Processing of PP/MWCNT nanocomposites and coating them with plasmonic NPs. (Credit: Sara Fateixa et al., 2023)

Affordably Detecting Water Pollutants Using 3D Printed Lattices And Plasmonic Nanoparticles

Although detecting pollution in surface waters has become significantly easier over the years, testing for specific pollutants still requires the taking of samples that are then sent to a laboratory for analysis. For something like detecting pesticide run-off, this can be a cumbersome and expensive procedure. But a 3D printed sensor demonstrated by [Sara Fateixa] and international colleagues offers hope that such tests can soon be performed in the field. The most expensive part of this setup is the portable Raman spectrometer that is used to detect the adsorbed molecules on the printed test strips.

The printed structure itself forms a plasmonic structure with gold or silver as the plasmonic metals deposited on the polypropylene (PP) and multi-walled carbon nanotube (MWCNT, 4% by weight) material. The mixture of PP and MWCNTs is to use both the bio-compatible properties of the former, while using the latter to make the PP significantly easier to print with and enhancing its mechanical properties.

Hamamatsu Raman Spectroscopy SERS Detection Module C13560.
Hamamatsu Raman Spectroscopy SERS Detection Module C13560.

For the experiment, researchers used a few prepared sensors to detect herbicides, including paraquat. This herbicide is cheap, widely used, and banned in various countries. After dissolving it in low concentrations in both tap water and sea water, a 3D printed sensor with Ag coating was was exposed to each sample before being left to dry at room temperature. Afterwards a Hamamatsu C13560 portable Raman spectrometer was used to analyze the sensors using surface-enhanced Raman scattering (SERS). The combination of plasmonic structures and Raman scattering means a significantly enhanced sensitivity, on the order of singular molecules, and is what makes SERS such a useful analytical technique.

In the resulting scan results, the herbicides showed up clearly, and further long-duration testing of newly printed sensors showed them to be very stable, even after 150 days of being stored. This makes it a promising new way to affordably and quickly perform tests for pollution, requiring only minimal local infrastructure to produce and analyze the sensors.

Heading: Processing of PP/MWCNT nanocomposites and coating them with plasmonic NPs. (Credit: Sara Fateixa et al., 2023)

Internet Of Clams

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.

Clam Sensor Wiring Mississippi River Project

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.

We’ve written about a clam-shaped underwater sensor before, and also reported on the potential of using clams as batteries. This biological sensing technique came to our attention via [Embedded FM podcast #357].

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UnifiedWater Finds Potable Water And Stops Polluters

Millions of people all over the world don’t have access to clean drinking water, and it’s largely because of pollution by corporations and individuals. Solving this problem requires an affordable, scalable way to quickly judge water quality, package the data, and present it to an authority that can crack down on the polluters before the evidence dissipates. Ideally, the solution would be open source and easy to replicate. The more citizen scientists, the better.

[Andrei Florian]’s UnifiedWater flows directly from this line of thinking. Dip this small handheld device below the surface, and it quickly takes a bunch of water quality and atmospheric readings, averages them, and sends the data to a web dashboard using an Arduino MKR GSM.

UnifiedWater judges quality by testing the pH and the turbidity of the water, which gauges the amount of impurities. Commercial turbidity sensors work by measuring the amount of light scattered by the solids present in a liquid, so [Andrei] made a DIY version with an LED pointed at a photocell. UnifiedWater also reads the air temperature and humidity, and reports its location along with a timestamp.

This device can run in one of two modes, depending on the application. The enterprise mode is designed for a fleet of devices placed strategically about a body of water. In this mode, the devices sample continuously, taking readings every 15 minutes, and can send notifications that trigger on predefined thresholds. There’s also a one-and-done individual mode for hikers and campers who need to find potable water. Once UnifiedWater takes the readings, the NeoPixel ring provides instant color-coded judgment. Check out the demo after the break.

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Hackaday Prize Entry: Volturnus ROV Rules The River

Water is kind of like information: both are a vital part of life and are found all around us. But not all water or information is healthy. Much of it may look harmless, but is actually polluted. A staggering number of people in the world have no access to fresh, clean water. ROVs can collect samples and detect pollution, but commercial types are way too expensive for the legions of people who need them.

UV light reveals the presence of optical brightening agents in a sample of lake water.

[allai5] wants to be the catalyst for change. She’s the president of Rogue Robotics, a group of high school students throughout central New Jersey who have pooled their talents to design and build a simple, open-source ROV that’s affordable, repeatable, and environmentally friendly. The team uses Volturnus ROV to collect water samples and UV light to determine the presence of a general type of pollutant known as optical brightening agents (OBAs). This is the stuff they add to laundry detergents and copy paper to whiten the fibers’ appearance. By design, OBAs fluoresce brightly under UV light. After soaking a cotton pad in water sample, it’s easy to see if OBAs are present.

At 12″ x 12″ x 18″, Volturnus ROV is compact enough to explore most of the nooks and crannies of any body of water. It moves under the power of three thrusters—500 GPH bilge pump motors driven by a pair of L298N controllers—and is controlled by an Arduino Mega using a wireless joystick. The driver of the ROV navigates the drink through the eyes of a waterproof car back-up camera whose feed is flipped with a Python script.

Volturnus ROV is not a one-stop solution for dealing with marine pollution. The team would like to add filtration in the future and move the electronics to the bottom so it can go faster. Rogue Robotics’ aim has always been to make an ROV that does a few things well. Right now, it’s an excellent jumping-off point for awareness and blueprint for action. Find your inspiration after the break.

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