Electrochemical visualization of latent fingerprints using polyphenazine dyes on brass cartridges

Electrochemical visualization of latent fingerprints using polyphenazine dyes on brass cartridges | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Electrochemical visualization of latent fingerprints using polyphenazine dyes on brass cartridges Sára Hermochová, Petr Hlavín, Michal Novotný, Martin Vrňata, Gabriela Broncova This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4183306/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 13 Jun, 2024 Read the published version in Monatshefte für Chemie - Chemical Monthly → Version 1 posted 4 You are reading this latest preprint version Abstract This work is focused on the visualization of latent fingerprints left on unfired brass cartridges. Polymer films were prepared from 2 mM neutral red or 5 mM toluidine blue using two different electrochemical methods (cyclic voltammetry or chronoamperometry) with relatively short polymerization times. The conditions for the deposition of conductive polymers, poly(neutral red) and poly(toluidine blue), from a neutral medium (phosphate buffer with 0.1 M KNO 3 or 0.1 M KNO 3 , respectively) were optimized to preserve genetic information while producing highquality visualization of the remaining fingerprints on the brass substrates. The surface morphology and quality of the polymer films after the electrochemical deposition of both polyphenazine dyes were optically characterized. Phenazine dyes, which were used for the visualization of fingerprints, have been shown to provide different degrees of homogeneity in the deposited film. Furthermore, the dependence of the stability of the monomer solutions on their age, use and storage conditions are discussed. Finally, a methodology is proposed for how to apply this technique of visualizing latent fingerprints with observed details of papillary lines in forensic practice. Brass cartridge Latent fingerprint Dyes Electrochemical polymerizations Cyclic voltammetry Material science Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Introduction Fingerprints, also known as dactyloscopic traces, are created by friction ridges placed on the palms and fingers and are used as basic evidence to identify people due to their uniqueness. Fingerprints can be found in visible, plastic or latent forms. Latent fingerprints, which are invisible to the naked eye, are found most often at crime scenes [ 1 , 2 ]. For their visualization, it is necessary to select a suitable dactyloscopic method. Latent fingerprints are formed mainly by secretions from two types of glands and/or various contaminants, such as cosmetic products, soap residues, bacterial spores, or even chemical substances [ 1 ]. Eccrine sweat glands are located mainly on the papillary lines, whereas sebaceous sweat glands are found throughout the body (at the highest concentration on the scalp skin), except on the hands and feet. The sebaceous fingerprint is largely made up of free fatty acids and their esters. A substantial portion of both sebaceous and eccrine fingerprints consists of water, which can easily evaporate during fingerprint aging [ 1 – 4 ]. To date, there are only a few techniques that can successfully make fingerprints visible on metallic materials [ 5 ]. To choose the most appropriate method, it is necessary to consider, for example, the character of the trace, its assumed age, and the character of the material on which the trace is deposited [ 6 ]. At crime scenes, there are often smooth or rough non-porous surfaces on which fingerprints are applied; therefore, they are easily destroyed, especially if some time has elapsed since their deposition. The recovery rate of fingerprints from firearms and ammunition is very low, so the cyanoacrylate fumigation process is frequently used to visualize them. However, the combination of cyanoacrylate fumigation together with the application of “Gun blue” and a fluorescent dye provides a better quality fingerprint [ 5 , 6 ]. Both of these methods are unfavorable for the health of users; therefore, other suitable methods for visualizing fingerprint on these materials are being sought out. Recently, the use of conductive polymers has been offered as a possibility because, when a conductive polymer film is applied, its formation and resulting thickness can be easily regulated to achieve optimal results. With the help of conductive polymers, it is possible to effectively visualize even lowquality fingerprints on cartridges [ 7 ]. Suitable conductive polymers such as poly(3,4ethylenedioxythiophene) (PEDOT) [ 7 – 9 ], polyaniline (PANI) [ 10 ], polypyrrole (PPy) [ 9 ], and poly(neutral red) (PNR) [ 11 , 12 ] can be deposited on metal material either potentiostatically [ 7 , 8 ] or by means of cyclic voltammetry [ 12 ]. Compared to the relatively lengthy polymerization of cyanoacrylate, both electrochemical methods are relatively simple and fast. The fingerprint can be visualized within 4 minutes [ 11 , 12 ]. In our experiments, colored polymer films of PNR and poly(toluidine blue) (PTB) are applied on the working electrode (i.e., brass cartage) from the monomer solution [ 13 ]. Moreover, these polyphenazine dyes can also be used as electron mediators and have been shown to be promising sensitive layers for electrochemical sensors for the detection of various analytes [ 14 ]. Polyphenazine dyes can be electrochemically deposited on various metal substrates [ 15 ], which is advantageous for cartridges commonly made from metals such as copper, nickel, aluminum and their alloys (brass or steel) [ 1 , 4 , 16 ]. During the application, polymer films are deposited directly on the metal substrate between the papillary lines of the fingerprint; this procedure creates so-called negative image [ 2 , 6 , 8 ]. Due to the presence of sebum, the fingerprint acts as an insulating mask. The goals of this work were to i) compare the quality of visualization latent fingerprints on unfired cartridges using both polyphenazine thin films, ii) evaluate the homogeneity of applied polymer films and iii) characterize this procedure for future application on fired cartridges from forensic practice. Results and Discussion Cyclic voltammetry or chronoamperometry are electrochemical methods suitable for the deposition of polyphenazine dyes on metal substrates. These methods enable close monitoring and control of the formation of the emerging polymer layer. Visualization of fingerprint with electrochemical deposition of poly(neutral red) From the study by Broncová et al. (2021), cyclic voltammetry can be used to visualize fingerprints and that PNR can be applied to a brass substrate from a solution consisting of 0.1 M NaNO 3 in phosphate buffer with 2 mM neutral red (NR) [ 11 ]. Figure 1 a shows the deposition processes of PNR on brass cartridges of the .45AUTO type. During PNR deposition, a cathodic peak around a potential of 0.07 V was observed in the first cycle. This peak shifted to a potential of 0.01 V as the number of cycles increased. The current apparently changed during polymerization, which indicated the formation of a polymer film on the brass substrate. The shift of the cathodic peak occurring during PNR deposition varies for different brass cartridges, indicating changes in the redox behavior of a given substrate. Observed differences are due to the composition or structure of the brass surface. During PNR deposition on cartridges, the mean potential of cathodic peaks was 0.04 ± 0.01 V. The repetition of PNR deposition on brass cartridges of the same or different sizes is shown in Fig. 1 b, where the effect of the cartridge size on the current response in the cyclic voltammogram is evident. Equally sized cartridges (A to C) exhibited the same current response for the 7th cycle of PNR deposition on their surface, while the larger cartridge (D) provided a much higher current signal. From the pictures obtained after the polymerization (Fig. 2 ), it is clear that the resulting film has a relatively coarse structure. The PNR film was applied almost homogeneously but only in the spaces between the papillary lines. On one part of the cartridge, the PNR is applied only outside the fingerprint area, and on another cartridge, the PNR is also applied through the sebum. However, the fingerprints are of good quality and can be easily used for identification. Visualization of fingerprint with electrochemical deposition of poly(toluidine blue) Figure 3 a shows the representative deposition of PTB on brass cartridges of type 9 mm with chronoamperometry method. The current first increased dramatically from 16 mA to approximately 23 mA and then fluctuated only slightly at this current value. The curves in Fig. 3 b represent the repeated deposition of PTB on the surface of the same (9 mm cartridges E to G) and larger cartridges (.45 AUTO, cartridge marked H), respectively. The outline of these curves is very similar to the curves of electrodeposition of PEDOT on cartridges presented by Costa et al. [ 7 ]. During the electrolytic process, the brass is partially dissolved, and at the same time, the PTB polymer layer is deposited on the brass surface. The dissolution of the brass surface, however, does not occur throughout the deposition but only at the beginning, causing stronger anchoring of the polymer film on the surface. To avoid over-layering of the fingerprint by the polymer layer, as observed by Costa et al. [ 7 ] at the potentiostatic deposition of PEDOT, the thickness of the deposited polymer layer was not allowed to be greater than the thickness of the fingerprint grease. The thickness of the resulting film was regulated either by varying the potential within a certain interval (for the CV experiments) or by applying a constant potential and varying the deposition time of the film. Furthermore, a greasy fingerprint has been successfully visualized with PTB on the cartridges multiple times, Fig. 4 . It can be seen from the images that the resulting film is very fine, yet the characteristic ridges of the fingerprint can be found. It is evident that PTB compared with PNR, is more homogeneously applied and only in the space between the papillary lines and not on the fingerprint. The print is visualized in very good quality and can be used for possible identification. Comparison of polyphenazine dyes deposition Part of this study was to also compare the quality of the created PNR and PTB polymer films. Although NR and toluidine blue (TB) differ in their structure in only one atom (N versus S), the behavior of these substances during deposition is vastly different, and it is necessary to take this into account. Age and stability of the monomer solutions before deposition of polyphenazine dyes First, we examined the usability of the NR and TB monomer solutions. To ensure the stability of the monomer solution, it is necessary to keep the solution in the refrigerator before each use and re-homogenize it in an ultrasonic bath to ensure the perfect dissolution of any monomer residues. We observed that the age of the NR monomer solution can have a positive effect on the quality of the visualized fingerprints. The freshly prepared solution tended to form an inhomogeneous polymer film with larger clusters of particles, Fig. 5 a. On the other hand, storing the solution for a longer period of time in the refrigerator enabled the creation of a more homogeneous and better quality polymer film. These findings suggest that the time variability and reuse of the supporting electrolyte also play a key role in the resulting quality of the electrochemical fingerprint visualization. On the contrary, the age of the TB monomer solution does not have such a visible effect as in the case of NR. The freshly prepared solution produced the same homogeneous PTB forms as the older solution, Fig. 5 b. The experiments revealed that the NR solution can be effectively used for electrochemical polymerization up to several times (maximum five times) compared to TB (three times). With further repeated use, the thickness of the polymer layer gradually decreased, and this resulted in a quality deterioration of fingerprint visualization. During PTB deposition, turbidity was observed in the monomer solution, indicating excessive dissolution of the brass cartridges. On the contrary, no such turbidity was observed in the solution after the application of PNR. The choice of supporting electrolyte for PNR and PTB the deposition was different. In the case of PNR, a phosphate buffer with 0.1 M KNO 3 was used. The pH of the solution at the end of the PNR deposition remained the same as that before polymerization. On the other hand, the supporting electrolyte for PTB polymerization consisted of only 0.1 M KNO 3 and produced a blue gelatinous compound at the bottom of the electrochemical cell after PTB deposition. The pH value of this supporting electrolyte was measured before and after the application of PTB and was 5.81 and 9.33, respectively. Thus, the electrochemical experiment alkalizes the pH of the nonbuffered solution. It is related to the formation of Cu(OH) 2, as described in experiments with PEDOT [ 7 ]. Second-level details of the fingerprint on cartridge cases after the application of polyphenazine films When optimizing the electrochemical deposition, it was necessary to “soften” the polymerization conditions to eliminate brass dissolution to a minimum by choosing a narrower potential range for cyclic voltammetry or setting lower potential values for chronoamperometry. The resulting polymer film was more homogeneous and brighter in color, as shown in Fig. 6 . In the visualized fingerprint on the cartridges, the second-level details found (1–26) are marked with numbers. Some of them can be observed with the naked eye, for example terminations, bifurcation, and eyelets. Morphology of deposited polyphenazine films The morphology of the polymer films, fingerprint and interface were determined using SEM. It is clear from Fig. 7 that PNR forms fibers with a diameter of about several units of micrometers, while PTB forms rather shorter oval (granular) structures. Both polymer films cover the brass surface without any defects. Conclusion This proposal of a simple fingerprint visualization method based on the electrochemical deposition of poly(neutral red) and poly(toluidine blue) from a neutral environment, where the damage to the genetic information is minimized, could facilitate the fingerprinting of cartridges in practice. The parameters of both visualization methods (base electrolyte, potential range, number of cycles or applied potential, and deposition time) were gradually optimized until the imprint was sufficiently visible. During experiments after optimizing the deposition conditions of polyphenazine dyes using both CV and chronoamperometry, considerable reproducibility was identified in the sebaceous fingerprint visualization process. Repeatable high-quality visualization was achieved even when the cartridge was replaced with a larger cartridge. The morphology and structure of the modified surfaces were studied. The thin layers were characterized microscopically to determine their homogeneity and assess the quality of visualization. Further development of the method and, above all, the application of the method to fired cartridges, which is a key topic in forensic practice, are expected. Materials and Methods All commercial chemicals were used as received without further purification. NR, TB, whose structures are depicted in Fig. 8 , H 2 SO 4 , KH 2 PO 4 , Na 2 HPO 4 .12H 2 O, KNO 3 , acetone and ethanol were obtained from Lachema, Lach-ner and Penta (Czech Republic), respectively. Phosphate buffer (pH = 7, UCT Prague) consisted of KH 2 PO 4 (3.39 g/l) and Na 2 HPO 4 .12H 2 O (8.95 g/l). Solutions of monomer dyes were prepared i) in pH = 7 phosphate buffer with 0.1 M KNO 3 for 2 mM NR and ii) in 0.1 M KNO 3 for 5 mM TB. All solutions were prepared by dissolving substances in redistilled water (UCT Prague). The visualization of sebaceous fingerprints was conducted on unfired caliber cartridges: 9 mm Luger and .45 AUTO. The Criminalistics Institute Prague, Police of the Czech Republic, provided disassembled cartridges for the experiments (the unfired cartridge was deprived of the projectile, the powder charge was removed, and the primer remained intact and was left in the cartridge). The cartridges were first chemically cleaned by soaking in a sequence of solutions: redistilled water, acetone, warm soapy water, and ethanol. Subsequently, a greasy fingerprint was applied to the dry substrate by i) washing the hands with warm soapy water, ii) allowing them to dry freely, iii) rubbing the right thumb against the bridge of the nose and forehead due to the formation of a greasy film, and iv) with a slight pressure for period of 1–2 s fingerprint was applied, according to the Beresford procedure [ 17 ]. An anonymous donor imprint was applied to all substrates. All visualized fingerprints were published with the consent of the donor. Electrochemical measurements were performed with a PGSTAT-12 Autolab potentiostat/galvanostat (Eco-Chemie, The Netherlands). The electrode cell was composed of a saturated Ag/AgCl reference electrode, a Pt large-area electrode as an auxiliary electrode, and brass cartridges as working electrodes, which were clamped with alligator clips, Fig. 9 . The deposition of polyphenazine dyes was carried out under the conditions listed in Table 1 , which were gradually optimized for the cartridges. After finishing the polymerization, the substrates were rinsed firstly in monomerfree base electrolyte and subsequently in redistilled water and allowed to air dry under laboratory conditions. Regular maintenance of the electrode system (cleaning) is required after every second to third use with sulfuric acid as the supporting electrolyte and cyclic voltammetry to guarantee the reproducibility and quality of the results. Table 1 Conditions for the deposition of polyphenazine dyes on brass cartridges with applied fingerprints Monomer NR TB Deposition technique Cyclic voltammetry Chronoamperometry Applied polymer PNR PTB Parameters Potential range = −0.2–0.5 V Applied potential = 0.5 V Scan rate = 50 mV s − 1 Time interval = 10 ms Number of cycles = 8 Time of applied potential = 120 s The visualized fingerprints were photographically documented using a Stemi 508 trino stereoscopic microscope equipped with an AxioCam 208 color camera (Zeiss, Germany), an SMZ1500 stereoscopic microscope complemented by a Canon 1100D digital SLR camera (Nikon, Japan) and a Mira 3 LMH scanning electron microscope (SEM) (Tescan, Czech Republic). Declarations Acknowledgements This project Advanced techniques of visualization of dactyloscopic traces, VK01010022, was supported by the Ministry of the Interior of the Czech Republic from the Program Open Calls for Security Research 2023–2029 (OPSEC). Special thanks go to Šárka Havlová for helping us take the SEM images. References Daluz HM (2015) Fundamentals of fingerprint analysis. CRC Press/Taylor & Francis Group, London Slaninova T, Broncova G, Straus J, Shishkanova TV (2019) Chem Listy 113:530 Girod A, Ramotowski R, Weyermann C (2012) Sci Int 223:10 Bleay SM, Croxton RS, De Puit M (2018) Fingerprint Development Techniques: Theory and Application. Wiley, Incorporated, Newark, United Kingdom Girelli CMA, Lobo BJM, Cunha AG, Freitas JCC, Emmerich FG (2015) Sci Int 250:17 Christofidis G, Morrissey J, Birkett JW (2018) J Forensic Sci 63:1616 Costa CV, Assis AML, Freitas JD, Tonholo J, Ribeiro AS (2020) Nano Sel. 1:405 Brown RM, Hillman AR (2012) Phys Chem Chem Phys 14:8653 Sapstead RM, Corden N, Robert Hillman A (2015) Electrochim Acta 162:119 Beresford AL, Hillman AR (2010) Anal Chem 82:483 Broncová G, Slaninová T, Trchová M, Prokopec V, Matějka P, Shishkanova TV (2021) Polymers 13:3220 Broncová G, Slaninová T, Dendisová M (2021) Chem Papers 75:6673 Girelli CMA, Segatto BR (2019) J Forensic Sci 64:1520 Zahran M (2023) Heliyon 9:e19943 Pauliukaite R, Ghica ME, Barsan MM, Brett CMA (2010) Anal Lett 43:1588 Cadd S, Islam M, Manson P, Bleay S (2015) Sci Justice 55:219 Beresford AL, Brown RM, Hillman AR, Bond JW (2012) J Forensic Sci 57:93 Supplementary Files Graphicalabstract.jpg Cite Share Download PDF Status: Published Journal Publication published 13 Jun, 2024 Read the published version in Monatshefte für Chemie - Chemical Monthly → Version 1 posted Reviewers agreed at journal 13 Apr, 2024 Reviewers invited by journal 12 Apr, 2024 Editor assigned by journal 30 Mar, 2024 First submitted to journal 28 Mar, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4183306","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":290651840,"identity":"a484636f-bdf6-440e-b2f9-202f39d88acf","order_by":0,"name":"Sára Hermochová","email":"","orcid":"","institution":"University of Chemistry and Technology Prague Faculty of Chemical Engineering: Vysoka skola chemicko-technologicka v Praze Fakulta chemicko-inzenyrska","correspondingAuthor":false,"prefix":"","firstName":"Sára","middleName":"","lastName":"Hermochová","suffix":""},{"id":290651841,"identity":"05bc2166-3e0b-4ba7-a36a-1eae499aa5ad","order_by":1,"name":"Petr Hlavín","email":"","orcid":"","institution":"Criminalistics Institute Prague, Police of the Czech Republic","correspondingAuthor":false,"prefix":"","firstName":"Petr","middleName":"","lastName":"Hlavín","suffix":""},{"id":290651842,"identity":"87196513-9c19-4ed4-bbf8-9f849f509e02","order_by":2,"name":"Michal Novotný","email":"","orcid":"","institution":"Institute of Physics Czech Academy of Sciences: Fyzikalni ustav Akademie ved Ceske republiky","correspondingAuthor":false,"prefix":"","firstName":"Michal","middleName":"","lastName":"Novotný","suffix":""},{"id":290651843,"identity":"56392aab-5ea9-498f-838c-cbcd61bb0319","order_by":3,"name":"Martin Vrňata","email":"","orcid":"","institution":"University of Chemistry and Technology Prague Faculty of Chemical Engineering: Vysoka skola chemicko-technologicka v Praze Fakulta chemicko-inzenyrska","correspondingAuthor":false,"prefix":"","firstName":"Martin","middleName":"","lastName":"Vrňata","suffix":""},{"id":290651844,"identity":"ff1ee641-319a-464c-ab25-20dbd4650d4d","order_by":4,"name":"Gabriela Broncova","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABFUlEQVRIie3QPUvEMBjA8ScU7pZI1+c4SL9CSkAcKn6VlkCmUxwdOgSEOB1d6zdxrBzEpYdr5Rbl1kMKLh6I2NY7F9tzdcifDiHk17wAuFz/MF9TgBhOAAK9mxo3A6KHCRYdwXa0m6JFS/gg4UA72Xzx/i/xH2S8tPXzFQaAy5f1ZRol2e1G1Nu7D/Czop/QC5nHJYY6uBEityrJV7PjybzkzUn7SVjMBCQGiUY7mh7phYCVUh4xHPjAG/DHTUM+8Uyj+ibBk5VvHfEG7lK1u2hM9oTxyiumHRn1E6xeJcQWpUHrCWoVC0tpJ3MjKJb9xM/OF+Q9jU6zwJA1TSPKHu6v661hbOjFfvp1Cnp4vcvlcrkO9QXGTFgAbmHImgAAAABJRU5ErkJggg==","orcid":"https://orcid.org/0000-0002-6559-7165","institution":"University of Chemistry and Technology Prague Faculty of Chemical Technology: Vysoka skola chemicko-technologicka v Praze Fakulta chemicke technologie","correspondingAuthor":true,"prefix":"","firstName":"Gabriela","middleName":"","lastName":"Broncova","suffix":""}],"badges":[],"createdAt":"2024-03-28 15:33:28","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4183306/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4183306/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s00706-024-03222-3","type":"published","date":"2024-06-13T14:56:12+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":54813984,"identity":"4aad778d-cecc-4089-814a-b1338dac6f62","added_by":"auto","created_at":"2024-04-17 06:54:49","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":7843292,"visible":true,"origin":"","legend":"\u003cp\u003eCyclic voltammogram of 2 mM NR in phosphate buffer with 0.1\u0026nbsp;M\u0026nbsp;KNO\u003csub\u003e3\u003c/sub\u003e on cartridges with fresh fingerprints in the potential range from –0.20 to 0.50 V (vs. Ag/AgCl) at a scan rate of 50 mV s\u003csup\u003e−1\u003c/sup\u003e; a) whole deposition process (8\u0026nbsp;cycles, cartridge D) and b) seventh cycle for\u0026nbsp;4\u0026nbsp;cartridges (A – D), compared deposition process\u003cbr\u003e\non cartridges A – C (9\u0026nbsp;mm) and D (.45 AUTO).\u003c/p\u003e","description":"","filename":"Fig1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4183306/v1/b8f26fafd9327da832e1bbaf.jpg"},{"id":54813982,"identity":"1b5fb8ee-976a-49fd-88a0-2dfdf8c30d73","added_by":"auto","created_at":"2024-04-17 06:54:49","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":2414247,"visible":true,"origin":"","legend":"\u003cp\u003eBrass cartridge cases A, B, C (9 mm) and D (.45 AUTO) with a visualized latent fingerprint by PNR. Cases A to C were photographed by the stereoscopic microscope Zeiss and D with a Nikon.\u003c/p\u003e","description":"","filename":"Fig2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4183306/v1/4f50a1364a4208ee940751d7.jpg"},{"id":54813981,"identity":"528cdab7-b45d-4178-a4c9-5b5fb599ed67","added_by":"auto","created_at":"2024-04-17 06:54:49","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":6010921,"visible":true,"origin":"","legend":"\u003cp\u003eChronoamperogram of 5 mM toluidine blue 0.1 M KNO\u003csub\u003e3\u003c/sub\u003e on\u0026nbsp;cartridges with a fresh fingerprint at a potential of 0.50 V (vs.\u0026nbsp;Ag/AgCl) for 120 s; a) representative deposition process (cartridge H) and b)\u0026nbsp;comparison of the deposition process on cartridges E – G (9 mm) and H\u0026nbsp;(.45 AUTO).\u003c/p\u003e","description":"","filename":"Fig3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4183306/v1/337c95b10e86df811f0a6443.jpg"},{"id":54813987,"identity":"6caedc66-ad19-4bb3-9c5b-61391b6e6750","added_by":"auto","created_at":"2024-04-17 06:54:50","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":9609435,"visible":true,"origin":"","legend":"\u003cp\u003eBrass cartridge cases E, F, G (9 mm) and H (.45 AUTO) with a visualized latent fingerprint by PTB. Cases E was photographed by stereoscopic microscope Zeiss and F – H with a Nikon.\u003c/p\u003e","description":"","filename":"Fig4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4183306/v1/75d909a5dc863f03ce996e9c.jpg"},{"id":54813985,"identity":"7bcc3347-ed1f-4a73-ba9f-45cc4a01dfa9","added_by":"auto","created_at":"2024-04-17 06:54:50","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":6035572,"visible":true,"origin":"","legend":"\u003cp\u003eHomogeneity of deposited polyphenazine layers on brass cartridges with fingerprint; a) PNR and b) PTB (images taken using a Nikon stereoscopic microscope).\u003c/p\u003e","description":"","filename":"Fig5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4183306/v1/56741d120041af8e4459ad5f.jpg"},{"id":54813988,"identity":"c73fa02f-dec1-47a8-b975-2c5d065f0133","added_by":"auto","created_at":"2024-04-17 06:54:50","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":10312182,"visible":true,"origin":"","legend":"\u003cp\u003eUnfired brass cartridges after deposition of; a) PNR on cartridge D and b) PTB on cartridge H with a visualized grease fingerprint and associated second-level details (images taken with a Nikon stereoscopic microscope).\u003c/p\u003e","description":"","filename":"Fig6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4183306/v1/6bdd27348d641c05acc27bc0.jpg"},{"id":54814408,"identity":"11765319-1c29-4ff8-809b-a052741a2221","added_by":"auto","created_at":"2024-04-17 07:02:50","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":1322086,"visible":true,"origin":"","legend":"\u003cp\u003eScanning electron microscopy images of the morphology of polyphenazine films taken in the mode of scattered electrons of; a) PNR and b) PTB.\u003c/p\u003e","description":"","filename":"Fig7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4183306/v1/6f3fa7e8423443a2e3f05007.jpg"},{"id":54814409,"identity":"35b7348b-7036-4deb-9c78-386c85a62722","added_by":"auto","created_at":"2024-04-17 07:02:50","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":65145,"visible":true,"origin":"","legend":"\u003cp\u003eStructures of the monomers; a) neutral red and b) toluidine blue.\u003c/p\u003e","description":"","filename":"Fig8.png","url":"https://assets-eu.researchsquare.com/files/rs-4183306/v1/ba2c2c48c52b150037bd893f.png"},{"id":54813983,"identity":"54e2942a-2fa5-49cd-853e-3692f76547d1","added_by":"auto","created_at":"2024-04-17 06:54:49","extension":"jpg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":787272,"visible":true,"origin":"","legend":"\u003cp\u003eElectrode arrangement: working electrode (WE) – 9 mm cartridge, counter electrode (CE) – large‑area Pt electrode, reference electrode (RE) – argentochloride electrode.\u003c/p\u003e","description":"","filename":"Fig9.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4183306/v1/3da6d6a93da1bdc3c654bde4.jpg"},{"id":58822442,"identity":"6fd3d35e-2895-44a9-985f-8da8bb15f3f9","added_by":"auto","created_at":"2024-06-21 16:43:49","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":44789850,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4183306/v1/f8d70356-96ff-45ab-97d3-1dc71dcb060d.pdf"},{"id":54813979,"identity":"01379fdf-85ea-48c1-b2e0-f7f311423be1","added_by":"auto","created_at":"2024-04-17 06:54:49","extension":"jpg","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":1911897,"visible":true,"origin":"","legend":"","description":"","filename":"Graphicalabstract.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4183306/v1/9cb5d567760eaff666e1bc9d.jpg"}],"financialInterests":"","formattedTitle":"Electrochemical visualization of latent fingerprints using polyphenazine dyes on brass cartridges","fulltext":[{"header":"Introduction","content":"\u003cp\u003eFingerprints, also known as dactyloscopic traces, are created by friction ridges placed on the palms and fingers and are used as basic evidence to identify people due to their uniqueness. Fingerprints can be found in visible, plastic or latent forms. Latent fingerprints, which are invisible to the naked eye, are found most often at crime scenes [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. For their visualization, it is necessary to select a suitable dactyloscopic method.\u003c/p\u003e \u003cp\u003eLatent fingerprints are formed mainly by secretions from two types of glands and/or various contaminants, such as cosmetic products, soap residues, bacterial spores, or even chemical substances [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Eccrine sweat glands are located mainly on the papillary lines, whereas sebaceous sweat glands are found throughout the body (at the highest concentration on the scalp skin), except on the hands and feet. The sebaceous fingerprint is largely made up of free fatty acids and their esters. A substantial portion of both sebaceous and eccrine fingerprints consists of water, which can easily evaporate during fingerprint aging [\u003cspan additionalcitationids=\"CR2 CR3\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eTo date, there are only a few techniques that can successfully make fingerprints visible on metallic materials [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. To choose the most appropriate method, it is necessary to consider, for example, the character of the trace, its assumed age, and the character of the material on which the trace is deposited [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. At crime scenes, there are often smooth or rough non-porous surfaces on which fingerprints are applied; therefore, they are easily destroyed, especially if some time has elapsed since their deposition.\u003c/p\u003e \u003cp\u003eThe recovery rate of fingerprints from firearms and ammunition is very low, so the cyanoacrylate fumigation process is frequently used to visualize them. However, the combination of cyanoacrylate fumigation together with the application of \u0026ldquo;Gun blue\u0026rdquo; and a fluorescent dye provides a better quality fingerprint [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Both of these methods are unfavorable for the health of users; therefore, other suitable methods for visualizing fingerprint on these materials are being sought out. Recently, the use of conductive polymers has been offered as a possibility because, when a conductive polymer film is applied, its formation and resulting thickness can be easily regulated to achieve optimal results. With the help of conductive polymers, it is possible to effectively visualize even lowquality fingerprints on cartridges [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Suitable conductive polymers such as poly(3,4ethylenedioxythiophene) (PEDOT) [\u003cspan additionalcitationids=\"CR8\" citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e], polyaniline (PANI) [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e], polypyrrole (PPy) [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e], and poly(neutral red) (PNR) [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e] can be deposited on metal material either potentiostatically [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e] or by means of cyclic voltammetry [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Compared to the relatively lengthy polymerization of cyanoacrylate, both electrochemical methods are relatively simple and fast. The fingerprint can be visualized within 4 minutes [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn our experiments, colored polymer films of PNR and poly(toluidine blue) (PTB) are applied on the working electrode (i.e., brass cartage) from the monomer solution [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Moreover, these polyphenazine dyes can also be used as electron mediators and have been shown to be promising sensitive layers for electrochemical sensors for the detection of various analytes [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. Polyphenazine dyes can be electrochemically deposited on various metal substrates [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e], which is advantageous for cartridges commonly made from metals such as copper, nickel, aluminum and their alloys (brass or steel) [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. During the application, polymer films are deposited directly on the metal substrate between the papillary lines of the fingerprint; this procedure creates so-called negative image [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Due to the presence of sebum, the fingerprint acts as an insulating mask.\u003c/p\u003e \u003cp\u003eThe goals of this work were to i) compare the quality of visualization latent fingerprints on unfired cartridges using both polyphenazine thin films, ii) evaluate the homogeneity of applied polymer films and iii) characterize this procedure for future application on fired cartridges from forensic practice.\u003c/p\u003e"},{"header":"Results and Discussion","content":"\u003cp\u003eCyclic voltammetry or chronoamperometry are electrochemical methods suitable for the deposition of polyphenazine dyes on metal substrates. These methods enable close monitoring and control of the formation of the emerging polymer layer.\u003c/p\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eVisualization of fingerprint with electrochemical deposition of poly(neutral red)\u003c/h2\u003e \u003cp\u003eFrom the study by Broncov\u0026aacute; et al. (2021), cyclic voltammetry can be used to visualize fingerprints and that PNR can be applied to a brass substrate from a solution consisting of 0.1 M NaNO\u003csub\u003e3\u003c/sub\u003e in phosphate buffer with 2 mM neutral red (NR) [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e1\u003c/span\u003ea shows the deposition processes of PNR on brass cartridges of the .45AUTO type. During PNR deposition, a cathodic peak around a potential of 0.07 V was observed in the first cycle. This peak shifted to a potential of 0.01 V as the number of cycles increased. The current apparently changed during polymerization, which indicated the formation of a polymer film on the brass substrate.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe shift of the cathodic peak occurring during PNR deposition varies for different brass cartridges, indicating changes in the redox behavior of a given substrate. Observed differences are due to the composition or structure of the brass surface. During PNR deposition on cartridges, the mean potential of cathodic peaks was 0.04\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01 V. The repetition of PNR deposition on brass cartridges of the same or different sizes is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e1\u003c/span\u003eb, where the effect of the cartridge size on the current response in the cyclic voltammogram is evident. Equally sized cartridges (A to C) exhibited the same current response for the 7th cycle of PNR deposition on their surface, while the larger cartridge (D) provided a much higher current signal.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFrom the pictures obtained after the polymerization (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e2\u003c/span\u003e), it is clear that the resulting film has a relatively coarse structure. The PNR film was applied almost homogeneously but only in the spaces between the papillary lines. On one part of the cartridge, the PNR is applied only outside the fingerprint area, and on another cartridge, the PNR is also applied through the sebum. However, the fingerprints are of good quality and can be easily used for identification.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eVisualization of fingerprint with electrochemical deposition of poly(toluidine blue)\u003c/h3\u003e\n\u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003ea shows the representative deposition of PTB on brass cartridges of type 9 mm with chronoamperometry method. The current first increased dramatically from 16 mA to approximately 23 mA and then fluctuated only slightly at this current value. The curves in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003eb represent the repeated deposition of PTB on the surface of the same (9 mm cartridges E to G) and larger cartridges (.45 AUTO, cartridge marked H), respectively. The outline of these curves is very similar to the curves of electrodeposition of PEDOT on cartridges presented by Costa et al. [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. During the electrolytic process, the brass is partially dissolved, and at the same time, the PTB polymer layer is deposited on the brass surface. The dissolution of the brass surface, however, does not occur throughout the deposition but only at the beginning, causing stronger anchoring of the polymer film on the surface.\u003c/p\u003e \u003cp\u003eTo avoid over-layering of the fingerprint by the polymer layer, as observed by Costa et al. [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e] at the potentiostatic deposition of PEDOT, the thickness of the deposited polymer layer was not allowed to be greater than the thickness of the fingerprint grease. The thickness of the resulting film was regulated either by varying the potential within a certain interval (for the CV experiments) or by applying a constant potential and varying the deposition time of the film.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFurthermore, a greasy fingerprint has been successfully visualized with PTB on the cartridges multiple times, Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e4\u003c/span\u003e. It can be seen from the images that the resulting film is very fine, yet the characteristic ridges of the fingerprint can be found. It is evident that PTB compared with PNR, is more homogeneously applied and only in the space between the papillary lines and not on the fingerprint. The print is visualized in very good quality and can be used for possible identification.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eComparison of polyphenazine dyes deposition\u003c/h2\u003e \u003cp\u003ePart of this study was to also compare the quality of the created PNR and PTB polymer films. Although NR and toluidine blue (TB) differ in their structure in only one atom (N versus S), the behavior of these substances during deposition is vastly different, and it is necessary to take this into account.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003eAge and stability of the monomer solutions before deposition of polyphenazine dyes\u003c/h2\u003e \u003cp\u003eFirst, we examined the usability of the NR and TB monomer solutions. To ensure the stability of the monomer solution, it is necessary to keep the solution in the refrigerator before each use and re-homogenize it in an ultrasonic bath to ensure the perfect dissolution of any monomer residues.\u003c/p\u003e \u003cp\u003eWe observed that the age of the NR monomer solution can have a positive effect on the quality of the visualized fingerprints. The freshly prepared solution tended to form an inhomogeneous polymer film with larger clusters of particles, Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e5\u003c/span\u003ea. On the other hand, storing the solution for a longer period of time in the refrigerator enabled the creation of a more homogeneous and better quality polymer film. These findings suggest that the time variability and reuse of the supporting electrolyte also play a key role in the resulting quality of the electrochemical fingerprint visualization. On the contrary, the age of the TB monomer solution does not have such a visible effect as in the case of NR. The freshly prepared solution produced the same homogeneous PTB forms as the older solution, Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e5\u003c/span\u003eb.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe experiments revealed that the NR solution can be effectively used for electrochemical polymerization up to several times (maximum five times) compared to TB (three times). With further repeated use, the thickness of the polymer layer gradually decreased, and this resulted in a quality deterioration of fingerprint visualization.\u003c/p\u003e \u003cp\u003eDuring PTB deposition, turbidity was observed in the monomer solution, indicating excessive dissolution of the brass cartridges. On the contrary, no such turbidity was observed in the solution after the application of PNR.\u003c/p\u003e \u003cp\u003eThe choice of supporting electrolyte for PNR and PTB the deposition was different. In the case of PNR, a phosphate buffer with 0.1 M KNO\u003csub\u003e3\u003c/sub\u003e was used. The pH of the solution at the end of the PNR deposition remained the same as that before polymerization. On the other hand, the supporting electrolyte for PTB polymerization consisted of only 0.1 M KNO\u003csub\u003e3\u003c/sub\u003e and produced a blue gelatinous compound at the bottom of the electrochemical cell after PTB deposition. The pH value of this supporting electrolyte was measured before and after the application of PTB and was 5.81 and 9.33, respectively. Thus, the electrochemical experiment alkalizes the pH of the nonbuffered solution. It is related to the formation of Cu(OH)\u003csub\u003e2,\u003c/sub\u003e as described in experiments with PEDOT [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eSecond-level details of the fingerprint on cartridge cases after the application of polyphenazine films\u003c/h3\u003e\n\u003cp\u003eWhen optimizing the electrochemical deposition, it was necessary to \u0026ldquo;soften\u0026rdquo; the polymerization conditions to eliminate brass dissolution to a minimum by choosing a narrower potential range for cyclic voltammetry or setting lower potential values for chronoamperometry. The resulting polymer film was more homogeneous and brighter in color, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e6\u003c/span\u003e. In the visualized fingerprint on the cartridges, the second-level details found (1\u0026ndash;26) are marked with numbers. Some of them can be observed with the naked eye, for example terminations, bifurcation, and eyelets.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eMorphology of deposited polyphenazine films\u003c/h2\u003e \u003cp\u003eThe morphology of the polymer films, fingerprint and interface were determined using SEM. It is clear from Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e7\u003c/span\u003e that PNR forms fibers with a diameter of about several units of micrometers, while PTB forms rather shorter oval (granular) structures. Both polymer films cover the brass surface without any defects.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThis proposal of a simple fingerprint visualization method based on the electrochemical deposition of poly(neutral red) and poly(toluidine blue) from a neutral environment, where the damage to the genetic information is minimized, could facilitate the fingerprinting of cartridges in practice. The parameters of both visualization methods (base electrolyte, potential range, number of cycles or applied potential, and deposition time) were gradually optimized until the imprint was sufficiently visible.\u003c/p\u003e \u003cp\u003eDuring experiments after optimizing the deposition conditions of polyphenazine dyes using both CV and chronoamperometry, considerable reproducibility was identified in the sebaceous fingerprint visualization process. Repeatable high-quality visualization was achieved even when the cartridge was replaced with a larger cartridge.\u003c/p\u003e \u003cp\u003eThe morphology and structure of the modified surfaces were studied. The thin layers were characterized microscopically to determine their homogeneity and assess the quality of visualization.\u003c/p\u003e \u003cp\u003eFurther development of the method and, above all, the application of the method to fired cartridges, which is a key topic in forensic practice, are expected.\u003c/p\u003e"},{"header":"Materials and Methods","content":"\u003cp\u003eAll commercial chemicals were used as received without further purification. NR, TB, whose structures are depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e8\u003c/span\u003e, H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e, KH\u003csub\u003e2\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e, Na\u003csub\u003e2\u003c/sub\u003eHPO\u003csub\u003e4\u003c/sub\u003e.12H\u003csub\u003e2\u003c/sub\u003eO, KNO\u003csub\u003e3\u003c/sub\u003e, acetone and ethanol were obtained from Lachema, Lach-ner and Penta (Czech Republic), respectively. Phosphate buffer (pH\u0026thinsp;=\u0026thinsp;7, UCT Prague) consisted of KH\u003csub\u003e2\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e (3.39 g/l) and Na\u003csub\u003e2\u003c/sub\u003eHPO\u003csub\u003e4\u003c/sub\u003e.12H\u003csub\u003e2\u003c/sub\u003eO (8.95 g/l). Solutions of monomer dyes were prepared i) in pH\u0026thinsp;=\u0026thinsp;7 phosphate buffer with 0.1 M KNO\u003csub\u003e3\u003c/sub\u003e for 2 mM NR and ii) in 0.1 M KNO\u003csub\u003e3\u003c/sub\u003e for 5 mM TB. All solutions were prepared by dissolving substances in redistilled water (UCT Prague).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe visualization of sebaceous fingerprints was conducted on unfired caliber cartridges: 9 mm Luger and .45 AUTO. The Criminalistics Institute Prague, Police of the Czech Republic, provided disassembled cartridges for the experiments (the unfired cartridge was deprived of the projectile, the powder charge was removed, and the primer remained intact and was left in the cartridge).\u003c/p\u003e \u003cp\u003eThe cartridges were first chemically cleaned by soaking in a sequence of solutions: redistilled water, acetone, warm soapy water, and ethanol. Subsequently, a greasy fingerprint was applied to the dry substrate by i) washing the hands with warm soapy water, ii) allowing them to dry freely, iii) rubbing the right thumb against the bridge of the nose and forehead due to the formation of a greasy film, and iv) with a slight pressure for period of 1\u0026ndash;2 s fingerprint was applied, according to the Beresford procedure [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. An anonymous donor imprint was applied to all substrates. All visualized fingerprints were published with the consent of the donor.\u003c/p\u003e \u003cp\u003eElectrochemical measurements were performed with a PGSTAT-12 Autolab potentiostat/galvanostat (Eco-Chemie, The Netherlands). The electrode cell was composed of a saturated Ag/AgCl reference electrode, a Pt large-area electrode as an auxiliary electrode, and brass cartridges as working electrodes, which were clamped with alligator clips, Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e9\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe deposition of polyphenazine dyes was carried out under the conditions listed in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, which were gradually optimized for the cartridges. After finishing the polymerization, the substrates were rinsed firstly in monomerfree base electrolyte and subsequently in redistilled water and allowed to air dry under laboratory conditions. Regular maintenance of the electrode system (cleaning) is required after every second to third use with sulfuric acid as the supporting electrolyte and cyclic voltammetry to guarantee the reproducibility and quality of the results.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eConditions for the deposition of polyphenazine dyes on brass cartridges with applied fingerprints\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMonomer\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNR\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eTB\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDeposition technique\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCyclic voltammetry\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eChronoamperometry\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eApplied polymer\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePNR\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePTB\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eParameters\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePotential \u003c/p\u003e \u003cp\u003erange\u0026nbsp;=\u0026nbsp;\u0026minus;0.2\u0026ndash;0.5\u0026nbsp;V\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eApplied potential\u0026thinsp;=\u0026thinsp;0.5 V\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eScan rate\u0026thinsp;=\u0026thinsp;50 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eTime interval\u0026thinsp;=\u0026thinsp;10 ms\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNumber of cycles\u0026thinsp;=\u0026thinsp;8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eTime of applied potential\u0026nbsp;=\u0026nbsp;120 s\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe visualized fingerprints were photographically documented using a Stemi 508 trino stereoscopic microscope equipped with an AxioCam 208 color camera (Zeiss, Germany), an SMZ1500 stereoscopic microscope complemented by a Canon 1100D digital SLR camera (Nikon, Japan) and a Mira 3 LMH scanning electron microscope (SEM) (Tescan, Czech Republic).\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAcknowledgements\u003c/h2\u003e \u003cp\u003eThis project Advanced techniques of visualization of dactyloscopic traces, VK01010022, was supported by the Ministry of the Interior of the Czech Republic from the Program Open Calls for Security Research 2023\u0026ndash;2029 (OPSEC). Special thanks go to Š\u0026aacute;rka Havlov\u0026aacute; for helping us take the SEM images.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eDaluz HM (2015) Fundamentals of fingerprint analysis. CRC Press/Taylor \u0026amp; Francis Group, London\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSlaninova T, Broncova G, Straus J, Shishkanova TV (2019) Chem Listy 113:530\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGirod A, Ramotowski R, Weyermann C (2012) Sci Int 223:10\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBleay SM, Croxton RS, De Puit M (2018) Fingerprint Development Techniques: Theory and Application. Wiley, Incorporated, Newark, United Kingdom\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGirelli CMA, Lobo BJM, Cunha AG, Freitas JCC, Emmerich FG (2015) Sci Int 250:17\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChristofidis G, Morrissey J, Birkett JW (2018) J Forensic Sci 63:1616\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCosta CV, Assis AML, Freitas JD, Tonholo J, Ribeiro AS (2020) Nano Sel. 1:405\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBrown RM, Hillman AR (2012) Phys Chem Chem Phys 14:8653\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSapstead RM, Corden N, Robert Hillman A (2015) Electrochim Acta 162:119\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBeresford AL, Hillman AR (2010) Anal Chem 82:483\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBroncov\u0026aacute; G, Slaninov\u0026aacute; T, Trchov\u0026aacute; M, Prokopec V, Matějka P, Shishkanova TV (2021) Polymers 13:3220\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBroncov\u0026aacute; G, Slaninov\u0026aacute; T, Dendisov\u0026aacute; M (2021) Chem Papers 75:6673\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGirelli CMA, Segatto BR (2019) J Forensic Sci 64:1520\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZahran M (2023) Heliyon 9:e19943\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePauliukaite R, Ghica ME, Barsan MM, Brett CMA (2010) Anal Lett 43:1588\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCadd S, Islam M, Manson P, Bleay S (2015) Sci Justice 55:219\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBeresford AL, Brown RM, Hillman AR, Bond JW (2012) J Forensic Sci 57:93\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"monatshefte-fur-chemie-chemical-monthly","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"mccm","sideBox":"Learn more about [Monatshefte für Chemie - Chemical Monthly](https://www.springer.com/journal/706)","snPcode":"706","submissionUrl":"https://www.editorialmanager.com/mccm/","title":"Monatshefte für Chemie - Chemical Monthly","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Brass cartridge, Latent fingerprint, Dyes, Electrochemical polymerizations, Cyclic voltammetry, Material science","lastPublishedDoi":"10.21203/rs.3.rs-4183306/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4183306/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis work is focused on the visualization of latent fingerprints left on unfired brass cartridges. Polymer films were prepared from 2 mM neutral red or 5 mM toluidine blue using two different electrochemical methods (cyclic voltammetry or chronoamperometry) with relatively short polymerization times. The conditions for the deposition of conductive polymers, poly(neutral red) and poly(toluidine blue), from a neutral medium (phosphate buffer with 0.1 M KNO\u003csub\u003e3\u003c/sub\u003e or 0.1 M KNO\u003csub\u003e3\u003c/sub\u003e, respectively) were optimized to preserve genetic information while producing highquality visualization of the remaining fingerprints on the brass substrates. The surface morphology and quality of the polymer films after the electrochemical deposition of both polyphenazine dyes were optically characterized. Phenazine dyes, which were used for the visualization of fingerprints, have been shown to provide different degrees of homogeneity in the deposited film. Furthermore, the dependence of the stability of the monomer solutions on their age, use and storage conditions are discussed. Finally, a methodology is proposed for how to apply this technique of visualizing latent fingerprints with observed details of papillary lines in forensic practice.\u003c/p\u003e","manuscriptTitle":"Electrochemical visualization of latent fingerprints using polyphenazine dyes on brass cartridges","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-04-17 06:54:44","doi":"10.21203/rs.3.rs-4183306/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2024-04-13T04:37:57+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-04-12T18:38:25+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-03-30T05:19:30+00:00","index":"","fulltext":""},{"type":"submitted","content":"Monatshefte für Chemie - Chemical Monthly","date":"2024-03-28T11:33:00+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"monatshefte-fur-chemie-chemical-monthly","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"mccm","sideBox":"Learn more about [Monatshefte für Chemie - Chemical Monthly](https://www.springer.com/journal/706)","snPcode":"706","submissionUrl":"https://www.editorialmanager.com/mccm/","title":"Monatshefte für Chemie - Chemical Monthly","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"fce9f7a8-6f6a-436a-9989-bbfdfba9de65","owner":[],"postedDate":"April 17th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2024-06-21T14:56:12+00:00","versionOfRecord":{"articleIdentity":"rs-4183306","link":"https://doi.org/10.1007/s00706-024-03222-3","journal":{"identity":"monatshefte-fur-chemie-chemical-monthly","isVorOnly":false,"title":"Monatshefte für Chemie - Chemical Monthly"},"publishedOn":"2024-06-13 14:56:12","publishedOnDateReadable":"June 13th, 2024"},"versionCreatedAt":"2024-04-17 06:54:44","video":"","vorDoi":"10.1007/s00706-024-03222-3","vorDoiUrl":"https://doi.org/10.1007/s00706-024-03222-3","workflowStages":[]},"version":"v1","identity":"rs-4183306","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4183306","identity":"rs-4183306","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}