Browsing by Author "Civitci, F."

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Disposable cartridge biosensor platform for portable diagnostics
(SPIE , 2017) Yaras, Y. S.; Cakmak, O.; Gunduz, A. B.; Saglam, G.; Olcer, S.; Mostafazadeh, A.; Baris, I.; Civitci, F.; Yaralıoğlu, Göksen Göksenin; Urey, H.; Electrical & Electronics Engineering; YARALIOĞLU, Göksen Göksenin
We developed two types of cantilever-based biosensors for portable diagnostics applications. One sensor is based on MEMS cantilever chip mounted in a microfluidic channel and the other sensor is based on a movable optical fiber placed across a microfluidic channel. Both types of sensors were aimed at direct mechanical measurement of coagulation time in a disposable cartridge using plasma or whole blood samples. There are several similarities and also some important differences between the MEMS based and the optical fiber based solutions. The aim of this paper is to provide a comparison between the two solutions and the results. For both types of sensors, actuation of the cantilever or the moving fiber is achieved using an electro coil and the readout is optical. Since both the actuation and sensing are remote, no electrical connections are required for the cartridge. Therefore it is possible to build low cost disposable cartridges. The reader unit for the cartridge contains light sources, photodetectors, the electro coil, a heater, analog electronics, and a microprocessor. The reader unit has different optical interfaces for the cartridges that have MEMS cantilevers and moving fibers. MEMS based platform has better sensitivity but optomechanical alignment is a challenge and measurements with whole blood were not possible due to high scattering of light by the red blood cells. Fiber sensor based platform has relaxed optomechanical tolerances, ease of manufacturing, and it allows measurements in whole blood. Both sensors were tested using control plasma samples for activated-Partial-Thromboplastin-Time (aPTT) measurements. Control plasma test results matched with the manufacturer’s datasheet. Optical fiber based system was tested for aPTT tests with human whole blood samples and the proposed platform provided repeatable test results making the system method of choice for portable diagnostics.
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A prism-based non-linear optical readout method for MEMS cantilever arrays
(Elsevier, 2016-10-15) Adiyan, U.; Civitci, F.; Yaralıoğlu, Göksen Göksenin; Urey, H.; Electrical & Electronics Engineering; YARALIOĞLU, Göksen Göksenin
This paper demonstrates the use of a single right-angle prism for the optical readout of micro-electro-mechanical systems (MEMS) cantilever arrays. The non-linear reflectivity arisen from the internal reflection at the right-angle prism’s hypotenuse plane enables the measurement of cantilever deflections. The cantilever arrays used in the experiments are made of electroplated nickel structures and actuated at resonance by an external electro-coil. A laser beam illuminates multiple cantilevers, and then it is partially reflected by the prism. The prism reflectivity changes with the cantilever deflection and modulates the laser intensity at the photodetector. The detection sensitivity of the optical readout system is determined by the initial angle of incidence at the prism’s hypotenuse plane, numerical aperture of the illumination system and the polarization of the laser beam. In this paper, we showed both theoretically and experimentally that self-sustained oscillations of two MEMS cantilevers with simple rectangular geometry is achievable using only one actuator and one photodetector. The gain saturation mechanism for the oscillators was provided by the optical non-linearity in the prism readout, which eliminates the requirement for separate sensing electronics for each cantilever. Based on our analytical and experimental data, we found that the prism incident angle around 41.2° is desirable in the closed-loop system due to high responsivity. Finally, we demonstrated simultaneous self-sustained oscillations of two cantilevers in closed-loop with resonant frequencies in the range 25–30 kHz. It was shown that multiple oscillations are obtainable if the cantilever resonant frequencies are separated from each other by at least 3 dB bandwidth.