Inorganic fluorescent nanoprobes for cellular and subcellular imaging

• We discuss the limitations of fluorescent dye-based probes for cellular imaging.
• We describe the unique properties of inorganic fluorescent nanoprobes.
• Cellular uptake is critical for nanoparticles in cellular and subcellular imaging.
• We describe applications of nanoprobes for intracellular imaging.
• More attention needs to be paid to the potential cytotoxicity of nanoparticles.

The imaging of essential events and physiological states at cellular and subcellular levels plays key roles in studies of biological mechanism and applications of clinical diagnostics. Fluorescent imaging is a powerful technique for cell imaging due to its unique advantages. However, traditional fluorescent dye probes for imaging face significant challenges in investigating spatiotemporal dynamics of molecules or biological structures in cells. With the rapid development of nanotechnology, inorganic nanoparticle (NP)-based fluorescent probes are being constructed and show great improvements in photophysical properties and bioavailability, which enable more sensitive, longer-term imaging in cells. This review introduces several types of inorganic fluorescent nanoprobe, including dye-containing silica NPs, quantum dots, metal nanoclusters and upconversion NPs, and then discusses the cellular uptake process and applications of these nanoprobes for cellular and subcellular imaging. We also cover the ongoing challenges of NPs in clinical applications.