[3분논문] 제5회 - 표면플라즈몬을 이용한 광측정

황용섭의 3분논문 제5회입니다.

총시간은 3분 44초입니다. 

재미있게 논문 보면서 들어보세요.

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# 논문표지

# 간단한 정보

글쓴이: Peter Zijlstra, Pedro M. R. Paulo and Michel Orrit

제목: Optical detection of single non-absorbing molecules using the surface plasmon resonance of a gold nanorod

학술지: Nature Nanotechnology

발행년월: 2012년 4월

이어가기: http://dx.doi.org/10.1038/nnano.2012.51

# 용어

- surface plasmon: 표면 플라즈몬. 금속과 유전체 사이에 생기는 전자기파로 작은 공간에 빛을 모을 수 있다는 장점을 가지고 있다.

- photothermal microscopy: 광열 현미경 측정. 빛을 입사시켜 열을 발생시킨 뒤 광특성을 측정하는 방법이다.

# 발췌

1. 초록의 첫 문장에서 

Existing methods for the optical detection of single molecules require the molecules to absorb light to produce fluorescence1 or direct absorption signals2, 3, 4. This limits the range of species that can be detected, because most molecules are purely refractive.

2. 초록의 마지막 문장에서

The sensitivity of our device is ~700 times higher than state-of-the-art plasmon sensors15 and is intrinsically limited by spectral diffusion of the surface plasmon resonance.

3. 두번째 쪽 왼쪽 단(段) 첫 문단에서

When a single protein binds to the receptors on the surface of the nanorod, the longitudinal SPR shifts to the red due to the locally increased index of refraction. This shift results in a change of the absorption cross-section of the nanorod at the wavelength of the heating beam.

# 그림

Figure 1: Principle of the method.

a, A single gold nanorod functionalized with biotin is introduced into an environment with the protein of interest. Binding of the analyte molecules to the receptors induces a redshift of the longitudinal SPR (exaggerated in the illustration). This shift is monitored at a single frequency using photothermal microscopy. b, Calculation in the discrete dipole approximation of the electric field intensity around a gold nanorod, evaluated on resonance with its longitudinal SPR (Supplementary Section S5). The size of the nanorod was set to 31 nm × 9 nm to match the SPR used in the experiments. c, Relative change in the photothermal signal (that is, absorption cross-section) as a function of the heating-laser wavelength for a redshift of 1 nm. Plotted for SPR linewidths, Γ, of 85 meV (blue dotted line), 110 meV (red solid line) and 150 meV (green dashed line). The red square indicates the working point in our experiments, in which we use a heating laser with a wavelength of 785 nm. The calculation of the cross-section was carried out in the electrostatic approximation.

Figure 2: Photothermal time trace showing single-molecule binding events.

The normalized photothermal signal as a function of time for biotin-functionalized gold nanorods in the presence of a streptavidin–R-phycoerythrin conjugate. The photothermal signal was recorded on three different nanorods in the presence of different concentrations of the protein. The red lines are fits to the time traces using a step-finding algorithm²⁶. The right-hand axis corresponds to the estimated SPR redshift, based on a sensitivity of the photothermal signal of 5% per nanometre redshift, deduced from the linewidth of this particular nanorod (Fig. 1c).

# 결론

표면플라즈몬을 이용해 전기장의 세기를 향상시킨 뒤 단백질 분자를 광측정하였다. 적은 개수의 분자를 비파괴 방법으로 측정할 수 있다는 점에서 의미가 큰 연구이다. 

끝.

2012년 4월 23일