Meixian Li

Over 700 million people worldwide are estimated to suffer from chronic kidney disease (CKD), and creatinine is a critical biomarker for diagnosing and managing CKD. However, conventional detection relies on invasive blood sampling and time-consuming protocols and is susceptible to interference from endogenous substances and drugs. This highlights an urgent demand for convenient, non-invasive, and accurate monitoring strategies. This study presents a wearable electrochemical microneedle (MN) patch for minimally invasive and enzyme-free creatinine detection in transdermal interstitial fluid (ISF). Solid polycarbonate MNs are coated with conductive poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate). Copper ions (Cu2+) are immobilized on the surface through immersion treatment via coordination and electrostatic interactions, and a Nafion film is finally deposited to enhance stability and anti-interference ability. Quantitative detection is based on the peak current generated from the electrochemical oxidation of in situ formed Cu0 to Cu+, which subsequently undergoes specific coordination with creatinine. The patch exhibits a linear detection range of 5.00–300 μM for creatinine with a minimum detectable concentration of 1.00 μM. Benefiting from the strong coordination effect and permselectivity of Nafion, the patch shows high stability, excellent anti-interference ability, and reliable sensing performance. Integrated with a handheld potentiostat, this compact, lightweight, and low-cost sensor achieves real-time and accurate creatinine sensing within 90 s in ISF of live rabbit models, showing great promise for long-term home-based CKD management.

Chronic kidney disease (CKD) is a global public health issue, with high prevalence and mortality. As cystatin C is a biomarker for the early diagnosis of CKD, there is an urgent need to develop a simple and inexpensive method for the detection of Cys C in human plasma. Herein, a sensitive method with flexible electrochemical aptamer-based (E-AB) sensing interfaces has been established using poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate)-treated paper-based electrodes. Introduction of MoS₂ quantum dots increased the specific surface area and realized effective immobilization of the thiolated Cys C aptamer (Cys C Apt) modified with methylene blue through the formation of disulfide bonds. The E-AB sensing interfaces were successfully applied to the quantification of Cys C in human venous whole blood and plasma samples based on the binding-induced conformational change mechanism of Cys C Apt by employing square wave voltammetry. The flexible E-AB sensing interfaces show significant potential to be developed into wearable patches for in vivo detection of Cys C, which will pave the way for early diagnosis and long-term monitoring of CKD.

Chromatography experiments form an important component of an Instrumental Analysis Laboratory Course. In order to meet the demands of cultivating innovative talents with scientific thinking skills for the evolving educational objectives， the Instrumental Analysis Laboratory Course in the College of Chemistry and Molecular Engineering at Peking University has been reformed since 2017， with a focus on chromatography experiment teaching as a pilot project. A series of well-designed reform measures， including strengthening the design of the experimental content， focusing on the analysis of actual samples， increasing student participation， enhancing their freedom of exploration and the division of labor and cooperation， and adopting a teaching form with both virtual and real components， have been introduced. These measures have effectively stimulated students’ subjective learning initiatives， improved their understanding of the principles of instrumental analysis and the structures and functions of instruments， cultivated their abilities to comprehend， analyze， and solve problems， and strengthened their scientific thinking and literacy. Overall， the developed program has powerfully contributed to realizing the core goal of cultivating innovative talents.

The mechanisms of electrochemical/chemical oxygen reduction catalyzed by an iron porphyrin were studied by in situ EC-MS/CR-MS assisted by electrochemical characterization and stopped-flow UV-vis spectroscopy.

Molecular catalysis of water oxidation has been intensively investigated, but its mechanism is still not yet fully understood. This study aims at capturing and identifying key short-lived intermediates directly during the water oxidation catalyzed by a cobalt-tetraamido macrocyclic ligand complex using a newly developed an in situ electrochemical mass spectrometry (EC-MS) method. Two key ligand-centered-oxidation intermediates, [(L^2-)Co^IIIOH] and [(L^2-)Co^IIIOOH], were directly observed for the first time, and further confirmed by ¹⁸O-labeling and collision-induced dissociation studies. These experimental results further confirmed the rationality of the water nucleophilic attack mechanism for the single-site water oxidation catalysis. This work also demonstrated that such an in situ EC-MS method is a promising analytical tool for redox catalytic processes, not only limited to water oxidation.

Charge (ion and electron)-transfer reactions at a liquid/liquid interface are critical processes in many important biological and chemical systems. An ion-transfer (IT) process is usually very fast, making it difficult to accurately measure its kinetic parameters. Nano-liquid/liquid interfaces supported at nanopipettes are advantageous approaches to study the kinetics of such ultrafast IT processes due to their high mass transport rate. However, correct measurements of IT kinetic parameters at nanointerfaces supported at nanopipettes are inhibited by a lack of knowledge of the nanometer-sized interface geometry, influence of the electric double layer, wall charge polarity, etc. Herein, we propose a new electrochemical characterization equation for nanopipettes and make a suggestion on the shape of a nano-water/1,2-dichloroethane (nano-W/DCE) interface based on the characterization and calculation results. A theoretical model based on the Poisson-Nernst-Planck equation was applied to systematically study how the electric double layer influences the IT process of cations (TMA⁺, TEA⁺, TPrA⁺, ACh⁺) and anions (ClO₄^-, SCN^-, PF₆^-, BF₄^-) at the nano-W/DCE interface. The relationships between the wall charge conditions and distribution of concentration and potential inside the nanopipette revealed that the measured standard rate constant (k⁰) was enhanced when the polarity of the ionic species was opposite to the pipette wall charge and reduced when the same. This work lays the right foundation to obtain the kinetics at the nano-liquid/liquid interfaces.

Molybdenum disulfide nanomaterials nowadays are very popular in electrocatalysis field due to their outstanding catalytic performance toward many electrochemical reactions. However, the electrochemical oxidation reaction of molybdenum disulfide nanomaterials in the range of positive potential has not been studied thoroughly. Herein, we have investigated electro-oxidation of molybdenum disulfide nanomaterials and put forward a new reaction mechanism: molybdenum disulfide nanomaterials are electro-oxidized with water to form molybdenum oxysulfide (MoOS₂) and hydrogen ions, leading to the release of hydrogen on the counter electrode. Various characterization methods such as contact angle measurement, scanning electron microscope (SEM), transmission electron microscope (TEM) with energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge structure (XANES) spectroscopy, time-of-flight secondary ion mass spectrometry (ToF-SIMS), and gas chromatography (GC) were applied to attest the doping of oxygen and the generation of hydrogen. Based on this reaction, we constructed a novel ultrasensitive electrochemical sensor for detecting trace water with the minimum detectable content of 0.0010% (v/v) in various organic solvents and ionic liquids, which is comparable to the Karl Fischer titration, but with much simpler reagent.