What assays should I use to determine total protein content?

Determining total protein content is often essential before analyzing protein samples. There are several assays that can be used to determine total protein content. It is important to choose the correct assay, depending on the amount and purity of the protein available as well as the accuracy required. Here’s a look at the four main types of assays you can choose from to determine total protein count along with the advantages and disadvantages of each. 

1. UV absorption is the simplest of the assays. You don’t need to use any assay reagents. However, the error rate is high in protein mixtures or complex samples such as cell lysates. 
2. Colorimetric dye based assays involve protein-dye binding and detection of change in color. These fast and simple assays are compatible with most solvents, salts, reducing substances, buffers, metal-chelating agents, and thiols. On the downside, they are incompatible with surfactants and have a higher protein-protein variation as compared to copper-based assays. 
3. Biuret methods involve protein-copper chelation and secondary detection of reduced copper. This assay is compatible with most surfactants but is incompatible with common reducing agents and substances that reduce copper. 
4. Fluorescent dye assays involve protein-dye binding and direct detection of increased fluorescence associated with the bound dye. This assay for protein quantitation is highly sensitive and can be successfully performed with a small protein sample. Timing is not a critical factor, which allows the assays to be adapted for automated handling in high-throughput applications. The only downside is that it requires specialized equipment, which can be expensive.