Application of scanning electron microscopy and X-ray microanalysis: FE-SEM, ESEM-EDS, and EDS mapping for studying the characteristics of topographical microstructure and elemental mapping of human cardiac calcified deposition

A comparative evaluation of recarbonated CaCO3 derived from limestone under oxy-fuel circulating fluidized bed conditions

SO₂ emissions from coal-fired boilers are air pollutants and a source of acid rain, causing extensive environmental pollution. Limestone (CaCO₃) is a Ca-based sorbent which is injected into circulating fluidized bed (CFB) boilers, where it combines with SO₂ to produce calcium sulfate (CaSO₄). As a result, SO₂ emissions from a power plant are reduced. In this study, CaCO₃ addition was proposed and the desulfurization efficiency improved. The direct desulfurization reaction is dominant in a commercial CFB boiler due to the high CO₂ partial pressure, but CaO is formed at a fast reaction rate by calcination in the high temperature or in the low CO₂ partial pressure region. When CaO remains in the loop seal, it is exposed to a high CO₂ partial pressure condition moving through the recirculation section for an extended period and re-injected into the furnace as recarbonated CaCO₃. To analyze the direct desulfurization reaction kinetics, a shrink core model in which the reaction proceeds inside the particle was adopted. Surface observations through FE-SEM of CaSO₄ produced by the 180 minute long desulfurization experiment using TGA suggest that the CaSO₄ crystal growth rate increased after the pre-treatment (recarbonation) of limestone. Recarbonation lowered the limestone crystallinity, causing a faster reaction. The CaCO₃ recarbonation increased the Ca utilization by more than 20% when the direct desulfurization reaction occurred. The TGA experiments show that recarbonation contributes to CaSO₄ conversion. Increasing the desulfurization efficiency using recarbonation can reduce the fixed investment and operating costs of oxy-fuel CFB plants because only desulfurization in the furnace is able to meet SO₂ emission regulations or lower the flue gas desulfurization (FGD) dependence. Accordingly, the desulfurization conversions of recarbonated CaCO₃ and limestone were compared in this study. Morphological changes in the limestone were also evaluated using XRD, FE-SEM, and other analysis methods.

Incorporation of Hybrid Nanomaterial in Dental Porcelains: Antimicrobial, Chemical, and Mechanical Properties

Biofilm formation on biomaterials is a challenge in the health area. Antimicrobial substances based on nanomaterials have been proposed to solve this problem. The aim was to incorporate nanostructured silver vanadate decorated with silver nanoparticles (β-AgVO3) into dental porcelains (IPS Inline and Ex-3 Noritake), at concentrations of 2.5% and 5%, and evaluate the surface characteristics (by SEM/EDS), antimicrobial activity (against Streptococcus mutans, Streptococcus sobrinus, Aggregatibacter actinomycetemcomitans, and Pseudomonas aeruginosa), silver (Ag+) and vanadium (V4+/V5+) ions release, and mechanical properties (microhardness, roughness, and fracture toughness). The β-AgVO3 incorporation did not alter the porcelain's components, reduced the S. mutans, S. sobrinus and A. actinomycetemcomitans viability, increased the fracture toughness of IPS Inline, the roughness for all groups, and did not affect the microhardness of the 5% group. Among all groups, IPS Inline 5% released more Ag+, and Ex-3 Noritake 2.5% released more V4+/V5+. It was concluded that the incorporation of β-AgVO3 into dental porcelains promoted antimicrobial activity against S. mutans, S. sobrinus, and A. actinomycetemcomitans (preventing biofilm formation), caused a higher release of vanadium than silver ions, and an adequate mechanical behavior was observed. However, the incorporation of β-AgVO3 did not reduce P. aeruginosa viability and increased the surface roughness of dental porcelains.

Magnetic Field Triggerable Macroporous PDMS Sponge Loaded with an Anticancer Drug, 5-Fluorouracil

This study aims to prepare, optimize, and characterize magnetic-field-sensitive sugar-templated polydimethylsiloxane (PDMS) sponges for localized delivery of an anticancer drug, 5-fluorouracil (FLU). For this purpose, different concentrations of carbonyl iron (CI) and magnetite Fe₃O₄ nanopowders were embedded as magnetosensitive materials in PDMS resins for the fabrication of macroporous sponges via a sugar-template process. The process is environmentally friendly and simple. The fabricated interconnected macroporous magnetic particles loaded PDMS sponges possess flexible skeletons and good recyclability because of their recoverability after compression (deformation) without any breakdown. The prepared magnetic PDMS sponges were evaluated for their morphology (SEM and EDS), porosity (absorbency), elastic modulus, deformation under a magnetic field, thermostability, and in vitro cell studies. All physicochemical and magnetomechanical analysis confirmed that the optimized magnetic-field-sensitive PDMS sponge can provide an efficient method for delivering an on-demand dose of anticancer drug solutions at a specific location and timing with the aid of controlled magnetic fields.

Molecular Aspects and Prognostic Significance of Microcalcifications in Human Pathology: A Narrative Review

The presence of calcium deposits in human lesions is largely used as imaging biomarkers of human diseases such as breast cancer. Indeed, the presence of micro- or macrocalcifications is frequently associated with the development of both benign and malignant lesions. Nevertheless, the molecular mechanisms involved in the formation of these calcium deposits, as well as the prognostic significance of their presence in human tissues, have not been completely elucidated. Therefore, a better characterization of the biological process related to the formation of calcifications in different tissues and organs, as well as the understanding of the prognostic significance of the presence of these calcium deposits into human tissues could significantly improve the management of patients characterized by microcalcifications associated lesions. Starting from these considerations, this narrative review highlights the most recent histopathological and molecular data concerning the formation of calcifications in breast, thyroid, lung, and ovarian diseases. Evidence reported here could deeply change the current point of view concerning the role of ectopic calcifications in the progression of human diseases and also in the patients’ management. In fact, the presence of calcifications can suggest an unfavorable prognosis due to dysregulation of normal tissues homeostasis.

Considerations and Influencing Parameters in EDS Microanalysis of Biogenic Hydroxyapatite

Calcium phosphates (CPs) used as biomaterials have been intensively studied in recent years. In most studies, the determination of the chemical composition is mandatory. Due to the versatility and possibilities of performing qualitative and quantitative compositional analyses, energy dispersive spectrometry (EDS) is a widely used technique in this regard. The range of calcium phosphates is very diverse, the first method of approximating the type of compound being EDS microanalysis, by assessing the atomic Ca/P ratio. The value of this ratio can be influenced by several factors correlated with instrumental parameters and analysed samples. This article highlights the influence of the electron beam acceleration voltage (1 kV-30 kV) and of the particle size of calcium phosphate powders on the EDS analysis results. The characterised powders were obtained from bovine bones heat-treated at 1200 °C for 2 h, which have been ground and granulometrically sorted by mechanical vibration. The granulometric sorting generated three types of samples, with particle sizes < 20 μm, < 40 μm and < 100 μm, respectively. These were morphologically and dimensionally analysed by scanning electron microscopy (SEM) and compositionally by EDS, after the spectrometer was calibrated with a standard reference material (SRM) from NIST (National Institute of Standards and Technology). The results showed that the adjusting of acceleration voltage and of the powder particle size significantly influences the spectrum profile and the results of EDS analyses, which can lead to an erroneous primary identification of the analysed calcium phosphate type.

A Novel Approach for Detecting Unique Variations among Infectious Bacterial Species in Endocarditic Cardiac Valve Vegetation

Infectious endocarditis (IE) remains one of the deadliest heart diseases with a high death rate, generally following thrombo-embolic events. Today, therapy is based on surgery and antibiotic therapy. When thromboembolic complications in IE patients persist, this is often due to our lack of knowledge regarding the pathophysiological development and organization of cells in the vegetation, most notably the primordial role of platelets and further triggered hemostasis, which is related to the diversity of infectious microorganisms involved. Our objective was to study the organization of IE vegetations due to different bacteria species in order to understand the related pathophysiological mechanism of vegetation development. We present an approach for ultrastructural analysis of whole-infected heart valve tissue based on scanning electron microscopy and energy-dispersive X-ray spectroscopy. Our approach allowed us to detect differences in cell organization between the analyzed vegetations and revealed a distinct chemical feature in viridans Streptococci ones. Our results illustrate the benefits that such an approach may bring for guiding therapy, considering the germ involved for each IE patient.

Alcalase Microarray Base on Metal Ion Modified Hollow Mesoporous Silica Spheres as a Sustainable and Efficient Catalysis Platform for Proteolysis

The industrial exploitation of protease is limited owing to its sensitivity to environmental factors and autolysis during biocatalytic processes. In the present study, the alcalase microarray (Bacillus licheniformis, alcalase@HMSS-NH₂-Metal) based on different metal ions modified hollow mesoporous silica spheres (HMSS-NH₂-Metal) was successfully developed via a facile approach. Among the alcalase@HMSS-NH₂-Metal (Ca²⁺, Zn²⁺, Fe³⁺, Cu²⁺), the alcalase@HMSS-NH₂-Fe³⁺ revealed the best immobilization efficiency and enzymatic properties. This tailor-made nanocomposite immobilized alcalase on a surface-bound network of amino-metal complex bearing protein-modifiable sites via metal-protein affinity. The coordination interaction between metal ion and alcalase advantageously changed the secondary structure of enzyme, thus significantly enhanced the bioactivities and thermostability of alcalase. The as-prepared alcalase@HMSS-NH₂-Fe³⁺ exhibited excellent loading capacity (227.8 ± 23.7 mg/g) and proteolytic activity. Compared to free form, the amidase activity of alcalase microarray increased by 5.3-fold, the apparent kinetic constant V_max/K_m of alcalase@HMSS-NH₂-Fe³⁺ (15.6 min⁻¹) was 1.9-fold higher than that of free alcalase, and the biocatalysis efficiency increased by 2.1-fold for bovine serum albumin (BSA) digestion. Moreover, this particular immobilization strategy efficiently reduced the bioactivities losses of alcalase caused by enzyme leaking and autolysis during the catalytic process. The alcalase microarray still retained 70.7 ± 3.7% of the initial activity after 10 cycles of successive reuse. Overall, this study established a promising strategy to overcome disadvantages posed by free alcalase, which provided new expectations for the application of alcalase in sustainable and efficient proteolysis.

X-ray-Based Spectroscopic Techniques for Characterization of Polymer Nanocomposite Materials at a Molecular Level

This review provides detailed fundamental principles of X-ray-based characterization methods, i.e., X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy, and near-edge X-ray absorption fine structure, and the development of different techniques based on the principles to gain deeper understandings of chemical structures in polymeric materials. Qualitative and quantitative analyses enable obtaining chemical compositions including the relative and absolute concentrations of specific elements and chemical bonds near the surface of or deep inside the material of interest. More importantly, these techniques help us to access the interface of a polymer and a solid material at a molecular level in a polymer nanocomposite. The collective interpretation of all this information leads us to a better understanding of why specific material properties can be modulated in composite geometry. Finally, we will highlight the impacts of the use of these spectroscopic methods in recent advances in polymer nanocomposite materials for various nano- and bio-applications.

Differential diagnosis of calcified nodules from a medieval Székely woman in Transylvania

OBJECTIVE

To differentially diagnose two calcified objects found with the well-preserved and nearly complete skeletal remains excavated in June 2012 by the Haáz Rezső Múzeum in Odorheiu Secuiesc, Romania.

MATERIAL

Two objects measuring 25.55 × 18.23 mm and 17.62 × 16.38 mm found with the skeletal remains of a probable female approximately 25-35 years old at the time of death.

METHODS

Analysis utilized X-ray, SEM, EDS, CT scanning, and gross morphology to assess pathological conditions with calcification as a common sign.

RESULTS

Multiple analyses of the objects revealed two roughened ovoid nodes with internal hollows and openings. Elemental analysis indicated an organic origin, likely representing calcified soft tissue.

CONCLUSIONS

Differential diagnosis determined the calcified nodules to be consistent with calcified tumors, and most consistent with a calcified leiomyoma with cystic degeneration, potentially uterine.

SIGNIFICANCE

The identification of the calcified nodules as most consistent with calcified uterine leiomyomas adds to the paucity of paleopathological literature on calcified leiomyomas and calcified tumors more broadly. It also allows for an important discussion of the health of women in medieval Transylvania.

LIMITATIONS

Interpretation would be aided if a more precise origination within the body was known. Careful excavation and improved recognition of organic objects is necessary for a more definite diagnosis.

SUGGESTIONS FOR FURTHER RESEARCH

Soft tissue calcifications are a common process in a wide variety of diseases and can arise in all areas of the body. Pathological calcifications are relatively common in modern contexts, but remain rare in paleopathological literature.

Color and genesis of californite from Pakistan: insights from μ-XRF mapping, optical spectra and X-ray photoelectron spectroscopy

Four californite samples from Pakistan with yellowish-green, green and reddish-brown colors were investigated by combining the methods of μ-XRF mapping, XRD, Raman spectra, optical spectra, EPMA and XPS. The results show that the californite is composed mainly of microcrystalline vesuvianite and smaller amounts of clinochlore. Based on the distribution of the clinochlore, the californite can be divided into three types. The gem-quality californite is composed of microcrystalline vesuvianite and has a translucent appearance. The ordinary-quality californite contains microcrystalline vesuvianite as well as clinochlore, and it has an opaque appearance. The transitional-type has properties that are intermediate between those of gem- and ordinary-quality californite. Octahedrally coordinated iron and chromium in the clinochlore reduce the transparency and contribute to the opaque green and yellowish-green colors of the californite. At sites where there is no clinochlore, Cr³⁺ in the octahedrally coordinated site Y3 of the vesuvianite is mainly responsible for the green tone of the californite, Fe³⁺ and Mn³⁺ at the Y3 site contribute mainly to the yellowish-green and reddish-brown colors, respectively. The Fe²⁺ → Fe³⁺ charge transfer also occurs in vesuvianite and partly influences the appearance of the californite. The actual color of californite that lacks clinochlore is due to the synergy of Cr³⁺, Fe³⁺ and Mn³⁺ crystal field transfers at the octahedral site Y3 as well as the Fe²⁺ → Fe³⁺ charge transfer in the vesuvianite. Vesuvianite in the californite can be assigned to the P4/n space group, and the occurrence of clinochlore reflects the fact that the californite from Pakistan formed under medium-grade metamorphic conditions at temperatures of ~300–500 °C. The content of clinochlore provides a basis for grading the quality of the californite.

Echocardiographic manifestations and chemical composition of stenotic bicuspid aortic valves

Bicuspid aortic valve (BAV) is an inherited form of heart disease with only two aortic valve leaflets via a disorder of cardiac valvulogenesis. We investigated the in vivo echocardiographic features of cardiac morphology in patients with BAV and the ex vivo compositional components of all the excised BAV leaflets isolated from BAV patients. Three BAV patients were randomly selected. All patients underwent 2D transthoracic echocardiography (TTE) with a Doppler ultrasound tool. The compositional components of each respective BAV leaflet for all the excised BAVs were determined by a portable fiber-optic Raman spectroscopy. Preoperative TTE revealed the thickened and calcified BAV leaflets, and stenotic aortic flow for all BAV patients. These BAV patients exhibited severe aortic stenosis (AS) by the lower values of aortic valve area (AVA) index. One patient showed a more significant left ventricle hypertrophy, whereas two patients exhibited a significant aortic regurgitation (AR). In addition, three different Raman spectral patterns were summed up from 121 randomized Raman determinations for all the excised BAV leaflets. The main calcified deposition in each BAV leaflet was formed by large amounts of calcium hydroxyapatite and type-B carbonate apatite (Raman bands at 960 and 1070 cm^-1). The calcified BAV leaflets were composed of different compositional components such as calcium hydroxyapatite, type-B carbonate apatite, lipids, proteins, cholesterol and β-carotene. The rare NL subtype of type 1 BAV morphotype was found in one patient, but two patients had the purely BAV morphotype with two equal-sized leaflets.

Energy Dispersive X-ray (EDX) microanalysis: A powerful tool in biomedical research and diagnosis

The Energy Dispersive X-ray (EDX) microanalysis is a technique of elemental analysis associated to electron microscopy based on the generation of characteristic Xrays that reveals the presence of elements present in the specimens. The EDX microanalysis is used in different biomedical fields by many researchers and clinicians. Nevertheless, most of the scientific community is not fully aware of its possible applications. The spectrum of EDX microanalysis contains both semi-qualitative and semi-quantitative information. EDX technique is made useful in the study of drugs, such as in the study of drugs delivery in which the EDX is an important tool to detect nanoparticles (generally, used to improve the therapeutic performance of some chemotherapeutic agents). EDX is also used in the study of environmental pollution and in the characterization of mineral bioaccumulated in the tissues. In conclusion, the EDX can be considered as a useful tool in all works that require element determination, endogenous or exogenous, in the tissue, cell or any other sample.

Effects of in-office bleaching on human enamel and dentin. Morphological and mineral changes

BACKGROUND

The effects of HP-based products upon dental enamel and dentin are inconclusive.

AIM

To evaluate changes in micromorphology and composition of calcium (Ca) and phosphate (P) in enamel and dentin after the application of 37.5% hydrogen peroxide (HP) and 35% carbamide peroxide (CP) METHODS: Crowns of 20 human teeth were divided in two halves. One half was used as control specimen and the other as experimental specimen. The control specimens were kept in artificial saliva, and the experimental specimens were divided into four groups (n=5 each): group 1 (enamel HP for 45min); group 2 (dentin HP for 45min); group 3 (enamel CP for 90min); and group 4 (dentin CP for 90min). The morphological changes were evaluated using confocal laser scanning microscopy (CLSM), while the changes in the composition of Ca and P were assessed using environmental scanning electron microscopy combined with a microanalysis system (ESEM+EDX). The results within each group and between groups were compared using the Wilcoxon test and Mann-Whitney U-test, respectively (p<0.05).

RESULTS

Similar morphological changes in the enamel and no changes in dentin were assessed with both products. Ca and P decreased in enamel and dentin, without significant differences between them or with respect to their control specimens (p>0.05).

CONCLUSIONS

When bleaching products with a neutral pH are used in clinical practice, both, the concentration and the application time should be taken into account in order to avoid possible structural and mineral changes in enamel and dentin.

Quartz Crystal Microbalance Assay of Clinical Calcinosis Samples and Their Synthetic Models Differentiates the Efficacy of Chelation-Based Treatments

This paper sets out in vitro protocols for studying the relative effectiveness of chelators used in the dissolution-based treatment of hard calcinosis. Pulverized hard calcinosis samples from human donors or synthetic hydroxyapatite nanoparticles were deposited by electrophoretic deposition on the surface of a quartz crystal microbalance sensor. Over 150 deposits of <20 μg were dissolved over the course of 1 h by aliquots of buffered, aqueous solutions of two calcium chelators, EDTA and citrate, with the surface-limited dissolution kinetics monitored with <1 s time resolution. There was no statistically significant difference in dissolution rate between the four synthetic hydroxyapatite materials in EDTA, but the dissolution rates in citrate were lower for hydroxyapatite produced by acetate or nitrate metathesis. Hard calcinosis and synthetic hydroxyapatites showed statistically identical dissolution behavior, meaning that readily available synthetic mimics can replace the rarer samples of biological origin in the development of calcinosis treatments. EDTA dissolved the hydroxyapatite deposits more than twice as fast as citrate at pH 7.4 and 37 °C, based on a first-order kinetic analysis of the initial frequency response. EDTA chelated 6.5 times more calcium than an equivalent number of moles of citrate. Negative controls using nonchelating N,N,N',N'-tetraethylethylenediamine (TEEDA) showed no dissolution effect. Pharmaceutical dissolution testing of synthetic hydroxyapatite tablets over 6 h showed that EDTA dissolved the tablets four to nine times more quickly than citrate.

Spectral and morphological classification of different chronic and acute Taiwanese gallstones via FTIR, SEM and ESEM-EDX microanalyses

BACKGROUND

Gallstone disease is one of the leading upper gastrointestinal surgical problems in different countries.

AIMS

To analyze the chronic gallstones and acute gallbladder sludge retrieved from 36 Taiwanese patients.

METHODS

FTIR microspectroscopy was used to classify the types of gallstones, and an ESEM-EDX microanalysis was first applied to determine the microstructural features and elemental compositions of the various gallstones. Bacteria presented on the surface of gallstones were also detected by SEM.

RESULTS

Four types of gallstones were obtained from these 36 Taiwanese patients: calcium bilirubinate (CaBR) stones (30.6%), cholesterol stones (19.4%), mixed stones including 6 subtypes (47.2%), and acute gallbladder sludge (2.8%) made of CaBR and protein/insoluble biomaterials. Bacteria imprints and bacterial discharges or bacterial biofilms were also found on the surface of gallstones and acute sludge under a SEM observation. ESEM-EDX results revealed that calcium was found to be the main constituent of all of the types of stones except cholesterol stones, and aluminum was also presented in most of the stones and sludge samples. Chloride was only detected in the acute gallbladder sludge.

CONCLUSION

FTIR spectra, morphological features, and elemental compositions of the acute gallbladder sludge were different from those of the chronic gallstones.

Dual-Energy Computed Tomography Gemstone Spectral Imaging: A Novel Technique to Determine Human Cardiac Calculus Composition

OBJECTIVE

Understanding the chemical composition of any calculus in different human organs is essential for choosing the best treatment strategy for patients. The purpose of this study was to assess the capability of determining the chemical composition of a human cardiac calculus using gemstone spectral imaging (GSI) mode on a single-source dual-energy computed tomography (DECT) in vitro.

METHODS

The cardiac calculus was directly scanned on the Discovery CT750 HD FREEdom Edition using GSI mode, in vitro. A portable fiber-optic Raman spectroscopy was also applied to verify the quantitative accuracy of the DECT measurements.

RESULTS

The results of spectral DECT measurements indicate that effective Z values in 3 designated positions located in this calculus were 15.02 to 15.47, which are close to values of 15.74 to 15.86, corresponding to the effective Z values of calcium apatite and hydroxyapatite. The Raman spectral data were also reflected by the predominant Raman peak at 960 cm for hydroxyapatite and the minor peak at 875 cm for calcium apatite.

CONCLUSIONS

A potential single-source DECT with GSI mode was first used to examine the morphological characteristics and chemical compositions of a giant human cardiac calculus, in vitro. The CT results were consistent with the Raman spectral data, suggesting that spectral CT imaging techniques could be accurately used to diagnose and characterize the compositional materials in the cardiac calculus.

Preparation and Characterization of Ultrarapidly Dissolving Orodispersible Films for Treating and Preventing Iodine Deficiency in the Pediatric Population

Iodine deficiency is a public health problem that is easily prevented in many countries through having a salt iodization program. However, the World Health Organization (WHO) recommends that particular population groups including infants and young children have a sufficient level of daily iodine intake, while also reducing salt consumption in their diet. While many iodine supplements are available, swallowing tablet supplements is physically difficult for young children; thus, there is a need for the development of novel iodine delivery systems for pediatric patients. In this study a novel, ultrarapidly dissolving, nanofiber-based orodispersible film formulation containing iodine which is constructed from nanofibers was manufactured using an electrospinning technique. The potassium iodate (KIO3)-loaded poly(ethylene oxide) (PEO) fiber orodispersible films dissolve within seconds on wetting (applying on the tongue) without the need for the consumption of water. The electrospinning process and KIO3 loading did not alter the crystallinity and conformation of PEO. With high loading, KIO3 nanocrystals are present in the fibers. This formulation design allows easy administration of iodine for preventing childhood iodine deficiency. We have also described a novel and easy method for producing and harvesting nanocrystals of inorganic salts that can be potentially adopted for use in other relevant fields.

Overview about the localization of nanoparticles in tissue and cellular context by different imaging techniques

The increasing interest and recent developments in nanotechnology pose previously unparalleled challenges in understanding the effects of nanoparticles on living tissues. Despite significant progress in in vitro cell and tissue culture technologies, observations on particle distribution and tissue responses in whole organisms are still indispensable. In addition to a thorough understanding of complex tissue responses which is the domain of expert pathologists, the localization of particles at their sites of interaction with living structures is essential to complete the picture. In this review we will describe and compare different imaging techniques for localizing inorganic as well as organic nanoparticles in tissues, cells and subcellular compartments. The visualization techniques include well-established methods, such as standard light, fluorescence, transmission electron and scanning electron microscopy as well as more recent developments, such as light and electron microscopic autoradiography, fluorescence lifetime imaging, spectral imaging and linear unmixing, superresolution structured illumination, Raman microspectroscopy and X-ray microscopy. Importantly, all methodologies described allow for the simultaneous visualization of nanoparticles and evaluation of cell and tissue changes that are of prime interest for toxicopathologic studies. However, the different approaches vary in terms of applicability for specific particles, sensitivity, optical resolution, technical requirements and thus availability, and effects of labeling on particle properties. Specific bottle necks of each technology are discussed in detail. Interpretation of particle localization data from any of these techniques should therefore respect their specific merits and limitations as no single approach combines all desired properties.