New post from optoelectronic advance Detection of label-free traces of biomolecules by liquid interface enhanced Raman scattering using a microfluidic chip is discussed.
Surface-enhanced Raman scattering (SERS) has attracted attention in biotechnology. It’s because of high sensitivity to translate surface resonance of metal nanoparticles. Trace detection of large molecular weight biomolecules remains a challenge because treatment of the SERS substrate with coupling or cross-linking agents is required. The researchers applied SERS with the help of a liquid interface to achieve label-free trace detection of biomolecules. The results indicate that they are promising for the early diagnosis of HIV infection and Alzheimer’s disease.
Surface-enhanced Raman scattering (SERS), based on the optical near-field effect induced by the surface plasmon of noble metal nanoparticles or elicited nanostructures. Lasersamplifies Raman signals up to 1014 times compared to regular Raman. Due to its enhanced intensity, SERS technology continues to attract increasing interest in trace-level detection and analysis of biomaterials. Interest has increased in areas such as imaging of organelles in single cellThey track cancer cells and identify vital signs.
SERS technology can be used in the field of biomedicine to diagnose disease at an early stage as well as in the treatment of tumors. Although the optimization factor for SERS usually ranges from 106– 108 Due to the use of new SERS substrates and methods, single-molecule detection by label-free SERS is impractical due to SERS flash, and the origin of this phenomenon is due to the escape of the analyte molecules from hot spots. Moreover, biomolecules, including DNA and proteins, are difficult to detect directly by SERS. Additional treatments using a SERS substrate are required to bind biomolecules.
The research team proposed LI-SERS, which achieves a SERS boosting factor greater than 1014, much higher than the normal SERS method. The microfluidic SERS chip features an Ag-Cu SERS substrate embedded in a small, compact glass channel. The femtosecond (fs) hybrid laser treatment created the micro-turf canal.
fs hybrid laser processing enables the creation of more complex 3D structures with enhanced functionality for biochips, sensors and microelectronic devices. When the interface between analyte solution and air on a SERS substrate in a microfluidic channel was irradiated by a Raman excitation laser, the intensity of LI-SERS was increased by six orders of magnitude compared to normal SERS. The LI-SERS mechanism is attributed to the synergistic effect of Marangoni flux induced by laser irradiation and optical confinement. This laser beam will direct the analyte particles to the hot spots where the collected particles are trapped by the optical force. Thus, the analyte particles were immobilized on the SERS substrate while achieving strong Raman scattering.
This study showed that the LI-SERS method is applicable for further practical use. It is particularly useful for the detection of trace-free label-free biomolecules with large molecular masses, including DNA bases, DNA sequences, and amyloid beta (Aβ). Due to the superior sensitivity and self-stabilization of LI-SERS, discrimination of DNA bases and DNA sequences was obtained with a detection limit of 1 fM without the need for additional treatments featuring coupling or cross-linking means. Moreover, LI-SERS technology can detect unlabeled Aβ, a biomarker of Alzheimer’s disease, at levels below 1 PM, and with a linear correlation between the Raman signal and Aβ concentration in the range 1 nM to 1 PM. The label-free biosensing capability of LI-SERS offers great potential for early disease diagnosis in clinics.
In conclusion, the authors provide an overview of the scope of the LI-SERS method for trace detection of biomolecules in microfluidic SERS chips with special reference to the ultra-trace detection of DNA bases and Aβ. The liquid interface was allowed to form in the micro-channel. Marangoni flux and optical trapping effects induced by LI-SERS showed a detection limit of 1 fM for label-free DNA bases. The outstanding features of the LI-SERS method, including the superior sensitivity and versatility associated with the collection and self-inactivation of analytes molecules in hotspots, will be useful in early-stage diagnoses of disease such as viral infections and Alzheimer’s disease.
Shi Bai et al., Uncovering the label-free effect of biomolecules by liquid interface-enhanced Raman scattering using a microfluidic chip, optoelectronic advance (2022). DOI: 10.29026 / oea.2022.210121
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