Synthesis And Application Of Azo Enhanced Raman Scattering Probes For PH Analysis

Proton concentration is an important indicator for physiological and environmental systems.The pH values in cells and body fluids affect biological functions of organisms,and the pH values of ecological environment such as natural water and soils affect the life of plants and animals.Up to date,the most popular method for detecting pH is a pH meter.However,this method usually requires a homogeneous solution,and it is difficult to detect heterogeneous samples such as cells and soils.Small-molecule probes provide a solution to detect pH of heterogeneous samples due to their advantages of small size and potential application in optical imaging.Fluorescent pH probes have been widely studied,but the broad bands and photostability of fluorescence signals limit their applications.In comparison,Raman scattering results from the transition of molecular vibrational and rotational energy states.It provides more information of chemical bonds of a molecule than fluorescence spectroscopy.The figureprint spectrum of Raman signal could provide more accurate information in heterougeous samples.However,Raman spectroscopy is several orders of magnitude less sensitive than fluorescence.It usually requires signal enhancement based on nano-materials or sophisticated optical instruments.Our research group previously found that the conjugation of azo group significantly enhanced Raman scattering of various vibrational modes through Resonance Raman effect and flurorescence quenching effect.This discovery was named as Azo-enhanced Raman Scattering(AERS).Based on the mechanism of AERS,we designed and synthesized azo-enhanced Raman pH probes and applied them for the pH detection of cell lysosomes and soil samples.The major contents of the thesis are as follows:(1)We designed and synthesized a ratiometric lysosome targeting AERS-pH probe Lyso-pH.The azobenzene functional group played a dual role of Raman enhancement and pH response.The pH response range was 4.0-6.5.Under acidic conditions,the nitrogen atom on the azo group was protonated and N=N became N-N.The adjacent benzene ring became a quinone structure,which destroys the original conjugated system.As a result,under acidic conditions the characteristic azobenzene Raman peak of v(N=N)decreased and the stretching mode of quinone ring increased,respectively.With this small molecure Raman probe,we successfully imaged pH disctribution of cell lysosomes and monitored pH change of lysosomes.(2)We synthesized four solid-phase AERS-pH probes.Their pH response ranges were 1.0-3.0,3.0-6.0,6.0-11.0 and 11.0-14.0.Using resin beads as the carrier,we covalent attached AERS-pH probes through solid-phase synthesis.A pH device was assembled with these pH probes and successfully detected soil pH and environmental pH changes.