Multifunctional terahertz microscopy for biochemical and chemical imaging and sensing

Abstract

Laser-excited terahertz emission microscopy (LTEM) has exhibited great potential for studying the dynamic physical properties of various materials and device evaluation. In this study, an up-to-date version of LTEM, the terahertz chemical microscopy, was developed for biochemical and chemical imaging and sensing. By functionalizing a terahertz semiconductor emitter with an ion-sensitive membrane, a DNA aptamer, and a specific polymer, the change in the terahertz signal amplitude attributed to the surface electrical potential change was successfully detected. Accordingly, the measurement of calcium ions (Ca²⁺), stress biomarker cortisol, and 2, 4, 6-trinitrotoluene (TNT) explosive was achieved. Measured of charged Ca²⁺ was via the change in the electrical potential of the ion-sensitive membrane with ion accumulation. For non-charged cortisol and TNT measurements, the surface potential change was recorded by the conformational change of the negatively charged DNA aptamer bound to cortisol and the charge-transfer complex formation between TNT and polyethylenimine polymer, respectively. Moreover, the specificity of this sensing approach was demonstrated by molecular docking and measuring the interfering substances such as sodium ions, potassium ions, brain chemicals histamine and dopamine, and TNT analogues. The results showed that the developed multifunctional terahertz microscopy technique can be used for trace biochemical and chemical sensing via visualization of the terahertz amplitude distribution.

Keywords: DNA aptamer; Ion selective membrane; Molecular docking; Polyethylenimine polymer; Surface electrical potential; Terahertz microscopy.