Using screened sensors effectively
The new internal screening layer cuts out the majority of interfering signals and makes the sarissaprobe® biosensors much more selective compared to the earlier versions. Nevertheless it is essential that the experimenter still performs controls (with appropriately chosen reference sensors) to establish the origin of the signal recorded by the biosensors and to eliminate the possiblity that it derives from some electroactive interferent. Note that the ATP-Null sensor (SA1002) which does not possess any enzymes can be used as a reference sensor for all sarissaprobe® sensors. More specific reference sensors for adenosine and acetylcholine measurements are sarissaprobe®-INO (SA1004) and sarissaprobe®-ACH-Null (SA1006) respecitvely.
The internal screening layer can become less effective during operational use and prolonged storage (>2 months dry). We strongly recommend testing the integrity of this layer with an electroactive substance such as 5-HT (e.g. at 10 µM). This is especially important if you wish to obtain differential recordings between sensors -both need to exhibit the same selectivity. If the screening has weakened, even although sensitivity to the analyte of interest is good, it is possible repair damage to the internal screening layer and restore selectivity by means of the following process:
Rescreening the sensors
For expert users only
- Make a 100 mM solution of sodium phosphate buffer pH 7.4 (this can be stored for future use).
- Make a 10 mM solution of 1,3 diaminobenzene (also known as m-phenylene diamine) in the phosphate buffer. This solution should be made fresh each time.
- In a small chamber filled with the 1,3 diaminobenzene solution place the sensor tip and an Ag/AgCl reference, connect to potentiostat, and cycle the sensors from 200 to 800 mV and back again at a rate of 10 mV/s. Perform 3 complete cycles. The deposition current should decrease from cycle to cycle as the screening layer grows.
- Wash sensor with deionised water.
- Retest sensor against interferences and its analyte.
This procedure should only be performed by users who have attained expertise in the use and handling of the sensors. Note that 1,3 diaminobenzene is harmful; be sure to follow the correct safety precautions for its handling and disposal. Do not use the same Ag/AgCl reference for rescreening and physiological measurements.
Improving operational stability of sensors
When used in tissue biosensors can lose sensitivity gradually, leading to limits on the operational stability and life of sensors. This is due to several factors, but adsorption of proteins onto the biosensor surface is an important contributor. The adsorbed proteins impede analyte access into the biosensor matrix and hence reduce sensitivity. This protein adsorption can be significantly reduced by an external coating of polyethyleneglycol (PEG). We recommend that the user dips the rehydrated biosensors into a 50% solution of PEG (20k molecular weight) for 10-15 mins before use with tissue. Excess PEG should then be rinsed off with pure water, and the sensors used in the normal way. This will protect the biosensors for several hours. If need be this procedure can be repeated each time the sensor is reused.
Specification
- needle shaped electrode (Pt/Ir wire)
- sensor length 2mm or 0.5mm X 50µm (diam)
- response time: 10-90% rise time ≤ 10 sec
- sensitivity: 0.5 nA per µM
- linear range: 0.5 µM to 50 µM
- selectivity: specific for ATP versus UTP, ADP and adenosine
- shelf-life (dry): ≥ 6 months @ 4° C
- shelf-life (wet): ≤ 5 days
- calibration: single point
- re-use: subject to calibration
- applications: in vitro, in vivo
- tissues: brain; blood vessels; gut; retina
