Trace Elements In Biological Tissues Research Articles

Elemental Bio-imaging of Biological Samples by Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry

Abstract Trace elements play very important roles in biological organism and are closely related to many diseases. New analytical methods are urgently needed for in situ determination of trace elements in biological tissues or single cells. A method based on laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) was developed here for in situ analysis. Line ablation mode was chosen and the output energy of the laser was optimized at a low fluence of less than 1 J cm −2 . Two kinds of elemental image of both a coronal section from mouse brain and single cells exposed to gold nanoparticles were obtained by the developed method. Due to the unique characteristic, such as good spatial resolution, excellent detection limit, and reasonable running cost, LA-ICP-MS will be applied widely and become a useful tool in biomedical research in the future.

Laser spectrometry for multi-elemental imaging of biological tissues.

An increasing interest has arisen in research focused on metallic and organic ions that play crucial roles in both physiological and pathological metabolic processes. Current methods for the observation of trace elements in biological tissues at microscopic spatial resolution often require equipment with high complexity. We demonstrate a novel approach with an all-optical design and multi-elemental scanning imaging, which is unique among methods of elemental detection because of its full compatibility with standard optical microscopy. This approach is based on laser-induced breakdown spectroscopy (LIBS), which allows the elements in a tissue sample to be directly detected and quantified under atmospheric pressure. We successfully applied this method to murine kidneys with 10 µm resolution and a ppm-level detection limit to analyze the renal clearance of nanoparticles. These results offer new insight into the use of laser spectrometry in biomedical applications in the field of label-free elemental mapping of biological tissues.

A quantitative x-ray detection system for gold nanoparticle tumour biomarkers

X-ray fluorescence techniques have proven beneficial for identifying and quantifying trace elements in biological tissues. A novel approach is being developed that employs x-ray fluorescence with an aim to locate heavy nanoparticles, such as gold, which are embedded into tissues. Such nanoparticles can be functionalized to act as markers for tumour characteristics to map the disease state, with the future aim of imaging them to inform cancer therapy regimes. The uptake of functionalized nanoparticles by cancer cells will also enable detection of small clusters of infiltrating cancer cells which are currently missed by commonly used imaging modalities. The novel system, consisting of an energy-resolving silicon drift detector with high spectral resolution, shows potential in both quantification of and sensitivity to nanoparticle concentrations typically found in tumours. A series of synchrotron measurements are presented; a linear relationship between fluorescence intensity and gold nanoparticle (GNP) concentration was found down to 0.005 mgAu ml−1, the detection limit of the system. Successful use of a bench-top source, suitable for possible future clinical use, is also demonstrated, and found not to degrade the detection limit or accuracy of the GNP concentration measurement. The achieved system sensitivity suggests possible future clinical usefulness in measuring tumour uptake in vivo, particularly in shallow tumour sites and small animals, in ex vivo tissue and in 3D in vitro research samples.

Leaching of Trace Elements from Biological Tissue by Formalin Fixation

In studies of trace elements in biological tissue, it is imperative that sample handling does not substantially change element concentrations. In many cases, fresh tissue is not available for study, but formalin-fixed tissue is. Formalin fixation has the potential to leach elements from the tissue, but few studies have been published in this area. The concentrations of 19 elements were determined by high-resolution inductively coupled plasma mass spectrometry in formalin in which human and rat brain samples had been stored for different time durations ranging from weeks up to several years. Additional analysis was carried out in fixed brain samples. There was substantial leaching of elements from the tissue into the formalin, and the leaching varied considerably between different elements. For example, formalin concentrations of As, Cd, Mg, Rb, and Sb increased more than 100-fold upon long-term (years) storage, while for Ni and Cr, the leaching was negligible. The degree of leaching was strongly time-dependent. In conclusion, formalin fixation and storage of biological tissue has the potential to leach substantial fractions of several trace elements from the tissue. The potential of leaching must be critically considered when using formalin-fixed biological tissue in trace metal analysis.

Breast cancer detection using neutron stimulated emission computed tomography: Prominent elements and dose requirements

Neutron stimulated emission computed tomography (NSECT) is being developed to noninvasively determine concentrations of trace elements in biological tissue. Studies have shown prominent differences in the trace element concentration of normal and malignant breast tissue. NSECT has the potential to detect these differences and diagnose malignancy with high accuracy with dose comparable to that of a single mammogram. In this study, NSECT imaging was simulated for normal and malignant human breast tissue samples to determine the significance of individual elements in determining malignancy. The normal and malignant models were designed with different elemental compositions, and each was scanned spectroscopically using a simulated 2.5 MeV neutron beam. The number of incident neutrons was varied from 0.5 million to 10 million neutrons. The resulting gamma spectra were evaluated through receiver operating characteristic (ROC) analysis to determine which trace elements were prominent enough to be considered markers for breast cancer detection. Four elemental isotopes (133Cs, 81Br, 79Br, and 87Rb) at five energy levels were shown to be promising features for breast cancer detection with an area under the ROC curve (A(Z)) above 0.85. One of these elements--87Rb at 1338 keV--achieved perfect classification at 10 million incident neutrons and could be detected with as low as 3 million incident neutrons. Patient dose was calculated for each gamma spectrum obtained and was found to range from between 0.05 and 0.112 mSv depending on the number of neutrons. This simulation demonstrates that NSECT has the potential to noninvasively detect breast cancer through five prominent trace element energy levels, at dose levels comparable to other breast cancer screening techniques.

Proton induced X-ray analysis of Nd:YAG

Proton induced X-ray emission (PIXE) is famously effective for revealing trace elements in biological tissue in which the majority elements (H, C, N and O) have low Z. When the majority elements in a compound have high atomic numbers, the yield of K and L X-rays following proton bombardment often mask those of lighter trace elements, or dominate the counting rate to such an extent that the time required to detect a small signal with statistical significance becomes prohibitively long. We have confronted these difficulties with a PIXE analysis of YAG crystals and ceramics with neodymium doping up to nine atomic percent. The K X-rays of aluminum (1.74keV) and yttrium (15keV) dominate the PIXE spectrum. The L X-rays from neodymium group near 5keV provide determination of the neodymium content of Nd:YAG to 1:1000. Clear signals of traces of zinc, nickel and copper were recovered from the spectra of some of the samples by persistent experiments at low counting rates that avoided pile up of the signals from the majority elements. An appropriate polyethylene filter was used to prevent scattered protons from striking the detector and its supporting structure. Double proton beam collimation prevented spurious PIXE from the chamber walls, beam stop and the primary collimator. No material was near the sample except a polyethylene film strip that supported the sample.

Determination of trace elements in biological tissues by aluminum block digestion and spike-height flame atomic absorption spectrometry

A method for the determination of cadmium, copper, lead, and zinc in biological tissues using small volumes of digest is described. An aluminium heating block is used to digest samples and elements are determined by spike-height flame atomic absorption spectrometry. Interferences have been assessed and the sample decomposition procedure evaluated.

Determination of trace elements in human serum by energy dispersive X-ray fluorescence

A system of energy dispersive X-ray fluorescence spectrometry (EDXRF) has been described to measure the concentrations of iron, copper, zinc, bromine, selenium and arsenic in human serum of healthy adults. Methods of sample preparations, standardization, and analysis have been presented. Data have been presented to show the accuracy, precision and sensitivity of the EDXRF system. The major advantages of using this system for the determination of trace elements in biological tissues are the relatively small sample size, ease of sample preparation, and the ability to perform rapid multi-element analysis on a single sample. The need for multi-element analysis has become apparent from the increased knowledge of trace element interactions in biological systems. The EDXRF system provides a solution for this need. Although the present system was applied only to the measurement of six elements, in principle the concentrations of V, Cr, Mn, Ni and Ti could also be routinely determined with improvements in technology and sensitivity.

Retention of metabolised trace elements in biological tissues following different drying procedures. Part II. Caesium, cerium, manganese, scandium, silver and tin in rat tissues.

Losses of silver, cerium, caesium, manganese, scandium and tin during freeze drying and oven drying at 80, 105 and 120 °C were studied in rat tissues and faces that contained radioactive isotopes. No loss was observed for any of these elements on freeze drying. A significant loss of tin was observed in muscle even at 80 °C, and in kidney and liver at 105 °C. Also, cerium and manganese were lost from heart and muscle at this temperature. An increase in the temperature to 120 °C was found to be safe only for silver and caesium in all of the tissues. For the remaining four elements the following losses were observed: up to 5% for cerium in brain and heart, for scandium in fur and heart and for manganese in liver and muscle; up to 10% for scandium in kidney and muscle and for tin in blood, fur, heart, liver, ovary and uterus; and over 10% for tin in brain, kidney, lung and muscle.

Analysis of human blood and liver tissue for copper, zinc and iron by the method of proton-induced X-ray emission analysis

The method of proton-induced X-ray emission (or PIXE) analysis has been investigated with reference to the study of minor and trace elements in biological tissue. Methods of specimen preparation have been investigated, and optimum instrumental conditions arrived at. The lower limits of detection for lead and zinc in blood have been investigated and have been found to be approximately 0.3 and 0.1 ppm for lead and zinc respectively, for a proton energy of 2.5 MeV. The concentrations of copper, zinc and iron have been studied in normal and diseased human liver tissue. In cirrhotic tissue the copper levels are substantially raised. We note also a diminution in liver iron in a case of alcoholic cirrhosis associated with clinical anaemia; and a blood zinc deficiency in primary biliary cirrhosis. The results are discussed in relation to existing work.

Retention of the metabolized trace elements in biological tissues following different drying procedures: I. Antimony, cobalt, iodine, mercury, selenium and zinc in rat tissues

Loss of Sb, Co, I, Hg, Se and Zn during freeze-drying and oven-drying at 80, 105 and 120 °C were studied in rat tissues that contained metabolized radioactive isotopes. No loss was observed for any of the 6 elements on freeze-drying. However, tissue-specific differences were observed in many cases for Hg, Se, I and Sb on oven-drying. A significant loss of Hg was observed in liver even at 80 °C, and for brain 105 °C. Se was lost from whole blood, brain, lung and muscle at 120 °C. Sb was lost from whole blood at 105 °C, but from brain, kidney, lung and spleen at 120 °C. Iodine was also lost from whole blood, kidney, blood serum, erythrocytes, brain, lung and muscle at 120 °C. Although the losses were statistically significant, they remained in most cases between 2 and 10%, with the exception of Hg at 120 °C, where the loss in some of the tissues were unpredictable. For urine, freeze-drying and oven-drying at 80 °C was found to be relatively safe for Hg and I. At 105 °C and above, serious loss of Hg was observed. In this experiment, the elements Zn, Co, Sb and Se were not studied for urine.