Nature has evolved a stunning array of biosensors for detecting the physical world.
A single E. coli cell, for example, can precisely sense chemical gradients and “swim” toward or away from them. Some bird species, including robins and warblers, can see magnetic fields using cryptochrome proteins embedded in their eyes to guide them during their annual migration. Bogong moths use photons from distant stars as a compass while soaring 1,000 kilometers across southeast Australia. In other words, organisms can sense not only tastes and smells, but also individual molecules, magnetic fields, and infrared or ultraviolet light.
Humans have long used other creatures’ senses to aid and extend our own, too. As far back as 1,000 BCE, humans employed pigeons to carry messages across cities and kingdoms, taking advantage of their remarkable homing instinct. Dogs’ superior sense of smell is often used to sniff out disease, truffles, contraband, and explosives. And today, the city of Poznań, in Poland, uses just eight mussels to monitor their water quality.
But increasingly, over the last quarter century, scientists have not only used entire organisms to sense the natural world, but have also taken particular genes from those organisms and adapted them into molecular biosensors. Just as a smoke detector has a sensor that detects particles in the air and a buzzer that then alerts us, all human-made biosensors have two basic components.
One of the mussels used to monitor Poznań’s water supply. Credit: Julia Pelka
The first is the sensor itself — an enzyme, antibody, or engineered cell — that physically recognizes a target, whether a pollutant, virus, or rise in temperature. The second is the transducer, which converts that recognition event into a signal we can perceive, such as a glowing light.
Although bioengineers have adapted hundreds of biosensors from nature, they have been less successful in making better transducers. Nearly every biosensor today still relies on a narrow set of outputs (aka “reporters”), such as green fluorescent protein (GFP), luciferase, or colorful pigments. Most transducers can only be seen from close up with a direct line of sight, usually using a microscope. And almost all man-made reporters fail to work inside the body or at a distance. This is because visible light does not penetrate solid materials, such as human skin, and easily “blends in” with other photons in the environment.
Recently, however, bioengineers have developed transducers that transcend such limitations. To make biosensors that work inside the body, scientists have discovered genetically encoded transducers that can be measured using ultrasound or even MRI machines. And for a recent paper in Nature Biotechnology, scientists have reported — for the first time — a new type of transducer that can even be seen from up to 90 meters away using “hyperspectral” cameras mounted to drones. This new technology makes it feasible to monitor individual molecules, as sensed by engineered bacteria, across entire ecosystems.
Hyperspectral Photos
The first hyperspectral cameras were developed in the early 1980s by NASA scientists, who wanted to capture information about Earth, including mineral deposits and ocean algal blooms, from the air. Unlike conventional cameras, which record just three bands of light (red, green, blue), hyperspectral cameras split incoming light into hundreds of narrow spectral bands, including ultraviolet and near-infrared wavelengths.
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