Optofluidics

Summary

Optofluidics is a research and technology area that combines the advantages of fluidics (in particular microfluidics) and optics. Applications of the technology include displays, biosensors, lab-on-chip devices, lenses, and molecular imaging tools and energy. History The idea of fluid-optical devices can be traced back at least as far as the 18th century, when spinning pools of mercury were proposed (and eventually developed) as liquid-mirror telescopes. In the 20th century new technologies such as dye lasers and liquid-core waveguides were developed that took advantage of the tunability and physical adaptability that liquids provided to these newly emerging photonic systems. The field of optofluidics formally began to emerge in the mid-2000s as the fields of microfluidics and nanophotonics were maturing and researchers began to look for synergies between these two areas. One of the primary applications of the field is for lab-on-a-chip and biophotonic products. C

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https://en.wikipedia.org/wiki/Optofluidics

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During the last decade, the development of optofluidic chips has become a large field of research. The integration of nano and microstructures with microfluidics layers allowed for the miniaturisation of a number of tools traditionally used in laboratories and optofluidic systems found their main applications in lab-on-a-chip and sensing platforms. At the same time, optical tweezers have become the tool of choice for the trapping and the manipulation of nano and micrometer-sized objects, that can be inert (dielectric or metallic particles) or biological (proteins, bacteria, viruses,...). In this context, nanostructures are the ideal candidate for tweezers miniaturisation, thanks to their ability to strongly confine light in small volumes and hence to generate intense gradient forces. This work reports on the fabrication of an optofluidic chip based on a two-dimensional photonic crystal cavity and on its use in particle and bacteria differentiation. The cavity has a hollow design that maximises the overlap between the confined field and the trapped objects and it supports Self-Induced Back-Action effects that allow for reducing the trapping power (down to few microwatts) and to simultaneously acquire information of the trapped specimen. The system is excited in an end-fire setup and the detection is carried out by recording the light intensity transmitted through the photonic crystal. The fabrication process, that is entirely carried out in the Institue of Physics and in the Center of MicroNanoTechnology cleanrooms, is first detailed. For the cavity design normally used, typical quality factors of 10000 were obtained. Moreover, SU8 mode adaptors were developed to increase the coupling with lensed fibers and a microfluidic membrane presenting two injection channels is proposed for rapid switch between liquids. The trapping and the differentiation of 250 and 500 nm polystyrene is then presented. The differentiation can be achieved qualitatively by direct observation of the transmitted intensity records and quantitatively by the use of histograms and of statistical moments. Finally, the trapping of seven species of living bacteria is shown and their Gram-type is determined by the analysis of the induced transmission increase. This ability to probe the cell wall of bacteria in a fast, label-free and non-destructive way paves the way for applications in biological and biomedical environments.

EPFL2019

Development of Elastomeric Optofluidic Devices for Lasing and Sensing

Wuzhou Song

The term of optofluidics defines an emergent research field that combines microfluidics and optics. In many lab-on-a-chip applications, these two technologies are used in combining the microfluidics for sample delivery and optics for sensing and controlling. Optofluidic represents the implementation of optics in microfluidic platform that produces an unprecedented level of integration. Moreover, optofluidic devices are easily and highly reconfigurable, which can be a significant advantage to the traditional solid optical components. As an elastomer, PDMS (polydimethylsiloxane) is one of the most popular materials in microfluidics. It exhibits excellent elasticity, bio-compatibility and optical transparence. Most microfluidic chips are made of PDMS using soft lithography. And multi-layer soft lithography has enabled large-scale integration of monolithic microfluidic valves and pumps on a single chip. Thus to develop the optofluidic elements within PDMS microfluidic chip is one of the most promising and desirable ways towards further integration of optofluidic and microfluidic functions together for more complex lab-on-a-chip applications. During my doctoral research, we worked on a batch of optofluidic devices that are based on PDMS material and soft lithography. They include the optofluidic dye lasers, optofluidic interferometer, optofluidic switch, and optofluidic differential spectroscopy. Such optofluidic elements provide a broad spectrum of toolbox with different optical functions that can be easily into many other PDMS microfluidic chips. They are compatible to the conventional PDMS microfluidic chip in terms of fabrication, operation and control. And they could provide important optical functions in lab-on-a-chip systems. For examples, the optofluidic dye laser can be integrated as a widely tunable coherent source for chip-scale fluorescence spectroscopy or cell flow cytometry. The optofluidic membrane interferometer can be easily integrated into conventional PDMS microfluidic chip for multi-site pressure and flow monitoring with high precision. Optofluidic switch can compose a reconfigurable optical circuit on single microfluidic chip. Optofluidic differential spectroscopy provides a simple and highly sensitive method for in-line measuring of solution concentration. Among these devices, we have also developed and summarized a series of novel optofluidic turning methods that are controlled by pneumatic actuation. These simple turning methods also take the advantages of high precision and reliability. In addition to these elastomeric optofluidic devices, we are also working on several other optofluidic projects. In the last chapter of this thesis, we will give a partial preview of these works and also our perspective on the nano-optofluidics which represents a new trend of optofluidics.

EPFL2012

Gram-type differentiation of bacteria with 2D hollow photonic crystal cavities

Romuald Houdré, Rita Therisod

Fast and label-free techniques to analyze viruses and bacteria are of crucial interest in biological and bio-medical applications. For this purpose, optofluidic systems based on the integration of photonic structures with microfluidic layers were shown to be promising tools for biological analysis, thanks to their small footprint and to their ability to manipulate objects using low powers. In this letter, we report on the optical trapping of living bacteria in a 2D silicon hollow photonic crystal cavity. This structure allows for the Gram-type differentiation of bacteria at the single cell scale, in a fast, label-free, and non-destructive way. (C) 2018 Author(s).

2018

Development of Elastomeric Optofluidic Devices for Lasing and Sensing

Wuzhou Song

EPFL2012

EPFL2019