At the core of this development is the neuromast, a specialized sensory organ found in fish, which plays a crucial role in their lateral line system. This organ enables fish to perceive minute water movements, pressures, and vibrations, allowing them to navigate murky waters, evade predators, and communicate in complex ways. Inspired by this natural marvel, the research team engineered an optical neuromast structure using advanced 3D-nanoprinting technology, meticulously replicating its architecture and functional characteristics at the nanoscale. This approach allows for the detection of varied mechanical and optical underwater signals, surpassing the capabilities of traditional sensors.

The construction of this neuromast fiber involved the precise layering of nanomaterials into a fiber form that responds optically to external stimuli. By harnessing the principles of photonics, these fibers transduce mechanical disruptions into optical signals without the need for bulky electronic components. This method offers significant advantages, including enhanced sensitivity, broad bandwidth, and immunity to electromagnetic interference—an essential feature for underwater applications where electronic noise can hinder conventional sensing technologies.

What sets this optical neuromast apart is its integrative design, which combines multiple sensing modes within a single fiber platform. This multifunctionality enables the simultaneous detection of water flow, pressure fluctuations, and biogenic signals such as those produced by swimming organisms or underwater vehicles. The device’s embedded nanostructures facilitate distinct optical responses for different stimuli, offering a rich dataset for real-time monitoring and analysis. This capability holds immense potential for environmental surveillance, marine biology, and defense sectors.

The researchers employed two-photon polymerization, a sophisticated additive manufacturing technique, to fabricate the neuromast fibers with sub-micrometer precision. This method allows the creation of highly complex three-dimensional structures that mirror the natural morphology of fish neuromasts. Compared to conventional lithographic techniques, two-photon polymerization provides greater control over feature size and spatial arrangement, critical factors in achieving bio-mimetic functionality and optical accuracy at the nanoscale.

Extensive characterization of the device confirmed its exceptional sensitivity and robustness in underwater environments. Laboratory tests demonstrated the fiber’s ability to detect water motions with speeds as low as a few millimeters per second, reminiscent of the sensitivity exhibited by biological neuromasts. Moreover, the optical output remained stable under varying temperatures and salinity conditions, underscoring the device’s suitability for deployment in diverse marine settings, from shallow coastal zones to deeper oceanic depths.

Beyond sensitivity, the optical neuromast offers intriguing advantages in signal processing and data transmission. The fiber’s optical nature permits direct interfacing with existing photonic communication systems, eliminating the latency and noise associated with electrical signal conversion. This characteristic enables the potential for real-time underwater sensory networks, where distributed neuromast fibers could collectively sense and relay complex environmental information across vast aquatic expanses.

The implications of this technology extend far beyond environmental monitoring. In the realm of autonomous underwater vehicles (AUVs) and robotics, the optical neuromast sensor could provide crucial proprioceptive feedback, allowing machines to maneuver with heightened awareness of their hydrodynamic surroundings. This capability would enhance obstacle avoidance, current sensing, and cooperative behaviors in robotic swarms, facilitating more efficient and adaptive underwater operations.

From a materials science perspective, the integration of soft polymeric elements within the nanoprinted fiber offers mechanical flexibility akin to the biological counterparts’ hair cells. This compliance not only enables efficient mechanical-to-optical transduction but also contributes to the longevity and durability of the sensor under repetitive mechanical stresses common in aquatic environments. Consequently, the sensor exhibits resilience against biofouling and mechanical degradation, two major challenges for long-term marine sensing devices.

The interdisciplinary nature of this research reflects a broader trend toward “neuromorphic” engineering, where biological systems inform the design of artificial sensors and circuits. By mimicking the neuromast’s ability to convert mechanical stimuli into optical signals, the team highlights new pathways for bridging the gap between biological efficiency and technological innovation. This biomimicry may inspire a new generation of sensors that operate seamlessly within natural environments, exhibiting adaptability and energy efficiency far superior to traditional devices.

The research also opens intriguing possibilities for studying aquatic life in situ without intrusion. By deploying arrays of optical neuromast fibers, scientists could non-invasively monitor fish schools, track migration patterns, and capture ecological dynamics through subtle hydrodynamic cues. Such insights could revolutionize marine biology by providing high-resolution spatiotemporal data on underwater ecosystems, potentially aiding conservation efforts and informing environmental policies.

Notably, the fabrication process demonstrates remarkable scalability, making the transition from laboratory prototypes to commercially viable devices feasible. The ability to mass-produce these nanoprinted fibers promises to fuel rapid adoption across various maritime sectors. Moreover, the environmental footprint of manufacturing stays minimal due to the precision and additive nature of the employed printing techniques, aligning well with sustainability goals in the tech industry.

The researchers emphasize that this optical neuromast technology serves as a versatile platform that can be customized for specific applications by tuning structural parameters and material compositions. For example, modifications in nanostructure geometry can alter sensitivity ranges or wavelength responsiveness, enabling tailored solutions for unique detection challenges such as pollution tracking, underwater acoustics, or bio-signal monitoring.

Future work is poised to integrate these fibers into complex sensor networks interconnected via optical fibers and wireless communication links, forming intelligent underwater sensor arrays. Such systems could autonomously monitor marine infrastructures, detect early signs of environmental hazards, and contribute to the burgeoning field of the Internet of Underwater Things (IoUT). The optical neuromast’s inherent advantages of miniaturization and multifunctionality make it a compelling candidate for these ambitious endeavors.

In conclusion, this pioneering 3D-nanoprinted optical neuromast marks a paradigm shift in underwater sensing technology. By harnessing nature’s design principles and state-of-the-art nanofabrication, the researchers have crafted a device that not only mimics biological excellence but also extends beyond it through optical multifunctionality and robust engineering. As this technology matures, it promises to deepen our understanding of aquatic environments and enhance human capabilities in marine exploration, surveillance, and robotics, underscoring the power of biomimicry in driving innovation.

Subject of Research: Bio-inspired underwater sensing technology based on 3D-nanoprinted optical neuromasts.

Article Title: From fish to fiber: 3D-nanoprinted optical neuromast for multi-integrated underwater detection.

Article References:
Li, L., Fan, X., Chen, G. et al. From fish to fiber: 3D-nanoprinted optical neuromast for multi-integrated underwater detection. Nat Commun 16, 7390 (2025). https://doi.org/10.1038/s41467-025-62559-3

Image Credits: AI Generated

Photon avalanche, a rare and powerful photophysical phenomenon, diverges fundamentally from conventional fluorescence behaviors through its exceptionally nonlinear emission response to light excitation. Unlike linear fluorescence where emitted light intensity directly correlates with the excitation source, photon avalanche systems undergo a dramatic, abrupt surge in emission intensity once the excitation threshold is crossed. This effect is analogous to a runaway chain reaction or avalanche, propelled by intricate energy transfer dynamics within the material, amplifying light output exponentially rather than incrementally.

Central to this advancement is a meticulous redesign of lanthanide-doped nanocrystals, achieved through sublattice reconstruction by substituting lutetium ions within the crystal lattice framework. This subtle yet profound alteration induces significant local crystal field distortions, effectively enhancing interionic interactions that are pivotal for photon avalanche phenomena. Such structural manipulation enables a robust positive feedback loop among excited-state absorption (ESA) and cross-relaxation (CR) processes involving thulium ions (Tm³⁺), which mutually reinforce each other to escalate the excited-state population exponentially.

The research, spearheaded by Professor Liu Xiaogang of the NUS Department of Chemistry in collaboration with Professor Liang Liangliang from China’s Xiamen University, breaks new ground by demonstrating the capacity to engineer photon avalanche effects in nanocrystals with optical nonlinearities that leap beyond 500, a figure that eclipses prior benchmarks by an order of magnitude. This ultrahigh-order nonlinear optical response transcends limitations historically imposed on fluorescent probes and nanomaterials, ushering in new possibilities for ultrasensitive detection technologies.

At the core of the photon avalanche mechanism lies a sophisticated interplay of photophysical processes. Initially, ground-state absorption excites electrons to intermediate energy levels, which subsequently undergo excited-state absorption to higher energy states. This excited population then facilitates cross-relaxation energy transfer between neighboring lanthanide ions, effectively creating a regenerative cycle. The positive feedback loop generated between ESA and CR engenders a rapid and exponential increase in photon emission, akin to an optical cascade, which amplifies even minuscule fluctuations in excitation into significant emission shifts.

The nanoscopic scale engineering achieved by the team is particularly notable. By introducing lattice distortions at the nanoscale, the materials demonstrate enhanced energy transfer dynamics that magnify nonlinear responses. For instance, 27-nanometer nanocrystals exhibited optical nonlinearities exceeding 150, sufficient for super-resolution imaging modalities using only a single beam of excitation light. Notably, these materials achieved spatial resolution around 33 nanometers laterally and 80 nanometers axially—rivaling the performance of complex techniques such as Stimulated Emission Depletion (STED) microscopy without demanding elaborate instrumentation or high excitation intensities.

Scaling up to larger nanodisks of approximately 170 nanometers revealed even more pronounced nonlinearities exceeding 500. Fascinatingly, these larger structures exhibited spatially heterogeneous emission patterns within individual nanocrystals, enabling imaging capabilities that surpass the physical dimensions of the emitters themselves. Such spatial resolution and emission patterning introduce novel avenues for precise manipulation and detection at the nanoscale, leveraging the intrinsic nonlinear dynamics of photon avalanche materials.

The implications of this pioneering work extend far beyond imaging. The ultrahigh nonlinear response of these engineered nanomaterials opens pathways toward creating cost-effective and compact optical amplifiers capable of transducing subtle changes across a variety of stimuli—including light intensity, temperature fluctuations, and environmental variables—into amplified optical signals. These properties render photon avalanche nanomaterials ideal candidates for next-generation chemical and biosensors with extraordinary sensitivity.

Moreover, the research lays a strong foundation for advancements in quantum photonics. The precise control over nonlinear emission and feedback mechanisms underpinning photon avalanche phenomena may be harnessed to develop novel optical switches and photon sources critical for quantum information processing. The ability to spatially and intensity-specifically control emission at the nanoscale also hints at potential breakthroughs in high-density data storage and encryption technologies, where information can be encoded and retrieved through modulated optical signals with sub-wavelength precision.

Professor Liu reflects on the broader significance of the findings: “By integrating photon avalanche effects with atomically precise nanomaterials design, we are challenging the conventional thresholds of nonlinear optics. This convergence paves the way for an entirely new generation of light-driven technologies that promise unprecedented speed, compactness, and sensitivity.”

Published in the journal Nature on June 18, 2025, this research represents a milestone in photonics and materials science, potentially catalyzing a suite of technological innovations across biomedical imaging, sensing, and quantum device engineering. The combination of experimental insight and nanoscopic control achieved in this study exemplifies the growing interdisciplinarity driving modern scientific frontiers.

In conclusion, the NUS-led team’s success in pushing optical nonlinearity beyond previously attainable limits through careful lattice engineering not only enhances fundamental understanding of photophysical mechanisms but also unlocks myriad practical applications. As photon avalanche nanophotonics matures, it promises to transform how scientists and engineers exploit light-matter interactions for precision imaging, sensing, and information technologies in the years to come.

Subject of Research: Not applicable

Article Title: Optical nonlinearities in excess of 500 through sublattice reconstruction.

News Publication Date: 18 June 2025

Web References:
https://www.nature.com/articles/s41586-025-09164-y
http://dx.doi.org/10.1038/s41586-025-09164-y

Image Credits: National University of Singapore

Keywords

Physical sciences, Chemistry