NHEK Neutral Red Uptake Assay for Ocular Irritation Step-by-Step
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The cells to be used for the 96-well assays are stored in a liquid nitrogen freezer. When ready for use, the cells are thawed, resuspended, and transferred to a culture flask, where they will grow and multiply until optimal conditions have been achieved.
Trypsin solution is added to the flask to remove the cells. The cells are resuspended in medium, counted, and “seeded” into 96-well plates using a multichannel pipet.
The test material is serially diluted to make a range of doses.
The test article dilutions are added to the inner wells containing cells.
Each plate also contains 12 negative, or solvent, control wells which are used to determine % of control viability.
Test Article Removal and Rinse
The test material is removed by decanting.
The plates are rinsed with a buffered saline solution to remove any residual test material.
Addition of Vital Dye
A solution of Neutral Red, a vital dye, is added to the 96-well plate. The plates are incubated at standard culture conditions to allow neutral red uptake by the cells.
Addtion of Solvent
After the 3 hour neutral red incubation, excess neutral red is decanted and solvent is added to all wells.
The solvent extracts the neutral red dye contained within the cells.
96-well Plate Reading
The 96-well plates are placed on a plate shaker to fully extract the neutral red and evenly distribute the dye in each well.
A spectrometer measures the absorbance of each sample at a specific wavelength.
The absorbance values (optical density) are then used to determine the viability of each well by comparing the optical density of the each test material treated well compared the negative (or solvent ) control wells.