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Deciphering ion channel activity and signaling interactions within cells is one of the key tasks of neuroscience. Currently, measuring this electrophysiological activity is done using patch-clamp1-4 or voltage-sensitive imaging5-8. Unfortunately, these techniques are unable to balance between single-channel sensitivity and highthroughput detection. Here we introduce a label-free electrochemical-modulated interferometric scattering microscope (EM-iSCAT) to measure ion channel activity on living cells at both whole-cell and single-channel levels. We visualize the cellular responses dynamics to osmotic stimulation, and record open-close trajectories of single N-methyl-D-aspartate receptors channels with a frame rate of 1.5 kHz. Furthermore, we localize and distinguish different kinds of ion channels (Na+, K+, Ca2+) on cell membrane and monitor spatio-temporal heterogeneous responses between different cells in a network. The high-throughput and single-channel sensitive nature of EMiSCAT microscopy allows monitoring simultaneously the activity of individual channels, their localization, and clustering in the cellular community. Our imaging concept opens the possibility to study any kind of ion channels, and more broadly, cell communication mediated by ion channels.

Energy carrier evolution is crucial for material performance. Ultrafast microscopy has been widely applied to visualize the spatiotemporal evolution of energy carriers. However, direct imaging of small amounts of energy carriers on nanoscale remains difficult due to extremely weak transient signals. Here we present a method for ultrasensitive and high-throughput imaging of energy carrier evolution in space and time. This method combines femtosecond pump-probe techniques with interferometric scattering microscopy (iSCAT), named Femto-iSCAT. The interferometric principle and unique spatially-modulated contrast enhancement increase the transient image contrast by >2 orders of magnitude and enable the exploration of new science. We address three important and challenging problems: transport of different energy carriers at various interfaces, heterogeneous hot electron distribution and relaxation in single plasmonic resonators, and distinct structure-dependent edge state dynamics of carriers and excitons in optoelectronic semiconductors. Femto-iSCAT holds great potential as a universal tool for ultrasensitive imaging of energy carrier evolution in space and time.

IR spectroscopy has been widely used for chemical identification and quantitative analysis of reactions occurring in a specific time and space domains by measuring an average signal of the entire system1. Achieving IR measurements with nanometer-scale spatial resolution is highly desirable to obtain a detailed understanding of the composition, structure and function of interfaces2-5. The challenges in IR nanoscopy yet exist owing to the small molecular cross section and pristine optical diffraction limit. Although atomic force microscopy (AFM) based techniques, such as scattering-type scanning near-field optical microscopy and photothermal-induced resonance microscopy (PTIR), can acquire IR spectroscopy in a few tens of nanometer scale resolution6-9, IR measurements with monolayer level sensitivity remains elusive and can only be realized under critical conditions10,11. Herein, we demonstrate sub-10 nm spatial resolution sampling a volume of ~360 molecules with a strong field enhancement at the sample-tip junction by implementing noble metal substrates (Au, Ag, Pt) in photo-induced force microscopy (PiFM). This technique shows versatility and robustness of PiFM, and is promising for application in interfacial studies with hypersensitivity and super spatial resolution., Comment: 9 pages;4 figures

Heat transfer and dissipation exists in almost any physical, chemical or biological systems. Cells, as the basic unit of life, undergo continuous heat transfer and dissipation during their metabolism. The heat transfer and dissipation within cells related to not only fundamental cellular functions and biochemical reactions, but also several important applications including heat-induced control of biological processes and treatment of diseases. Unfortunately, thus far, we still know very little about the heat transfer and dissipation properties at cellular or subcellular level. Here, we demonstrated a methodology of transient microscopy to map the heat transfer coefficients in single cells, with a temporal resolution of ~5 us and a spatial resolution of ~250 nm (close to diffraction limit). The heat transfer coefficients of different location within single cells were obtained for the first time, the inner part of cells exhibited nonuniform heat transfer properties, and it suggested a self-consistent heat transfer regulation that responds to environmental temperature., Comment: 14 pages, 4 figures