Emanuel Weber

In-Line Characterization of Micro-Droplets Based on Partial Light Reflection at the Solid-Liquid Interface

In this paper a novel optofluidic setup, fabricated on a single layer device for in line droplet characterization yielding droplet size, droplet frequency, and optical proper ties with compatibility for full on chip integration is presented. Chips were fabricated using a simple, fast, and cost effective technology. A T junction arrangement on the device is used for droplet generation. The optical part of the setup consists of an external light source, external silicon photodetectors, integrated air micro lenses, and an integrated waveguide. The design makes use of partial light reflection/transmission at the solid liquid interface to count, size, and discriminate droplets based on their optical properties. When passing the interrogation point, droplets having a lower refractive index as the continuous phase result in light deflections. Both, reflected and transmitted light, are detected simultaneously. A relation of those two signals is then used for the analysis resulting in a continuously stable signal. The generated pattern is unique for different droplets and can be exploited for droplet characterization. Using this arrangement, droplets of de ionized water (DI) were counted at frequencies of up to 320 droplets per second. In addition, information about the droplet sizes and their variations could be obtained. Finally, 5 mol/L CaCl 2 and DI droplets, having different indices of refraction were examined and could clearly be discriminated based on their unique reflected and transmitted light signals. This principle can be applied for the detection of dissolved molecules in droplets as long as they influence the index of refraction. Examples could be the determination of DNA or protein content in the droplet.

On-Chip Light Modulation Applying Optofluidic Principles

Optofluidics is a promising approach for the realization of novel and versatile lab-on-a-chip devices. We present optofluidic switches for reconfigurable on-chip light modulation. Compared with other researches mechanically moving elements were entirely omitted which reduces wearing and eliminates any sticking issues completely. The first modulator is based on the hydrodynamic control of streams of liquids in a microfluidic channel. Properly choosing the refractive index of the employed liquids allows light guidance in a core stream that can be steered in the channel. The advanced device is based on total internal reflection at the solid-liquid interface of a liquid filled microfluidic channel. Depending on the refractive index of the fluid, light is either reflected and guided toward the first output or transmitted and routed to another position. Placing two channels after each other provides three possible optical outputs. Compared with the hydrodynamic realization, the consumption of liquids is kept at the very minimum because no permanent flow through the device is needed. Fluorescence images were taken to evaluate the operation of the devices. Both principles can be upgraded in terms of light modulation possibilities by either increasing the width of the channel in the hydrodynamic realization or integration of more than two channels into the advanced modulator.

Detection of Dissolved Lactose Employing an Optofluidic Micro-System.

In this work, a novel optofluidic sensor principle is employed for a non-invasive and label-free characterization of lactose containing liquid samples. Especially for medicine and food industry, a simple, fast and accurate determination of the amount of lactose in various products is highly desirable. The presented system exploits the impact of dissolved molecules on the refractive index for sample characterization. On the optofluidic chip, a microfluidic channel filled with the analyte is hit by slightly diverging laser light. The center incident angle of the beam on-chip is set close to the critical angle for total internal reflection. Both the reflected and the transmitted light signals are recorded at the solid-liquid interface. The ratio of those two signals is then used as representative value for the analyte. Using this principle, lactose containing samples were differentiated based on their concentrations at a step size of 10 mmol/L. The use of the signals ratio instead of a single signal approach improves the stability of the system significantly, allowing for higher resolutions to be achieved. Furthermore, the fabrication of the devices in PDMS ensures biocompatibility and provides low absorbance of light in the visible range.

In-line characterization and identification of micro-droplets on-chip

Abstract We present an integrated optofluidic sensor system for in-line characterization of micro-droplets. The device provides information about the droplet generation frequency, the droplet volume, and the content of the droplet. Due to its simplicity this principle can easily be implemented with other microfluidic components on one and the same device. The sensor is based on total internal reflection phenomena. Droplets are pushed through a microfluidic channel which is hit by slightly diverging monochromatic light. At the solid-liquid interface parts of the rays experience total internal reflection while another part is transmitted. The ratio of reflected to transmitted light depends on the refractive index of the solution. Both signals are recorded simultaneously and provide a very stable output signal for the droplet characterization. With the proposed system passing droplets were counted up to 320 droplets per second and droplets with different volumes could be discriminated. In a final experiment droplets with different amounts of dissolved CaCl2 were distinguished based on their reflected and transmitted light pattern. This principle can be applied for the detection of any molecules in microdroplets which significantly influence the refractive index of the buffer solution.

Biopsy analysis using a quadruple infrared sensor

In this contribution, infrared absorbance measurements by using a quadruple sensor have been performed for the first time to indicate the presence of cancer cells in melanoma biopsies. To verify the fidelity of the obtained results, they have been compared with results achieved by histopathology analysis and by using Fourier transform infrared (FTIR) spectroscopic imaging of tissue arrays. A significant agreement has been found between the different methods, demonstrating the potential of the quadruple infrared sensor as a label-free and cost-effective instrument to support the experts in their examination and diagnosis of tissue biopsies.

Thermo-optofluidics — On-chip light modulation as an application

In this paper thermo-optofluidics is introduced as a new subfield of microfluidics. The presented principle allows on-chip light modulation in a repeatable manner. Compared to other, previously reported thermo-optic devices the achievable maximum switching frequency can be more than doubled. On the design a liquid core/solid cladding waveguide is exposed to varying temperatures (ΔT of approx. 8.5°C). The temperature related changes of the refractive indices of core and cladding are of opposite directions resulting in a controllable on-off switching of light confinement within the waveguide. Besides on-chip light modulation, temperature sensing as well as various analysis setups can be realized using this novel principle.

Optofluidische Komponenten in der FlüssigkeitssensorikOptofluidic Elements in Liquid-based Sensor Systems

Zusammenfassung In der biotechnologischen Flüssigkeitssensorik spielen adaptive optische Systeme zur Anregung und Detektion von Lumineszenzsignalen eine wichtige Rolle. Diese Arbeit untersucht zwei Typen von optofluidischen Elementen, welche sowohl den Funktionsumfang als auch die Sensitivität sogenannter “Lab-on-a-chips” erhöhen können. Im ersten Teil wird eine hydrodynamisch verformbare Flüssigkeitslinse mit dreidimensionaler Fokusveränderbarkeit auf Basis einer mikrofluidischen Kanalstruktur diskutiert. Das zweite Sensorsystem beinhaltet einen adaptierbaren Flüssigkeitslichtleiter. Die Prototypen wurden in einem transparenten Photopolymer mit Mikro-Stereolithographie gefertigt.