Fully Integrated Multiplexed Wristwatch for Real-Time Monitoring of Electrolyte Ions in Sweat.

Considerable progress has already been made in sweat sensors based on electrochemical methods to realize real-time monitoring of biomarkers. However, realizing long-term monitoring of multiple targets at the atomic level remains extremely challenging, in terms of designing stable solid contact (SC) interfaces and fully integrating multiple modules for large-scale applications of sweat sensors. Herein, a fully integrated wristwatch was designed using mass-manufactured sensor arrays based on hierarchical multilayer-pore cross-linked N-doped porous carbon coated by reduced graphene oxide (NPCs@rGO-950) microspheres with high hydrophobicity as core SC, and highly selective monitoring simultaneously for K+, Na+, and Ca2+ ions in human sweat was achieved, exhibiting near-Nernst responses almost without forming an interfacial water layer. Combined with computed tomography, solid-solid interface potential diffusion simulation results reveal extremely low interface diffusion potential and high interface capacitance (598 µF), ensuring the excellent potential stability, reversibility, repeatability, and selectivity of sensor arrays. The developed highly integrated-multiplexed wristwatch with multiple modules, including SC, sensor array, microfluidic chip, signal transduction, signal processing, and data visualization, achieved reliable real-time monitoring for K+, Na+, and Ca2+ ion concentrations in sweat. Ingenious material design, scalable sensor fabrication, and electrical integration of multimodule wearables lay the foundation for developing reliable sweat-sensing systems for health monitoring.

Highly Accurate Determination of the Total Amount of Pb2+ and Pb(OH)+ in a Natural Water Environment Revealed by Dynamic Simulation and DFT Calculation: Benefit from the Electron Inverse Effect of Pt Nanoclusters over Defective g-C3N4.

Although utilizing nanomaterial-modified electrodes for lead ion detection has achieved great success, most of them are carried out under acidic conditions and ignore the variation of Pb(II) speciation at different pH conditions, leading to the potential inaccuracy of Pb(II) detection in a neutral natural water environment. Thus, designing a novel catalyst with high accuracy for the detection of various forms of the total amount of Pb(II) (Pb2+ and Pb(OH)+) in neutral waters is significant. Herein, Pt nanoclusters (Pt NCs) were elaborately constructed and stabilized on the Co single-atom-doped g-C3N4 with abundant N vacancies (Pt NCs/VN-C3N4), which achieved the ultrasensitive detection (102.16 µM µA-1) of Pb(II) in neutral conditions. The dynamic simulation and theoretical calculations reveal that the parallel deposition of Pb2+ and Pb(OH)+ occurs on the electrode surface modified by Pt NCs/VN-C3N4, and the current peaks of Pb(II) are cocontributed by Pb2+ and Pb(OH)+ species. An "electron inverse" phenomenon in Pt NCs/VN-C3N4 from the VN-C3N4 substrate to Pt NCs endows Pt NCs in an electron-rich state, serving as active centers to promote rapid and efficient reduction for both Pb2+ and Pb(OH)+, facilitating the accurate detection of the total amount of Pb(II) in all forms in the actual water environment.

Ion-Electron Transduction Layer of the SnS2-MoS2 Heterojunction to Elevate Superior Interface Stability for All-Solid Sodium-Ion Selective Electrode.

The high selectivity and fast ion response of all-solid sodium ion selective electrodes were widely applied in human sweat analysis. However, the potential drift due to insufficient interfacial capacitance leads to the deterioration of its stability and ultimately affects the potential accuracy of ion analysis. Designing a novel ion-electron transduction layer between the electrode and the ion selective membrane is an effective method to stabilize the interfacial potential. Herein, the SnS2-MoS2 heterojunction material was constructed by doping Sn in MoS2 nanosheets and used as the ion electron transduction layers of an all-solid sodium ion selective electrode for the first time, achieving the stable and efficient detection of Na+ ions. The proposed electrode exhibited a Nernst slope of 57.86 mV/dec for the detection of Na+ ions with a detection limit of 10-5.7 M in the activity range of 10-6-10-1 M. Via the electronic interaction at the heterojunction interfaces between SnS2 and MoS2 materials, the micro-nanostructure of the SnS2-MoS2 heterojunction was changed and SnS2-MoS2 as the ion-electron transduction layer acquired excellent capacitance (699 µF) and hydrophobicity (132°), resulting in a long-term potential stability of 1.37 µV/h. It was further proved that the large capacitance and high hydrophobicity of the ion-electron transduction layer are primary reasons for the excellent stability of the all-solid sodium ion selective electrode toward Na+ ions.

Revealing the solid-solution interface interference behaviors between Cu2+ and As(III) via partial peak area analysis of simulations and experiments.

The mutual interference in the sensing detection of heavy metal ions (HMIs) is considerably serious and complex. Besides, the co-existed ions may change the stripping peak intensity, shape and position of the target ion, which partly makes peak current analysis inaccurate. Herein, a promising approach of partial peak area analysis was proposed firstly to research the mutual interference. The interference between two species on their electrodeposition processes was investigated by simulating different kinetics parameters, including surface coverage, electro-adsorption, -desorption rate constant, etc. It was proved that the partial peak area is sensitive and regular to these interference kinetics parameters, which is favorable for distinctly identifying different interferences. Moreover, the applicability of the partial peak area analysis was verified on the experiments of Cu2+, As(III) interference at four sensing interfaces: glassy carbon electrode, gold electrode, Co3O4, and Fe2O3 nanoparticles modified electrodes. The interference behaviors between Cu2+ and As(III) relying on solid-solution interfaces were revealed and confirmed by physicochemical characterizations and kinetics simulations. This work proposes a new descriptor (partial peak area) to recognize the interference mechanism and provides a meaningful guidance for accurate detection of HMIs in actual water environment.

Bimodal interferences of Pb(II) induced by parallel deposition in Pb(II)-Cu(II) electrochemical detections: Voltammetric signals analysis combined with numerical simulations on transient interfacial phenomena.

The perplexity of double peaks in Pb(II) detections has been a threat to the reliability of Pb(II) electroanalysis results for a long term. For the complexity of electrode interfaces, rare studies were taken on mechanisms of Pb(II) double peaks through interfacial kinetics. In this work, analyses on experimental signals and interfacial simulations were working together to reveal that the generation of Pb(II) double peaks in Pb(II)-Cu(II) systems is the deposition of Pb(II) on Cu deposits occurring in parallel. By applying anode stripping voltammetry and cyclic voltammetry, a parallel deposition reaction was found to influence the shape of Pb(II) peaks, and the existence of the second peak was controlled through the adjustment of experimental conditions. A kinetic model was built to reveal the interference of electroanalysis signals caused by a parallel deposition reaction and simulations based on the model were combined with experiments to illustrate that double peaks of Pb(II) were caused by the parallel deposition on Cu(II) deposits. This work proposes another insight of Pb(II) double peaks from macroscale kinetics and pays more attention on the dynamic procedure of electroanalysis interfaces, which makes the study on environmental electroanalysis interface phenomena more clear and is enlightening to develop efficient electrical methods for pollutant monitoring.

Practical Strategy for Arsenic(III) Electroanalysis without Modifier in Natural Water: Triggered by Iron Group Ions in Solution.

Significant progress has been made in nanomaterial-modified electrodes for highly efficient electroanalysis of arsenic(III) (As(III)). However, the modifiers prepared using some physical methods may easily fall off, and active sites are not uniform, causing the potential instability of the modified electrode. This work first reports a promising practical strategy without any modifiers via utilizing only soluble Fe3+ as a trigger to detect trace-level As(III) in natural water. This method reaches an actual detection limit of 1 ppb on bare glassy carbon electrodes and a sensitivity of 0.296 µA ppb-1 with excellent stability. Kinetic simulations and experimental evidence confirm the codeposition mechanism that Fe3+ is preferentially deposited as Fe0, which are active sites to adsorb As(III) and H+ on the electrode surface. This facilitates the formation of AsH3, which could further react with Fe2+ to produce more As0 and Fe0. Meanwhile, the produced Fe0 can also accelerate the efficient enrichment of As0. Remarkably, the proposed sensing mechanism is a general rule for the electroanalysis of As(III) that is triggered by iron group ions (Fe2+, Fe3+, Co2+, and Ni2+). The interference analysis of coexisting ions (Cu2+, Zn2+, Al3+, Hg2+, Cd2+, Pb2+, SO42-, NO3-, Cl-, and F-) indicates that only Cu2+, Pb2+, and F- showed inhibitory effects on As(III) due to the competition of active sites. Surprisingly, adding iron power effectively eliminates the interference of Cu2+ in natural water, achieving a higher sensitivity for 1-15 ppb As(III) (0.487 µA ppb-1). This study provides effective solutions to overcome the potential instability of modified electrodes and offers a practical sensing platform for analyzing other heavy-metal anions.