SPT has promoted the study of intracellular transport dynamics, but there are still some challenges. To date, most SPT studies on intracellular dynamics have been carried out at the cellular level
in vitro; however, the environment in Petri dishes is quite different from that in real tissue (Li
et al. 2021; Pampaloni
et al. 2007), and the characteristics and functions of cells in 3D tissue remain to be investigated in the future (Han
et al. 2020; Jiang
et al. 2021). Therefore, SPT technology in 3D tissue imaging
in vivo is of great significance and has profound prospects. To observe tissues, new 3D imaging techniques are needed. Lattice light-sheet microscopy (LLSM) technology is an effective method for observing deep tissue (Li
et al. 2015a; Liu
et al. 2018) and provides high spatial-temporal resolution for observing the subcellular dynamics within cells or tissues. In addition to microscope developments, new probes are also needed. Compared with visible light, a fluorescent probe with near-infrared (NIR) emission can achieve deeper penetration and better imaging quality, which is suited for live tissue imaging (Cai
et al. 2019; Dai
et al. 2021; Li
et al. 2019; Smith
et al. 2009). Single-walled carbon nanotubes (SWCNTs) have unique intrinsic fluorescence emission in the second NIR window (1000–1700 nm), which makes them candidate fluorescent probes for SPT in deep tissue (Bachilo
et al. 2002; Hong
et al. 2015; Welsher
et al. 2009). In brain tissue, SWCNTs have been tracked to reveal the nanoscale organizational structure of the extracellular space (Godin
et al. 2017). In addition, QDs in NIR emission are another promising probe for SPTs in deep tissue (Cassette
et al. 2013; Liu
et al. 2020a; Zhou
et al. 2015). Recently, a new kind of QD emitting at 1600 nm allowed
in vivo confocal 3D imaging of tumour vasculatures in mice at a depth of 1.2 mm (Zhang
et al. 2018). Although SPT in real tissue is still challenging, it is believed that with the development of optical microscopy and NIR probes, SPT will extend the study of intracellular transport dynamics
in vivo, with promising applications in biophysical studies and biomedical diagnosis.