For preparing small quantities of fluorescein diacetate (FDA), I’d get a few inexpensive laboratory consumables. You don’t need elaborate equipment.
- For handling the powder: a small stainless-steel micro-spatula (ideally one with a narrow V-shaped/scoop end), plus weighing boats or weighing paper. Don’t try to pick up individual milligram quantities with tweezers.
- For making your stock: small amber glass bottles, perhaps 5–10 mL, with screw caps. FDA is light sensitive.
- For measuring the solvent: a 1–5 mL syringe is adequate for making a stock solution, although a pipette is nicer.
- For dispensing the stock: I’d buy an adjustable P20 micropipette (2–20 µL) and P200 (20–200 µL), with their corresponding disposable tips. Those two cover most microscopy experiments.
- For very small microscope preparations: the P20 is particularly useful. For example, you can accurately add 5, 10 or 20 µL of stock to a specimen.
- For mixing/storage: 1.5 or 2 mL microcentrifuge/Eppendorf tubes are extremely useful. Amber tubes are ideal for fluorescent dyes, although ordinary tubes wrapped in foil work.
For your particular setup, I’d start with micro-spatula + weighing boats + P20 + P200 + tips + some 1.5-mL tubes + a few amber bottles.
One thing I’d change from our earlier discussion: rather than routinely weighing 50 mg, once you have a reasonable balance you could make a relatively concentrated FDA stock once and then use the micropipettes for subsequent experiments. That greatly reduces the amount of powder handling.
How much do I need to dospense onto each slide of prepared solution?
For a standard microscope slide, you need very little.
If you’re putting a coverslip over the specimen, typically 10–20 µL total liquid is plenty. For a standard 22 × 22 mm coverslip, I’d start with about 15 µL. You want enough to fill the space beneath the coverslip without a large amount squeezing out around the edges.
For FDA staining, however, the important number is the final FDA concentration, not simply the volume placed on the slide. A common starting range for viability staining is roughly 5–20 µg/mL FDA, depending on the specimen.
So, for example, you might prepare 1 mL of staining solution at 10 µg/mL, then pipette 15–20 µL of that already-diluted solution onto each specimen/slide. One millilitre would therefore be enough for roughly 50 slides at 20 µL each.
This is why I’d recommend a P20 micropipette (2–20 µL) for your slides. It will be much easier and more reproducible than a Pasteur pipette.
Tell me what you’re planning to examine first — pond water, yeast, cheek cells, plant material, etc. — and I can give you the appropriate FDA concentration and a simple stock → working solution → slide recipe.