Chiral Molecular Detection In Interface Of Using Sum Frequency Generation Vibrational Spectroscopy Twin Polarization Angle Method

Chirality is a ubiquitous phenomenon in nature,ranging from molecules to cells,even to galaxies in the universe.Since the discovery of chirality,people have been studying its role in production and life.Today,chirality has entered many fields of life,such as pesticides,medicine,catalysis and other fields.Chiral characterization methods include linear spectroscopy: Circular Dichroism(CD),Raman Optical Activity Spectroscopy(ROA),etc;second-order non-linear spectroscopy: Second Harmonic Generation Circular Dichroism(SHG-CD),Sum Frequency Generation Optical Active(SFG-OA)etc.Among them,second-order nonlinear optics can measure the chirality of the interface,and the obtained chiral sensitivity is high.By performing spectral analysis on it,microscopic information such as the ratio and relative phase between the second-order polarizability of the interface can be obtained.The work of this article optimizes and improves the original TPA detection system,formula deduction,numerical simulation,and experimental verification of the improved detection system.On the one hand,it shows that the improved TPA system has improved in experimental efficiency and accuracy.On the other hand,it also confirmed the feasibility of the TPA system in the detection of DNA molecule chirality.The main work of the paper: the original SFG-VS TPA(Sum-Frequency Generation-Vibrational Spectroscopy Twin Polarization Angle)optical path has been optimized and improved in two aspects: one is to change the original manual adjustment of the half-wave plate to the electric adjustment Wave plate;the second is to increase the original single optical path detection to dual optical path detection,which can detect two polarized lights at the same time.The improved system was numerically simulated to verify the accuracy and reliability of its chiral detection.TPA detection of oligonucleotide molecules AS1411,TG14,Oxy28,GC.It was verified that salt ions can enhance the stability of double-stranded DNA;spectral differences in the formation of G-quadruplexes with different structures were observed.The manual SFG-VS TPA before the improvement needs auxiliary detection of other spectrums to accurately obtain the relative sign and size of the second-order polarizability under the four polarization combinations.The relative sign and size of the second-order polarizability under four polarization combinations can be used to more effectively characterize the interface molecular chirality.Spectral detection of the G-rich oligonucleotide molecules showed that the G-quadruplex structure formed by the folding of the oligonucleotides of different sequences was different under the concentration of 1mM calcium ion,and the AS1411 formed a single molecule parallel Structure;TG14 forms a b-type single-molecule antiparallel structure;Oxy28 forms a-type single-molecule antiparallel structure.According to these laws,it can be inferred that some other oligonucleotide sequences that may form a G-quadruplex structure may adopt a folding structure.These analyses help to understand the mechanism of the G-quadruplex structure on the target molecule.