Will 1% Triton X-100 affect the results when using a BCA kit to measure protein in cell lysates?

Bradford assay underestimation is a common phenomenon, and it is more affected by detergents, alkaline lysis buffers, and protein types than the BCA assay. Switching to BCA is fine, but do not directly compare data from the two methods, as absolute values inherently differ. Western blot loading amounts should be readjusted based on BCA results and validated with an internal control. Empirically, if the cell lysate contains 1% Triton, BCA usually gives more stable results. It is recommended to run the standard curve and samples from the same batch on the same day to avoid differences between reagent batches. If the readings for certain samples remain abnormal, check the CV of replicate wells, then consider dilution or spike recovery.

Whether dilution is needed cannot be generalized. If the total cellular protein concentration is typically between 1–5 mg/mL, it is recommended to dilute to within the linear range of the standard curve; the upper linear limit for the common BCA assay is around 2 mg/mL, and Triton will be diluted accordingly. You can prepare three dilution levels, such as 1:5, 1:10, and 1:20, and check whether the calculated results are linearly consistent. If a low-concentration sample already reads close to the lower limit of the standard curve, do not dilute further. If the results are inconsistent after dilution, this indicates significant matrix interference; the standards should also be prepared in lysis buffer containing the same Triton, or consider removing the detergent by precipitation before measurement.

1% Triton X-100 is generally better tolerated in BCA than in Bradford, but it is not completely without interference. It is recommended to first perform a spike-and-recovery experiment: add the same standard protein to pure water and to lysis buffer containing 1% Triton, respectively, and check whether the recovery rate is within an acceptable range. For 30 samples, if the expected concentration is not low, you can first dilute 5- to 10-fold with PBS or lysis buffer to reduce Triton to below 0.1%, which will make the results more stable. BCA formulations differ among manufacturers, and the instructions will state the tolerated concentration. Empirically, most can withstand up to around 1%, but do not rely only on the instructions; validation with your own system is more reliable.

A 562 nm reading itself is sufficient; the absorption peak of the BCA product is around 562, so a standard microplate reader is fine. What needs more attention is the temperature and bubbles after the reaction is complete. If you read directly after incubation at 37°C, condensation or bubbles may be present in the wells, especially at the edge wells where temperature is uneven, which can easily cause replicate well variability. It is recommended to cool to room temperature after completion, briefly centrifuge or tap gently to remove bubbles, and then read at 562 nm. If 30 samples are on the same plate, try to avoid the edge wells as much as possible, or place blanks and standards to correct for edge effects. Do not wait too long before and after reading, to avoid continued deepening of color development.

Standards must be prepared in the same lysis buffer system; at least the blank and low-concentration points should be diluted with lysis buffer containing 1% Triton and protease inhibitors. This is because Triton, protease inhibitors, and salt ions all contribute some background, especially at low protein concentrations, where they can elevate the intercept and cause sample readings to be falsely high or low. You can set aside a separate tube of protein-free lysis buffer as diluent and for blank wells. Preparing the standard curve directly in water may yield values that are more inconsistent with Bradford. Alternatively, you can prepare two standard curves—one in lysis buffer matrix and one in pure water matrix—to compare the differences before deciding whether samples need to be diluted.