Gerçek zamanlı kütle, özkütle, viskozite ve pıhtılaşma ölçümleri için mikroçubuk tabanlı mikroakışkan algılayıcılar

Miniaturization of sensor technologies and the development of lab-on-a-chip (LoC) devices in the last decade enabled new opportunities in diagnostics and therapeutics to improve human health. Despite the great technological advances in research labs, there are only a few commercially successful LoC devices used for point-of-care diagnostics applications. Such applications demand simple sensor readout and single-use disposable sensors, which are difficult requirements to achieve due to mechanical, fluidic, optical, and electronic interface and integration problems. This thesis focuses on the development of a fully integrated LoC measurement system that use micro-electro-mechanical-system (MEMS) based microcantilevers operated in a microfluidic cartridge with simple interface and simple sensor readout. Microcantilever biosensors developed in this research have been adapted for different point-of care applications (blood plasma viscosity and coagulation time measurements), liquid property monitoring and immunoassay detection purposes. The cantilevers are made of electroplated Nickel and fabricated with a simple process using Koç University Micro/Nano Fabrication Clean Room. Cantilever designs varied according to the application. The length of the cantilevers are between 60 µm and 200µm, the width varies between 5 µm and 100µm and the thickness is generally in the order 1- 2µm. They are fully immersed in liquid and actuated by an external electro-coil that operates close to cantilever resonant frequencies and sensing is conducted by means of an optical read-out. A unique optical interferometric method or a laser Doppler Vibrometer is employed for the optical read-out. Both actuation and read-out are conducted remotely. Thus electrical connections to the cantilevers are not required. This feature enables the use of the developed technology as a point of care device with disposable cartridges. The oscillation dynamics of the cantilevers change due to the variations in the liquid properties or the accreted mass on the cantilever surface. The changes in the dynamics are either tracked with lock-in amplifier or phase-locked loop (PLL) based electronics that follows the optical detector. The lock-in amplifier method tracks the phase difference between the actuation signal (coil drive current) and the sensor signal (photo detector output) whereas the PLL method tracks the oscillation frequency real-time by using a fixed phase difference between the actuation and the sensor signals. The cantilever biosensor platform has been used for four biological applications during this thesis research. First, the system is utilized as a viscosity sensor and viscosities blood plasma and blood serum are measured. Blood plasma viscosity can be used for the diagnosis of several diseases such as cardiovascular disorders, rheumatoid arthritis, and certain autoimmune diseases. The proposed system enables fast and convenient measurements with small sample volumes (~10µl), which is superior to common bench-top clinical devices and makes the system suitable for point of care use. New protocols are developed, the systems repeatability and reliability is also tested with reference measurements using commercial laboratory devices. For viscosity detection a detection limit of 0.01 mPa.s is achieved for blood plasma with error less than 6%. Second, a novel method is proposed and demonstrated to separate the coupled effects of density and viscosity on the cantilever oscillation dynamics. A set of equations and a simple algorithm is developed to relate the density and the viscosity to the frequency shifts of the cantilevers. We found that the effect of the density and the viscosity can be well separated if cantilevers have different widths. The method uses the PLL based system to track the resonant frequencies of two cantilevers with different widths immersed in the same liquid. Precise density and viscosity measurements are performed and compared with the reference measurements. The measurement error with the new method was lower than 3 % in density in the range 995 to 1150 kg/m3 and 4.6 % in viscosity in the range 0.935 to 4 mPa.s. Based on the signal-to-noise ratio, the minimum detectable difference in the viscosity is 1.6x 10-3 mPa.s and the density is 0.3 kg/m3. As the third application, the system is adapted for blood plasma coagulation time tests. Periodical coagulation time tests are required for patients who are receiving anticoagulant therapy, undergoing pre-operation evaluation or for patients under risk of embolism, stroke or atrial fibrillation. In general practice, patients need to visit a hospital or a central laboratory periodically for coagulation tests. Such a procedure puts a significant burden on the health-care provider and increases the return time and the cost of the test. Thus, fast, reliable and simple assays are needed to monitor the coagulation parameters. For this purpose the MEMS chips containing cantilevers are integrated with microfluidic channels and multiplexed coagulation time measurements are enabled from single cartridge. New protocols are developed for standard coagulation tests (Prothrombin time (PT) and activated partial thromboplastin time (aPTT)). The tests are conducted not only with standard control plasma samples but also with human plasma samples. The measurement system has an overall 7.28 % and 6.33 % CV (Coefficient of Variation) for PT and aPTT, respectively which are comparable with the commercial devices with different technologies. As the fourth application, the system is tested for immunoassay detection in parallel channels. The proteins of Hepatitis B, Hepatitis C, HIV and Syphilis antigens are detected with reasonable detection limits. The technology developed in this thesis is simple to use, label-free, can be integrated in a disposable cartridge, and suitable for multiple tests in the same cartridge; therefore, it has high potential for point-of-care and home diagnostics applications.