A quick fix for spotting bacteria in water

Bacterial Aqua Sensor
Tom Hansen: alumnus, computer science; graduate student, freshwater sciences<
Marcia Silva: alumna, environmental engineering

A casual chat among colleagues at the School of Freshwater Sciences (SFS) turned into an idea for a portable and inexpensive sensor that quickly detects bacteria in water.

Doctoral student Tom Hansen and recent alumna Marcia Silva remember talking about the value of such a device, but not with the intent of acting on it.

But then the pair heard Dean David Garman and Distinguished Professor Rudi Strickler also talking about the need for such a tool.

“All four of us had the same idea,” says Silva. “It just didn’t happen on the same day or in one discussion.”

Using a laser beam produced by a laser pointer and a sensor similar to one found in a cell phone camera, their device works by creating a holographic image of particles found in a water sample.

The laser’s light waves pass through the sample and scatter off a photographic plate behind it. But the waves also bounce off of particles in the water, creating an interference pattern. Software powered by a computer no bigger than the palm of your hand, which Hansen ordered online, translates interference patterns into a 3D image.

Each partner in this team has brought an expertise to bear. Silva’s doctoral degree is in environmental engineering and her dissertation involved modeling the transport of bacteria on beaches. The research gave her experience in image processing of bacteria tagged with florescent markers.

As the information technology processing consultant at the school, Hansen has been involved in creating or modifying equipment that makes wireless data collection on the Lake Michigan possible.

The creative environment of the workplace brought them together. Silva came to UWM to attend graduate school from her hometown of Porto Alegre on the southern-most tip of Brazil. Hansen is all Milwaukee.

Four engineering students enrolled in the course Product Realization assist on the design and construction of software and hardware needed in the final prototype. The team has the additional benefit of six Lubar School of Business students who are working on a marketing plan for the aqua sensor as part of their for-credit entrepreneurship course.

The team already has a testing prototype, but much work remains. Their prototype, for example, cost nearly $200 to assemble. But for it to be mass-produced, says Hansen, they will have to reduce the cost of producing the device to around $50.

The team currently has submitted the device through the “Product Realization” course a second time to further hone its sensitivity and reduce it size.. Meanwhile, the UWM Research Foundation is actively exploring intellectual property protection for it.

“I’m confident we can be successful in that it can find bacteria in clean water,” says Silva. “What is unknown is whether it can work in water from the field that will have lots of material in it.”

The team is using a microfluidic technique to concentrate the bacterial in a field water sample that might contain a plethora of matter and organisms.

Important to the pair is that any claims they make about the sensor’s capabilities be proven, so they are taking a scientific approach.

Hansen, who was fascinated with creating gadgetry even as a child, says one perk of working in an academic environment is that ideas can present themselves while you’re involved in an unrelated research project, as this one did. But, he says, he would also like to be able to create products for the market.

“Who knows where this thing might take us? But I don’t want the sensor to just exist. I want to take it to the next level.”


The team is talking with two potential collaborators who can help identify uses for the device in the medical field. They also have been approached by a company about licensing the product once it’s completed.