Among the labeling methods, fluorescent labeling has the upper hand due to its non-destructive nature and the high sensitivity of the fluorescence technique, as well as meeting the requirements of small measurement volume and low concentration of the fluorescent material. Fluorescent labeling is generally accomplished by using a reactive derivative of the fluorophore that selectively binds to a functional group contained in the target biomolecule.
Mostly, the followed fluorescent labeling techniques generally adopted, allow specific labeling with functional groups attached to an amino acid with high selectivity and specificity. The fluorophores are designed with a reacting moiety, which may be bound covalently or non-covalently to the target biomolecules. Fluorescent molecule attachment to the biomolecules can be achieved chemically or biologically[1].
Voltage sensitive dyes offer the opportunity to monitor cell electrical activity, e.g. in neurons. The chromophore is believed to undergo a large electronic charge shift as a result of excitation from the ground to the excited state and this underlies the putative electrochromic mechanism for the sensitivity of these dyes to membrane potential[2].