Novel Method to Simultaneously Adjust the Size and pH Value of Individual Microdroplets in Silicone Oil

Gengchao Chen,Xianmin Zhang,Ning Li

doi:10.1109/access.2019.2925771

Abstract

In this paper, a strategy to modify each micro-droplet's volume and synchronously adjust its pH value as required based on the electrolysis reaction in silicone oil is demonstrated. A pair of platinum electrodes fixed onto the jaws of a vernier caliper was used to modify the micro-droplet's volume and adjust its pH value by simply adjusting the distance between the two electrodes. To get a micro-droplet with desirable volume and pH values, three models, the relationship between the droplet's volume and its diameter when the droplet was placed on a fluorinated ethylene propylene (FEP)-covered glass substrate, the relationship between the distance of the two electrodes and the size of the resulted micro-droplet, and the relationship between the pH value and the micro-droplet's consuming rate, were built through the least square method. In our experiments, a droplet (5% sodium chloride solution, 1.4 uL, pH = 7) could consume 98.9% of its initial volume and form a new droplet with a volume of 0.016 μL and pH of 12.2. In addition, to validate that this method is also suitable in the acid and alkaline solutions, 0.001 mol/L NaOH and H 2 SO 4 solutions were, respectively, operated using the same procedure. Both the volume and pH values could be controlled, which proved the potential application of our proposed method in analytical chemistry, precision engineering, and so on.

Highlights

Micro-sized water droplets have been widely used in multiple research fields, such as analytical chemistry [1], [2], precision engineering [3]–[7], biological sciences [8]–[12], etc. [13]–[17]
We propose and investigate a strategy to modify the size of droplets while simultaneously adjusting their pH value based on the electrolysis of water droplets in silicone oil
This paper proposed a low-cost, high-efficient strategy capable of modifying the size of droplets and synchronously adjusting their pH values as demand based on the electrolysis reactions in silicone oil, which is unable or very difficult to be achievable before our study

Summary

INTRODUCTION

Micro-sized water droplets have been widely used in multiple research fields, such as analytical chemistry [1], [2], precision engineering [3]–[7], biological sciences [8]–[12], etc. [13]–[17]. To form size-controllable and pH-desirable microdroplets, the current methods mainly rely on making the desired pH solution and cutting it into. G. Chen et al.: Novel Method to Simultaneously Adjust the Size and pH Value of Individual Microdroplets in Silicone Oil it is very difficult to control the break-off point of liquids precisely [31], [45]. The size of the produced micro-droplet is controlled by tuning the magnitude of power voltage [34], [35] For this method, the manipulated solution is often limited to conductive liquids [45]. The cutting methods available lack the ability to form high-precision microdroplets in a common lab These methods are not capable of adjusting pH values and sizes after droplet formation. The ambient temperature and pressure were 25 C◦ and 1 atm, respectively

RESULT

COMPARISON OF THREE MODELS IN THE THREE DIFFERENT SOLUTIONS ABOVE

Findings

CONCLUSION