Glucose is polar because of the hydroxyl bonds in it. The formula C6H12O6 leads it to have many OH groups that are attached to the molecule. As we know from alcohols, hydroxyl groups make the molecule polar. This is the same reason water is polar. The difference in the electronegativity of Oxygen and Hydrogen causes the Oxygen to be slightly negative and Hydrogen slightly positive. The molecule is still neutral overall but we can tell at certain points, it actually has a charge.