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.

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.

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.

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.