Method for detecting and measuring gunshot residue

Abstract

The present invention pertains to a method for detecting gunshot residue comprising the steps of - contacting a solid substrate suspected of containing gunshot residue with a reagent composition comprising a liquid medium and a halide reagent capable of reacting with lead to form a lead halide perovskite, and - subjecting the substrate to a light source with a wavelength that is shorter than the emission wavelength of the lead halide perovskite, and detecting the light emittance, wherein the solid substrate is a primary substrate, i.e., a substrate on which the gunshot residue was deposited as a direct result of the process of the gun being fired or a secondary substrate, i.e., a substrate which is suspected of containing lead-containing gunshot residue because it has been in contact with a primary substrate. It has been found that the method is highly sensitive and selective, and at the same time easy and fast to carry out. This makes it highly flexible. It has also been found that the test can be carried out without disturbing the deposition pattern of the GSR. In combination with the high sensitivity of the test and its ease of application this makes it possible to derive more information from a crime scene, or derive the same information in a more efficient and reliable manner.

Description

[0001] Method for detecting and measuring gunshot residue

[0002] Shooting incidents can have great societal impact, making forensic gunshot analysis of great importance. Shooting guns releases dust particles, which generally contain lead. The lead in these gunshot residues (GSR) offers opportunities for forensic studies ranging from identifying shooters, to estimating shooting distances and crime scene reconstructions. Although lead-free ammunition is available, forensic scenarios almost exclusively encounter lead-containing ammunition due to low prices and wide availability. Analysis of lead in GSR is therefore of great importance for forensics studies.

[0003] Currently, depending on the forensic situation, lead in GSR is analyzed using either simple coloring reactions or sophisticated analytical techniques. For identification of shooting suspects, GSR is analyzed by “stubbing” the hand of the suspect with a carbon sticker, which is then analyzed using scanning electron microscopy (SEM) equipped with energy dispersion spectroscopy (EDS). While EDS analysis is considered as the benchmark in GSR analysis, the requirement of expensive equipment and specialized training are major drawbacks. Moreover, processing of EDS results is laborious and can take days or even much longer, resulting in delays in forensic research and even a hindrance in timely evidence production for legal processes.

[0004] For estimating shooting distances, identifying ricochet markings, bullet holes, and similar crime scene reconstructions, GSR is analyzed using colorimetric reactions with rhodizonate. Rhodizonate changes color from yellow to brown upon complexation with lead and barium from the GSR. Despite widespread use and extensive optimization, this test has major drawbacks. Depending on the conditions, rhodizonate tests can react not only with lead, but also with, for instance, barium, cadmium, mercury, titanium, bismuth, and copper as well as with the keratinous structures of hair follicles and lingual papillae. This may result in false positives and complicated analysis. Moreover, the color change can be difficult to interpret, especially under poor lighting conditions. Hence, both for shooter identification and crime scene reconstruction analysis there are still major shortcomings and bottlenecks in current GSR characterization methods.

[0005] US20170153180 is directed to lead ion sensors for testing, detecting, and analyzing particlecontaining samples for GSR. As appears from the examples in the method of this reference, the actual detection takes place on the Pb2+ ions after they have been taken up in a liquid medium. The Pb2+ ions need to be present in a liquid medium during detection. This thus requires an additional processing step. In consequence, the method described herein cannot be used to detect GSR directly on the crime scene, e.g. on the hand of a shooter. It can also not be used for establishing GSR dispersion patterns which can, be used to obtain information on, e.g., shooting distance, type of gun, type of ammunition, the presence of further objects on the site of the incident, etc. The method described in US20170153180 has some further disadvantages. The examples show emission at a wavelength of about 420 nm, which is in the blue range. Emission at this wavelength makes it not straightforward to distinguish the signal from typical excitation sources for UV light. Additionally, because the excitation source needs to have higher energy, there will be more autofluorescence coming from the background, which will typically emit in the blue light. This will also interfere with the detection of the GSR. It should also be noted that the presence of sulphur atoms in the fluorophore described in this reference will make it impossible to subject a sample that has been treated with this compounds to the EDS analysis which is often used in the detection of GSR. This is because the K alpha of sulphur overlaps almost completely with the M alpha for lead.

[0006] Accordingly, there is need in the art for an improved method for detecting gunshot residue in which at least some of the problems describes above have been solved. In particular, there is need in the art for method for detecting GSR which is flexible, which can be used directly on a crime scene, and which can be used to obtain information on GSR dispersion patterns.

[0007] The present invention aims to provide a method for detecting GSR which solves these and further problems. In particular, the present invention is intended to provide a method that is flexible in that it can be used in a quick prescreen at a crime scene, e.g., to make a first selection of who may have been involved in a shooting incident, but also to support forensic conclusions regarding the type of gun used, the type of ammunition used, and the shooting distance. As compared to existing detection methods there is also a need for a detection method in which GSR can be transferred to a secondary substrate in a manner which is quick and reliable, and which makes for excellent retention of the GSR pattern. There is also a need in the field for a method which allows easy sampling but still allows the drawing of quantitative conclusions. A suitable method for detecting GSR should also be highly selective, i.e. , showing little interference with other components which may be present on a crime scene. Lack of interference with keratinous structures is of particular importance. For use on a crime scene it is advantageous for the detection method to also be effective at low- light conditions.

[0008] The present invention provides a method which solves these problems.

[0009] The invention pertains to a method for detecting gunshot residue comprising the steps of - contacting a solid substrate suspected of containing gunshot residue with a reagent composition comprising a liquid medium and a halide reagent capable of reacting with lead to form a lead halide perovskite, and

[0010] - subjecting the substrate to a light source with a wavelength that is shorter than the emission wavelength of the lead halide perovskite, and detecting the light emittance, wherein the solid substrate is a primary substrate, i.e. , a substrate on which the gunshot residue was deposited as a direct result of the process of the gun being fired or a secondary substrate, i.e., a substrate which is suspected of containing lead-containing gunshot residue because it has been in contact with a primary substrate.

[0011] In the method of the present invention, the lead in the GSR is reacted with a halide reagent to form a lead halide perovskite. The lead perovskite emits light in the visible range when subjected to light with a wavelength that is shorter than the emission wavelength of the lead halide perovskite, e.g., bright green light under ultraviolet (UV) irradiation. This makes lead detection straightforward, even under challenging conditions such as at a crime scene. Furthermore, the test results can be easily documented using conventional photographic means.

[0012] The sensitivity and selectivity of the method have been extensively investigated. It has been found that both false positives or false negatives were highly unlikely. Moreover, it has been shown that this perovskite-based lead test can be at least 1000 times more sensitive compared to state-of-the-art rhodizonate tests. The sensitivity of the claimed method is such that GSR can even be detected on the hands of a shooter or bystander after they have been washed. It has also been found that the test can be carried out without disturbing the deposition pattern of the GSR. In combination with the high sensitivity of the test and its ease of application this makes it possible to derive more information from a crime scene, or derive the same information in a more efficient and reliable manner. Specific advantages of the present invention and further embodiments thereof will become evident from the further specification.

[0013] It is noted that WO2022214430 describes a method for detecting lead using the reaction of lead with halide reagent capable of reacting with lead to form a lead halide perovskite. This reference describes the application of reagent to a wide range of lead-containing substrates, e.g. by swiping. While this reference shows that lead can be identified in lead-containing substrates, it does not recognise that it would be possible to detect specifically GSR, let alone that such detection would be possible in sufficient detail to allow drawing conclusions on forensic parameters such as distribution pattern, particle density, type of gun and ammunition, and shooting distance. In fact, WO2022214430 shows in Example 5 that detection of lead in the presence of other metals such as copper, nickel, or iron leads to a substantial reduction of luminescence intensity. As bullets, and thus GSR, generally contain further metals than lead, this teaches away from the use of the method of this reference in the detection of GSR. An additional surprising feature of the present invention resides in the fact that it has appeared that very small lead-containing particles are particularly susceptible to lead detection by reacting with a halide reagent. The examples in WO2022214430 provide no information on the basis of which this could be expected. Further, the applications illustrated in WO2022214430 focus on determining whether or not lead is present, without paying particular attention to how the lead is distributed. They do not provide a lead to the method described therein being possibly suitable for reliably detecting complicated patterns of lead particles in GSR, or in the ease of transferring GRS patterns to secondary substates for safeguarding and further analysis.

[0014] The method in general

[0015] In the present invention, a solid substrate suspected of containing gunshot residue is contacted with a halide reagent capable of reacting with lead to form a lead halide perovskite.

[0016] In general, perovskites are of the formula ABX3. Lead halide perovskites are of the general formula APbXa, in which X is a halogen selected from F, Cl, Br, and I. Lead halide perovskites of the formula APbXa may be organic or inorganic in nature. For inorganic lead halide perovskites, A will generally be a metal. For organic lead halide perovskites, A will be an organic cation. Examples include metal lead halide perovskites and organoamine lead halide perovskites. Different types of perovskite will be discussed in more detail below.

[0017] It is noted that in the context of the present invention it has been found to be irrelevant whether the lead halide perovskite is of the exact formula APbXa. In general, compounds of the overall formula APbXi.5-4 may generate luminescence. Also, it will be clear to the skilled person that in sample analysis it is not always possible to determine the exact boundary of the perovskite where this formula would apply.

[0018] Lead halide perovskite is of the formula APbXa, in which X is a halogen selected from F, Cl, Br, and I. As the lead is provided by the sample, the halide reagent should provide the other reactants for the perovskite formation. Accordingly, the reagent should provide the halide anion selected from F, Cl, Br, and I. It is preferred for the halide anion to be selected from Cl, Br, and I. The use of Br as anion is often preferred as bromide-containing perovskites provide a green luminescence that is easy to detect, also with the naked eye.

[0019] The use of a combination of different anions may also be attractive as they allow tuning of the luminescence spectrum. For example, a combination of Cl and Br can be used to provide luminescence in the blue region of the visual spectrum while a combination of Br and I can be used to provide luminescence in the red region of the visual spectrum. This may be particularly attractive if it is desired to reduce the effect of autofluorescence. If a combination of two or more halide anions is used, it is generally preferred for each of the anions to be present in an amount of at least 10 mol.% of the total amount of anion to obtain the desired tailoring of the luminescence.

[0020] For example, in one embodiment, the halide ions comprise a combination of 20-90 mol.% Cl in combination with 80-10 mol.% Br, in particular 30-90 mol.% Cl in combination with 70-10 mol.% Br, more in particular 40-90 mol.% Cl in combination with 60-10 mol.% Br. Selecting the ratio in this range will result in luminescence in the blue region of the visual spectrum.

[0021] In another embodiment, the halide ions comprise a combination of 20-90 mol.% I in combination with 50-10 mol.% Br, in particular 60-90 mol.% I in combination with 40-10 mol.% Br. Selecting the ratio in this range will result in luminescence in the red region of the visual spectrum.

[0022] The lead perovskite of the formula APbXa thus contains a monovalent cation A, which is to be provided by the reagent.

[0023] In one embodiment, the cation A is an inorganic metal cation capable of perovskite formation, e.g. cesium (Cs), potassium (K), sodium (Na), germanium (Ge), tin (Sn), rubidium (Rb), or combinations thereof. Within this group, cesium is considered preferred for reasons of performance and availability.

[0024] The lead perovskite of the formula APbXa may also contain a monovalent organoamine cation.

[0025] In one embodiment the organoamine cation is an organoammonium cation of the formula R1 R2R3N+, in which R1, R2, and R3 are selected from hydrogen and 01-010 alkyl, 04-010 aryl, 04-010 alkylaryl, and 04-010 arylalkyl, with at least one of R1 , R2, and R3 being selected from 01-010 alkyl, 04-010 aryl, 04-010 alkylaryl, and 04-010 arylalkyl. In one embodiment at least one of R1 and R2, more in particular both R1 and R2 are hydrogen. If R1 , R2, and R3 are not hydrogen, they are preferably selected from 01-04 alkyl, 06 aryl, and 07-010 alkylaryl. Examples of suitable organoammonium cations include methylammonium, ethylammonium, propylammonium, iso-propylammonium, n- butylammonium, iso-butylammonium, t-butylammonium, dimethylammonium, diethylammonium, benzylammonium, and phenylammonium. Within this group, methylammonium has been found to give good results.

[0026] In one embodiment, the organoamine cation is a cation of the formula R5R6C=NH2+in which R5 and R6 are selected from H, NH2, and C1-C6 alkyl, in particular C1-C4 alkyl, more in particular C1-C2 alkyl, with at least one of R5 and R6 being NH2. Examples of suitable compounds of this formula include formamidinium (R5 is H, R6 is NH2), guanidinium (R5 and R6 are NH2), and acetamidinium (R5 is CH3, R6 is NH2). Within this group, formamidinium is considered preferred.

[0027] In a further embodiment, the organoamine cation is a cyclic onium cation, e.g., a substituted or unsubstituted imidazolium cation, in particular an unsubstituted imidazolium cation.

[0028] In a further embodiment the organoamine cation is a diammonium compound, e.g., a cation of the formula R1 R2N+-A- R1’R2’N+wherein R1 , R2, RT, and R2’ are independently selected from hydrogen, C1-C10 alkyl, C4-C10 aryl, C4-C10 alkylaryl, and C4-C10 arylalkyl and A is C2-C10 alkylene, arylene, alkylarylene, or arylalkylene. In one embodiment R1 , R2, RT, and R2’ are all hydrogen. Where one or more of R1 , R2, R’Tand R2’ are not hydrogen, the preferences given above also apply here. Examples from compounds within this group include ethane-1 ,2-diammonium, propane-1 , 3-diammonium, and 1 ,4-benzene diammonium. In general, the use of halides of cesium, methylammonium, or formamidium is considered preferred at this point in time. Combinations of different types of anions can also be used.

[0029] The provision of the halide anion and the metal and / or organoamine cation can be carried out by providing the corresponding metal halides and / or organoamine halides. It is also possible to provide a source for the halide anion and combine it with a source for the cation. The sample can be contacted sequentially with the cation and the anion in either order. It is preferred, however, for the sample to be contacted simultaneously with the cation and the anion in a single reagent composition.

[0030] In the present invention, the reagent composition is provided in a liquid form. This encompasses solutions, but also suspensions, emulsions, dispersions, etc.

[0031] The reagent composition comprises a liquid medium. The medium may serve as a solvent for the halide reagent, but also as a dispersant in the case that the halide reagent does not fully dissolve. In general, it is preferred for the reagent composition to be a solution of the halide reagent in the medium, as solutions are less susceptible to becoming inhomogeneous during storage.

[0032] The reagent composition can be provided in a single step, as a solution or suspension. It is also possible, however, to provide the reagent composition in multiple steps, e.g., by providing the liquid medium in the form of a wetting liquid while the halide reagent is provided in solid form. This can, e.g., by carried out by wetting a primary substrate and contacting it with a dry carrier that has been provided with a halide reagent. This carrier preparation can be carried out, e.g., by impregnation of a carrier with a liquid medium comprising the halide reagent, followed by drying. It is also possible to subject a dry carrier that has been provided with a halide reagent to a wetting step, and contacting the wetted carrier comprising halide reagent with the primary substrate. The use of carriers and their interaction with primary and secondary substrates will be discussed in more detail below.

[0033] The nature of the liquid medium is not limiting in principle, except that the liquid medium should not react with the reagent in the time frame required to carry out the test. Examples of suitable liquid media include conventional organic solvents such as alcohols (methanol, ethanol, propanol, isopropanol, butanol, pentanol, hexanol, heptanol, octanol, decanol, etc.), aldehydes, and ketones such as acetone, methylethylketone, methylbutylketone, and polar aprotic solvents such as propylene carbonate (PC), dimethylacetamide (DMA) or N-methyl-2- pyrrolidone (NMP). Combinations of solvents may also be used. Isopropanol has been found to be particularly suitable. The method used herein can be applied using compounds and solvents which are acceptable from a health, safety, and environmental aspect, e.g. solvents with a relatively low toxicity.

[0034] Water may also be used as liquid medium. However, as water may interfere with perovskite formation, luminescence may only occur during drying of the sample. Additionally, water may lead to degradation of a perovskite that has been formed. This may make water less preferred, although it can be used under proper conditions. The same applies to other solvents which may interfere with perovskite formation, or which result in degradation of the resulting perovskite. It is within the scope of the skilled person to select a suitable solvent.

[0035] The step of contacting a solid substrate suspected of containing gunshot residue with a reagent composition comprising a liquid medium and a halide reagent capable of reacting with lead to form a lead halide perovskite is often carried out by spraying the reagent composition on the substrate. Spaying is often advantageous because it can be carried out in a controlled manner, and does not affect the pattern in which the GSR has been deposited. In some embodiments, the reagent composition may be applied in other ways. For example, where retention of the GSR pattern is not required, the reagent composition may be applied by wiping. In some embodiments the solid substrate suspected of containing gunshot residue is contacted with a carrier, e.g., a sheet, which has been impregnated with the liquid medium. Suitable carriers are discussed in more detail below. In some embodiments of the present invention the reagent composition comprising a liquid medium and a halide reagent may be present on a carrier. The carrier, liquid medium, and halide reagent may be combined in any sequence. In one embodiment, a carrier containing the reagent composition is obtained by first combining the halide reagent and the liquid medium, and then contacting the carrier with the reagent composition comprising the liquid medium and the halide reagent. This embodiment is generally preferred. In another embodiment, the carrier is first provided with the halide reagent, and the carrier provided with the halide reagent is provided with liquid medium. In a further, but generally less preferred embodiment, the carrier is first provided with the liquid medium, and then with the halide reagent.

[0036] In the method of the invention, the sample is subjected to a light source with a wavelength that is shorter than the emission wavelength of the lead halide perovskite. For example, a light source emitting green light can be used to detect a red emitting MAI-Br lead perovskite. However, in practice it is often convenient to have a light source emitting light outside the visible spectrum. Accordingly, a light source emitting in the UV range is considered preferred. The UV light source preferably emits light with a wavelength in the range of 100-450 nm, in particular in the range of 200-450 nm, more in particular in the range of 300-450 nm, e.g., in the range of 350-420 nm. Where a light source also emits light in the visible spectrum, filters may be applied to filter out the visible light.

[0037] The amount of reagent required will depend on the nature of the sample and the manner in which the reagent is applied. In general, the amount of reagent is not critical, as long as sufficient reagent is applied to obtain a reaction. It may be preferred for the concentration of the halide reagent in the reagent composition to be as high as possible. In one embodiment, the concentration of halide reagent is at least 0.2 mg / ml, more in particular at least 1 mg / ml, in some embodiments at least 2 mg / ml. Of course, the actual concentration will depend on the nature of the reagent and the nature of the liquid medium. As will be evident, the maximum concentration is the saturation concentration.

[0038] The photoluminescence generated by the presence of the lead halide perovskite can be detected with the naked eye or detected though suitable apparatus, e.g., recorded with a camera, analysed with a photoluminescence microscope, or detected with a photodiode. Where the image is recorded with a camera or other apparatus, suitable software can be applied to compensate for background illumination and background fluorescence. It is within the scope of the skilled person to select and apply suitable methods. As will be discussed in more detail below, in various embodiments light emittance from a crime scene sample may be compared with light emittance data generated by samples obtained under known conditions. As will be evident to the skilled person, it is possible to compare emittance data directly, but also by comparing visual images or other data.

[0039] Different detection methods may be applied under different circumstances, which highlights the flexibility of the method according to the invention.

[0040] As the light emission of the lead perovskite may deteriorate over time it is recommended to capture the light emittance using suitable apparatus as directly as possible after formation of the lead perovskite, e.g., within 30 minutes, in particular within 20 minutes, within 10 minutes, or even within 5 minutes. In one embodiment, in view of the often-immediate start of the luminescence, it is preferred that the steps of contacting the sample with the halide reagent and subjecting the sample to UV light, and detecting the light emittance are carried out simultaneously, in other words, that the sample is under UV light when the reagent is provided. In practical operation it may be preferred to switch on the light source before the reagent is applied, to identify the possible presence of luminescent compounds in the sample itself, and to be able to detect any change caused by the addition of the reagent. In some cases, it may be appropriate to contact the substrate with solvent only, in the absence of reagent, to verify that there is no interaction between the solvent and the substate which generates luminescence.

[0041] It may be possible to “refresh” the light emittance generated by the lead perovskite by reapplying the reagent to the substrate.

[0042] The carrier and the secondary substate

[0043] In some embodiments of the present invention, the detection takes place not on the primary substate, i.e. , a substrate on which the gunshot residue was deposited as a direct result of the process of the gun being fired, but rather on a secondary substrate, i.e., a substrate which is suspected of containing lead-containing gunshot residue because it has been in contact with a primary substrate suspected of containing lead-containing gunshot residue. The secondary substate can be obtained by the step of contacting a carrier with the primary substrate suspected of containing lead-containing gunshot residue, followed by removing the carrier from the primary substrate.

[0044] Suitable carrier materials depend on the exact method caried out. In all case, suitable carrier materials are materials which do not show light emittance at the wavelength at which the light emittance by the lead halide perovskite is determined, preferably not at all, and in any case at least not to such an extent that it interferes with the detection method. Where UV light is used as light source, suitable materials do not show emittance under UV light (fluorescence), preferably not at all, and in any case at least not to such an extent that it interferes with the detection method. The carrier should further be inert in that it does not react with the GSR, and stable in that it can be stored without degradation for the time period required for forensic evidence. Suitable requirements with respect to inertness and stability will be evident to the skilled person. Preferably, the carrier is flexible. In one embodiment, the carrier material is porous, so that it can pick up gunshot residue from the primary substrate and can be impregnated with the wetting liquid if so desired. In one embodiment, the carrier is provided with an adhesive to pick up gunshot residue from the primary substrate. It has been found that glass fiber based materials, e.g., glass fiber woven or non-woven materials are particularly suitable for use as carriers in the method of the invention, as they meet the requirements above. Other materials which have been found to be suitable include polymer materials such as polyimide, polyethylene (e.g., LDPE or high DPE), polymethylmethacrylate (PMMA) and nylon. Various textiles and other woven or non-woven materials may also be used, assuming that they meet the requirements as discussed above, either directly, or after having been subjected to a surface treatment to reduce inherent luminescence. The same applies to woven and non-woven materials based on natural fibers, e.g., cellulose-based fibers, such as paper-based materials. Carbon tapes have also been found to be suitable. If so desired, the color of the carrier material may be selected such that the light emittance can be easily detected.

[0045] In embodiments where it is intended to retain the pattern of the gunshot residue or where it is intended to contact the primary surface with a specified surface area of the secondary substrate woven or non-woven sheets, in particular glass fiber sheets have been found to be particularly suitable. It is preferred for the carrier sheet to have a relatively smooth surface structure, to allow better retention of the gunshot residue pattern.

[0046] The transfer process

[0047] In general, the transfer of GSR from the primary substrate to the secondary substrate takes place by contacting the primary substrate with the carrier, and removing the carrier from the primary substrate, therewith generating a secondary substrate. The transfer process can be improved by the application of some pressure. Depending on whether qualitative results are sufficient or whether quantitative results are aimed for, the pressure may or may not be regulated specifically. In general, a suitable pressure will be in the range of 0.1 to 100 MN / m2, As preferred pressures, values in the range of 0.1 to 50 MN / m2may be mentioned, in particular 0.1 to 20 MN / m2, more in particular 0.1 to 10 MN / m2, e.g., in the range of 1-5 MN / m2. Depending on whether it is intended to retain the pattern of the GSR, the carrier may be moved or not moved with respect to the primary substrate. For example, where the method is applied to just detect the present or absence of lead, the carrier may be moved with respect to the primary substrate. Where the method is applied to investigate the pattern or density of the GSR, the carrier should not be moved with respect to the substrate during sampling.

[0048] In general, the time required to effect transfer of the GSR is limited, in the order of seconds to minutes. In general, pressure will be applied for less than 10 minutes, in particular less than 5 minutes, more in particular less than 2 minutes, in some embodiments less than 1 minute, or even less than 30 seconds. As a minimum a time of 20 milliseconds may be mentioned.

[0049] The transfer process may be improved by the use of a wetting liquid during the transfer process. The wetting liquid, also sometimes indicated as transfer agent, may be applied to the primary substrate, to the carrier before application onto the primary substrate, or even on the carrier while it is present on the primary substrate. In general, it is preferred to apply the wetting liquid onto the primary substate before application of the carrier, or on the carrier before application onto the primary substate. Where the wetting liquid is applied onto the primary substrate, this is preferably done by a method which ensures a homogeneous distribution of the wetting liquid on the primary substrate. Application of the liquid by spraying is preferred, but other options are also possible, e.g., the use of a misting chamber. Where the wetting liquid is applied onto the carrier before application thereof onto the primary substrate, it can be carried out by any suitable method, e.g., by spraying, dipping, impregnation or in any other suitable manner.

[0050] The wetting liquid is present to improve the transfer of the GSR from the primary substrate to the carrier, to form a secondary substrate. The nature of the liquid is not limiting in principle, except that it should not interfere with the detection reaction. Examples of suitable liquid media include conventional organic solvents such as alcohols (methanol, ethanol, propanol, isopropanol, butanol, pentanol, hexanol, heptanol, octanol, decanol, etc.), aldehydes, and ketones such as acetone, methylethyl ketone, methylbutyl ketone, and polar aprotic solvents such as propylene carbonate (PC), dimethylacetamide (DMA) or N-methyl-2-pyrrolidone (NMP). Combinations of solvents may also be used. Isopropanol has been found to be particularly suitable. Water may also be used as wetting liquid. However, water may interfere with perovskite formation. Therefore, if water is used as wetting liquid, the sample is preferably dried before application of the reagent composition. Additionally, water may lead to degradation of a perovskite that has been formed. This may make water less preferred, although it can be used under proper conditions. The same applies to other solvents which may interfere with perovskite formation, or which result in degradation of the resulting perovskite. It is within the scope of the skilled person to select a suitable wetting liquid.

[0051] To limit the number of different components in the system, it may be attractive for the wetting liquid to be the same as the liquid medium in the halide reagent, e.g., isopropanol.

[0052] The wetting liquid may contain an acid to help transfer of the lead from the primary substrate onto the carrier. The nature and amount of the acid is not critical as long as the acid dissolves in the wetting liquid, does not affect the primary or secondary substrate, and does not interfere with perovskite formation. Suitable acid concentrations in the wetting liquid include a range of 0.01-5 wt.%, depending on the nature of the acid and of the wetting liquid.

[0053] Depending on the nature of the substrate and the transfer method, transfer of the GSR from the primary substrate can be carried out before or after perovskite formation, i.e. , before or after the provision of the halide reagent. Where it is desired to draw conclusions on the presence of GSR or its distribution on the crime scene and at the same time conserve the information in the form of a “copy” onto a carrier, it may be attractive for the wetting liquid to additionally contain a halide reagent capable of reacting with lead to form a lead halide perovskite. The reagent can be applied onto the primary substrate or onto the carrier, and the detection of the light emittance can be carried out on the primary substrate or on the secondary substrate that is obtained by contacting the carrier with the primary substrate in the presence of the reagent.

[0054] Quick crime scene screening

[0055] It has been found that the method of the present invention is particularly attractive for quick crime scene screening, e.g. to immediately determine whether any subjects at the crime scene have GSR on their person, whether it be on their hands or other body parts, clothes or shoes. This applies to alleged shooters, but also to victims and bystanders. In one embodiment, the substrate suspected of containing lead-containing gunshot residue is contacted with a reagent composition comprising a liquid medium and a halide reagent and subjecting the substrate to light with a wavelength that is shorter than the emission wavelength of the lead halide perovskite, resulting in the formation of light emittance, and detecting said light emittance, wherein the steps of applying the reagent composition and providing the light source are carried out within 5 minutes from each other, in particular within two minutes from each other, more in particular simultaneously.

[0056] It has been found, as also illustrated in the examples, that the method of the present invention is very suitable for detecting GSR also after a subject has washed their hands or their clothes.

[0057] An interesting embodiment here is to test the hands of a victim of a shooting incident for GSR. This will help to make clear whether or not the victim has also fired a gun.

[0058] If it is not desired to apply the reagent composition comprising a liquid medium and a halide reagent directly onto the subject, it is also possible to transfer possible GSR from the skin, clothes, shoes, or other property using a carrier as described herein, and detecting the GSR on the secondary substrate thus obtained.

[0059] Quantifying amounts of GSR

[0060] In one embodiment, the present invention pertains to a method for quantifying the amount of GSR present on a substrate. This makes it possible to gain further insights into what has happened on a crime scene, and, e.g., to distinguish between a shooter and bystanders. There are various ways to do this.

[0061] In one embodiment, the method according to the invention comprises the steps of

[0062] - contacting a predetermined area of a primary substrate suspected of containing lead- containing gunshot residue with a carrier, to transfer gunshot residue from a predetermined surface area of the primary substrate to the carrier, thus forming a secondary substrate,

[0063] - contacting the secondary substrate with the reagent composition comprising a liquid medium and a halide reagent capable of reacting with lead to form a lead halide perovskite,

[0064] - subjecting the secondary substrate to light with a wavelength that is shorter than the emission wavelength of the lead halide perovskite, resulting in the formation of light emittance, and detecting said light emittance.

[0065] In this embodiment a predetermined surface area of a primary substrate is contacted with a carrier. The idea is that the carrier picks up the GSR from the predetermined surface area of a primary substrate, and that detection of the GSR on the secondary substrate allows the drawing of conclusions on the GSR that was present on the predetermined area of primary substrate. In particular, by determining the intensity of the light emittance on the secondary substrate, the amount of gunshot reside can be determined, and compared with the intensity of the light emittance of other samples from the same crime scene, or with baseline data obtained under controlled conditions.

[0066] In another embodiment, the method according to the invention comprises the steps of

[0067] - contacting a primary substrate suspected of containing lead-containing gunshot residue with a carrier with a predetermined surface area, to transfer gunshot residue from a predetermined surface area of the primary substrate to the predetermined surface area of the carrier, thus forming a secondary substrate,

[0068] - contacting the secondary substrate with the reagent composition comprising a liquid medium and a halide reagent capable of reacting with lead to form a lead halide perovskite,

[0069] - subjecting the secondary substrate to light with a wavelength that is shorter than the emission wavelength of the lead halide perovskite, resulting in the formation of light emittance, and detecting said light emittance.

[0070] In this method, a carrier is used with a predetermined surface area, which is contacted with the primary substrate. By determining the intensity of the light emittance on the secondary substrate, the amount of gunshot reside can be determined, and compared with the intensity of the light emittance of other samples from the same crime scene, or with baseline data obtained under controlled conditions.

[0071] In one embodiment, the carrier with a predetermined surface area is contacted once with the primary substrate to transfer gunshot residue from a predetermined surface area of the primary substrate to the predetermined surface area of the carrier, thus forming the secondary substrate. It is, however, also possible to repeatedly apply the predetermined surface area of the carrier to the primary substate to collect gunshot residue from a number of locations on the primary substrate. This makes it possible to collect gunshot residue from a number of locations in a single sample. In one embodiment, the predetermined surface area of the carrier is contacted with a number of locations on the primary substrate which are close together, e.g., on the hand of a potential shooter or bystander. If it is desired to draw conclusions on the total amount of GSR care should be taken in sampling to ensure that the sample locations do not overlap.

[0072] When a single carrier is used to collect GSR from a number of locations care should be taken to ensure that the carrier is not oversaturated with GSR, as this may influence the total amount of GSR collected. Pattern detection and analysis

[0073] In one embodiment, the method of the present invention is applied to collect information from the pattern in which the GSR is deposited. In this case, the invention is directed to a method for detecting and analysing gunshot residue patterns comprising the steps of

[0074] - contacting a solid substrate suspected of containing lead-containing gunshot residue with a reagent composition comprising a liquid medium and a halide reagent capable of reacting with lead to form a lead halide perovskite, and

[0075] - subjecting the substrate to light with a wavelength that is shorter than the emission wavelength of the lead halide perovskite, resulting in the formation of a light emittance pattern, and detecting said light emittance pattern.

[0076] The light emittance pattern can be used to draw conclusions on what happened at the crime scene. For example, the light emittance pattern can show the distribution of the gunshot residue, providing information on, e.g., shooting distance and shooting angle. By comparing the light emittance pattern with one or more baseline light emittance patterns generated by known gunshot generating events and identifying similarities and dissimilarities between the light emittance pattern and the baseline pattern, information can be generated with respect to one or more of the distance between the detection location of the gunshot residue and the gun, the type of gun, and the type of ammunition. It has been found that the method according to the invention is so powerful that it is possible to detect the patterns in the gunshot residue which derive from the grooves in the gun barrel. This makes it possible to determine whether or not a particular type of gun was responsible for generating a particular GSR deposit.

[0077] Thus, in one embodiment, the method comprises the steps of comparing the light emittance pattern, or a visual image thereof, with one or more baseline light emittance patterns, or visual images thereof, generated by known gunshot generating events, and identifying similarities and dissimilarities between the light emittance pattern or image and the one or more baseline patterns or images. The one or more baseline light emittance patterns, or visual images thereof, may, e.g., have been generated by shooting guns of known type with known ammunition at a known substrate over a known distance, allowing the comparison of the light emittance pattern, or visual images thereof, with the one or more baseline pattern or visual images thereof, to generate information with respect to one or more of the distance between the detection location of the gunshot residue and the gun, the type of gun, and the type of ammunition. Testing kits

[0078] The invention pertains to test kits suitable for use in the method of the invention. Such test kits may comprise instructions describing how the test kit is to be used in the detection of gunshot residue and one or more of the following:

[0079] - reagent composition comprising a liquid medium and a halide reagent capable of reacting with lead to form a lead halide perovskite

[0080] - wetting liquid

[0081] - carrier material suitable to effect transfer of GSR to form a secondary substrate

[0082] - application means for the reagent composition, in particular in the form of a spray

[0083] - application means for the wetting liquid

[0084] - a light source, e.g. a UV light source

[0085] - detection or recording apparatus, e.g., a camera or photodiode

[0086] - optical filters, e.g., short pass filters for reducing the visible light from the UV light source or, if a camera is used, long pass filters on the camera for reducing the UV light reflecting from the sample, or band filters (i.e. a combination of short pass filters and long pass filters), or optical filters or glasses for the observer, e.g., orange filters or glasses which block blue light to improve the visibility of green light,

[0087] - material to protect the tester, e.g., gloves or safety glasses with UV protection

[0088] - a lead-containing control sample, which can be used to verify reagent quality,

[0089] - a sample collection unit, wherein multiple samples can be collected, for simultaneous or separate contacting with the reagent, directly, or at a later point in time

[0090] - a solvent blank, i.e., solvent not containing reagent, to verify whether there is any interaction between the solvent and the substrate which generates luminescence.

[0091] The test kit will generally comprise instructions describing how the test kit is to be used in the detection of gunshot residue, reagent composition comprising a liquid medium and a halide reagent capable of reacting with lead to form a lead halide perovskite, and optionally one or more of the cited further components.

[0092] The specifics as regards the various elements of the testing kit as applied above also apply here.

[0093] As will be evident to the skilled person, different embodiments of the present invention can be combined unless they are mutually exclusive. When amounts, concentrations, dimensions, and other parameters are expressed in the form of a range, a preferable range, an upper limit value, a lower limit value, or preferable upper and lower limit values, it should be understood that any ranges obtainable by combining any upper limit or preferable value with any lower limit or preferable value are also specifically disclosed, irrespective of whether the obtained ranges are clearly mentioned in the context.

[0094] It must be noted that as used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural references unless the context clearly dictates otherwise.

[0095] Furthermore, the terms “a” (or “an”), “one or more” and “at least one” can be used interchangeably herein.

[0096] The invention will be illustrated by the following examples, without being limited thereto or thereby.

[0097] The invention, specific embodiments thereof, and associated advantages will be discussed below. Reference will be made to the following figures:

[0098] Figure 1 shows photoluminescent lead detection of GSR.

[0099] Figure 2 shows photoluminescent lead detection upon transfer of the GSR pattern to a secondary substrate.

[0100] Figure 3 shows shooting distance analysis using photoluminescent lead detection.

[0101] Figure 4 shows shooter identification using photoluminescent lead detection.

[0102] Figure 5 shows bystander identification using photoluminescent lead detection.

[0103] Figure 6 shows photoluminescent lead detection upon transferring a GSR pattern from clothing or shoe sole of a bystander to a glass fiber cloth

[0104] Figure 7 shows photoluminescent lead detection upon transferring a GSR pattern from hands using a SEM stub with carbon tape

[0105] Examples

[0106] Example 1: use of the photoluminescent lead test in GSR analysis

[0107] In the following experiments, the GSR was visualised with UV light (365 nm). In the following, PL stands for photoluminescence. PL-Pb reagent stands for the reagent applied in the detection of lead (Pb) using photoluminescence (PL). Figure 1A shows a schematic representation of the test set-up. A PL measurement setup was used consisting of a box with a door covered on the inside with aluminium foil. The UV excitation source consisting of 15 2W UV LEDs was mounted on the top of the box with an inward angle of 10 degrees, 25 cm above the sample. The UV ring light was powered by a Siglent SPD1168X power supply running at 4.6 V and 7 amp. An opening was created in the top of the box for a Canon 800D camera equipped with a Sigma 17-70mm f / 2.8-4.5 DC Macro lens positioned 30 cm above the sample.

[0108] The PL-Pb reagent was applied by spraying it approximately 20 cm above the sample inside the UV illumination setup using an atomiser spray to obtain a mist resulting in a uniform thin film of PL-Pb reagent. Seven sprays per sample were applied in back-and-forth motion to allow even distribution of the reagent. After spraying, the sample was illuminated, visualized, and photographed.

[0109] The PL-Pb reagent was sourced from Lumetallix B.V. in Amsterdam, the Netherlands, and comprises isopropanol as liquid medium and methyl ammonium bromide as halide reagent capable of reacting with lead to form a lead halide perovskite. It has been found that this reagent produces enduring and clearly visible bright green PL for optimal forensic work, without interference with other components in the GSR, e.g., combustion products.

[0110] Figure 1B shows the deposition of GSR by firing a Walther P99Q NL with standard 9 mm full metal jacket bullets, upon a bleached, fluorescent cotton cloth placed at 5 cm distance.

[0111] Figure 1C reveals a well-defined bright green luminescent pattern on the cloth, which is clearly visible to the naked eye.

[0112] Figure 1 D shows, after approximately 30 minutes of applying the reagent in the absence of UV light, a persistent yellowing of the white cotton. This shows that besides as a PL-Pb reagent the PL-Pb reagent can also be used as a persistent colorimetric reagent.

[0113] Thus, visualization of GSR was successful with bright PL.

[0114] Example 2: transfer of GSR pattern to a secondary substrate

[0115] A transfer method was developed for indirect PL-Pb testing and used in the following experiment. The deposited GSR pattern was transferred by spraying the original substrate with the transfer agent using an atomizer spray, positioning the secondary substrate on top, and applying 1.6- 106N / m2compression using a hydraulic press. Once detached, the GSR pattern on the secondary substrate was visualised in the same way as example 1. Figure 2A shows a schematic visualisation of the optimised transfer method. The secondary substrate was a glass fiber cloth. This cloth was non-fluorescent, strongly adsorbs lead, and wettable for the transfer reagent, thus maximizing transfer while limiting undesired smearing for high transfer fidelity. Moreover, the surface of the cloth had limited structural features that can disturb the transfer.

[0116] The transfer agent was a solution of 0.25% benzoic acid in isopropanol (I PA). This transfer agents dries fast, causing minimal smearing, and stabilizes PL for optimal visualization of the transferred GSR.

[0117] For the following experiment, GSR was deposited by firing a Glock19 Gen5 upon a cotton cloth placed at 5 cm distance. Figure 2B shows the original shooting cloth created by discharging a Glock19 Gen5. Figures 20 and 2D show enlargements of Figure 2B. The GSR was transferred using the transfer method described above. The secondary substrate thus obtained was contacted with reagent and subjected to UV light in the manner described in example 1. The patters are in Figures 2E, 2F, and 2G, at the same enlargements as in Figures 2B, 20, and 2D, respectively.

[0118] Comparing the GSR pattern of the original cloth with the pattern transferred onto the secondary substrate, thus figure 2B with 2E, 20 with 2F, and 2D with 2G, shows that the microscopic pattern is well-preserved. Around the bullet entry hole, a polygonal pattern was found, which matches the hexagonal rifling of the pistol. Closer inspection of the secondary substrate revealed that even the micrometer features of the fiber structure of the original substrate can be resolved, which emphasizes the achievable fidelity with the method of the present invention.

[0119] Transfers for rhodizonate testing as currently used in forensic detection of gunshot residue are time-consuming or require addition of heat. In addition rhodizonate testing requires long pressing times (ca. 2 minutes). In contrast, the present invention provides a method which is fast due to not requiring a drying step and due to the fact that pressing time may be short. This may help to make the forensic workflow more time efficient. Additionally, the method of the present invention makes it possible to analyse GSR in great detail.

[0120] Example 3: Shooting distance analysis with photoluminescent lead test

[0121] To ascertain whether the sensitivity and fidelity of PL-Pb analysis can be exploited for determining shooting distance estimates. The first step for performing a shooting distance analysis is typically the measurement of a shooting distance series by shooting a firearm of interest on a substrate at different distances. This may also be indicated as providing a baseline pattern. Figure 3A shows a schematic visualisation of the shooting distance analysis.

[0122] The following experiment follows this procedure. A multiple shooting distance series ranging from 0 to 200 cm shooting distance (d) was created using a Glock 19 Gen5 pistol with 9 mm full metal jacket bullets. The resulting GSR patterns were transferred to glass fiber cloths following the transfer method described in example 2. The GSR pattern on the secondary substrate was visualised in the same way as in example 1.

[0123] Figure 3B at d = 0 cm shows a tightly clustered GSR pattern. Figure 30 at d = 5 cm shows a cluster spread out in a polygonal pattern. Figure 3D at d =10 cm shows a circular rippling pattern that is consistent with infrasonic compression waves from the muzzle blast. Figure 3E at d = 25 cm shows a pattern corresponding to the combustion plume. Beyond d = 50 cm, this pattern is not observable suggesting that the combustion plume is not reaching the substrate anymore, and we see the appearance of a speckling pattern in addition to a clear bullet wipe at the entry hole. Surprisingly, figure 3F at d = 200 cm shows a clearly visible speckling pattern and bullet wipe.

[0124] Thus, distance dependent PL-Pb patterns are in line with traditional shooting distance estimations, for example using rhodizonate, but give a more precise and faster result. To test the reproducibility, the shooting series were performed three times and showed similar pattern features at the same distances. Thus, this shooting distance analysis gives reproducible results.

[0125] Example 4: Shooter identification using the photoluminescent lead test

[0126] Typically, washing hands makes GSR detection very difficult because GSR particles are often undetectable with EDS after a single wash. Despite these complications, the ability to detect GSR can be relevant for forensic studies as suspects may try to tamper, conceal, or eliminate evidence. To determine if the sensitivity of PL-Pb is sufficient to detect GSR after different washing protocols.

[0127] For this, the professional shooter was asked to wash his hands thoroughly using water and soap and to dry his hands using clean disposable wipes. A PL-Pb reagent comprising isopropanol and methyl ammonium bromide was applied directly to the hands of the professional shooter using a spray bottle. Illumination occurred via UV flashlight. Figure 4A shows a strong PL signal after the shooter has washed his hands once.

[0128] The shooter was requested to wash his hands five times repeatedly using soap and a scrubber. The PL-Pb reagent was applied directly to his hands using a spray bottle. Illumination occurred via UV flashlight. Figure 4B still shows PL signal and the shooter was unable to acquire a negative response using our test.

[0129] Example 5: Sensitivity of photoluminescent lead test in the identification of bystanders

[0130] In view of the sensitivity shown in experiment 4, tests were performed on the hands of bystanders present in a shooting range who were standing at 2 meters distance during the firing of 10 shots. The PL-Pb reagent was applied directly to the hands of a bystander using a spray bottle. Illumination occurred via UV flashlight. Before shooting, the hands of the bystanders tested negative. Figure 5A shows that after the shooter fires the pistol, the hands of the bystanders emit clearly visible PL.

[0131] Figure 5B shows that casually washing of the hands of the bystanders and re-testing still yields a moderately heterogeneous PL signal.

[0132] Figure 5C and figure 5D show that even after extensive washing the hands, PL signal was detected focused on selected areas such as the fingernails and creases on the backside of fingers.

[0133] Thus, even after extensive washing of the bystander’s hands, PL is still detected. Thus, GSR is surprisingly difficult to remove — even after thorough washing — and, because of the nanogram sensitivity of PL-Pb of the invention, surprisingly simple to detect.

[0134] Example 6: Photoluminescent lead test upon transferring GSR pattern from the clothing and shoe sole of a bystander

[0135] In one experiment GSR was transferred by wiping a dry glass fiber cloth over the clothing of a bystander present in a shooting range was standing at 2 meters distance during the firing of 10 shots. In another experiment the bystander stepped on a glass fiber cloth prewetted with isopropanol, resulting in transfer of the GSR to the glass fiber cloth.

[0136] The GSR pattern on the secondary substrates was visualised in the same way as in example 1. Figure 6A shows bright PL upon wiping the clothing of a bystander with a dry glass fiber cloth.

[0137] Figure 6B shows bright PL upon transferring the GSR pattern on the shoe sole of a bystander to a isopropanol prewetted glass fiber cloth.

[0138] Thus, GSR is detectable on shooters and bystanders by swiping hands, shoes, clothing, or other items on a crime scene (e.g. steering wheels of cars, pockets in jackets etc.) on a glass fiber cloth and perform PL-Pb testing. Although spatial location of GSR may be lost, the advantage of this indirect testing method is that potential irritation or discoloration by the reagent can be avoided. Moreover, indirect testing limits potential interference with backgrounds (e.g. sweaty hands, fluorescent clothing) and other forensic methods, and GSR can be accumulated to achieve an even lower detection threshold.

[0139] Example 7: Photoluminescent lead detection upon transferring GSR pattern from hands using SEM stub with carbon tape

[0140] To assess if PL-Pb is also compatible with well-established EDS analysis (Energy-dispersive X-ray spectroscopy), the hand of the shooter was stubbed with a carbon tape used for EDS analysis. The stub was pressed firmly against the skin 25 times in the area between the index finger and thumb.

[0141] Figure 7A shows some dust and dead skin that was collected on the carbon tape of the stub.

[0142] Figure 7B shows minor autofluorescence resulting from dust being collected on the stub.

[0143] Afterwards, the PL-Pb reagent was directly applied to the stub and illuminated using the setup of from example 1. Figure 70 shows a bright PL signal after application of the PL-Pb reagent on the stub.

[0144] Thus, carbon tape used for EDS analysis can be tested with the method according to the invention. As a result, PL-Pb can be used as a valuable pre-screening technigue for detecting the presence of lead in GSR before EDS is used to measure the specific fingerprint elements characteristic for GSR.

Claims

CLAIMS1 . Method for detecting gunshot residue comprising the steps of- contacting a solid substrate suspected of containing gunshot residue with a reagent composition comprising a liquid medium and a halide reagent capable of reacting with lead to form a lead halide perovskite, and- subjecting the substrate to a light source with a wavelength that is shorter than the emission wavelength of the lead halide perovskite, and detecting the light emittance, wherein the solid substrate is a primary substrate, i.e. , a substrate on which the gunshot residue was deposited as a direct result of the process of the gun being fired or a secondary substrate,1.e., a substrate which is suspected of containing lead-containing gunshot residue because it has been in contact with a primary substrate.

2. Method according to claim 1 , wherein the secondary substrate is obtained by the step of contacting a carrier with the primary substrate suspected of containing lead-containing gunshot residue, followed by removing the carrier from the primary substrate.

3. Method according to claim 2, wherein the step of contacting a carrier with the primary substrate suspected of containing lead-containing gunshot residue is carried out in the presence of a wetting liquid.

4. Method according to claim 3, wherein the wetting liquid comprises acid in a liquid medium.

5. Method according to any one of claims 2-4, wherein the carrier is a glass-fiber-based material.

6. Method according to any one of the claims 2-5, wherein the step of contacting the carrier with the primary substrate suspected of containing lead-containing gunshot residue takes place at a pressure in the range of 0.1 to 100 MN / m2for a time of less than 10 minutes, in particular less than 5 minutes, more in particular less than 2 minutes, in some embodiments less than 1 minute, or even less than 30 seconds.

7. Method according to any one of claims 3-4, wherein the wetting liquid additionally comprises a halide reagent.

8. Method according to any one of the preceding claims, wherein the steps of applying the reagent composition and providing the light source are carried out within 5 minutes from each other, in particular within two minutes from each other, more in particular simultaneously.

9. Method according to any one of the preceding claims, which is a method for quantifying the amount of gunshot residue present on a substrate, the method comprising the steps of- contacting a predetermined area of a primary substrate suspected of containing lead- containing gunshot residue with a carrier to transfer gunshot residue from a predetermined surface area of the primary substrate to the carrier thus forming a secondary substrate,- contacting the secondary substrate with the reagent composition comprising a liquid medium and a halide reagent capable of reacting with lead to form a lead halide perovskite,- subjecting the secondary substrate to light with a wavelength that is shorter than the emission wavelength of the lead halide perovskite, resulting in the formation of light emittance, and detecting said light emittance.

10. Method according to any one of claims 1 to 8, which is a method for quantifying the amount of gunshot residue present on a substrate, the method comprising the steps of- contacting a primary substrate suspected of containing lead-containing gunshot residue with a carrier with a predetermined surface area, to transfer gunshot residue from a predetermined surface area of the primary substrate to the predetermined surface area of the carrier, thus forming a secondary substrate,- contacting the secondary substrate with the reagent composition comprising a liquid medium and a halide reagent capable of reacting with lead to form a lead halide perovskite,- subjecting the secondary substrate to light with a wavelength that is shorter than the emission wavelength of the lead halide perovskite, resulting in the formation of light emittance, and detecting said light emittance.

11. Method according to any one of claims 1 to 8, which is a method for detecting and analyzing gunshot residue patterns comprising the steps of- contacting a solid substrate suspected of containing lead-containing gunshot residue with a reagent composition comprising a liquid medium and a halide reagent capable of reacting with lead to form a lead halide perovskite, and- subjecting the substrate to light with a wavelength that is shorter than the emission wavelength of the lead halide perovskite, resulting in the formation of a light emittance pattern, and detecting said light emittance pattern.

12. Method according to claim 11, comprising the steps of comparing the light emittance pattern, or a visual image thereof, with one or more baseline light emittance patterns, or visual images thereof, generated by known gunshot generating events, and identifying similarities and dissimilarities between the light emittance pattern or image and the one or more baseline patterns or images.

13. Method according to claim 12, wherein the one or more baseline light emittance patterns, or visual images thereof, have been generated by shooting guns of known type with known ammunition at a known substrate over a known distance, allowing the comparison of the light emittance pattern, or visual images thereof, with the one or more baseline pattern or visual images thereof, to generate information with respect to one or more of the distance between the detection location of the gunshot residue and the gun, the type of gun, and the type of ammunition.

14. Method according to any one of the preceding claims, wherein the primary substrate is selected from- skin, clothes, shoes or property of a person suspected from having fired a gun, of a person who has been shot with a gun, or of a person in the vicinity of whom a gun has been fired,- locations in the vicinity of where a gun has been fired, or where a gunshot has hit.

15. Test kit for use in the method according to any one of the preceding claims, the test kit comprising instructions describing how the test kit is to be used in the detection of gunshot residue, a - reagent composition comprising a liquid medium and a halide reagent capable of reacting with lead to form a lead halide perovskite, and optionally one or more of the following:- wetting liquid- carrier material suitable to effect transfer of gunshot residue to form a secondary substrate- application means for the reagent composition, in particular in the form of a spray- application means for the wetting liquid- a light source, e.g. a UV light source- detection or recording apparatus, e.g., a camera or photodiode- optical filters, e.g., short pass filters for reducing the visible light from the UV light source or, if a camera is used, long pass filters on the camera for reducing the UV light reflecting from the sample, or band filters (i.e. a combination of short pass filters and long pass filters), or optical filters or glasses for the observer, e.g., orange filters or glasses which block blue light to improve the visibility of green light,- material to protect the tester, e.g., gloves or safety glasses with UV protection- a lead-containing control sample, which can be used to verify reagent quality,- a sample collection unit, wherein multiple samples can be collected, for simultaneous or separate contacting with the reagent, directly, or at a later point in time - a solvent blank, i.e., solvent not containing reagent, to verify whether there is any interaction between the solvent and the substrate which generates luminescence.

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