Single-beam optical trap-based surface-enhanced Raman scattering optofluidic molecular fingerprint spectroscopy detection system

In an article published in Opto-Electronic Advances a research team from the Key Laboratory of Optoelectronic Technology and System, Chongqing University, Chongqing, China discussed a single-beam optical trap-based surface-enhanced Raman scattering optofluidic molecular fingerprint spectroscopy detection system.

Raman spectroscopy is a non-destructive analytical technique that allows for precise analysis of substances according to their specific molecular Raman spectral characteristics. Traditional Raman spectroscopy techniques, however, have suffered from weak signal intensity which has limited their use in high-sensitivity detection applications. Surface-enhanced Raman scattering (SERS) technology by contrast can amplify Raman signals by several million times.

The optofluidic SERS system, which integrates SERS technology with so-called ‘lab-on-a-chip’ systems, enables precise control of fluid motion on a microscale and execution of complex experimental procedures. This results in rapid, portable and efficient on-site analysis, which is highly valuable for fields such as environmental monitoring, medical diagnostics and food safety. Especially for scenarios requiring immediate on-site testing, such as pathogen screening during an infectious disease outbreak or pollutant detection in environmental pollution incidents, this integrated technology offers significant convenience and timeliness.

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Currently, chips used for optofluidic SERS detection face several challenges, including maintaining stable enhancement effects over long periods and achieving timed and targeted detection. Employing optical tweezers technology to capture and aggregate metal nanoparticles can increase local electromagnetic field strength and improve signal uniformity.

Integrating SERS technology, optical tweezers and optofluidics on a chip to achieve a controllable mechanism for amplifying molecular fingerprint spectra is crucial for the development of Raman detection systems capable of detecting trace molecules.

The team reported a SERS optofluidic molecular fingerprint spectroscopy detection system based on a single-beam optical trap to aggregate free silver nanoparticles (AgNPs) within an optofluidic chip, thereby enhancing the SERS performance of molecules and achieving a controllable mechanism for amplifying molecular fingerprints.

Configured in this way, a single-mode fibre is used to couple a 1550nm laser into the SERS detection area of the optofluidic chip, creating a gradient optical field near the tapered fibre tip. The free AgNPs located in this gradient optical field are drawn towards the vicinity of the tapered fibre due to the force exerted by the optical field. As the AgNPs accumulate, the inter-particle distance significantly decreases. When 532 nm excitation light irradiates the aggregated region, localized ‘hot spots’ form, intensifying the Raman scattering signals of the target molecules in that area, thus enabling highly sensitive molecular fingerprint detection.

For Raman detection, users can directly examine the region near the tapered fibre tip within the detection chamber of the optofluidic chip. The core innovation of this study lies in developing a stable and controllable SERS detection platform optimised for two application scenarios. Firstly, under laboratory conditions, the platform provides a stable, reliable and highly sensitive environment for the Raman detection of liquid samples.

Moreover, the system can be integrated with a portable Raman spectrometer to create a portable SERS detection system equipped with an integrated portable Raman detection unit. The entire system can be conveniently installed in a laboratory toolkit or mobile device, allowing users to independently complete liquid SERS detection tasks after brief training. By integrating SERS, optical trapping and microfluidic chip technologies, this research offers a positioning and timing-controlled, highly sensitive and portable molecular fingerprint detection platform.

This innovative approach not only addresses some of the challenges faced by current SERS-based detection chips, such as maintaining stable enhancement effects over time and achieving timed, and targeted detection, but also expands the practical applications of SERS technology in various fields, including medical diagnostics and food safety.

For further reading please visit: 10.29026/oea.2025.240182