Science, 2010, 330, 353-356 Room-Temperature Detection of a Single Molecule’s Absorption by Photothermal Contrast A. Gaiduk, M. Yorulmaz, P. V. Ruijgrok, M. Orrit* Institute of Physics, Leiden University, Netherlands

Single-molecule Optical Detection ☆ Fluorescence E. Betzig et al., Science, 262, 1422. (1993) Intensity, Spectrum, Lifetime, Real-Time Imaging, …… Physics Chemistry Biology environmental intersystem crossing fluctuation spectral diffusion fluorescence switching enzymatic states quantum optics… photochemistry…. folding…. Very convenient technique Problems: Necessity of fluorescent label, blinking, fast photobleaching

Single-molecule Optical Detection ☆ Absorption Q: Is it impossible to probe the single molecule’s absorption at room-temperature ? A: No!, but challenging….. because… Very low absorption cross section of single molecules at r.t. (~ 10-16 cm2) (2) High background noise in a direct extinction measurement (based on the number of missing photons) ⇒It is very difficult to discriminate true absorption signal from scattering W. E. Moerner et al., Phys. Rev. Lett., 62, 2535. (1989) Limited to the cryogenic temperature experiments (~ 1.4 K)

Label-free Optical Microscopy ☆ Stimulated Emission X. S. Xie et al., Nature, 461, 1105. (2009) ☆ Thermal Lens Microscopy T. Kitamori et al., Anal. Chem., 73, 2112. (2001)

Photothermal Lens Effect

Photothermal Imaging B. Louis, M. Orrit et al., Science, 297, 1160. (2002) B. Louis et al., Phys. Rev. Lett., 93, 257402. (2004) B. Louis et al., Phys. Rev. B, 73 045424. (2006) M. Orrit et al., Chem. Sci., 1, 343. (2010)

Experimental Setup

Photothermal Images of Gold Nanospheres

Photothermal Images of Gold Nanospheres Key points to achieve single-molecule sensitivity Fast modulation of the pomp (heating) beam (1 MHz) 　　　⇒Elimination of mechanical, electronic, and laser noise The change of surrounding medium from to water to glycerol The use of relatively high probe power 　　 ⇒Increase of Photothermal signals and reduction of photon noise Detectable dissipated powers can be decreased as low as 3 nW with SNR (signal to noise ratio) of 8 in a 10 ms integration time

Calculation of the Dissipated Power

Samples

Photothermal Images of BHQ1-10T-BHQ1