The Bioimaging Story of AIEgens

Abstract

Observations of the micro world, especially the structures of organelles, have been attractive topics since the 17th century. As a powerful detection tool, the fluorescence technique has played a significant role in bioimaging to provide more details and enhance the signal-to-noise ratio compared to that of traditional optical microscopes. The boom of aggregate-induced emission luminogens (AIEgens) in the last two decades has revolutionized the design strategy of luminescent materials for biological applications. This Review summarizes the advantages and recent progress of AIEgens in imaging and tracking. Different imaging strategies of AIEgens including turn-on imaging, stimuli-response sensing, and long-term tracking are presented. NIR AIEgens used for in-depth bioimaging via different methods are also discussed. Finally, we propose several potential development directions for AIEgens in bioimaging.

Figure 1

Proposed mechanism of aggregation-induced emission. Reproduced with permission from ref (19). Copyright 2020 Wiley-VCH.

Scheme 1. Different Strategies of AIE Probes

Figure 2

(a) Schematic illustration of the process of bacteria imaging. (b) Microbial imaging application of COTh-Py. (i,ii) Bright-field and fluorescent images of Escherichia coli (E. coli) with 50 μM of COTh-Py for 1 h. (iii,iv) Bright-field and fluorescent images of Penicillium chrysogenum with 20 μM of COTh-Py for 2 h; scale bar is 20 μm. Reproduced with permission from ref (27). Copyright 2019 Springer Nature. (c) Molecule structure of TPABSM. (d) In vivo zebrafish embryo fluorescence and bright merged imaging stained with TPABSM; scale bar is 50 μm. Reproduced with permission from ref (28). Copyright 2022 American Chemical Society.

Figure 3

(a) Molecule structure of TPEMA. (b) Confocal images of CK in macrophages without (left) or with (right) pretreated with CK-BB for 30 min and then incubated with TPEMA for 30 min; scale bar is 5 μm. Reproduced with permission from ref (31). Copyright 2020 Wiley-VCH. (c) Design strategies for fluorogenic probes for tag proteins. (d) Time-lapse imaging of HEK293T cells expressing HaloTag-rhodopsin on the cell surface using Halo rhodamine-4 (0.5 μM); scale bar is 20 μm. (e) Time-lapse imaging of HEK293T cells expressing SNAP-tag-ADRβ2 (beta-2 adrenergic receptor) on the cell surface using SNAP rhodamine-3 (0.5 μM); scale bar is 20 μm. Reproduced with permission from ref (32). Copyright 2022 American Chemical Society.

Figure 4

Schematic illustration showing the intercalation of TICT-lipid with (a) Gram-negative and (b) Gram-positive bacteria. (c) Schematic illustration showing the fluorescence responses of TICT-lipid to the disruption effect of PMB on the outer membrane of Gram-negative bacteria. (d) Molecule structure of TICT-Lipid. (e) Normalized emission spectra of TICT-lipid postincubation with PBS (gray), E. coli^Ampr (red), and MRSA (blue). Inset: Photograph taken under a 365 nm UV lamp (from left to right: PBS, E. coli^Ampr, MRSA). (f) In situ emission spectra extracted from a panel of the inset. Inset: fluorescence image of E. coli^Ampr postincubation with PMB at concentrations of 4 μg mL^–1; scale bar is 10 μm. Reproduced with permission from ref (41). Copyright 2022 American Chemical Society. (g) Molecule structure of BODIPY1. (h) Fluorescence images of SH-SY5Y cells, which were pretreated with none, LPS, or nystatin (20 μM) for 40 min and then treated with BODIPY1 (5 μM) for another 30 min; scale bar is 50 μm. Reproduced with permission from ref (50). Copyright 2022 American Chemical Society.

Figure 5

(a) Schematic illustration of dhBBR’s fluorescent response to pH change. (b) Fluorescence images of A549 cells stained with dhBBR (1 μM) in PBS buffer with different pH values for 30 min; scale bar is 10 μm. (c) Fluorescence images of HeLa cells stained with dhBBR (1 μM) and curcumin (1 μM) after 200 s of light irradiation; scale bar is 10 μm. Reproduced with permission from ref (57). Copyright 2020 the Royal Society of Chemistry. (d) Synthesis of PNVCL and its thermoinduced conformational transformation. (e) Fluorescence images of MCF-7 cells labeled with PNVCL (250 μg mL^–1) at 25 and 38 °C for 24 h; scale bar is 10 μm. (f) Fluorescence images of MCF-7 cells after incubating with 500 μg mL^–1 PNVCL for different time intervals at 38 °C; scale bar is 10 μm. Reproduced with permission from ref (62). Copyright 2020 the Royal Society of Chemistry.

Figure 6

(a) Molecule structure of CSMPP. (b) Fluorescence images of HeLa cells with 200 nM LysoTracker Red (LTR) for 10 min and then costained with 2 μM CSMPP for 10 min. Fluorescence images of (i) CSMPP; (ii) LTR; (iii) merged (a) and (b); scale bar is 10 μm. (c) Fluorescence image of the whole body of the medaka larva after being fed with CSMPP for 4 h; scale bar is 1 mm. (d) Fluorescence images of the medaka larva’s caudal fin before amputation and after amputation at different times (12, 24, 48, 96, and 120 hpa); scale bar is 50 μm. Reproduced with permission from ref (70). Copyright 2020 Royal Society of Chemistry. (e) Molecule structure of CDPP-NCS. (f) Fluorescence image of RAW264.7 macrophages incubated with CDPP-NCS labeled S. aureus (red) at different times. [CDPP-NCS] = 10 μM; [Hoechst 33342] = 1 μM; scale bar is 10 μm. (g) Fluorescence image of CDPP-NCS labeled S. aureus (red) and lysosomes (green) stained with LysoTracker Green (LTG) after incubation for 6 h and the fluorescence intensity profiles in the yellow arrow from the image; scale bar is 10 μm. (h) Fluorescence image of CDPP-NCS labeled S. aureus (red) and lysosomes (green) stained with MitoTracker Green (MTG) after incubation for 6 h and the fluorescence intensity profiles in the yellow arrow from the image; scale bar is 10 μm. Reproduced with permission from ref (74). Copyright 2022 Elsevier.

Figure 7

(a) Molecule structure of TPE-PyN3. (b) Merged image of HeLa cells stained with TPE-PyN₃ and MitoTracker red FM; scale bar is 30 μm. (c) Fluorescent images of TPE-PyN3 or CellTracker Green CMFDA-stained HeLa cells at various passages; scale bar is 30 μm. (d) Tail rudiment of a living zebrafish embryo stained with TPE-PyN3 in different groups; scale bar is 300 μm. Reproduced with permission from ref (78). Copyright 2016 Wiley-VCH.

Figure 8

(a) Molecule structure of DCBT. (b) Typical bright field pictures of the mouse brain vasculature before and after skull clearing; scale bar is 1 mm. (c) Reconstructed 3D imaging of the neuron-vessel dual channel from 0 to 600 μm depth; scale bar is 100 μm. Reproduced with permission from ref (86). Copyright 2022 Elsevier. (d) Molecule structure of acceptor, donor 1, and donor 2. (e) Two-photon fluorescence image (left) and fluorescence lifetime image (right) of mouse brain–blood vessels at a depth of 100 μm; scale bar is 100 and 50 μm. (f,g) Plots of pixel intensity across the capillaries (marked with a yellow line) in the image of (e); horizontal coordinates: position (μm). Reproduced with permission from ref (89). Copyright 2022 Wiley-VCH.

Figure 9

(a) Schematic illustration of strategies for NIR-II bioimaging. (b) Schematic illustration of chemiluminescence imaging of the arthrosis in mice (up) and in vivo NIR-II CL imaging using 0.66 mg of TPE-BBT (line 1) and TPA-BBT (line 2) CLNPs after injection for 2 min (down); scale bar is 10 mm. (c) In vivo NIR-II CL imaging of TPE-BBT (up) and TPA-BBT (down) CLNPs of arthrosis inflammation at different postinjection times, respectively. Scale bar: 10 mm. Reproduced with permission from ref (93). Copyright 2022 American Chemical Society.

Scheme 2. Scale of AIE Bioimaging

(i) Detection of DNA. Reproduced with permission from ref (95). Copyright 2006 Royal Society of Chemistry. (ii) Detection of protein. Reproduced with permission from ref (96). Copyright 2007 American Chemical Society. (iii) Detection of glucose. Reproduced with permission from ref (97). Copyright 2011 American Chemical Society. (iv) Detection of bacteria. Reproduced with permission from ref (98). Copyright 2014 WILEY-VCH. (v) Imaging of cell membrane. Reproduced with permission from ref (99). Copyright 2019 Royal Society of Chemistry. (vi) Imaging of nucleus. Reproduced with permission from ref (100). Copyright 2017 Royal Society of Chemistry. (vii) Imaging of lysosome. Reproduced with permission from ref (101). Copyright 2021 Springer Nature. (viii) Imaging of mitochondria. Reproduced with permission from ref (102). Copyright 2016 WILEY-VCH. (ix) Imaging of zebrafish. Reproduced with permission from ref (28). Copyright 2022 American Chemical Society. (x) Imaging of tumor. Reproduced with permission from ref (103). Copyright 2012 WILEY-VCH. (xi) Imaging of cerebral vasculature. Reproduced with permission from ref (104). Copyright 2017 WILEY-VCH. (xii) Imaging of nonhuman primates. Reproduced with permission from ref (105). Copyright 2020 American Association for the Advancement of Science.