If you are receiving an unexpected higher result, there could be several reasons for this, including environmental factors or light leakage; here are the first areas to check:
Light Saturation - The photodetector used in the luminometer is extremely light-sensitive and can become "saturated" with light if exposed to ambient light such as that found in a normal laboratory. Although most modern luminometers contain redundancies that prevent such an occurrence, executing an RLU measurement with the chamber cap open can cause this problem. One solution, in this case, is to power down the luminometer and allow 4-6 hours for the photodetector assembly tube to return to normal.
Radio Frequency Interference - Many electronic devices emit radio frequencies (RF), which are a subset of a larger group called Electromagnetic Frequencies (EMF). Certain devices generate greater RF's than others and can artificially stimulate the luminometer electronics to emit high RLU's. These include wireless internet connections from personal computers or multi-function cellular telephones, very-high frequency (VHF) or ultra-high frequency (UHF) radios, cordless telephones, heavy equipment (motors, welding equipment), among others.
Helium Canisters - Avoid operating and storing the luminometer near Helium gas canisters. Helium gas can permanently damage the photomultiplier tube.
Contaminated Plastic Consumables - The various plastic parts used in 2nd Generation ATP testing should be sterile and free of ATP. It is important to ensure that unused plastic parts are stored in a clean environment in the sealed package in which they were received and that when in use, the surfaces that come in contact with reagents or samples are not contaminated in any way (for example, avoid touching pipette tips on a surface). If you suspect that you have received contaminated plastic parts, obtain a fresh, unused quantity and re-check background noise to confirm. Also, because of the risk of cross-contamination, these components are meant for one use only and should never be re-used.
Static Electricity Interference- Ground yourself before conducting tests (a common way to do this is to touch a faucet), use a different brand of gloves, or move to a different location. Avoid wearing any PPE that can generate static electricity.
Other Common Issues:
- Confirm the PhotonMaster Luminometer was at room temperature during testing. Taking a reading with a Luminometer directly from a hot truck or stored in sunlight or during winter can cause abnormal readings. Allow the device to return to room temperature.
- Are the tubes being transported or stored in a bag different than what was provided?
- Avoid storing tubes in direct sunlight. Storing the tubes in sunlight causes them to absorb UV which causes interference.
- Are the tubes scratched, dirty, or contaminated at all?