A facile fabrication of a hierarchical ZIF-8/MWCNT nanocomposite for the sensitive determination of rutin

Monitoring of Specific Phytoestrogens by Dedicated Electrochemical Sensors: A Review

Phytoestrogens are non-steroidal estrogens produced from plants that can bind with the human body's estrogenic receptor site and be used as a substitute for maintaining hormonal balance. They are mainly classified as flavonoids, phenolic acids, lignans, stilbenes, and coumestans; some are resocyclic acids of lactones, which are mycotoxins and not natural phytoestrogen. Phytoestrogens have many beneficial medicinal properties, making them an important part of the daily diet. Electrochemical sensors are widely used analytical tools for analysing various pharmaceuticals, chemicals, pollutants and food items. Electrochemical sensors provide an extensive platform for highly sensitive and rapid analysis. Several reviews have been published on the importance of the biological and medicinal properties of phytoestrogens. However, this review provides an overview of recent work performed through electrochemical measurements with electrochemical sensors and biosensors for all the classes of phytoestrogens done so far since 2019.

An electrochemical ratiometric immunosensor for the detection of NMP22 based on ZIF-8@MWCNTs@Chit@Fc@AuNPs and AuPt-MB

Nuclear matrix protein 22 (NMP22) is one of the most important tumor markers of bladder cancer and is significantly elevated in the urine of bladder cancer patients. Therefore, in this work, a highly sensitive ratiometric electrochemical immunosensor was constructed to detect NMP22 based on ZIF-8@MWCNTs@Chit@Fc@AuNPs composites. ZIF-8 had a large surface area and good adsorption ability. Multi-Walled Carbon Nanotubes (MWCNTs) can optimize the electrical conductivity of ZIF-8, so that the electrode surface of ferrocene (Fc) obtains a stable and strong electrochemical signal. In addition, AuPt-MB provided another strong detection signal methylene blue (MB) while immobilizing the secondary antibody (Ab2) through Au-N and Pt-N bonds. A ratiometric electrochemical sensor was formed based on ZIF-8@MWCNTs@Chit@Fc@AuNPs and AuPt-MB, which showed a great linear connection between IMB/IFc and the logarithmic concentration of NMP22 with a detection limit of 3.33 fg mL-1 (S/N = 3) under optimized specifications in the concentration interval of 0.01 pg mL-1 to 1000 ng mL-1. In addition, the ratiometric immunosensor showed good selectivity and stability.

Progress and opportunities for metal-organic framework composites in electrochemical sensors

Metal-organic framework composites have the advantages of large surface area, high porosity, strong catalytic efficiency and good stability, which provide a great possibility of finding excellent electrode materials for electrochemical sensors. However, MOF composites still face various challenges and difficulties, which limit their development and application. This paper reviews the application of MOF composites in electrochemical sensors, including MOF/carbon composites, MOF/metal nanoparticle composites, MOF/metal oxide composites and MOF/enzyme composites. In addition, the application challenges of MOF composites in electrochemical sensors are summarized. Finally, the application prospect for MOF composites is considered to promote the synthesis of more MOF composites with excellent properties.

Rapid and Sensitive Detection of Rutin in Food Based on Nitrogen-Doped Carbon Quantum Dots as Fluorescent Probe

The aim of this study was to establish a rapid detection method of rutin in food based on nitrogen-doped carbon quantum dots (N-CDs) as the fluorescent probe. N-CDs were prepared via a single-step hydrothermal process using citric acid as the carbon source and thiourea as the nitrogen source. The optical properties of N-CDs were characterized using an electron transmission microscope, X-ray diffractometer, Fourier-transform infrared spectrometer, and nanoparticle size potential analyzer. The UV/Vis absorption property and fluorescence intensity of N-CDs were also characterized using the respective spectroscopy techniques. On this basis, the optimal conditions for the detection of rutin by N-CDs fluorescent probes were also explored. The synthesized N-CDs were amorphous carbon structures with good water solubility and optical properties, and the quantum yield was 24.1%. In phosphate-buffered solution at pH = 7.0, Rutin had a strong fluorescence-quenching effect on N-CDs, and the method showed good linearity (R² = 0.9996) when the concentration of Rutin was in the range of 0.1-400 μg/mL, with a detection limit of 0.033 μg/mL. The spiked recoveries in black buckwheat tea and wolfberry were in the range of 93.98-104.92%, the relative standard deviations (RSD) were in the range of 0.35-4.11%. The proposed method is simple, rapid, and sensitive, and it can be used for the rapid determination of rutin in food.

Ultrasensitive Determination of Natural Flavonoid Rutin Using an Electrochemical Sensor Based on Metal-Organic Framework CAU-1/Acidified Carbon Nanotubes Composites

Rutin, a natural flavonol glycoside, is widely present in plants and foods, such as black tea and wheat tea. The antioxidant and anti-inflammatory effects of flavonoids are well known. In this study, a new electrochemical rutin sensor was developed using multiwalled carbon nanotubes/aluminum-based metal-organic frameworks (MWCNT/CAU-1) (CAU-1, a type of Al-MOF) as the electrode modification material. The suspension of multiwalled carbon tubes was dropped on the surface of the GCE electrode to make MWCNT/GCEs, and CAU-1 was then attached to the electrode surface by electrodeposition. MWCNTs and CAU-1 were characterized using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Due to the synergistic effect of CAU-1 and MWCNT-COOH, the prepared sensor showed an ultrasensitive electrochemical response to rutin. Under optimized conditions, the sensor showed a linear relationship between 1.0 × 10^-9~3.0 × 10^-6 M with a detection limit of 6.7 × 10^-10 M (S/N = 3). The sensor also showed satisfactory stability and accuracy in the detection of real samples.

Portable Wireless Intelligent Electrochemical Sensor for the Ultrasensitive Detection of Rutin Using Functionalized Black Phosphorene Nanocomposite

To build a portable and sensitive method for monitoring the concentration of the flavonoid rutin, a new electrochemical sensing procedure was established. By using nitrogen-doped carbonized polymer dots (N-CPDs) anchoring few-layer black phosphorene (N-CPDs@FLBP) 0D-2D heterostructure and gold nanoparticles (AuNPs) as the modifiers, a carbon ionic liquid electrode and a screen-printed electrode (SPE) were used as the substrate electrodes to construct a conventional electrochemical sensor and a portable wireless intelligent electrochemical sensor, respectively. The electrochemical behavior of rutin on the fabricated electrochemical sensors was explored in detail, with the analytical performances investigated. Due to the electroactive groups of rutin, and the specific π-π stacking and cation-π interaction between the nanocomposite with rutin, the electrochemical responses of rutin were greatly enhanced on the AuNPs/N-CPDs@FLBP-modified electrodes. Under the optimal conditions, ultra-sensitive detection of rutin could be realized on AuNPs/N-CPDs@FLBP/SPE with the detection range of 1.0 nmol L^-1 to 220.0 μmol L^-1 and the detection limit of 0.33 nmol L^-1 (S/N = 3). Finally, two kinds of sensors were applied to test the real samples with satisfactory results.

Ultrasensitive electrochemical sensor for detection of rutin antioxidant by layered Ti3Al0.5Cu0.5C2 MAX phase

MAX phases have attracted great attention due to unique features such as thermal and electrical conductivity, easy fabrication, heat resistant, and lightweight. In this study, an easy and green method was employed to successfully develop a Ti₃Al_0.5Cu_0.5C₂ MAX phase structure, and a Ti₃Al_0.5Cu_0.5C₂ based glassy carbon electrode (GCE) was applied for the electrochemical determination of rutin antioxidants in mandarin and kiwi samples. The developed Ti₃Al_0.5Cu_0.5C₂ MAX phase was characterized by different techniques such as X-ray photoelectron spectroscopy (XPS), thermogravimetry and differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), diffuse reflectance spectroscopy (DRS), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) to obtain information on the structural and morphological properties. Electrochemical methods such as cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were employed for the determination of rutin using Ti₃Al_0.5Cu_0.5C₂/GCE. The GCE modified with Ti₃Al_0.5Cu_0.5C₂ demonstrated amplified electrochemical response (ca. 4.25 times) in comparison to the bare GCE towards rutin, and exhibited ultra-sensitivity and selectivity in the presence of other interfering antioxidants. Under the optimum conditions, good linearity in the range of 0.02-50.00 μmol L^-1 was obtained for rutin analysis by the Ti₃Al_0.5Cu_0.5C₂-based sensor with a limit of detection (LOD, 3σ/K) as low as 0.015 μmol L^-1. The fabricated Ti₃Al_0.5Cu_0.5C₂ MAX phase was applied to determine trace levels of rutin in mandarin and kiwi samples with validation by high-performance liquid chromatography (HPLC), thus highlighting its potential for the electrochemical determination of small molecules in the agricultural field.