Biosensors are devices that exploit biological materials or living microorganisms to detect particular chemicals in their surroundings.
These biotech devices are becoming essential tools of the trade in wildlife conservation and ecological science.
They deliver quick, accurate, and detailed data vital in keeping wildlife safe from a myriad of threats, including illegal hunting, climate change, and other environmental threats.
The concept of a biosensor is familiar to all of us. Some are already in major use, with pregnancy and Covid-19 tests as well-known examples.
There is no single type of biosensor. Different devices contain different living organisms or biomaterials, each with various detection capabilities.
In conservation and ecology, biosensors are used to detect certain ions (to identify heavy metal pollution, for example), pathogens, enzymes, microplastics, or algal toxins.
Ecologists and conservators are already using biosensors to monitor pollution, animal pathogens, and even whether there are specific kinds of animals present in a particular habitat. New biosensors are constantly being developed for fresh applications.
Here’s how they help scientists monitor, understand, and ultimately help protect natural habitats.
The race to save coral
Coral reefs are one of the most spectacular natural artefacts. These mineral architectures harbour a huge density of marine wildlife, often found nowhere else.
They also support human life, harbouring new drugs (azidothymidine for HIV was discovered in a sponge in a Caribbean reef) or supporting local economies through tourism or fisheries.
Yet these shimmering incubators are fast disappearing. Human activity and climate change have driven a 14 percent decline in global reefs between 2009 and 2018. The loss in speeding up.
Scientific understanding and accurate measurement is essential to save the remaining reefs. Biomaterials are helping advance this by enabling real-time data collection on underwater threats.
Fighting coral bleaching
Biosensors help scientists understand the chemical composition of seawater in more detail than other methods.
One biosensor with potential in coral reef monitoring uses a mix of selected microalgae and microbes as sensing organisms. Scientists have demonstrated this device can detect petroleum hydrocarbons and heavy metals underwater.
There are even more exotic forms of biosensors that could be useful in marine monitoring. One of them exploits the sensitivity of protein nucleic acid phages. These can detect pathogens, herbicides, and disease markers – useful in reef research as these habitats are highly sensitive to a range of pollutants, including agricultural runoff into the sea.
Scientists are already using biosensors to study coral resilience during bleaching events. This happens when the seawater gets too warm, prompting coral to expel life-giving algae from their tissues. This puts the coral at risk of starvation and disease. It can take between 9 and 12 years for a recovery.
Coral probiotics are important to understand when it comes to safeguarding coral reefs from warming sea temperatures. These are microorganisms that support coral health, bolstering its defences against potentially lethal bleaching events.
Researchers at the Guangxi Laboratory in China recently developed a brand new type of biosensor to detect the coral probiotic species C. marina in order to learn more about the protection these organisms offer coral reefs.
To do this, they built a biosensor that exploits the sensitive properties of a biological substance called oligonucleotides. These are short DNA or RNA molecules and are already used in genetic testing and forensics. The researchers reported that their new biosensor had ‘excellent performance’, detecting the C. marina DNA even at very dilute concentrations.
Chinese universities have become a hotbed of research into biosensors for coral reef monitoring. Yet the country is also a major driver in the destruction of reefs as it vyes for territorial claims to low-lying reefs and islets in the South China Sea with the Philippines, Malaysia, Brunei, Taiwan, and Vietnam.
Rooting out poison-fishing in the Philippines
Biosensors can be highly sensitive, rapid, and accurate. This makes them ideal in helping authorities protect coral reefs by tracking down illegal fishers.
Sodium cyanide is a substance illegal fishers use in the water to stun fish while still keeping them alive. In the Philippines, some use this method of illegal fishing to collect tropical sea fish for the aquarium trade.
The process is gruesome: fishermen squirt bottles laced with sodium cyanide pellets into coral reef crevices where the fish of interest live.
Once stunned, the fish are easily collected and placed into seawater back on the boat. It is estimated that over 1 million kilos of the stuff have been used in Philippine reefs since the 1960s.
Needless to say, sodium cyanide is highly toxic to the fragile reef system. The cyanide disrupts the symbiotic algae that live inside the coral and which allows the coral to ‘eat’. Without them, the coral lacks the means to consume nutrients from the seawater around. Eventually, the coral reef starves.
Biosensors are now being used to combat cyanide fishing. Their rapidity is what gives them the advantage in this application: these light, portable devices can quickly and accurately detect the compound in the water without the need for lengthy analysis back in the laboratory, as with older methods of detection.
Speedy cyanide detection is paramount in this work: any fish poisoned by sodium cyanide can quickly recover thanks to their efficient detoxification mechanisms.
Living cyanide detectors
How can biosensors alert trackers to the presence of cyanide? There are several ways that living microorganisms are used to detect the poison. All depend on the specific ways these creatures respond to the chemical.
Some bacterial species can biodegrade cyanide. These bacteria are placed in the sensor. If the poison is present, the bacteria convert the cyanide into cyanate-consuming oxygen. This means any decrease in dissolved oxygen in the biosensor indicates the presence of cyanide.
Some cyanide biosensors exploit the way that cyanide restricts microbial respiration. The decrease in oxygen consumption by the microbe therefore acts as a reliable signal that the poison has been detected.
Other cyanide biosensing methods rely on how the cyanide disrupts enzyme production by the microbes.
Tracking invaders and diseases
Biosensors are also being used to monitor underwater ecological threats not from humans but from certain kinds of wildlife.
When invasive fish move into a new area, they can quickly upset the ecological balance of the habitat. Stronger species can quickly outcompete or consume existing fish, creating a less diverse habitat.
Yet monitoring invasive fish in real-time is incredibly difficult. It is impractical and expansive to install in-situ monitoring systems in fast and deep rivers and lakes.
Zebra mussels are a common invasive species around the world. They can cause widespread economic damage for humans by clinging to the insides of pipes. They also reduce the amount of food available for other aquatic species.
To detect populations quickly and accurately, Portuguese researchers have developed an enzyme-based biosensor that signals the presence of zebra mussel DNA in water.
The next frontier for biosensor applications in the field could be in wildlife disease detection. The US Geological Survey has pioneered in this area, developing a biosensor for a disease that has killed more than five million bats in North America since 2006.
White-nose syndrome is an infectious disease that afflicts bats while hibernating over winter. In some North American bat colonies, up to 99 percent have died from the ailment.
The new biosensor works to detect the DNA of the fungal agent that causes the disease through skin swabs or dropping samples of bats.
The biosensor could now aid early treatment, which depends on accurately detecting the bacteria and estimating how far the fungus has travelled.
The advantages of biosensors
Biosensors are now an integral part of monitoring environments and detecting threats to wildlife and habitats. Biomaterials can do things that other materials cannot when it comes to monitoring natural environments consistently and systematically.
Conventional methods rely on samples that need sending back to the lab – something that takes time and can lead to samples degrading in transit.
By contrast, biosensors offer simplicity, rapidity, portability, and affordability. Light and quick enough to work in-situ, scientists can take quick readings in the field. This property can make a crucial difference in applications where time is of the essence, such as detecting the signs of illegal hunting.
Conventional monitoring methods for coral reefs (for example, using satellite imagery of the water) are comparatively limited in that they tend to deliver on a basic set of information such as salinity, dissolved oxygen, and temperature.
For conservation relevance, scientists often need more detailed data, such as the presence of enzymes and pollutants or agriculture pesticides.
Biosensors are as diverse as the capabilities of the bacteria or biomaterials inside them, meaning they can be custom-made to pick up on environmental signals that other forms of analysis cannot.
This versatility is useful to ecologists and conservationists, who want a complete picture of the coral reef’s environmental condition. They offer a potent example of how biotech can widen the lens that science has on threatened habitats.
