Roziah Jarmin

Membrane support selection for ISFET as transducer for histamine detection

Histamine has been identified as chemical indicator to estimate the spoilage of food particularly in fish and fish products. Histamine produced in the fish muscle tissue by the action of bacterial decarboxylase enzyme on histidine, can cause poisoning if histamine content in spoilt fish exceeds the FDA safety limit of 100ppm. Ion Selective Field Effect Transistor (ISFET) was introduced by Bergveld in 1970 for the detection of H+ ions. Since then there has been a lot of progress on the applications of ISFET for the detection of other ions by applying a selective membrane on the gate insulator layer. In this report the ionophore-based sensor which employed potentiometry form of transduction made ISFET as a component for the detection of histamine. The selection of ISFET is done before the deposition of membrane on the gate insulator layer. Two types of polymers PVC and polyurethane were used for the membrane materials. These membranes were prepared by dissolving the polymer and the ionophore [Mn(TPP)Cl] in THF as the solvent. After depositing the membrane on the gate of the ISFET, it is left for the solvent to evaporate. A third membrane used was acrylate. In this case the membrane was photo-cured with a stream of nitrogen gas. From the sensitivity test it was found that PVC showed the highest sensitivity (36 mV/decade) followed by urethane (18.5 mV/decade) and acrylate (0.75 mV/decade). The modified ISFET is a promising device for detecting fish freshness. The advantage of ISFET being small and its ability to be integrated with electrochemical and silicon technology makes signal processing and on-site evaluation possible.

A new PSpice macro model for electrolyte insulator interface based Si3N4 Field Effect transistor responsive to H+ ion concentration for biomedical sensor

Innovation of ISFET with electrochemical and silicon technology has the advantage of ease of integration with associated signal processing, simplicity, portability and potential on-site screening. ISFET sensor plays a critical role in biomedical instrumentation system. It serves at the front end of instruments in signal acquisition and conditioning circuit, interfacing between the electronic signals and biological signals from physiologic systems being measured. ISFET sensor fabricated with CMOS technology benefits from low cost production, low power and miniaturization enabling for micro-system. OrCAD PSpice facilitates design and testing of circuitry before the costly fabrication, with a library of built in macro models. However, even with its current popularity, macro model for ISFET devices have not yet been made available. Our work contributes to the development of a new macro model for H+ ISFET in PSpice to allow the characterization and parameterization of such devices to be simulated before costly fabrication. Its functionality is verified by comparing its drain current characteristic against that generated from source code from previous work, with discrepancy in sensitivity of ±8% for pH [4 7 10]. It is also found that good performance of H+ ISFET can be achieved with smaller drain voltage which results in faster response, higher sensitivity to chemical input signal, higher reading of drain current, lower cut-off voltage and higher sensitivity in output voltage to change in pH, of 54.79 mV/pH at drain voltage of 0.1V, through simulated experimentation with the newly created macro model.

A study on freshness of fish by using fish freshness meter

Fishery products are important not only from a nutritional point of view, but also as an item of international trade and foreign exchange earner for a number of countries in the world. Fish are highly perishable, and prone to vast variations in quality due to the method of storage temperature and storage duration. Spoilage is much faster if the fish is not held at chill temperatures [1]. The purpose of this project is to study different method for identifying the freshness of fish. Previous method has been done using Identification of Colour Index where it focused on the fish eyes and gills. The results shown the fish eyes and gills have correlation with the level of freshness. The method that will be used in this experimental approach is using electrode which is applied on the fish muscle and skin. This method is believed to be more accurate in determining the freshness. The results of this study will help to improve the new technologies design in sensing fish freshness.

A ROIC for Mn(TPP)Cl-DOP-THF-Polyhema PVC membrane modified n-channel Si3N4 ISFET sensitive to histamine

Intolerance of histamine could lead to scombroid poisoning with fatal consequences. Current detection methods for histamine are wet laboratory techniques which employ expensive equipment that depends on skills of seasoned technicians and produces delayed test analysis result. Previous works from our group has established that ISFETs can be adapted for detecting histamine with the use of a novel membrane. However, work to integrate ISFETs with a readout interfacing circuit (ROIC) circuit to display the histamine concentration has not been reported so far. This paper concerns the development of a ROIC specifically to integrate with a Mn(TPP)Cl-DOP-THF-Polyhema PVC membrane modified n-channel Si3N4 ISFET to display the histamine concentration. It embodies the design of constant voltage constant current (CVCC) circuit, amplification circuit and micro-controller based display circuit. A DC millivolt source is used to substitute the membrane modified ISFET as preliminary work. Input is histamine concentration corresponding to the safety level designated by the Food and Drugs Administration (FDA). Results show the CVCC circuit makes the output follows the input and keeps VDS constant. The amplification circuit amplifies the output from the CVCC circuit to the range 2.406–4.888V to integrate with the microcontroller, which is programmed to classify and display the histamine safety level and its corresponding voltage on a LCD panel. The ROIC could be used to produce direct output voltages corresponding to histamine concentrations, for in-situ applications.

A Visual Basic Model for ISFET Sensitive to Histamine Ion

Histamine is a type of toxins produced in the fish muscles tissue. Human suffers from Scombroid poisoning, or histamine fish poisoning, if histamine over the tolerant limit is ingested, which brings on allergic reaction. The consequence can be fatal if trachea is blocked owing to swelling of the esophagus. Besides high performance liquid chromatography, which requires pre-treatment, complex procedure that calls for skilled laboratory engineers as well as expensive and nonportable, there has been no other method to detect for level of histamine concentration in fish. Ion Sensitive Field Effect Transistor is a biosensor, product of CMOS technology. It is highly sensitive in ion selection, low cost, portable and low power consumption, features suitable for miniaturization. ISFET fabrication is similar to MOSFET base-structure, except that the gate of MOSFET is replaced with a reference electrode, electrolyte and insulator of ISFET. It is this subtle difference that enables ISFET to produce gate voltage output, in response to change between electrolyte and electrostatic. Being a novel technique, it is necessary to parameterize the ISFET and characterize it for measuring level of concentration of Histamine. Our work here develops simulation model for ISFET biosensor for histamine ions, subsequence of our previous work in developing the theoretical model, using VB 6.0. The input is concentration of histamine between 0-300 ppm. The output is gate source voltage predicted at the Si3N4 gate of ISFET. Graphs of potential of electrolyte-insulator interface versus concentration of histamine, drain-source current versus drain-source voltage and drain-source current versus gatesource voltage are standard displays of the simulation model to identifying parameters for the ISFET model, which are then used to produce the characterization of ISFET. This allows iterative improvement to parameterization and characterization until an optimal ISFET model is obtained before fabrication, without incurring any hardware cost.