A nickel nanoparticle/nafion-graphene oxide modified screen-printed electrode for amperometric determination of chemical oxygen demand

An integrated smartphone-based electrochemical detection system for highly sensitive and on-site detection of chemical oxygen demand by copper-cobalt bimetallic oxide-modified electrode

A portable and integrated electrochemical detection system has been constructed for on-site and real-time detection of chemical oxygen demand (COD). The system mainly consists of four parts: (i) sensing electrode with a copper-cobalt bimetallic oxide (CuCoOx)-modified screen-printed electrode; (ii) an integrated electrochemical detector for the conversion, amplification, and transmission of weak signals; (iii) a smartphone installed with a self-developed Android application (APP) for issuing commands, receiving, and displaying detection results; and (iv) a 3D-printed microfluidic cell for the continuous input of water samples. Benefiting from the superior catalytic capability of CuCoOx, the developed system shows a high detection sensitivity with 0.335 μA/(mg/L) and a low detection limit of 5.957 mg/L for COD determination and possessing high anti-interference ability to chloride ions. Moreover, this system presents good consistency with the traditional dichromate method in COD detection of actual water samples. Due to the advantages of cost effectiveness, portability, and point-of-care testing, the system shows great potential for water quality monitoring, especially in resource-limited remote areas.

Research on Micro-Quantitative Detection Technology of Simulated Waterbody COD Based on the Ozone Chemiluminescence Method

Chemical oxygen demand (COD), reflecting the degree of waterbody contaminated by reduction substances, is an important parameter for water quality monitoring. The existing measurement method of waterbody COD takes time and is a complex system, which cannot meet the real-time monitoring requirements of river pollution indicators. We developed the vortex t-structure microfluidic detection chip with the help of microfluidic technology and designed the COD detection system with a high integration degree based on the principle of ozone chemiluminescence, and we have also carried out research on a waterbody COD quantitative detection test. The test results show that the detection chip can generate quantitative and controllable ozone-based bubbles; it also shows the advantages of a simple system and short test time without environmental pollution, which provides some technical support for the online real-time monitoring of river water quality.

A batch microfabrication of a microfluidic electrochemical sensor for rapid chemical oxygen demand measurement

Chemical oxygen demand (COD) is one of the key water quality parameters in environmental monitoring. However, fabricating a COD sensor with the characteristic of batch-processing and rapid measurement is always a challenging issue. This paper reports a microfluidic electrochemical sensor for the organic matter measurement based on advanced oxidization within a fixed microvolume detection chamber by a microfabrication technique/MEMS. By fabricating a silicon-based Ag/AgCl reference electrode and employing PbO₂ as the working electrode with Pt as the counter electrode, we verified the superiority of the as-fabricated sensor by continuous potassium acid phthalate detection; an acceptable limit of detection (4.17 mg L^-1-200 mg L^-1), a low limit of detection (2.05 mg L^-1), a desirable linearity (R² = 0.982) and relative stability at different pH values and Cl^- concentrations was witnessed. Particularly, a shorter detection time (2 s) was witnessed for the as-proposed sensor compared with traditional organic matter measurement methods. Each sensing process takes only 2 seconds for sensing because a micro-cavity with a volume of 2.5 μL was fabricated and used as a detection pool. Moreover, as the sensor was fabricated by a mass-production technique, potential response consistency of multiple sensors was expected and was verified via a series of parallel experiments. In this paper, a miniaturized (8 mm × 10 mm), low-cost and reliable COD sensor was designed and fabricated by MEMS, and it provided a core sensor component for construction of an online water environment monitoring network to meet the substantial demand for COD sensors in the Internet of Things (IOT) era.

Construction of a novel electrochemical biosensor based on a mesoporous silica/oriented graphene oxide planar electrode for detecting hydrogen peroxide

A constant magnetic field (CMF) was used to arrange the orientation of graphene oxide (GO) which was modified on a self-made screen-printed electrode. We evaluated the efficiency of this method for potential analytical application towards the sensing of hydrogen peroxide (H2O2). Mesoporous silica (MS)-encapsulated horseradish peroxidase (HRP) was immobilized on the electrode with vertically arranged GO to construct an H2O2 sensor (denoted as CMF/GO/HRP@MS). The linear range of the response of the CMF/GO/HRP@MS sensor to H2O2 was 0.1-235 μM, and the detection limit was as low as 0.01 μM. The results demonstrated that the vertical arrangement of GO resulting from the CMF on the electrode surface could increase the electron transfer rate. The excellent selectivity and anti-interference ability of this sensor to H2O2 in physiological samples may be attributed to the synergistic effect of mesoporous silica, GO and constant magnetic field.

Heparin sensing based on multisite-binding induced highly ordered perylene nanoaggregates

Heparin sensing based on highly ordered perylene nanoaggregates with ultra-low fluorescence and the use of host–guest complexes to improve the sensitivity.

A Self-Supported CuO/Cu Nanowire Electrode as Highly Efficient Sensor for COD Measurement

A self-supported CuO/Cu nanowire electrode (CuO/CuNWE), which was prepared by annealing Cu nanowires to form a porous Cu nanowire electrode (CuNWE) and then anodizing the as-prepared CuNWE in alkaline medium to generate Cu(OH)₂ nanowires followed by calcination, was employed for chemical oxygen demand (COD) determination using cyclic voltammetry (CV). The structure and electrochemical behavior of the CuO/CuNWE were investigated by scanning electron microscopy, X-ray diffraction, and CV. The results indicated that the as-synthesized CuO/CuNWE, in which CuO nanowires with a length of several micrometers and a diameter of 100 to 300 nm could be found, was stable in alkaline medium and more electrocatalytically active for oxidizing a wide range of organic compounds in comparison with the CuNWE. Under optimized alkaline concentration and scan rate, the CuO/CuNWE exhibited a good performance for COD measurement, with a linear range of 5 to 1153 mg L⁻¹, a sensitivity of 2.46× 10⁻² mA /(mg L⁻¹), and a detection limit of about 2.3 mg L⁻¹. In addition, an excellent correlation was observed in COD values obtained by our method and the classic dichromate method (r = 0.9995, p < 0.01, n = 11). Finally, our method was successfully used to measure the COD values in real water samples, showing great potential for practical application in water pollution control.

Synergistic effect of a cobalt fluoroporphyrin and graphene oxide on the simultaneous voltammetric determination of catechol and hydroquinone

Graphene oxide (GO) was modified with the cobalt(II) and zinc(II) complexes (CoTFPP and ZnTFPP) of 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin in order to improve the electrocatalytic activity of GO towards catechol (CC) and hydroquinone (HQ). It is found that the CoTFPP-modified GO on a glassy carbon electrode (GCE) displays the highest electrocatalytic activity. The response to CC (at 0.14 V vs. SCE) is linear in the 1-220 μM concentration range. The response to HQ (at 0.04 V vs. SCE) extends from 1 μM to 200 μM. The sensitivity and detection limits are 10.40 μA∙μM^-1∙cm^-2 and 0.17 μM for CC, and 8.40 μA∙μM^-1∙cm^-2 and 0.21 μM for HQ. Experimental results indicate that the Co(II) and Zn(II) ions in the porphyrins positively affect the electron transfer rate in the hybrid materials. The GCE modified with CoTFPP/GO was successfully applied to the simultaneous determination of CC and HQ in spiked samples of tap and lake water. Graphical abstract Schematic presentation of a voltammetric method for simultaneous determination of catechol (CC) and hydroquinone (HQ). It is based on the use of a cobalt (II) fluoroporphyrin (CoTFPP) functionalized graphene oxide (GO) hybrid.

A Nafion Film Cover to Enhance the Analytical Performance of the CuO/Cu Electrochemical Sensor for Determination of Chemical Oxygen Demand

We modified and evaluated the performance of a CuO/Cu electrochemical electrode for chemical oxygen demand (COD) determination by covering it with a Nafion (Nf) film. The resulting modified CuONf/Cu electrode sensor was used for the electrochemical determination of COD in river, slaughterhouse and estuarine water samples in order to evaluate its performance for this particular task. It was compared with the CuO/Cu sensor with no Nafion. The main electrochemical characteristics of interest, resistance, sensitivity, accuracy and reproducibility, were assessed by means of Linear Sweep Voltammetry using glucose as a standard. Results of these essays indicate that the procedure used produced smooth and firmly attached Nf films covering the whole copper surface. This sensor was shown to be resistant to interferences and effective in electro-oxidation of a wide range of organic compounds and therefore very useful for COD determination. Using the newly developed CuONf/Cu electrode an analytical linear range of 50 to 1000 mg·L⁻¹ COD, with a detection limit of 2.11 mg·L⁻¹ (n = 6) COD was achieved. The comparison shows that the CuONf/Cu sensor is more appropriate for COD determination than its counterpart with no Nafion.

A colorimetric and fluorescent dual-modal displacement probe based on host-assisted modulation of intramolecular charge transfer and deaggregation

A new colorimetric and fluorescent dual-modal displacement probe based on a supramolecular host–guest complex involving macrocycle encapsulation that modulated intramolecular charge transfer and deaggregation.