Raphael Thys
Tiny, portable spectrometers might someday fly on drones (like the one shown here) to monitor farm fields for pollutants or signs of crop disease.
Does that food contain gluten? Could the fumes coming from that burning plastic be toxic? Did pollutants reach this farmland? Lab tools called optical spectrometers can identify chemicals to answer such questions. And thanks to a super-tiny new design, that superpower could someday be in your hands.
Most spectrometers sit on a tabletop. This new one is smaller than a human skin cell. Its size and performance make it ideal for use in small devices. Those might include a smartphone or drone, says Zhipei Sun. He’s a physicist at Aalto University in Espoo, Finland. Sun led an international team that described this new device October 21 in Science.
A spectrometer works a bit like a recipe in reverse. Recipes explain how to combine ingredients to make something. Spectrometers deconstruct what’s in something. They use light to identify its ingredients. The ingredients could be any type of substance — from single elements to complex molecules.
When light interacts with matter, each ingredient in that substance slightly changes the light. A spectrometer helps identify such changes by studying a broad range of colors (or wavelengths) of that light.
Desktop spectrometers send light through a sample or examine light coming directly from one. That light travels through a prism or grating at one end of the machine. This separates the light into its component colors — not just one hue, such as blue or red, but the specific shades that can be used to identify each ingredient. As the light continues to move through the device, these colors spread out and separate.
Sensors at the far of end of the machine capture the amount (or intensity) of each color, explains Hoon Hahn Yoon. He’s another physicist at Aalto University. He’s also a co-developer of the new device. The end result of this light analysis is a graph. It maps the light’s color versus intensity. Scientists call this a sample’s optical spectrum.
Each molecule or pure element will create a unique pattern of changes in that spectrum. Scientists have already identified these patterns for many known substances. To identify what’s in a new sample, a computer compares its optical spectrum to these known patterns.
The super tiny new device is the first to offer spectral analyses as detailed as the large spectrometers do, says Yoon. That’s important, he adds, because the more detailed a spectrum, the more accurate the list of ingredients it gives.
The mini spectrometer developed at Aalto University is tiny compared to the chip on which it sits (shown on fingertip). And even that chip is dwarfed by today’s desktop spectrometers, such as the silver one shown in the background of this photo.
How they shrunk the device
Most spectrometers range from the size of a small refrigerator to a deck of cards, says Judith Dawes. She did not take part in the new work. But as a physicist at Macquarie University in Sydney, Australia, she works with optical tools. “As more and more of the technologies we use have been miniaturized,” she says, “we’ve realized it is possible to make spectrometers much smaller.”
Instead of prisms or gratings, the device by Sun’s team relies on two tiny flakes of semiconducting materials. One flake partly overlaps the other. Together, they sit on a computer chip. That chip is only the size of a rice grain.
Light shining on the flakes creates an electric current. That current’s strength is a measure of the intensity of the light. “This is the same basic technology that allows a photovoltaic solar cell to produce electricity from the sun,” Dawes explains.
To get a detailed spectrum, traditional spectrometers need lots of sensors. Each measures the intensity of just one color. The new device uses a single sensor to get data on all of the colors it measures, from visible light to the near-infrared. That data travels right from the chip to a computer. A computer program then uses artificial intelligence to match the resulting spectrum to known patterns in a database. Then it gives a readout of the chemicals to which it matched. Those chemicals are the ingredients of the sample.
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Looking ahead
Sun and Yoon think it might take only a few years to make this tiny spectrometer available for use in phones and other products. “There is still room for engineering advances,” Sun says. However, he sees “no fundamental barriers to overcome.”
“What can we do with such a tiny spectrometer?” asks Dawes. Its size “makes it ideal for placing on a compact drone” or into a device that could be implanted in the body, she says. Small changes in the spectrum of the light its chip measures could signal changes in its environment. One day, she says, it may even be possible that “these devices could help blind people ‘see’ colors through lightweight spectacles.”
Adding a micro-spectrometer to smart devices, such as phones, could lead to other possibilities. People with food allergies could check their food for troublesome ingredients, says Sun. Or people at risk for lung cancer could monitor the gases they exhale for signs of the disease.
Such devices also could make it easier to monitor crop health, pollution, food quality — even the progression of some diseases, his team says.
“This is the beginning of the story,” Sun says. The real story will be all the discoveries and insights that these micro-devices provide.
This is one in a series presenting news on technology and innovation, made possible with generous support from the Lemelson Foundation.
allergen: A substance that causes an allergic reaction.
allergy: The inappropriate reaction by the body’s immune system to a normally harmless substance. Untreated, a particularly severe reaction can lead to death.
artificial intelligence: A type of knowledge-based decision-making exhibited by machines or computers. The term also refers to the field of study in which scientists try to create machines or computer software capable of intelligent behavior.
cell: (in biology) The smallest structural and functional unit of an organism. Typically too small to see with the unaided eye, it consists of a watery fluid surrounded by a membrane or wall.
chemical: A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.
component: Something that is part of something else (such as pieces that go on an electronic circuit board or ingredients that go into a cookie recipe).
computer chip: A computer component that processes and stores information.
crop: (in agriculture) A type of plant grown intentionally grown and nurtured by farmers, such as corn, coffee or tomatoes. Or the term could apply to the part of the plant harvested and sold by farmers.
database: An organized collection of related data.
develop: To emerge or to make come into being, either naturally or through human intervention, such as by manufacturing.
drone: A remote-controlled, pilotless aircraft or missile.
electric current: A flow of electric charge — electricity — usually from the movement of negatively charged particles, called electrons.
element: (in chemistry) Each of more than one hundred substances for which the smallest unit of each is a single atom. Examples include hydrogen, oxygen, carbon, lithium and uranium.
engineering: The field of research that uses math and science to solve practical problems.
environment: The sum of all of the things that exist around some organism or the process and the condition those things create. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature and humidity (or even the placement of things in the vicinity of an item of interest).
fundamental: Something that is basic or serves as the foundation for another thing or idea.
gluten: A pair of proteins — gliadin and glutenin — joined together and found in wheat, rye, spelt and barley. The bound proteins give bread, cake and cookie doughs their elasticity and chewiness. Some people may not be able to comfortably tolerate gluten, however, because they have an allergy to it or suffer from celiac disease.
insight: The ability to gain an accurate and deep understanding of a situation just by thinking about it, instead of working out a solution through experimentation.
matter: Something that occupies space and has mass. Anything on Earth with matter will have a property described as "weight."
molecule: An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms (O2), but water is made of two hydrogen atoms and one oxygen atom (H2O).
monitor: To test, sample or watch something, especially on a regular or ongoing basis.
optical: An adjective that refers to light or vision.
peanut: Not a true nut (which grow on trees), these protein-rich seeds are actually legumes. They’re in the pea and bean family of plants and grow in pods underground.
photovoltaic: An adjective that describes the ability of certain technologies to convert sunlight into electricity.
physicist: A scientist who studies the nature and properties of matter and energy.
pollutant: A substance that taints something — such as the air, water, our bodies or products. Some pollutants are chemicals, such as pesticides. Others may be radiation, including excess heat or light. Even weeds and other invasive species can be considered a type of biological pollution.
prism: A triangular wedge of glass or another clear substance that can bend the components of white light into a rainbow-like succession of colored bands. (v.) To separate light into its component hues.
range: The full extent or distribution of something. For instance, a plant or animal’s range is the area over which it naturally exists.
sensor: A device that picks up information on physical or chemical conditions — such as temperature, barometric pressure, salinity, humidity, pH, light intensity or radiation — and stores or broadcasts that information. Scientists and engineers often rely on sensors to inform them of conditions that may change over time or that exist far from where a researcher can measure them directly.
smart device: Some product or machine that can send information to and retrieve information from the internet, or that can be controlled via the internet, such as by using an app on a smartphone.
solar cell: A device that converts solar energy to electricity.
spectrograph: An instrument used to record light and separate it into its spectrum.
spectrometer: An instrument that measures a spectrum, such as light, energy, or atomic mass. Typically, chemists use these instruments to measure and report the wavelengths of light that it observes. The collection of data using this instrument, a process is known as spectrometry, can help identify the elements or molecules present in an unknown sample.
spectrum: (in light and energy) The range of electromagnetic radiation types; they span from gamma rays to X rays, ultraviolet light, visible light, infrared energy, microwaves and radio waves.
toxic: Poisonous or able to harm or kill cells, tissues or whole organisms. The measure of risk posed by such a poison is its toxicity.
unique: Something that is unlike anything else; the only one of its kind.
verify: (n. verification) To demonstrate or confirm in some way that a particular claim or suspicion is true.
wavelength: The distance between one peak and the next in a series of waves, or the distance between one trough and the next. It’s also one of the “yardsticks” used to measure radiation. Visible light — which, like all electromagnetic radiation, travels in waves — includes wavelengths between about 380 nanometers (violet) and about 740 nanometers (red). Radiation with wavelengths shorter than visible light includes gamma rays, X-rays and ultraviolet light. Longer-wavelength radiation includes infrared light, microwaves and radio waves.
Journal: H.H. Yoon et al. Miniaturized spectrometers with a tunable van der Waals junction. Science. Vol. 378, October 20, 2022, p. 296. doi: 10.1126/science.add8544.