(b) A chemical change caused by the reaction between urease and urea occurs.

(c) The products formed are ammonium ions and carbon dioxide.

(d) The transducer detects the ammonium ions and the biochemical signal is converted into an electrical signal.

(e) The signal is amplified.

(f) The signal is then processed and a measurable signal is produced.

(g) The measurable signal can be in the form of digital display, a print-out or a colour change.

*The advantages of biosensors include high sensitivity, ability to detect small amounts of substrates small in size (portable), accurate, quick, safe, cheap (due to mass production) and can be used for early detection of medical problems.

There are two main types of biosensors to monitor blood glucose level:

a) Electronic biosensor

b) Dipstick

- the biosensor relies on the specificity of enzyme glucose oxidase

- glucose present inthe blood or urine sample is converted to gluconic acidand hydrogen preoxide by glucose oxidase 

Glucose + Oxygen ------> Gluconic Acid + Hydrogen

Preoxide glucose oxidase

- the acid or hydrogen ions produced attract electrons

- this in turn, produces a measurable small electric signal

-the size of electric signal is propotional to the glucose level in blood

- the biochemical signal is detected and converted into electrical signal by the transducer

- the electrical is amplified and sent to a microelectronics and data processor 

- the elctrical signal is used to produce a measurable signal, for example, digital display or print-out colour change.

- some glucose biosensors use a colour change to detect glucose in the urine sample.

- the commonly used dipstick consists of two enzymes, glucose oxidase, preoxidase and a hydrogen donor immobilised on a strip pf cellular fibre.

- a) when the strip is dipped into urine sample, the enzyme glucose oxidase catalyses the changing of glucose to gluconic acid and hydrogen preoxide 

Glucose + Oxygen -------> Glucagonic acid + Hydrogen preoxide 

(in urine sample)

-b) the hydrogen preoxide reacts with the colourless hydrogen donor to produce a coloured compound. The reaction is catalysed by preoxidase

XH2 + H2O2 ------> 2H2O + x

colourless hydrogen donor + hydrogen preoxide -----> water + coloured compound

- the type of intensity of colour indicates the concentration of glucose in the urine sample.

- the concentration of glucose can be measured quantitatively using calorimeter or to estiimate the amount by comparison with a colour reference card

- glucose biosensors are very sensitive and can detect low concentration of glucose.

- the enzyme glucose oxidase and preoxidase can be easily immobilised on a cellulose fibre strip. This is the basis of the dipstick test for quick dianogsis

- the glucose biosensor helps in early detection of medical cases, for example diabetes mellitus, leading to faster and better treatment for patients.

- safe to use and cost can be reduced in mass production.

- high fructose syrup contains 90% fructose and 10% glucose

- fructose is sweeter than glucose, hence, high fructose syrups are in the greater demand than pure glucose as sweeteners in food and drinks.

- the raw material for the production of high fructose syrup is starch (especially cornstarch)

- three main enzymes are used to convert starch into modified starch

-alpha- amylase is used to convert modified starch

-Glucoamylase is used to convert starch into modified starch into dilute glucose syrup

- glucose isomerase (which is immobilised by adsorption onto resin beads in a glass column is used to convert high glucose syrup into low fructose syrup which is then purified into high fructose syrup.

- to take measurement of metabolities (blood gases, lactate, urea, creatinine and glucose)

-in pregnancy test kits ( detects hCG in urine)

- to monitor the manufacturing of pharmaceutical compounds

ENVIROMENTAL MONITORING

- to measure BOD and toxic pollutants

- to check the quality of air

- to detects organophosphates from pesticides, heavy metals, nitrogen compounds

- to check the toxicity levels of waste water

FOOD INDUSTRY

-to measure carbohydrates, alcohols and acids during quality control process

-to check fermentation during the production of beer, yoghurt and soft drinks

-to detect pathogens in fresh meat, poultry and fish