The Isopropyl alcohol you are using has .1% or 1000ppm of water and what % of other contaminants? Those contaminants can leave a residue on the sensor. Eclipse is purified and contains less than 5ppm (.0005%) of contaminants and dries quickly leaving no residue. Eclipse was specifically formulated for cleaning sensors. While it is not cheap, it is not very expensive either. Especially when one considers how much it takes to clean a sensor. Good Luck and Enjoy your Nikons!