Microfluidics is a vibrant and expanding field that has the potential for solving many analytical challenges. Microfluidics shows promise to provide rapid, inexpensive, efficient, and portable diagnostic solutions that can be used in resource-limited settings. Microfluidic devices have gained immense interest as diagnostic tools for various diseases through biomarker analysis. My dissertation work focuses on developing electrokinetically operated integrated microfluidic devices for the analysis of biomarkers indicative of preterm birth risk. Preterm birth (PTB), a birth prior to 37 weeks of gestation, is the most common complication of pregnancy and the leading cause of neonatal deaths and newborn illnesses. In this dissertation, I have designed, fabricated and developed several microfluidic devices that integrate various sample preparation processes like immunoaffinity extraction, preconcentration, fluorescent labeling, and electrophoretic separation of biomarkers indicative of PTB risk. I developed microchip electrophoresis devices for separation of selected PTB biomarkers. I further optimized multiple reversed-phase porous polymer monoliths UV-polymerized in microfluidic device channels for selective retention and elution of fluorescent dyes and PTB biomarkers to facilitate on-chip labeling. Successful on-chip fluorescent labeling of multiple PTB biomarkers was reported using these microfluidic devices. These devices were further developed using a pH-mediated approach for solid-phase extraction, resulting in a ~50 fold enrichment of a PTB biomarker. Additionally, this approach was integrated with microchip electrophoresis to develop a combined enrichment and separation device that yielded 15-fold preconcentration for a PTB peptide. I also developed an immunoaffinity extraction device for analyzing PTB biomarkers directly from a human serum matrix. A glycidyl methacrylate monolith was characterized within microfluidic channels for immobilization of antibodies to PTB biomarkers. Antibody immobilization and captured analyte elution protocols were optimized for these monoliths, and two PTB biomarker proteins were successfully extracted using these devices. This approach was also integrated with microchip electrophoresis for combined extraction and separation of two PTB biomarkers in spiked human serum in <30 min. In the future, these optimized microfluidic components can be integrated into a single platform for automated immunoaffinity extraction, preconcentration, fluorescent labeling, and separation of PTB biomarkers. This integrated microfluidic platform could significantly improve human health by providing early diagnosis of PTBs.

Reducing cost and time is a major concern in clinical diagnostics. Current molecular diagnostics are multi-step processes that usually take at least several hours or even days to complete multiple reagents delivery, incubations and several washing processes. This highly labor-intensive work and lack of automation could result in reduced reliability and low efficiency. The Laboratory-on-a-chip (LOC), taking advantage of the merger and development of microfluidics and biosensor technology, has shown promise towards a solution for performing analytical tests in a self-contained and compact unit, enabling earlier and decentralized testing. However, challenges are to integrate the fluid regulatory elements on a single platform and to detect target analytes with high sensitivity and selectivity. The goal of this research work is to develop an AC electrokinetic (ACEK) flow through concentrator for in-situ concentration of biomolecules and develop a comprehensive understanding of effects of ACEK flow on the biomolecule transport (in-situ concentration) and their impact on electronic biosensing mechanism and performance, achieving automation and miniaturization. ACEK is a new and promising technique to manipulate micro/bio-fluids and particles. It has many advantages over other techniques for its low applied voltage, portability and compatibility for integration into lab-on-a-chip devices. Numerical study on preconcentration system design in this work has provided an optimization rule for various biosensor designs using ACEK technique. And the microfluidic immunoassay lab-chip designed based on ACET effect has showed promising prospect for accelerated diagnostics. With optimized design of channel geometry, electrode patterns, and properly selected operation condition (ac frequency and voltage), the preconcentration system greatly reduced the reaction time to several minutes instead of several hours, and improved sensitivity of the assay. With the design of immunoassay lab-chip, one can quantitatively study the effect of ACET micropumping and mixing on molecular level binding. Improved sensors with single-chip form factor as a general platform could have a significant impact on a wide-range of biochemical detection and disease diagnostics including pathogen/virus detection, whole blood analysis, immune-screening, gene expression, as well as home land security.

As compared with the concentration in sample when the detection limit of analyte is low, a preconcentration method can be used. In this study, cloud point extraction (CPE) was used as the preconcentration method. The aqueous solutions of nonionic and zwitterionic surfactant materials become cloudy when its temperature reaches the cloud point temperature and analyte collapses with surface active material. The volume of surfactant rich phase is much smaller than the solution volume and therefore a way high preconcentration factor was obtained. For the cloud point extraction of selenite, a fluorimetric ligand, 2,3-diminonaphthalene (DAN) was used and the hydrophobic Se(IV)-DAN complex formed (4,5-benzopiazselenol) was extracted with Triton X-114. The effects of pH, complexation period, reaction temperature, DAN concentration and surfactant concentration on the extraction efficiency were investigated. The extraction efficiency at the optimized conditions was 98 percent. Spectrofluorimetric determination of selenium was performed at excitation and emission wavelegths of 379 nm and 582 nm, respectively. The detection limit, established as 3s /slope where s is the standard deviation of 9 measurements of 0.020 mg/L Se (IV)-DAN complex after 10 fold preconcentration was 3.7 &micro / g/L Se. By using solid surface fluorescence measurements detection limit could be reduced down to 1.2 &micro / g/L. The obtained detection limits (3.7 and 1.2 &micro / g/L) were sufficiently low for detecting selenite in diverse samples. The accuracy of the method was confirmed by the analysis of trace elements in waste water Standard reference material (EnviroMAT- Waste Water LOW EU-L-1). The interference effects of some anions and cations were also tested.

Flame Atomic Absorption Spectrometry (FAAS) still keeps its importance despite the relatively low sensitivity / because it is a simple and economical technique for determination of metals. In recent years atom traps have been developed to increase the sensitivity of FAAS. Although the detection limit of FAAS is only at the level of mg/L, with the use of atom traps it can reach to ng/mL. Slotted quartz tube (SQT) is one of these atom traps, it is applied for determination of volatile elements / it is economical, commercially available and easy to use. In this study, a sensitive analytical method has been developed for the determination of lead with the help of SQT. Regarding the angle between the two slots of SQT, 120&deg / and 180&deg / configurations were used and the results were compared. There were three modes of SQT used. The first application was for providing longer residence time of analyte atoms in the measurement zone / 3 fold sensitivity enhancement was observed. The second mode was the usage of SQT for preconcentration of lead atoms. In the presence of a lean air-acetylene flame, analyte atoms were trapped in the inner surface of SQT for a few minutes. Then, by the help of a small volume (10-50 &amp / #956 / L) of Methyl isobutyl ketone (MIBK), analyte atoms were revolatilized and a rapid atomization took place. Using this mode, a sensitivity enhancement of 574 was obtained at a rather low (3.9 mL/min) suction rate / 1320 fold improvement was reached at higher sample suction rate (7.4 mL/min) for 5.0 min collection. The last mode involves coating of the inner surface of SQT with several kinds of transition metals. The best sensitivity enhancement, 1650 fold, was obtained by the Ta coated SQT. In addition, effects of some elements and anions on Pb signal in Tacoated-SQT-AT-FAAS were examined. Final step consists of surface analysis / chemical nature of Pb trapped on quartz and Ta surface, and the chemical nature of Ta on quartz surface were investigated by X-ray Photoelectron Spectroscopy (XPS) and Raman Spectroscopy.

In recent years speciation analysis is becoming more important as it is known that each chemical form of an element behaves differently in biological and environmental media. Since abundance of tellurium in earth crust is extremely low, very sensitive and accurate methods are needed to determine the concentration of tellurium. Hydride generation atomic absorption is a sensitive, fast and economical technique applied for the determination of tellurium. Speciation of tellurium can be achieved by making use of different kinetic behaviors of Te(IV) and Te(VI) upon its reaction with sodiumborohydride. A continuous flow hydride generation system was developed and parameters that affect the analytical signal were optimized. Sample solutions were prepared in 4.0 mol/L HCl / as reductant 0.5 % (w/v) sodiumborohydride in 0.5 % (w/v) NaOH was used. Quantitative reduction of Te(VI) was achieved through application of a microwave assisted prereduction of Te(VI) in 6.0 mol/L HCl solution. Sensitivity of the system was further enhanced by in-situ trapping of the formed H2Te species in a previously heated graphite furnace whose surface was modified using Pd or Ru. Overall efficiency of pyrolytic coated graphite surface was found to be 15% when hydrides are trapped for 60 seconds at 300 oC. LOD and LOQ values were calculated as 86 pg/mL and 287 pg/mL according to peak height values. Efficiency was increased by 46% and 36% when Pd and Ru modifiers were used, respectively. With Ru modified graphite tube 173 fold enhancement was obtained over 180 seconds trapping period with respect to direct ETAAS. LOD values were 6.4 and 2.2 pg/mL for Pd and Ru treated systems, respectively, for 180 s collection of 9.6 mL sample solution.

ABSTRACT DETERMINATION OF CADMIUM USING SLOTTED QUARTZ TUBE ATOM TRAP ATOMIC ABSORPTION SPECTROMETRY AND METAL COATINGS &Ouml / zcan Gurbetoglu, G. Pelin M.S., Department of Chemistry Supervisor: Prof. Dr. O. Yavuz Ataman July 2010, 76 pages Flame atomic absorption spectroscopy (FAAS) is a common technique for detecting metals and metalloids in environmental, biological and metallurgical samples. Although it is a rather old technique, it is still very reliable, simple to use and inexpensive. The technique can be used to determine the concentration of over 70 different metals in a solution. However, it has detection limits at mg/L levels. Some atom trapping methods have been developed to reach the detection limits of ng/mL levels. Slotted quartz tube (SQT) is one of these atom trapping methods. It is an important technique, since it is easy to use, applicable in all laboratories, commercially available and economical. This thesis consists of development of a sensitive method for cadmium with the help of SQT atom trap. In this study, it was used for two different purposes. One was for keeping the analyte atoms more in the light path / in other words, for increasing the residence times of analyte atoms in the measurement zone. This first application was provided a 2.9 times enhancement with respect to conventional FAAS. Second application was for trapping the analyte on the surface of the SQT, in other words, for performing on-line preconcentration of cadmium in SQT. In the presence of a lean flame, analyte samples were trapped and collected for a few minutes at a low suction rate. After finishing the collection period, analyte atoms were revolatilized with the help of a small volume of (10-50 &micro / L) methyl isobutyl ketone (MIBK) and a rapid atomization occurred. This introduction also altered the flame composition momentarily and analyte atoms were released from the surface of the SQT. Application of this method enhanced the sensitivity 2065 times with respect to conventional FAAS. Another approach to this type of atom trapping has been investigated also in this study, which was coating of SQT with some metals having low volatility. Therefore, some transition metals were coated to the surface of SQT and among them zirconium was selected as the best coating material as having the most sensitivity enhancement factor. That is why, rest of the study was performed with the Zr coated SQT. The enhancement was 3368 as compared with FAAS. Cd determination with this method provides LOD value of 8 pg/mL and Co value of 19 pg/mL. In order to see the effect of some other type of elements or ions on determination of cadmium, interference study was done.

Selenium is a trace and essential element for good health but required only in very narrow range. Hence, determination of selenium in trace level in any matrix related with human health is important. A preconcentration method is performed to obtain a low detection limit for analyte. In this study, the methodology of cloud point extraction (CPE) was used as the preconcentration method for speciation of selenium in vitamin tablets. Non-ionic surfactant Triton X-114 and a fluorimetric ligand, 2,3- diaminonaphtalene (DAN) were used for the extraction of trace levels of organic and inorganic selenium species as a prior step to their determination by spectrofluorimetry. The aqueous solutions of nonionic and zwitterionic surfactant materials become cloudy when temperature reaches the cloud point temperature and analyte collapses with surface active material. The volume of surfactant rich phase is smaller than the solution volume and by this way high preconcentration factor was obtained. Optimization of the CPE parameters affecting complexation and phase separation was performed. Standard addition method was used in the quantitative measurements. Spectrofluorimetric determination of selenium was done using excitation and emission wavelegths of 380 nm end 570 nm respectively. The detection limit, established as 3s /slope where s is the standard deviation of 12 measurements of 0.02 mg/L Se-DAN complex after 10 fold preconcentration was 2.3 &micro / g/L. Accuracy of the method was checked using EnviroMat Waste Water, EU-L-2 as SRM and the result was in good agreement with certified value.Besides, selenium rich vegetables (dill, watercress herb and garlic) were grown in a pot at a controlled atmosphere.Selenium in plants (dill, watercress gerb and garlic), both control and enriched groups was determined by ICP-MS.

Flame Atomic Absorption Spectroscopy (FAAS) has lover sensitivity than similar analytical methods, however it has an important place for analysis due to its easy application and economic practicability especially in metal determinations. In order to increase the sensitivity of FAAS from mg/L level to ng/L level, various atom trap systems have been used. One of these atom traps, Slotted Quartz Tube (SQT), which is easy, economical and useful for volatile element determination, is used in this study as a sensitive analytical method for determination of tellurium. In the study, determination of Te by SQT is handled in three different modules. First, only with SQT itself, longer residence time for Te atoms in the measurement zone is provided and consequently 3.2 fold sensitivity enhancement is obtained both for Te (VI) and Te (IV). In the second module, SQT is used for concentration of tellurium species in a lean flame by sending the analyte into SQT for a definite time and trapping them on the inner surface of the SQT. After trapping the analyte, in order to determine the Te concentration, a small volume (10-50 &micro / L) of organic solvent such as methyl ethyl ketone (MEK) is introduced to the flame for revolatilization and a rapid atomization of Te on the surface is provided. In this trapping method, for 5 minutes collection with a 6 mL/min suction rate, 143 fold enhancement for Te (VI) and 142 fold enhancement for Te (IV) were obtained. In the third module, different from the second one, the inner surface of the SQT is coated with different metals for increasing the amount of Te trapped on the surface and the best enhancement for tellurium is obtained with Tantalum-coated SQT with 252 fold enhancement for Te (VI) and 246 fold enhancements for Te (IV). All improvements are calculated according to the signals obtained in FAAS method. Separate calibration plots were used for Te (IV) and Te (VI).

For the first time, octahydroxyl methylresorcinarene with four hexyl groups on the lower rim was utilized in the in-situ preparation of a silica-based sol-gel organic-inorganic hybrid coating for sample preconcentration by capillary microextraction (CME). Tetraethoxysilane (TEOS) was chosen as a sol gel precursor to create a cross-linked sol-gel network via acid-catalyzed hydrolytic polycondensation reactions. Sol-gel chemistry helped in the in situ preparation of resorcinarene-containing extraction phase in the form of a surface coating. It also provided an effective means to chemically bind the coating to the inner surface of fused silica capillary via condensation of the hydroxyl groups in the sol-gel network with the silanol groups on the fused silica capillary inner surface. These chemically bonded sol-gel coatings demonstrated excellent thermal stability (up to 350 oC). The sol-gel resorcinarene coatings successfully extracted traces of polycyclic aromatic hydrocarbons (PAHs), ketones, phenols, amines, and alcohols from aqueous samples providing parts per trillion level detection limits (0.828 - 46.01 ng/L) in GC using a Flame Ionization Detector (FID). CME was performed by passing the aqueous samples through the resorcinarene coated microextraction capillary (10 cm). The extracted analytes where then thermally desorbed into the GC column connected to the exit end of the sol-gel microextraction capillary via a press-fit quartz connector. Peak area relative standard deviation (RSD %), a measure of the extraction performance reproducibility for the coated capillary, was found in the range of (1.1 % - 8.3 %). The sol-gel resorcinarene sorbent was characterized by FTIR spectrum which indicated the presence of hydroxyl groups in the coating even after the sol-gel reactions were completed which explains the affinity of the resorcinarene sol-gel coating toward polar analytes. Scanning Electron Microscopy (SEM) images of the coating reveraled the porous morphology and thickness of 3.5 - 4.0 µm for the coating. The sol-gel resorcinarene coated capillary provided excellent extraction performance for wide range of analytes.

En aquesta tesi, proposem la fabricació y la caracterització d’un microconcentrador de gasos, per ser acoblat amb un microsistema de detecció, per millorar el seu límit de detecció davant els gasos tòxics. Aquest estudi s’aplica especialment al benzè, que es un compost d’alta cancerigenitat. El preconcentrador proposat esta basat en estructura plana, que, es una opció de fabricació més simple y permet una millor aïllament tèrmic amb el resta d’unitats del microsistema, qu’els estructures 3D proposats a la literatura. No obstant, els factors de concentració obtinguts amb l’estructura plana queden generalment més baixos, per causa de la menor quantitat de material absorbent que pot acollir. En aquesta tesis, es va superar aquest problema mitjançant l’utilització del carboní actiu, un adsorbent d’alta capacitat d’adsorció, així com l’optimització de les condicions de funcionament del dispositiu. Finalment, acoblant el microconcentrador amb un micro-cromatògraf, vam aconseguir una detecció sensible y selectiva del benzè en barreja amb altres volàtils a l’aire. / The present thesis focuses on the fabrication and characterization of a gas microconcentrator for to be coupled with a detection microsystem, in order to lower its detection limit towards toxic gases and vapours in contaminated areas. This study was more especially applied to the preconcentration of benzene, a cancerigenic compound at low ppb level. A preconcentrator based on a planar structure was proposed regarding its simpler fabrication, better thermal insulation and lower power consumption, compared to the 3D structures proposed conventionally in literature. In order to obtain higher concentration factors with such structure, its small size was compensated by using a high adsorption capacity adsorbent such as activated carbon as well as the optimization of the preconcentration conditions of the device. Finally, the microconcentrator was validated as injection unit when coupled with a microchromatographic system, where a sensitive and selective analysis of benzene in mixture with other VOCs was achieved.