The reporter learned from Peking University that the researcher Ma Renmin and Professor Dai Lun collaborated to implement a new laser-enhanced surface plasmon detection technology.
The strength detection quality factor of this new detection technology is about 400 times higher than that of conventional surface plasmon (SPR) detectors. At the same time, the cost is low and the size is only on the order of micrometers. Thousands of detectors can be prepared on the end face of a single hair.
"The detector's extremely high sensitivity, low cost and small size may make it play an important role in the early diagnosis of diseases, safety monitoring in public places and environmental food hygiene," said Ma Renmin.
The surface plasmon is a local electromagnetic mode localized at the interface of the metal medium. By coupling the electromagnetic wave in the optical band with the oscillation of the free electrons in the precious metal, the energy of the electromagnetic field is limited to a small scale, and its oscillation The frequency is very sensitive to the surrounding environment. A surface plasmon detector formed by detecting changes in the plasmon resonance mode caused by changes in the surrounding refractive index is a new type of detector that is real-time and does not require fluorescent labeling. In the past 20 years, it has achieved great success in the fields of disease diagnosis, biochemistry research and application, and environmental monitoring.
Ma Renmin said that the ohmic loss caused by the oscillation of free electrons in the metal used to generate plasmon resonance is inevitable in traditional plasmon detectors. From the basic physical principle, it is to further improve the detector. A barrier to sensitivity. Ma Renmin's research team introduced the laser principle into the surface plasmon detector, which compensated the ohmic loss by using the stimulated radiation in the laser, based on the detection of the gas phase ultra-sensitive explosives (Nature Nanotechnology, 2014). A liquid phase laser enhanced surface plasmon (LESPR) detector was implemented.
The new detector mainly comprises a metal layer and a gain dielectric layer, and a gain dielectric layer is formed on the metal layer; a surface plasmon mode is formed at the interface between the gain dielectric layer and the metal layer, and the mode is limited by the boundary of the gain dielectric layer Forming a surface plasmon laser cavity; the liquid to be tested is covered on the gain medium layer; the excitation light is incident on the gain medium layer through the liquid to be tested, and the gain medium generates stimulated radiation under excitation of the excitation light, and is amplified by laser cavity feedback A surface plasmon laser is generated, the wavelength and intensity of the surface plasmon laser being related to the refractive index of the liquid to be tested.
In the experiment, cadmium selenide nanocrystals with a wavelength of about 700 nm synthesized by Professor Dylan were used as gain materials, and their luminescence wavelengths were located at the window wavelengths of 700 nm to 900 nm, which are smaller in biological tissues and water scattering and absorption. They use gold compared to metallic silver, which is commonly used in plasmonic lasers.
"Although gold has a high ohmic loss, its chemical properties are far more stable than silver, and it is suitable for applications in biological and other complex environments," said Professor Dylan.
In the experiment, in addition to the expected laser effect to compensate for the ohmic loss, the resonance line width of the plasmon resonance is significantly narrowed. They also found that the laser-enhanced surface plasmon detector has a conventional surface plasmon detector. It has the advantages of Gaussian spectral line type and no background radiation.
"These features make the laser-enhanced surface plasmon detector with a intensity detection factor of up to 84,000, which is about 400 times higher than the quality factor of the traditional surface plasmon detector." Ma Renmin said, "At the same time Because the microcavity effect is used, the size of the entire laser-enhanced surface plasmon detector is only on the order of micrometers. Thousands of detectors can be prepared on the end face of a single strand of hair, which is low-cost and small. Advantages of large-scale integration."
The work has been accepted and published by the well-known journal Nanophotonics in the field. Wang Xingyuan, a postdoctoral fellow at Peking University, and Wang Yilun and Wang, the doctoral students, are the co-first authors of the article. Professor Ma Renmin and Professor Dai Lun are the authors of the communication. At the same time, they also applied for invention patents for the detector.
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