO4), is presented with the aim of establishing the influence of the operational parameters on the process efficiency. The results demonstrate that both the electrode material and the supporting electrolyte have a strong influence on the rate of atrazine removal. In the chloride medium, the rate of atrazine removal is always greater than in sulfate under all conditions employed. Furthermore, in the sulfate medium, atrazine degradation was significant only at the BDD electrode. The total organic carbon (TOC) load decreased by 79% and 56% at the BDD and DSA electrodes, respectively, in the chloride medium. This trend was maintained in the sulfate medium but the TOC removal was lower (i.e. 33% and 13% at BDD and DSA electrodes, respectively). CA, a stable atrazine degradation intermediate, was also studied and it is efficiently removed using the BDD electrode in both media, mainly when high current densities are employed. The use of the BDD electrode in the chloride medium not only degrades atrazine but also mineralized cyanuric acid leading to the higher TOC removal.

Optimized paper-based electrochemical sensors treated in acidic media to detect carbendazim on the skin of apple and cabbage.

Wearable sensors such as those made with paper are needed for non-destructive routine analysis of pesticides on plants, fruits, and vegetables. Herein we report on electrochemical sensors made with screen-printed carbon electrodes on kraft and parchment papers to detect the fungicide carbendazim. A systematic optimization was performed to find that electrochemical sensors on kraft paper treated in an acidic medium led to the highest performance, with a detection limit of 0.06 µM for carbendazim. The enhanced sensitivity for this sensor was attributed to the porous nature of kraft paper, which allowed for a large electrode surface area, and to the carboxylic groups formed during electrochemical activation. As a proof-of-concept, the electrochemical sensor attached to the skin of apple and cabbage was used to detect carbendazim with the same performance as the gold standard method, thus demonstrating that the sensor can be used in the farm and on supermarket shelves.

Sustainable plant-wearable sensors for on-site, rapid decentralized detection of pesticides toward precision agriculture and food safety.

The synergy between eco-friendly biopolymeric films and printed devices leads to the production of plant-wearable sensors for decentralized analysis of pesticides in precision agriculture and food safety. Herein, a simple method for fabrication of flexible, and sustainable sensors printed on cellulose acetate (CA) substrates has been demonstrated to detect carbendazim and paraquat in agricultural, water and food samples. The biodegradable CA substrates were made by casting method while the full electrochemical system of three electrodes was deposited by screen-printing technique (SPE) to produce plant-wearable sensors. Analytical performance was assessed by differential pulse (DPV) and square wave voltammetry (SWV) in a linear concentration range between 0.1 and 1.0 µM with detection limits of 54.9 and 19.8 nM for carbendazim and paraquat, respectively. The flexible and sustainable non-enzymatic plant-wearable sensor can detect carbendazim and paraquat on lettuce and tomato skins, and also water samples with no interference from other pesticides. The plant-wearable sensors had reproducible response being robust and stable against multiple flexions. Due to high sensitivity and selectivity, easy operation and rapid agrochemical detection, the plant-wearable sensors can be used to detect biomarkers in human biofluids and be used in on-site analysis of other hazardous chemical substances.

Label-Free Electrochemical Immunosensor Made with Tree-like Gold Dendrites for Monitoring 25-Hydroxyvitamin D3 Metabolite.

Flexible, fully printed immunosensors can meet the requirements of precision nutrition, but this demands optimized molecular architectures to reach the necessary sensitivity. Herein, we report on flexible and label-free immunosensor chips made with tree-like gold dendrites (AuDdrites) electrochemically formed by selective desorption of l-cysteine (L-cys) on (111) gold planes. Electrodeposition was used because it is scalable and cost-effective for a rapid, direct growth of Au hyperbranched dendritic structures. The 25-hydroxyvitamin D3 (25(OH)D3) metabolite was detected within 15 min with a limit of detection (LOD) of 0.03 ng mL-1. This high performance was possible due to the careful optimization of the electroactive layer and working conditions for square wave voltammetry (SWV). Electrocrystallization was manipulated by controlling the deposition potential and the molar ratio between HAuCl4 and L-cys. Metabolite detection was performed on human serum and saliva samples with adequate recovery between 97% and 100%. The immunosensors were stable and reproducible, unresponsive to interference from other molecules in human serum and saliva. They can be extended for use as wearable sensors with their mechanical flexibility and possible customization.

Photocatalysis of TiO2 Sensitized with Graphitic Carbon Nitride and Electrodeposited Aryl Diazonium on Screen-Printed Electrodes to Detect Prostate Specific Antigen under Visible Light.

We report on a photoelectrochemical (PEC) device to detect prostatic-specific antigen (PSA) under visible LED light irradiation within the point-of-care (POC) paradigm. The device consists of a 3D printed miniaturized photoelectrochemical system and a disposable PEC immunosensor made with screen-printed carbon electrodes (SPCEs). The SPCEs were coated with nickel single atoms anchored on graphitic carbon nitride (Ni-gC3N4), titanium dioxide nanoparticles (TiO2), and aryl diazonium salt prepared from p-aminobenzoic acid. The electrodeposited aryl diazonium on Ni-gC3N4/TiO2 decreased the recombination of photogenerated charge carriers, leading to a 3.1-fold increase in the photocurrent compared to pure TiO2. This functionalization strategy provides carboxylic groups to anchor antibodies via the carbodiimide reaction, which may be extended to any other type of immunosensor. Under optimal conditions, the PEC immunosensor was able to detect PSA from 10-16 to 10-8 g mL-1 with a detection limit of 0.06 fg mL-1. The device robustness was confirmed with reproducibility and stability tests. PSA could also be detected in human serum samples, which demonstrates the potential of the PEC immunosensor for clinical diagnosis.

Wearable sensors made with solution-blow spinning poly(lactic acid) for non-enzymatic pesticide detection in agriculture and food safety.

On-site monitoring the presence of pesticides on crops and food samples is essential for precision and post-harvest agriculture, which demands nondestructive analytical methods for rapid, low-cost detection that is not achievable with gold standard methods. The synergy between eco-friendly substrates and printed devices may lead to wearable sensors for decentralized analysis of pesticides in precision agriculture. In this paper we report on a wearable non-enzymatic electrochemical sensor capable of detecting carbamate and bipyridinium pesticides on the surface of agricultural and food samples. The low-cost devices (

Low-cost bacterial nanocellulose-based interdigitated biosensor to detect the p53 cancer biomarker.

Low-cost sensors to detect cancer biomarkers with high sensitivity and selectivity are essential for early diagnosis. Herein, an immunosensor was developed to detect the cancer biomarker p53 antigen in MCF7 lysates using electrical impedance spectroscopy. Interdigitated electrodes were screen printed on bacterial nanocellulose substrates, then coated with a matrix of layer-by-layer films of chitosan and chondroitin sulfate onto which a layer of anti-p53 antibodies was adsorbed. The immunosensing performance was optimized with a 3-bilayer matrix, with detection of p53 in MCF7 cell lysates at concentrations between 0.01 and 1000 Ucell. mL-1, and detection limit of 0.16 Ucell mL-1. The effective buildup of the immunosensor on bacterial nanocellulose was confirmed with polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS) and surface energy analysis. In spite of the high sensitivity, full selectivity with distinction of the p53-containing cell lysates and possible interferents required treating the data with a supervised machine learning approach based on decision trees. This allowed the creation of a multidimensional calibration space with 11 dimensions (frequencies used to generate decision tree rules), with which the classification of the p53-containing samples can be explained.

Biomimetic electrochemical sensors: New horizons and challenges in biosensing applications.

The urge to meet the ever-growing needs of sensing technology has spurred research to look for new alternatives to traditional analytical methods. In this scenario, the glucometer is the flagship of commercial electrochemical sensing platforms, combining selectivity, reliability and portability. However, other types of enzyme-based biosensors seldom achieve the market, in spite of the large and increasing number of publications. The reasons behind their commercial limitations concern enzyme denaturation, and the high costs associated with procedures for their extraction and purification. In this sense, biomimetic materials that seek to imitate the desired properties of natural enzymes and biological systems have come out as an appealing path for robust and sensitive electrochemical biosensors. We herein portray the historical background of these biomimicking materials, covering from their beginnings until the most impactful applications in the field of electrochemical sensing platforms. Throughout the discussion, we present and critically appraise the major benefits and the most significant drawbacks offered by the bioinspired systems categorized as Nanozymes, Synzymes, Molecularly Imprinted Polymers (MIPs), Nanochannels, and Metal Complexes. Innovative strategies of fabrication and challenging applications are further reviewed and evaluated. In the end, we ponder over the prospects of this emerging field, assessing the most critical issues that shall be faced in the coming decade.

Development and validation of an advanced electrochemical sensor for the fast and cheap determination of hydrochlorothiazide in urine samples using the Monte-Carlo method for uncertainty evaluation.

This work describes the development, optimization, and validation of an electrochemical method for the determination of hydrochlorothiazide (HCTZ) in urine. The method allows fast, cheap and reliable determinations of recent administrations of this diuretic that can be used in doping control in sport. The response of the sensor was determined by differential pulse voltammetry (DPV). The glassy carbon electrode was modified with multiwall carbon nanotubes (MWCNT) and gold nanoparticles. The sensor is calibrated in the analysed sample matrix by the cumulative standard addition method. The method validation was based on the bottom-up evaluation of the measurement uncertainty were components were combined using the Monte Carlo Method (MCM) applicable with no restrictions regarding components uncertainty value and measurement function linearity. The developed metrological models were implemented in MS-Excel spreadsheets. The adequacy of the electrochemical measurements was assessed by comparing their relative standard uncertainty with a target value of 20% and by evaluating the compatibility of measurements with determinations performed by a reference procedure. The tools developed for the construction and optimization of working electrodes are applicable to measurements of other analytes and matrices. The used cumulative standard addition method and respective measurement uncertainty models are applicable to any kind of non-destructive chemical measurement of a solution.

Electrocatalytic Oxidation of Methanol, Ethanol, and Glycerol on Ni(OH)2 Nanoparticles Encapsulated with Poly[Ni(salen)] Film.

This study describes a systematic investigation of the electrocatalytic activity of poly[Ni(salen)] films, as catalysts for the electro-oxidation of Cn alcohols (Cn = methanol, ethanol, and glycerol) in alkaline medium. The [Ni(salen)] complex was electropolymerized on a glassy carbon surface and electrochemically activated in NaOH solution by cyclic voltammetry. X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy results indicate that during the activation step the polymeric film hydrolyzes, leading to the formation of ß-Ni(OH)2 spherical nanoparticles, with an average size of 2.4 ± 0.5 nm, encapsulated with the poly[Ni(salen)] film. Electrochemical results obtained together with the in situ Fourier transform infrared spectroscopy confirm that the electro-oxidation of methanol, ethanol, and glycerol occurs by involving a cycling oxidation of ß-Ni(OH)2 with the formation of ß-NiOOH species, followed by the charge transfer to the alcohols, which regenerates ß-Ni(OH)2. Analyses of the oxidation products at low potentials indicate that the major product obtained during the oxidation of methanol and glycerol is the formate, while the oxidation of ethanol leads to the formation of acetate. On the other hand, at high potentials (E = 0.6 V), there is evidence that the oxidation of Cn alcohols leads to carbonate ions as an important product.

Determination of Parathion and Carbaryl Pesticides in Water and Food Samples Using a Self Assembled Monolayer /Acetylcholinesterase Electrochemical Biosensor.

An acetylcholinesterase (AchE) based amperometric biosensor was developed by immobilisation of the enzyme onto a self assembled modified gold electrode. Cyclic voltammetric experiments performed with the SAM-AchE biosensor in phosphate buffer solutions (pH = 7.2) containing acetylthiocholine confirmed the formation of thiocholine and its electrochemical oxidation at Ep = 0.28 V vs Ag/AgCl. An indirect methodology involving the inhibition effect of parathion and carbaryl on the enzymatic reaction was developed and employed to measure both pesticides in spiked natural water and food samples without pre-treatment or pre-concentration steps. Values higher than 91-98.0% in recovery experiments indicated the feasibility of the proposed electroanalytical methodology to quantify both pesticides in water or food samples. HPLC measurements were also performed for comparison and confirmed the values measured amperometrically.

Functionalized polyacrylamide as an acetylcholinesterase-inspired biomimetic device for electrochemical sensing of organophosphorus pesticides.

A plethora of publications has continuously reported electrochemical biosensors for detection of pesticides. However, those devices rarely accomplish commercial application due to technical issues associated with the lack of stability and high cost of the biological recognition element (enzyme). Alternatively, the biomimetic catalysts have arisen as a candidate for application in electrochemical biosensors to overcome the enzymatic drawbacks, combining low cost scalable materials with superior stability. Herein, for the first time, we propose a biomimetic biosensor for organophosphorus pesticide detection employing a functionalized polyacrylamide, polyhydroxamicalkanoate (PHA), which mimics the performance of the acetylcholinesterase (AChE) enzyme. The PHA bears functional groups inserted along its backbone chain working as active sites. Thereby, PHA was immobilized on screen printed electrodes (SPE) through a blend formation with poly(ethylene glycol) methyl ether (mPEG) to prevent its leaching out from the surface. Under optimum conditions, the biomimetic sensor was employed for the amperometric detection of paraoxon-ethyl, fenitrothion and chlorpyrifos ranging from 1.0 and 10.0µmolL-1 with a limit of detection of 0.36µmolL-1, 0.61µmol L-1, and 0.83µmolL-1, respectively. Typical AChE-based interfering species did not affect the PHA performance, which endorsed its superior behavior. The proposed biomimetic biosensor, denoted as SPE/PHA/mPEG, represents a significant advance in the field, offering a new path for low cost devices by means of an artificial enzyme, simple configuration and superior stability. Moreover, the biosensor performance can be further improved by modifying the electrode surface to enhance electronic transfer rate.

Electrochemical oxidation of benzene on boron-doped diamond electrodes.

This work presents an electrochemical investigation of the benzene oxidation process in aqueous solution on boron-doped diamond (BDD) electrodes. Additionally, in order to determine the main products generated during the oxidation process, electrolysis and high performance liquid chromatography experiments were carried out. The complete degradation of this compound was performed aiming to a further application in waste water treatment. The cyclic voltammetry studies indicate that benzene is irreversibly oxidized in acid medium (H2SO4 0.5 M) on the BDD electrode surface at 2.0 V versus Ag/AgCl in a diffusion controlled process. During the cycling, other products are generated, and a pair of peaks was observed that can be associated with the oxi-reduction of anyone of the following species: hydroquinone, benzoquinone, resorcinol or catechol. The electrolysis experiments were carried out at 2.4 and 2.5 V on the BDD electrode surface in a solution containing 1x10(-2) M of benzene (below the saturation concentration in aqueous solution), for 3 and 5 h, respectively. The main products measured were: hydroquinone, resorcinol, p-benzoquinone, catechol and phenol. The complete electrochemical benzene degradation was performed in the electrolysis experiments using a rotating BDD disc electrode (2.5 V for 5 h) and the main products detected were all measured at concentrations lower than 10(-5) M in this condition. The boron-doped diamond electrode had proved to be a valuable tool for the electrochemical degradation of the benzene, a very stable chemical compound.

Decoration of reduced graphene oxide with rhodium nanoparticles for the design of a sensitive electrochemical enzyme biosensor for 17ß-estradiol.

A novel nanocomposite material consisting of reduced graphene oxide/Rh nanoparticles was prepared by a one-pot reaction process. The strategy involved the simultaneous reduction of RhCl3 and graphene oxide with NaBH4 and the in situ deposition of the metal nanoparticles on the 2D carbon nanomaterial planar sheets. Glassy carbon electrode coated with this nanocomposite was employed as nanostructured support for the cross-linking of the enzyme laccase with glutaraldehyde to construct a voltammperometric biosensor for 17ß-estradiol in the 0.9-11 pM range. The biosensor showed excellent analytical performance with high sensitivity of 25.7AµM-1cm-1, a very low detection limit of 0.54pM and high selectivity. The biosensor was applied to the rapid and successful determination of the hormone in spiked synthetic and real human urine samples.

Sensitive detection of estriol hormone in creek water using a sensor platform based on carbon black and silver nanoparticles.

We report the electrochemical detection of estriol using carbon black nanoballs (CNB) decorated with silver nanoparticles (AgNP) as electrode material. Homogeneous, porous films on glassy carbon electrodes (GCE) were obtained, with diameters of 20 - 25nm for CNB and 5 - 6nm for AgNP. CNB/AgNP electrodes had increased conductivity and electroactive area in comparison with bare GCE and GCE/CNB, according to cyclic voltammetry and electrochemical impedance spectroscopy. The oxidation potential peak was also down shifted by 93mV, compared to the bare GC electrode. Differential pulse voltammetry data were obtained in 0.1molL-1 PBS (pH 7.0) to detect estriol without the purification step, in the linear range between 0.2 and 3.0µmolL-1 with detection and quantification limits of 0.16 and 0.5µmolL-1 (0.04 and 0.16mgL-1), respectively. The sensor was used to detect estriol in a creek water sample with the same performance as in the official methodology based on high performance liquid chromatography.