Voltammetric co-determination of lead and copper in gunshot residue based on iron oxide particle/spent coffee grounds-modified electrode.

A novel electrochemical sensor was developed for the detection of lead (Pb) and copper (Cu) ions using spent coffee grounds decorated with iron oxide particles (FeO/SCG). The FeO-decorated SCG was used to modify a glassy carbon electrode (GCE). FeO, SCG, and FeO/SCG were characterized by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The electrochemical properties of the modified electrode were characterized by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The electrode modifications increased the active surface area and electron transfer and enhanced the accumulation of the target analyte. In the optimal condition, the developed sensor showed linear ranges of 1.0 µg L-1-0.05 mg L-1 and 0.05 mg L-1-0.8 mg L-1 for Pb2+ and 5.0 µg L-1-0.1 mg L-1 and 0.1 mg L-1-0.8 mg L-1 for Cu2+. The limit of detection (LOD) was 1.0 µg L-1 for Pb2+ and 2.4 µg L-1 for Cu2+. The developed sensor was successfully applied to determine Pb2+ and Cu2+ in bullet holes. The results were in good agreement with those obtained by inductively coupled plasma optical emission spectrometry (ICP/OES).

Waste DVD polycarbonate substrate for screen-printed carbon electrode modified with PVP-stabilized AuNPs for continuous free chlorine detection.

An electrochemical free chlorine sensor was developed by modifying a lab-made screen-printed carbon electrode (SPCE) with gold nanoparticles synthesized with polyvinylpyrrolidone (AuNPs-PVP). The electrode was made by screen printing carbon ink on a waste digital versatile disc (SPC-wDVD). PVP was used to stabilize AuNPs. Scanning electron microscopy showed that AuNPs aggregated without the stabilizer. The electrochemical behavior of the SPC-wDVD was evaluated by comparison with commercial SPCEs from two companies. Electrochemical characterization involved cyclic voltammetry and electrochemical impedance spectroscopy. The detection of free chlorine in water samples was continuous, facilitated by a flow-injection system. In the best condition, the developed sensor exhibited linearity from 0.25 to 3.0 and 3.0 to 500 mg L-1. The limit of detection was 0.1 mg L-1. The stability of the sensor enabled the detection of free chlorine at least 475 times with an RSD of 3.2 %. The AuNPs-PVP/SPC-wDVD was able to detect free chlorine in drinking water, tap water and swimming pool water. The agreement between the results obtained with the proposed method and the standard spectrophotometric method confirmed the precision of the developed sensor.

Synthesis of flower-like ZnO nanoparticles for label-free point of care detection of carcinoembryonic antigen.

In this work, flower-like ZnO nanoparticles (ZnONPs) were synthesized using zinc nitrate (Zn(NO3)2 6H2O) as a precursor with KOH. The morphology of the ZnONPs was controlled by varying the synthesis temperature at 50, 75 and 95 °C. The morphology and structure of ZnONPs were characterized using Scanning Electron Microscopy, and X-Ray Diffraction and Brunauer-Emmett Teller analysis. ZnONPs were successfully synthesized by a simple chemical precipitation method. A synthesis temperature of 75 °C produced the most suitable flower-like ZnONPs, which were combined with graphene nanoplatelets to develop a label-free electrochemical immunosensor for the detection of the colon cancer biomarker carcinoembryonic antigen in human serum. Under optimum conditions, the developed immunosensor showed a linear range of 0.5-10.0 ng mL-1 with a limit of detection of 0.44 ng mL-1. The label-free electrochemical immunosensor exhibited good selectivity, reproducibility, and repeatability, and recoveries were excellent. The immunosensor is used with a Near-Field Communication potentiostat connected to a smartphone to facilitate point-of-care cancer detection in low-resource locations.

A dual-electrode label-free immunosensor based on in situ prepared Au-MoO3-Chi/porous graphene nanoparticles for point-of-care detection of cholangiocarcinoma.

A novel label-free electrochemical immunosensor was prepared for the detection of carbohydrate antigen 19-9 (CA19-9) and carcinoembryonic antigen (CEA) as biomarkers of cholangiocarcinoma (CCA). A nanocomposite of gold nanoparticles, molybdenum trioxide, and chitosan (Au-MoO3-Chi) was layer-by-layer assembled on the porous graphene (PG) modified a dual screen-printed electrode using a self-assembling technique, which increased surface area and conductivity and enhanced the adsorption of immobilized antibodies. The stepwise self-assembling procedure of the modified electrode was further characterized morphologically and functionally. The electroanalytical detection of biomarkers was based on the interaction between the antibody and antigen of each marker via linear sweep voltammetry using ferrocyanide/ferricyanide as an electrochemical redox indicator. Under optimized conditions, the fabricated immunosensor showed linear relationships between current change (ΔI) and antigen concentrations in two ranges: 0.0025-0.1 U mL-1 and 0.1-1.0 U mL-1 for CA19-9, and 0.001-0.01 ng mL-1 and 0.01-1.0 ng mL-1 for CEA. The limits of detection (LOD) were 1.0 mU mL-1 for CA19-9 and 0.5 pg mL-1 for CEA. Limits of quantitation (LOQ) were 3.3 mU mL-1 for CA19-9 and 1.6 pg mL-1 for CEA. The selectivity of the developed immunosensor was tested on mixtures of antigens and was then successfully applied to determine CA19-9 and CEA in human serum samples, producing satisfactory results consistent with the clinical method.

A portable electrochemical immunosensor for ovarian cancer uses hierarchical microporous carbon material from waste coffee grounds.

A simple label-free electrochemical immunosensor for ovarian cancer (OC) detection was developed using a hierarchical microporous carbon material fabricated from waste coffee grounds (WCG). The analysis method exploited near-field communication (NFC) and a smartphone-based potentiostat. Waste coffee grounds were pyrolyzed with potassium hydroxide and used to modify a screen-printed electrode. The modified screen-printed electrode was decorated with gold nanoparticles (AuNPs) to capture a specific antibody. The modification and immobilization processes were characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The sensor had an effective dynamic range of 0.5 to 50.0 U mL-1 of cancer antigen 125 (CA125) tumor marker with a correlation coefficient of 0.9995. The limit of detection (LOD) was 0.4 U mL-1. A comparison of the results obtained from human serum analysis with the proposed immunosensor and the results obtained from the clinical method confirmed the accuracy and precision of the proposed immunosensor.

Disposable label-free electrochemical immunosensor based on prussian blue nanocubes for four breast cancer tumor markers.

A compact and low-cost multi-electrode array (MEA) is presented, comprising four working electrodes with shared reference and auxiliary electrodes. Prussian blue was electrodeposited on the MEA using chronoamperometry with a positive potential of 0.3 V. Prussian blue nanocubes (PBNCs) were formed, which were observed using scanning electron microscopy. The precision of the four working electrodes was demonstrated using ferric/ferro cyanide (RSD <5.8%). The surface roughness of the working electrodes of the fabricated MEA was investigated by atomic force microscopy and compared with that of a commercial MEA. The PBNCs were the platform for a label-free immunosensor that detected four breast cancer tumor markers (CEA, CA125, CA153, and CA199) using specific antibodies. The processes of antibody immobilization were investigated using cyclic voltammetry and electrochemical impedance spectroscopy. The immunosensor was evaluated using real human serum samples, yielding acceptable recoveries (95.1-104.1%, RSD < 3.9) for the four tumor markers. These findings confirmed that our label-free immunosensor based on PBNCs could be a promising device for point-of-care testing and could pave the way for the establishment of new platforms for the screening of various breast cancer tumor markers.

Extraction and electrochemical detection for quantification of trace-level DNA.

A novel strategy was developed to extract, detect, and quantify trace-level DNA. For the extraction step, a composite of methylene blue (MB), poly(acrylic acid) (PAA), and modified iron oxide magnetic nanoparticles (IOMNPs) (PAA/IOMNPs) was used to adsorb DNA from the sample. MB-PAA/IOMNPs with adsorbed DNA were then separated from the solution with an external magnet and MB-DNA was eluted from PAA/IOMNPs with acetic acid. In the detection step, MB-DNA was adsorbed on the surface of 3-aminopropyltriethoxysilane (APTES)-modified glassy carbon electrode via electrostatic force. DNA was quantified by measuring the oxidation peak of MB at a potential -0.13 V vs. Ag/AgCl using differential pulse voltammetry. Under the optimal experimental conditions, the DNA sensor showed linear ranges from 0.001 to 0.005 pg µL-1, 0.005 to 0.070 pg µL-1, and 0.070 to 0.400 pg µL-1 and a limit of detection of 0.87 fg µL-1. The proposed sensor detected trace DNA in real samples with recoveries that ranged from 80.4 to 90.4%.

Multiplexed label-free electrochemical immunosensor for breast cancer precision medicine.

A novel multiplexed label-free electrochemical immunosensor was fabricated using graphene/methylene blue-chitosan/antibody and bovine serum albumin on indium tin oxide glass electrode for the simultaneous determination of three types of tumor markers including carcinoembryonic antigen (CEA), cancer antigens 153 (CA153), and cancer antigen 125 (CA125). Cyclic voltammetry, electrochemical impedance spectroscopy, and scanning electron microscopy were employed to monitor each fabrication step. Under the optimized experiment conditions, the immunosensor exhibited good reproducibility and selectivity with linear ranges of 0.10-1.00 pg mL-1 and 1.00-100.00 pg mL-1 for CEA, 0.10-2.50 mU mL-1 and 2.50-100.00 mU mL-1 for CA153, 0.10-2.50 mU mL-1 and 2.50-100.00 mU mL-1 for CA125, a detection limit of 0.04 pg mL-1 for CEA, 0.04 mU mL-1 for CA153, and 0.04 mU mL-1 for CA125. This electrochemical immunosensor was successfully applied to detect three tumor markers in blood serum samples with good recoveries. The reliability of the electrochemical immunosensor to detect three tumor markers in blood serum samples was in good agreement (P > 0.05) with that of the enzyme-linked fluorescent assay method.