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. Author manuscript; available in PMC: 2009 Jul 16.
Published in final edited form as: Methods Cell Biol. 2008;84:143–179. doi: 10.1016/S0091-679X(07)84006-4

Table 1.

Capabilities of optical systems.

Absorbance Interference Fluorescence
Sensitivitya 0.1 OD 0.1 mg/ml 100 pM
Rangeb 2–3 logs 3–4 logs 6–8 logs
Precisionc Good Excellent Good
a

The sensitivity is the minimum amount of signal needed to obtain good results. For the interference optical system, the signal is relatively insensitive to the type of biological material, so that a 1 mg/ml sample results in a displacement of ~3.25 fringes. Sensitivity of the fluorescence system is for fluorescein (molar extinction coefficient ~65,000 at 488 nm, quantum yield ~0.9).

b

The range refers to the concentration range accessible by the optical system.

c

The precision of the optical system is estimated by comparing the signal to noise ratio. For the absorbance and fluorescence detectors, this ratio is ~100 (e.g. the uncertainty in a 1 OD reading is about 0.01 OD, and the uncertainty in a fluorescence intensity reading is about 1% of the signal). For the current interference optical system, this ratio is closer to 1000.