Label-free Detection Of Circulating Melanoma Cells By In Vivo Photoacoustic Flow Cytometry

Circulating tumor cell(CTC)is an important indication of tumor metastasis.Currently most of the CTC detection methods are based on in vitro detection or labeling targets.In vivo photoacoustic flow cytometry(PAFC)can realize in vivo and label-free detection of CTC.Photoacoustic effect is the process when laser irradiates on biological tissue,the tissue absorbs energy from photons,produces thermal expansion and produces ultrasound.In this master project,the PAFC system based on photoacoustic effect is proposed to detect signals of CTC for melanoma diagnosis at early stage and monitoring the development of disease.The system is designed mainly including four parts of image navigation,photoacoustic signal excitation,photoacoustic signal detection and photoacoustic signal processing.In the image navigation part,CCD camera is used to locate blood vessels,leading the laser to excite photoacoustic signals of detected targets.In photoacoustic signal excitation part,the laser of high pulse repetition rate is shaped to a slim beam and focused on the blood vessels to excite photoacoustic signals of targets flowing in the blood vessels.Photoacoustic signal detection part mainly includes transduce between acoustic signal and electrical signal,signal amplification and signal storage.In photoacoustic signal processing part,the recorded data can be confirmed by methods of threshold,difference and the analysis of single period signal and so on.As melanin contained in melanoma cells has specific absorption at 1064 nm of wavelength compared to blood background,The PAFC system selects laser 1064 nm of wavelength for in vivo and label-free detection of circulating melanoma cells.The system includes two laser paths,1064 nm and 532 nm of wavelength.It is used to monitor CTC as the melanoma tumor developed,research on the connection of CTC with the development of tumor and lifespan.The result of intravenous injection of melanoma cells to mimic CTC indicates that the number of CTCs increases rapidly and decreases as metabolize.After 20 minutes,the number increases and decreases again.The result of orthotopic tumor model indicates CTC number increases and deadline of mice decreases as tumor grows.CTC detection by PAFC system is of great significance for early diagnose of tumor.