We have developed a novel mediated biochemical oxygen demand (BOD) biosensor based on immobilized Bacillus subtilis (B. subtilis) on three-dimensional (3D) porous graphene-polypyrrole (rGO-PPy) composite. The 3D porous rGO-PPy composite was prepared using hydrothermal method following with electropolymerization. Then the 3D porous rGO-PPy composite was used as a support for immobilizing negatively charged B. subtilis denoted as rGO-PPy-B through coordination and electrostatic interaction. Further, the prepared rGO-PPy-B was used as a microbial biofilm for establishing a mediated BOD biosensor with ferricyanide as an electronic acceptor. The indirect determination of BOD was performed by electrochemical measuring ferrocyanide generated from a reduced ferricyanide mediator using interdigited ultramicroelectrode array (IUDA) as the working electrode. The experimental results suggested a good linear relationship between the amperometric responses and BOD standard concentrations from 4 to 60 mg/L, with a limit detection of 1.8 mg/L (S/N ≥ 3). The electrochemical measurement of real water samples showed a good agreement with the conventional BOD₅ method, and the good anti-interference as well as the long-term stability were well demonstrated, indicating that the proposed mediated BOD biosensor in this study holds a potential practical application of real water monitoring.

A novel electrochemical sensor based on electropolymerized ion imprinted poly (o-phenylenediamine) PoPD/electrochemical reduced graphene (ERGO) composite on glass carbon electrode (GCE) was fabricated for selective and sensitive determination of trace Cd(II) in water. ERGO was first deposited on the surface of GCE by electrochemical cyclic voltammetry (CV) scanning to enhance the electron transport activity at electrode surface. The ion imprinted polymer (IIP) of imprinted PoPD was then in situ electropolymerized on ERGO via CV scanning with oPD as functional monomer and Cd(II) ions as template, following removal of the template using electrochemical peroxidation method. The obtained imprinted PoPD/RERGO composites were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray energy spectroscopy (EDS) for the observation of their morphologies and components. The electrochemical behavior of the imprinted PoPD/ERGO/GCE was performed by CV and SWASV. The fabricated sensor of the imprinted PoPD/ERGO/GCE showed a good selectivity toward target Cd(II) ions in the presence of other heavy metal ions. Under the optimized experimental conditions, the sensor exhibited a good linear relationship between SWASV stripping peak values and Cd(II) concentration in the range of 1 to 50 ng/mL, with the limit of detection as 0.13 ng/mL (S/N = 3). The proposed electrochemical sensor of imprinted PoPD/ERGO/GCE was successfully applied for trace Cd(II) determination in real water samples.

Three-dimensional (3D) porous graphene-based materials have displayed attractive electrochemical catalysis and sensing performances, benefiting from their high porosity, large surface area, and excellent electrical conductivity. In this work, a novel electrochemical sensor based on 3D porous reduced graphene (3DPrGO) and ion-imprinted polymer (IIP) was developed for trace cadmium ion (Cd(II)) detection in water. The 3DPrGO was synthesized in situ at a glassy carbon electrode (GCE) surface using a polystyrene (PS) colloidal crystal template and the electrodeposition method. Then, IIP film was further modified on the 3DPrGO by electropolymerization to make it suitable for detecting Cd(II). Attributable to the abundant nanopores and good electron transport of the 3DPrGO, as well as the specific recognition for Cd(II) of IIP, a sensitive determination of trace Cd(II) at PoPD-IIP/3DPrGO/GCE was achieved. The proposed sensor exhibited comprehensive linear Cd(II) responses ranging from 1 to 100 μg/L (R2 = 99.7%). The limit of detection (LOD) was 0.11 μg/L, about 30 times lower than the drinking water standard set by the World Health Organization (WHO). Moreover, PoPD-IIP/3DPrGO/GCE was applied for the detection of Cd(II) in actual water samples. The satisfying recoveries (97–99.6%) and relative standard deviations (RSD, 3.5–5.7%) make the proposed sensor a promising candidate for rapid and on-site water monitoring.

A novel multi-functional microfluidic paper-based analytical device (μPAD) integrated with ion imprinted polymers (IIPs) for separation and rGO/pSPCE for sensing was proposed for specific, portable and low-cost detection of trace Cd(ii) in water.

Heavy metal ions (HMIs) are among the significant pollutants in natural water systems. Nanocomposite-modified sensor membranes can amplify the advantages of electrochemical sensors. Developing efficient, portable and environmentally sustainable methods to monitor and qualify trace-level HMIs is of great significance. This study demonstrates a highly sensitive and rapid analytical approach for on-site determination of HMIs using chip-based microsensor. We employed ultrasonic pretreatment combined with in-situ electropolymerization to synthesize 1T-phase molybdenum disulfide (MoS2) on screen-printed carbon electrodes (SPCEs) modified with a polypyrrole (PPy) nanocomposite. Square wave stripping voltammetry was used to simultaneously detect zinc (Zn²⁺), cadmium (Cd²⁺), and lead (Pb²⁺), showcasing the potential of MoS₂-modified SPCEs for real-time monitoring of heavy metal pollutants. The microsensor exhibits high sensitive, rapid response, strong anti-interference capability and acceptable stability with a linear detection range of 5–50 ppb and trace-level detection limits of 0.27, 0.13 and 0.28 ppb for Zn2+, Cd2+, Pb2+, respectively. The results underscore the excellent capture properties and high selectivity of 1T-MoS2 towards Zn2+, Cd2+, Pb2+. Furthermore, integration of the sensor chip with a portable electrochemical analyzer enables real-time, on-site quantification of HMIs.