Groundbreaking Ultra-Precision Sensor Technology Developed for Single-Molecule Detection

Abstract
The “hotspots”, which are typically found in nanogaps between metal structures, are critical for the enhancement of the electromagnetic field. Surface-enhanced Raman scattering (SERS), a technique known for its exceptional sensitivity and molecular detection capability, relies on the creation of these hotspots within nanostructures, where localized surface plasmon resonance (LSPR) amplifies Raman signals. However, creating adjustable nanogaps on a large scale remains challenging, particularly for applications involving biomacromolecules of various sizes. The development of tunable plasmonic nanostructures on flexible substrates represents a significant advance in the creation and precise control of these hotspots. This work introduces tunable nanogaps on flexible substrates, utilizing thermally responsive materials to allow real-time control of gap width for different molecule sizes. Through advanced nanofabrication techniques, uniform, tunable nanogaps are achieved over large areas of wafer scale, enabling dynamic modulation of SERS signals. This approach results in an enhancement factor of over ≈10⁷, sufficient for single-molecule detection, with a detection limit as low as 10⁻¹2 m. The thermally tunable nanogaps provide a powerful tool for the precise detection of molecules and offer significant advantages for a wide range of sensing and analytical applications.

A research team, affiliated with the Nano Optics Group within the Department of Physics at UNIST has announced the successful implementation of a plasmonic structure capable of precisely adjusting nanometer-sized gaps in response to temperature changes. This technology enables real-time adjustment of nanogaps to match the size of molecules, allowing for detection capabilities that significantly surpass conventional sensors.

The flexible nanogap structures developed in this research serve as a key component in Surface-Enhanced Raman Spectroscopy (SERS). SERS is an analytical technique that utilizes a strong near-field created by localized surface plasmon resonance induced by incident light on metallic nanostructures based on gold thin films, amplifying Raman signals of molecules by millions of times. By employing flexible substrates, researchers have achieved the dynamic modulation of nanogaps, thus opening up the possibility of effectively analyzing various sizes of molecules that were previously challenging to assess.

Figure 1. a) Schematic representation of the SERS sensing mechanism, showing molecules trapped in the nanogap. b) Schematic diagram of the transfer process of nanogaps with micrometer periodicity onto a flexible substrate. FE-SEM images of the top view of the nanogap c) before and d) after strain (scale bars: 10 µm). (The inset shows a close-up of a single gap from the top, (scale: 1 µm).

The research team successfully developed a method for adjusting nanogaps through temperature control, achieving a remarkable enhancement factor of approximately 10⁷ in SERS signals and reaching a detection limit as low as 10⁻¹² M, suitable for single-molecule detection.

Dr. Mahsa Haddadi Moghaddam, who led the research, stated, “The ability to precisely control nanogaps using temperature changes allows us to achieve much higher sensitivity than conventional SERS sensors. This technology has significant potential, particularly for accurate analyses at the single-molecule level and in various environmental and medical diagnostic applications.”

The research findings have been published online in Advanced Optical Materials, ahead of its formal publication. The study was conducted with support from the National Research Foundation of Korea (NRF).

Journal Reference
Mahsa Haddadi Moghaddam, Sobhagyam Sharma, Daehwan Park, and Dai Sik Kim, “Tuning 1D Plasmonic Gap at Nanometer Scale for Advanced SERS Detection,” Adv. Opt. Mater., (2025).