Study On The Development Of Latent Fingerprint On Thermal Paper By Vacuum Vaporization Of Ninhydrin

With the development of society,thermal paper has been widely used as recording paper for transformation,so thermal paper used by criminal can often be collected at the crime scene.How to develop the latent fingerprints on thermal paper without destroying the background information on it has always been a hot issue for forensic examiners.At present,common method is mainly based on the solution,which will not only ruin the background information on thermal paper easily but will also influence the DNA testing largely.The vacuum vaporization of ninhydrin is a method of sublimation when developing latent fingerprints.In theory,it has little influence on DNA testing,and thus it offers more evidence for investigation and trials of cases in combination with DNA testing.In this study,a modified devise,CSI801 vacuum indanedione,based on the vacuum 502 heating fumigation cabinet,was put forward by the author.To determine the main variables influencing the experimental results and the optimal values,numerous preliminary experiments were conducted,including the quantity of ninhydrin crystal(100mg,300 mg,500mg),the vacuum degree(10kPa,15 kPa,20kPa),the fuming time(20min,30min),the heating temperature(125-150??150-175?).Through the comprehensive data analysis,36 set of conditions based on the permutation and combination of these variables were examine,and found the optimal condition of 500 mg ninhydrin crystal,with temperature from 150? to 175?,15 kPa vacuum and 20 min of fuming time,for the development of latent fingerprints on thermal paper.To investigate the applicability of the optimal conditions to various porous subject,the developing effects on different kinds of thermal paper and common porous paper were compared.The experimental results suggested that this condition was suitable for a variety of thermal paper,common porous paper.Through comparison with the results of 1,2-indenedione,this study evaluated the advantages and disadvantages of this method from the perspective of the sensitivity and the ability to develop aged fingerprints.The results showed that both methods were of rather high sensitivity there was little difference in the effect of them.It was found that more than 50% of both the fifth consecutive fingermarks and the 30-day-old fingermarks developed by vacuum vaporization of ninhydrin had three-level feature.The influence of the vacuum vaporization of ninhydrin on DNA testing after developing latent fingerprints on thermal paper was studied.Statistical analysis was conducted from three dimensions including locus number,allele number and peaks of alleles.The results showed that there was no significant effect on DNA testing after using this method.The study found that the vacuum vaporization of ninhydrin successfully developed the latent fingerprints on thermal paper.It has the advantages of easy operation,high sensitivity,with intact background information on treated thermal paper,and no obvious influence on the subsequent DNA testing.