Bioanalytics in Quantitive (Bio)imaging/Mapping of Metallic Elements in Biological Samples

Quantitative elemental mapping of biological tissues by laser-induced breakdown spectroscopy using matrix recognition

The present study demonstrates the importance of converting signal intensity maps of organic tissues collected by laser-induced breakdown spectroscopy (LIBS) to elemental concentration maps and also proposes a methodology based on machine learning for its execution. The proposed methodology employs matrix-matched external calibration supported by a pixel-by-pixel automatic matrix (tissue type) recognition performed by linear discriminant analysis of the spatially resolved LIBS hyperspectral data set. On a swine (porcine) brain sample, we successfully performed this matrix recognition with an accuracy of 98% for the grey and white matter and we converted a LIBS intensity map of a tissue sample to a correct concentration map for the elements Na, K and Mg. Found concentrations in the grey and white matter agreed the element concentrations published in the literature and our reference measurements. Our results revealed that the actual concentration distribution in tissues can be quite different from what is suggested by the LIBS signal intensity map, therefore this conversion is always suggested to be performed if an accurate concentration distribution is to be assessed.

Health Risk Assessment Based on Source Identification of Heavy Metal(loid)s: A Case Study of Surface Water in the Lijiang River, China

In this study, 24 surface water samples were collected from the main trunk/tributary of the Lijiang River during the wet season (April) and the dry season (December) in 2021. The total concentration of 11 heavy metal(loid)s (Al, Cu, Pb, Zn, Cr, Ni, Co, Cd, Mn, As, and Hg) was determined to investigate their physicochemical properties and spatial-temporal distribution characteristics. The heavy metal evaluation index (HEI) and the positive matrix factorization (PMF) model were employed to evaluate water quality and to reveal quantitatively identified pollution sources for further investigation to obtain a health risk assessment using the hazard index (HI) and carcinogenic risk (CR) of various pollution sources. The mean concentrations of heavy metal(loid)s in surface water in the wet and dry seasons were ranked as: Al > Mn > Zn > Ni > Cd > Cr > Cu > As >Hg = Pb > Co, with the mean concentration of Hg being higher than the national Class II surface water environmental quality standard (GB3838-2002). In terms of time scale, the concentration of most heavy metal(loid)s was higher in the wet season; most heavy metal(loid)s were distributed mainly in the midstream area. HEI index indicated that the main water quality status was “slightly affected” in the study area. Five potential sources of pollution were obtained from the PMF model, including industrial activities, traffic sources, agricultural activities, domestic waste emissions, and natural resources. The source-oriented risk assessment indicated that the largest contributions of HI and CR were agricultural sources in the Lijiang River. This study provides a “target” for the precise control of pollution sources, which has a broad impact on improving the fine management of the water environment in the basin.

Elemental Profiling of North-East Indian Tea (Camellia sinensis) by ICP-MS and Assessment of Associated Health Risk

Tea is a perennial crop that requires acidic soil for better plant growth. Due to the acidic nature of tea-growing soil, metals can be easily absorbed by tea plants from growing medium. Other anthropogenic activities are also the major contributor of element in the tea. This study provided a comprehensive database of 24 elements which were analyzed by inductively coupled plasma mass spectrometry (ICP-MS). Selected 24 elements belong to alkali metal (Li, Rb, Cs), alkaline earth metal (Be, Sr, Ba), transition metal (V, Cr, Mn, Co, Ni, Cu, Zn, Ag, Cd, Hg), basic metal (Al, Ga, Sn, Tl, Pb), metalloid (As), non-metal (Se), and actinide (U). Total 321 drier mouth samples were collected during 2020-2021 from eight different regions (Darjeeling, Terai, Dooars, North Bank, Upper Assam, South Bank, Cachar, and Tripura) of north-east India. No inorganic mercury as well as uranium was detected in any tested tea samples. Mean concentrations of Be, As, Ga, Tl, Li, Se, Cd, Ag, Cs, V, Co, and Pb were at trace level, whereas macro-element mean concentrations were distributed in the manner of Al > Mn > Rb > Ba > Zn > Cu > Sr > Cr > Ni > Sn. Human health risk for non-carcinogenic and carcinogenic metals was also assessed for the studied elements. Hazard quotients (HQs) and hazard index (HI) values (< 1) for non-carcinogenic elements indicated no risk. The incremental lifetime cancer risk (ILCR) values for carcinogenic elements indicated no risk for As, Cd, and Pb and medium level risk for Ni. Study concluded that north-east Indian tea would not pose any health hazard.

Comparative Study on the Distribution of Essential, Non-Essential Toxic, and Other Elements across Trophic Levels in Various Edible Aquatic Organisms in Sri Lanka and Dietary Human Risk Assessment

Thirty-six elements are categorized as essential but toxic in excess amount (EBTEs), non-essential toxic (NETs), and Other in 29 different edible aquatic species dwelling in offshore pelagic, and coastal and estuarine (CE) ecosystems were investigated in Sri Lanka. Elements were analyzed using an energy-dispersive X-ray fluorescence (EDXRF) spectrometer, and an NIC MA-3000 Mercury Analyzer. EBTEs showed a negative relationship, whereas NETs showed a positive relationship between the concentration (mg/kg wet weight) and trophic levels in both ecosystems. EBTEs showed trophic dilution, whereas NETs showed trophic magnification. Some elements in a few organisms exceeded the maximum allowable limit which is safe for human consumption. There was a positive relationship (R² = 0.85) between the concentration of mercury and body weight of yellowfin tuna (YFT). For the widely consumed YFT, the calculated hazard index (HI) for the non-carcinogenic health and exposure daily intake of NETs for adults were 0.27 and 9.38 × 10^-5 mg/kg bw/day, respectively. The estimated provisional tolerable weekly intake (PTWI) (μg/kg bw/w) was 0.47 for arsenic and 0.05 for antimony, cadmium, mercury, and lead. The HI and PTWI values were below the recommended limits; thus, consumption of YFT does not pose any health risk for Sri Lankan adults.

Quantitative mapping of mercury and selenium in mushroom fruit bodies with laser ablation-inductively coupled plasma-mass spectrometry

This work describes the development of a novel method for quantitative mapping of Hg and Se in mushroom fruit body tissues with laser ablation coupled to inductively coupled plasma-mass spectrometry (LA-ICP-MS). Different parameters of the protocol for preparation of the standards used for quantification via external calibration were assessed, e.g., the dissolution temperature of gelatin standards and the addition of chitosan and L-cysteine as additives to the gelatin-based calibration droplets to better match the sample matrix. While chitosan was not suited for this purpose, the presence of L-cysteine considerably improved the figures of merit of the calibration, leading to limits of detection of 0.006 and 0.3 µg g-1 for Hg and Se, respectively, at a pixel size of 20 × 20 µm. Further, an in-house reference material, ideally suited for the validation of the method for application to mushroom samples, was successfully prepared from a paste of Boletus edulis. The newly developed method was used to investigate the distribution of Hg and Se in tissue sections of five porcini mushroom individuals of three different species (Boletus edulis, Boletus aereus, and Boletus pinophilus) and one sample of a parasol mushroom (Macrolepiota procera). For one sample, additional areas were ablated at higher spatial resolution, with a laser spot size down to 5 µm, which allows a detailed investigation of the spatial distribution of Hg and Se in mushrooms.

Skin Minerals: Key Roles of Inorganic Elements in Skin Physiological Functions

As odd as it may seem at first glance, minerals, it is what we are all about…or nearly. Although life on Earth is carbon-based, several other elements present in the planet’s crust are involved in and often indispensable for functioning of living organisms. Many ions are essential, and others show supportive and accessory qualities. They are operative in the skin, supporting specific processes related to the particular situation of this organ at the interface with the environment. Skin bioenergetics, redox balance, epidermal barrier function, and dermal remodeling are amongst crucial activities guided by or taking advantage of mineral elements. Skin regenerative processes and skin ageing can be positively impacted by adequate accessibility, distribution, and balance of inorganic ions.

Trace elements distribution in tropical tree rings through high-resolution imaging using LA-ICP-MS analysis

BACKGROUND

The distribution of trace elements in tree rings although poorly known may be useful to better understand environmental changes, pollution trends, long-term droughts, forest dieback processes, and biology of trees.

METHOD

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is used for imaging micronutrients and potentially toxic elements distribution, allowing the investigation of trace elements at high spatial resolution within the tree rings. To ensure a more efficient determination of micronutrients and potentially toxic elements, LA-ICP-MS instrumental conditions were optimized and carbon, a major element in wood, is used as an internal standard during analysis to correct for random fluctuations.

RESULTS

Spatial distributions maps of Ba, Cu, Fe, Mn, Ni, and Pb in growth layers of six tropical tree species were built-up using the LA-iMageS software, namely: Amburana cearensis (Fabaceae), Cedrela fissilis (Meliaceae), Hymenaea courbaril (Fabaceae), Maclura tinctoria (Moraceae), Parapiptadenia zehntneri (Fabaceae), Peltogyne paniculata (Fabaceae). A correlation between the trace element composition and different cell types (parenchyma, fiber, and vessel) was distinctly observed. It was observed a general pattern of Ba, Cu, Ni, Mn, and Pb accumulation mainly in the axial parenchyma and vessels. But the elemental composition of xylem cells is strongly species dependent. The multivariate analysis also points to a distinct accumulation of minerals between heartwood and sapwood in the same species.

CONCLUSIONS

Imaging both essential and deleterious element distributions in the tree rings may improve visualization and can effectively contribute to understanding the lifetime metabolism of trees and evaluating the effects of environmental changes related to climatic seasonality, pollution, and future paleoclimate reconstructions.

Subcellular Localization of Copper-Cellular Bioimaging with Focus on Neurological Disorders

As an essential trace element, copper plays a pivotal role in physiological body functions. In fact, dysregulated copper homeostasis has been clearly linked to neurological disorders including Wilson and Alzheimer’s disease. Such neurodegenerative diseases are associated with progressive loss of neurons and thus impaired brain functions. However, the underlying mechanisms are not fully understood. Characterization of the element species and their subcellular localization is of great importance to uncover cellular mechanisms. Recent research activities focus on the question of how copper contributes to the pathological findings. Cellular bioimaging of copper is an essential key to accomplish this objective. Besides information on the spatial distribution and chemical properties of copper, other essential trace elements can be localized in parallel. Highly sensitive and high spatial resolution techniques such as LA-ICP-MS, TEM-EDS, S-XRF and NanoSIMS are required for elemental mapping on subcellular level. This review summarizes state-of-the-art techniques in the field of bioimaging. Their strengths and limitations will be discussed with particular focus on potential applications for the elucidation of copper-related diseases. Based on such investigations, further information on cellular processes and mechanisms can be derived under physiological and pathological conditions. Bioimaging studies might enable the clarification of the role of copper in the context of neurodegenerative diseases and provide an important basis to develop therapeutic strategies for reduction or even prevention of copper-related disorders and their pathological consequences.

Gadolinium as an Emerging Microcontaminant in Water Resources: Threats and Opportunities

As a result of high doses of paramagnetic gadolinium (Gd) chelates administered in magnetic resonance imaging (MRI) exams, their unmetabolized excretion, and insufficient removal in wastewater treatment plants (WWTPs), large amounts of anthropogenic Gd (Gdanth) are released into surface water. The upward trend of gadolinium-based contrast agent (Gd-CA) administrations is expected to continue growing and consequently higher and higher anthropogenic Gd concentrations are annually recorded in water resources, which can pose a great threat to aquatic organisms and human beings. In addition, the feasibility of Gd retention in patients administered with Gd-CAs repeatedly, and even potentially fatal diseases, including nephrogenic systemic fibrosis (NSF), due to trace amounts of Gd have recently arisen severe health concerns. Thus, there is a need to investigate probable adverse health effects of currently marketed Gd-CAs meticulously and to modify the actual approach in using Gd contrast media in daily practice in order to minimize unknown possible health risks. Furthermore, the employment of enhanced wastewater treatment processes that are capable of removing the stable contrast agents, and the evaluation of the ecotoxicity of Gd chelates and human exposure to these emerging contaminants through dermal and ingestion pathways deserve more attention. On the other hand, point source releases of anthropogenic Gd into the aquatic environment presents the opportunity to assess surface water—groundwater interactions and trace the fate of wastewater plume as a proxy for the potential presence of other microcontaminants associated with treated wastewater in freshwater and marine systems.

Multimodal imaging of undecalcified tissue sections by MALDI MS and μXRF

Matrix-assisted laser desorption/ionisation mass spectrometric imaging (MALDI MSI) is a technique that provides localized information on intact molecules in a sample. Micro X-ray fluorescence (μXRF) imaging allows the examination of the spatial distribution of elements in a sample without any morphological changes. These methods have already been applied separately to different tissues, organs, plants and bacterial films, but, to the best of our knowledge, they have yet to be coupled in a multimodal analysis. In this proof-of-principle study, we established and tested sample preparation strategies, allowing the multimodal analysis of lipids (sphingomyelin and phosphatidylcholines) and elements relevant to bone structures as calcium, phosphorous and sulphur in the very same sample section of a chicken phalanx without tissue decalcification. The results of the investigation of such parameters as adhesive tapes supporting tissue sections, and the sequence of the imaging experiments are presented. We show specific lipid distributions in skin, cartilage, muscle, nail, and the intact morphology of bone by calcium and phosphorus imaging. A combination of molecular and elemental imaging was achieved, thus, providing now for the first time the possibility of gathering MALDI MSI and μXRF information from the very same sample without any washing steps omitting therefore the analytical artifacts that inevitably occur in approaches using consecutive tissue sections. The proposed combination can benefit in research studies regarding bone diseases, osteoporosis, osteoarthritis, cartilage failure, bone/tendon distinguishing, where elemental and lipid interaction play an essential role.

Mass spectrometry is a multifaceted weapon to be used in the battle against Alzheimer's disease: Amyloid beta peptides and beyond

Amyloid-β peptide (Aβ) accumulation and aggregation have been considered for many years the main cause of Alzheimer's disease (AD), and therefore have been the principal target of investigation as well as of the proposed therapeutic approaches (Grasso [2011] Mass Spectrom Rev. 30: 347-365). However, the amyloid cascade hypothesis, which considers Aβ accumulation the only causative agent of the disease, has proven to be incomplete if not wrong. In recent years, actors such as metal ions, oxidative stress, and other cofactors have been proposed as possible co-agents or, in some cases, main causative factors of AD. In this scenario, MS investigation has proven to be fundamental to design possible diagnostic strategies of this elusive disease, as well as to understand the biomolecular mechanisms involved, in the attempt to find a possible therapeutic solution. We review the current applications of MS in the search for possible Aβ biomarkers of AD to help the diagnosis of the disease. Recent examples of the important contributions that MS has given to prove or build theories on the molecular pathways involved with such terrible disease are also reviewed.

iQuant2: Software for Rapid and Quantitative Imaging Using Laser Ablation-ICP Mass Spectrometry

We report on the development of a software program named iQuant2 which creates visual images from two-dimensional signal intensity data obtained by a laser ablation-ICP-mass spectrometry (LA-ICPMS) technique. Time-resolved signal intensity profiles can be converted to position resolved signal intensity data based on the rastering rate (μm s⁻¹) of the laser ablation. Background signal intensities obtained without laser ablation (gas blank) are used as the background, and all of the blank-subtracted intensity data can be used for the imaging analysis. With this software, deformation of the created image can be corrected visually on a PC screen. The line profile analysis between the user-selected points can be observed using the iQuant2 software. To accomplish this, data points on the profile line were automatically calculated based on the interpolation between the analysis points. The resulting imaging data can be exported and stored as JPEG, BMP or PNG formats for further processing. Moreover, a semi-quantitative analysis can be made based on the coupling of the external correction of the RSF (relative sensitivity factor) using NIST SRM610 with normalization of the corrected signal intensity data being 100%. The calculated abundance data for major elements are in reasonable agreement with the values obtained by electron probe micro analyzer (EPMA). With the software developed in this study, both the rapid imaging and semi-quantitative determinations can be made.

Elemental bioimaging by means of LA-ICP-OES: investigation of the calcium, sodium and potassium distribution in tobacco plant stems and leaf petioles

Laser ablation-inductively coupled plasma-optical emission spectroscopy (LA-ICP-OES) is presented as a valuable tool for elemental bioimaging of alkali and earth alkali elements in plants. Whereas LA-ICP-OES is commonly used for micro analysis of solid samples, laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) has advanced to the gold standard for bioimaging. However, especially for easily excitable and ubiquitous elements such as alkali and earth alkali elements, LA-ICP-OES holds some advantages regarding simultaneous detection, costs, contamination, and user-friendliness. This is demonstrated by determining the calcium, sodium and potassium distribution in tobacco plant stem and leaf petiole tissues. A quantification of the calcium contents in a concentration range up to 1000 μg g-1 using matrix-matched standards is presented as well. The method is directly compared to a LA-ICP-MS approach by analyzing parallel slices of the same samples.

Analytical Techniques in Lipidomics: State of the Art

Current studies related to lipid identification and determination, or lipidomics in biological samples, are one of the most important issues in modern bioanalytical chemistry. There are many articles dedicated to specific analytical strategies used in lipidomics in various kinds of biological samples. However, in such literature, there is a lack of articles dedicated to a comprehensive review of the actual analytical methodologies used in lipidomics. The aim of this article is to characterize the lipidomics methods used in modern bioanalysis according to the methodological point of view: (1) chromatography/separation methods, (2) spectroscopic methods and (3) mass spectrometry and also hyphenated methods. In the first part, we discussed thin layer chromatography (TLC), high-pressure liquid chromatography (HPLC), gas chromatography (GC) and capillary electrophoresis (CE). The second part includes spectroscopic techniques such as Raman spectroscopy (RS), Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance (NMR). The third part is a synthetic review of mass spectrometry, matrix-assisted laser desorption/ionization (MALDI), hyphenated methods, which include liquid chromatography-mass spectrometry (LC-MS), gas chromatography-mass spectrometry (GC-MS) and also multidimensional techniques. Other aspects are the possibilities of the application of the described methods in lipidomics studies. Due to the fact that the exploration of new methods of lipidomics analysis and their applications in clinical and medical studies are still challenging for researchers working in life science, we hope that this review article will be very useful for readers.

Chemical bioimaging for the subcellular localization of trace elements by high contrast TEM, TEM/X-EDS, and NanoSIMS

Chemical bioimaging offers an important contribution to the investigation of biochemical functions, biosorption and bioaccumulation processes of trace elements via their localization at the cellular and even at the subcellular level. This paper describes the combined use of high contrast transmission electron microscopy (HC-TEM), energy dispersive X-ray spectroscopy (X-EDS), and nano secondary ion mass spectrometry (NanoSIMS) applied to a model organism, the unicellular green algae Chlamydomonas reinhardtii. HC-TEM providing a lateral resolution of 1nm was used for imaging the ultrastructure of algae cells which have diameters of 5-10μm. TEM coupled to X-EDS (TEM/X-EDS) combined textural (morphology and size) analysis with detection of Ca, P, K, Mg, Fe, and Zn in selected subcellular granules using an X-EDS probe size of approx. 1μm. However, instrumental sensitivity was at the limit for trace element detection. NanoSIMS allowed chemical imaging of macro and trace elements with subcellular resolution (element mapping). Ca, Mg, and P as well as the trace elements Fe, Cu, and Zn present at basal levels were detected in pyrenoids, contractile vacuoles, and granules. Some metals were even localized in small vesicles of about 200nm size. Sensitive subcellular localization of trace metals was possible by the application of a recently developed RF plasma oxygen primary ion source on NanoSIMS which has shown good improvements in terms of lateral resolution (below 50nm), sensitivity, and stability. Furthermore correlative single cell imaging was developed combining the advantages of TEM and NanoSIMS. An advanced sample preparation protocol provided adjacent ultramicrotome sections for parallel TEM and NanoSIMS analyses of the same cell. Thus, the C. reinhardtii cellular ultrastructure could be directly related to the spatial distribution of metals in different cell organelles such as vacuoles and chloroplast.

Techniques for measuring cellular zinc

The development and improvement of fluorescent Zn²⁺ sensors and Zn²⁺ imaging techniques have increased our insight into this biologically important ion. Application of these tools has identified an intracellular labile Zn²⁺ pool and cultivated further interest in defining the distribution and dynamics of labile Zn²⁺. The study of Zn²⁺ in live cells in real time using sensors is a powerful way to answer complex biological questions. In this review, we highlight newly engineered Zn²⁺ sensors, methods to test whether the sensors are accessing labile Zn²⁺, and recent studies that point to the challenges of using such sensors. Elemental mapping techniques can complement and strengthen data collected with sensors. Both mass spectrometry-based and X-ray fluorescence-based techniques yield highly specific, sensitive, and spatially resolved snapshots of metal distribution in cells. The study of Zn²⁺ has already led to new insight into all phases of life from fertilization of the egg to life-threatening cancers. In order to continue building new knowledge about Zn²⁺ biology it remains important to critically assess the available toolset for this endeavor.