Terahertz Wave Testing Characteristic Absorption Spectra Of Water-Containing Biological Samples

The Terahertz(THz)wave photon energy(0.4-41 meV)is on the same order of magnitude as the rotational and vibrational energy levels of a large number of organic matter and biological macromolecules,so the characteristic absorption spectra of these samples can be obtained relatively nondestructive,and the qualitative or quantitative detection can be carried out.However,the active biological sample contains a lot of water inside,and the water absorbs terahertz waves strongly,which masks the characteristic absorption spectrum of the biological sample.In response to this problem,this paper designed,optimized and built two terahertz time-domain spectroscopy systems(THz-TDS),"static”and "transient",which respectively realized the characteristic spectrum detection of ultra-low concentration biomacromolecule solutions and living cells.Static THz-TDS uses LT-GaAs photoconductive antenna as terahertz radiation source,ZnTe crystal as terahertz detector,supplemented by terahertz parallel plate metal waveguide and terahertz metal surface plasmon waveguide to enhance the local terahertz electric field strength,so as to realize the terahertz wave transmission detection of water-containing samples.The biomacromolecule solutions of a-lactose,4-aminobenzoic acid,L-arginine,L-glutamic acid and D(+)Cellobiose were detected by static THZ-TDS.The concentrations are 1.754×10-9 mol/L,1.46×10-10 mol/L,2.0115×10-9 mol/L,4.898×10-9 mol/L and 0.877×10-9 mol/L,respectively.The characteristic absorption spectra obtained all have characteristic absorption peaks similar to those of the solid samples.Transient THz-TDS uses LiNbO₃ crystal as a strong terahertz radiation source,and ZnTe crystal combined with CCD as a terahertz detector.Among them,through the tilt wave front technology,non-collinear phase matching is achieved in the LiNbO₃ crystal,and a strong terahertz radiation electric field with an average power of 500 ?W is obtained,and the terahertz wave transmission detection of living cells is realized;The time of measuring a single complete terahertz pulse is only 155 ps by using CCD orthogonal balance detection technology.The HeLa living cells with 5.78×103(per/mm2),1.16×104(per/mm2)and 1.74×104(per/mm2)were detected by transient THz-TDS,and the amplitude of characteristic absorption peak increased linearly with cell concentration.