Sensors aren’t just limited to the electrical, mechanical, or chemical realm. Up until 1986, canaries were used as Carbon Monoxide detectors, and food tasters are still used by some heads of state. These so-called sentinel species have been known and used for decades if not centuries. But recent projects using clams to detect water pollution are providing real-time electronic feedback. They are using the species Actinonaias ligamentina, which, as you no doubt recall, was declared “Mussel of the Month” by the University of Wisconsin’s MUSSEL Project back in January 2010. They are more commonly known as mucket clams or mucket mussels, and are particularly sensitive to water pollution — they will clam-up, so to speak, in the presence of contaminated water.
Several municipalities along the Mississippi River installed clam-based sensors back in 2015, and another system was installed in the Anacostia River Estuary in 2011. Polish director Julia Pekla produced a documentary about the clam-based sensors installed at the Dębiec Water Treatment Plant on the Wisła River near Warsaw which has been in operation since 1994. Her documentary is titled “Gruba Kaśka (Fat Kathy)” and won the In Vivo Award at the 2020 Imagine Science Film’s 13th annual film festival (see trailer below).
As shown in the lead photo, a simple electrical contact is mounted on each clam, which closes a circuit with the base contact when the shell is clamped shut. The systems along the Mississippi River use multiple clams, 11 in Minneapolis Minnesota and 16 in Moline Illinois. The system in Poland uses eight clams — when four or more clams are in agreement the system automatically shuts down and alerts the operators. These clams only work for three months, after which they are put into retirement with a mark so they won’t be required to serve again.
An international team at Penn State led by [Larry Cheng] made a breakthrough in printing sensors directly on skin without heat. The breakthrough here is the development of a room-temperature sintering technique. Typical sintering of copper happens at 300 C, and can be further lowered to 100 C by adding nanoparticles. But even 100 C is too hot, since skin starts to burn at around 40 C.
You can obtain their journal article if you want the details, but basically their technique combines the ingredients in peelable face masks and eggshells. With this printed circuit is applied to the skin, the sintering process only requires a hair dryer on the cool setting, and results can bend and fold without breaking the connections. A hot shower will remove the circuit without damaging the circuit or your skin. [Larry] says the circuits can be recycled.
They are using these sensors to monitor temperature, humidity, blood oxygen levels, and heart performance indicators. They’ve even linked these various on-body sensors with a WiFi network for ease of monitoring. After reading this report, we’re left wondering, if the sensor is directly on your skin, can it be really called wearable?
We’ve written about printable inks before, but for printed circuit board applications. We can’t help but wonder if this technology would help solve some problems inherent in that technology, as well. Thanks to [Qes] for the tip.