Sensores são dispositivos capazes de captar um determinado sinal físico -químico do meio e converte-lo num sinal elétrico mensurável por meio de um transdutor. Biossensor é um sensor que tem como parte funcional um receptor biológico específico a determinado analito alvo. Os sinais físico-químicos experimentados por estes dispositivos são convertidos em sinais elétricos de magnitude proporcional à concentração de um ou mais compostos químicos. Neste trabalho, foi construído um sensor de pH utilizando filmes finos comerciais de óxido de estanho dopado com flúor (FTO) como receptor a íons. O sensor foi feito ligando-se amostras de FTO ao terminal de porta de um transistor de efeito de campo do tipo MOS (Metal Oxide Semiconductor). Quando colocado em solução, os íons presentes interagem com a amostra sendo adsorvidos na superfície do filme de FTO. O potencial gerado pelos íons adsorvidos modulam a tensão na porta do transistor e, desta maneira, pode -se determinar a concentração dos íons presentes na solução de acordo com a magnitude da resposta do transistor. A este tipo de dispositivo dá -se o nome de EGFET (Extended Gate Field Effect Transistor). O EGFET construído apresentou responsividade de 55 mV/pH e resposta linear em soluções de pH 2 ao 12. Através de técnicas de imobilização enzimática foi possível ligar covalentemente proteínas urease sobre a superfície dos filmes de FTO, convertendo o sensor de pH em biossensor de ureia. Soluções tampão com diferentes pHs e concentrações foram testadas e determinou -se que as condições ideais para o uso deste biossensor de ureia são soluções tampão com pH = 6 e concentração de 10mM. Nessas condições, o biossensor apresentou uma responsividade de 114,5 mV/p(ureia) e linearidade no intervalo de concentrações de ureia entre 3,2.10 -4 e 3,2.10 -2 mol/L. / Sensors are devices capable of capturing a certain physical-chemical signal from environment and convert it into a measurable electrical signal by a transducer. Biosensor is a sensor which has a biological sensing element as receptor specific to a particular target analyte. The physical-chemical signals experienced by these devices are converted into electrical signals with magnitude proportional to the concentration of one or more chemical compounds. In this work, we built a pH-sensor using commercial thin films of tin oxide doped with fluorine (FTO) as ions receptor. The sensor was made by linking FTO samples to the gate of a field effect transistor MOS type. In solution, the ions interact with the sample being adsorbed on the surface of FTO film. The potential generated by the ions adsorbed on film\'s surface modulate the gate voltage of the transistor and, in this way, we can determine the concentration of ions present in solution correlated with the magnitude of the transistor response. This kind of device is given the name of EGFET (Extended Gate Field Effect Transistor). The EGFET built exhibits sensitivity of 55 mV/pH and linear response in the range of pH 2 to 12. Through enzyme immobilization techniques we could covalently bind urease proteins on the surface of FTO film, changing the pH-sensor in urea biosensor. Buffer solutions with differents pHs and concentrations were tested and was determined that optimal environment conditions for this urea biosensor is buffer solutions with pH = 6 and 10mM of concentration. Under these conditions, the biosensor showed sensitivity of 114.5 mV/p(urea) and linear response in the range of 3,2.10 -4 to 3,2.10 -2 mol/L

Este trabalho descreve os resultados do estudo de materiais como óxido de manganês, nanotubos de carbono e feltro de carbono (puro e recoberto com nanotubos ou polianilina-Pani), assim como do desenvolvimento de dispositivos. Os dispositivos estudados estão relacionados a sensores de pH, utilizando esses materiais como membranas seletivas de H+ . Essas membranas funcionam como parte de dispositivos denominados EGFETs, cujo princípio de funcionamento é semelhante ao ISFET. Inicialmente utilizamos o óxido de manganês produzido através do método hidrotérmico com posterior fabricação de filmes finos desse material através da técnica de spray-pyrolysis. Esses filmes foram depositados variando a temperatura de deposição, a concentração da solução e o tipo de superfície do substrato de vidro, com o objetivo de investigar a resposta elétrica do EGFET em função da concentração de íons de H+ . As melhores sensibilidades foram de 50,1 mV/pH e 75 mV/pH no filmes produzidos no substrato de vidro rugoso e vidro liso, respectivamente, com 2g/l de concentração e temperatura de 80o C em ambos os filmes. Num segundo momento, trabalhamos com a produção de nanotubos de carbono e posterior fabricação de filmes finos também pela técnica de spray-pyrolysis, tendo como parâmetros, os mesmos utilizados na primeira parte. Os filmes finos que melhor responderam foram aqueles produzidos a 80o C no vidro rugoso e 100o C no vidro liso, com sensibilidades de 51,6 mV/pH e 53,1 mV/pH, respectivamente, ambos com 3g/l de concentração. Finalmente, utilizamos os feltros de carbono (FC) como membrana seletiva e também como substrato para os nanotubos de carbono (NTC) e a polianilina (Pani). Como membrana, os feltros tiveram uma sensibilidade de 65,47 mV/pH. NTC purificados e não purificados foram também depositados utilizando FC como substrato. NTC não purificados apresentaram pior resposta, enquanto que a parte que foi purificada teve um ligeiro aumento na sensibilidade, sendo de 67,7 mV/pH. Houve ainda o recobrimento dos FC e dos FC/NTC com a Pani. As membranas que contém Pani, são mais estáveis do que as outras amostras, sendo que a Pani no estado deprotonado tem melhor sensibilidade e estabilidade do a Pani no estado protonado. A melhor sensibilidade obtida com a participação da Pani foi de 46,4 mV/pH, que mesmo assim não supera a das demais amostras. Esses materiais se mostram como potenciais para uso de sensores de pH e posteriormente para uso como biossensores. / This work presents the results related to the study of materials such as manganese oxide, carbon nanotubes and carbon felt (pure and with deposition of nanotubes and polyaniline-Pani). The development of devices related to pH sensors is also presented. The materials are used as H+ selective membranes in sensors based on the EGFET configuration, almost similar to the ISFET. We produced manganese oxide by the hydrothermal method with subsequent deposition of thin films using spray pyrolysis. We varied the deposition temperature, concentration of solution and glass substrates surface with the aim of studying the electrical response of the EGFET as a function of the concentration of H+ ions. The best sensitivities were 50.1 mV/pH and 75 mV/pH for films grown on rough and flat substrates, respectively, with a concentration of 2g/l and substrate temperature of 80o C for both films. In the sequence, carbon nanotubes were investigated with the production of thin films also using the spray pyrolysis technique with the same deposition parameters. Films produced at 80o C on rough substrates and at 100o C on flat substrates presented sensitivities of 51.6 mV/pH and 53.1 mV/pH, respectively. Both were produced with a concentration of 3g/l. Finally, carbon felts (FC) were used as selective membranes and also as substrates for the deposition of NTC and Pani. As single membrane FC presented a sensitivity of 65.47 mV/pH. Purified and non-purified NTC were deposited on FC. Non-purified NTC presented the worst response, while purified NTC presented an increase in sensitivity to about 67.7 mV/pH. Pani was then deposited over FC and FC/NTC. Membranes that contain Pani were more stable than other samples. Pani was used either protonated or deprotonated. Deprotonated samples presented a better response. The best response with Pani was about 46.4 mV/pH, which is not as good as the one corresponding to other samples. These materials are promising candidates for a future use as H+ sensors, and also as biosensors.

In recent years, as biological information analysis technology rapidly develops in hematology, biochemistry and microbiology areas, demand for portable measurement systems become more and more important. This study makes efforts in developing disposable hydrogen and potassium ion sensor and microsystem for analysis application. The measured ion concentration data by this analysis microsystem provide people a judgement on their health condition, and furthermore an important reference for medical treatment for patients. There are several advantages in using IC or MEMS technology to manufacture portable measurement system, the advantages are down-scaling, short reaction time, trace chemical analysis, low power dissipation, and low cost. So the thesis uses extended gate field effect transistor, in order to measure multiple ions at the same time, multiple transistors are manufactured on the same chip with an ion selective membrane on top of the gate sensitive layer. This allows the measurement result of the multiple ion be shown at the same time. The main processing steps of the ion sensor developed in this study involve at least four photolithographic and three thin-film deposition processes. Based on the measurement result, the hydrogen ion sensor¡¦s sensitivity is 30.7 mV/decade for a sensing range pH1 ~ pH13. The sensitivity of the potassium ion sensor is 11.5 mV/decade for a sensing range 10-1M to 10-3M.

As working time increases for most people, dining out and staying up late is inevitable, resulting in bad health conditions. The concentrations of calcium and sodium ion in human blood not only respond directly to health conditions, but can also obtain symptoms of different diseases by observing it. This shows that the concentrations of calcium and sodium ion in human blood are an important index of health. In order to manufacture disposable ion sensor and make it easy to measure, this study uses extended gate field effect transistor (EGFET) with an ion selective membrane(ISM) on top of the gate sensitive layer to replace traditional ion sensitive field effect transistor (ISFET). The ISM adsorbs the appointed ion by means of ion selective medicament which is covered by a macromolecule. The main processing steps of the extended gate field effect transistor developed in this study involve at least four photolithographic and two thin-film deposition processes. The influence of the channel¡¦s width to length ratio, the design of channel, the area of the gate sensitive layer, the energy and dose of ion implantation used for the transistor and ion sensor were investigated. Based on the measurement results of the ion sensor, a sensitivity of 40mV/decade with linearity of 98.589 % is measured for calcium ion concentration in human blood ranging from 5 ¡Ñ 10-3 mol/L to 5 ¡Ñ 10-4 mol/L. On the other hand, a sensitivity of 56 mV/decade with linearity of 98.589 % is measured for sodium ion concentration in human blood ranging from 1 mol/L to 10-1 mol/L.

The evaluation of concentration of ions and molecules with the help of biosensors have been regarded as an emerging technology. Bio and chemical sensors have a variety of applications in the field of medicine, military, environmental and food industries alike. With an estimated investment growth of over 4.31% in the development of pH sensors in the next five year, the objective of a developing a robust measurement system is all the more required. The scope of this research is to evaluate the ability of conducting polymer-based gel electrolytes for pH sensitivity, as a function of the transistor characteristics using an Extended Gate Field Effect Transistor or a conducting film in an electrochemical cell. Polymer gels were prepared by dissolving a suitable conducting polymer in an acidic media. The interaction of the gel with a buffer solution of known pH was collected as electric signals using a glassy carbon as an electrode. The electrochemical cell was further connected to the gate of a Metal-Oxide-Semiconductor Field Effect transistor (MOS-FET). The drain current was measured under two conditions; a) voltage across the gate (VGS) was kept constant, with varying voltage across the drain (VDS) and b) voltage across drain was fixed, while gate voltage changed. The drain current versus voltage of the transistor was plotted as a function of the ion interaction between the gel and the buffer. Different plots were recorded for different values of pH solutions. Final results were plotted to calculate the change in threshold voltage, for every change in pH of the observed solution. pH sensitivity of the gels was further tested through the Electrochemical Impedance Spectroscopy method, using a potentiostat and a three-electrode electrochemical cell. With a small excitation, the AC current flowing through the circuit at different frequencies were recorded and the plots discussed, to evaluate sensitivity to pH.

This dissertation explores the different ways to create thin film-based biosensors that are capable of rapid and label-free detection of cortisol, a non-specific biomarker closely linked to stress, within the physiological range of 10pM to 10 uM. Increased cortisol levels have been linked to stress-related diseases, such as chronic fatigue syndrome, irritable bowel syndrome, and post-traumatic stress disorder. It also plays a role in the suppression of the immune system as well. Therefore, accurate measurement of cortisol in saliva, serum, plasma, urine, sweat, and hair, is clinically significance to predict physical and mental diseases. In this dissertation, thin film-based electrochemical immunosensors were fabricated using a self-assembled monolayer (SAM) functionalized by cortisol specific antibodies to detect cortisol at 10 pM level sensitivities in the presence of a redox probe. The fabricated electrochemical cortisol immunosensors were able to detect cortisol in human saliva samples and the outcomes were validated using the standard Enzyme Linked Immuno Sorbent Assay (ELISA) technique. With the aim of improving signal amplification and label-free cortisol detection, copper nanoparticles were incorporated on screen-printed carbon electrodes (SPCE) for the fabrication of electrochemical cortisol immunosensor. This SPCE-based sensor showed a sensitivity of 4.21µA/M and the limit of detection 6.6nM. Both the SAM and SPCE-based immunosensors were not thermally stable due to the instability of antibodies at room temperature. To address this issue, an antibody-free immunosensor was fabricated. Molecular Imprinted Polymer (MIP) was used to template the target cortisol molecule. The MIP-based sensing platform was prepared using polypyrrole, a thermally stable conducting polymer. The conductivity of the polymer ensured good electrical performance. The polypyrrole-based MIP was synthesized by means of electrochemical polymerization and was used to detect cortisol within the physiological range at room temperature. MIP-based sensors exhibited the detection limit of 1 pM, and were cost-effective, easy to fabricate, temperature stable, and reusable. The sensing performance of the resulting sensors was comparable to those of commercially available technologies, such as ELISA. Aiming to perform cortisol sensing at point-of-care (POC), an Extended Gate Field Effect Transistor (EGFET) was integrated with a developed MIP cortisol sensor. The as developed MIP-EGFET sensor was used to detect the cortisol concentration in the range of 1 pM to 100 nM. A few of the major advantages of the developed sensor are its ability to provide a direct readout and simpler electronic systems, which are necessary for miniaturized Point of Care devices.