Advanced healthcare requires novel technologies capable of real-time sensing to long-term health monitoring. One example includes biomarker detection for disease diagnosis and deciding treatment options. But several limitations exist with current technologies; however, the COVID pandemic brought these limitations to a global presence as the authorities struggled to quickly authorize a facile test for the early detection of SARS-CoV-2. An important next step is to research alternate strategies, utilize the current infrastructure available, and build sensors that meet standards the current technologies fail to. One of the strategies involves identifying novel sensing parts. To this end, we turned our attention to bacteria as they provide a plethora of novel sensing parts. Bacteria respond to stimuli using a wide range of biomolecules that include enzymes and transcription factors. Our group reported an optical progesterone biosensor based on a novel progesterone responsive allosteric transcription factor (aTF). Firstly, the electrochemical transduction of the binding affinity between this aTF and its cognate DNA sequence is discussed. The binding and unbinding of aTF-DNA results in an impedance change and is directly proportional to progesterone concentration. The limit of detection is comparable to the optical progesterone sensor and relevant to the physiological ranges of progesterone present in bodily fluids. Secondly, to convert the sensor into a point of care system, the expression of the aTF-enzyme fusion protein that undergoes the binding-unbinding event is discussed. The enzyme in presence of its excess substrate acts as a signal amplifier to track the binding changes. The signal depends on the proximity of the fusion protein to the electrode surface and correlates to the progesterone concentration. As we recover from the deadly COVID pandemic, we realize that early diagnosis is a key pillar of disease containment, in addition to other approaches such as contact tracing, distancing, and personal protective equipment. A truly transformative technology in the fight against future viruses is a rapid and quantitative point-of-care (POC) test with a low limit of detection and a high specificity. To that end, an inverted glucometer technology for the detection of infectious diseases is presented. As a model system, SARS-CoV-2 antigens – nucleocapsid protein, antibodies against it, and an inflammatory biomarker are detected. Antigen of interest is sandwiched between capture and detection reagents with biotin and glucose oxidase tags respectively. Glucose oxidase, a widely used enzyme in glucometers, amplifies the output signal in presence of excess glucose. The following chapters encompass designs, different immobilization techniques, characterization, and optimization methods to develop biosensors that meet requirement standards. This research serves as a platform for development of state of the art technologies for diagnostics applications. / 2025-01-16T00:00:00Z

An impedance bioanalyzer system comprising an in-vitro biotransducer, instrumentation and control software for the measurement of urea, potentially in blood dialysate, has been developed. The biotransducer comprises of a microlithographically fabricated interdigitated microsensor electrode (IME) onto which was cast a biorecognition layer conferred with the specificity of the enzyme urease. Urease hydrolysis of urea produces NH4+, HC03- and OH- ions that decrease the device's impedance. The temporal rate of change (kinetic) and the extent of change (equilibrium) of ion concentration were measured as the sensor's response. Five formats: [i) unPEGylated urease-containing poly(hydroxyethylmethacrylate) [p(HEMA)] hydrogel, ii) PEGylated urease-containing p(HEMA) hydrogel, iii) via glutaraldehyde crosslinking in the presence of albumin, iv) the direct covalent immobilization of urease to the IME, and v) solution borne urease]. Michaelis-Menten parameters KM, ZMAX and kcat revealed the following rank: PEGylated urease-Gel >> Free Urease > unPEGylated urease-Gel = BSA in Glutaraldehyde > covalently immobilized urease. The unPEGylated-urease sensor provided a higher enzyrne- substrate binding rate and catalysis rate than PEGylated and thus provided a faster impedimetric response to various molar concentrations of urea. Long-term stability (one month) of the PEGylated-urease hydrogel was favorable. A dedicated three-element array impedimetric instrument, the 3EIC BioAnalyzer was designed and produced. A pair of demodulating logarithmic amplifiers (AD8302) was used to calculate the change in phase and amplitude corresponding to the impedimetric response to a 4.0 kHz, 50 mVPP sine wave from a function generator (MAX038). A graphic user interface (GUI), programmed in LabVIEW 7.0 established instrument control, data acquisition via a USB-48A-30A16 μDAQ and graphical data presentation of temporal impedimetric responses.

Udder illnesses can have an essential influence on quantity and quality of the milk. A diagnosis is possible with the help of the deviation of milk contents, especially over the change of the somatic cells. The cell count consequently makes an important health and quality criterion of the milk. In order to determine the cell count and other contents directly after the vormilk, the relation between the count of the milk cells and the impedimetric quanities of the milk was examined systematically in a new measure cell with alternating current. The measurements were executed isotherm with different temperatures over a wide frequency area (10 Hz -13 MHz) and the results were compared with the cell counts obtained with standard procedures (Fossomatic). Relations between the measured complex electric quantities and the content of the milk like lactose and cell count were produced with help of statistical methods. No direct relation is found between the impedimetric qualities (complex condauctance, conductance or capacity) of milk and the number of cells found in it. Cause of that is the inhomogeneity of the cells, that varies considerably regarding their size and mass. The lactose concentration correlates good with impedimetric quantities (amplitude, phase shift, capacity and conductance) of milk. Particularly with the condactance of the milk a statistically secured relation is found over the entire frequency area (10 Hz - 13 MHz). The lactose concentration correlates on the other hand well with the cell count and makes a statistically secured prognosis of this quantity with high precision possible. Future it is possible to determine the cell count with the help of the complex conductivity, for what simple conductivity measuring instruments are suitable. / Eutererkrankungen können einen wesentlichen Einfluss auf Menge und Qualität der Milch haben. Eine Diagnose ist an Hand der Abweichung von Milchinhaltstoffen, insbesondere über die Veränderung der somatischen Zellen möglich. Die Zellzahl stellt somit ein wichtiges Gesundheits- und Qualitätskriterium der Milch. Um die Zellzahl und andere Inhaltsstoffe direkt nach dem ersten Gemelk zu bestimmen, wurde der Zusammenhang zwischen der Zahl der Milchzellen und den impedimetrischen Eigenschaften der Milch in neuartigen Messzelle mit Wechselstrom systematisch untersucht. Die Messungen wurden isotherm bei verschiedenen Temperaturen über einen weiten Frequenzbereich von 10 Hz - 13 MHz durchgeführt und die Ergebnisse mit denen nach Standardverfahren (Fossomatic) erhaltenen Zahlen verglichen. Mit Hilfe statistischer Methoden wurden Relationen zwischen den erhaltenen komplexen elektrischen Größen und den Inhaltstoffen der Milch wie Laktose und Zellzahl hergestellt. Es konnte kein direkter Zusammenhang zwischen den impedimetrischen Eigenschaften (komplexer Leitwert, Wirkleitwert oder Kapazität) der Milch und der Zahl darin befindlicher Zellen gefunden werden. Ursache dafür ist die Inhomogenität der Zellen, die hinsichtlich ihrer Größe und Masse beträchtlich variieren. Dagegen lässt sich die Laktosekonzentration gut mit den impedimetrischen Eigenschaften (Amplitude, Phasenverschiebung, Kapazität und Wirkleitwert) der Milch korrelieren. Besonders mit dem Wirkleitwert der Milch ist ein statistisch abgesicherter Zusammenhang über den gesamten Frequenzbereich (10 Hz bis 13 MHz) zu finden. Die Laktosekonzentration wiederum korreliert gut mit der Zellzahl und ermöglicht mit hoher Genauigkeit eine statistisch gesicherte Voraussage dieser Größe. Damit ist es möglich, zukünftig die Zellzahl über den Laktosegehalt anhand der komplexen Leitfähigkeit zu bestimmen, wozu einfache Leitfähigkeitsmessgeräte geeignet sind.

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Submitted by Jos? Henrique Henrique (jose.neves@ufvjm.edu.br) on 2017-09-22T18:10:08Z No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) marcelo_sousa_xavier.pdf: 3096603 bytes, checksum: dae91257943ac86316978d8deb31ff3e (MD5) / Approved for entry into archive by Rodrigo Martins Cruz (rodrigo.cruz@ufvjm.edu.br) on 2017-10-09T13:42:33Z (GMT) No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) marcelo_sousa_xavier.pdf: 3096603 bytes, checksum: dae91257943ac86316978d8deb31ff3e (MD5) / Made available in DSpace on 2017-10-09T13:42:33Z (GMT). No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) marcelo_sousa_xavier.pdf: 3096603 bytes, checksum: dae91257943ac86316978d8deb31ff3e (MD5) Previous issue date: 2017 / A Leishmaniose Visceral Canina (LVC) ? considerada um problema de sa?de p?blica causada por um protozo?rio do g?nero Leishmania que acomete c?es, o qual no ciclo urbano de transmiss?o ? o principal reservat?rio. Neste trabalho, investigou-se o desenvolvimento de um imunossensor impedim?trico sobre eletrodos de grafite (EG) e eletrodos impressos de ?xido de grafeno (EIG) modificados com filmes polim?ricos para detec??o de Leishmaniose infantum em amostras de soros caninos. Os EG e o EIG foram modificados pela eletrodeposi??o do ?cido 2-hidroxicin?mico (2-HCA). A eletropolimeriza??o do 2-HCA foi realizada por voltametria c?clica (VC), utilizando-se solu??o monom?rica 2,50 mM preparada em H2SO4 0,50 M contendo 1,0 mL de etanol. Para o EG utilizou-se 100 ciclos de potencial na faixa de +0,20 a +1,20 V a 50 mV/s e para o EIG 15 ciclos consecutivos de potencial de 0,00 a +1,00V a 100 mV/s. Para ambos os eletrodos modificados o poli(2-HCA) apresentou caracter?sticas adsortivas e eletroativas. Estudos de Espectroscopia de Imped?ncia Eletroqu?mica (EIE) foram realizados para avaliar as propriedades el?tricas dos eletrodos modificados. Para o EG/2-HCA utilizou-se o circuito equivalente descrito como (Rs(RQp)(Qdl[RtcW]) onde obteve-se o valor de resist?ncia a transfer?ncia de carga (Rtc) de 13,2 k?, enquanto que para EIG/2-HCA o circuito equivalente proposto foi o de Randles, no qual o valor de Rtc foi de 4,2 k?. Visando a miniaturiza??o do sistema, optou-se pelo desenvolvimento do biossensor sobre os EIG. Desta forma, foram colocados sobre a superf?cie dos EIG/2-HCA, utilizando a t?cnica de adsor??o, 35 ?L de diferentes concentra??es do ant?geno L. infantum (Ag) (15, 30, 50, 70 e 100 ?g/mL), sendo realizados testes de intera??o com amostras de soros caninos contendo os anticorpos positivos (Ac+) de L. infantum em diferentes propor??es 1:80, 1:160, 1:320, 1:640 e 1:1280 dilu?dos em tamp?o HBS-EP pH 7,40 com 20 minutos de intera??o a 37 ?C. Os melhores resultados foram obtidos utilizando-se o ant?geno em concentra??o de 50 ?g/mL durante 20 min a 37 ?C e a dilui??o do soro de 1:320. Posteriormente, avaliou-se o tempo de imobiliza??o do Ag e de imunorrea??o Ag-Ac em 20, 40 e 60 minutos. Obteve-se 20 min de como tempo ideal de imobiliza??o de Ag e para imunorrea??o Ag-Ac+. Ap?s otimiza??o destes par?metros, avaliou-se a resposta do imunossensor na presen?a de amostras de soros caninos diagnosticados como positivos (Ac+) e negativos (Ac-) para Leishmaniose infantum, onde observou-se valores de Rtc para o sistema Ag-Ac+ 82% maior do que o obtido para o Ag-Ac-, demonstrando margem de seguran?a confi?vel no reconhecimento do analito de interesse. O imunossensor proposto para detec??o de Leishmaniose infantum apresentou boas perspectivas para aplica??o ao diagn?stico da doen?a, podendo-se tornar mais uma alternativa para realiza??o de testes r?pidos e de simples aplica??o para detec??o de LVC. / Disserta??o (Mestrado) ? Programa de P?s-Gradua??o em Qu?mica, Universidade Federal dos Vales do Jequitinhonha e Mucuri, 2017. / Visceral Canine Leishmaniasis (LVC) is considered a public health issue caused by a protozoan of the Leishmania genre that attacks dogs, which is the main reservoir in the urban transmission cycle. In this work, we investigated the development of an impedimetric immunosensor on graphite electrodes (GE) and graphene oxide-modified screen-printed carbon electrode (GSP) both modified with polymeric films to detect Leishmaniose infantum in canine serum samples. The GE and GSP were modified by the electrodeposition of 2-hydroxycinnamic acid (2-HCA). Electropolymerization of 2-HCA was performed by cyclic voltammetry (CV) using a 2.50 mM monomeric solution prepared in 0.50 M H2SO4 containing 1.0 mL of ethanol. For the EG and EIG, 100 cycles of potential between +0.20 and +1.20 V at 50 mV/s and 15 cycles of potential between 0.00 and + 1.00 V at 100 mV/s were used, respectively. Poly(2-HCA) shown adsorptive and electroactive characteristics for both electrodes. Electrochemical Impedance Spectroscopy (EIS) studies were performed to evaluate the electrical properties of the modified electrodes. For the GE/2-HCA was used an equivalent circuit described as (Rs(RpQp)(Qdl[RtcW]), and a resistance of charge transfer (Rct) of 13.2 k? was obtained. For GSP/2-HCA the proposed equivalent circuit was that of Randles in which the value of Rct obtained was 4.2 k?. For system miniaturization it was developed the biosensor over GSP. Thus, 35 ?L of different concentrations of L. infantum antigen (Ag) (15, 30, 50, 70 e 100 ?g/mL) were placed on the GSP/2-HCA surface using the adsorption technique. Interaction tests were carried out with canine serum samples containing the positive antibodies (Ac+) of L. infantum in different proportions of 1:80, 1:160, 1:320, 1:640 e 1:1280, diluted in HBS-EP buffer pH 7.4 with 20 minutes of interaction at 37 ?C. The best results were obtained using the antigen at a concentration of 50 ?g/mL for 20 min at 37 ?C and a serum dilution of 1:320. Subsequently, the Ag immobilization and Ag-Ac immunoreaction time were evaluated in 20, 40 and 60 min. 20 min was obtained as the ideal time for Ag immobilization and Ag-Ac+ immunoreaction. After optimization of these parameters, the immunosensor response was evaluated in the presence of canine serum diagnosed as positive (Ac+) and negative (Ac-) for Leishmaniose infantum, where the Rct values for the Ag-Ac+ system were 82% higher than those obtained for Ag-Ac-, demonstrating a reliable safety margin in the recognition of the analyte of interest. The proposed immunoassay for the detection of Leishmaniasis infantum presented good prospects for application in the diagnosis of the disease, and it could become an alternative for performing rapid tests and simple application for the detection of LVC.

Philosophiae Doctor - PhD / In this work, DNA aptamer biosensor systems were developed for the detection of l7p-estradiol - an estrogeneous endocrine disrupting chemical (EDC). Endocrine disrupting chemicals are group of compounds that impact negatively on the endocrine system of humans and wildlife. High concentrations of l7p-estradiol in water or food chain disrupts the physiology of the endocrine system of various animal species, leading to feminisation in fish and stimulates the proliferation of cancer cells in humans. Aptasensor systems for the determination of l7pestradiol were prepared with three immobilization platforms: (i) poly(3,4- ethylenedioxythiophene) {PEDOT} doped with gold nanoparticles (AuNPs) to form PEDOTIAuNPs polymeric nanocomposite, (ii) generation 1 poly(propylene thiophenoimine)-copoly( 3 ,4-ethy lenedioxythiophene) dendritic star copolymer (G 1PPT -co-PEDOT), and (iii) generation 2 poly (propylene thiophenoimine)-co-poly(3,4-ethylenedioxythiophene) dendritic star copolymer (G2PPT-co-PEDOT). The morphological properties of the sensor platforms were interrogated by scanning emission microscopy (SEM) and atomic force microscopy (AFM), while their spectroscopic characteristics were studied by Fourier transform infra red spectroscopy (FTIR) and fluorescence spectroscopy. The electrochemical behaviour of the platforms and the aptasensors were studied by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and square wave voltammetry (SWV). The DNA aptamer developed for detecting 17~-estradiol and which was used in the fabrication of all aptamer biosensors in this study is a 76-mer biotinylated aptamer (5'-BiotinGCTTCCAGCTTATTGAATTACACGCAGAGG TAGCGGCTCTGCGCATTCAATGCTGCGCGCTGAAGCGCGGAAGC-3'). AulPEDOTIAuNPslAptamer (platform 1) was obtained by covalently attaching streptavidin to the polymeric nanocomposite platform using carbodiimide chemistry and the aptamer immobilized via streptavidin-biotin interaction. The electrochemical signal generated from the aptamer-target molecule interaction was monitored electrochemically using cyclic voltammetry and square wave voltammetry in the presence of [Fe(CN)6J 3-/4- as a redox probe. The signal current observed was inversely proportional to the concentration of 17Bestradiol. The aptasensor demonstrated specificity toward 17~-estradiol. The detectable concentration range of the 17B estradiol was 0.01 nM-O .09 nM with a detection limit of 3.2 pM. The 76-mer biotinylated aptamer for 17~-estradiol was incorporated into a generation 1 poly(propylenethiophenoimine )-co-poly(3 ,4-ethylenedioxythiophene) dendritic star copolymer modified Au electrode via biotin-avidin interaction (platform 2). The Bode plot shows that the charge transfer dynamics of the nanoelectrode can be frequency modulated while the AulG 1PPTco- PEDOT nanoelectrode exhibited greater semi-conductor behavior (higher phase angle value) than AulG 1PPT due to the incorporation of charged functionalized dendrimer at low frequencies (100 mHz). The biosensor response to 17~-estradiol was based on the decrease in the SWV current as the EDC binds to the ssDNA aptamer on the biosensor. The dynamic linear range of the sensor was 0.01-0.07 nM with a detection limit of7.27 pM. Synthesis of electro synthetic generation G2PPT-co-PEDOT (platform 3) was performed by copolymerization of PEDOT with G2PPT dendrimer modified electrode immersed in a solution of 0.1 M LiCI04 containing 0.1 M EDOT monomer and 0.1 M sodium dodecyl sulphate (SDS) for ten (10) cycles. The electrochemical behaviour of the dendritic star copolymer was investigated with CV and EIS in LiCI04 and phosphate buffer solutions. The results show that the electrochemical deposition of G2PPT-co-PEDOT on gold electrode decreased the electrochemical charge transfer resistance when compared to AuiPEDOTILiCI04 and AuiLiCI04 interfaces. Bode impedimetric analysis indicates that G2PPT-co-PEDOT is a semiconductor. The fabrication of two novel aptasensors (based on platforms 2 and 3) simultaneously on a screen printed micro array electrode of 96-well multichannel electrochemical robotic sensor testing system for the detection of endocrine disrupting l7~-estradiol, was also carried out. The aptasensors responses to l7~-estradiol, based on the decrease in the SWV current, were evaluated.

Resistances in two-dimensional matrices can be measured by addressing individual sensors one by one using two multiplexers. Thereby, it is assumed that the injected measurement current flows only through the target sensor. Nevertheless, if no special precautions are taken, a part of the injected current may flow through other sensors and this can significantly affect the measurement accuracy. This so-called cross-talk effect is therefore crucial for the measurement of two-dimensional sensor matrices. One possible solution to overcome this problem is to use the short-circuiting method, which sets the same potentials on both sides of the non-target sensors and avoids thereby the cross-talk currents leading to an improvement of measurement accuracy. The short-circuiting method is widely used because it requires no addition of further components, like diodes or MOSFETS, into the matrix. Nowadays, most of the short-circuiting methods are designed for the measurement of purely resistive (e.g., the zero potential circuit driving by DC signals) or capacitive sensor matrices. Thereby, capacitive matrix measurement methods are mainly designed to realize a high scanning speed and do not focus on reducing measurement deviations as they are more conceived for touch screens. In this thesis, the development of accurate measurement methods is focused, to reduce the cross-talk effects in two-dimensional impedimetric sensor matrices, where both the real part and imaginary part of the impedance need to be accurately measured. A multi-row excitation strategy using AC signals having different frequencies is proposed to avoid DC deviations due to the non-ideal behavior of electronic components and to enable simultaneous impedance measurement of all sensors. First, a novel method is proposed, to enable a multiplexer-free simultaneous measurement of resistive sensors in the two-dimensional matrix. This method is named the AC - Zero Potential Circuit (AC-ZPC Type 0), and it is extended for the measurement of impedimetric sensors. Then, based on analytical investigations, two advanced methods are proposed to realize higher measurement accuracy. The first advanced method (AC-ZPC Type 1) corrects the deviations caused by the row interface impedance by introducing a column with reference elements and dispenses with the measurement of the row side excitation signals. The second advanced method (AC-ZPC Type 2) extends the basic AC-ZPC method further. It uses a voltage follower on the row input side to reduce the row interface impedance and introduces a row and a column with reference elements. This method reduces the deviations related to the non-ideal features of the column side amplifier circuits, including their input/output impedance, open-loop gain factor, leakage current, and load impedance. The evaluation of the three proposed methods is carried out first by simulations and then on a specially developed experimental platform. In the simulations, the measurement deviations achieved by the proposed methods are less than 0.005% for the impedimetric targets composed of parallel RC pairs in the range from 2 kΩ||362 pF to 100 kΩ ||$ 7 pF. The feasibility of these proposed methods has been validated by the experimental investigations. Thereby, the AC-ZPC Type 2 method has shown better accuracy than the AC-ZPC Type 1 method. For purely resistive targets in the range from 2 kΩ to 100 kΩ, the averaged absolute deviation of 0.087% is achieved by the AC-ZPC Type 2 method, which is 20% less than the DC-ZPC methods.:1 Introduction 2 Theoretical background 3 Measurement methods for 2D sensor matrices 4 Novel methods for impedimetric sensor matrices 5 Performance in reducing cross-talk effects 6 Practical validation of the proposed methods 7 Conclusion and outlook References Appendix A Operational amplifier model Appendix B Calculation of the resistive and capacitive parts of a time constant unit Appendix C Supplements to performance investigation / Widerstände in zweidimensionalen Matrizen können gemessen werden, indem einzelne Sensoren mit zwei Multiplexern angesprochen werden. Dabei wird davon ausgegangen, dass der eingespeiste Messstrom nur durch den Zielsensor fließt. Ohne besondere Vorkehrungen kann jedoch ein Teil des eingespeisten Stroms durch andere Sensoren fließen, was die Messgenauigkeit erheblich beeinträchtigen kann. Dieser so genannte Übersprechungseffekt ist daher für die Messung von zweidimensionalen Sensormatrizen von entscheidender Bedeutung. Eine mögliche Lösung zur Überwindung dieses Problems ist die Kurzschlussmethode, bei der auf beiden Seiten der nicht zu messenden Sensoren die gleichen Potenziale angelegt werden und dadurch die Übersprechungsströme vermieden werden, was zu einer Verbesserung der Messgenauigkeit führt. Die Kurzschlussmethode ist weit verbreitet, da sie keine weiteren Komponenten, z.B. Dioden oder MOSFETS, in der Matrix erfordert. Heutzutage sind die meisten Kurzschlussverfahren für die Messung von rein resistiven (z.B. die Nullpotenzialschaltung, die durch Gleichstromsignale angetrieben wird) oder kapazitiven Sensormatrizen ausgelegt. Dabei sind kapazitive Matrixmessverfahren hauptsächlich auf eine hohe Messgeschwindigkeit ausgelegt und konzentrieren sich nicht auf die Reduzierung von Messabweichungen, da sie eher für Touchscreens konzipiert sind. In dieser Dissertation ist die Entwicklung präziser Messmethoden das Ziel, um die Übersprechungseffekte in zweidimensionalen impedimetrischen Sensormatrizen zu reduzieren, bei denen sowohl der Realteil als auch der Imaginärteil der Impedanz genau gemessen werden müssen. Es wird eine mehrreihige Erregungsstrategie unter Verwendung von Wechselstromsignalen mit unterschiedlichen Frequenzen vorgeschlagen, um Gleichstromabweichungen aufgrund des nicht idealen Verhaltens elektronischer Komponenten zu vermeiden und die gleichzeitige Impedanzmessung aller Sensoren zu ermöglichen. Zunächst wird eine neue Methode vorgeschlagen, die eine multiplexerfreie gleichzeitige Messung von Widerstandssensoren in einer zweidimensionalen Matrix ermöglicht. Diese Methode wird als AC-Nullpotenzialschaltung (AC-ZPC Typ 0) bezeichnet und für die Messung von impedimetrischen Sensoren erweitert. Anschließend werden auf der Grundlage analytischer Untersuchungen zwei fortschrittliche Methoden vorgeschlagen, um eine höhere Messgenauigkeit zu erzielen. Die erste fortschrittliche Methode (AC-ZPC Typ 1) korrigiert die durch die Impedanz der Reihenschnittstelle verursachten Abweichungen durch die Einführung einer Spalte mit Referenzelementen und verzichtet auf die Messung der reihenseitigen Anregungssignale. Die zweite fortgeschrittene Methode (AC-ZPC Typ 2) erweitert die grundlegende AC-ZPC Methode weiter. Sie verwendet einen Spannungsfolger auf der Reiheneingangsseite, um die Reihenschnittstellenimpedanz zu verringern, und führt eine Reihe und eine Spalte mit Referenzelementen ein. Diese Methode reduziert die Abweichungen, die mit den nicht idealen Eigenschaften der spaltenseitigen Verstärkerschaltungen zusammenhängen, einschließlich ihrer Eingangs-/Ausgangsimpedanz, des Open-Loop-Verstärkungsfaktors, des Leckstroms und der Lastimpedanz. Die Bewertung der drei vorgeschlagenen Methoden erfolgt zunächst durch Simulationen und dann auf einer speziell entwickelten Versuchsplattform. In den Simulationen liegen die mit den vorgeschlagenen Methoden erzielten Messabweichungen bei weniger als 0,005% für die aus parallelen RC-Paaren bestehenden impedimetrischen Ziele im Bereich von 2 kΩ||362 pF bis 100 kΩ ||$ 7 pF. Die Durchführbarkeit der vorgeschlagenen Methoden wurde durch die experimentellen Untersuchungen bestätigt. Dabei hat die AC-ZPC Typ 2 Methode eine bessere Genauigkeit als die AC-ZPC Typ 1 Methode gezeigt. Für rein resistive Ziele im Bereich von 2 kΩ bis 100 kΩ wird mit der AC-ZPC Typ 2-Methode eine gemittelte absolute Abweichung von 0.087% erreicht, was 20% weniger ist als bei den DC-ZPC-Methoden.:1 Introduction 2 Theoretical background 3 Measurement methods for 2D sensor matrices 4 Novel methods for impedimetric sensor matrices 5 Performance in reducing cross-talk effects 6 Practical validation of the proposed methods 7 Conclusion and outlook References Appendix A Operational amplifier model Appendix B Calculation of the resistive and capacitive parts of a time constant unit Appendix C Supplements to performance investigation

Udder illnesses can have an essential influence on quantity and quality of the milk. A diagnosis is possible with the help of the deviation of milk contents, especially over the change of the somatic cells. The cell count consequently makes an important health and quality criterion of the milk. In order to determine the cell count and other contents directly after the vormilk, the relation between the count of the milk cells and the impedimetric quanities of the milk was examined systematically in a new measure cell with alternating current. The measurements were executed isotherm with different temperatures over a wide frequency area (10 Hz -13 MHz) and the results were compared with the cell counts obtained with standard procedures (Fossomatic). Relations between the measured complex electric quantities and the content of the milk like lactose and cell count were produced with help of statistical methods. No direct relation is found between the impedimetric qualities (complex condauctance, conductance or capacity) of milk and the number of cells found in it. Cause of that is the inhomogeneity of the cells, that varies considerably regarding their size and mass. The lactose concentration correlates good with impedimetric quantities (amplitude, phase shift, capacity and conductance) of milk. Particularly with the condactance of the milk a statistically secured relation is found over the entire frequency area (10 Hz - 13 MHz). The lactose concentration correlates on the other hand well with the cell count and makes a statistically secured prognosis of this quantity with high precision possible. Future it is possible to determine the cell count with the help of the complex conductivity, for what simple conductivity measuring instruments are suitable. / Eutererkrankungen können einen wesentlichen Einfluss auf Menge und Qualität der Milch haben. Eine Diagnose ist an Hand der Abweichung von Milchinhaltstoffen, insbesondere über die Veränderung der somatischen Zellen möglich. Die Zellzahl stellt somit ein wichtiges Gesundheits- und Qualitätskriterium der Milch. Um die Zellzahl und andere Inhaltsstoffe direkt nach dem ersten Gemelk zu bestimmen, wurde der Zusammenhang zwischen der Zahl der Milchzellen und den impedimetrischen Eigenschaften der Milch in neuartigen Messzelle mit Wechselstrom systematisch untersucht. Die Messungen wurden isotherm bei verschiedenen Temperaturen über einen weiten Frequenzbereich von 10 Hz - 13 MHz durchgeführt und die Ergebnisse mit denen nach Standardverfahren (Fossomatic) erhaltenen Zahlen verglichen. Mit Hilfe statistischer Methoden wurden Relationen zwischen den erhaltenen komplexen elektrischen Größen und den Inhaltstoffen der Milch wie Laktose und Zellzahl hergestellt. Es konnte kein direkter Zusammenhang zwischen den impedimetrischen Eigenschaften (komplexer Leitwert, Wirkleitwert oder Kapazität) der Milch und der Zahl darin befindlicher Zellen gefunden werden. Ursache dafür ist die Inhomogenität der Zellen, die hinsichtlich ihrer Größe und Masse beträchtlich variieren. Dagegen lässt sich die Laktosekonzentration gut mit den impedimetrischen Eigenschaften (Amplitude, Phasenverschiebung, Kapazität und Wirkleitwert) der Milch korrelieren. Besonders mit dem Wirkleitwert der Milch ist ein statistisch abgesicherter Zusammenhang über den gesamten Frequenzbereich (10 Hz bis 13 MHz) zu finden. Die Laktosekonzentration wiederum korreliert gut mit der Zellzahl und ermöglicht mit hoher Genauigkeit eine statistisch gesicherte Voraussage dieser Größe. Damit ist es möglich, zukünftig die Zellzahl über den Laktosegehalt anhand der komplexen Leitfähigkeit zu bestimmen, wozu einfache Leitfähigkeitsmessgeräte geeignet sind.