Biosensors Flashcards
What is a biosensor?
Biological component (antibody/enzyme/DNA) bound to a transducer (detects electrical potential, current, conductance, temperature, mass)
What are the methods of attaching the biological component to the transducer?
Membrane entrapment - semi permeable membrane
Physical adsorption - ionic/vdw/hydrophobic/hydrophillic
Porous entrapment - activated carbon
Covalent bond - very strong
What are the essential characteristics of a biosensor?
Reproducible (inter) Repeatable (intra) Sensitivity Specificity Not use analyte
What are the four common types of biosensors?
Resonance Based
Thermal
ISFET
Electrochemical (Conductiometric, Potentiometric, Amperometric)
How does resonance based biosensor work?
Uses a light wave transducer. Based on mass detection. Antibody bound to a membrane. When analyte binds, the mass of the membrane changes. The resonance changes when analyte binds, can directly relate this to the amount of analyte bound.
How does thermal based biosensor work?
Detection of increase or decrease of energy. Based on enzymatic reaction. When enzyme binds analyte, endothermic or exothermic reaction occurs. Compare this to a control channel with no enzyme. Used in pesticide and pathogenic bacteria detection.
How does ISFET based biosensor work?
Ion selective Field Effect Transitor. Measures H+ ions. pH sensitive membrane separates source and drain electrode. When analyte binds enzyme, produces H+ as part of by product. The greater the analyte, the more H+ produced and the greater current produced across the elctrodes. Used for non glass pH detection.
What are the types of electrochemical biosensor?
Conductiometric
Potentiometric
Amperometric
How does conductiometric biosensor work?
Measures change in conductance. Rare in medical applications. used when no net production of ions/electrons from a reaction. two forms - gas and enzyme based. E.g. urea detection and formaldehyde
How does potentiometric biosensor work?
Measure P.D between 2 electrodes. Reference (Ag/AgCl) and measurement one (which has enzymes bound to outside to convert substrate to produce H+) - used in glass pH detection
What is the main type of commercially available biosensor?
Glucose - 85% of market
What is a first generation glucose Biosensor?
1st - GoX localised near the platinum electrode. GoX converts glucose to gluconolacctone. This reduces GoX. GoX then donates its electrons to O2 (cofactor) which is converted into H202 in order to return to its oxidised form. This requires the use of O2 and as a result performance reduces over time with depletion of O2. It also requires a very high operating P.D in order to strip the H202 of its electrons.
What is a second generation glucose Biosensor?
Involves the use of mediators - e.g. ferracynaide or ferracene. These sit in between the GoX and the electrode and transfer e- to the electrode. Allow for operation at a lower operating potential and dont require the use of o2 as a cofactor.
What are the properties of a mediator?
Stable in oxidised/reduced form
Does not react with O2
Cheap
pH independent
How does the pregnancy test biosensor work?
During pregnancy, there is an increase in HCG hormone due to increased secretion from the developing placenta after fertilisation. This hormone stops the inside lining of the uterus being shed and allows for the placenta to develop.
HCG is picked up by antibodies with reactive dye enzymes in the REACTION zone. They are then transported down to the TEST zone, where they are sandwiched with the immobilised enzymes. A CONTROl zone is used to ensure the test is working
