and ed ▁DNA ▁compr ising ▁several ▁head - to - tail ▁copies ▁of ▁the ▁circular ▁template . ▁The ▁resulting ▁nan op article ▁self - ass emb les ▁into ▁a ▁tight ▁ball ▁of ▁DNA ▁approximately ▁ 3 0 0 ▁nan om eters ▁( nm ) ▁across . ▁Nan ob alls ▁remain ▁separated ▁from ▁each ▁other ▁because ▁they ▁are ▁neg atively ▁charged ▁naturally ▁rep el ▁each ▁other , ▁reducing ▁any ▁tang ling ▁between ▁different ▁single ▁str and ed ▁DNA ▁lengths . ▁ ▁DNA ▁nan ob all ▁pattern ed ▁array ▁ ▁To ▁obtain ▁DNA ▁sequence , ▁the ▁DNA ▁nan ob alls ▁are ▁attached ▁to ▁a ▁pattern ed ▁array ▁flow ▁cell . ▁ ▁The ▁flow ▁cell ▁is ▁a ▁ ▁sil icon ▁wa fer ▁co ated ▁with ▁sil icon ▁dio x ide , ▁tit an ium , ▁hex am eth y ld is il az ane ▁( H MD S ), ▁and ▁a ▁phot ores ist ▁material . ▁The ▁DNA ▁nan ob alls ▁are ▁added ▁to ▁the ▁flow ▁cell ▁and ▁select ively ▁bind ▁to ▁the ▁posit ively - charg ed ▁am inos il ane ▁in ▁a ▁highly ▁ordered ▁pattern , ▁allowing ▁a ▁very ▁high ▁density ▁of ▁DNA ▁nan ob alls ▁to ▁be ▁sequ enced . ▁ ▁Im aging ▁ ▁After ▁each ▁DNA ▁nucle ot ide ▁incorpor ation ▁step , ▁the ▁flow ▁cell ▁is ▁im aged ▁to ▁determine ▁which ▁nucle ot ide ▁base ▁bound ▁to ▁the ▁DNA ▁nan ob all . ▁ ▁The ▁flu or oph ore ▁is ▁excited ▁with ▁a ▁las er ▁that ▁exc ites ▁specific ▁w avel