Cell adhesion is a pH-dependent phenomenon: the cells required Mg2+ or Ca2+ for attachment to substrates at pH higher than the isoelectric point of the proteins coating a plastic surface, but not at lower pH. With increasing pH from 3.4, cell adhesiveness to substrates decreased up to about pH 5.8. In the presence of Mg2+ or Ca2+ it increased again above this pH, while in Mg2+- and Ca2+-free medium it decreased further.
Low temperature prevented both cell adhesion and spreading. The cells once attached to substrates in the presence of Mg2+ were not detached by EDTA.
Cell adhesiveness to substrates was not always raised with increasing concentration of divalent cations, and higher concentration of Ca2+ tended to inhibit the initiation of cell attachment.
So, if your PBS lacks calcium and magnesium, then your cell adhesion will decrease. Normal media has these cations. If you want to keep you cells attached in PBS, add 1mM of CaCl2 and 1mM MgCl2 to your PBS. Also, cell adhesion depends on the temperature of your PBS. For example, cold (1-4℃) PBS will detach cells from plastic pretty well.
M. Takeichi, T.S. Okada, Roles of magnesium and calcium ions in cell-to-substrate adhesion, Experimental Cell Research, Volume 74, Issue 1, 1972, Pages 51-60, ISSN 0014-4827, https://doi.org/10.1016/0014-4827(72)90480-6.
Souce: NovoPro 2019-05-31