1 mRNA In the serum

miRNA in the serum. Then a commercial kit was used to extract and isolate miRNA from the

exosomes. These steps ensure the yield and stability of miRNA and firmly underline the subsequent

experiments. Then we further validated through mass spectromery and proved that the RNAs in the

exosomes are mainly miRNAs which is consistent with the study of Valadi [24] . The miRNAs in the

exosomes are significantly richer than fresh serum. The serum without the exosomes still contain a

certain amount of miRNA, but the content is significantly lower than that in the exosomes. The

serum after repeated freeze-thaw was not found with any miRNA, but the exosomes thereby

isolated were still identified with a certain level of miRNAs. Afterwards, we used transcriptase-

polymerase chain reaction (RT-PCR) to detect three types of miRNAs in the exosomes. At present,

the methods for miRNA detection include Northern Blot, microarray chip, in-situ hybridization,

RTPCR, rolling circle amplification, and the use of conjugated polymers. Though microarray analysis

is able to analyze the miRNA expression profile, there are many novel chips and improved

techniques, but the sensitivity and specificity of microarray analysis should be further improved.

Various probe making techniques, amplification methods and detection methods should be further

integrated and improved. Analysis of in-situ hybridization shows that though the use of LNA probe

improves the analytical sensitivity and reliability, the effort and sensitivity of hybridization remain to

be improved. The sensitivity of new methods such as ISH should be further enhanced together with

in-situ amplification techniques. Though the existing miRNA amplification methods have pros and

cons, RT-PCR is the most widely-used amplification method, and there are many types of commercial

kits. Here we used RT-PCR into miRNAs detection. Compared with other methods, RT-PCR is superior

in terms of no-marking, simple operations, low cost, and high sensitivity, RT-PCR is able to get results

within short time, detect the expressions of multiple miRNAs, and even require less RNAs. Here RT-

PCR was successfully used to identify the expressions of mir-21, -133a and -181b in the serum

exosomes of colon cancer patients. We also prove that mir-21 is significantly higher expressed in

exosomes derived from colon cancer patients, especially in patients at the first diagnosis or before

any treatment. The mir-21 expression is about 5 folds than normal people. The difference is

significantly larger than the direct mir-21 extraction from the serum and facilitates early diagnosis.

Our study is almost limited by the relatively small number of cases of colon cancer patients;

however, our study showed that Exosomes can enhance the stability and integrity of miRNAs and

prevent miRNAs from RNA enzyme digestion and other environmental damage which maybe applied to clinical drug department.