Heavy metal ion contamination has become a global problem. The typical detection method is done by water samples collected in filed and sent to a laboratory and detected by Inductively coupled plasma-atomic emission spectrometry (ICP-AES), Inductively coupled plasma-optical emission spectrometry (ICP-OES), Inductively coupled plasma-mass spectrometry (ICP-MS), Flame atomic absorption spectrometry (FLAA), or graphite crucible atomic absorption spectrometry. However, these methods require a lot of labor work for collection and pre-treatment. It is expensive and time-consuming. Ion-selective electrode (ISE) can be made as a portable device, but its detection limit is not good enough to satisfy the regulation. Thus, this project will develop highly sensitive and selective field-effect transistor-based heavy metal ion sensors, which can perform the detection limit as good as ICP-MS, and on the other hand, can connect to wireless and Internet. Finally, due to the small size, simplicity, low cost, and real-time detection, the sensor array fabricated on one chip can monitor lead, cadmium, and mercury ions simultaneously in drinking water, vegetables, and Chinese medicine. Finally, a hand-held readout device will also be developed and transit signals to smartphones with Blue Tooth, followed by data transmission to the cloud for further Internet-of-Things (IoT) applications.