Nav: Home

Quantum physics and origami for the ultimate get-well card

March 29, 2019

Paper-based diagnostic tests are cheap, convenient and biodegradable. However, their use is limited by conventional dyes - which are not bright enough to show trace amounts of analyte, are prone to fading, and can be environmentally toxic.

Now researchers are using quantum physics to overcome these limitations, says a review published in Frontiers in Bioengineering and Biotechnology. The bizarre optical properties of tiny metal particles - smaller than light waves - can be captured on paper to detect even a single target molecule in a test sample. These hyper-sensitive testing devices could be assembled and customized at the point of use in low-resource environments, with virtually limitless applications spanning medicine, forensics, manufacturing and environmental safety.

"A new generation of paper-based analytical devices is being developed, which use metal nanoparticles for analyte identification," says lead author Dr. Eden Morales-Narváez of the Center for Optics Research in Mexico. "These will allow low-cost testing in low-resource settings from clinics to crime scenes to contaminated water sources."

Paper-based diagnostics are smart but not bright

Paper is an ideal medium for cheap, accessible diagnostic devices - and has come a long way already from pregnancy-test-style strips that simply mix a sample with a test chemical.

"Paper devices can filter, concentrate and mix reagents with controlled timing and sequence - by using guidelines that can be scored, drawn or even printed on," explains Morales-Narváez. "Some groups have even used origami to vary flow direction and add processing steps that allow more sophisticated, duplicate or parallel reactions using a single paper device."

The real difficulty comes in reading the results of these paper-based tests.

"Test reactions are set up so that if the substance of interest or 'analyte' - a biomarker or pollutant, for instance - is present in a sample, a colored pigment is produced or altered.

"The problem is that conventional pigments produce colors by selectively absorbing some wavelengths and simply reflecting others - for example, red ink appears red because it absorbs strongly in the blue and green spectral regions.

"This means that for a visible color change to occur, relatively large amounts of analyte are required. In other words, the test is not very sensitive."

To make matters worse, the test result cannot be saved as a record because pigments are prone to fading, and in some cases cannot be safely discarded because of pigment toxicity.

A quantum physics solution

What paper-based tests need is an ultra-bright color indicator. Cue metal nanoparticles (MNPs).

"MNPs are can give a brighter, lasting color signal, since they dramatically amplify a particular wavelength of light - rather than simply reflecting it," sums up Morales-Narváez.

As the name suggests, MNPs are nanometer-sized pieces of metal. At about 10-100 times smaller than light waves, their behavior enters the strange realm of quantum physics.

"Put simply: metals consist of a fixed lattice of positive ions, which share a "cloud" of negatively charged free electrons.

"In nanometer-sized pieces of metal, certain wavelengths of light make these free electrons vibrate with respect to the fixed positive ions in the metal. This vibration amplifies the light, emitting a brighter color."

Still confused? Remember that light is a visible electromagnetic field. Imagine a cube of metal placed inside this field. Electrons, being negatively charged, will move to positive pole of the field, uncovering positive metal ions at the negative pole. When the field is gone (or rather as it - the light wave - oscillates) the electrons move in the opposite direction, repelled by each other and attracted back towards the uncovered positive metal ions. The electrons oscillate back and forth in this way with the changing polarity of the electromagnetic field.

Ultra-sensitive paper-based diagnotics

Crucially, the particular wavelength that causes the free electrons to vibrate is tuneable - so the color amplified by MNPs depends on their shape, size and spacing, as well as the type of metal and surrounding medium.

As a result, there are various ways to couple a paper-based test reaction to a change in MNP color.

"You can make MNPs that bind the analyte, then let these flow in solution over fixed biorecognition elements on the paper such as antibodies, that also bind the analyte. A positive test will cause the MNPs to accumulate and so change their spacing and surroundings.

"Alternatively, MNPs can be released from a holding molecule when this reacts with an analyte.

"Some analytes can even erode MNPs, causing a color change directly. For example, ammonia and other volatile compounds from food spoilage, or UV radiation from sun exposure."

The result: ultra-sensitive paper diagnostics.

"MNPs can produce visible color changes at even attomolar concentrations of analyte," confirms Morales-Narváez.

That's about 30 molecules per drop of test sample. But if the paper test is read by a special machine rather than the human eye, the sensitivity is even higher still.

"Combined with a scanning technique called Raman spectroscopy, MNPs can report detection of a single molecule of analyte."

With over 10,000 research articles exploring the use of MNPs published in 2018 alone, it may not be long before quantum physics-powered paper diagnostic devices enter the mainstream.
Please link to the original research article in your reporting:

Frontiers is an award-winning Open Science platform and leading Open Access scholarly publisher. Our mission is to make research results openly available to the world, thereby accelerating scientific and technological innovation, societal progress and economic growth. We empower scientists with innovative Open Science solutions that radically improve how science is published, evaluated and disseminated to researchers, innovators and the public. Access to research results and data is open, free and customized through Internet Technology, thereby enabling rapid solutions to the critical challenges we face as humanity. For more information, visit and follow @FrontiersIn on Twitter.


Related Quantum Physics Articles:

Quirky response to magnetism presents quantum physics mystery
In a new study just published and highlighted as an Editor's Suggestion in Physical Review Letters, scientists describe the quirky behavior of one such magnetic topological insulator.
Evidence of power: Phasing quantum annealers into experiments from nonequilibrium physics
Scientists at Tokyo Institute of Technology (Tokyo Tech) use commercially available quantum annealers, a type of quantum computer, to experimentally probe the validity of an important mechanism from nonequilibrium physics in open quantum systems.
Adapting ideas from quantum physics to calculate alternative interventions for infection and cancer
Published in Nature Physics, findings from a new study co-led by Cleveland Clinic and Case Western Reserve University teams show for the first time how ideas from quantum physics can help develop novel drug interventions for bacterial infections and cancer.
Quantum physics: Realization of an anomalous Floquet topological system
An international team led by physicists from the Ludwig-Maximilians Universitaet (LMU) in Munich realized a novel genuine time-dependent topological system with ultracold atoms in periodically-driven optical honeycomb lattices.
Quantum physics provides a way to hide ignorance
Students can hide their ignorance and answer questions correctly in an exam without their lack of knowledge being detected by teachers -- but only in the quantum world.
Quantum physics: Physicists develop a new theory for Bose-Einstein condensates
Bose-Einstein condensates are often described as the fifth state of matter: At extremely low temperatures, gas atoms behave like a single particle.
Attosecond physics: Quantum brakes in molecules
Physicists have measured the flight times of electrons emitted from a specific atom in a molecule upon excitation with laser light.
Quantum physics: On the way to quantum networks
Physicists at Ludwig-Maximilians-Universitaet (LMU) in Munich, together with colleagues at Saarland University, have successfully demonstrated the transport of an entangled state between an atom and a photon via an optic fiber over a distance of up to 20 km -- thus setting a new record.
Quantum physics: Controlled experiment observes self-organized criticality
Researchers from Cologne, Heidelberg, Strasbourg and California have observed important characteristics of complex systems in a lab experiment.
A platform for stable quantum computing, a playground for exotic physics
Harvard University researchers have demonstrated the first material that can have both strongly correlated electron interactions and topological properties, which not only paves the way for more stable quantum computing but also an entirely new platform to explore the wild world of exotic physics.
More Quantum Physics News and Quantum Physics Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Debbie Millman: Designing Our Lives
From prehistoric cave art to today's social media feeds, to design is to be human. This hour, designer Debbie Millman guides us through a world made and remade–and helps us design our own paths.
Now Playing: Science for the People

#574 State of the Heart
This week we focus on heart disease, heart failure, what blood pressure is and why it's bad when it's high. Host Rachelle Saunders talks with physician, clinical researcher, and writer Haider Warraich about his book "State of the Heart: Exploring the History, Science, and Future of Cardiac Disease" and the ails of our hearts.
Now Playing: Radiolab

Insomnia Line
Coronasomnia is a not-so-surprising side-effect of the global pandemic. More and more of us are having trouble falling asleep. We wanted to find a way to get inside that nighttime world, to see why people are awake and what they are thinking about. So what'd Radiolab decide to do?  Open up the phone lines and talk to you. We created an insomnia hotline and on this week's experimental episode, we stayed up all night, taking hundreds of calls, spilling secrets, and at long last, watching the sunrise peek through.   This episode was produced by Lulu Miller with Rachael Cusick, Tracie Hunte, Tobin Low, Sarah Qari, Molly Webster, Pat Walters, Shima Oliaee, and Jonny Moens. Want more Radiolab in your life? Sign up for our newsletter! We share our latest favorites: articles, tv shows, funny Youtube videos, chocolate chip cookie recipes, and more. Support Radiolab by becoming a member today at