Abstract
The discrimination accuracy for human and nonhuman blood is important for customs inspection and forensic applications. Recently, Raman spectroscopy has shown effectiveness in analyzing blood droplets and stains with an excitation wavelength of 785 nm. However, the discrimination of liquid whole blood in a vacuum blood tube using Raman spectroscopy, which is a form of noncontact and nondestructive detection, has not been achieved. An excitation wavelength of 532 nm was chosen to avoid the fluorescent background of the blood tube, at the cost of reduced spectroscopic information and discrimination accuracy. To improve the accuracy and true positive rate (TPR) for human blood, a dual-model analysis method is proposed. First, model 1 was used to discriminate human-unlike nonhuman blood. Model 2 was then used to discriminate human-like nonhuman blood from the "human blood" obtained by model 1. A total of 332 Raman spectra from 10 species were used to build and validate the model. A blind test and external validation demonstrated the effectiveness of the model. Compared with the results obtained by the single partial least-squares model, the discrimination performance was improved. The total accuracy and TPR, which are highly important for practical applications, increased to 99.1% and 97.4% from 87.2% and 90.6%, respectively.
Highlights
Considering the safety of the practitioners, we explored a discrimination method involving measurement of blood samples in their original containers, which has been considered in diffuse reflectance spectroscopy [24]
Compared with the results obtained by the traditional PLS model, the discrimination accuracy and especially the true positive rate (TPR) of human blood are improved
When the excitation wavelength was 532 nm, the Raman spectra of the blood collected from chickens, ducks, geese, and doves differed from those collected from pigs, rabbits, and sheep
Summary
To prevent genetic terrorist activities and combat crime, correctly discriminating human blood is important for customs inspection departments and forensic investigations [1,2,3,4] Many methods, such as, DNA tests [5, 6], latex agglutination [7], highperformance liquid chromatography [8,9,10], and mass spectrometry [11], have been used to discriminate human and nonhuman blood and have exhibited effectiveness. (in this paper, the excitation wavelength is 785 nm) owing to the small difference in the Raman spectra of nonhuman blood from different species To solve this problem, in this study, we proposed a dual-model analysis method, in which the first model was used to discriminate human and nonhuman blood for all blood samples, and the second model was used to discriminate human and nonhuman blood using the “human blood” determined by the first model. Compared with the results obtained by the traditional PLS model, the discrimination accuracy and especially the true positive rate (TPR) of human blood are improved
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