Image created by Dr. Michael J. Miller
A more efficient, low-cost system to help detect microbes in water quickly and easily, could help save millions of lives yearly in developing countries.
Recently, scientists from the Phutung Research Institute in Nepal, the University of São Paulo in Brazil, and the University of York in the UK collaborated to devise a fluorescence detection system.
Unlike conventional instruments that have lenses, this system doesn’t use lenses for microbial detection in drinking water.
Not only, can this fluorescence detection system help detect unsafe water sources but also it can be used to regulate water safety for sporting activities like swimming. This was a concern at the Paris Olympics too.
Dr. Ashim Dhakal, research team leader from the Phutung Research Institute in Nepal told Interesting Engineering that the instrument uses an excitation light source to excite the target molecules from the bacteria in the water sample.
Explaining the process he says that the molecules absorb the energy from the light, lose some of it as heat, and emit the rest of the energy via lower-energy light. The absorption and emission are dependent on the electronic configuration of the target molecules.
“The amount of the emitted light is measured using a detector to quantify the target molecules, which allows us to infer the presence of the bacteria in the sample.”
Referring to the physical form, Dhakal told IE that an LED is used as the excitation source and a photodiode as the detector with their driver-electronics.
“Typically, lenses are used in these systems to maximize the amount of excitation light reaching the target molecules and to collect the emitted light from the molecules,” he added.
Addressing challenges
The challenge faced with microbial detection systems is the usage of lenses because they have to be a specific kind – the limited availability of Numerical Aperture (NA) lenses and integrating them into the design is also a complex process.
The scientist says the new approach completely removes the lenses in the instrument – while significantly enhancing the performance.
The new microbial detection system in water is designed as a lensless fluorescence system with large (1-2 mm2) LEDs and detectors.
According to a statement by the scientists these LEDs recently became available in UV wavelengths. They work by using UV light to excite proteins from harmful microbes and then detecting the resulting fluorescence.
Dhakal says the system targets proteins derived from the amino acid called Tryptophan.
“Tryptophan is the most fluorescent among amino acids called essential amino acids that humans and most of the animals that harbour coliform E. coli in their gut can not synthesize themselves.”
He added that Tryptophan and its derivatives are actively produced and metabolized by E. coli, and are found both within and outside the cells of these bacteria.
“This makes fluorescence from these proteins an appropriate proxy to look for the presence of E coli in water samples.”
The key technology that enabled the new lensless system is the availability of low-cost, large-area (> 1 mm2) LEDs in the deep-UV ( < 280 nm). This was made possible due to Nobel-prize-winning fabrication processes using gallium nitride alloys, Dhakal said.
Easy-to-use microbial detection system
Additionally, recent progress in manufacturing large-area, low-noise, and low-cost photodiodes contributed to the development of the microbial detection system.
The lifespan of the system was expanded as the LEDs utilize less power compared to lensed systems.
What makes this system unique is the measurement results – which are interpretable via simple numbers and traffic-light indicators by ordinary people – available within seconds. This makes it easy to use and allows the stakeholders to take immediate action.
Dhakal noted that a lensless design eliminates costly lenses and the resources needed to align the lenses accurately.
“It also eliminates the associated weight and volume,” he added. “These all together make a lensless system more portable, affordable, and practical in resource-limited settings.”
The team of researchers is currently developing versions that can be integrated into existing water treatment and monitoring infrastructures. They hope for the system to be straightforward.
The lead researcher spotlighted the practical considerations that need to be pondered over.
These include the availability and stability of the power supply, managing the pressure and streamlining the flow from the pipelines, a more robust housing, and regular cleaning of the optical windows to remove the fouling.
The study was published in the journal Optica.