Jian Wang

Scanning ion conductance microscopy (SICM) enables high-resolution, noncontact, in situ characterization of specimens in liquid environments, providing simultaneous access to three-dimensional (3D) topographical, electrical, and mechanical properties. Despite its versatility, the inherent imaging principle limits scanning speed, presenting a significant challenge to further development. This work introduces an adaptive scanning strategy leveraging the distinctive nonmonotonic (“rise-then-fall”) approach curve observed in asymmetric self-referenced SICM (ASR-SICM). By employing a two-stage approach strategy, the nanopipette modulates its velocity based on its proximity to the sample surface, thereby enhancing both temporal resolution and imaging fidelity. The effectiveness of the proposed method was evaluated through finite element simulations and theoretical calculations, where the influences of electrolyte configuration and nanopipette structural parameters on the approach curve and feedback range were systematically analyzed. Additionally, the impact of different threshold settings on scanning time was examined. Subsequently, approach curves under different electrolyte conditions were measured on PDMS substrates, and the imaging accuracy was evaluated using fixed macrophages. Finally, comparative experiments on micropatterned polydimethylsiloxane (PDMS) substrates and MCF-7 cells demonstrate that the proposed method achieves equivalent average pixel rates up to 3.02 times and 1.85 times that of the conventional method, respectively, with the mean square error (MSE) on PDMS as low as 62.4% of the conventional value. These findings validate the potential of the adaptive scanning approach to overcome the scanning speed limitations of SICM, improving both imaging efficiency and quality.

G-triplexes are noncanonical DNA structures formed by three guanine tracts, but their sequence design rules for small-molecule binding remain unclear. In this work, we carried out a systematic sequence screening to optimize G-triplex sequences for improved interaction with methylene blue (MB), and applied the best sequence in an electrochemical biosensor for melamine detection. Over 80 candidate sequences were designed by varying loop nucleotides, 5'-flanking bases, and strand length, and were evaluated by square wave voltammetry. The optimal sequence F9 (5'-ATGGGAGGGTGGG-3') achieved the highest current suppression (ΔI/I₀ ≈ 0.81), outperforming all tested G-triplex and several well-known G-quadruplex sequences. Circular dichroism confirmed that F9 folds into a parallel G-triplex with a melting temperature of 65.1 °C, which increased to 70.0 °C upon MB binding. Electrochemical titration gave a 1:1 binding ratio with an association constant of 9.37 × 10⁵ M^-1. Molecular dynamics simulations showed that MB binds to the 5'-face of the G-triplex by π-π stacking, with a computed binding free energy of -151.9 kJ/mol. A hairpin probe (MelaPin) combining the F9 sequence with a poly-T melamine recognition region was then constructed. The resulting biosensor showed a linear response over 1-100 μM melamine with a detection limit of 0.74 μM, and a recovery of 96.0 ± 0.8% in spiked infant formula. This work provides a practical framework for G-triplex sequence design and shows that the G-triplex/MB system can serve as a simple, label-free signal module for electrochemical sensing.

Cell adhesion to the extracellular matrix (ECM) regulates essential biological processes and plays a critical role in disease progression. Current adhesion assays often rely on labeling or lack single-cell resolution. Here, we present a phase angle-responsive light-addressable electrochemical sensor (LAES) for label-free, single-cell imaging of cell-substrate adhesion. By analyzing the phase angle, which is the temporal offset between voltage and photocurrent, we achieve robust detection of interfacial dielectric changes, overcoming limitations of conventional amplitude-based LAES. This platform enables the quantitative assessment of cell adhesion across diverse cell types and semiconductor substrates. Dynamic modulation of adhesion using ECM coatings and trypsin treatment further confirms the sensitivity of phase angle imaging to adhesion strength. A point-contact electrical equivalent circuit model supports the observed correlation between phase angle shifts and cell-substrate junction resistance. This work establishes phase angle-based LAES as a powerful tool for single-cell adhesion mapping with strong potential for mechanobiology and adhesion-targeting therapeutic screening.

Scanning ion conductance microscopy (SICM) has emerged as a powerful tool for high-resolution, in situ imaging in liquid environments, widely used in biomedical and materials science. Conventional SICM relies on identical electrolyte concentrations inside and outside the nanopipette to maintain stable ionic current signals, constraining its applicability under asymmetric or electrolyte-free bath conditions. To address this limitation, we developed a modified single pipette-based self-referenced SICM (SR-SICM), which enables high-resolution imaging in solvent-flexible environments. By coating the nanopipette exterior with silver to serve as an integrated reference electrode, the ionic current circuit is confined to the probe tip, effectively eliminating interference from the external bath. Finite Element Method (FEM) was employed to elucidate SR-SICM operation and optimize parameters. Simulations revealed a nonmonotonic current-distance profile arising from the competing effects of localized ion enrichment and restricted ion transport, especially under electrolyte-free conditions. Experimental validation confirmed the dual-phase behavior, resulting in an extended feedback range compared to conventional SICM. Imaging of poly(dimethylsiloxane) (PDMS) structures and biological samples demonstrated the robustness and versatility of SR-SICM across diverse solvent systems. This approach significantly broadens the operational scope of SICM, enabling stable, high-resolution imaging in environments previously inaccessible to conventional systems.

Scanning Electrochemical Cell Microscopy (SECCM) has emerged as a powerful tool in electrochemical research due to its ability to measure morphology and electrochemical information simultaneously at the nano- or microscale. However, traditional SECCM using liquid probes suffers from issues, such as evaporation, solution residue, and droplet deformation. This study introduced a hydrogel-based SECCM probe and comprehensively explored its superiority over liquid probes through both theoretical and experimental approaches. Finite element simulations demonstrated that hydrogel probes significantly reduce the contact area with samples and minimize the retraction distance. These effects are attributed to the restriction of the solution flow by the hydrogel's 3D network structures. SECCM experimental results further confirmed the superior stability and efficiency of the hydrogel probes in imaging applications. In addition, the hydrogel probe was successfully applied to characterize Au/ITO interfaces, enabling the concurrent acquisition of localized morphological and electrochemical information, thereby demonstrating its feasibility for standard SECCM measurements. These findings provide a valuable reference for the emerging field of hydrogel probes in SECCM research and development.

Light-addressable electrochemistry (LAE) enables the activation and detection of localized faradaic electrochemical processes on a flat, unconstructed semiconductor electrode through targeted light illumination, making it a promising approach for single-cell electrochemistry. Herein, we report a direct current (DC) redox imaging technique for single retinal pigment epithelial cells utilizing LAE with an α-Fe₂O₃ electrode activated by a constant, focused laser beam. The proposed DC-LAE method showed micron-scale resolution and was successfully used to image single cells under physiological conditions. We demonstrated that the visualization was primarily due to the hindrance of photoinduced OH^- oxidation by adherent cells, resulting in a reduction of local photocurrents. Inspired by this funding, electroactive substances with high redox activities, such as hydroquinone (HQ), l-ascorbic acid (AA), and potassium ferricyanide (K₄Fe(CN)₆) were introduced into the culture medium. These substances significantly enhanced the DC redox imaging performance under low-intensity laser conditions without compromising cell viability. We believe that integrating pure DC-LAE with cell imaging advances quantitative analyses of cellular electrochemical behavior, offering valuable insights into cellular functions and processes.

Accurate and reliable gesture recognition using Electrical Impedance Tomography (EIT) holds significant potential for human-computer interaction and assistive technologies, yet ensuring consistent performance across multiple sessions remains challenging due to factors such as system noise, electrode shifts, and frequency-dependent signal variation. To address these issues, we propose an optimized EIT-based gesture recognition system featuring a dual-ring electrode configuration, an enhanced classification algorithm, and a high-frame-rate data acquisition approach. By systematically examining the Similarity Evaluation Index (SEI) at various frequencies, we identified 10 kHz as the optimal operating frequency, achieving an SEI of 16.5%, substantially exceeding the baseline SEIL value. Our improved neural network architecture, PEU-SFU-ResNet50, further enhances feature extraction and classification robustness, attaining 88.18% accuracy in inter-session tests—approximately 12% higher than the baseline model—and demonstrating 98% accuracy in single-session scenarios, outperforming standard ResNet50 and ANN. Ablation experiments and cross-validation validated the efficacy and robustness of our proposed system, underscoring its potential for multi-session gesture recognition applications.

The light-addressable electrochemical sensor (LAES) is a powerful tool for single-cell imaging due to its label-free and probe-free advantages. In this work, we report a photocurrent polarity-switchable LAES using a single-phase photoelectrode of a BiFeO₃ thin film for living cell imaging. The proposed BiFeO₃ could show both p- and n-type photocurrent behavior by simply altering the external bias voltage. LAES imaging of the same individual MCF-7 cells was performed in anodic and cathodic modes. Decreases in both photocurrents were observed due to the hindering effect of the adherent cells on local photoinduced Faraday currents. Furthermore, the dynamic photocurrent changes on cells after trypsin treatment were imaged and studied at anode and cathode polarities. Both polarities showed an increase in local photocurrents on cells as the cell-substrate junction weakened, and this change displayed heterogeneous characteristics. This is the first time that LAES cell imaging was achieved in a p-type mode. Meanwhile, our photocurrent polarity-switchable imaging approach overcomes the limitations of conventional photoelectrodes, which have been confined to single-polarity operation. We believe this work has the potential to significantly broaden the application scope of LAES in single-cell visualization and analysis, offering great insights into cellular behavior and function.