There are two compounds commonly used to dye fill cells during whole-cell patch-clamp recordings: neurobiotin and biocytin (although many alternatives exist, such as lucifer yellow, horseradish peroxidase, and Alexa 488). Conventional wisdom holds that neurobiotin and biocytin are the smallest and least toxic. Here is a dump of what I currently know about each based on personal experience and talking with lab members:

Neurobiotin (from Vector Labs)

• Fills cells far more completely, and faster, at lower concentrations.
• Possibly some toxicity, although this seems to be cell-type, and concentration specific.

Biocytin (from Fisher)

• May be less toxic
• Still fills far better than most alternatives.

So, if worried about effects from toxicity and you do not need a full fill for post-hoc identification, biocytin may be better. If you find you need better fills, or you’re not worried about toxicity, neurobiotin is probably the better option.

Note: we custom order neurobiotin to use a citrate counterion instead of chloride, since we were worried about the effects on Drosophila neurons. The minimum order size as of 2022 is 2g, and Vector labs has offered to split the minimum order size among two labs and ship it out individually.