As novel fluorescent nanomaterials, quantum dots (QDs) have played important roles in many fields, such as chemical analysis, biology sensor, molecular imaging, owing to their excellent optical properties. Studies on the properties of single quantum dots can help to find new experimental phenomenology which can't be found in the ensemble-approach, provide a mentality to improve the properties of quantum dots, contribute to a better application of quantum dots in various fields. In this review, identifications criterion of single quantum dots, photo-properties (such as fluorescence enhancement, bleaching, blinking, bluing, etc.) of single quantum dots, and quantum dots application (such as single quantum dots tracking, single quantum dots biosensor, super-localization technology) at single nanoparticle levels are commented. The challenges and existing problems of application of single quantum dots are summarized. In the future, synthesis in quantum dots should simultaneously satisfy many excellent photo-properties, including small size, high quantum yield, non-blinking, lager blue shift range, no-biotoxicty. Meanwhile, plasmonic quantum dots that not only exhibit strong fluorescence, but also become excellent probes for surface plasmon scattering, are another significant research field.

Contents
1 Introduction
2 Single molecule/nanoparticle detection
3 Photo-properties of single quantum dots
3.1 Fluorescence enhancement and bleaching
3.2 Blinking
3.3 Spectral blue shift
4 Application of quantum dots at single nanoparticle level
4.1 Single quantum dots tracking
4.2 Single quantum dots biosensor
4.3 Quantum dots in super-localization technology
4.4 Other application
5 Conclusion and outlook