Measuring surface plasmon resonance of gold nanoparticles using near-field scanning optical microscopy

초록

In recent years, study on the synthesis and application of gold nanoparticles are progressing actively. Gold nanospheres and gold nanorods show highly resonant absorption in visible region whose resonant wavelengths depend on their sizes and shapes. This behavior is originated from a surface plasmon resonance due to a collective excitation of the plasma localized near the surface [1]. Since gold nanoparticles have resonant behavior and non-toxicity, using them as nanoprobes has been attempted to the fields of biomolecule imaging, bio sensor and thermal therapy, etc [2, 3, 4]. In this study, gold nanospheres and gold nanorods were synthesized for examining surface plasmon resonance of gold nanoparticles and evaluating their size effect. The seed-mediated growth method was chosen for synthesis, because it has two advantages superior to the electrochemical growth method. They are the controllability of nanoparticle size and the high productivity of nanoparticles at once [5]. The protocol of making gold nanospheres and gold nanorods was based on synthesizing HAuCl4 with sodium citrate and HAuCl4 with cetyl trimethylammonium bromide (CTAB), respectively. The absorbance characteristic of synthesized gold nanoparticles were analyzed by using UV-VIS spectrophotometer, and also the distribution of the evanescent filed close to the surface of gold nanoparticles were measured by using near-field scanning optical microscopy (NSOM). NSOM system was constructed with five parts such as NSOM head, sample, oscillator, optical signal detecting, and data acquisition. NSOM head part was composed of tuning fork and optical fiber probe. In NSOM head part, tuning fork used as a resonator for measuring shear force, and optical fiber probe used for measuring evanescent field. Sample part was comprised with sample stage, PZT and PZT controller, and oscillator part was comprised with lock-in amplifier and circuit. Optical source part included with power supply and He-Ne laser, and PMT modu