Sensing pH of individual microdroplet by combining SERS and indicator paper

Aerosol pH and Ion Activities of HSO4– and SO42– in Supersaturated Single Droplets

“…Therefore, direct experimental results are required to evaluate the performance of different models in treating SO 4 2– –HSO 4 – equilibrium and further for pH predictions. Recently, several experimental approaches have been developed to determine aerosol pH, such as measurements using pH-indicator paper, 13 , 23 − 26 UV–Vis spectrometry, 27 − 29 and Raman microspectroscopy. 30 − 35 Raman spectroscopy particularly has the capacity to measure ion concentrations of individual droplets.…”

Direct measurement of the pH of aerosol particles using carbon quantum dots

“…pH deviates from simple proton concentration in nonideal solutions and aqueous particles are thought to be variable and highly concentrated and, therefore, far from ideal. 1,22,24,25 Neither external mixtures nor phase states are accounted for in PILS or lter samples, where populations of atmospheric aerosol particles are almost certainly not uniform and levels of acidity can vary between particles and from phase to phase. 10,26 For these reasons, thermodynamic modeling has been used to predict properties and behavior of atmospheric aerosol particles, including acidity.…”

“…2,15 Models offer the best predictions for particle acidity, but different modeling methods disagree on specic pH values for atmospheric aerosols based on differing priorities, sometimes overlooking important factors like organic components and nonideality. 12,20,22,[24][25][26] Because of the complications associated with proxy methods and modeling, some attention has been given to the direct measurement of aerosol particle acidity. Rindelaub et al have used Raman spectra of lab-generated model aerosol particles to measure pH by the relative concentration of acid-conjugate base pairs, which provided quantitative results for particles containing no more than four species.…”

“…29 Others have expanded on this paper-based technique, both modifying the way color responses are processed and applying the measurement for a select number of purposes. 25,[30][31][32] These pH paper measurements, while improved, can still have a range of obstacles in determining pH and are limited to measuring the average pH of populations of impacted particles. Relatively large amounts of impacted liquid aerosol mass are required to illicit a color response from the color indicator paper and that color response is regularly nonuniform.…”

A SERS pH sensor for highly alkaline conditions and its application for pH sensing in aerosol droplets

“…30,31 Gong et al directly measured the pH of micron-sized droplets with SERS-activated pH paper. 32 Though many probes were reported to respond under alkaline [33][34][35] or acidic conditions, [36][37][38] few could work in highly alkaline or acidic environments. 39 This presents a huge challenge in some cases.…”