Integrierte optische Detektoren auf Basis amorphen Siliziums und flüssige Lichtwellenleiter für mikrofluidische Anwendungen

The objective of this thesis was to integrate microotical components, such as amorphous silicon based pin-diodes and liquid core planar waveguides for luminescence detection in a micro total analysis system. The concept is called application specific lab-on-microchip (ALM) and contains microfluidic networks and microoptical components monolithically integrated on top of a standard application specific integrated circuit (ASIC). Glass substrates has been used for the study of the microfluidic networks and microoptical components instead of externally fabricated ASICs.

Several processes for the fabrication has been developed. The processes involved the fabrication of a glass substrate with metal contacts and a polymer layer (SU-8) to realize the microfluidic network. A thinner top plate is used to seal the fluid capillaries. This plate contains the pin-diodes which are manufactured by plasma enhanced chemical vapor deposition. In the concept external generated excitation light is guided towards the fluidic capillaries, filled with a methylene iodide mixture (CH 2 I 2 :CH 2 Cl 2 ), orthogonally to the active sensor detection direction. No additional fabrication steps are needed to build the liquid core planar waveguides. Furthermore, an inverted liquid core planar rip-waveguide structure has been investigated by numerical calculations.

By bringing the optoelectronic components in such close proximity, the fraction of photons which strike the pin-detector has been discussed analytically and design solutions are proposed. The pin-diode layer stack is isolated by SU-8 and has been integrated with the microfluidic channels to test the sensor sensitivity. While sputtered chromium is used for the rear contact a sputtered ZnO:Al (TCO) with a thickness of 225 nm acts as front contact in the optical path to the microfluidic capillary. Its transmission is approximately 90 % for visible and near IR light and the layer resistance is on the order of 30 ohms per square. In particular, the dark current density corresponds to 1,3 × 10 -10 A/cm 2 @ 300 K and rises exponentially with the temperature. The spectral response is ranging from 320 nm to 780 nm and exhibits a quantum efficiency of approximately 70 % @ 600 nm at room temperature.

Lab-on-microchip test results demonstrate a significant difference in the normalized intensity spectrum of anthracene derivatives Ox and Ox-H + as a consequence of the fluorescence spectrum shift upon protonation by hydrochloric acid from pH 7 to pH 2. The experimental limit of detection has been determined to ~25 fmol.

An electrochemiluminescence based detection of an azacrown ether appended trisphenanthroline ruthenium(II) complex is a well suited technique since there is no need of excitation light to generate luminescence. The combination of a chemical sensor molecule and an amorphous silicon based optical sensor exhibits a limit of detection of ~66 nM according to a detection volume of 1,2 nl, respectively. Furthermore, an electrochemiluminescence enhancement of I/I 0 =8.2 has been observed for Hg 2+ ions without any shift in the emission spectra. Therefore, it is believed that this technology holds great potential to reach detection limits less than 1 nM and compete against bulk optical approaches.