Real-Time Detection of Organic Compounds in Liquid Environments Using Polymer-Coated Thickness Shear Mode Quartz Resonators
详细信息 查看全文
- 作者：Rupa Patel ; Rongnong Zhou ; Kristofer Zinszer ; Fabien Josse ; and Richard Cernosek
- 刊名：Analytical Chemistry
- 出版年：2000
- 出版时间：October 15, 2000
- 年：2000
- 卷：72
- 期：20
- 页码：4888 - 4898
- 全文大小：146K
- 年卷期：v.72,no.20(October 15, 2000)
- ISSN：1520-6882
文摘
The selection of sensitive coatings is a critical task in thedesign and implementation of chemical sensors usingcoated thickness shear mode quartz crystal resonators(QCRs) for detection in liquid environments. This designor selection is performed through a study of the sorptionprocess in terms of the partition coefficients of the analytesin the coatings. The partition coefficient, which is controlled by the chemical and physical properties of thecoating materials, determines the inherent selectivity andsensitivity toward analyte molecules. The selection of thecoatings is logically determined by the interactions between coating and target analyte molecules, but can alsobe made through a systematic variation of the coating'sproperties. The determination of the partition coefficientsis only accurate if all contributions to the total measuredfrequency shifts, 
fs, of the coated QCR can be established. While mass loading is often assumed to be thedominant factor used in determining partition coefficients,viscoelastic effects may also contribute to fs. Both theeffect of viscoelastic properties and the effect of massloading on the sensor responses are investigated by usinga network analyzer and oscillator circuit and by characterizing the total mechanical impedance of the loaded sensor.Different types of coatings including rubbery and glassypolymers are investigated, and the targeted analytesinclude classes of polar compounds (methanol), nonpolarcompounds (toluene, xylenes), and chlorinated hydrocarbons (trichloroethylene, tetrachloroethylene, etc). It isseen that changes in viscoelastic properties due to analytesorption may be significant enough to place the sensor inthe nongravimetric regime. However, for most applications involving the detection of relatively low concentrations of organic compounds and the use of acousticallythin films, changes in the complex shear modulus of thecoatings contribute less than 5% of the total shift in theseries resonant frequency, depending on the coating. Inthat case, the measured fs and, hence, the calculatedsensitivity/partition coefficients can still be used for anapproximate classification and selection of the coatingsfor operation in a complex solution of water/analytemolecules.
fs, of the coated QCR can be established. While mass loading is often assumed to be thedominant factor used in determining partition coefficients,viscoelastic effects may also contribute to fs. Both theeffect of viscoelastic properties and the effect of massloading on the sensor responses are investigated by usinga network analyzer and oscillator circuit and by characterizing the total mechanical impedance of the loaded sensor.Different types of coatings including rubbery and glassypolymers are investigated, and the targeted analytesinclude classes of polar compounds (methanol), nonpolarcompounds (toluene, xylenes), and chlorinated hydrocarbons (trichloroethylene, tetrachloroethylene, etc). It isseen that changes in viscoelastic properties due to analytesorption may be significant enough to place the sensor inthe nongravimetric regime. However, for most applications involving the detection of relatively low concentrations of organic compounds and the use of acousticallythin films, changes in the complex shear modulus of thecoatings contribute less than 5% of the total shift in theseries resonant frequency, depending on the coating. Inthat case, the measured fs and, hence, the calculatedsensitivity/partition coefficients can still be used for anapproximate classification and selection of the coatingsfor operation in a complex solution of water/analytemolecules.