Preliminary Application Of Near-field Terahertz Spectroscopic Imaging In The Detection Of Biological Samples

The terahertz time-domain spectroscopy(THz-TDS)and spectroscopic imaging technologies have shown promising applications in the detection of biological samples,but the traditional far-field THz-TDS system used in current research is limited by low spatial resolution due to optical diffraction.Although the emerging photoconductive microprobe(PCM)-based near-field THz-TDS system can be potentially used to detect biological samples with a relative high resolution,hitherto little work has been done in this aspect.In this work,we used the home-built near-field THz-TDS system to conduct preliminary detection of pork tissue slices and cultured cells in vitro,and compared the results with those obtained by a far-field THz-TDS system.In the near-field THz-TDS system,when the optical delay line is driven by a stepper motor,a rapid THz imaging method with fixing the optical delay line was used to detect pork tissue slices.The results show that the muscle region and adipose region in the porcine tissue can be clearly discriminated in the THz near-field images with a good contrast,far better than the images of the samples imaged by using the conventional terahertz time-domain spectroscopy.By measuring the HeLa cells and A549 cells that have been treated by washing and freezing with the same near-field THz-TDS system,it was found that the amplitude of the THz spectrum of A549 cells was greater than HeLa cells in the range of 0.4~1.4 THz;however,no difference could possibly be measured with the far-field THz-TDS system.Therefore,the amplitude of the near-field THz spectrum of cells could be used as a reliable basis for distinguishing different types of cells.In addition,we further improved the performance of the near-field THz system by driving the optical delay line with a voice coil motor.Using this system,we measured the pork tissue slices and found that the best imaging results were achieved by using the THz peak-to-peak value in time-domain and the spectral data in 0.65~0.90 THz frequency range.This research provides the basic foundation for the application of PCM-based near-field THz-TDS system in the high spatial resolution detection of biological samples.