Sarah Unterkofler

Photonic crystal fibres for chemical sensing and photochemistry

In this review, we introduce photonic crystal fibre as a novel optofluidic microdevice that can be employed as both a versatile chemical sensor and a highly efficient microreactor. We demonstrate that it provides an excellent platform in which light and chemical samples can strongly interact for quantitative spectroscopic analysis or photoactivation purposes. The use of photonic crystal fibre in photochemistry and sensing is discussed and recent results on gas and liquid sensing as well as on photochemical and catalytic reactions are reviewed. These developments demonstrate that the tight light confinement, enhanced light-matter interaction and reduced sample volume offered by photonic crystal fibre make it useful in a wide range of chemical applications.

Microfluidic integration of photonic crystal fibers for online photochemical reaction analysis.

Liquid-filled hollow-core photonic crystal fibers (HC-PCFs) are perfect optofluidic channels, uniquely providing low-loss optical guidance in a liquid medium. As a result, the overlap of the dissolved specimen and the intense light field in the micronsized core is increased manyfold compared to conventional bioanalytical techniques, facilitating highly-efficient photoactivation processes. Here we introduce a novel integrated analytical technology for photochemistry by microfluidic coupling of a HC-PCF nanoflow reactor to supplementary detection devices. Applying a continuous flow through the fiber, we deliver photochemical reaction products to a mass spectrometer in an online and hence rapid fashion, which is highly advantageous over conventional cuvette-based approaches.

Doppler velocimetry on microparticles trapped and propelled by laser light in liquid-filled photonic crystal fiber

Laser Doppler velocimetry is used to measure very accurately the velocity and position of a microparticle propelled and guided by laser light in liquid-filled photonic crystal fiber. Periodic variations in particle velocity are observed that correlate closely with modal beating between the two lowest order guided fiber modes.

Long-distance laser propulsion and deformation- monitoring of cells in optofluidic photonic crystal fiber

We introduce a unique method for laser-propelling individual cells over distances of 10s of cm through stationary liquid in a microfluidic channel. This is achieved by using liquid-filled hollow-core photonic crystal fiber (HC-PCF). HC-PCF provides low-loss light guidance in a well-defined single mode, resulting in highly uniform optical trapping and propulsive forces in the core which at the same time acts as a microfluidic channel. Cells are trapped laterally at the center of the core, typically several microns away from the glass interface, which eliminates adherence effects and external perturbations. During propagation, the velocity of the cells is conveniently monitored using a non-imaging Doppler velocimetry technique. Dynamic changes in velocity at constant optical powers up to 350 mW indicate stress-induced changes in the shape of the cells, which is confirmed by bright-field microscopy. Our results suggest that HC-PCF will be useful as a new tool for the study of single-cell biomechanics.

Fluorescence blinking of the RC-LH1 complex from Rhodopseudomonas palustris.

We investigate fluorescence blinking of individual RC-LH1 (reaction-centre-light-harvesting 1) complexes from the photosynthetic purple bacterium Rhodopseudomonas palustris. For both the on- and off-periods the telegraph-like intermittency of the fluorescence intensity follows power-law statistics with exponents between 1 and 2. Yet, this behaviour was only observed for a small fraction of the complexes studied. We argue that the majority of the complexes reside in a prolonged on-state, due to a mechanism that is similar to the Coulomb blockade in semiconductor quantum dots, and which results here from the photoinduced charges located within the RC upon photoexcitation of the LH1 antenna.

Photochemistry in Hollow-core Photonic Crystal Fiber Microreactors

Hollow-core photonic crystal fiber uniquely allows low-loss propagation of light in liquid-filled microchannels, thus enabling highly efficient photochemistry, photo-switching, and photocatalysis at optical powers that are five orders of magnitude lower than in conventional systems.

Optically monitored catalytic photonic crystal fibre microreactor

Here we show that by depositing metallic catalyst nanoparticles in the core of the fibre, we can turn the HC-PCF into a catalytically active microreactor. As a proof-of-principle experiment, we investigated the well-known catalytic hydrogenation of azobenzene in a kagomé HC-PCF, whose core wall has been decorated with rhodium (Rh) catalyst nanoparticles. The reaction was monitored online by in-fibre absorption spectroscopy.

Laser Propulsion of Particles and Cells in Hollow-Core Photonic Crystal Fiber

We review our work on laser propulsion of microparticles and red blood cells in hollow-core photonic crystal fiber. A recently discovered optothermal trapping mechanism based on optically induced thermal creep flow is discussed.

Laser propulsion of microparticles in hollow-core photonic crystal fiber: A review of recent developments

We review our recent work on laser propulsion of microparticles in hollow-core photonic crystal fibers (HC-PCF).

Optofluidic hollow-core photonic crystal fiber coupled to mass spectrometry for rapid photochemical reaction analysis

Optofluidic hollow-core photonic crystal fibers facilitate both efficient excitation of photochemical reactions and instantaneous feeding of the products into a mass spectrometer for rapid molecular structure determination using low sample volumes.