The telomerase ribonucleoprotein is a reverse transcriptase that plays a critical role in the maintenance of telomere length by synthesizing telomeric DNA repeats using its instinct RNA as the template and thus protects chromosome ends from degradation and fusion. Most normal somatic cells do not express detectable telomerase activity and telomeres shorten progressively with each cell division, while in almost all kinds of cancer cells human telomerase exhibits high activity, suggesting that there is a direct association between telomerase activity and various diseases including cancer and age-related diseases, and that telomerase could be used both as a diagnostic biomarker for the early detection of human cancer and as a potential target for anti-cancer therapy. However, fully understanding the biochemical action of human telomerase is presently a huge challenge since it is a very big complex. Moreover, it is remarkably difficult to get enough amount of heloenzyme for traditional enzyme analysis. Novel and advanced methods therefore should be employed to assay human telomerase and understand enzymatication. Single molecule techniques such as single-molecule fluorescence resonance energy transfer (smFRET) technique and two-color coincidence detection (TCCD) not only can detect dynamic of individual molecule and flexibility of enzyme catalysis, but also can check very little amount of samples in solution or on surface, which can not be performed by bulk experiment. In this review, we summarize the progress and prospect of telomerase research and describe several latest single-molecule methods applied to assaying telomerase structure, function, activity and dynamics.

Contents
1 Introduction
2 Single molecule fluorescence technique
2.1 Development of single molecule fluorescence techniques
2.2 Classification of single molecule fluorescence techniques
2.3 Common single molecule fluorescence techniques
3 Telomere, telomerase and cancer
3.1 Structure and function of telomere and telomerase
3.2 Relationship between telomere, telomerase and cancer
3.3 Telomerase as a diagnostic biomarker and therapeutic target for cancer
4 Single molecule fluorescence studies of human telomerase
4.1 Common methods for telomerase detection
4.2 Single molecule fluorescence techniques applied to telomerase detection
5 Conclusion