Dynamic photonic barcodes record energy transfer at the biointerface

Dynamic photonic barcodes record energy transfer at the biointerface
Dynamic photonic barcodes enable molecular detection. Credit: Zhou et al., doi 10.1117/1.AP.2.6.066002

Optical barcodes enable detection and tracking via unique spectral fingerprints. They’ve been widely applied in areas ranging from multiplexed bioassays and cell tagging to anticounterfeiting and security. Yu-Cheng Chen of the Bio+Intelligent Photonics Laboratory at Nanyang Technological University notes that the concept of optical barcodes typically refers to a fixed spectral pattern corresponding to a single target.


“Optical barcodes have lacked the capability to characterize dynamic changes in response to analytes through time,” says Chen. Thanks to Chen’s research, that’s about to change.

Chen’s group recently developed bioresponsive dynamic barcodes, introducing the concept of resonance energy transfer at the interface of the microcavity. As reported in Advanced Photonics, the team demonstrated the barcode experimentally to detect molecules in a droplet. The radiative energy from a single microdroplet is transferred to binding biomolecules, converting dynamic biomolecular information into more than trillions of distinctive photonic barcodes.

Cavity-enhanced radiative energy transfer

The system is based on a whispering-gallery mode resonator (WGMR). The majority of WGMRs are classified as passive. As such, they require evanescent wave coupling and operate based on mode changes induced by perturbations. “In contrast,” explains Chen, “active resonators that utilize the analyte as a gain medium can support free-space excitation and collection to acquire more biological information from emission signals.”

Dynamic photonic barcodes record energy transfer at the biointerface
Concept of cavity-enhanced energy transfer. (b) Schematic diagram interpreting cavity energy transfer and the photonic barcoding. The top panel illustrates WGM with and without the acceptor near the cavity boundary. The bottom panel shows the corresponding spectra and photonic barcodes before and after energy transfer. (c) Dynamic optical spectra and corresponding photonic barcodes from binding biomolecules. Credit: Zhou et al., doi 10.1117/1.AP.2.6.066002

According to Chen, the trouble when considering molecular detection is the mode occupation factor of the analyte outside the cavity: It is only a few tenths from that inside the cavity, leading to a reduced effective Q-factor and unsatisfactory signal-to-noise ratio. The concept of resonant energy transfer separates donor molecules and acceptor molecules at the cavity interface, where radiative energy transfer happens. Radiative energy transfer is accompanied by electromagnetic radiation (unlike conventional non-radiative fluorescence resonance energy transfer, known as FRET). Because of that radiation, energy transfer can occur even in situations where the donor and acceptor are separated.

“In the presence of cavity-enhanced mechanisms, efficient energy transfer and coupling between donors and acceptors may lead to enhanced light-matter interactions and signal-to-noise ratio,” says Chen.

The developed system takes advantage of an effect whereby the high concentration of dye (donor) inside the microdroplet triggers a cavity-enhanced energy transfer to excite the molecules (acceptor) attached to the cavity interface.

“When biomolecules bind to the cavity interface, the number of binding molecules alters the amount of energy transfer, resulting in distinctive modulated fluorescence emission peaks,” says Chen. Dynamic spectral barcoding was achieved by a significant improvement in the signal-to-noise ratio upon binding to target molecules.

According to the authors, this biomolecular encoding system illuminates a beacon for real-time

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Microsoft may earn an Affiliate Commission if you purchase something through recommended links in this article



Microsoft may earn an Affiliate Commission if you purchase something through recommended links in this article



Microsoft may earn an Affiliate Commission if you purchase something through recommended links in this article



Microsoft may earn an Affiliate Commission

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Impact craters reveal details of Titan’s dynamic surface weathering

Impact craters reveal details of Titan's dynamic surface weathering
This composite image shows an infrared view of Saturn’s moon Titan from NASA’s Cassini spacecraft, captured in 2015. Several places on the image, visible through the moon’s hazy atmosphere, show more detail because those areas were acquired near closest approach. Image Credit: NASA/JPL/University of Arizona/University of Idaho

Scientists have used data from NASA’s Cassini mission to delve into the impact craters on the surface of Titan, revealing more detail than ever before about how the craters evolve and how weather drives changes on the surface of Saturn’s mammoth moon.


Like Earth, Titan has a thick atmosphere that acts as a protective shield from meteoroids; meanwhile, erosion and other geologic processes efficiently erase craters made by meteoroids that do reach the surface. The result is far fewer impacts and craters than on other moons. Even so, because impacts stir up what lies beneath and expose it, Titan’s impact craters reveal a lot.

The new examination showed that they can be split into two categories: those in the fields of dunes around Titan’s equator and those in the vast plains at midlatitudes (between the equatorial zone and the poles). Their location and their makeup are connected: The craters among the dunes at the equator consist completely of organic material, while craters in the midlatitude plains are a mix of organic materials, water ice, and a small amount of methane-like ice.

From there, scientists took the connections a step further and found that craters actually evolve differently, depending on where they lie on Titan.

Some of the new results reinforce what scientists knew about the craters—that the mixture of organic material and water ice is created by the heat of impact, and those surfaces are then washed by methane rain. But while researchers found that cleaning process happening in the midlatitude plains, they discovered that it’s not happening in the equatorial region; instead, those impact areas are quickly covered by a thin layer of sand sediment.

That means Titan’s atmosphere and weather aren’t just shaping the surface of Titan; they’re also driving a physical process that affects which materials remain exposed at the surface, the authors found.

“The most exciting part of our results is that we found evidence of Titan’s dynamic surface hidden in the craters, which has allowed us to infer one of the most complete stories of Titan’s surface evolution scenario to date,” said Anezina Solomonidou, a research fellow at ESA (European Space Agency) and the lead author of the new study. “Our analysis offers more evidence that Titan remains a dynamic world in the present day.”

Unveiling Secrets

The new work, published recently in Astronomy & Astrophysics, used data from visible and infrared instruments aboard the Cassini spacecraft, which operated between 2004 and 2017 and conducted more than 120 flybys of the Mercury-size moon.

“Locations and latitudes seem to unveil many of Titan’s secrets, showing us that the surface is actively connected with atmospheric processes and possibly with internal ones,” Solomonidou said.

Scientists are eager to learn more

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