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*