It is the most prevalent method for obtaining information about the elemental composition of samples including their molecular structure, qualitative, and quantitative composition of complex mixtures, the composition and structure of isotopic properties of atoms in samples (We Q et al. 2016). It is an analytical technique in which the atoms are separated, ionized according to their m/z ratio. The major MS techniques which have been applied for the fingerprint analysis are matrix-assisted desorption ionization mass spectroscopy (MALDI-MS), laser desorption ionization mass spectroscopy (LDI-MS, electron impact mass spectroscopy (EI-MS), and surface-assisted laser desorption ionization mass spectroscopy (SALDI-MS). These were mainly utilized to study the aging and degradation of fingerprints, use of nanoparticles in the enhancement, development of their chemical profiles and development of new MALDI matrices (Gonzales, M., 2020).
Gas chromatography mass spectrometry
In contrast to other mass spectrometric technique, separation is carried out in gas chromatography and liquid chromatography only, as it is quite laborious. Many steps are required for the preparation of sample, to develop and optimize a method. Moreover, they require expensive inputs and apparatus, but they have been well established as a standard in the forensic analysis of evidences, namely ink, soil, paint, fingerprints and others.
Archer E N, et al. studied the chemical changes in lipid component of a fingerprint over time by aid of GCMS. Tetradecanoic acid, palmitoleic acid, oleic acid, squalene, and cholesterol were observed to vary at different levels. The loss of squalene was noted at a reduced rate in the prints stored in the dark (detected even after 33 days) than in the prints stored in the light (not detected after 9 days of storage) (Archer et al. 2004).
Michalski S, et al. identified possible fatty acids, which aid in the profiling of an individual. By the aid of GC–MS, individuals of different gender and races were classified on the basis of varying ratios of fatty acid methyl esters. Moreover, the intravariability and intervariability of some compounds were recorded to be high, suggesting the possibility to individualize on the basis of chemical profile. Two-dimensional GC proved to be beneficial due to its ability to separate complex organic mixtures based upon classes of compounds present (Michalski et al. 2013).
Cadd J S, et al. investigated differences between the extraction and separation methods of fatty compounds from fingerprints to obtain a range of sebaceous substances. Sebaceous and eccrine prints were considered, and seven solvent systems previously used in literature were explored to determine their extraction efficiency. The outcome recommended the use of MeOH/TMSCl for the derivatization of fatty acids followed by the use of CHCl3 for the extraction of squalene, cholesterol, FAMEs, and wax esters (Cadd et al. 2015).
Shi Jun-Wen, et al. employed the use of air-flow assisted desorption electrospray ionization mass spectrometry imaging in four kinds of fingerprints, i.e., sweat, inked, sunscreen, and foundation, for the analysis of constituents of fingerprint and for obtaining its high-resolution image. The overlapped fingerprints were distinguished in accordance with the chemical information obtained in the results (Jun Wen et al. 2019).
Matrix-assisted laser desorption ionization–mass spectroscopy imaging and laser desorption ionization
MALDI-MS is a particular technique which is highly efficient in the detection of high molecular weight molecules (Schriemer and L. L. 1996). It utilizes a matrix to aid in the ionization and desorption of laser desorption imaging which increases the yield of analyte ions. Thus, with increased ion yield better structural information about the object of interest could be identified. It has been widely used till now for the detection of endogenous lipids in sebaceous and eccrine prints thus demonstrating the sensitivity of the instrument in analyzing the object of interest in trace quantities (Wolstenholme 2009).
Wolstenholme R, et al. employed MALDI-MSI for the imaging of endogenous lipids obtained from ungroomed and groomed prints. Oleic acid was used as a part of the methodology and was detected along with its degraded products after a passage of 7 days, at different temperatures. The imaging of fingerprint samples was then performed. The fingerprint’s pattern was confirmed by analyzing the m/z values of degraded products of oleic acid which enabled the distinction of the different fingerprints (Wolstenholme 2009).
Lauzon N, et al. investigated the use of MALDI and LDI IMS for detection of chemical constituents in the finger print. Polymeric substances such as polyethylene glycol and polypropylene glycol found in hand lotions were observed on the ungroomed fingerprint. For IMS analyses, the fingerprint motif was observed on paper after silver deposition, and numerous compounds of squalene, wax esters, fatty acids, DAGs, and TAGs were detected. The use of 2-MBT was found to be most suitable matrix for IMS of constituents from latent fingerprint (Lauzon et al. 2015).
Groeneveld G, et al. employed different variants of MALDI MS technique for the detection and mapping of drugs of abuse and their metabolites in fingerprints with and without prior development with cyanoacrylate fuming or by the technique of vacuum metal deposition. Seventeen compounds were selected from five different classes of drug: amphetamines, alkaloids, opioids, cannabinoids, and designer drugs. VMD treatment was found to be more capable than cyanoacrylate fuming and the quality of ridge pattern was found to be strongly molecule dependent (Groeneveld et al. 2015).
Time-of-flight secondary ion mass spectrometer
It is a surface sensitive analytical technique which utilizes a pulsed ion beam for the removal of molecules from the outermost shell of the sample. It is applied in forensic science for the visualization, characterization, and analysis of fingerprints left after their contamination by traces of drugs, cosmetics, and other such surface contaminants (Szynkowska et al. 2009).
Rowell F, et al. investigated the use of hydrophobic silica dusting agent containing carbon black as a matrix to detect illicit drugs and contact residues using SALDI-TOF-MS in positive ion reflectron mode. The dusting agent produced developed marks for visualizing the prints while acting as a SALDI-TOF MS enhancer that was equivalent to the standard matrix enhancer 2,3-dihydroxybenzoic acid (DHB). Analysis was performed by direct MS of the pre-dusted fingerprints on the surface of a target plate and, lifted using commercial tape. The presence of the parent drug and its metabolites was confirmed as characteristic and unique fragmentation patterns were observed in each case (Rowell et al., 2009).
Hinder J S and Watts F J demonstrated the use of ToF-SIMS in the analysis of latent fingerprints with a view of forensic and biomedical applications (Hinder and Watts 2010). Szynkowska, et al. demonstrated that SIMS could be employed to produce images of whole fingerprints on inorganic surfaces such as steel, brass and glass. The detection of various exogenous substances, i.e., industrial lubricants, personal care products and pharmaceuticals on different organic surfaces was confirmed. SIMS images, even at low resolution was able to differentiate regions of underlying substrate materials and that of latent fingerprint. Fingerprint images acquired by SIMS imaging were capable of visualizing the minutiae associated with fingerprints in high resolution (Szynkowska et al. 2010).
Vibrational spectroscopy imaging
Fourier transform infrared spectroscopy
The vibrational spectroscopic imaging is another important technique for the reconstruction of latent fingerprints by generating the chemical contrast using the spectroscopic signatures identified in the fingerprint deposits. The previous studies have successfully detected the presence of latent prints on various surfaces using the infrared technique, the reconstructed images of the print were of sebaceous and eccrine residues which could also be used as an evidence (Williams and S. R. 2004)(Crane and B. G. 2007)(Ricci and Bleay 2007).
Ricci C, et al. investigated the combination of ATR-FTIR imaging with tape-lifting for the examination of fingerprint of an individual after the handling of illicit drugs. The variation in the distribution of amino acids and lipids were also identified using this approach. Crane J N, et al. utilized FTIR technique to obtain the detailed image of unprocessed groomed latent fingerprint on various substrates. In addition, the trace components present on various substrates were also preserved (Crane et al. 2007).
Tantouh M, et al. employed the use of FTIR in imaging fingerprints on different surfaces. Separate methodologies were employed in each surface for obtaining better quality of final fingerprint image. It was detected that FTIR gave high-quality images of cyanoacrylate fumed fingerprints on various substrates (Tantouh et al. 2007). Chen T, et al. investigated the use of infrared chemical images which indicated the presence of explosive, RDX mixed with natural secretions even in overlapped fingerprints (Chen et al. 2009). Ng Ronnie Hei Ping, et al. investigated the combined application of FTIR and Raman for imaging latent fingerprints. Spectral searching algorithms were tested for the detection of targeted substances in fingerprint out of which Spectral Angle Mapper correlational algorithms gave the best results. A total of 42 inferior quality spectra were observed and later characterized from the images of latent prints uncontaminated in nature. Aspirin, diazepam, and explosives deposited on the contaminated fingerprints were also detected Ng Ronnie et al. 2009.
Antoine M K, et al. compared the groomed fingerprint samples of father and son pair over a passage of 4 week using FTIRM. At the end of study, significant compositional differences were obtained between the respective prints. Thus, the study confirmed the use of FTIR spectrum for the determination of age of person using compositional difference (Antoine et al. 2010). Banas A, et al. employed FTIR to determine the ability of adhesive tapes to transfer exogenous substances together with fingerprint marks. The contaminated fingerprints were prepared using explosives and non-controlled substances like sugar and aspirin on different substrates. The prints were treated with gray, white, and black powders and underwent FTIR analysis. It was concluded that the time taken to identify the exogenous substances in fingerprint was increased because of presence of other contaminants (Banas et al. 2014).
It is a non-destructive chemical technique used to obtain detailed information regarding the chemical structure, polymorphy, phase, crystallinity, and their molecular interactions. Raman spectroscopy is a useful technique in the analysis of latent fingerprints as it allows the non-destructive analysis of the print and the subsequent identification (Daya and H. G. 2004)
Widjaja E, investigated the integrated results of Raman spectral mapping, tape-lift, and multivariate BTEM, to derive chemical information of latent fingerprints along with trace materials. Three model cases were developed, i.e., sebum-rich fingerprint obtained after touching forehead, drug model consisting of l-arginine, ibuprofen, and sodium bicarbonate; and additive model comprising of sucrose and aspartame. By the employment of advanced multivariate data analysis technique, pure component spectra of both lifting media and trace materials were achieved. The quality of pure component spectral reconstructions of the three cases was very high (Widjaja 2009). The results were achieved by the integration of tape-lift method and Raman spectroscopic imaging with effective multivariate curve resolution method. Emmons, et al. demonstrated in his study that explosives could be detected in contaminated fingerprints using bright field Raman imaging and Pearson’s cosine cross- correlation analysis of the specific region of range 550 cm− 1 to 1850 cm− 1 (Emmons et al. 2009).
Immunogenic and nucleic acid reagents
Aptamers can be termed as oligonucleotide or peptide molecules which bind to specific target molecule. Aptamers when form a specific and stable three dimensional structure can easily bind a large number of targets (Stoltenburg and R. C. 2007). The aptamers are said to highly specific shown by the aptamer-target binding complexes which have been found to be in higher quantities than antigen-antibody complex (Yang and Y. D. 2007).
Russel, et al. demonstrated that a smoker’s fingerprint can be examined by the combination of gold nanoparticles with the antibodies which were specific to cotinine and secondary antibody tagged with a dye. Fluorescence images revealed the minute second and third level details indicating simultaneous detection of chemical composition along with the physical features (Leggett and Lee‐Smith 2007). Later in the study, Russel et al. further documented that by utilizing magnetic particles tagged with anti-cotinine antibodies to image the cotinine present in the latent fingerprints of smokers and concluded that the probable identity of an individual could be established within 15 min (Hazarika and Jickells 2010).
In a study, the use of gold NPs in conjugation with anti-l-amino acid antibodies was demonstrated for the visualization of latent fingerprints, particularly aged and degraded ones on non-porous surfaces (Spindler et al. 2011). Xu L R, et al. demonstrated the presence of epidermal growth, lysozyme, and dermicidin in the print residue. Through this study not only the ridge patterns but also the chemical constituents of the fingerprints were obtained effectively. Xiang Rang, et al. investigated nucleic acid controlled AgNCs platform for the visualization of latent fingerprints. Multi-color images for visualization of fingerprint pattern and the chemical constituents of fingerprints were obtained. Emission modulating region and aptamers region provide a simultaneous identification of multiple components (Rang et al. 2015).