silicon has a molecular weight of 14
a 1 molar solution is 14 g of silicon in 1 litre which is a concentration of (wt/Volume)
14 g/L = 0.014 g/mL
So 1 M = 0.014g/mL or 14 mg/mL
1 mM = 0.000014 g/mL = 0.014 mg/mL = 14 µg/mL
1 µM =0.00000014 g/mL = 0.000014 µg/mL = 0.014 µg/mL
therefore to convert µM to µg/mL multiply by 0.014
it ain't rocket science