Quantum dot probes for cellular analysis

Highly fluorescent and robust semiconductor nanocrystals (known as quantum dots or QDs) play a pivotal role in biological applications. In particular, the excellent optical properties of QDs make them more suitable for immunolabeling, molecular imaging, and multiplexed biological detection for cellular analysis than conventional fluorescent dyes. Many studies have applied QD probes for in vitro and in vivo assays, showing great improvements with respect to gaining insight into bioanalytical chemistry, target specificity, and cytotoxicity. In this review, we discuss the optical properties, specificity, and cytotoxic effects of QDs as well as the progress achieved in multicolor cellular imaging, immunolabeling for signaling pathways, and molecular detection at the cellular level. In addition, carbon QDs as alternatives to the toxic cadmium-based QDs and their applications in biotechnology are discussed. Despite the rapid development and recent progress of QD probes, much more work is required to determine the toxicity of cadmium-containing QDs used in live cells and animals.