Impedance spectroscopy (IS) is an important technique for monitoring and detection of biomaterials. In order to enable point-of-care systems, low-cost IS systems capable of rapidly measuring a wide range of biomaterials are required. This thesis presents two IS systems, one in Printed Circuit Board level and the other in Integrated Circuit level. The board level system is built for preliminary experimental data collection; it is capable of measuring impedance from 1KHz to 100KHz with 200mV signal injection into cell sample. Experimental results show that magnitude and phase error are less than 6.6% and 2.2%, respectively. An IC level IS front-end is also proposed which utilizes a time-to-digital converter (TDC) and a peak detector circuit (PDC) for quick measurement of both impedance phase and magnitude, respectively. Designed in a 0.18μm CMOS process, the front-end is capable of performing impedance measurements in 6μs at frequencies ranging from 100Hz-10MHz and with a 100Ω-1MΩ dynamic range. Simulation results with cell impedance models show that the system achieves <2.5% magnitude and <2.2 degree phase error. The front-end consumes 28mW total power and occupies 0.4mm^2 area.

Ringdown spectroscopy (RDS) is an absorption spectroscopic and detection technique that makes use of an optical cavity to realize a long effective pathlength through a sample and to render the measurement independent of intensity. These two features give RDS an advantage over traditional absorption techniques and allows its application in measuring concentrations of strongly absorbing analytes present in trace amounts, or in measuring weak absorptions for analytes in higher concentrations. The resonant optical cavities used here are created from optical fibre. This permits the easy construction of an inexpensive apparatus for RDS. The performance of various cavity geometries (linear, circular) in three ranges of the visible and near infrared spectrum (405, 800, and 1550 nm) was examined. Concurrent multiexponential decays arising from core modes, cladding modes, and amplified spontaneous emission were analyzed in the framework of an exponential decay model transformed into the frequency domain. The small mode field diameter of light within a fibre is well suited to probing very small liquid volumes on the order of pico- or femtolitres. This uniquely positions optical waveguide-based RDS for application in absorption detection for separation techniques such as capillary electrophoresis (CE) and high performance liquid chromatography (HPLC) where high time resolution detection is required across narrow separation channels. The experimental and theoretical work presented here was preformed with an eye towards this purpose. / Thesis (Master, Chemistry) -- Queen's University, 2007-07-04 16:23:53.173

Cavity ring-down spectroscopy (CRDS) is an absorption spectroscopic technique. In CRDS the concentration of an analyte is determined by measuring the reduction in finesse of an optical cavity made from two highly reflective (R>99.9%) mirrors once a sample is introduced. Optical loss is traditionally determined from the exponential intensity decay of a short laser pulse that was injected into the cavity. This decay is the longest for an empty, high finesse cavity and is reduced when the sample absorbs or scatters light. In this project, the optical cavity is made from fiber optic waveguides and the light source is a continuous wave (cw) diode laser. It is used to detect analytes such as acetylene, ammonia and other amines through their overtone absorption in the telecom region at 1500 nm. The experiment is done by increasing the ratio of desired loss (extinction caused by the sample), to undesirable loss (from the waveguide or solvents) through amplification of the ringdown signal using an erbium doped fiber amplifier (EDFA). The EDFA is inserted into a fiber-optic loop and its gain is increased above the lasing threshold. The gain of the, now lasing, fiber loop is "clamped" to a high and constant value, thereby removing unwanted gain fluctuations, and all losses in the loop are compensated for. If one now inserts a laser light pulse at the lasing wavelength of the loop it would circulate through the loop indefinitely, whereas a light pulse at a wavelength that is being absorbed by an analyte would experience a decrease with time at a rate that depends only on the magnitude of the sample absorption. By enclosing the sample gap with a gas cell both acetylene and ammonia have been detected down to ~25 ppm and ~5.9 Torr respectively. Subsequently, a 1% solution of aminotoluene was detected in an interrogation volume of 5.65 pL by having inserted a fiber with a hole drilled in it as the sample gap. At present, the drilled fiber has been replaced with photonic crystal fiber such that small volumes of gases may be detected with a longer effective path length. / Thesis (Master, Chemistry) -- Queen's University, 2011-09-23 18:27:47.65

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