I have thought it is better to suck the sensor than blow i have done it twice with a bulb blower by getting the air out and pointing it close to the sensor and move it around while exspelleng the air i did this twice and it work ,i then took a photo of a white piece of paper and put it on my computer and enlarged it,i thought if you can see a speck of dust on a photo you would see it on a photo of white printer paper ! and i did this and it was clean no dust at all,in the mean time i have found and orded a vaccuun cleaner but one that fits to your computer USB i have not tried this but i think it will be ideal,so i have orded one it costs just over £10 cheap !this is where i got it from,take a look.
http://www.innovasis.co.uk/home.php?cet=3
what it is realy for is cleaning your key board.