title: Comparison of preprocessing methods and storage times for touch DNA samples.
abstract: OBJECTIVE
  To select appropriate preprocessing methods for different substrates by comparing the effects of four different preprocessing methods on touch DNA samples and to determine the effect of various storage times on the results of touch DNA sample analysis.
  
  
  METHODS
  Hand touch DNA samples were used to investigate the detection and inspection results of DNA on different substrates. Four preprocessing methods, including the direct cutting method, stubbing procedure, double swab technique, and vacuum cleaner method, were used in this study. DNA was extracted from mock samples with four different preprocessing methods. The best preprocess protocol determined from the study was further used to compare performance after various storage times. DNA extracted from all samples was quantified and amplified using standard procedures.
  
  
  RESULTS
  The amounts of DNA and the number of alleles detected on the porous substrates were greater than those on the non-porous substrates. The performances of the four preprocessing methods varied with different substrates. The direct cutting method displayed advantages for porous substrates, and the vacuum cleaner method was advantageous for non-porous substrates. No significant degradation trend was observed as the storage times increased.
  
  
  CONCLUSIONS
  Different substrates require the use of different preprocessing method in order to obtain the highest DNA amount and allele number from touch DNA samples. This study provides a theoretical basis for explorations of touch DNA samples and may be used as a reference when dealing with touch DNA samples in case work.
authors.forename: Hui
authors.initials: H
authors.lastname: Dong
authors.forename: Jing
authors.initials: J
authors.lastname: Wang
authors.forename: Tao
authors.initials: T
authors.lastname: Zhang
authors.forename: Jian-Ye
authors.initials: JY
authors.lastname: Ge
authors.forename: Ying-Qiang
authors.initials: YQ
authors.lastname: Dong
authors.forename: Qi-Fan
authors.initials: QF
authors.lastname: Sun
authors.forename: Chao
authors.initials: C
authors.lastname: Liu
authors.affiliation: Cai-xia Li, Key Laboratory of Forensic Genetics, Institute of Forensic Science, Ministry of Public Security, Beijing100038, China, licaixia@tsinghua.org.cn.
authors.forename: Cai-Xia
authors.initials: CX
authors.lastname: Li
mesh_terms: D000483:Alleles; D004247:DNA / Q000032:analysis; D016172:DNA Fingerprinting / Q000379:methods*; D006225:Hand; D006801:Humans; D013048:Specimen Handling / Q000379:methods*; D014110:Touch
chemical_list: D004247:DNA