Quartz crystal sensor may be one of your choices.

ChemFET Sensors (https://www.ifm.liu.se/edu/coursescms/tftb34/archive/Electronic_noses_and_tongues.pdf)

Other references : 

http://www.hindawi.com/journals/ijelc/2012/986025/

http://www.hindawi.com/journals/ijelc/2012/986025/tab1/

http://www.electronictongue.com/index.html

http://w3.ualg.pt/~hgomes/html/classes/Biosensores/electronic_tongue/e-toungue.pdf

http://www.azosensors.com/Article.aspx?ArticleID=108#2

http://www.le.ac.uk/eg/tcp1/book/Chapter14/ch14_2.pdf

There are different types of sensors that can be used to build an electronic tongue. In many cases depends on the final application the selection of sensors. Thats means, if You need to measure the color of a sample, optical sensors should be used. For ions, electrochemical sensors may be useful, and for molecules, amperometrica based sensors or optical transducers could be applied.

Thanks