function based sensing Flashcards
Define function based sensing
A function based detector is defined as a naturally occurring biological organism or portion of that organism (whether organ, tissue, cell, or receptor) that reacts in a measurable way when exposed to a range of chemical or biological toxic material.
eg canary in coal mine
differences between structure and function based sensing
Structure sensing is based in finding the agent that causes the problem
Function based sensing is looking for evidence that the agent is present eg contrails/emissions to find planes
Describe a cell based system (x2)
inherent system where natural processes are exploited for detection
Engineered system, where a cell ahs been genetically engineered or had sensing materials added to them
what is a hybrid system?
Hybrid systems exploit part of the functional process within a cell based response system, even as they are targeted at a specific characterized function.
Describe an enzyme based chem detection system
NAIAD - nerve agent detection system
The bioreceptor in this case is the enzyme
butyrylcholinesterase , which exhibits the same enzyme activity as human acetylcholinesterase.
The enzyme is immobilized onto a temperature
controlled pad that is continually washed with butyrylthiocholine methane sulfonate in an aqueous
phosphate buffer.
The enzyme catalyses the hydrolysis of the ester, producing butrylthiocholine , and the concentration is monitored by an electrochemical cell arrangement
(this is the transduction system).
If nerve agent is present, it inhibits the butyrylcholinesterase , which in turn causes an alteration in the electrical potential within the electrochemical cell, thus triggering an alarm at a present level.
This type of detector is extremely sensitive to low levels of nerve agents such as tabun and sarin. Also HCN.
Describe an ion based sensing system
, Competitive assay. Here a similar membrane is formed except that it contains hapten linked gramicidin, ( G h ). The membrane is rinsed with a streptavidin solution after which an appropriate
biotinylated, hapten specific Fab′ is added, forming complexes between the MSL α and the G h . The G h is thus tethered distant from its immobilized inner layer partners, G T , preventing the formation of
dimers and lowering the electrical conductance of the membrane. The sensor is stored in this state until the addition of analyte competes with the hapten for the Fab′, liberating the channel and resulting in an increase in the membrane conductance
How can chromoatophores be used in sensing?
Fish chromatophores from Betta splendens are used as the cytosensor element in the development of a portable microscale device capable of detecting certain environmental toxins and bacterial pathogens by monitoring changes in pigment granule distribution.
Cell based biosensor prototype. The
chamber containing chromatophores
has wicks inserted for sample delivery,
and is placed into the holder. An agent
can be applied to the top wick, and the
response of the chromatophores is
imaged using the LED light source, lens
and camera. The image is then
processed by the statistical program
present in the computer.
A heterogeneous population of
chromatophores is always present in
primary tissue culture, and not all cells
respond equally when exposed to many of
the environmental toxins tested.
define a chromatophore
Chromatophores, which are pigment cells responsible for the brilliant colours of fish, amphibians, and reptiles.
considerations of function based systems (7)
- slow (minutes to hours) response time
- mostly lab based rather than field deployable
- Cell based assays prone to poisoning by environmental pollutants
- Prone to false alarms if not carefully characterised for selectivity, specificity and sensitivity
- Process of sampling air and getting sample to the cell needs attention
- preparation of sample adds time to the overall response time
- needs a life support system is still living
Examples of function based sensing
canaries in coal mines, sarin
Chickens as sentinels for encephalitis virus
Daphnia to indicate water quality
Poland, 8 regularly changes mussels are used to detect water quality changes
limitations of function based sensing?
less specific
less selective
therefore potential for false positives is high
Do not measure concentrations
rely on transduction devices to measure response
Strengths of functional detection
can detect presence of wide range of unknown chembio agents
Describe an example hybrid system
PANTHER
PAthogen Notification for THreatening Environemtnal Releases
uses cellular analysis and notification of antigen risks and yields to detect pathogens including anthrax, plague, e.coli etc
How does PANTHER work
use genetically engineered jellyfish cells to use antibodies to bind to threats. once a binding has occurred, Ca ++ are released. A bioluminescent protein from the jellyfish cells is released in response to the Ca++ increase, emitting light which is then detected.
