Fluorescent Cell Viability Assay Kit: Simple, Sensitive, and Multiplex-Compatible

I. What is Fluorescent Cell Viability Assay?

Fluorescent cell viability assay is a highly sensitive technique that utilizes fluorescent dyes or probes to quantitatively analyze the number and proportion of live cells within a cell population. Compared to traditional colorimetric methods (such as MTT), it generally offers higher sensitivity, a wider linear range, and better compatibility, making it particularly suitable for high-throughput screening and multiplex detection.

The core concept is: It leverages the unique metabolic activity or intact cell membranes of live cells to convert non-fluorescent substrates into fluorescent products, or to allow specific fluorescent dyes to enter and accumulate within the cells. Thereby, the viability status of the cells is indirectly reflected by detecting the intensity of the fluorescent signal.

II. Core Working Principles

Fluorescent cell viability assays are primarily based on the following two mechanisms:

1. Based on Metabolic Activity:
   
   

   • Principle: Live cells exhibit high esterase activity. The detection reagent contains a non-fluorescent, cell membrane-permeable substrate (e.g., an acetate derivative). Once this substrate enters a live cell, it is hydrolyzed by intracellular esterases, producing a fluorescent molecule that cannot cross the cell membrane and is thus "trapped" within the cytoplasm of the live cell.
     
     

   • Result: The intensity of the fluorescent signal is proportional to the number of live cells in the sample. Dead cells, due to loss of esterase activity or compromised membrane integrity, cannot effectively accumulate the fluorescent product.
     
     

2. Based on Membrane Integrity:
   
   

   • Principle: Utilizes the property of certain dyes (e.g., Propidium Iodide, PI) that can only enter the cell nucleus through the damaged membranes of dead cells and emit strong fluorescence upon binding to DNA.
     
     

   • Result: Often used in combination with metabolic activity-based dyes, it allows for simultaneous detection of both live and dead cells, enabling a more comprehensive analysis of cell status.
     
     

III. Main Advantages

• High Sensitivity: Fluorescent signals are far more sensitive than color changes, allowing detection of smaller cell numbers or more subtle changes in viability.
  
  

• Wide Dynamic Range: The linear range of fluorescent signals is very broad, allowing for accurate data acquisition over a wide span of cell concentrations without the need for multiple sample dilutions.
  
  

• High-Throughput Compatibility: Highly suitable for 96, 384, and even 1536-well plates, easily automated, making it ideal for drug screening.
  
  

• Suitable for Multiplexing: Can use fluorescent probes with different excitation/emission wavelengths to detect multiple parameters in the same well (e.g., simultaneously detecting live cells, dead cells, and apoptosis).
  
  

• Homogeneous Assay Format: Most reagents operate in a "add-mix-measure" one-step process, requiring no washing steps, saving time and effort.
  
  

Standard Operating Procedure for Fluorescent Cell Viability Assay Kits

Using the UA-Glo® Fluorescent Cell Viability Assay as an example

1. Cell Preparation

1. Seed the cells to be tested at an appropriate density in a 96-well or 384-well cell culture plate. Black-walled, clear-bottom plates are recommended.
   
   

2. Add the test compounds at appropriate concentrations to the wells of the cell plate. Keep the concentration of organic solvents in the culture medium below 1%. Continue incubation for an appropriate duration according to experimental requirements.
   
   

2. Cell Viability Assay

1. Take out the fluorescent cell viability assay reagent. After the CTF Buffer is completely dissolved, equilibrate it to room temperature. Vortex the CTF Substrate to mix it thoroughly, then briefly centrifuge to collect the substrate at the bottom of the tube.
   
   

2. Prepare the CTF Reaction Solution: The CTF Substrate is a 100x stock. Dilute it to a 1x working solution using the CTF Buffer according to the required volume, and mix thoroughly.
   
   

3. Take out the cell culture plate to be assayed. Add an equal volume of the 1x CTF Reaction Solution to each well (e.g., add 100 µl of 1x CTF Reaction Solution to 100 µl of culture medium).
   
   

4. Shake the plate gently at low speed for 20 seconds to mix. Protect from light and incubate at 37°C for 60 minutes before fluorescence detection. *Note: Different cell types process the CTF Substrate at different rates. The optimal reading time needs to be optimized for specific cell types. The earliest reading can be taken 30 minutes after adding the reagent. Generally, the signal-to-noise ratio is higher when reading at 60 minutes or later. It is recommended not to exceed 3 hours for reading.*
   
   

5. Read the fluorescent signal using a fluorescence microplate reader with Ex 380-400 nm and Em 505 nm.
   
   

6. If needed, proceed with downstream multiplexing analysis, such as Caspase-3/7 apoptosis assay.