Studies On The Urease LB Films Field Effect Transistor Biosensor And Capacitance Biosensor

Biosensor is a new subject and technology, which comes from the combination and growth of many subjects, such as biology, chemistry, physics, medicine, electronic technology and so on. Due to their advantages of high selectivity, fast analytical speed, simple operation and low price of instrument, biosensors have been used widely in the fields such as clinical medicine, food industry, environment control, martial medicine, etc.Urease biosensors have important applications in clinical medicine and determination of heavy-metal ions in water. Generally urease is immobilized onto the surface of signal transducer by covalent attachment, cross-linking, entrapment and so on. Langmuir-Blodgett films technology is considered as a desirable tool for manufacturing elements with biological functions such as biosensor, since the structures of LB films much resemble biological membrane environment, and the quantity of enzyme on transducer can be controlled accurately. Up to now, almost no papers concerning with urease/amphiphile mixed LB films and pure urease LB films have been reported. Considering the advantages of LB films technology in making biosensor and present research status of urease biosensor, in this thesis, we have prepared urease/amphiphile mixed LB films and pure urease LB films, and transferred the films onto the surface of signal transducer by the LB films technology. The characteristics of the urease biosensors are investigated subsequently. The main contents are listed as follows:1. Experimental conditions for the formation of urease/amphiphile mixed Langmuir films at the air/water interface and the transfer of the Langmuir films onto the surface of different substrates have been explored. The optimized condition is: urease concentration 8 mg L"1, PH value of subphase 5.5, association time of ureaes with amphiphiles 2 h, the temperature of subphase 10癈, SiO2/Si substrate with hydrophobic surface. Under the condition, transfer ratios are in the desirablerange. FTIR spectrum shows that the peaks at 1648 cm"1 and 1538 cm"1 are correlated to the absorption of peptide of urease molecule, which manifests that urease molecules have been transferred successfully onto the surface of the substrate.2. Urease-based field effect transistor biosensor has been fabricated by the transfer of urease/amphiphile mixed Langmuir films onto ion-sensitive field effect transistor (ISFET). Its function has been studied with ISFET meter, and the intensity of output signals shows linear relationship with the logarithmic urea concentration from 0 to 20 mM. The detection limit of the biosensor for the urea determination is 0.2 mM, and the response of the biosensor can be achieved within 15s.3. Experimental conditions for formation of pure urease Langmuir films at the air/water interface and the stability of such films have been studied. The transfer ratios of the Langmuir films onto the surface of hydrophilic and hydrophobic SiCVSi substrates have been determined. Under the optimized condition: P=20 mNm" , Curease=: 8 mgL" , PH=6.5, T=20癈, stable pure urease Langmuir films can be formed at the air/water interface, and it can be transferred successfully onto the hydrophobic surface of SiOi/Si substrate. When the number of the transferred layers is 2, transfer ratios are desirable.4. Urease capacitance biosensor has been manufactured by LB films technology, its function has been studied with the electrochemical AC impedance measurement. The intensity of output signals shows linear relationship with the logarithmic urea concentration from 0.1 to 6 mM. the sensitivity of determination for urea concentration is 22 mV/PUrea.