The present invention provides an isolated nucleic acid sequence encoding a non-oligomerizing Clavularia teal fluorescent protein variant having a tyrosine-derived chromophore, as well as fragments and derivatives thereof. Embodiments of injection systems, injection units, injection needles and handling methods for them are also disclosed in which the risk of injury and contamination for the user is reduced by providing approaches for covering the ends of the cannulas of the injection needles during a number of handling steps. For each net group, shift registers connecting nets in the group are initialized identically to one value and are initialized to a different unique value from shift registers connecting nets of other net groups.