I tried using cotton buds with alcohol but seems to leave a stain on the sensor. In the end, I just use the plain cotton buds and clean away. Had a hard time cleaning. The dust seems very stubborn, difficult to remove and keep moving to different positions .... And though the blotch seems major, I can't see any dust speck on the sensor. Just gotta based in on guesswork and from where the dust appear on the taken shot.
But I was rather "suay". I didn't know the blotch on my sensor until 5 mths later after using the cam, and it's brand new. It only appeared when I took night shots using small apertures. And I thought it was a stain on my UV filter ... Now I browse through my previous pics taken 5 mths ago and indeed, could faintly see the blotch on some pictures ...