carbon nanotube signal amplification for ultrasensitive fluorescence polarization detection of dna methyltransferase activity and inhibition a versatile sensing platform based on multiwalled carbon nanotube mwcnt signal amplification and fluorescence polarization fp is developed for the simple and ultrasensitive monitoring of dna methyltransferase mtase activity and inhibition in homogeneous solution this method uses a dyelabeled dna probe that possess a doubledstranded dna dsdna part for mtase and its corresponding restriction endonuclease recognition and a singlestranded dna part for binding mwcnts in the absence of mtase the dyelabeled dna is cleaved by restriction endonuclease and releases very short dna carrying the dye that cannot bind to mwcnts which has relatively small fp value however in the presence of mtase the specific recognition sequence in the dyelabeled dna probe is methylated and not cleaved by restriction endonuclease thus the dyelabeled methylated dna product is adsorbed onto mwcnts via strong stacking interactions which leads to a significant increase in the fp value due to the enlargement of the molecular volume of the dyelabeled methylated dnamwcnts complex this provides the basic of a quantitative measurement of mtase activity by using the mwcnt signal amplification approach the detection sensitivity can be significantly improved by two orders of magnitude over the previously reported methods moreover this method also has high specificity and a wide dynamic range of over five orders of magnitude additionally the suitability of this sensing platform for mtase inhibitor screening has also been demonstrated this approach may serve as a general detection platform for sensitive assay of a variety of dna mtases and screening potential drugs