Carbon quantum dots (CQDs)

a novel class of carbon nanomaterials

have received wide attention due to their strong quantum confinement effect and stable photoluminescence property. Compared with traditional metal quantum dots

CQDs also show relatively lower toxicity and better biocompatibility for potential biological applications. Brief introductions of synthetic methods are summarized here

focusing on two main directions: top-down route and bottom-up route. The prominent physicochemical properties including photoluminescence

low toxicity and up-conversion photoluminescence are reviewed in details. Furthermore

current applications in bioimaging are introduced in the review.