Particle Guidance and Photochemistry in Hollow-Core Photonic Crystal Fibre

T. G. Euser1, M. K. Garbos1, J. S. Y. Chen1, N. J. Farrer2, M. Scharrer1, P. J. Sadler2 and P. St. J. Russell1

1 Max Planck Institute for the Science of Light, Günther-Scharowsky-Str. 1/Bau 24, 91058 Erlangen, Germany 2 Department of Chemistry, University of Warwick, CV4 7AL Coventry, United Kingdom

www.pcfiber.com

We discuss two recent applications of hollow-core photonic crystal fibre.

PARTICLE GUIDANCE IN LIQUID-FILLED HOLLOW CORE PHOTONIC CRYSTAL FIBRE

In optical tweezers, radiation forces near the focus of a laser beam allow trapping and micromanipulation of particles and cells. In hollow-core photonic crystal fibre (PCF), light propagates in a single, non-diffracting optical mode. Consequently, radiation forces are constant along the fibre, allowing guidance and propulsion of particles over long distances. We have recently demonstrated that �m-sized particles can be controllably launched into and propelled by the fundamental mode of a fluid-filled PCF [1]. Figure 1 shows the loading process (A-D) and light driven motion (E-H) of a glass sphere that is pushed through a liquid-filled core by the radiation pressure provided by a laser beam incoming from the left. The particle attains a speed of ~100 �m per second, i.e., 50 times its diameter in one second. Particles can also be held stationary against a liquid counter-flow by careful balancing of the drag and radiation forces. The technique offers a unique way to study the viscous forces acting on single particles in microfluidic channels. By loading the liquid with photo-activated chemicals, a particle could be coated with successive layers of different materials in a highly controlled manner.

Figure 1. Loading and guidance of a borosilicate particle in liquid-filled hollow-core photonic crystal fibre.

PHOTOCHEMISTRY IN PHOTONIC CRYSTAL FIBRE NANOREACTORS

The development of new photo-activated anticancer complexes is of major importance for the effective treatment of cancer. Such complexes are inert, nontoxic and are activated only locally in cancer cells by light. A new method allows for rapid investigation of the photochemical properties of such photochemical compounds [2].

The unique properties of liquid-filled hollow-core photonic crystal fibres are used to bring together the fields of microfluidics, chemistry, and optics. The tiny hollow core (shown in Figure 2A) is loaded with chemicals and acts as a miniature photochemical reactor. Both the chemicals and the excitation light are confined to the core. Consequently, the entire sample volume interacts strongly with the light, resulting in over 10,000 times shorter reaction times than in conventional cuvettes. An additional advantage is that the required sample volume is reduced by four orders of magnitude to 2.7 nL per cm interaction length.

Figure 2. (A) SEM of a kagomé hollow-core photonic crystal fibre. (B) In-fibre measurement of the temporal evolution of the absorption spectrum of vitamin B12 upon excitation with blue laser light.

The reaction is monitored in real-time by in-fibre broadband absorption spectroscopy, offering insight into the chemical dynamics. As a proof-of-principle study, the photochemical conversion of vitamin B12a to vitamin B12b upon excitation with blue laser light was investigated (see Figure 2B). In a continuous-flow configuration, we envisage this method could be applied to the investigation of the effect of excitation wavelength and light dosage on photoactivated anticancer complexes.

ACKNOWLEDGMENT

NJF and PJS thank the EPSRC (EP/G006792/1) and MRC (G070162) for support. This work is part of the Körber project on sensing and biomedical applications of photonic crystal fibre http://www.pcfiber.com/koerber

REFERENCES [1] T. G. Euser, M. K. Garbos, J. S. Y. Chen, and P. St.J. Russell,

“Precise balancing of viscous and radiation forces on a particle in liquid-filled photonic bandgap fiber,” Optics Letters, 34, pp. 3674-3676 (2009).

[2] Jocelyn S. Y. Chen, Tijmen G. Euser, Nicola J. Farrer, Peter J. Sadler, Michael Scharrer, and Philip St.J. Russell, “Photochemistry in Photonic Crystal Fiber Nanoreactors,” Chemistry - A European Journal, 16, pp. 5607-5612 (2010).