An innovative and reliable electrochemical sensor was proposed for simple, sensitive and selective determination of F⁻ ions. The sensor based on the fabrication of porous and electroactive Fe-based metal organic frameworks [MIL-101(Fe)]. It was blended with graphite powder and liquid paraffin oil to from carbon paste electrode (CPE). The MIL-101(Fe)@CPE was characterized using different techniques such as scanning electron microscope, powder X-ray diffraction spectroscopy, Fourier transform infrared spectroscopy, energy dispersive X-ray, cyclic voltammetry, electrochemical impedance spectroscopy, differential pulse voltammetry. The MIL-101(Fe)@CPE exhibited two redox peaks (anodic and cathodic) corresponding to Fe³⁺ and Fe²⁺, respectively. The determination of F⁻ ions based on the formation of a stable fluoroferric complex with Fe³⁺/ Fe²⁺, decreasing the currents of redox species. It was found that the anodic peak current (Ipa) is linearly proportional to the concentration of F⁻ in the range of 0.67–130 μM with a limit of detection (S/N = 3) of 0.201 μM. The electrode exhibited good selectivity towards F^- detection with no significant interferences from common anions. The as-fabricated sensor was applied for the determination of F⁻ in environmental water samples with recoveries % and RSDs % in the range of 98.1%–102.4% and 2.4%–3.7%, respectively.

A molecularly imprinted electrochemical sensor was fabricated for sensitive and selective detection of anti-COVID 19 drug favipiravir (FAV). The sensor is based on the synthesis of biomass-derived carbon (BC) and nickel disulfide nanospheres (NiS₂ NS), which were used to decorate glassy carbon electrode (GCE). Then, the gold nanoparticles (AuNPs) were electro- deposited on the surface of NiS₂ NS/BC/GCE to enhance conductivity, increase electron transfer, and aid polymerization of p-aminothiophenol (p-ATP) functional monomer. The fabrication steps were characterized using different morphological and electrochemical techniques. Variables affecting the formation of molecularly imprinted layers and the determination of FAV were optimized. Under optimum conditions, the oxidation current (Ipa) was increased upon addition of FAV in the range of 0.42–1100 nM with a limit of detection (LOD, S/N) of 0.13 nM. The as-fabricated sensor possesses several advantages such as high sensitivity and selectivity, good reproducibility, and acceptable stability. Furthermore, the proposed molecularly imprinted –based electrochemical sensor was efficiently applied for the determination of FAV in tablets and human serum samples with recoveries % of 99.2 to 102.1 % and RSDs % in the range of 2.4–3.2 %, which confirms the reliability of the sensor to detect FAV in different matrices.

Graphical abstract

Copper based-metal organic frameworks modified with gold nanoparticles (AuNPs@Cu-MOF) was fabricated via facile approach. The nanocomposite was used to decorate glassy carbon electrode (GCE) for the electrochemical sensing of D- penicillamine (D-PA). The nanocomposite was characterized using different techniques such as scanning electron microscope (SEM), transmission electron microscope (TEM), energy dispersive X-ray spectroscopy (EDX), powder X-ray spectroscopy (PXRD), thermogravimetry (TGA), nitrogen adsorption–desorption isotherms, and Fourier Transform infrared spectroscopy (FTIR). Formation of a new anodic peak of Cu(II)-D-PA complex at + 0.38 V was used to detect D-PA. Cyclic and square wave voltammetric studies proved that AuNPs elevated the conductivity of Cu-MOF. The sensor exhibited wide linear range (0.4–75 × 10⁻⁷ M) and low detection limit (0.11 × 10⁻⁷ M) with a good sensitivity (0.9 ± 0.01 μA/μM). It was successfully applied for the estimation of D-PA in different real samples with recoveries % and relative standard deviations % (RSDs %) in the range of 95.6–102.5% and 2.4–3.3%, respectively.

An one-pot hydrothermal method was developed for synthesis of carbon quantum dots co-doped with copper and nitrogen (Cu, N@CQDs). The synthesized Cu, N@CQDs has unique advantages such as high fluorescence quantum yield (39.1%) and high catalytic activity. Oxidative coupling of amoxicillin (AMX) with 4-aminoantipyrine (4-NH₂-APE) in the presence of H₂O₂ as an oxidant to produce pink quinoneimine chromogen was carried out with the aid of Cu, N@CQDs as a peroxidase-like catalyst. This system was used for the colorimetric and fluorometric assays of AMX with reliable results. Colorimetric method is based on the measurement of a pink-colored product at λ_max = 505 nm while the fluorometric assay is based on the quenching of the fluorescence emission of Cu, N@CQDs at 440 nm after excitation at 370 nm. For the colorimetric method, the absorption intensity linearly increased over the concentration range 4.3–110.0 µM with LOD (S/N = 3) of 1.3 µM. For the fluorometric method, the emission intensity of Cu, N@CQDs linearly decreased upon addition of AMX in the concentration range 0.2–120.0 µM with a limit of detection (LOD, S/N = 3) of 0.06 µM. The proposed system was applied to the determination of AMX in different real samples such as pharmaceutical capsules, human serum, milk, and conduit water samples with recoveries in the range 95.8–104.1% and relative standard deviation (RSD %) less than 4.1%.

A simple, cost-effective, and convenient bimodal strategy for the detection of toxic flavonoid rutin was proposed. The strategy depends on fluorometric and electrochemical determination of rutin using new type of nitrogen and sulfur co-doped carbon dots (N, S@C-dots). The fluorescence detection based on quenching the emission of N, S@C-dots by rutin through inner-filter effect (IFE), while the electrochemical detection based on direct oxidation of rutin at glassy carbon electrode (GCE) modified with N, S@C-dots. Many factors affecting fluorometric and electrochemical measurements were optimized. The decrease of emission intensity and the increase of the electrochemical signal are linear over the concentration range of 0.02−92.3 μM and 0.2−130 × 10⁻⁸ M, respectively. The limits of detections (LODs) were found to be 8.0 nM and 0.8 nM for the fluorometric and electrochemical methods, respectively. Moreover, short response times (2.0 and 2.5 min) were achieved using the fluorometric and electrochemical methods, respectively. The selectivity of the fluorometric sensor towards rutin was enhanced; in the presence of other interfering flavonoids; by the addition of bovine serum albumin (BSA).

A gold nanoparticle–modified copper-based metal organic framework (Au NPs@Cu-BDC) was fabricated for the electrochemical determination of cysteine (Cys-SH). The nanocomposites were characterized using different techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), powder X-ray spectroscopy (PXRD), thermogravimetry (TGA), nitrogen adsorption–desorption isotherms, and Fourier transform infrared spectroscopy (FTIR). Formation of a new anodic peak of Cu(II)-Cys complex at + 0.43 V was used to detect Cys-SH. Cyclic and square wave voltammetric studies proved that the Au NPs enhanced the conductivity of Cu-BDC. The proposed electrode exhibited a linear range of 0.0015–10.5 μM and low detection limit of 0.0004 μM with a good sensitivity of 0.78 ± 0.01 μA μM. The as-fabricated electrode was successfully used for the estimation of Cys-SH in real samples (human plasma, urine, and saliva) with recovery % of 99–100% and RSD % of 2.7–3.6%, respectively.

Pathogenic bacteria cause disease outbreaks and threaten human health, prompting the research on advanced detection assays. Herein, we developed a selective molecular imprinted aptasensor for sensitive and prompt quantitation of Staphylococcus aureus (S. aureus) bacteria. The aptasensor was constructed by immobilization of aptamer on gold nanoparticles modified magnetic nanoparticles (apt-AuNPs@ Fe₃O₄). A functional monomer (o-phenylenediamine, o-phen) was electro-polymerized on the surface of the as-synthesized nanocomposite in the presence of a template (S. aureus). After removing S. aureus, the formed imprinted sites were available to extract pathogenic bacteria from complicated matrices. The surface morphology of the as-fabricated nanocomposites was characterized using different spectroscopic and electrochemical methods. Moreover, we thoroughly evaluated factors affecting the synthesis and determination procedures. The molecular imprinted aptasensor exhibited a wide linear range of 10¹–10⁷ CFU mL⁻¹ with a Limit of Detection, LOD (signal to noise = 3) of 1 CFU mL⁻¹. The aptasensor detected S. aureus in milk, conduit water, and apple juice samples with good recoveries % and satisfactory relative standard deviations (RSDs %) values.

In this study, iron and nitrogen co-doped carbon dots (Fe/N@C-dots) were fabricated via one pot hydrothermal method. The as-synthesized Fe/N@C-dots exhibited unique properties such as high catalytic activity and fluorescence quantum yield (33.8%). The peroxidase-like activity of Fe/N@C-dots was used to detect H₂O₂ in the presence of phenol and 4-aminoantipyrine (4-AMAP) to yield a pink colored product (quinoneimine chromogen), which was measured at λ_max = 505 nm (colorimetric method). Moreover, the pink colored product quenched the fluorescence of Fe/N@C-dots via inner-filter effect and static quenching (fluorometric method). The enzyme like activity of Fe/N@C-dots was cascaded with the enzymatic activity of glucose oxidase (GOx) to evaluate the practical application of Fe/N@C-dots to develop dual-channel sensor (fluorometric and colorimetric) for high selective and sensitive detection of glucose. It was found that the absorption intensities were increased linearly with glucose concentration in the range of 2.13–130 μM with LOD (S/N = 3) of 0.58 μM, while fluorescence intensities were decreased linearly after addition of glucose in the range of 1.33–140 μM with LOD (S/N = 3) of 0.36 μM. The Fe/N@C-dots/4-AMAP/phenol/GOx system along with the fluorometric method were applied efficiently to determine glucose in many samples including human serum, urine, and saliva with acceptable recoveries % in the range of 93.8–106.1% and RSD % not more than 3.7%, suggesting the reliability of the as-fabricated biosensor.

Background: Linifanib (LFB) is a multi-targeted receptor tyrosine kinase inhibitor used in
the treatment of hepatocellular carcinoma and other types of cancer. The charge-transfer (CT)
interaction of LFB is important in studying its receptor binding mechanisms and useful in the
development of a reliable CT-based spectrophotometric assay for LFB in its pharmaceutical
formulation to assure its therapeutic benefits.
Purpose: The aim of this study was to investigate the CT reaction of LFB with 2,3-dichloro-
3,5-dicyano-1,4-benzoquinone (DDQ) and its application in the development of a novel 96-
microwell spectrophotometric assay for LFB.
Methods: The reaction was investigated, its conditions were optimized, the physicochemical
and constants of the CT complex and stoichiometric ratio of the complex were determined.
The solid-state LFB-DDQ complex was synthesized and its structure was analyzed by
UV-visible, FT-IR, and 1H-NMR spectroscopic techniques, and also by the computational
molecular modeling. The reaction was employed in the development of a novel 96-microwell
spectrophotometric assay for LFB.
Results: The reaction resulted in the formation of a red-colored product, and the spectrophotometric
investigations confirmed that the reaction had a CT nature. The molar absorptivity
of the complex was linearly correlated with the dielectric constant and polarity index of
the solvent; the correlation coefficients were 0.9526 and 0.9459, respectively. The stoichiometric
ratio of LFB:DDQ was 1:2. The spectroscopic and computational data confirmed the
sites of interaction on the LFB molecule, and accordingly, the reaction mechanism was
postulated. The reaction was utilized in the development of the first 96-microwell spectrophotometric
assay for LFB. The assay limits of detection and quantitation were 1.31 and 3.96
μg/well, respectively. The assay was successfully applied to the analysis of LFB in its bulk
and tablets with high accuracy and precision.
Conclusion: The assay is simple, rapid, accurate, eco-friendly as it consumes low volumes
of organic solvent, and has high analysis throughput.
Keywords: linifanib, 2,3-dichloro-3,5-dicyano-1,4-benzoquinone, charge-transfer reaction,
spectroscopic techniques, 96-microwell spectrophotometric assay, high-throughput
pharmaceutical analysis