DNA_NN1 Sorts_NN2 Carbon_NN1 Nanotubes_VVZ Specific_JJ sequences_NN2 separate_VV0 nanotubes_NN2 according_II21 to_II22 chirality_NN1 Single-walled_NN1 carbon_NN1 nanotubes_NN2 (_( SWNTs_NP1 )_) show_VV0 great_JJ promise_NN1 as_CSA components_NN2 of_IO nanoscale_NN1 electronic_JJ devices_NN2 ,_, but_CCB most_RGT commercial_JJ applications_NN2 have_VH0 been_VBN stymied_VVN by_II the_AT difficulty_NN1 in_II isolating_JJ nanotubes_NN2 of_IO identical_JJ chirality_NN1 from_II a_AT1 synthetic_JJ mixture_NN1 ._. 
Now_RT ,_, Xiaomin_NP1 Tu_NP1 and_CC Ming_NP1 Zheng_NN1 of_IO DuPont_NP1 Central_JJ Research_NN1 &;_NULL Development_NN1 ,_, together_RL with_IW Suresh_NP1 Manohar_NP1 and_CC Anand_NP1 Jagota_NP1 of_IO Lehigh_NP1 University_NN1 ,_, have_VH0 shown_VVN that_CST the_AT unique_JJ molecular_JJ properties_NN2 of_IO DNA_NN1 can_VM be_VBI exploited_VVN to_TO sort_VVI SWNTs_NP1 (_( Nature_NN1 2009_MC ,_, 460_MC ,_, 250_MC )_) ._. 
SWNT_NP1 synthesis_NN1 produces_VVZ a_AT1 mixture_NN1 of_IO nanotubes_NN2 with_IW nonuniform_JJ diameters_NN2 and_CC chiralities_NN2 and_CC ,_, therefore_RR ,_, heterogeneous_JJ physicochemical_JJ properties_NN2 ._. 
Having_VHG previously_RR shown_VVN that_CST a_AT1 particular_JJ DNA_NN1 sequence_NN1 could_VM form_VVI an_AT1 ordered_JJ structure_NN1 on_II SWNTs_NP1 ,_, Zheng_NP1 and_CC colleagues_NN2 reasoned_VVD that_CST they_PPHS2 might_VM be_VBI able_JK to_TO find_VVI a_AT1 DNA_NN1 sequence_NN1 to_TO purify_VVI each_DD1 type_NN1 of_IO SWNT_NP1 in_II a_AT1 synthetic_JJ mixture_NN1 ._. 
The_AT problem_NN1 was_VBDZ identifying_VVG the_AT correct_JJ DNA_NN1 molecules_NN2 among_II an_AT1 unfeasibly_RR large_JJ number_NN1 (_( 1018_MC )_) of_IO possible_JJ 30-nucleotide_JJ sequences_NN2 ._. 
To_TO reduce_VVI the_AT DNA_NN1 library_NN1 to_II a_AT1 more_RGR manageable_JJ size_NN1 of_IO 350_MC oligonucleotides_NN2 ,_, the_AT researchers_NN2 devised_VVD a_AT1 scheme_NN1 that_CST considered_VVD all_DB possible_JJ DNA_NN1 sequences_NN2 composed_VVN of_IO mono-_NN1 ,_, di-_NN1 ,_, tri-_NN1 ,_, and_CC tetranucleotide_VV0 repeats_NN2 ._. 
They_PPHS2 added_VVD each_DD1 DNA_NN1 oligonucleotide_NN1 to_II a_AT1 random_JJ mixture_NN1 of_IO SWNTs_NP1 ._. 
Then_RT ,_, they_PPHS2 used_VVD ion-exchange_JJ chromatography_NN1 to_TO separate_VVI the_AT 350_MC solutions_NN2 into_II fractions_NN2 ,_, which_DDQ they_PPHS2 analyzed_VVD spectroscopically_RR for_IF the_AT presence_NN1 of_IO specific_JJ DNA-SWNT_JJ hybrids_NN2 ._. 
The_AT study_NN1 yielded_VVD more_DAR than_CSN 20_MC sequences_NN2 that_CST could_VM together_RL purify_VVI all_DB 12_MC major_JJ chiral_NN1 semiconducting_VVG SWNTs_NP1 ._. 
To_TO explain_VVI the_AT SWNT-sorting_JJ ability_NN1 of_IO DNA_NN1 ,_, the_AT authors_NN2 propose_VV0 a_AT1 model_NN1 in_II which_DDQ the_AT recognition_NN1 sequences_NN2 form_VV0 stable_JJ hydrogen-bonded_JJ DNA_NN1 barrels_NN2 around_II specific_JJ SWNTs_NP1 ._. 
The_AT ordered_JJ structure_NN1 minimizes_VVZ interactions_NN2 with_IW the_AT ion-exchange_JJ chromatography_NN1 resin_NN1 and_CC causes_VVZ early_JJ elution_NN1 ._. 
"_" This_DD1 is_VBZ a_AT1 very_RG impressive_JJ study_NN1 that_CST reports_VVZ the_AT most_RGT selective_JJ method_NN1 yet_RR found_VVN for_IF isolating_VVG specific_JJ structural_JJ forms_NN2 of_IO SWNTs_NP1 from_II mixed_JJ samples_NN2 ,_, "_" R._NP1 Bruce_NP1 Weisman_NN1 of_IO Rice_NN1 University_NN1 says_VVZ ._. 
"_" The_AT main_JJ limitation_NN1 is_VBZ the_AT small_JJ scale_NN1 and_CC high_JJ expense_NN1 ._. "_" 
Zheng_NN1 tells_VVZ C_NP1 &EN;_NULL that_CST the_AT major_JJ obstacle_NN1 to_II scaling_VVG up_RP the_AT method_NN1 is_VBZ the_AT high_JJ cost_NN1 of_IO DNA_NN1 ,_, which_DDQ could_VM decrease_VVI if_CSW oligonucleotide_NN1 suppliers_NN2 shift_VV0 their_APPGE business_NN1 model_NN1 to_TO meet_VVI the_AT demands_NN2 of_IO the_AT nanoelectronics_NN1 industry_NN1 ._. 
