Nitrite (NO₂⁻), an important intermediate in the biological nitrogen cycle, can be considered as a life-threatening marker since it leads to the production of carcinogenic nitrosamines when it reacts with secondary amines in the digestive system, besides being a methemoglobinemia risk factor in the children. Herein, we reported a fluorescence detection method for rapid, selective, and sensitive detection of NO₂⁻ in water samples. The method is based on the modification of α-MnO₂ nanorods with fluorescein dye (FLR@ α-MnO₂ NR) where the former acts as a quencher and the latter acts as a fluorescence reporter. After the addition of NO₂⁻ to the FLR@ α-MnO₂ NR system, it reduces α-MnO₂ NR to soluble Mn²⁺ and liberates FLR, restoring the fluorescence of FLR (Turn On). The nanoprobe, with λ_ex/λ_em at 490/518 nm, has a linear range of 0.83–67.0 µM with a limit of detection (LOD) of 0.27 µM, for analysis of NO₂⁻. The proposed method was successfully applied to the determination of NO₂⁻ in natural water samples.

A sensitive and selective molecular imprinted polymeric network (MIP) electrochemical sensor is proposed for the determination of anti-cancer drug oxaliplatin (OXAL). The polymeric network [poly(pyrrole)] was electrodeposited on a glassy carbon electrode (GCE) modified with silver nanoparticles (Ag) functionalized Cu-metal organic framework (Cu-BDC) and nitrogen-doped carbon nanotubes (N-CNTs). The MIP-Ag@Cu-BDC /N-CNTs/GCE showed an observable reduction peak at −0.14 V, which corresponds to the Cu-BDC reduction. This peak increased and decreased by eluting and rebinding of OXAL, respectively. The binding constant between OXAL and Cu-BDC was calculated to be 3.5 ± 0.1 × 10⁷ mol⁻¹ L. The electrochemical signal (∆i) increased with increasing OXAL concentration in the range 0.056–200 ng mL⁻¹ with a limit of detection (LOD, S/N = 3) of 0.016 ng mL⁻¹. The combination of N-CNTs and Ag@Cu-BDC improves both the conductivity and the anchoring sites for binding the polymer film on the surface of the electrode. The MIP-based electrochemical sensor offered outstanding sensitivity, selectivity, reproducibility, and stability. The MIP-Ag@Cu-BDC /N-CNTs/GCE was applied to determine OXAL in pharmaceutical injections, human plasma, and urine samples with good recoveries (97.5–105%) and acceptable relative standard deviations (RSDs = 1.8–3.2%). Factors affecting fabrication of MIP and OXAL determination were optimized using standard orthogonal design using L₂₅ (5⁶) matrix. This MIP based electrochemical sensor opens a new venue for the fabrication of other similar  sensors and biosensors.

In this research paper, a highly sensitive and selective molecular imprinted polymeric network (MIP) based electrochemical sensor was developed for the determination of histamine (HIS). The functional monomer (pyrrole) was electro-polymerized over the surface of AuNPs functionalized Fe-metal organic framework (Fe-BDC) and nitrogen-sulfur co-doped graphene quantum dots (N, S-GQDs). The MIP-Au@Fe-BDC/ N, S-GQDs /GCE exhibited an observable peak at −0.12 V, which corresponds to the anodic peak of Fe-BDC. This peak was increased and decreased by eluting and rebinding of HIS, respectively. This might be due to the binding constant between Fe-BDC and HIS is 3.5 × 10⁶ mol⁻¹ L. The electrochemical signal (Δi) was increased with the increase of HIS concentration in the range of 0.078–250 nM with a limit of detection (LOD, S/N = 3) of 0.026 nM. The combination of N, S-GQDs and Au@Fe-BDC improves the conductivity and the anchoring sites for binding the polymer film on the surface of the modified electrode. Factors affecting fabrication of MIP and HIS determination were optimized using standard orthogonal design using L25 (5⁶) matrix. The MIP-based electrochemical sensor offered outstanding sensitivity, selectivity, reproducibility, and stability. The proposed electrode was used to quantify HIS in human serum and canned tuna fish samples with recoveries % and relative standard of deviations % (RSDs %) in the range of 97.2–103 % and 1.8–3.8%, respectively. The as-synthesized MIP-based electrochemical sensor opens a new venue for the fabrication of MIP-based sensors and biosensors.

Silver nanoparticles (AgNPs) modified boron and sulfur co-doped reduced graphene oxide (B, S@rGO) were prepared by one-pot hydrothermal method for the first time. The combination between AgNPs and B, S@rGO decreases stacking of B, S@rGO and decreases the particle size of AgNPs; in addition, it enhances the effective surface area and electro-catalytic activities of the nanocomposite. The morphology and structure of AgNPs/B, S@rGO were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR), energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron microscope (XPS), Raman spectroscopy, UV-Vis spectroscopy, thermogravimetric analysis (TGA), and Brunauer–Emmett–Teller (BET). The electro-catalytic activity of AgNPs/B, S@rGO was studied using cyclic voltammetry (CV), electron impedance spectroscopy (EIS), and differential pulse voltammetry (DPV). Because of the synergetic effects of AgNPs and B, S@rGO, the modified electrode displayed considerably enhanced sensitivity to ivermectin (IVM) determination. The voltammetric response is linear over the range of 0.3–60.0 nM with LOD (S/N = 3) of 0.1 nM. The proposed sensor exhibited good selectivity, reproducibility, and long-term stability. The modified electrode was used to analyze IVM in injections, urine, and tap-water with recoveries % of 99.6–105.8% and RSDs of 2.14–3.65%.