Surface-assisted Laser Desorption/ionization Mass Spectrometry Research Articles

Improving performance of SALDI-MS by regulating density of plasmonic nanoparticles

Surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) emerges as an effective method for analyzing small molecules. At the current stage, its application is still limited by its detection sensitivity. According to the mechanism of SALDI-MS, the sensitivity highly depends on the laser desorption/ionization (LDI) efficiency. In this study, we adjust the localized surface plasmon resonance (LSPR) between particles by changing the gap, thereby improving the efficiency of LDI. The gaps of nanoparticles can be adjusted by the ionic strength in the solution. With the decrease of the gaps, the thermal effect of the nanoparticles is gradually enhanced and the number of excited electrons is also increased, which improves the sensitivity of SALDI-MS. The prepared substrate with optimized gaps has wide applicability for the detection of small biomolecules and dye molecules. Moreover, the substrate can successfully detect trace small molecules in complex samples. The analysis of sulfonamide in lake water shows the commendable performance of the substrate. The relative standard deviations (RSD) of spot-to-spot and batch-to-batch are 3.73% and 7.22% respectively, confirming the high reproducibility and the detection limit is as low as 100 pM, indicating the high sensitivity of the substrate. The results demonstrate that adjusting the LSPR of metal nanoparticles is a promising method for improving the performance of SALDI-MS.

A single atom cobalt anchored MXene bifunctional platform for rapid, label-free and high-throughput biomarker analysis and tissue imaging

Few of single-atom materials have been served as platform to analyze small molecules for surface assisted laser desorption/ionization mass spectrometry (SALDI-MS). Herein, a novel single Co atom-anchored MXene (Co–N–Ti3C2) is prepared to achieve enhanced SALDI-MS and mass spectrometry imaging (MSI) performance for the first time. The Co–N–Ti3C2 films were prepared by a simple in situ self-assembly strategy to generate an efficient SALDI-MS platform. Compared to typical inorganic/organic matrices, Co–N–Ti3C2 films exhibit superior performance in small molecules detection with ultra-high sensitivity (LOD at amol level), excellent repeatability (CV <4%), clean background and wide analyte coverage, enabling accurate quantitative analysis of various low-concentration metabolites from 1 μL biofluid in seconds. Its usage efficiently enhanced SALDI-MS detection of various small-molecule biomarkers such as amino acids, succinic acid, itaconic acid, arachidonic acid, citrulline, prostaglandin E2, creatinine, uric acid, glutamine, D-mannose, cholesterol and inositol in positive ion mode. The blood glucose level in humans was successfully determined from a linearity concentration range (0.25–10 mM). Notably, the Co–N–Ti3C2 assisted SALDI-MSI enables study the spatial distribution of small molecules covering the range central to metabolomics at a high resolution on a tissue section. Furthermore, Co–N–Ti3C2 platform revealed a specific peak profile that distinguishes osteoarthritis (OA) from rheumatoid arthritis (RA) tissue. Density functional theory theoretical investigation revealed that single Co atoms anchored on Ti3C2 could highly enhanced the ionization ability of metabolites, resulting in high-sensitivity and heterogeneous metabolome coverage.

Boric acids decorated polymers with Au nanoparticle anchor assisted laser desorption/ionization for qualitive and quantitative analysis of hydroxytyrosol in red wines

Hydroxytyrosol possesses a variety of biological and pharmacological activities that are beneficial to human health. However, the methodologies for its detection always suffered from problems. In this work, the gold nanoparticle modified polymer decorated with boric acids (pMBA/VPBA@Au) was synthesized and used both as the adsorbent and matrix to enrich and ionize small molecule substances through surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS). The pMBA/VPBA@Au displayed a low detection limit (8 × 10−6 M) and high selectivity (1:100) for the enrichment of hydroxytyrosol, and the linear correlation curve between the concentration of hydroxytyrosol and the intensity of MS had a good correlation (10−4-10−2 M, R2 = 0.997). Additionally, the pMBA/VPBA@Au was used to quantify hydroxytyrosol in red wines, and the contents were 0.053–0.094 μg/mL. In general, a simple and novel method for the detection of hydroxytyrosol by SALDI-MS using boric acid functionalized polymer was developed for the first time, showing a good practical application value.

Development of nanomaterial enabling highly sensitive surface-assisted laser desorption/ionization mass spectrometry peptide analysis.

Surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) is an approach derived from matrix-assisted laser desorption/ionization (MALDI)-MS which overcomes the drawbacks associated with the use of organic matrices required to co-crystallize with the analytes. Indeed, nanomaterials commonly used in SALDI-MS as inert surfaces to promote desorption/ionization (D/I) ensure straightforward direct deposition of samples while providing mass spectra with ions only related to the compound of interest. The objective of this study was to develop a novel SALDI-MS approach based on steel plates that are surfaces very rapidly and easily tuned to perform the most efficient peptide detection as possible. To compare the SALDI efficacy of such metal substrates, D/I efficiency and deposit homogeneity were evaluated according to steel plate fabrication processes. The studied surfaces were nanostructured steel plates that were chemically modified by perfluorosilane and textured according to different frequencies and laser writing powers. The capacity of each tested 100 surfaces was demonstrated by comparative analyses of a mixture of standard peptides (m/z 600-3000) performed with a MALDI-TOF instrument enabling MALDI, SALDI and imaging experiments. A peptide mix was used to screen the different surfaces depending on their D/I efficiency and their ability to ensure homogeneous deposit of the samples. For that purpose, deposition homogeneity was visualized owing to reconstructed ionic images from all protonated or sodiated ions of the 10 peptides constituting the standard mix. Seven surfaces were then selected satisfying the required D/I efficiency and deposit homogeneity criteria. Results obtained with these optimal surfaces were then compared with those recorded by MALDI-MS analyses used as references.

Use of Nanoparticle Decorated Surface-Enhanced Raman Scattering Active Sol-Gel Substrates for SALDI-MS Analysis.

Spectroscopy and mass spectrometry techniques are sometimes combined into the same analytical workflow to leverage each technique's analytical benefits. This combined workflow is especially useful in forensic and medical contexts where samples are often precious in nature. Here, we adopt metal nanoparticle (NP) doped sol-gel substrates, initially developed for surface-enhanced Raman scattering (SERS) analysis, as surface-assisted laser desorption/ionization-mass spectrometry (SALDI-MS) substrates. Using dried blood and sample protocols previously developed for SERS analysis, we observe heme-related spectral features on both silver and gold NP substrates by SALDI-MS, demonstrating dual functionality for these orthogonal techniques. Modifying the dried blood extraction procedures also allows for the observation of blood triacylglycerols by SALDI-MS. This is the first demonstration of a SERS/SALDI-MS substrate based on a sol-gel scaffold and the first demonstration of a gold NP sol-gel substrate for SALDI-MS which features lower substrate-related SALDI-MS background compared to the silver substrate.

Continuous synthesis of BaFe2O4 and BaFe12O19 nanoparticles in a droplet microreactor for efficient detection of antihistamine drugs in oral fluid using surface-assisted laser desorption/ionization mass spectrometry.

Surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) has received considerable attention as a complementary approach to matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS), offering substantial potential for analyzing molecules in the low-mass region. Herein, we propose a facile method, a microreactor for the synthesis of two types of barium ferrite (BaFe2O4 and BaFe12O19) nanoparticles (NPs) within moving droplets for detecting antihistamine (AH) drugs in oral fluid (OF). The synthesized BaFe2O4 and BaFe12O19 NPs exhibited small particle size, good ultraviolet absorption, and excellent performance in SALDI-MS, as determined by survival yield measurements. The limits-of-detection for AH drugs were in the range of 1 pg mL-1 to 100 ng mL-1, and spot-spot reproducibility of the SALDI substrates was satisfactory. Moreover, when analyzing cetirizine in OF, the obtained recoveries of cetirizine were 101% and 99% using BaFe2O4 and BaFe12O19 NP, respectively. Furthermore, the proposed method was validated by analyzing OF samples from a healthy volunteer who consumed a 5 mg levocetirizine tablet for seven days. SALDI-MS analysis confirmed the successful detection of endogenous components, the parent ion of cetirizine, and other exogenous substances. This study reports an advanced application of droplet microreactor technology for designing and synthesizing a wide range of novel and efficient SALDI-MS substrates for various applications.

Effects of High-Quality Carbon Nanowalls Ionization-Assisting Substrates on Surface-Assisted Laser Desorption/Ionization Mass Spectrometry Performance.

Surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) is performed using carbon nanowalls (CNWs) for ionization-assisting substrates. The CNWs (referred to as high-quality CNWs) in the present study were grown using a radical-injection plasma-enhanced chemical vapor deposition (RI-PECVD) system with the addition of oxygen in a mixture of CH4 and H2 gases. High-quality CNWs were different with respect to crystallinity and C-OH groups, while showing similar wall-to-wall distances and a wettability comparable to CNWs (referred to as normal CNWs) grown without O2. The efficiency of SALDI was tested with both parameters of ion intensity and fragmental efficiency (survival yield (SY)) using N-benzylpyridinuim chloride (N-BP-CI). At a laser fluence of 4 mJ/cm2, normal CNWs had an SY of 0.97 and an ion intensity of 0.13, while 5-sccm-O2- high-quality CNWs had an SY of 0.89 and an ion intensity of 2.55. As a result, the sensitivity for the detection of low-molecular-weight analytes was improved with the high-quality CNWs compared to the normal CNWs, while an SY of 0.89 was maintained at a low laser fluence of 4 mJ/cm2. SALDI-MS measurements available with the high-quality CNWs ionization-assisting substrate provided high ionization and SY values.

Covalent Bonding and Coulomb Repulsion-Guided AuNP Array: A Tunable and Reusable Substrate for Metabolomic Characterization of Lung Cancer Patient Sera.

Surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) has gained increased attention in the metabolic characterization of human biofluids. However, the stability and reproducibility of nanoparticle-based substrates remain two of the biggest challenges in high-salt environments. Here, by controlling the extent of Coulomb repulsion of 26 nm positively charged AuNPs, a homogeneous layer of covalently bonded AuNPs on a coverslip with tunable interparticle distances down to 16 nm has been successfully fabricated to analyze small biomolecules in human serum. Compared with the self-assembled AuNP array, the covalently bonded AuNP array showed superior performances on stability, reproducibility, and sensitivity in high-salt environments. The stable attachment of AuNPs maintained a detection reproducibility with a RSD less than 12% and enabled the reusability of the array for 10 experiments without significant signal deterioration (<15%) and carryover effects. Moreover, the closely positioned AuNPs allowed the coupling of photoinduced plasmons to generate an enhanced electric field, which promotes the generation of excited electrons to facilitate the desorption/ionization processes instead of the heat dissipation, thus enhancing the detection sensitivity with detection limits down to the femtomole level. Combined with machine learning methods, the AuNP array has been successfully applied to discover seven biomarkers for differentiating early-stage lung cancer patients from healthy controls. It is anticipated that this simple approach of developing robust AuNP arrays can also be extended to other types of NP arrays for wider applications of SALDI-MS technology.

Magnetic Nanoparticle-Based Surface-Assisted Laser Desorption/Ionization Mass Spectrometry for Cosmetics Detection in Contaminated Fingermarks: Magnetic Recovery and Surface Roughness.

In this work, we propose a matrix-free approach for the analysis of fingermarks (FMs) contaminated with five cosmetic products containing different active pharmaceutical ingredients (APIs) using surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS). For this purpose, a magnetic SALDI substrate based on Fe3O4-CeO2 magnetic nanoparticles was prepared, characterized, and optimized for the analysis of contaminated FMs without sample pretreatment. Initially, groomed FM and cosmetic products were separately analyzed, and their major components were successfully detected. Subsequently, FMs contaminated with Ordinary serum and Skinoren, Dermovate, Bepanthen, and Eucerin creams were analyzed, and components of FM and cosmetics were detected. The stability of the cosmetics in FMs was studied over an interval of 28 days, and all components showed good stability in FM for 4 weeks. Recovery of contaminated FMs from different surfaces utilizing a few microliters of the magnetic substrate was carried out using a simple external magnetic field from ceramic, plastic, metal, and glass. Successful retrieval of the API and FM components was achieved with magnetic recovery, and glass exhibited the best recovery, whereas ceramic tile demonstrated the lowest recovery. This was supported by atomic force microscopy study, which revealed that the ceramic surface had higher roughness than the other surfaces employed in this study, which adversely affected the magnetic maneuvering. This proof-of-concept investigation extends the application of SALDI-MS in forensic analysis of contaminated FMs by exploring cosmetics as exogenous materials and their stability and recovery from different surfaces.

Aptamer-conjugated graphene oxide-based surface assisted laser desorption ionization mass spectrometry for selective extraction and detection of Aβ1-42 in an Alzheimer's disease SH-SY5 cell model.

The generation and accumulation of amyloid-beta peptide (Aβ1–42) in amyloid plaques are key characteristics of Alzheimer’s disease (AD); thus, specific detection of Aβ1–42 is essential for the diagnosis and treatment of AD. Herein, an aptamer-conjugated graphene oxide (Apt-GO) sensor was synthesized by π-π and hydrophobic interactions using thiol poly (ethylene glycol) amine (SH-PEG-NH2) as a spacer unit. Then, it was applied to selective capture of Aβ1–42, and the resulting complex was directly analyzed by surface-assisted laser desorption ionization mass spectrometry (SALDI-MS). The results revealed that the Apt-GO could enhance the detection specificity and reduce non-specific adsorption. This method was validated to be sensitive in detecting Aβ1–42 at a low level in human serum (ca. 0.1 μM) within a linear range from 0.1 to 10 μM. The immobilizing amount of aptamer on the GO was calculated to be 36.1 nmol/mg (RSD = 11.5%). In conclusion, this Apt-GO-based SALDI-MS method was sensitive and efficient in selective extraction and detection of Aβ1–42, which proved to be a good option for early AD diagnosis.

Boron-doped carbon nanowalls for fast and direct detection of cytochrome C and ricin by matrix-free laser desorption/ionization mass spectrometry

Detecting proteins via surface assisted laser desorption/ionization mass spectrometry (SALDI-MS) method is still highly challenging, and only few examples of nanomaterials have been demonstrated to perform such detection so far. In this study, carbon nanowalls (CNWs), vertically aligned graphene sheet-based materials, presenting specific morphology, dimensions, and boron doping levels have shown improved performances for both qualitative and quantitative detection of Cytochrome C under optimized experimental conditions. Boron doped carbon nanowalls (B-CNWs) with a [B]/[C] ratio of 5000 ppm and growing time of 4 h have shown the best performance in terms of signal intensity and reliability. Then, the detection of ricin, a ribosomal-inhibiting protein (RIP) classified as category B bioterrorism agent by CDC (Centre of Disease and Control and Prevention), was performed. For the first time, direct SALDI-MS detection of ricin B chain was reported without tedious sample preparation steps or database interrogation, and results were obtained within few minutes and a limit of detection (LOD) of 0.5 pmol/μl was obtained. Thanks to the introduction of galactosamine residues on B–CNW, we were able to selectively detect ricin B chain protein in complex media such as serum and soft drinks with enhanced signal intensity. B-CNWs are not toxic and are adaptable to any commercial MALDI-TOF mass spectrometer, showing their great potential as SALDI based materials.

Au NPs decorated holey g-C3N4 as a dual-mode sensing platform of SERS and SALDI-MS for selective discrimination of L-cysteine

Development of reliable sensing strategy combining surface-enhanced Raman scattering (SERS) and surface-assisted laser desorption/ionization-mass spectrometry (SALDI-MS) is of significant interest to distinguish cysteine enantiomers in body fluid for understanding their physiological roles and toxicity hazards. In this work, a SERS/SALDI-MS dual-mode sensing platform of gold nanoparticles (Au NPs) decorated holey carbon nitride (hg-C3N4) was fabricated for sensitive detecting cysteine. The designed Au@hg-C3N4 matrix featured a uniform distribution of Au NPs with the help of anchoring effect of hg-C3N4 holey structure, which was conducive to produce highly repeatable signals. Moreover, the combination of Au NPs and holey g-C3N4 endowed this matrix with superior enrichment capacity, enhanced charge transfer and strong UV absorption. These merits allowed the matrix to acquire high sensitivity and enhanced reproducibility for l-cysteine by means of SERS/SALDI-MS. Likewise, reliable detection of l-cysteine and efficient recognition of d-cysteine in human serum jointly revealed its prospect for detecting cysteine enantiomers in body fluids. This work offers a reliable SERS/SALDI-MS strategy for determining L/D-cysteine enantiomers, and the designed Au@hg-C3N4 matrix becomes a potential application candidate for selective detection of bio-enantiomers.

Dual-Mechanism-Driven Strategy for High-Coverage Detection of Serum Lipids on a Novel SALDI-MS Target.

Serum lipid metabolites have been emerging as ideal biomarkers for disease diagnosis and prediction. In the current stage, nontargeted or targeted lipidomic research mainly relies on a liquid chromatography-mass spectrometry (LC-MS) platform, but future clinical applications need more robust and high-speed platforms. Surface-assisted laser desorption ionization mass spectrometry (SALDI-MS) has shown excellent advantages in the high-speed analysis of lipid metabolites. However, the platform in the positive ion mode is more inclined to target a certain class of lipids, leading to the low coverage of lipid detection and limiting its practical translation to clinical applications. Herein, we proposed a dual-mechanism-driven strategy for high-coverage detection of serum lipids on a novel SALDI-MS target, which is a composite nanostructure comprising vertical silicon nanowires (VSiNWs) decorated with AuNPs and polydopamine (VSiNW-Au-PDA). The performance of laser desorption and ionization on the target can be enhanced by charge-driven desorption coupled with thermal-driven desorption. Simultaneous detection of 236 serum lipids (S/N ≥ 5) including neutral and polar lipids can be achieved in the positive ion mode. Among these, 107 lipid peaks were successfully identified. When combined with VSiNW-Au-PDA and VSiNW chips, 479 lipid peaks can be detected in serum samples in positive and negative ion modes, respectively. Based on the platform, serum samples from 57 hepatocellular carcinoma (HCC) patients and 76 healthy controls were analyzed. After data mining, 14 lipids containing different lipid types (TAG, CE, PC) were selected as potential lipidomic biomarkers. With the assistance of an artificial neural network, a diagnostic model with a sensitivity of 92.7% and a specificity of 96% was constructed for HCC diagnosis.

Forensic analysis of cosmetic smudges using surface-assisted laser desorption/ionization mass spectrometry: recovery and ageing study

Owing to its tendency to persist over prolonged periods, cosmetic evidence recovered from crime scenes can assist in linking a suspect to a certain crime or victim, or exonerating a suspect. This work presents a preliminary study in which surface-assisted laser desorption/ionization-mass spectrometry (SALDI-MS) was employed to analyze five cosmetic products recovered from different surfaces and collected at different time points. Topical over-the-counter (OTC) preparations, including Bepanthen cream, Reparil gel, Eucerin cream, Soskin serum, and Clofen creamagel containing dexpanthenol, diethylamine salicylate, urea, salicylic acid (SA), and diclofenac sodium (DCS) as active pharmaceutical ingredients (APIs), respectively, were used in this study. Due to their intricate nature and texture, five cosmetic product smudges were freshly deposited in small amounts on the target plate and directly subjected to SALDI-MS analysis without performing an extraction. The five APIs were successfully detected, along with other ingredients present in the intricate cosmetic matrices; the presence of waxes and polymers in the preparations did not hinder ionization of the target analytes. Since only trace amounts of cosmetics are often encountered at crime scenes; therefore, limits of detection (LOD) were determined for each API using optimum solvents. The LOD were determined as 300, 30, 6, 1.20, and 600 ng/mL for dexpanthenol, salicylate, urea, SA, and DCS, respectively. Furthermore, the relative standard deviations of the amounts of each API detected were calculated and estimated to be between 0.40 and 17.95%, indicating good reproducibility of the results. Subsequently, models of forensic samples were prepared wherein cosmetic smudges were deposited on three different surfaces (plastic, glass, and stainless steel) and recovered via extraction and swabbing. The model indicated that direct swabbing of the sample onto the target plate was the best recovery approach which, owing to its simplicity, can be implemented at a crime scene. Finally, an ageing study was performed, which showed successful detection of all the APIs on their optimum surfaces, even after 38 days post-deposition. The imposed lockdown during the global COVID-19 pandemic has increased the necessity for more advanced recovery and detection techniques that can coincide with massive delays and sample backlogs in forensic laboratories. Therefore, SALDI-MS provides better discrimination power, faster analysis duration, and reduces the matrix effect when employed for small sample volumes, such as cosmetic smudges.

SALDI Substrate-Based FeNi Magnetic Alloy Nanoparticles for Forensic Analysis of Poisons in Human Serum.

In this study, FeNi magnetic alloy nanoparticles (MANPs) were employed for the forensic analysis of four poisons—dimethametryn, napropamide, thiodicarb, and strychnine—using surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS). FeNi MANPs were prepared via coprecipitation using two reducing agents, sodium borohydride (NaBH4) and hydrazine monohydrate (N2H4·H2O), to optimize the prepared MANPs and investigate their effect on the performance of SALDI-MS analysis. Thereafter, SALDI-MS analysis was carried out for the detection of three pesticides and a rodenticide. The prepared substrate offered sensitive detection of the targeted analytes with LOD values of 1 ng/mL, 100 pg/mL, 10 ng/mL, and 200 ng/mL for dimethametryn, napropamide, thiodicarb, and strychnine, respectively. The relative standard deviation (%RSD) values were in the range of 2.30–13.97% for the pesticides and 15–23.81% for strychnine, demonstrating the good spot-to-spot reproducibility of the FeNi substrate. Finally, the MANPs were successfully employed in the analysis of poison-spiked blood serum using a minute quantity of the sample with an LOD of 700 ng/mL dimethametryn and napropamide, 800 ng/mL thiodicarb, and 500 ng/mL strychnine. This study has great potential regarding the analysis of several poisons that may be found in human serum, which is significant in cases of self-harm.

High-density Si nanopillars modified with Ag nanoislands: Sensitive SALDI-MS chip for sulfonamides

In recent years, the abuse of antibiotics has brought adverse effects on water environment and food safety, to monitor the antibiotic content in water and foodstuffs is imperative for environmental protection and human health. In this work, a chip, composed of high-density Si nanopillars and Ag nanoislands, is prepared for sensitive detection of sulfonamides with surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS). In this chip, the high-density Si nanopillars can absorb laser energy efficiently and promote electron transfer as antennas; the Ag nanoislands can enhance the thermal effect; the formation of the Schottky barrier and the conductive nanolayer between Si/Ag can extend the lifetime of electrons and promote electron tunneling effect. Therefore, the heterostructure presents high detection sensitivity (the limit of detection of sulfamethazine is as low as 3 amol); in addition, the satisfactory coefficients of determination (> 0.99) show that the chip is applicable for rapid quantification of sulfonamides. Further, the sulfacetamides spiked in milk and lake water can be sensitively identified and rapidly quantified. The prepared chip presents a considerable potential for food and environment monitoring.

Magnetic carbon nanoparticles derived from candle soot for SALDI MS analyses of drugs and heavy metals in latent fingermarks

For decades, the analysis of fingerprints (FP) has been used as the primary biometric mean of human identification. In parallel, the chemical analysis of latent fingermark (LFM) with particular reference to “touch chemistry”, offersadditional intelligence to forensic examination; as such,continuous improvements in the versatility and sensitivity of detection of the molecular make up of FM is of obvious importance. In this light, we propose a facile approach to synthesize magnetic carbon nanoparticles (MCNPs) from candle soot for extraction and detection of endogenous and exogenous FM components. Initially, endogenous components of FM including fatty acids (FAs), squalene andtriacylgycerols(TAGs), were successfully extracted and detected using the developed MCNPs and surface assisted laser desorption/ionization-mass spectrometry (SALDI-MS). Furthermore, the MCNPs enabled the detection of exogenous substances including antihistamine,β-blocker, antibiotic drugs and lead in contaminated FMs, whilst providing characteristic and unique fragmentation patterns for each drugs in the FM. The influence of environmental factors such as temperature on the stability of the exogenous substances in FM was investigated by exposing the contaminated FM to different temperatures over 24 h, the findings revealed thedrugs' instability at high temperatures and undergo different degrees of degradationwhereas lead was more resilient to thermal stress. The detection oftriprolidine, metoprolol and sulfamethoxazolefrom pharmaceutical tablets in FM was successfully achieved by gently touching the tablet powder. Thelimit of detection (LOD) values of the drugs in the tablet forms were 50, 200 and 750 ng mL−1for triprolidine, metoprolol and sulfamethoxazole, respectively and their recovery rates were91.17% fortriprolidine, 94.67% formetoprolol and 120.86% for sulfamethoxazole. Finally, to create a genuine casework scenario, contaminated FM was deposited on glass and metal surfaces then subjected to extraction usingMCNPs and magnet without compromising the FM impression. Substrate control experiments revealed that the glass surface exhibiting some background signal, however, they did not interfere with the analysis and satisfactory extraction efficiency of endogenous and exogenous components of the FM on both surfaces was obtained using the MCNPs. Overall, this study proves the capability of MCNPs as new SALDI-MS substrate for both extraction and detection of FM components gathering more information pertaining to the donor’s lifestyle.

One-step fabrication of high-density Si nanotips as SALDI-MS substrate for highly sensitive detection

The high sensitivity of surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) analysis depends on the enhancement of the signal intensity and the reduction of the background. Here, high-density Si nanotips were prepared as SALDI-MS substrate by taking template-free reactive ion etching for sensitive detection. The high-density Si nanotips act as tiny antennas to concentrate the laser energy and generate photo-induced electrons on a small area, which promotes desorption and ionization of molecule, enhancing the signal intensity. Additionally, the high stability of Si nanotips under laser irradiation ensures low background interference. The applicability of the substrate was demonstrated by the detection of various small molecules, e.g., fatty acids, amino acids, environmental pollutants and drugs. In addition, this substrate can be successfully applied for detecting trace small molecules in complex sample, such as 10−9 M verapamil in serum and 10−12 M crystal violet in lake water. Moreover, the banned fungicides left on the fish skin was also detected. The substrate is compatible with imaging, and the endogenous and exogenous substances in fingerprint were visualized by MS imaging. These results demonstrate the easily prepared high-density Si nanotips SALDI-MS substrate is of high detection sensitivity and great value toward large-scale practical applications.

SALDI-MS and SERS Multimodal Imaging: One Nanostructured Substrate to Rule Them Both.

Imaging techniques based on mass spectrometry or spectroscopy methods inform in situ about the chemical composition of biological tissues or organisms, but they are sometimes limited by their specificity, sensitivity, or spatial resolution. Multimodal imaging addresses these limitations by combining several imaging modalities; however, measuring the same sample with the same preparation using multiple imaging techniques is still uncommon due to the incompatibility between substrates, sample preparation protocols, and data formats. We present a multimodal imaging approach that employs a gold-coated nanostructured silicon substrate to couple surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) and surface-enhanced Raman spectroscopy (SERS). Our approach integrates both imaging modalities by using the same substrate, sample preparation, and data analysis software on the same sample, allowing the coregistration of both images. We transferred molecules from clean fingertips and fingertips covered with plasticine modeling clay onto our nanostructure and analyzed their chemical composition and distribution by SALDI-MS and SERS. Multimodal analysis located the traces of plasticine on fingermarks and provided chemical information on the composition of the clay. Our multimodal approach effectively combines the advantages of mass spectrometry and vibrational spectroscopy with the signal enhancing abilities of our nanostructured substrate.

Laser Desorption Ionization–Mass Spectrometry with Graphite Carbon Black Nanoparticles for Simultaneous Detection of Taste- and Odor-Active Compounds

There is no analytical system to directly and simultaneously detect taste- and odor-active compounds. Graphite carbon black (GCB) nanoparticles, a chemical adsorbent for a variety of compounds, including gaseous molecules, which consists of nanoparticles made from multilayered sheets of sp2-conjugated atomic carbon, have the characteristics required for a surface-assisted laser desorption ionization–mass spectrometry (SALDI-MS) material. Thus, in this study, GCB-LDI-MS was developed for the simultaneous detection of taste- and odor-active compounds. The proposed GCB-LDI-MS successfully detected volatile compounds, including ethyl esters, alcohols, fatty acids, and aldehydes with up to 16 carbons (maximum carbon number of the tested compounds), which could not be detected by conventional matrix-assisted-LDI-MS. Moreover, a series of taste-active compounds (e.g., amino acids and sugars) and various volatile compounds (e.g., ethyl esters, aldehydes, alcohols, fatty acids, and lactones) as a mixture in liquid samples were also detected by the present GCB-LDI-MS. Thus, the proposed simple and rapid detection technique can digitize the analysis of flavor compounds, which provides an analytical concept for flavor scanning to evaluate the palatability of food products.