Direct Sample Analysis Research Articles

Cu/Ag Nanoparticle-Based Surface-Enhanced Raman Scattering Substrates for Label-Free Bacterial Detection

Surface-enhanced Raman spectroscopy (SERS) is a promising analytical technique for fast and accurate disease detection due to its attractive features. However, realizing label-free direct detection is still challenging as most probes have extremely low Raman cross sections and little affinity to SERS substrates. Disappointingly, SERS spectra of most bacteria and other biological samples look similar as the differences in their molecular compositions are subtle and not detectable. Hence, the fabrication of highly enhancing plasmonic nanoparticles with excellent uniformity is demanded. Moreover, as SERS substrates are not reusable, cost-effective and simplistic fabrication methods are critical. Here, we report a facile approach to synthesizing Ag nanoparticle array on Cu-foil in less than 3 min, using only Cu-foil, silver nitrate, and hydroquinone. We employed the idea of galvanic replacement in combination with a seed-mediated particle-growth approach. The label-free bacterial detection has shown that our Cu/Ag nanoparticle substrate is superior to highly acclaimed Ag nanocubes. Creating strong second and third-generation SERS hot-spots through cooperative interaction of homo- (Ag–Ag) and heterogeneous (Ag–Cu) surfaces contributes mainly to the observed excellent enhancement. Interestingly, direct liquid bacteria sample analysis showed a 6-fold higher detection sensitivity than completely dried samples. We believe that our approach will offer remarkable advantages and change how SERS substrates are prepared and conducted in SERS-based bacterial detection.

Inductively Coupled Plasma-Tandem Mass Spectrometry (ICP-MS/MS) and Its Applications

During the last about 10 years, the inductively coupled plasma tandem quadrupole mass spectrometry (ICP-MS/MS) technique with reaction cell is being utilized for the analyses of several trace elements/isotopes at very low concentration levels in a variety of matrices including geological, environmental, biological, medical, nuclear, agriculture, food, material and metallurgical sciences. Both solution nebulization, as well as direct analysis of samples by laser ablation (LA-ICP-MS/MS), are utilized for sample introduction. In fact, ICP-MS/MS technique with collision reaction cells eliminated the need for laborious chemical separations using methods such as ion-exchange or solvent extraction procedures to eliminate/minimize spectral and matrix interference effects as these interferences are removed using online chemical reactions within the instrument itself (chemical resolution). In addition, the technique is hyphenated with chromatographic techniques such as GC and HPLCfor a variety of applications. The detection limits for several elements in the periodic table lie in the pg/ml-fg/ml range, and the technique compares favourably with the expensive, complex, and superior high resolution-ICP-MS (HR-ICP-MS), both in terms of the detection limits as well as the ability to remove the most complex interferences. Thus, the ICP MS/MS made the determinations of elemental as well as isotopic concentrations very simple andeasy even in complex materials with several novel quantification approaches. This article provides an overview of these new developments during the last decade along with several applications in all areas of science and technology.

Inductively Coupled Plasma-Tandem Mass Spectrometry (ICP-MS/MS) and Its Applications

During the last about 10 years, the inductively coupled plasma tandem quadrupole mass spectrometry (ICP-MS/MS) technique with reaction cell is being utilized for the analyses of several trace elements/isotopes at very low concentration levels in a variety of matrices including geological, environmental, biological, medical, nuclear, agriculture, food, material and metallurgical sciences. Both solution nebulization, as well as direct analysis of samples by laser ablation (LA-ICP-MS/MS), are utilized for sample introduction. In fact, ICP-MS/MS technique with collision reaction cells eliminated the need for laborious chemical separations using methods such as ion-exchange or solvent extraction procedures to eliminate/minimize spectral and matrix interference effects as these interferences are removed using online chemical reactions within the instrument itself (chemical resolution). In addition, the technique is hyphenated with chromatographic techniques such as GC and HPLCfor a variety of applications. The detection limits for several elements in the periodic table lie in the pg/ml-fg/ml range, and the technique compares favourably with the expensive, complex, and superior high resolution-ICP-MS (HR-ICP-MS), both in terms of the detection limits as well as the ability to remove the most complex interferences. Thus, the ICP MS/MS made the determinations of elemental as well as isotopic concentrations very simple andeasy even in complex materials with several novel quantification approaches. This article provides an overview of these new developments during the last decade along with several applications in all areas of science and technology.

Qualitative imaging of elemental spatial distribution in stalagmites through laser ablation inductively coupled plasma mass spectrometry analysis

The laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) technique is considered versatile for multi-elemental analysis and imaging because it is easy to handle, compatible with different types of solid samples, requires minimal sample preparation, and provides high spatial resolution and sensitivity. One of the challenges of imaging analysis is to obtain accurate and precise spatial information of elements distribution in the sample, so the optimization of the laser ablation (LA) parameters is essential. In this context, this study aimed to optimize the LA parameters for direct analysis of speleothem samples. Laser intensity, frequency, and spot diameter were evaluated through multivariate experimental design and multi-response data, the influence of ablation scan speed and the use of 44Ca as an internal standard (IS) for the qualitative image of 66Zn, 137Ba, 55Mn, 57Fe, 88Sr, 60Ni, and 26Mg distribution in the sample were also evaluated. The multivariate optimization revealed positive interactions between the parameters evaluated, i.e., the greater the laser intensity, LA frequency, and spot diameter, the greater the analyte signal and, thus the sensitivity. Therefore, 90% laser ablation intensity, 20 Hz repetition rate, and 100 µm spot diameter were selected. In the scan speed evaluation, the images obtained with 40 and 20 µm s-1 were very similar for all isotopes. The use of 44Ca as IS did not impact the resolution of the images. The use of 44Ca can provide important information about the speleothem formation and paleoclimate changes.

Wooden-Tip Electrospray Mass Spectrometry Characterization of Human Hemoglobin in Whole Blood Sample for Thalassemia Screening: A Pilot Study

Traditional analytical methods for thalassemia screening are needed to process complicated and time-consuming sample pretreatment. In recent decades, ambient mass spectrometry (MS) approaches have been proven to be an effective analytical strategy for direct sample analysis. In this work, we applied ambient MS with wooden-tip electrospray ionization (WT-ESI) for the direct analysis of raw human blood samples that were pre-identified by gene detection. A total of 319 whole blood samples were investigated in this work, including 100 α-thalassemia carriers, 67 β-thalassemia carriers, and 152 control healthy samples. Only one microliter of raw blood sample was directly loaded onto the surface of the wooden tip, and then five microliters of organic solvent and a high voltage of +3.0 kV were applied onto the wooden tip to generate spray ionization. Multiply charged ions of human hemoglobin (Hb) were directly observed by WT-ESI-MS from raw blood samples. The signal ratios of Hb chains were used to characterize two main types of thalassemia (α and β types) and healthy control blood samples. Our results suggested that the ratios of charged ions to Hb chains being at +13 would be an indicator for β-thalassemia screening.

Discrimination between Wild and Farmed Sea Bass by Using New Spectrometry and Spectroscopy Methods.

European sea bass (Dicentrarchus labrax L.) is one of the most economically important fish species in the Mediterranean Sea area. Despite strict requirements regarding indications of production method (wild/farmed), incorrect labelling of sea bass is a practice still frequently detected. The aim of this study was to evaluate the capabilities of two techniques, Near-InfraRed (NIR) spectroscopy and mass spectrometry, to discriminate sea bass according to the production method. Two categories were discriminated based on the docosahexaenoic and arachidonic fatty acid ratio by using a Direct Sample Analysis (DSA) system integrated with a time-of-flight (TOF) mass spectrometer. The cut-off value of 3.42, of fatty acid ratio, was able to discriminate between the two types of fish with sensitivity and specificity of 100%. It was possible to classify fish production by using multivariate analysis with portable NIR. The results achieved by the developed validation models suggest that this approach is able to distinguish the two product categories with high sensitivity (100%) and specificity (90%). The results obtained from this study highlight the potential application of two easy, fast, and accurate screening methods to detect fraud in commercial sea bass production.

Paper-Based Biosensor System for Fast and Sensitive Phenolic Compounds Detection

In this original paper, the development of a paper-based, sensitive, low-cost, quantitative and consistent biosensor system was demonstrated for the suitable “naked-eye” detection of phenolic compounds (specifical catechol). The Paper-based system depends on the enzymatic color-changing reaction that observed by using chromogenic agent of 4-AAP (4-aminoantipyrine) which has a specific color changing reaction in the presence of horseradish peroxidase (HRP) enzyme, phenol and H2O2. The visual result was associated with the catechol concentration by using image processing software to evaluate the quantitative detection. The developed biosensor system demonstrated a linear detection range from catechol between 2,5 µM to 100 µM with 2.6% to 9.3 % of sd results. The detection limit was also calculated as 2,25 µM. Specificity, selectivity, stability and direct real sample analysis demonstrated the potential applicability of the developed paper-based biosensor system for catechol detection in food samples with minimal investment and an easy-to-use method.

Direct Urine Resistance Detection Using VITEK 2

Urinary tract infections (UTIs) are the most common infectious diseases in both communities and hospitals. With non-anatomical or functional abnormalities, UTIs are usually self-limiting, though women suffer more reinfections throughout their lives. Certainly, antibiotic treatment leads to a more rapid resolution of symptoms, but also it selects resistant uropathogens and adversely affects the gut and vaginal microbiota. As uropathogens are increasingly becoming resistant to currently available antibiotics, it could be time to explore alternative strategies for managing UTIs. Rapid identification and antimicrobial susceptibility testing (AST) allow fast and precise treatment. The objective of this study was to shorten the time of diagnosis of UTIs by combining pathogen screening through flow cytometry, microbial identification by matrix-assisted laser desorption ionisation time-of-flight mass spectrometry (MALDI-TOF MS), and the VITEK 2 system for the direct analysis of urine samples. First, we selected positive urine samples by flow cytometry using UF5000, establishing the cut-off for positive at 150 bacteria/mL. After confirming the identification using MALDI-TOF MS and filtering the urine samples for Escherichia coli, we directly tested the AST N388 card using VITEK 2. We tested a total of 211 E. coli from urine samples. Cefoxitin, ertapenem, imipenem, gentamicin, nalidixic acid, ciprofloxacin, fosfomycin, and nitrofurantoin had no major important errors (MIE), and ampicillin, cefuroxime, and tobramycin showed higher MIEs. Cefepime, imipenem, and tobramycin had no major errors (ME). Fosfomycin was the antibiotic with the most MEs. The antibiotic with the most minor errors (mE) was ceftazidime. The total categorical agreement (CA) was 97.4% with a 95% CI of (96.8–97.9)95%. The direct AST from the urine samples proposed here was shorter by one day, without significant loss of sensibility regarding the standard diagnosis. Therefore, we hypothesize that this method is more realistic and better suited to human antibiotic concentrations.

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Applications of ambient ionization mass spectrometry in 2021: An annual review.

Ambient ionization mass spectrometry (AIMS) has revolutionized the field of analytical chemistry, enabling the rapid, direct analysis of samples in their native state. Since the inception of AIMS almost 20 years ago, the analytical community has driven the further development of this suite of techniques, motivated by the plentiful advantages offered in addition to traditional mass spectrometry. Workflows can be simplified through the elimination of sample preparation, analysis times can be significantly reduced and analysis remote from the traditional laboratory space has become a real possibility. As such, the interest in AIMS has rapidly spread through analytical communities worldwide, and AIMS techniques are increasingly being integrated with standard laboratory operations. This annual review covers applications of AIMS techniques throughout 2021, with a specific focus on AIMS applications in a number of key fields of research including disease diagnostics, forensics and security, food safety testing and environmental sciences. While some new techniques are introduced, the focus in AIMS research is increasingly shifting from the development of novel techniques toward efforts to improve existing AIMS techniques, particularly in terms of reproducibility, quantification and ease-of-use.

Quantification of protein and phosphorus in livestock feed using mobile NMR sensor technology

Low-field NMR sensor technology is proposed for accurate and operationally simple on-farm or laboratory determination of protein and phosphorus constituents in livestock feed. The total phosphorus content is determined directly on the native sample, while quantification of digestible protein involves enzymatic digestion here adapted to provide the total protein content. Comparison with traditional laboratory reference analysis for the total protein and phosphorus contents of 31 feed samples (including various grains, feed mixtures, and commercial feed products for cattle, pigs, horses, poultry, and sheep) demonstrate the feasibility and good accuracy of the NMR measurements. Table of contents entry – for TOC only. • Mobile, multinuclear, low-field NMR for on-farm measurements. • Total/digestible protein and total phosphorus contents. • Direct analysis of bulk sample (raw material for phosphorus, digested for protein). • Feasibility and accuracy demonstrated on feed for a wide range of animals.

Chemical fingerprinting of phenolic compounds in Finnish berry wines using Fourier transform ion cyclotron resonance mass spectrometry

Chemical fingerprinting of phenolic compounds present in Finnish berry wines was performed using a direct-infusion Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The main aim of this study was to compare the phenolics profiles of wines produced from natural and/or cultivated berries and to demonstrate the feasibility of FT-ICR MS for a direct chemical analysis of the wine samples without chromatographic separation. First, phenolic compounds were recovered from the wine samples by solid-phase extraction (SPE), and the total phenolic content (TPC) was then determined by a Folin-Ciocalteau assay. The TPC of the original berry wines varied from 421 to 2108 mg/L, while the TPC of the extracts was 157–1525 mg/L. Over fifty phenolic compounds were tentatively identified from the wine samples by FT-ICR MS, whose concentrations highly varied depending on the types of berries used in the winemaking process.

Determination of glyphosate exposure in the Iberian hare: A potential focal species associated to agrosystems

Glyphosate is the most used herbicide worldwide. It is a small and highly polar pesticide whose physicochemical properties makes its analytical determination difficult. Here, a procedure based on liquid chromatography-high resolution tandem mass spectrometry (LC-HRMS/MS) was developed for glyphosate determination in samples of gastric content from wildlife. Iberian hare (Lepus granatensis), a herbivorous mammal species, strongly associated to agrosystems was selected as model species. The procedure involves direct analysis of sample without derivatization or instead of neither further cleaning steps. The procedure was validated by inter-day accuracy and precision studies with gastric content of hare spiked with glyphosate at ecologically relevant concentrations for the species (0.1–6 μg/g), and with 1 μg/g of isotopically labelled internal standard (glyphosate-2-13C,15N). Finally, glyphosate residues in hunted animals from pesticide-treated and pesticide-free areas (n = 75 and 28, respectively), as well as from hares found dead in the field (n = 11) were analysed. The linearity of both standards in extraction solutions and procedural calibration curves with spiked samples was similar, both with determination coefficients (r2) higher than 0.99. Satisfactory recoveries in spiked samples were achieved within the range of 95% to 118% (CV ≤ 20%). The limit of detection of glyphosate in hare gastric content was 0.03 μg/g. Prevalence of glyphosate in hunted animals from pesticide-treated areas ranged between 9 and 22%, increasing to 45% in animals found dead. The glyphosate concentrations detected in the gastric content of hares ranged from 0.11 to 16 μg/g. No residues were detected in animals from pesticide-free areas. In practice, the developed methodology may be particularly useful in the context of research and other work on the exposure in wildlife of one of the most used pesticides nowadays.

Gold in pyrites and sulfides by scintillation analysis

The method of scintillation atomic emission spectrometry (SAES) allows determination of the form of the element present in the sample and the size of inclusions in addition to the total content of the element in the direct analysis of powder samples. The aim of the work is to verify the expedience of using the direct method of analysis of individual gold particles in studying the possible forms of gold appearance in pyrites and sulfides, including the so-called «invisible» finely divided gold. The measurements were carried out both on individual pyrite single crystals, and on the samples of sulfide gold and brown coal deposits of Kazakhstan. The studies were carried out on a Grand-Potok complex (VMK Optoelektronika, Ltd.) equipped with a laser ablation system and a system for injection of aqueous solutions and aerosols samples. The samples of pyrite crystals of various sizes were analyzed to determine the content and speciation of gold in the samples. No dependence of the gold content on the crystal size was noted for all the studied pyrites. It is shown that gold and other precious metals are concentrated in the surface layers of pyrite crystals and in crystal lattice defects in the bulk of the crystal (according to SAES data during laser ablation of the sample in an arc discharge). The total content of gold in the bulk of pyrite crystals is about 2 g/ton, platinum and silver is less than 0.02 g/ton, while the content of Au, Ag, Pt on the surface ranges from 2 to 5 g/ton. The detection limit of gold determination by the SAES method is 0.01 g/ton. The SAES method can be used for determination of the gold speciation in pyrites and sulfides (finely dispersed, individual particles up to 1 μm or even less).

Silica Nanochannel Array Film Supported by ß-Cyclodextrin-Functionalized Graphene Modified Gold Film Electrode for Sensitive and Direct Electroanalysis of Acetaminophen.

Convenient and sensitive detection of active analytes in complex matrix is crucial in biological, medical, and environmental analysis. Silica nanochannel array film (SNF) equipped electrochemical sensors have shown excellent anti-fouling performance in direct analysis of complex samples. In this work, we demonstrated an electrochemical sensor with anti-fouling performance for highly sensitive detection of acetaminophen (APAP) based on SNF supported by ß-cyclodextrin-graphene (CDG) nanocomposite modified Au film electrode (AuF). Because of their rich surface hydroxyls and 2D lamellar structure, CDG on AuF can serve as the nanoadhesive for compact binding SNF, which can be grown by electrochemical assisted self-assembly method in a few seconds. Attributable to the electrocatalytic property of graphene and the synergistic enrichment from both CD and SNF nanochannels towards analyte, the SNF/CDG/AuF sensor demonstrates sensitive detection of acetaminophen ranged from 0.2 to 50 μM with an ultralow limit-of-detection of 14 nM. Taking advantage of the anti-fouling ability of SNF, the sensor is able to realize accurate and convenient analysis of APAP in commercially available paracetamol tablets.

Stir bar sorptive-dispersive microextraction by a poly(methacrylic acid-co-ethylene glycol dimethacrylate)-based magnetic sorbent for the determination of tricyclic antidepressants and their main active metabolites in human urine

A poly(methacrylic acid-co-ethylene glycol dimethacrylate)-based magnetic sorbent was used for the rapid and sensitive determination of tricyclic antidepressants and their main active metabolites in human urine. This material was characterized by magnetism measurements, zeta potential, scanning electron microscopy, nitrogen adsorption–desorption isotherms, and thermogravimetric analysis. The proposed analytical method is based on stir bar sorptive-dispersive microextraction (SBSDME) followed by liquid chromatography–tandem mass spectrometry. The main parameters involved in the extraction step were optimized by using the response surface methodology as a multivariate optimization method, whereas a univariate approach was employed to study the desorption parameters. Under the optimized conditions, the proposed method was properly validated showing good linearity (at least up to 50 ng mL−1) and enrichment factors (13–22), limits of detection and quantification in the low ng L−1 range (1.4–7.0 ng L−1), and good intra- and inter-day repeatability (relative standard deviations below 15%). Matrix effects were observed for the direct analysis of urine samples, but they were negligible when a 1:1 v/v dilution with deionized water was performed. Finally, the method was successfully applied to human urine samples from three volunteers, one of them consuming a prescribed drug for depression that tested positive for clomipramine and its main active metabolite. Quantitative relative recoveries (80–113%) were obtained by external calibration. The present work expands the applicability of the SBSDME to new analytes and new types of magnetic sorbents.Graphical abstract

Aerosol dilution for the introduction of complex matrix samples in plasma-based spectrometry techniques: a tutorial review

Aerosol dilution (AD) is a sample introduction tool that allows the direct analysis of complex matrix samples by plasma-based analytical techniques.

Comparison of non-destructive techniques and conventionally used spectrometric techniques for determination of elements in plant samples (coniferous leaves)

Conventionally used spectrometric techniques of inductively coupled plasma optical emission spectrometry (ICP-OES) and inductively coupled plasma optical emission spectrometry (ICP-MS) usually involve time-consuming sample preparation procedure of a sample dissolution which requires the usage of aggressive and toxic chemicals. The need for suitable and sustainable analytical methods for direct multi-elemental analysis of plant samples has been increased in recent years. Spectrometric techniques for direct sample analysis, instrumental neutron activation analysis (INAA) and X-ray fluorescence (XRF) have been applied in environmental studies and various fields of screening tests. Nevertheless, these techniques are not commonly used for plant sample analysis and their performances need to be evaluated. This research aimed to assess how reliable non-destructive techniques are in the determination of elements in plants compared to conventionally used spectrometric techniques. A total of 49 plant samples of four conifer species (Pinus nigra, Abies alba, Taxus baccata and Larix decidua) were measured using two conventionally applied (ICP-MS, ICP-OES) and two non-destructive techniques (wavelength dispersive XRF (WD-XRF), INAA). The comparison was performed by investigation of relative ratios of concentrations and by correlation analysis. Moreover, precision of the techniques was examined and compared. The quality control included analysis of NIST pine needles certified reference material (1575a) using all examined techniques. Our results suggest that additional analytical and quality control steps are necessary for reaching the highest accuracy of multi-elemental analysis.

Vertically Ordered Mesoporous Silica-Nanochannel Film-Equipped Three-Dimensional Macroporous Graphene as Sensitive Electrochemiluminescence Platform.

Three-dimensional (3D) electrochemiluminescence (ECL) platform with high sensitivity and good anti-fouling is highly desirable for direct and sensitive analysis of complex samples. Herein, a novel ECL-sensing platform is demonstrated based on the equipment of vertically ordered mesoporous silica-nanochannel films (VMSF) on monolithic and macroporous 3D graphene (3DG). Through electrografting of 3-aminopropyltriethoxysilane (APTES) onto 3DG as molecular glue, VMSF grown by electrochemically assisted self-assembly (EASA) method fully covers 3DG surface and displays high stability. The developed VMSF/APTES/3DG sensor exhibits highly sensitized ECL response of tris(2,2′-bipyridyl) ruthenium (Ru (bpy)3 2+) taking advantages of the unique characteristics of 3DG (high active area and conductivity) and VMSF nanochannels (strong electrostatic enrichment). The VMSF/APTES/3DG sensor is applied to sensitively detect an important environmental pollutant (4-chlorophenol, with limit of detection or LOD of 30.3 nM) in term of its quenching effect (ECL signal-off mode) toward ECL of Ru (bpy)3 2+/tri-n-propylamine (TPrA). The VMSF/APTES/3DG sensor can also sensitively detect the most effective antihistamines chlorpheniramine (with LOD of 430 nM) using ECL signal-on mode because it acts as co-reactant to promote the ECL of Ru (bpy)3 2+. Combined with the excellent antifouling ability of VMSF, the sensor can also realize the analysis of actual environmental (lake water) and pharmaceutical (pharmacy tablet) samples. The proposed 3D ECL sensor may open new avenues to develop highly sensitive ECL-sensing platform.

At-line coupling of hollow fiber liquid-phase microextraction to capillary electrophoresis for trace determination of acidic drugs in complex samples

Direct analysis of complex samples is demonstrated by the at-line coupling of hollow fiber liquid-phase microextraction (HF-LPME) to capillary electrophoresis (CE). The hyphenation of the preparative and the analytical technique is achieved through a 3D-printed microextraction device with an HF located in a sample vial of a commercial CE instrument. The internal geometry of the device guides the CE separation capillary into the HF and the CE injection of the HF-LPME extract is performed directly from the HF lumen. The 3D-printing process ensures uniform dimensions of the devices, their constant position inside the sample vial, and excellent repeatability of the HF-LPME as well as the CE injection. The devices are cheap (∼0.01 €) and disposable, thus eliminating any possible sample-carryover, moreover, the at-line CE analysis of the extract is performed fully autonomously with no need for operator's intervention. The developed HF-LPME/CE-UV method is applied to the determination of acidic drugs in dried blood spot and wastewater samples and is characterized by excellent repeatability (RSD, 0.6–9.6%), linearity (r2, 0.9991–0.9999), enrichment (EF, 29–97), sensitivity (LOD, 0.2–3.4 μg/L), and sample throughput (7 samples/h). A further improvement of selected characteristics of the analytical method is achieved by the at-line coupling of HF-LPME to capillary isotachophoresis (ITP) with electrospray ionization-mass spectrometry (ESI-MS). The HF-LPME/ITP-ESI-MS system facilitates enhanced selectivity, matrix-free analytical signals, and up to 34-fold better sensitivity due to the use of ESI-MS detection and additional on-capillary ITP preconcentration of the HF-LPME extracts.