Hi Fitria Nurul Mutmainah ,

DLS determines a hydrodynamic size based upon the free diffusion of particles in dispersion.

This measurement principle means that there are limitations to the size and types of material that DLS can accurately report sizes for, and this means DLS isn’t suitable for measuring mammalian cells, which are bigger than the absolute maximum measurable size by DLS (~10 micron).

Fitria Nurul Mutmainah To add to Alex's answer, In this size range (and for red and white blood cells too) then laser diffraction can be used if there is sufficient concentration of cells and a minimum sample volume, on dilution if necessary, of 7 mL or so.

If the size of the cell size is too big such (> 1 um), I guess still the DLS can be used for the measurement, provided the cell should be dispersed in a dilute solution (size < 10 um). Above 10 um, the particle surpasses the Brownian regime, and the existing model may not be valid. But for bigger length scale, any optical microscope can be used to estimate the size. If the cell is transparent then the phase contrast microscopy can be useful in that case.

Thank you so much for the answer Alexander Malm

Thank you for helping to add the answer Alan F Rawle

Hisay Lama I measured it using a small quantity of the cells in medium solution, however during some data there were peaks present on the range of

Dear Fitria Nurul Mutmainah , osteoblasts (and osteosarcoma) cells are large, generally 20 to 50 µm. This far exceeds the upper detection limit of DLS, which is 10 µm. So the instrument will essentially be "blind" to cells that size (they will not appear at all in the particle size distribution). The peaks you are observing < 50 nm likely represent cell debris and/or exosomes shed by your cells.