A Study on the Blue Fluorescence Characteristics of Silica Nanoparticles with Different Particle Size

실리카 나노 입자의 크기에 따른 청색 형광 특성 연구

Abstract

Organic dye-doped silica nanoparticles are used as a promising nanomaterials for bio-labeling, bio-imaging and bio-sensing. Fluorescent silica nanoparticles(NPs) have been synthesized by the modified $St{\ddot{o}}ber$ method. In this study, dye-free fluorescent silica NPs of various sized were synthesized by Sol-Gel process as the modified $St{\ddot{o}}ber$ method. The functional material of APTES((3-aminopropyl)triethoxysilane) was added as an additive during the Sol-Gel process. The as-synthesized silica NPs were calcined at $400^{\circ}C$ for 2 hours. The surface morphology and particle size of the as-synthesized silica NPs were characterized by field-emission scanning electron microscopy. The fluorescent characteristics of the as-synthesized silica NPs was confirmed by UV lamp irradiation of 365 nm wavelength. The photoluminescence (PL) of the as-synthesized silica NPs with different size was analyzed by fluorometry. As the results, the as-synthesized silica NPs exhibits same blue fluorescent characteristics for different NPs size. Especially, as increased of the silica NPs size, the intensity of PL was decreased. The blue fluorescence of dye-free silica NPs was attributed to linkage of $NH_2$ groups of the APTES layer and oxygen-related defects in the silica matrix skeleton.

유기 염료가 도핑 된 실리카 나노입자는 바이오 라벨링, 바이오 이미징 및 바이오 센싱에 사용되고 있는 유망한 나노소재이다. 일반적으로 형광 실리카 나노입자는 수정된 스토버 방법($St{\ddot{o}}ber$ Method)으로 합성된다. 본 연구에서는 다양한 크기를 갖는 염료가 첨가되지 않은 형광 실리카 나노입자를 수정된 스토버 합성법인 졸겔 공정으로 합성하였다. 졸겔 공정 중에 기능성 물질인 APTES를 첨가제로 첨가하였다. 졸겔 공정으로 합성된 실리카 나노입자는 $400^{\circ}C$에서 2시간 동안 하소되었다. 합성된 실리카 나노입자의 표면형상과 크기를 전계방출 주사전자현미경으로 조사하였고, 합성된 실리카 나노입자의 형광 특성은 파장 365 nm의 자외선 램프를 조사하여 확인하였다. 또한 합성된 실리카 나노입자의 광발광 (PL) 특성을 형광 분석 형광법으로 조사하였다. 그 결과 합성된 실리카 나노입자는 입자의 크기와 무관하게 모두 청색 형광 특성을 갖는 것으로 확인되었다. 특히, 실리카 나노입자의 크기가 증가할수록 PL 강도는 감소하였다. 염료가 첨가되지 않은 실리카 나노입자의 청색 형광 특성은 APTES 층의 $NH_2$ 기능기와 실리카 매트릭스 뼈대 내부의 산소관련 결함과의 결합에 기인하는 것으로 추정된다.

Fig. 1. FE-SEM images of as-synthesized BFSNPs for different average particle size (a) 140 nm, (c) 190 nm (e) 240 nm. Statistical analysis results of particle size distribution for different average particle size of (b) 140 nm, (d) 190 nm, and (f) 240 nm, respectively.

Fig. 2. Photographs of as-synthesized BFSNPs dispersed solutions(concentration of 11.6 mg/mL) with different particle size for different irradiation conditions (a) under daylight, (b) under UV Lamp of 365 nm wavelength.

Fig. 3. Photograph of as-synthesized BFSNPs(190 nm) dispersed solutions under 365 nm UV lamp irradiation for different synthetic process (a) un-calcined BFSNPs (b) calcined BFSNPs at 400 ^oC in conventional furnace with atmospheric pressure.

Fig. 4. Photoluminescence(PL) spectra of as-synthesized BFSNPs dispersed solutions for different particle size. The PL spectra of BFSNPs dispersed solutions were measured with quartz cell by fluorometry.

Table 1. Summary of the synthesis conditions of blue fluorescent silica nanoparticles (BFSNPs) for different size.