Can phosphorylated protein microarrays use RIPA to lyse cells? Will the background be very high?

RIPA usually contains 0.1% SDS, which is fine for WB, but many protein arrays (especially phospho-arrays) are sensitive to SDS and ionic strength, which can easily interfere with spotting antibody binding and increase background. I recommend prioritizing the lysis buffer from the manufacturer's kit, or preparing a mild SDS-free lysis buffer (e.g., containing 1% NP-40, 150 mM NaCl, Tris pH 7.5), supplemented with fresh phosphatase inhibitors and protease inhibitors. For adherent cells, lyse directly in the plate; for tissue, first mince and homogenize, then centrifuge at 4°C and collect the supernatant. If RIPA must be used, first test a single array on a small scale to check the background—don't run the full set right away.

Loss of phosphorylation signal is mostly not due to the chip itself, but rather insufficient suppression of phosphatases between lysis and loading. Experience shows: prepare lysis buffer fresh immediately before use, add phosphatase inhibitor Cocktail at a sufficient 1× concentration, and optionally supplement with 1 mM Na3VO4 and 1 mM NaF; perform all operations on ice, and avoid repeated freeze-thaw cycles for tissue samples. Quantify immediately after lysis; protein concentration generally needs to be 0.5–2 mg/mL, and prepare 20–50 μg total protein per array/well, with the volume according to the instructions. Do not boil and denature before loading; many chips require non-denaturing conditions. Run a pilot experiment: use serum starvation/stimulation control lysates to run a small chip and confirm the signal window.

Common causes of high background: excessive protein loading, residual SDS, insufficient blocking, and inadequate washing. It is recommended to first set the protein concentration at around 1 mg/mL, quantify with BCA, and do not exceed 2 mg/mL; after centrifuging the lysis buffer, collect the supernatant to avoid interference from viscous genomic DNA, and shearing can be performed by sonication or passing through a 26G needle. Use the blocking solution recommended by the manufacturer, do not skip the room-temperature blocking time, and use a shaker for membrane/well washing. For phosphorylation arrays, it is best to perform stimulated/unstimulated conditions in the same batch, and normalize to a total protein array or housekeeping proteins on the same array. If the background remains high, serially dilute the samples to find the loading amount with the best signal/background ratio.