a T7—dCas9 multi-output DNA sensor designed to detect ctDNA! Cancer is a leading cause of death worldwide, accounting for 8.8 million deaths in 2015, and the most common cause of cancer death is lung cancer (1.69 million deaths). Nowadays, multiple lung cancer detection methods are developed, one of them being liquid biopsy. The technique of liquid biopsy is much better than the popular biopsy as it obviates pain and complication incurred to patients by detecting various tumor markup, including short strand circulating tumor DNA (CtDNA) in the blood. However, it still requires laboratory apparatus such as PCR instrument.
Thus our primary task is to devise a more efficient, rapid and convenient lung cancer prognosis method. We construct a paper chip containing powerful biosensor capable of detecting the fusion gene, EML4-ALK, which only exists only in NSCLC (non small cell lung cancer) patients’ blood. Specific targeted drug for this mutation has been produced, which means patients can receive precise treatment as soon as possible when the detection result is positive.
The biosensor, dCasentry, consists of paired dCas9 protein guided by sgRNA and linked with split T7 RNA polymerase that serves as a switch. When the targeting lung cancer mutation gene is detected, visible signal will be released as the T7 RNA polymerase starts transcription. DCasentry not only deals with low ctDNA concentration in blood but also capable of producing various kinds of signal output, such as GFP and RFP.
We adopt freeze-dried paper chip as the vector of the detection system to simplify its operation as well as storage. The DNA device and proteins needed for detection are mixed with cell-free system and freeze-dried on the paper chip. During testing, the blood sample of the patient provides a liquid environment to reactivate the cell-free system. The product will be presented as a kit, containing including hemostix, a hand power centrifuge, NASBA reaction system and the paper screening chip, that can be widely used on the medical field.

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