Research Reveals Adaptive Gap-Tunable Raman Spectroscopy


Gap plasmon (GP) resonance in static surface-enhanced Raman spectroscopy (SERS) structures is generally too narrow and not tunable. Here, we present an adaptive gap-tunable SERS device to selectively enhance and modulate different vibrational modes via active flexible Au nanogaps, with adaptive optical control. The tunability of GP resonance is up to ∼1200 cm-1 by engineering gap width, facilitated by mechanical bending of a polyethylene terephthalate substrate. We confirm that the tuned GP resonance selectively enhances different Raman spectral regions of the molecules. Additionally, we dynamically control the SERS intensity through the wavefront shaping of excitation beams. Furthermore, we demonstrate simulation results, exhibiting the mechanical and optical properties of a one-dimensional flexible nanogap and their advantage in high-speed biomedical sensing. Our work provides a unique approach for observing and controlling the enhanced chemical responses with dynamic tunability.

Professor Daeshig Ghim and his research team in the Department of Physics at UNIST, in collaboration with Professor Yong Doug Suh in the Department of Chemistry at UNIST, who concurrently holds the position of Associate Director at the IBS Center for Multidimensional Carbon Materials (CMCM), has achieved a groundbreaking milestone in sensor technology. Together with Professor Young-Duck Park and his research team in the Department of Physics from POSTECH, they have unveiled an adaptive gap-tunable broadband nanogap gold (Au) spectral sensor that enables precise control of nanogaps, using flexible materials. The newly-developed technology enables rapid inspection of various substances, including infectious diseases and viruses, by identifying molecular fingerprints with a single nano spectrometer sensor.

In light of recent pandemic outbreak, like COVID-19, the pressing need for swift and accurate analysis techniques has been underscored. Raman spectroscopy, facilitated by Au nanostructures, offers high sensitivity in detecting molecular vibrations, known as 'molecular fingerprints,' to provide internal structure and chemical information of materials. This capability can significantly aid in the prompt identification of virus presence.

Traditional high-sensitivity Raman spectroscopy sensors are limited in their applicability, as they can detect only one type of virus with a single device, posing challenges in terms of productivity, detection speed, and cost for clinical use. However, the collaborative research team has successfully developed a one-dimensional structure of Au nanogaps that can accommodate molecules within a few millimeters, enabling large-area high-sensitivity Raman sensing. By integrating flexible materials onto a substrate of the Au nanogap spectral sensor, the team has achieved the flexibility to adjust gap width according to the size and type of substances, including viruses, leading to the creation of a versatile broadband active nano spectrometer source technology.

To enhance the sensor sensitivity and control, the team has applied adaptive optics (AO) technologies, akin to that used in space optics, such as the James Webb Telescope. Moreover, they have devised a conceptual model to extend the successful one-dimensional structure to a two-dimensional spectroscopic sensor, demonstrating the potential for significant signal amplification in Raman spectroscopy. This breakthrough opens the doors for real-time testing, allowing for rapid virus detection within seconds, a process that previously took days.

The groundbreaking achievements of the research team, which are currently pending patent approval, are poised to revolutionize the response to infectious diseases by enabling high-sensitivity real-time testing to prevent rapid transmission. Taeyoung Moon, the lead author of the study, emphasized the significance of this milestone, stating, "Our study not only delves into the fundamental scientific understanding of various substances, from molecules to viruses, but also offers a practical solution for swiftly detecting emerging viruses with a tailored sensor."

The findings of this study have been published in the latest issue of Nano Letters. This has been carried out in collaboration with researchers from POSTECH, including Yeonjeong Koo, Mingu Kang, and Hyeongwoo Lee.

Journal Reference

Taeyoung Moon, Huitae Joo, Bamadev Das, et al., "Adaptive Gap-Tunable Surface-Enhanced Raman Spectroscopy," Nano Lett., (2024).

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