SERS PH Probes Based On Acid-base Indicators And Their Application In Aerosol PH Measurement

Accurate measurement of pH is of great significance in many fields such as industrial production,soil treatment,food processing,medical diagnosis and environmental monitoring.Meanwhile,microenvironmental pH has gradually become a research hotspot in recent years.As a key factor,it affects the physiological process of cells,the pathogenesis of diseases and the phase change information of aerosol particlesAt present,pH electrode is the most commonly used method for pH measurement.However,due to the large size of the electrode and its vulnerability to electrical interference and mechanical damage,it is impossible to measure pH in a micro environment.To date,several methods have been developed for pH analysis in microenvironments,such as microelectrodes,nuclear magnetic resonance,ultraviolet and fluorescence spectroscopy.In addition,SERS pH sensor has the advantages of simple operation,low energy consumption,free from the interference of photobleaching and quenching,etc.,which makes it stand out from the existing methodsSERS,as a fingerprint spectroscopy technology,has the advantages of high sensitivity,simple operation,free from water phase interference and so on,and has been widely used in the field of analysis and detection.Single particle pH analysis can be realized through SERS,and now there are many applications in the field of pH sensor analysis.However,in the existing reports,the preparation process of SERS pH probe is generally complicated and costly.Therefore,this paper aims to propose SERS pH probe based on common acid-base indicator and successfully apply it to pH measurement in aerosol droplets.The specific work is as follows:(1)SERS pH probes based on 15 common acid-base indicators were prepared to analyze the SERS response and pH sensing ability of each probe.Gaussian 09 W software was used for theoretical calculation of the probes with good performance,and the SERS spectra of each probe were peak allocated.The results showed that 8 indicators,such as methyl orange,met the basic conditions for SERS pH probes,and the accuracy and reliability of the analytical results of 8 probes were verified by gaussian calculation results.(2)8 pH probe calibration curves were generated by BR buffer solution,hydrochloric acid and sodium hydroxide,and the pH calculation formula of each probe was obtained by Origin 2021 software.At the same time,the stability and reversibility of each probe were characterized,and the interference degree of buffer solution,coexisting ions and ion strength on the probe was analyzed.The results showed that the stability of methyl orange,methyl red,phenolphthalein and phenolphthalein probes was poor.The reversibility of phenolphthalein and phenolphthalein probe was not good.At the same time,the analysis results of methyl orange and phenol red probes were greatly disturbed by cations.In addition,the kinds of buffer solution had significant influence on the measurement results of litmus and phenolphthalein probes.Finally,there may be deviations in the analysis results of methyl orange,phenolic red,phenolphthalein,phenolphthalein and alizarin yellow R probes when the ionic strength of the detection environment is high.(3)The droplet generated by 5 kinds of salt solution was prepared,and the droplet collecting device was designed and the performance of the device was tested.The pH of each droplet was tested by 8 kinds of probes proposed in this paper.At the same time,the pH sensing performance of 4-MBA probe was analyzed experimentally,and the probe was selected to verify the measurement results of each probe.The results showed that the size of the droplets in the device did not change significantly within 6 minutes,and under the condition of0.85 MW laser power and integration once every second,the droplets still maintained their original size after 5 SERS measurements.At the same time,it is found that there are different pH values between phosphate,sulfate and nitrate droplets and the body solution,while there is no significant difference between acetate droplets,carbonate droplets and the body solution.After 4-MBA probe verification,it was found that the analytical results of 8 probes in solution state all had good accuracy and stability.Among them,methyl orange,malachite green,litmus,phenolphthalein and alizarin Yellow R probes could still ensure good pH sensing ability under microsample size.However,the analytical results of methyl red,phenol red and phenolphthalein probes in micron-sized droplets are not reliable.