Learned from Peking University, Ma Yanmin researcher at the university and professor Dai Lun cooperate to realize a new laser enhanced surface plasmon detection technology.
The strength of this new probing technology is about 400 times greater than that of conventional 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 face of a hair strand.
"The extremely high sensitivity, low cost and small size of the detector may make it an important player in early diagnosis of disease, safety monitoring in public places and environmental food hygiene," said Ma Renmin.
Surface Plasmon is a localized electromagnetic mode localized at the interface of the metal medium. By coupling the electromagnetic wave of the optical frequency band with the oscillation of free electrons in the noble metal, the energy of the electromagnetic field is limited to a very small scale, and the oscillation Frequency is very sensitive to the surrounding environment. The surface plasmon detector, which is formed by detecting the change of the plasmon resonance mode caused by the change of the surrounding refractive index, is a new type of detector which 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 free electrons in the plasmon resonance generating metal is unavoidable in the traditional plasmon detector. From the basic physical principle, it is to further improve the detector Sensitivity of the obstacles. Ma Renmin's research team introduced the principle of laser into surface plasmon polariton and compensated for the ohmic loss by using the stimulated emission of laser light. On the basis of the previous detection of gas-phase hypersensitive explosives (Nature Nanotechnology, 2014) A liquid-phase laser-enhanced surface plasmon polariton (LESPR) detector was implemented.
The new detector mainly comprises a metal layer and a gain medium layer, wherein the gain medium layer is formed on the metal layer; a surface plasmon mode is formed on the interface of the gain medium layer and the metal layer, and the mode is limited by the boundary of the gain medium layer to Forming a surface plasmon laser cavity; the liquid under test covers the gain medium layer; the excitation light is incident on the gain medium layer through the liquid to be measured, the gain medium generates stimulated radiation under pumping of the excitation light, A surface plasmonic laser is generated whose wavelength and intensity depend on the refractive index of the liquid to be measured.
In the experiment, Professor Dai Lun synthesis of CdSe nanocrystals about 700 nm wavelength as a gain material, the wavelength of its emission just in the biological tissue and water scattering and absorption of small window wavelength of 700 nm to 900 nm. They use gold compared to the metallic silver commonly used in plasmonic lasers.
"Although gold has higher ohmic losses, its chemical properties are far more stable than silver and are suitable for applications in biology and other complex environments," says Professor Dai Lun.
In experiments, in addition to unexpectedly narrowing the resonant linewidth of plasmon resonance with the expected laser effects compensating for ohmic losses, they also found that laser-enhanced surface plasmons with conventional surface plasmon detectors do not Has the advantages of Gaussian spectral line and background-free radiation.
"These features make laser-enhanced surface plasmon detectors have a strength detection quality factor of up to 84,000, which is about 400 times higher than the quality factor of a conventional surface plasmon detector," said Ma Renmin. Because of the microcavity effect, the entire laser-enhanced surface plasmon detector is only on the order of microns in size, and thousands of detectors can be made on the end face of a hair strand with low cost, small size The advantages of large-scale integration. "
The work has now been published in the field of well-known journal Nanophotonics published Peking University postdoctoral Wang Xingyuan, doctoral student Wang Yilun and Wang for article co-author, researcher Ma Renmin and Professor Dai Lun as the corresponding author. At the same time they also applied for a patent for the detector.
The working principle of the centrifugal separator includes centrifugal filtration and centrifugal sedimentation. Centrifugal filtration is the centrifugal pressure generated by the suspension under the centrifugal force field, acting on the filter medium, so that the liquid passes through the filter medium to become a filtrate, and the solid particles are trapped on the surface of the filter medium, thereby achieving liquid-solid separation; centrifugal sedimentation is to use The principle that each component with different density of suspension (or emulsion) settles quickly in the centrifugal force field to achieve liquid-solid (or liquid-liquid) separation.
The centrifugal separator has two functions: centrifugal filtration and centrifugal sedimentation. Centrifugal filtration is the centrifugal pressure generated by the suspension in the centrifugal force field, which acts on the filter medium, so that the liquid passes through the filter medium and becomes the filtrate, while the solid particles are trapped on the surface of the filter medium to achieve liquid-solid separation; centrifugal sedimentation is used The principle that the components of the suspension (or emulsion) with different densities settle rapidly in the centrifugal force field to achieve liquid-solid (or liquid-liquid) separation.
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