Representation of the three-step study workflow. The workflow includes (A) sample collection of four samples from their personal phones and eight samples from each individual’s right hand. (B) The samples are then analyzed using LC-MS/MS to characterize the chemical composition of hands and phones. (C) Data interpretation involves a statistical pipeline to compare and correlate phone and hand samples. Integrative computational methods were used for chemical characterization of hand and phone molecules, spatial mapping to display the localization of molecules, and hierarchical clustering to provide lifestyle information.

Comparison of molecular profiles between phones and hands of individuals. Bray–Curtis distances over all metabolites were measured from collected LC-MS data to compare (A) phone samples, (B) hand samples separately, and (C) phone and hand samples combined, within the same individual (blue) and between different individuals (red). P values were calculated using 1,000 random permutations.

Chemical uniqueness and relationship between phone and hand samples. Random forest classifier was used to predict the chemical uniqueness of (A) phone samples collected from 39 persons on time 1 and (B) phone samples collected 4 mo later (time 2) from 10 individuals. Random forest models were also constructed to predict (C) hands collected on time 1 and (D) time 2. Models generated from hand samples (C) time 1 and (D) time 2 were used to predict, either phone samples together collected on (E) time 1 and (F) time 2, respectively, then distinctly from (G and H) the back of phones and (I and J) the front of phones. Random forest prediction accuracies are as follows: (A) 88%, (B) 94%, (C) 99%, (D) 100%, (E) 51%, (F) 55%, (G) 69%, (H) 85%, (I) 33%, and (J) 25%. Color scale represents the percentage of samples, and the accuracy is calculated as the percentage of all samples that are correctly classified to each individual. The diagonal line represents perfect prediction.

Representation of the number of chemical features detected on phones and hands of 39 individuals. (A–D) Number of chemical features in each sample was calculated from LC-MS data using the OpenMS pipeline for features extraction (), and then mapped using 2D models of phone and hand to represent the number of features detected at each site using a color scale (red, highest number of features; blue, lowest number of features). A significantly higher number of chemicals were detected on the back of phones than on the front (P < 0.0005, based on 10,000 random permutations of the number of metabolites per sample). (A) Individuals 1–10, (B) individuals 11–20, (C) individuals 21–30, and (D) individuals 31–39. E represents a correlation graph between the number of features detected on hands and those detected on phones. The number of molecular features detected at each collection site were summed for each hand and phone of every individual.

Representation of number of chemical features detected on phones and hands of 39 individuals. A–C were generated from LC-MS/MS clusters provided by the molecular network represented in , gnps.ucsd.edu/ProteoSAFe/status.jsp?task=eea01f9ec9ea44bc80d76de30da67be4, ftp://massive.ucsd.edu/MSV000078993. (A) Venn diagram representing the number of shared nodes (5,452 out of 10,383; ∼53%) between all hands (brown) and phones (blue), and unique hand (4,376 out of 10,383; ∼42%) and phone nodes (555 out of 10,383; ∼5%). The frequency of molecules found on (B) phones and (C) hands was calculated by counting in how many volunteers each MS/MS cluster from the network was detected (; gnps.ucsd.edu/ProteoSAFe/status.jsp?task=eea01f9ec9ea44bc80d76de30da67be4).

Molecular network to highlight unique chemicals from hand and phone of each person. Molecular network was generated from LC-MS/MS data collected from hands and phones of 39 individuals, using a cosine threshold of 0.65. Networking parameters included the following: precursor m/z tolerance of 1 Da, fragment mass tolerance of 0.5 Da, minimum matched fragments ions 4 (see details in , ). The network was exported and displayed in Cytoscape and resulted in a total of 10,383 nodes, representing consensus of at least three MS/MS spectra. A color and size (bigger size) coding was used in Cytoscape to highlight the unique nodes that match between a hand and a phone of a same person. Every color is specific to each person represented in this network. Note that only matched MS/MS spectra between hands and phones were represented in this figure; nodes that are specific to hands or phones only were also present, as well as shared nodes between several persons. The molecular network is accessible here: gnps.ucsd.edu/ProteoSAFe/status.jsp?task=eea01f9ec9ea44bc80d76de30da67be4, ftp://massive.ucsd.edu/MSV000078993). A–G represent subnetworks that were enlarged and highlighted in .

Molecular networking to characterize and match lifestyle chemistries from hands and phones of individuals. The full network is shown in for dataset ftp://massive.ucsd.edu/MSV000078993 and ftp://massive.ucsd.edu/MSV000078832. Each node, representing a minimum of three identical MS/MS spectra, corresponds to a consensus MS/MS spectra. An edge represents the similarity between MS/MS spectra. The network nodes were annotated with colors. Each color represents unique molecular features matched between hand and phone of the same individual. Single nodes represent very unique features found in hand and phone of an individual that do not display structural similarities with any other molecule in the network. Representative lifestyle molecular annotations include molecules from hygiene/beauty products, diet, and medicines such as the following: (A) skin inflammation treatment clobetasol propionate, (B) trihydropalmitic acid, (C) trehalose fatty acids, (D) hair loss treatment minoxidil, (E) antifungal medication ketoconazole, (F) sinensetin flavonoid found in citrus, and (G) antidepressant medication (citalopram) and its metabolite (citalopram N-oxide). Green circles highlight compounds that are associated with the chemical structures shown in the figure.

ESI-Q-TOF MS/MS fragmentation of clobetasol propionate, trihydroxy palmitic acid, trehalose fatty acids, minoxidil, tetrahydrozoline, ketoconazole, and sinensetin. (A) Database match to clobetasol propionate based on GNPS database. ESI-Q-TOF MS/MS of m/z 467.199, retention time (RT) of 5.6 min in hand (Upper) and phone (Middle) and from GNPS database (Lower) of individual 9. Major fragment of 373.16 ion results from the consecutive loss of hydroxyl and chloroacetyl groups, whereas 355.15 fragment results from the loss of fluorine, hydroxyl, and chloroacetyl groups together; similarly, fragments of 375.15 and 357.14 ions resulted from the loss of hydroxyl, propionate groups and fluorine, hydroxyl, and propionate, respectively. Identification is based on MS/MS fragmentation, GNPS database interrogation, and volunteer’s lifestyle. (B) ESI-Q-TOF MS/MS of m/z 305.233, RT of 3.7 min in hand and phone of individual 9, and from METLIN database. Dominant fragment ions m/z 269, m/z 251, and m/z 233 result from the loss of hydroxyl groups. Identification is based on MS/MS fragmentation and METLIN database interrogation. ESI-Q-TOF MS/MS fragmentation of (C) α,α′-trehalose 6-palmitate [M+Na]⁺ m/z 603.333, RT of 6.0 min and (D) its analog [M+Na]⁺ m/z 631.367, RT of 6.6 min (delta m/z of 28.034 corresponding to a C₂H₄) in hand (Upper) and phone (Lower) of volunteer 38. A loss of m/z 162 characteristic of a single sugar moiety was observed in the fragmentation pattern. This induces the release of the fatty acid chain linked to another sugar moiety (m/z 441.282 for C and m/z 469.312 for D). Database match to α,α′-trehalose 6-palmitate (molecule used as pigment dispersant in cosmetics) based on METLIN database. Identification is based on MS/MS fragmentation, METLIN database interrogation, and the lifestyle of volunteer 38, who is a female who uses makeup. ESI-Q-TOF MS/MS fragmentation of (E) minoxidil (hair regrowth treatment) m/z 210.135, RT of 2.5 min in hand (Upper), phone (Middle) of volunteer 2 and in GNPS library (Lower). The cleavage of the primary amine group yields to the dominant fragment ion m/z 193, and the loss of hydroxyl group releases the fragment ion m/z 178. m/z 164.08 fragment resulted from the cleavage of a pyrimidine ring with a consecutive loss of amine and n-oxide groups. (F) Database match to tetrahydrozoline (active ingredient of eye drop) from NIST database. Shown is ESI-Q-TOF MS/MS fragmentation of m/z 201.139, RT of 2.5 min in hand (Upper), phone (Middle) of volunteer 10 and from NIST database (Lower). The loss of imidazole group yield to the fragment ion with m/z 131. Identifications are based on MS/MS fragmentation, GNPS and NIST databases, and validation of using a hair regrowth treatment by volunteer 2 and eye drop by volunteer 10. ESI-Q-TOF MS/MS fragmentation of (G) ketoconazole (antifungal medication) m/z 531.154, RT of 4.2 min in hand (Upper), phone (Middle) of individual 16, and in METLIN database (Lower). Fragment ion with m/z 489.143 results from the loss of acetyl group, and then the cleavage in the ether group releases fragment ion with m/z 177. (H) METLIN database match to Sinensetin (found in citrus). Shown is ESI-Q-TOF MS/MS fragmentation of m/z 373.128, RT of 4.6 min in hand (Upper), phone (Middle) of volunteer 32, and from METLIN database (Lower). Dominant fragmentation products with m/z 357, m/z 343, and m/z 312 correspond to the cleavage of methyl groups, and the further loss of hydroxyl groups yield to fragmentation products m/z 329 and m/z 295. Identification is based on MS/MS fragmentation, METLIN database, and based on the validation of using ketoconazole medication by volunteer 16 and the lifestyle of individual 32, who is a huge consumer of oranges.

ESI Q-TOF MS/MS fragmentation of citalopram and its metabolite citalopram N-oxide. (A) ESI-Q-TOF MS/MS fragmentation of (A) citalopram (antidepressant medication) m/z 325.172, RT of 3.8 min in hand (Upper) and phone (Middle) of volunteer 21, and from GNPS database (Lower) and (B) its metabolite citalopram N-oxide m/z 341.163, RT of 3.9 min (delta m/z of 15.990 corresponding to an oxidation) in hand (Upper) and phone (Middle) of volunteer 21. The cleavage between the tertiary amine group results in the m/z 280.109 fragment ion. Fragment ion with m/z 109.044 is a characteristic fragment of the fluorobenzene group, observed in the fragmentation spectra of both (A) citalopram and (B) citalopram N-oxide. Identification is based on MS/MS fragmentation, GNPS database match, and the confirmation of using citalopram oral medication by volunteer 21.

Representation of lifestyle chemicals detected on hands and phones of several individuals. Subnetworks were highlighted from the molecular network in (gnps.ucsd.edu/ProteoSAFe/status.jsp?task=eea01f9ec9ea44bc80d76de30da67be4, ftp://massive.ucsd.edu/MSV000078993), and the color coding was used to highlight the individuals where each lifestyle chemical was found. ESI-Q-TOF MS/MS fragmentation of (A) nobiletin m/z 403.136, RT of 4.8 min in hands of individuals 32 (Upper) and 12 (Middle), and from GNPS database. Dominant fragmentation products with m/z 388, m/z 373, and m/z 327 correspond to the loss of methyl groups, and the further loss of hydroxy groups yield to fragmentation products with m/z 358 and m/z 342. B shows ESI-Q-TOF MS/MS fragmentation of chlorhexidine m/z 505.232 RT of 4.0 min in hand of individual 11 (Upper) and from GNPS database (Lower). Major fragments with m/z 336 and 353 results from the loss of chlorophenyl with imidamide group and –NH and chlorophenyl with imidamide group, respectively. (C) MS/MS fragmentation of avobenzone m/z 311.162, RT of 7.3 min in phones of individuals 22 and 1 (). (D) MS/MS fragmentation of caffeine m/z 195.088, RT of 2.3 min, in phone of individual 2 and hand of individual 3 and from NIST database. (E) ESI-Q-TOF MS/MS fragmentation of diethyltoluamide (DEET) m/z 192.139, RT of 4.3 min, which was applied more than 1 mo before the first sample collection, in hand (Upper) and phone (Middle) of individual 1 and from GNPS database (Lower). Identification of these chemicals was based on MS/MS fragmentation, GNPS, NIST, METLIN libraries, and validation based on lifestyle of individuals.

Molecular network to highlight lifestyle chemicals that last on phones. A represents the molecular network generated from LC-MS/MS of hand samples collected on time 1 (T1) and phone samples collected 4 mo later [time 2 (T2)] from 10 same individuals randomly selected among a total of 39. Network was generated using a cosine threshold of 0.65. Networking parameters included the following: precursor m/z tolerance of 1 Da, fragment mass tolerance of 0.5 Da, minimum matched fragments ions 4, and a minimum cluster size of 2, gnps.ucsd.edu/ProteoSAFe/status.jsp?task=60b0ae8123284d6980204c6650c400d5, ftp://massive.ucsd.edu/MSV000079825. A color coding is used to highlight molecular features that are found on phone of each individual 4 mo later and still match the original hand signature. Examples of these lifestyle chemicals are as follows: (B) DEET detected on phone of volunteer 1, (C) trehalose fatty acid molecular family that is still detected on individual 38, and (D) minoxidil that is still detected on individual 2 samples 4 mo later. Note: Minoxidil was also detected on phone of individual 37, 4 mo later as this person started to use minoxidil before time 2 sample collection and was not using it when samples were collected 4 mo earlier, gnps.ucsd.edu/ProteoSAFe/status.jsp?task=60b0ae8123284d6980204c6650c400d5. All of these chemicals were previously highlighted in , and and . They were detected on hands and phones of individuals at the first sample collection (DEET, volunteers 1 and 12; trehalose fatty acids, volunteer 38; and minoxidil, volunteer 2).

Molecular network to highlight lifestyle chemistries detected only on hands of individuals but not on their phones. ESI-Q-TOF MS/MS fragmentation of (A) antihistaminic (chlorpheniramine) m/z 275.129, RT of 3.1 min in hand (Upper) of volunteer 37 and from GNPS database (Lower). Dominant fragment ion (m/z 230) results from the loss of tertiary amine. B shows MS/MS fragmentation of Ibuprofen m/z 207.124, RT of 5.4 min in hand (Upper) of individual 35 and from NIST database (Lower). The release of the carboxylic group results in the dominant fragment ion (m/z 161). (C) MS/MS fragmentation of pet pesticide (pyriproxyfen) m/z 322.141, RT of 6.6 min from hand of individual 35, and from NIST database. The cleavage of the ether bond releases two dominant fragment ions m/z 227.107 and m/z 96.044. Subnetworks were highlighted from the molecular network in (gnps.ucsd.edu/ProteoSAFe/status.jsp?task=60b0ae8123284d6980204c6650c400d5, ftp://massive.ucsd.edu/MSV000078993), and the color coding was used to highlight hands of individuals where each lifestyle chemical was found. Identification of these chemicals was based on MS/MS fragmentation, GNPS, NIST databases, and validation based on lifestyle of individuals.

Evaluation of chemicals that persist on phones 4 mo after the first sample collection. A–C were generated from the output of molecular network of LC-MS/MS data collected from hand, gnps.ucsd.edu/ProteoSAFe/status.jsp?task=ff2d50726af84006b2eec3fd983e63f2, or phone samples, gnps.ucsd.edu/ProteoSAFe/status.jsp?task=027732e55c344fa4bd940430c9e144fd, collected on time 1 and phone samples collected 4 mo later (time 2). A represents the percentage of stable chemicals, per individual, that still match the original hand (orange) or phone (gray) signature. Venn diagrams display the number of chemicals that (B) persist on phones (blue) and match the original hand signature (orange) (169 out of 1,569; ∼11%) and (C) the original phone signature (purple) (214 out of 767; ∼28%).

Hierarchical cluster heat map to predict lifestyle of individuals based on phone and hand chemical signatures. The heat map (left image) was generated using Jaccard dissimilarity method, from , which represents the detection/no detection of annotated chemicals on hands and phones. Hierarchical clustering of this table results in chemical clusters that provide information about the lifestyle of an individual. A high-resolution heat map is shown in . Each color is associated to an individual and represents a combination of lifestyle chemicals found on hands and phones of six volunteers: (A) volunteer 1, (B) volunteer 16, (C) volunteer 21, (D) volunteer 9, (E) volunteer 2, and (F) volunteer 38. The legend uses pictographs to represent the origin of every molecule from the lifestyle sketch associated with an individual.

Hierarchical cluster heat map representing presence and absence of annotated molecules on hands and phones of 39 individuals. (A) The heat map was generated using Jaccard dissimilarity method, from , which represents the detection/no detection of identified chemicals on 39 hands and phones. Hierarchical clustering highlights combination of chemical lifestyles that can be used to provide information about the lifestyle of an individual. All putative molecular identifications from GNPS database are available here: gnps.ucsd.edu/ProteoSAFe/result.jsp?task=0671dd76c8334d528f5b4b5ac243e045&view=group_by_compound. B and C highlight chemicals detected on hands and phones reflecting exposure to plasticizers. B represents a plasticizer dibutyl phthalate detected on phones of individuals 5, 32, and 25, and on hands of individuals 39 and 33. C highlights the detection of dicumyl peroxide on hands of individuals 7 and 8, and phones of individuals 9 and 28; and the detection of tris(2-butoxyethyl) phosphate on phones of individuals 23, 8, 22, and 21, and on hands of individuals 21, 22, 27, and 26.

Spatial mapping of lifestyle chemicals detected on hands and phones of individuals. Two-dimensional spatial maps generated from LC-MS1 data display the localization and abundance of molecules of interest on hands and phones of four individuals. Figure highlights phone and hand localization of (A) the hair loss treatment molecule minoxidil (m/z 210.135; RT, 150.8 s) on person 2, (B) sinensetin (m/z 373.125; RT, 230 s) on person 32, (C) antidepressant citalopram (m/z 325.171; RT, 228) and its metabolite citalopram N-oxide (m/z 341.163; RT 230) on person 21, and (D) trehalose fatty acids (m/z 631.363; RT 391) and its analog (m/z 603.336; RT 361) on person 38. Color scale is associated to the relative abundance of features, with red corresponding to the highest relative abundance; this is indicated as a plus (+), and the minus (−) is the lowest abundance.

Two-dimensional spatial maps of hands and phones of 39 individuals. This spatial map has to be used along with the mapping file .CSV () to visualize the distribution and relative abundance of molecules in hands and phones of 39 individuals. The two files are simply dragged and dropped to ili-toolbox.github.io/ for visualization. From Top to Bottom, each column represents hand and phone of individuals: the first column, individuals 1–10; the second column, individuals 11–20; the third column, individuals 21–30; and the last column, individuals 31–39.