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Abstract: Colloidal all‐inorganic lead halide perovskite quantum dots (QDs) are high‐performance light‐emitting materials with size‐dependent optical properties and can be readily synthesized by mixing ionic precursors. However, the low formation energy of the perovskite lattice makes their growth too fast to control under regular reaction conditions. Diffusion‐regulated CsPbBr3 perovskite QD growth is reported on a nanometer‐sized liquid/liquid (L/L) interface supported in a micropipette tip without long‐chain organic ligands. The precursors are divided into two immiscible solutions across the L/L interface to avoid additional nucleation, and the QD growth kinetics are regulated by the constrained cationic diffusion field depending on the size of the micropipette tip. QDs with unprecedentedly small sizes (2.7 nm) are obtained due to the slowed‐down growth rates. The synthesis approach demonstrates the potential of micro‐controlled colloidal QD synthesis for mechanistic studies and micro‐fabrications. 

Cell–cell interactions are critical for transmitting signals among cells and maintaining their normal functions from the single-cell level to tissues. In cancer studies, interactions between drug-resistant and drug-sensitive cells play an important role in the development of chemotherapy resistance of tumors. As metabolites directly reflect the cell status, metabolomics studies provide insight into cell–cell communication. Mass spectrometry (MS) is a powerful tool for metabolomics studies, and single cell MS (SCMS) analysis can provide unique information for understanding interactions among heterogeneous cells. In the current study, we utilized a direct co-culture system (with cell–cell contact) to study metabolomics of single cells affected by cell–cell interactions in their living status. A fluorescence microscope was utilized to distinguish these two types of cells for SCMS metabolomics studies using the Single-probe SCMS technique under ambient conditions. Our results show that through interactions with drug-resistant cells, drug-sensitive cancer cells acquired significantly increased drug resistance and exhibited drastically altered metabolites. Further investigation found that the increased drug resistance was associated with multiple metabolism regulations in drug-sensitive cells through co-culture such as the upregulation of sphingomyelins lipids and lactic acid and the downregulation of TCA cycle intermediates. The method allows for direct MS metabolomics studies of individual cells labeled with fluorescent proteins or dyes among heterogeneous populations.