d-Luciferin Substrate Solution (7.5 mg/mL)

• 1. Combine 1.0 g of d-luciferin potassium salt powder with 133.3 mL of sterile phosphate-buffered saline (PBS) or Dulbecco's phosphate-buffered saline (D-PBS) without Mg²⁺ or Ca²⁺.

• 2. Filter-sterilize using a 0.22-µm membrane filter.

• 3. Aliquot the solution into sterile opaque tubes or wrap tubes in foil.

• 4. Store aliquots at −20°C for at least 6 mo.

• 5. Thaw sufficient quantities before injecting animals. Avoid repeated freeze–thaw cycles.

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