Acta Physico-Chimica Sinica ›› 2019, Vol. 35 ›› Issue (4): 371-377.doi: 10.3866/PKU.WHXB201805022

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Multi-Mode Full Spectrum Dark Field Microscope for Single Nanoparticle Localized Surface Plasmon Resonance Dynamics Study

Lei LIU1,2,Yaya HAO1,Suhui DENG1,Kun WANG1,Jiang LI1,Lihua WANG1,Chunhai FAN1,Jiajun LI1,*(),Huajie LIU1,*()   

  1. 1 Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, P. R. China
    2 University of Chinese Academy of Sciences, Beijing 100049, P. R. China
  • Received:2018-03-12 Published:2018-09-13
  • Contact: Jiajun LI,Huajie LIU E-mail:jiajunli@sinap.ac.cn;liuhuajie@sinap.ac.cn
  • Supported by:
    the National Natural Science Foundation of China(21775157);the National Natural Science Foundation of China(21722310);the National Natural Science Foundation of China(U1532119);the National Natural Science Foundation of China(61378062);the National Natural Science Foundation of China(61665006);the Instrument Developing Project of the Chinese Academy of Sciences

Abstract:

In the last few decades, noble metal nanoparticles (MNP) have been widely used as imaging probes, in the field of bio-imaging, due to their localized surface plasmon resonance (LSPR) phenomenon. Compared to fluorescent probes, MNP imaging exhibits high sensitivity and outstanding signal-to-noise ratio, while the particle itself has good photostability; this makes the MNP probe the perfect candidate for long-term imaging. Currently the most popular MNP imaging and analysis method employs a dark-field microscope with a spectroscope. Since most dark-field microscopes use halogen lamp or mercury lamp as their illumination source, the illumination intensity and wavelength spectrum are limited. Both camera and spectroscopy require longer exposure time to collect sufficient scattering signal to generate a reasonable quality image and scattering spectrum. The narrow illumination spectrum also limits the size of the MNP that can be used (larger-diameter MNP tend to scatter in the near-infrared region). Therefore, a high-intensity and wide-spectrum illumination source is urgently needed in MNP imaging. In this study, we custom-designed a multi-mode dark field microscope by using a supercontinuum laser, comprising of a lightsheet illumination mode for wide-field imaging and a back focus mode for live spectrum analysis, as its illumination source. The total output of the supercontinuum laser was 2 W. Since it was a coherent illumination source it could be focused by the microscope objective to a near diffraction limit area for sufficient intensity. Moreover, since its wavelength spectrum was between 450 nm and 2200 nm, which covered most of the visible and near infrared region, it made the detection of the large-diameter MNP single particle possible. In the back-focus mode, the supercontinuum laser first passed through an annular filter and then entered the objective from the microscope back port. In the lightsheet illumination mode, the laser was focused by a 400-mm cylindrical concave mirror to create a "sheet" and illuminate the sample from its side. In both the illumination modes, the illumination radiation was blocked from the camera to obtain the dark field illumination effect. By using a multi-mode dark field microscope, we could observe a 30-nm-diameter MNP single particle with a color CCD camera in its lightsheet illumination mode and a spectrum time resolution of 1 ms in its back-focus illumination mode. This custom-designed microscope could not only be used to study the MNP single particle in living cells, but more importantly, its application could also be potentially extended to all the MNP-probe-based cell imaging.

Key words: Dark field spectroscopy, Wide field spectroscopy, Focus laser dark field spectroscopy, Nano probe, Rapid spectrum analysis

MSC2000: 

  • O649