A High Performance Impedance-based Platform for Evaporation Rate Detection

Summary

This paper presents an impedance-based apparatus for evaporation rate detection of solutions. It offers clear advantages over a conventional weight loss approach: a fast response, high-sensitivity detection, a small sample requirement, multiple sample measurements, and easy disassembly for cleaning and reuse purposes.

Abstract

This paper describes the method of a novel impedance-based platform for the detection of the evaporation rate. The model compound hyaluronic acid was employed here for demonstration purposes. Multiple evaporation tests on the model compound as a humectant with various concentrations in solutions were conducted for comparison purposes. A conventional weight loss approach is known as the most straightforward, but time-consuming, measurement technique for evaporation rate detection. Yet, a clear disadvantage is that a large volume of sample is required and multiple sample tests cannot be conducted at the same time. For the first time in literature, an electrical impedance sensing chip is successfully applied to a real-time evaporation investigation in a time sharing, continuous and automatic manner. Moreover, as little as 0.5 ml of test samples is required in this impedance-based apparatus, and a large impedance variation is demonstrated among various dilute solutions. The proposed high-sensitivity and fast-response impedance sensing system is found to outperform a conventional weight loss approach in terms of evaporation rate detection.

Introduction

Evaporation is a type of liquid vaporization and occurs along the gas-liquid interface of a collective body of water. The water molecules near the surface become capable of escaping from the liquid due to collision of water molecules. The evaporation rate is an important key factor during the process of evaporation. Generally, a balance or volumetric tube^1-3 is widely-used to detect the evaporation of solutions. However, it takes a long time to measure the evaporation rate due to the precision limitation of a balance or a volumetric tube. For this reason, a responsive and high-sensitivity instrument must be developed to probe into the details of the evapora....

Protocol

1. Experimental Chip Module

1. Fabricate the indium tin oxide (ITO) electrode chip by photolithography and chemical wet etching processes
   1. Obtain an ITO substrate (370 mm x 480 mm x 0.5 mm (L x W x H)) with a 2,600 Å ITO layer commercially (See Materials List). Slice the ITO substrate to the dimensions of 90 mm x 90 mm x 0.5 mm with a glass cutter for the ITO electrode patterning process in a 4 inch aligner.
   2. Use an ultrasonic cleaner to clean the ITO glass with acetone and then with deionized water, for 15 min each. Dry the ITO glass with clean dry air.
   3. Dispense 5 ml of positive photoresist solution onto the s....

Results

During the evaporation process, the conductive ions in the tested solution became concentrated with the decreasing solution volume, and the impedance of this solution decreased. The rates of weight loss and impedance decrease in the evaporation progress for each tested solution were measured. For comparison purposes, the data in the rates of weight loss and impedance decrease were normalized to water and then plotted together in Figure 5. As illustrated in Figure 5, the weight loss demon.......

Discussion

The critical step for evaporation measurement in this impedance-based detection is the preparation of the tested solutions. Deionized water cannot be used due to its enormous impedance. Instead, tap water containing conductive ions was used to prepare hyaluronic acid solutions for experiments. However, the electrical properties of tap water were not constant for use. Therefore, normalization, such as the relative evaporation rate to water in this study, was adopted as an alternative index for.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
95% ethanol	Echo Chemical Co., Ltd., Miaoli, Taiwan	484000001103C-00EC
Acetone	Avantor Performance Materials Inc., Center Valley, PA, USA	JTB-9005-68
Development solution	Kemitek Industrial Crop., Hsinchu, Taiwan	12F01031	KTD-1
Etching solution	eSolv Technology Co., Taipei, Taiwan		EG-462
Hyaluronic acid	Shandong Freda Biopharm Co., Ltd., Jinan, China	1010212	Molecular weight 980k, Cosmetic Grade
Photoresist solution	AZ Electronic Materials Taiwan Co., Ltd., Hsinchu, Taiwan	65101M19	AZ6112
8-well silicone array	Greiner bio-one Inc., Frickenhausen, Baden-Württemberg, Germany	FlexiPERM
ITO glass	GemTech Optoelectronics Co., Taoyuan, Taiwan
Vial	Sigma-Aldrich Co. LLC., St. Louis, MO, USA	854190
Film photomask	Taiwan Mesh Co., Ltd, Taoyuan, Taiwan
Lock-in amplifier	Stanford Research Systems, Inc., Palo Alto, CA, USA	SR830
Switch relay	Instrument Technology Research Center, National Applied Research Laboratories, Hsinchu, Taiwan
Electronic balance machine	Radwag Inc., Radom, Poland	AS 60/220/C/2