# Preparation of all-trans retinal food
Jelly hubertus Maria Soffers

## Retinal Food Preparation

**Protocol modified from:**

- [Optogenetics teaching
  protocol](https://bdsc.indiana.edu/stocks/teach/teach_optogenetics.html)
- [Molasses food
  recipe](https://bdsc.indiana.edu/information/recipes/molassesfood.html)

------------------------------------------------------------------------

## Preparation of All-Trans Retinal (ATR)

- Suspend ATR in ethanol to make a 250 mM stock solution.
- Prepare fly food with a 1:200 dilution → final concentration 0.2 mM.
- ATR does not fully dissolve, resuspend as much as possible.
- Store 1 mL aliquots at -20°C (stable indefinitely).

> [!WARNING]
>
> ### Light Sensitivity of ATR
>
> All-trans retinal is highly light sensitive. Avoid exposure to strong
> white light and keep solutions covered with foil whenever possible.

## Fly Media Options

### Option 1: Pre-made fly media

- Purchase fly media online [Archon
  Scientific](https://www.archonscientific.com/)
- Supplement with ATR as needed
- **Clark lab:**
  - Drip ATR onto food surface
- **Lacin lab:**
  - Scrape food from ~40 vials (~5 mL each)
  - Microwave to melt and cool
  - Add 2 vials of 250 mM ATR to 40 vials

### Option 2: Prepare your own fly media

**Consumables and Equipment:**

- Please refer to the vendors listed by the Bloomington Drosophila Stock
  Center for supplies and equipment. [Vendors Fly
  supplies](https://bdsc.indiana.edu/information/supplies.html).
  - Genesee Scientific is amongst the most cometitvely priced vendors
    for fly vials, plugs and food.
- A simple kettle on heat plate or turkey roaster oven (~\$75.00) are
  economic solutions for cookign the fly food.
  - [Turkey Roaster Oven](https://tinyurl.com/2zt2zp9u)

**Recommended mix:**

- Nutri-Fly™ Molasses formulation Genesee Scientific\]() (Costs \<
  \$3.00 per liter)
  - [Nutru-Fly™](https://www.geneseesci.com/product/nutri-fly-bloomington-formulation-pre-mixed-fly-food/?srsltid=AfmBOor7IYFAjLV5lrm_Cydmj536lWIh9ff9YYbLvvVLfIfIvCrOnJii)
- Or use the recipe below:

##### Yield

- Makes ~**1.2 L**
- Enough for ~**100 vials**

##### Ingredients

| Ingredient                 | Amount    |
|----------------------------|-----------|
| Water                      | 1041.5 mL |
| Yeast Red Star Active Dry) | 26.4 g    |
| Yellow cornmeal            | 40.8 g    |
| Agar                       | 9.6 g     |
| Molasses                   | 64.83 mL  |
| Tegosept (20% in ethanol)  | 12 mL     |
| Propionic acid             | 6.0 mL    |
| Extra water                | 141 mL    |

Ingerient vendor: We recommend [Genessee
Scientific](https://www.geneseesci.com/applications/drosophila-research/food-fillers/)
\#### Instructions

1.  Add ¼ of the water and stir with:
    - agar
    - yeast
    - cornmeal
    - molasses (≥10 minutes)
2.  Add remaining water and boil for 20 minutes, stirring to dissolve
    lumps
3.  Add remaining cold water to cool faster
4.  When mixture is \< 80°C, add:
    - acid
    - tegosept
5.  Add 6 mL of 250 mM ATR

> [!WARNING]
>
> ### Protect from Light During Preparation
>
> After adding ATR, minimize light exposure. Work quickly and keep
> containers covered with foil when possible.

6.  Dispense ~5 mL per vial
7.  Dry overnight:
    - cover with cheesecloth
    - seal with Press’n Seal
    - cover tray with foil (light protection)
8.  Storage:Best used within 4–6 weeks

> [!TIP]
>
> ### Storage Tip
>
> Keep prepared vials covered with aluminum foil and store in low-light
> conditions to preserve ATR activity.