ACS Measurement Science Au最新文献

We report mapping the mechanical properties of human red blood cells at submicron scales. Mapping is achieved via a new approach to scanning ion conductance microscopy correlated with optical microscopy. A three-point calibration and affine transformation are utilized to correlate pixel locations registered in optical images with pipette position, which facilitates initial targeting and subsequent tracking and analysis of red blood cells. By recording the response of pipette approach curves and sample compliance at each approach, maps of the Young's modulus of samples and pipette indentation are recorded at subcellular spatial resolution. Comparison of normal and diamide-treated red blood cells shows a significant increase in cell stiffness and a concomitant decrease in deformability, clearly demonstrating the quantitative abilities of the correlative approach taken here for stiffness measurements of intact cellular samples.

Studying cells exposed to low and controllable oxygen levels is key to investigating various fundamental aspects of pathological states, such as stroke and cancer. At present, available methodologies applied in vitro focus on large groups of cells exposed to low oxygen conditions through slow-time approaches, such as environmental incubators or microfluidic devices. Here, we demonstrate a novel approach for titrating the local oxygen concentration around individual adhered PC12 cells, enabling single cells within a population to be exposed to hypoxic-like conditions. A 25 μm diameter platinum disk microelectrode performing the oxygen reduction reaction (ORR) at constant current (galvanostatic control) is used as a microscale oxygen scavenger that can be positioned precisely over individual cells. By coupling the galvanostatic oxygen challenge with confocal laser scanning microscopy (CLSM) and a commercially available hypoxia dye (Image-iT Green hypoxia reagent), we monitor the response of single cells when exposed to depleted oxygen concentrations over time. Numerical simulations are used to characterize the oxygen and pH gradient imposed by the microelectrode at different cathodic currents, revealing that within seconds, the oxygen depletion zone reaches a steady-state condition, extending a few microelectrode radii into solution, while the corresponding pH gradient is strongly compressed by the buffer solution. Cells under the microelectrode show a marked increase in average fluorescence rate relative to control, reporting their hypoxic conditions and demonstrating the effectiveness of the proposed method. Heterogenous cell response in a challenged group is also observed, highlighting the ability of this approach to investigate the natural heterogeneity in cell populations. This work provides a platform and roadmap for future studies of cellular systems where the ability to control and vary oxygen concentration on a rapid time scale would be beneficial.

Scanning electrochemical cell microscopy (SECCM) produces nanoscale-resolution electrochemical maps of electrode surfaces using the meniscus at the tip of an electrolyte-filled nanopipette as a mobile electrochemical cell. While the use and range of applications of SECCM have grown rapidly since its introduction, the pathway to performing SECCM measurements can be daunting to those without direct access to expert users. This work fills this expertise gap by providing a step-by-step guide to performing one's first SECCM experiments, including troubleshooting strategies, videos/images, suggested parameters and experimental systems, and representative data (of both successful experiments and common problems). No background in SECCM is assumed and fundamentals are clearly explained at each stage with a rationale for the experimental steps provided. This work provides an entry point for the uninitiated to understand and use this powerful nanoscale electrochemical characterization technique.

Although the role of kynurenic acid (KYNA) is not yet fully understood, recent research has implicated this tryptophan (Trp) metabolite as a significant biomarker in neurodegenerative diseases. In this study, we developed an immunosensor platform based on self-assembled polyelectrolyte multilayers (PEMs), employing an enzyme-labeled immunoreagent in a competitive displacement format that requires only a single wash step. This immunosensor enables the detection of KYNA and Trp with detection limits (LOD) of 9 pg/mL and 1.2 ng/mL, respectively. Results validated by traditional ELISA methods indicated elevated levels of KYNA and an increased KYNA/Trp ratio in the cerebrospinal fluid (CSF) of Alzheimer's patients compared to controls, consistent with previous findings. Additionally, this immunosensor platform can be readily adapted to detect other neuroactive Trp metabolites by substituting specific immunoreagents, supporting a flexible profile-based approach. This platform could serve as a rapid, cost-effective clinical tool for monitoring neurological and psychiatric disorders, potentially advancing therapeutic strategy development.

Here, we propose new single-frequency effective capacitance C _ec and membrane resistance Z readout principle for solid-contact ion-selective electrodes (SCISEs). Conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) doped with polystyrenesulfonate (PSS^-), i.e., PEDOT(PSS), as solid contact and valinomycin-based membrane were prepared for K⁺-SCISEs. At high frequencies, the membrane resistance of K⁺-SCISEs corresponding to impedance absolute value Z was recorded constantly as KCl aqueous solution diluted with water. The membrane resistance Z increases as the electrolyte concentration decreases. Under identical dilution steps, the linear slope of the logarithmic membrane resistance logZ vs loga _K+ for K⁺-SCISEs with the spin-coated membrane is larger than that of the electrode covered with the drop-cast membrane. As the K⁺-SCISE resistance with the spin-coated membrane was reduced to hundreds of Ω, the logZ of K⁺-SCISEs is linearly proportional to loga _K+ in the range of -1 to -3.4, providing a possibility of utilizing membrane resistance Z as a calibration-free analytical signal for SCISEs. The effective capacitance C _ec of K⁺-SCISEs with the spin-coated membrane was performed in 0.1 M KCl applied with single frequency ranging from 1 MHz and decreases by a factor of 10 to 10 mHz. The obtained C _ec of K⁺-SCISEs with the spin-coated membrane is linearly proportional to logfin the range of 1 MHz to 10 Hz with a slope of ca. -0.97, while at a low frequency ranging from 1 Hz to 10 mHz, the linear slope of logC _ec vs logf is suppressed, where Warburg diffusion takes effect. Furthermore, the membrane resistance Z is independent of applied high frequencies, and the effective capacitance C _ec is independent of the excitation amplitude.

Stem cells are a class of multipotential cells with the capability of self-replication, which can differentiate into multiple functional cells under extra stimulus. The differentiation of stem cells has important implications for tissue regeneration. Therefore, controllable regulation of dental pulp stem cell (DPSC) behaviors is critical for repairment and regeneration of damaged teeth tissues. Rapid promotion of DPSCs, directed differentiation, and revealing molecular events within the organelle level during the cell differentiation process are in great demand for regeneration of teeth, which remains a great challenge. Herein, we developed a highly effective and uncomplicated stimulation platform to promote the DPSCs for odontogenic differentiation based on impulse electrical stimulation and revealed the molecular stress response of mitochondria during cell differentiation based on fluorescence imaging combined with surface-enhanced Raman spectroscopy (SERS). Our approach can greatly shorten the DPSC differentiation time from usually more than 20 days to only about 3 days under 0.8 V for 5 min every day than drug stimulation. Notably, the glycogen and adenosine triphosphate levels within mitochondria were apparently elevated, which is conducive to improving the progression of cell differentiation. Simultaneously, the expression of mitofusin1 and mitofusin2 within mitochondria was significantly down-regulated during the differentiation process. Mechanistically, the molecular insights into mitochondria within DPSCs were clearly revealed through SERS spectra. It demonstrated that the expression of phenylalanine was significantly reduced, whereas the contents of tryptophan within mitochondria were promoted during the cell differentiation process. This study provides a comprehensive and clinically feasible strategy for the rapid promotion of DPSCs-directed differentiation and reveals the molecular dynamic changes within mitochondria, which broadens the biomedical cognition of electrical stimulation for dental pulp stem cell differentiation and provides a potential application for teeth tissue regeneration in the future.

Temperature plays a crucial role in biological functions in normal physiological and pathological states and is intricately linked with chemical dynamics in vivo at the cellular, circuit, and system levels. Despite advances in temperature measurement technologies for internal monitoring, systems capable of simultaneously tracking localized temperature and chemical changes are still underdeveloped. In this study, we introduce dual-sensing hybrid fibers with a miniature footprint of <400 μm in diameter, fabricated using the thermal drawing process. These fibers exhibit precise temperature sensitivity, detecting changes as small as 0.5 °C, and demonstrate highly sensitive and reversible pH detection, a critical physiological parameter. Furthermore, through laser micromachining and surface functionalization, we highlight the potential of these fibers for wearable applications in dual pH and temperature sensing. This innovative dual-sensing technology offers a versatile platform for probing temperature and chemical signaling in vivo and wearable applications, with significant implications for therapeutic development and a deeper understanding of biological processes in various environments.

The interest in assessing the behavior of rare-earth elements (REE) in the natural environment is constantly increasing due to their numerous applications in both environmental and technological fields. However, current methodologies for analyzing REE distributions are based on normalization of REE concentration profiles to lithological values, potentially resulting in different outcomes depending on which lithological values are used for normalization, affecting the interpretability of the data. The present work proposes an alternative approach for analyzing REE concentration profiles by applying principal component analysis (PCA) to create REE chemometric maps. The data compression allows the visualization of the REE distribution using a red-green-blue (RGB) color scale (PC1 = red channel; PC2 = green channel; PC3 = blue channel) directly on a geographical map, reflecting the chemical properties of rare-earth elements. This highlights similarities and differences in the compositional REE distribution of natural soils, facilitating the interpretability of REE data and potentially leading to new insights related to seemingly unrelated samples. Additionally, PCA applied to soil variables correlates with REE patterns and provides deeper insights into soil properties in an unsupervised manner, enhancing the interpretation of soil characteristics and implementing the ability to monitor environmental changes and study soil evolution processes. Of particular significance is the fact that applying the proposed methodology to non-normalized data yields results that are consistent with those derived from normalized data sets. Therefore, this approach not only overcomes normalization challenges but also supports the classical approach from a new methodological perspective, paving the way for broader applications.

Miniaturized biomedical sensor development requires improvements in lithographic processes in terms of cost and scalability. Of particular promise is nanoimprint lithography (NIL), but this can suffer from a lack of high-fidelity pattern reproducibility between master and imprinted substrates. Herein, we present a multidisciplinary investigation into gold- and iron-coated NIL sensors including custom optics and spectroscopy, scanning probe microscopy, and data analysis insights. Polyurethane NIL-made nanodome arrays were interrogated with white light transmission spectroscopy, coupled with principal component analysis (PCA) to investigate potential offsets in the photon-substrate plane interaction angle, an imperfection in NIL substrates. Large-angle mismatches (2-10°) were found to be easily discernible by PCA with statistically significant differences (p = 0.05). Unexpected dips in some spectra are postulated to be due to interacting localized and propagating plasmon polaritons, which is supported with a coupled two-oscillator model. General insights are made regarding the interpretation of PCA loadings, which should be related to physical phenomena, and where maximum variance is not necessarily the most meaningful criterion. Smaller angles (<1°) show no significant differences with overlapping confidence intervals in PCA space. Surface-enhanced Raman spectroscopy (SERS) measurements on gold-coated nanodomes returned relative standard deviations of 6-10% via analysis of gelatin, which is of interest as a nasal lining approximation. Interestingly, nanodomes coated in iron produced small, but useful SERS enhancements, which was subsequently interrogated via scanning thermal probe microscopy showing temperature increases of up to 5 °C over the area of one nanostructure (∼1 μm²). Nanostructures remained intact despite the surprising large local temperature increase relative to a gold-coated comparison sample (∼2 °C). The current study provides a framework for the rapid and accurate quality control assessment of imperfections in NIL-produced nanostructures for sensing applications in SERS and surface plasmon resonance, which may need precisely fabricated nanostructures.