Quantitative Real‐Time Monitoring of Antibody‐Induced Internalization of Epidermal Growth Factor Receptor on Single Living Mammalian Cells Using Scanning Electrochemical Microscopy

Spontaneous-stimulated Raman co-localization dual-modal analysis approach for efficient identification of tumor cells

The study of highly heterogeneous tumor cells, especially acute myeloid leukemia (AML) cells, usually relies on invasive analytical methods such as morphology, immunology, cytogenetics, and molecular biology classification, which are complex and time-consuming to perform. Mortality is high if patients are not diagnosed in a timely manner, so rapid label-free analysis of gene expression and metabolites within single-cell substructures is extremely important for clinical diagnosis and treatment. As a label-free and non-destructive vibrational detection technique, spontaneous Raman scattering provides molecular information across the full spectrum of the cell but lacks rapid imaging localization capabilities. In contrast, stimulated Raman scattering (SRS) provides a high-speed, high-resolution imaging view that can offer real-time subcellular localization assistance for spontaneous Raman spectroscopic detection. In this paper, we combined multi-color SRS microscopy with spontaneous Raman to develop a co-localized Raman imaging and spectral detection system (CRIS) for high-speed chemical imaging and quantitative spectral analysis of subcellular structures. Combined with multivariate statistical analysis methods, CRIS efficiently differentiated AML from normal leukocytes with an accuracy of 98.1 % and revealed the differences in the composition of nuclei and cytoplasm of AML relative to normal leukocytes. Compared to conventional Raman spectroscopy blind sampling without imaging localization, CRIS increased the efficiency of single-cell detection by at least three times. In addition, using the same approach for further identification of AML subtypes M2 and M3, we demonstrated that intracytoplasmic differential expression of proteins is a marker for their rapid and accurate classifying. CRIS analysis methods are expected to pave the way for clinical translation of rapid tumor cell identification.

High-Content Label-Free Single-Cell Analysis with a Microfluidic Device Using Programmable Scanning Electrochemical Microscopy

The cellular heterogeneity and plasticity are often overlooked due to the averaged bulk assay in conventional methods. Optical imaging-based single-cell analysis usually requires specific labeling of target molecules inside or on the surface of the cell membrane, interfering with the physiological homeostasis of the cell. Scanning electrochemical microscopy (SECM), as an alternative approach, enables label-free imaging of single cells, which still confronts the challenge that the long-time scanning process is not feasible for large-scale analysis at the single-cell level. Herein, we developed a methodology combining a programmable SECM (P-SECM) with an addressable microwell array, which dramatically shortened the time consumption for the topography detection of the micropits array occupied by the polystyrene beads as well as the evaluation of alkaline phosphatase (ALP) activity of the 82 single cells compared with the traditional SECM imaging. This new arithmetic was based on the line scanning approach, enabling analysis of over 900 microwells within 1.2 h, which is 10 times faster than conventional SECM imaging. By implementing this configuration with the dual-mediator-based voltage-switching (VSM) mode, we investigated the activity of ALP, a promising marker for cancer stem cells, in hundreds of tumor and stromal cells on a single microwell device. The results discovered that not only a higher ALP activity is presented in cancer cells but also the heterogeneous distribution of kinetic constant (k_f value) of ALP activity can be obtained at the single-cell level. By directly relating large numbers of addressed cells on the scalable microfluidic device to the deterministic routing of the above SECM tip, our platform holds potential as a high-content screening tool for label-free single-cell analysis.

Systematic Analysis of Different Cell Spheroids with a Microfluidic Device Using Scanning Electrochemical Microscopy and Gene Expression Profiling

The 3D cell spheroid is an emerging tool that allows better recapitulating of in vivo scenarios with multiple factors such as tissue-like morphology and membrane protein expression that intimately coordinates with enzyme activity, thus providing a psychological environment for tumorigenesis study. For analyzing different spheroids, conventional optical imaging may be hampered by the need for fluorescent labeling, which could cause toxicity side effects. As an alternative approach, scanning electrochemical microscopy (SECM) enables label-free imaging. However, SECM for cell spheroid imaging is currently suffering from incapability of systematically analyzing the cell aggregates from spheroid generation, electrochemical signal gaining, and the gene expression on different individual cell spheroids. Herein, we developed a top-removable microfluidic device for cell aggregate yielding and SECM imaging methodology to analyze heterotypic 3D cell spheroids on a single device. This technique allows not only on-chip culturing of cell aggregates but also SECM imaging of the spheroids after opening the chip and subsequent qPCR assay of corresponding clusters. Through employment of the micropit arrays (85 × 4) with a top withdrawable microfluidic layer, uniformly sized breast tumor cell and fibroblast spheroids can be simultaneously produced on a single device. By leveraging voltage-switching mode SECM at different potentials of dual mediators, we evaluated alkaline phosphatase without disturbance of substrate morphology for distinguishing the tumor aggregates from stroma. Moreover, this method also enables gene expression profiling on individual tumor or stromal spheroids. Therefore, this new strategy can seamlessly bridge SECM measurements and molecular biological analysis.

Electrochemical Biosensing System for Single Cells, Cellular Aggregates and Microenvironments

Applications of electrochemical biosensing for surveying intact cells and tissues have been focus of attention. Two experimental approaches have been used when performing amperometric measurements on biological cells, the stylus-type microelectrode probes and the electrode-integrated microdevices based on lithographic technologies. For the probe scanning approach, various types of microsensors were developed to monitor localized physical or chemical natures at a variety of surfaces in situ under wet conditions. Scanning electrochemical microscopy (SECM) has been applied for monitoring local oxygen, enzyme activity, and collection of transcripts. For the non-scanning type of approach, electrode array devices allow very rapid response, parallel monitoring, and multi-analyte assay. Sveral topics of on-chip-culture system were introduced especially concerning on gene expression monitoring by reporter system and reconstruction of in vivo-like nature by controlling microenvironments. Electrochemical reporter assay has been demonstrated to monitor the gene expression process of the gene-modified cultured cells. Long-term monitoring of cellular function of spheroids and three dimensionally-cultured cells were carried out by controlling microenvironments on the cellular chip.