Xueliang Niu

The sensitive detection of luteolin is crucial for monitoring its levels in botanical sources, assessing its clinical pharmacokinetics, and guaranteeing the efficacy of luteolin-containing products. In this study, a high-performance electrochemical sensing platform for luteolin detection was developed based on a gold nanoparticle (AuNPs)/Ti₃C₂T_x-MXene composite. Ti₃C₂T_x-MXene was first etched from the Ti₃AlC₂-MAX phase using hydrofluoric acid and further functionalized with polyethylenimine to endow it with a positive surface charge. This modification facilitated the electrostatic self-assembly of negatively charged AuNPs onto the MXene surface, forming a stable AuNPs-MXene composite with enhanced electrical conductivity and a large effective surface area. The electrochemical behavior of luteolin at the AuNPs-MXene-modified glassy carbon electrode was systematically investigated. Cyclic voltammetry and density functional theory calculations confirmed an adsorption-controlled, reversible redox process involving two electrons and two protons at the catechol hydroxyl groups of luteolin. Molecular electrostatic potential maps and highest occupied molecular orbital distribution further verified the catechol hydroxyls as the primary redox-active sites. Under optimal conditions, the sensor displayed a wide linear response range from 1.0 × 10⁻⁴ μM to 100 μM and a low detection limit of 0.034 nM, outperforming most previously reported electrochemical sensors for luteolin. Its practical application was validated by determining luteolin in commercial Duyiwei capsules and chrysanthemum samples via the standard addition method. This work not only offers a reliable tool for luteolin detection but also extends the application of MXene-based composites in the electrochemical sensing of flavonoids. Graphical Abstract

A novel electrodeposited solid-contact material for ion-selective electrodes, formed by co-anchoring ethyl viologen and ferrocene on porous graphene, paves the way for calibration-free applications.

The conventional electrochemical detection strategy for alpha-fetoprotein (AFP) is limited by the antigen-antibody (Ag-Ab) reactions and suffers from low sensitivity and poor reproducibility due to the inconsistency of Ab-modified electrodes. Herein, we designed and explored a sandwich-type electrochemical sensor for highly sensitive detection of AFP based on aptamer (Apt)–AFP–Ab interaction mode with silver@gold (Ag@Au) core-shell nanoparticles (NPs) as a signal amplifier. AuNPs were electrodeposited onto MXene (Ti₃C₂T_X)-modified glassy carbon electrode (GCE) to get AuNPs/MXene/GCE and further used as the signal amplification substrate. The tetrahedral DNA-linked AFP aptamers were immobilized onto AuNPs/MXene/GCE surface via Au–S bonds and used as the sensing and recognition platform for AFP capturing. Ag@AuNPs with core-shell structures were synthesized, characterized, and bound with Ab as detection elements by catalyzing H₂O₂ reduction. In the presence of AFP, a stable Apt–AFP–Ab sandwich structure was formed owing to the high affinities of aptamer and Ab toward the target AFP. The catalytic current produced by H₂O₂ reduction increased linearly with the logarithm of AFP concentration from 5 × 10⁻⁴ ng/mL to 1 × 10⁵ ng/mL, accompanied by a low detection limit (1.6 × 10⁻⁴ ng/mL). Moreover, the novel sandwich-type electrochemical sensor shows high sensitivity, outstanding selectivity, and promising performance in the analysis of actual samples, displaying a broad application prospect in bioanalysis. Graphical abstract

A facile and novel electrochemical sensing platform is reported for quercetin determination with MoS₂ nanoflowers-3D graphene aerogel (3D MoS₂-GA) nanocomposite as signal amplified material. The 3D MoS₂-GA nanocomposite was synthesized through a two-step hydrothermal method, in which MoS₂ nanoflowers were prepared in advance. Characterizations of 3D MoS₂-GA were performed by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The 3D MoS₂-GA-modified glassy carbon electrode (3D MoS₂-GA/GCE) was used to investigate the electrochemical behaviors of quercetin with electrochemical parameters calculated, reaction mechanism discussed, and experimental conditions optimized. Notably, the redox peak current densities of quercetin on 3D MoS₂-GA/GCE raised 5.14 and 6.40 times compared with those on a bare GCE. Furthermore, a novel electroanalytical approach was proposed for the sensitive determination of quercetin within the concentration range 0.01 ~ 5.0 μmol/L, accompanied by a low detection limit of 0.0026 μmol/L (at a working potential of 0.38 V vs. Ag/AgCl). The recovery for practical sample analysis ranges from 97.0 to 105%, and the relative standard deviation is less than 4.2%. This established method shows reliable performance in determination of quercetin in tablets and urine samples. Graphical abstract

Noble bimetallic nanomaterials have aroused great interest in the field of electrochemistry for their special properties. Herein Au@Ag nanoparticles loaded on a three-dimensional (3D) N-doped graphene aerogel (NGA) were designed, synthesized, and used as electrode modifiers. The structure and composition of Au@Ag/3DNGA nanocomposite was characterized and confirmed using different techniques such as SEM, TEM, Raman, XRD, XPS and UV-vis, revealing that the N-doped 3D architecture was well formed with uniform size and core-shell like Au@Ag bimetallic nanoparticles anchored homogeneously. The Au@Ag/3DNGA nanocomposite was further modified on the surface of a carbon ionic liquid electrode (CILE) to get a novel sensing platform. Electrochemical behaviors of baicalein were investigated using Au@Ag/3DNGA/CILE as the working electrode, showing obviously enhanced performance compared to that on CILE and 3DNGA/CILE. Electrochemical reaction process of baicalein was investigated and the electrochemical parameters were calculated. Under the optimized conditions, the sensitive differential pulse voltammetric oxidation response of baicalein was used for ultrasensitive detection of baicalein with a wider calibration range of 1.0 × 10⁻³ ∼ 10.0 μmol L⁻¹ and a lower detection limit of 0.345 nmol L⁻¹ (3S₀/S). The proposed method could be successfully applied for baicalein analysis in dual yellow oral liquid with the recovery of 95.3–106.0%, showing reliable application.

Developing a green, cost‐efficient air‐cathode catalyst with high oxygen evolution and reduction reaction (OER/ORR) performance for rechargeable Zn‐air batteries (ZABs) has gained attention. Iron‐containing nitrogen‐doped graphene (Fe/N‐G) that contains Fe‐N_x coordination sites is prepared by pyrolyzing the complex of iron ion and PANI sheets intercalated with the unique layer gaps of H‐montmorillonite nanoreactors. The transmission electron microscopy (TEM), X‐ray diffraction (XRD), and X‐ray photoelectron spectroscopy (XPS) analysis confirm that there are no crystalline materials, such as iron lattice, iron carbide, or iron nitride. The as‐prepared Fe/N‐G show a high electrocatalytic activity in ORR with a 4e⁻ transfer process and the half‐wave potential of Fe/N‐G (0.877 V vs reversible hydrogen electrode—RHE), which is better than that of Pt/C in oxygen saturated 0.1 m KOH solution. In an acid electrolyte, the Fe/N‐G possesses a half‐wave potential similar to that of 20 wt% Pt/C. For OER, the Fe/N‐G exhibits the overpotential of 400 mV versus RHE at 10 mA cm⁻². However, the Fe/N‐G as the air‐cathode of the homemade rechargeable ZABs exhibits a high power density (156.8 mW cm⁻²) and an excellent long discharge–charge cycling stability (787 cycles) at 20 mA cm⁻². This work provides an inspiring guideline to prepare a high‐performance bifunctional air‐cathode for a rechargeable ZAB.

Aiming to improve the electron transfer efficiency between redox protein/enzyme and electrode, Pt-3D graphene oxide aerogel (3DGA) nanocomposite was synthesized via a facile one-step hydrothermal method and used as a new biocompatible carrier for protein/enzyme. The morphology and structure of Pt-3DGA nanocomposite were characterized by SEM, TEM, XPS, XRD, Raman and BET. Then a new modified electrode was fabricated with Pt-3DGA-horseradish peroxidase (HRP) biocomposite suspension and Nafion solution coated on carbon ionic liquid electrode (CILE). The performances of Nafion/Pt-3DGA-HRP/CILE were further checked by various methods with the well-maintained 3D structure, good retention of bioactivity of HRP and the enhanced electrochemical ability. Direct electrochemistry of HRP was investigated with a pair of well-shaped redox peaks appeared with the peak-to-peak separation as 78 mV. Electrochemical parameters including electron transfer coefficient (α) and heterogeneous electrode reaction rate constant (k_s) are calculated to be 0.52 and 3.35 s⁻¹, respectively. Nafion/Pt-3DGA-HRP/CILE shows outstanding electrocatalytic activity towards trichloroacetic acid (TCA) reduction with a wide detection range of 0.5 ∼ 42.0 mmol/L. Nafion/Pt-3DGA-HRP/CILE can be successfully utilized for the analysis of TCA contents in real samples with good recovery.