An affibody-conjugated nanoprobe for IGF-1R targeted cancer fluorescent and photoacoustic dual-modality imaging

Dual-modal molecular imaging that combines photoacoustic imaging with near-infrared fluorescence imaging integrates the benefits of both imaging modalities and may achieve more precise detection of disease. In this study, silver sulfide quantum dots (Ag₂S QDs) with superior photoacoustic properties and a strong fluorescent emission in the NIR region were successfully synthesized. They were further modified with the insulin-like growth factor 1 receptor (IGF-1R) targeted small scaffold protein, Affibody (Z_IGF-1) to achieved targeted photoacoustic/fluorescent dual-modal imaging of cancer. Our results showed that the prepared nanoprobe had good tumor targeting properties in vivo, and the probe also showed good biocompatibility without any significant toxicity.

Ag2[Fe(CN)5NO]-Fabricated Hydrophobic Cotton as a Potential Wound Healing Dressing: An In Vivo Approach

There have been reports of different types of wound dressings for various functions and purposes. Cotton being one of the most widely used wound dressing material due to its non-toxic, biodegradable, and other properties is used for fabrication as well as in the form of scaffolds for faster and effective wound closure. Our research team has already demonstrated the role of silver nitroprusside nanoparticles (SNPNPs) for wound healing and antibacterial activity. In the current study, we have developed cotton fabric impregnated with SNPNPs (SNPCFs) which remain photo inert and displayed long-term antimicrobial activity due to the surface modification with the silver nitroprusside complex. These SNPCFs were characterized by various analytical techniques (XRD, FTIR, UV spectroscopy, TGA, TEM, FESEM, EDAX, ICP-OES). The fabricated cotton dressings with nanoparticles showed an improved water contact angle (113-130°) than that of bare cotton gauze (60°) and exhibited more antibacterial property in case of both Gram-negative bacteria (Klebsiella aerogenes and Escherichia coli) and Gram-positive bacteria (Pseudomonas aeruginosa and Bacillus subtilis) even after several washings. The biocompatible nature of SNPCFs was assessed by in vivo chorioallantoic membrane assay that showed no obstruction in the formation of blood vessels. The SNPCFs exhibited better wound healing activity compared to the bare cotton and AgCFs as observed in the C57BL6/J mouse. The histopathological investigation reveals increase in re-epithelialization and deposition of connective tissue. The macrophage (M2) counts in SNPCF-treated skin tissues were supportive of more wound healing activity than mice treated with cotton fabric impregnated with chemically synthesized silver nanoparticles. Based on biodistribution analysis using ICP-OES, the data illustrated that a significant amount of silver is absorbed in the skin tissues of mice as compared to the blood and kidney. Furthermore, the absence of silver from the vital organs (heart, liver, and kidney) corroborates our hypothesis that the SNPCFs can act excellently in treating wounds when topically applied over skin. Thereafter, all these results highlight a strong possibility that SNPCFs exemplify the potential as a new antimicrobial and wound healing agent in future times.

Ultrafast synthesis of ultrasmall polyethylenimine-protected AgBiS2 nanodots by "rookie method" for in vivo dual-modal CT/PA imaging and simultaneous photothermal therapy

Developing a biocompatible nanotheranostic platform integrating diagnostic and therapeutic functions is a great prospect for cancer treatment. However, it is still a great challenge to synthesize nanotheranostic agents using an ultra-facile method. In the research reported here, ultrasmall polyethylenimine-protected silver bismuth sulfide (PEI-AgBiS2) nanodots were successfully synthesized using an ultra-facile and environmentally friendly strategy (1 min only at room temperature), which could be described as a "rookie method". PEI-AgBiS2 nanodots show good monodispersity and biocompatibility. For the first time, PEI-AgBiS2 nanodots were reported as a powerful and safe nanotheranostic agent for cancer treatment. PEI-AgBiS2 nanodots exhibit excellent computed tomography (CT) and photoacoustic (PA) dual-modal imaging ability, which could effectively guide photothermal cancer therapy. Furthermore, PEI-AgBiS2 nanodots exhibit a high photothermal conversion efficiency (η = 35.2%). The photothermal therapy (PTT) results demonstrated a highly efficient tumor ablation ability. More importantly, the blood biochemistry and histology analyses verify that the PEI-AgBiS2 nanodots have negligible long-term toxicity. This work highlights that PEI-AgBiS2 nanodots produced using this extremely effective method are a high-performance and safe PTT agent. These findings open a new gateway for synthesizing nanotheranostic agents by using this ultra-facile method in the future.

Engineered Multifunctional Nanomedicine for Simultaneous Stereotactic Chemotherapy and Inhibited Osteolysis in an Orthotopic Model of Bone Metastasis

A novel multifunctional Ag₂ S quantum dot (QD)-based nanomedicine of alendronate (Ald)/doxorubicin (DOX)@Ag₂ S is developed for highly effective bone tumor therapy in an orthotopic model. The bone-targeting and osteolysis inhibition of Ald and the chemotherapeutic effect of DOX on the bone tumor are in situ visualized by Ag₂ S QDs with emission in the second near-infrared window.

The effect of chronic silver nanoparticles on aquatic system in microcosms

Silver nanoparticles (AgNPs) inevitably discharge into aquatic environments due to their abundant use in antibacterial products. It was reported that in laboratory conditions, AgNPs display dose-dependent toxicity to aquatic organisms, such as bacteria, algae, macrophytes, snails and fishes. However, AgNPs could behave differently in natural complex environments. In the present study, a series of microcosms were established to investigate the distribution and toxicity of AgNPs at approximately 500 μg L^-1 in aquatic systems. As a comparison, the distribution and toxicity of the same concentration of AgNO₃ were also determined. The results showed that the surface layer of sediment was the main sink of Ag element for both AgNPs and AgNO₃. Both aquatic plant (Hydrilla verticillata) and animals (Gambusia affinis and Radix spp) significantly accumulated Ag. With short-term treatment, phytoplankton biomass was affected by AgNO₃ but not by AgNPs. Chlorophyll content of H. verticillata increased with both AgNPs and AgNO₃ short-term exposure. However, the biomass of phytoplankton, aquatic plant and animals was not significantly different between control and samples treated with AgNPs or AgNO₃ for 90 d. The communities, diversity and richness of microbes were not significantly affected by AgNPs and AgNO₃; in contrast, the nitrification rate and its related microbe (Nitrospira) abundance significantly decreased. AgNPs and AgNO₃ may affect the nitrogen cycle and affect the environment and, since they might be also transferred to food web, they represent a risk for health.

Blood Clearance, Distribution, Transformation, Excretion, and Toxicity of Near-Infrared Quantum Dots Ag2Se in Mice

As a novel fluorescent probe in the second near-infrared window, Ag2Se quantum dots (QDs) exhibit great prospect in in vivo imaging due to their maximal penetration depth and negligible background. However, the in vivo behavior and toxicity of Ag2Se QDs still largely remain unknown, which severely hinders their wide-ranging biomedical applications. Herein, we systematically studied the blood clearance, distribution, transformation, excretion, and toxicity of polyethylene glycol (PEG) coated Ag2Se QDs in mice after intravenous administration with a high dose of 8 μmol/kg body weight. QDs are quickly cleared from the blood with a circulation half-life of 0.4 h. QDs mainly accumulate in liver and spleen and are remarkably transformed into Ag and Se within 1 week. Ag is excreted from the body readily through both feces and urine, whereas Se is excreted hardly. The toxicological evaluations demonstrate that there is no overt acute toxicity of Ag2Se QDs to mice. Moreover, in regard to the in vivo stability problem of Ag2Se QDs, the biotransformation and its related metabolism are intensively discussed, and some promising coating means for Ag2Se QDs to avert transformation are proposed as well. Our work lays a solid foundation for safe applications of Ag2Se QDs in bioimaging in the future.

Tissue distribution and acute toxicity of silver after single intravenous administration in mice: nano-specific and size-dependent effects

BACKGROUND

Silver nanoparticles (AgNPs) are an important class of nanomaterials used as antimicrobial agents for a wide range of medical and industrial applications. However toxicity of AgNPs and impact of their physicochemical characteristics in in vivo models still need to be comprehensively characterized. The aim of this study was to investigate the effect of size and coating on tissue distribution and toxicity of AgNPs after intravenous administration in mice, and compare the results with those obtained after silver acetate administration.

METHODS

Male CD-1(ICR) mice were intravenously injected with AgNPs of different sizes (10 nm, 40 nm, 100 nm), citrate-or polyvinylpyrrolidone-coated, at a single dose of 10 mg/kg bw. An equivalent dose of silver ions was administered as silver acetate. Mice were euthanized 24 h after the treatment, and silver quantification by ICP-MS and histopathology were performed on spleen, liver, lungs, kidneys, brain, and blood.

RESULTS

For all particle sizes, regardless of their coating, the highest silver concentrations were found in the spleen and liver, followed by lung, kidney, and brain. Silver concentrations were significantly higher in the spleen, lung, kidney, brain, and blood of mice treated with 10 nm AgNPs than those treated with larger particles. Relevant toxic effects (midzonal hepatocellular necrosis, gall bladder hemorrhage) were found in mice treated with 10 nm AgNPs, while in mice treated with 40 nm and 100 nm AgNPs lesions were milder or negligible, respectively. In mice treated with silver acetate, silver concentrations were significantly lower in the spleen and lung, and higher in the kidney than in mice treated with 10 nm AgNPs, and a different target organ of toxicity was identified (kidney).

CONCLUSIONS

Administration of the smallest (10 nm) nanoparticles resulted in enhanced silver tissue distribution and overt hepatobiliary toxicity compared to larger ones (40 and 100 nm), while coating had no relevant impact. Distinct patterns of tissue distribution and toxicity were observed after silver acetate administration. It is concluded that if AgNPs become systemically available, they behave differently from ionic silver, exerting distinct and size-dependent effects, strictly related to the nanoparticulate form.

In vivo cancer targeting and fluorescence-CT dual-mode imaging with nanoprobes based on silver sulfide quantum dots and iodinated oil

In this article, a fluorescence-CT dual-mode nanoprobe is successfully synthesized by making use of distearoylphosphatidylethanolamine-poly(ethylene glycol)-folate (DSPE-PEG2000-FA) and other amphiphilic molecules to coat silver sulfide (Ag2S) quantum dots (QDs) and iodinated oil simultaneously. In vitro experiments show that the fluorescence wavelength of the nanoprobe is 1170 nm in the near infrared-II region. Its size is 139.6 nm, it has good dispersibility, and it has low cellular toxicity at concentrations up to 25 μg mL(-1) Ag. In vivo experiments revealed that the probe has a rather long circulation time (blood half-life of 5.7 hours), and the tissue histopathological tests show that it is not obviously harmful to major organs' normal function. Biochemical analysis (glutamic pyruvic transaminase and glutamic oxaloacetic transaminase levels) and blood analysis (white blood cell, red blood cell, hemoglobin and blood platelet counts) reveal that it has little influence on blood within 15 days of administration. When injected into HeLa xenograft nude mice by the tail vein, the probe elicited intensely enhanced fluorescence and X-ray computed tomography (CT) signals in the tumors after 24 hours, and the structure, size and position of tumor tissue were shown clearly. In a word, the probe has good tumor targeting capabilities, and it has significant value in fluorescence-CT dual-mode imaging in vivo.

Speciation Matters: Bioavailability of Silver and Silver Sulfide Nanoparticles to Alfalfa (Medicago sativa)

Terrestrial crops are directly exposed to silver nanoparticles (Ag-NPs) and their environmentally transformed analog silver sulfide nanoparticles (Ag2S-NPs) when wastewater treatment biosolids are applied as fertilizer to agricultural soils. This leads to a need to understand their bioavailability to plants. In the present study, the mechanisms of uptake and distribution of silver in alfalfa (Medicago sativa) were quantified and visualized upon hydroponic exposure to Ag-NPs, Ag2S-NPs, and AgNO3 at 3 mg total Ag/L. Total silver uptake was measured in dried roots and shoots, and the spatial distribution of elements was investigated using transmission electron microscopy (TEM) and synchrotron-based X-ray imaging techniques. Despite large differences in release of Ag(+) ions from the particles, Ag-NPs, Ag2S-NPs, and Ag(+) became associated with plant roots to a similar degree, and exhibited similarly limited (<1%) amounts of translocation of silver into the shoot system. X-ray fluorescence (XRF) mapping revealed differences in the distribution of Ag into roots for each treatment. Silver nanoparticles mainly accumulated in the (columella) border cells and elongation zone, whereas Ag(+) accumulated more uniformly throughout the root. In contrast, Ag2S-NPs remained largely adhered to the root exterior, and the presence of cytoplasmic nano-SixOy aggregates was observed. Exclusively in roots exposed to particulate silver, NPs smaller than the originally dosed NPs were identified by TEM in the cell walls. The apparent accumulation of Ag in the root apoplast determined by XRF, and the presence of small NPs in root cell walls suggests uptake of partially dissolved NPs and translocation along the apoplast.

Cellular uptake and toxicity effects of silver nanoparticles in mammalian kidney cells

The rapid progress and early commercial acceptance of silver-based nanomaterials is owed to their biocidal activity. Besides embracing the antimicrobial potential of silver nanoparticles (AgNPs), it is imperative to give special attention to the potential adverse health effects of nanoparticles owing to prolonged exposure. Here, we report a detailed study on the in vitro interactions of citrate-coated AgNPs with porcine kidney (Pk15) cells. As uncertainty remains whether biological/cellular responses to AgNPs are solely as a result of the release of silver ions or whether the AgNPs themselves have toxic effects, we investigated the effects of Ag(+) on Pk15 cells for comparison. Next, we investigated the cellular uptake of both AgNPs and Ag(+) in Pk15 cells at various concentrations applied. The detected Ag contents in cells exposed to 50 mg l(-1) AgNPs and 50 mg l(-1) Ag(+) were 209 and 25 µg of Ag per 10(6) cells, respectively. Transmission electron microscopy (TEM) images indicated that the Pk15 cells internalized AgNPs by endocytosis. Both forms of silver, nano and ionic, decreased the number of viable Pk15 cells after 24 h in a dose-dependent manner. In spite of a significant uptake into the cells, AgNPs had only insignificant toxicity at concentrations lower than 25 mg l(-1) , whereas Ag(+) exhibited a significant decrease in cell viability at one-fifth of this concentration. The Comet assay suggested that a rather high concentration of AgNP (above 25 mg l(-1) ) is able to induce genotoxicity in Pk15 cells. Further studies must seek deeper understanding of AgNP behavior in biological media and their interactions with cellular membranes.

[APPROACHES TO ENHANCING THE ORGANISM'S RESISTANCE TO THE ADVERSE EFFECTS OF NANOMATERIALS AS EXAMPLIFIED BY NANOSILVER AND NANOCOPPER OXIDE]

Subchronic intoxications in rats induced by repeated intraperitoneal injections of stable water suspensions of silver or copper oxide nanoparticles in low dosage were manifested by adverse shifts in some functional and biochemical indices, by development of histo-structural changes in different tissues and by poly-organ fragmentation of DNA. All these manifestations of toxicity were substantially attenuated against the background of parallel oral administration of bioprotective complexes comprising vitamins, trace elements, pectin, some amino acids and a fish oil preparation rich in omega-3 fee fatty acids, this composition has been adjusted to mechanisms of action of this or that nanomaterial.

Pulmonary and cardiovascular responses of rats to inhalation of silver nanoparticles

Exposure to wet aerosols generated during use of spray products containing silver (Ag) has not been evaluated. The goal was to assess the potential for cardiopulmonary toxicity following an acute inhalation of wet silver colloid. Rats were exposed by inhalation to a low concentration (100 μg/m(3) ) using an undiluted commercial antimicrobial product (20 mg/L total silver; approximately 33 nm mean aerodynamic diameter [MAD]) or to a higher concentration (1000 μg/m(3)) using a suspension (200 mg/L total silver; approximately 39 nm MAD) synthesized to possess a similar size distribution of Ag nanoparticles for 5 h. Estimated lung burdens from deposition models were 0, 1.4, or 14 μg Ag/rat after exposure to control aerosol, low, and high doses, respectively. At 1 and 7 d postexposure, the following parameters were monitored: pulmonary inflammation, lung cell toxicity, alveolar air/blood barrier damage, alveolar macrophage activity, blood cell differentials, responsiveness of tail artery to vasoconstrictor or vasodilatory agents, and heart rate and blood pressure in response to isoproterenol or norepinephrine, respectively. Changes in pulmonary or cardiovascular parameters were absent or nonsignificant at 1 or 7 d postexposure with the exceptions of increased blood monocytes 1 d after high-dose Ag exposure and decreased dilation of tail artery after stimulation, as well as elevated heart rate in response to isoproterenol 1 d after low-dose Ag exposure, possibly due to bioavailable ionic Ag in the commercial product. In summary, short-term inhalation of nano-Ag did not produce apparent marked acute toxicity in this animal model.

Distribution and systemic effects of intranasally administered 25 nm silver nanoparticles in adult mice

Previous work indicates that silver nanoparticles (AgNPs) given IP to mice alter the regulation of inflammation- and oxidative stress-related genes in brain. Here we assessed the distribution and toxic potential of AgNP following intranasal (IN) exposure. Adult male C57BL/6J mice received 25-nm AgNP (100 or 500 mg/kg) once IN. After 1 or 7 days, histopathology of selected organs was performed, and tissue reduced glutathione (GSH) levels were measured as an indicator of oxidative stress. Aggregated AgNP were found in spleen, lung, kidney, and nasal airway by routine light microscopy. Splenic AgNP accumulation was greatest in red pulp and occurred with modestly reduced cellularity and elevated hemosiderin deposition. Aggregated AgNP were not associated with microscopic changes in other tissues except for nasal mucosal erosions. Autometallography revealed AgNP in olfactory bulb and the lateral brain ventricles. Neither inflammatory cell infiltrates nor activated microglia were detected in brains of AgNP-treated mice. Elevated tissue GSH levels was observed in nasal epithelia (both doses at 1 day, 500 mg/kg at 7 days) and blood (500 mg/kg at 7 days). Therefore, IN administration of AgNP permits systemic distribution, produces reversible oxidative stress in the nose and in blood, and mildly enhances macrophage-mediated erythrocyte destruction in the spleen.

[Characteristics of rat ceruloplasmin from the serum of animals, which received salts of silver with food]

Abiogenic Ag(I) ions have electronic structure, similar to Cu(I) ions and can compete with Cu(I) for binding sites of proteins which transport copper from extracellular media to sites of cuproenzyme formation in the cell. Rodents receiving Ag-salts with food develop extracellular deficiency of copper associated with ceruloplasmin (Cp, the major copper-transporting protein in blood serum of vertebrates). The present work focuses on the studies of biochemical and physicochemical properties of Cp, obtained from blood serum of rats, which received AgCl with food for 4 weeks (Ag-rats). Cp-fractions from blood serum of Ag-rats (Ag-Cp) were obtained by ion-exchange chromatography with stepped gradient of NaCl. Each fraction was tested for oxidase and ferroxidase activities by direct measurement of catalytic activity in the gel, and for specific activity in holo-Cp in oxidation of chromogenic substrate. Molecular mass, electrophoretic mobility and ratio of apo- and holo-forms in Ag-Cp fractions were evaluated by immunoblotting. Ag-Cp samples did not contain products of spontaneous partial proteolytic degradation, characteristic of holo-Cp samples. Fractions of Ag-Cp and holo-Cp (from blood serum of control rats) were compared by optical spectra, tertiary structure, susceptibility to thermal denaturation, and by atomic Cu and Ag content. Ag-Cp contained 1-2% Cp, which is similar by spectral and catalytic properties with holo-Cp. [Ag]:[Cu] ration in Ag-Cp samples was about 4:1. As evidenced by circular dichroism and differential scanning calorimetric studies, the major apo-fraction of Ag-Cp lacked tertiary structure of native Cp and was significantly misfolded, which might explain its resistance to spontaneous partial proteolytic degradation.

Internal redistribution of radiolabelled silver among tissues of rainbow trout (Oncorhynchus mykiss) and European eel (Anguilla anguilla): the influence of silver speciation

Influence of water Ag(I) speciation on pharmacokinetics of Ag(I) during a post-exposure period was investigated in rainbow trout (Oncorhynchus mykiss) and European eel (Anguilla anguilla). The rainbow trout is sensitive to waterborne ionic Ag(+) whereas the eel is tolerant. The fish were acclimated to either of two chloride concentrations, 10 or 1200 microM, in synthetic soft water and then exposed to a sublethal 24-h pulse of 1.3 microgl(-1) of 110mAg(I) added as 110mAgNO(3) in these waters. The protocol provided exposures to mainly the free ion Ag(+) (low chloride water) or mainly AgCl(aq) (high chloride water). Contents and concentrations of 110mAg(I) in tissues and body fluids were then monitored over a 67-day post-exposure period in Ag(I)-free water of the same chloride levels. Changing the speciation of Ag(I) in the water had no effect on the whole body load of 110mAg(I), but did result in differences in internal distribution. In trout, changing water Ag(I) speciation significantly altered elimination or accumulation of Ag(I) in several body compartments. Notably, trout exposed to AgCl(aq) eliminated 110mAg(I) from the kidney more quickly than trout exposed to Ag(I) primarily as Ag(+). This elimination was matched by higher concentrations of 110mAg in liver of trout exposed to Ag(I) primarily as AgCl(aq). In eel, shifting speciation from Ag(+) to AgCl(aq) hastened elimination of 110mAg(I) from mid and posterior intestine and increased 110mAg(I) retention in kidney. While there was no difference between the two fish species in whole body 110mAg(I) load, most internal body compartments of trout had higher 110mAg(I) concentrations than those in eel early in the experiment. Because tissue-specific elimination times were longer in eel than in trout, these differences were generally cancelled by the end of the 67-day depuration period. The only exception was the liver, which in trout continued to accumulate 110mAg(I) throughout the experiment but in eel remained unchanged. The combined effect of 110mAg(I) movements in the two species was that trout retained all their accumulated 110mAg(I) through the 67-day period, whereas the body burden of 110mAg(I) in eel was reduced to half initial values by day 67.

Kinetics of radiolabelled silver uptake and depuration in the gills of rainbow trout (Oncorhynchus mykiss) and European eel (Anguilla anguilla): the influence of silver speciation

We examined the influence of speciation on the kinetics of silver uptake and depuration in the gills of two freshwater fish, the rainbow trout (Oncorhynchus mykiss) which has high branchial Na(+) and Cl(-) uptake rates and is relatively sensitive to silver, and the European eel (Anguilla anguilla, yellow stage) which has low ion uptake rates and is relatively resistant to silver. Fish previously acclimated to the appropriate chloride level were exposed to 110mAgNO(3) (1.3 microg l(-1), sublethal) for 24 h in synthetic softwater with either low (10 microM) or high (1200 microM) chloride concentration, and then followed over a subsequent 67-day post-exposure period in silver-free water of the same chloride content. The exposures were therefore mainly to the free ion, Ag(+) in the low chloride water versus mainly to the neutral aqueous complex, AgCl(aq) in the high chloride water. In trout, but not in eel, water chloride is known to protect against physiological disturbances and toxicity caused by Ag(+). In both fish species, at both chloride levels, silver uptake exhibited complex kinetics. Gill silver loading occurred slowly until 6 h, then rose greatly to a peak at 12 h, followed by significant net depuration thereafter during continued exposure. By 24 h, net gill loading was three- to fivefold greater from AgCl(aq) than from Ag(+) exposure in both species, and threefold greater in trout than in eel under both conditions, with trout holding a lower fraction of the whole body burden in their gills. During the post-exposure period, depuration of silver from the gills occurred rapidly in trout, but very slowly in eel, such that gill silver burdens were greater in eel throughout the 67-day period on both an absolute and relative basis (e.g. 35% of whole body burden in eel versus <3% in trout at day 8). The kinetics of depuration were described by two phase exponential models, with break points between the fast and slow phases at 1 and 15 days for trout and eel, respectively. We conclude that speciation affects not only uptake rates but also the kinetics of depuration. When silver is loaded from AgCl(aq) it is clearly more labile than from Ag(+) exposures, with 1.6-1.8-fold greater loss rates during the fast phases in both species. Differences in branchial silver uptake between eel and trout correlate well with differences in acute toxicity, but are not as large as differences in ion uptake rates. The complex time-dependent patterns of gill loading, and the higher loading from AgCl(aq) than from Ag(+), mean that gill total silver burden is not an appropriate endpoint for biotic ligand modelling.

Ultrasound-facilitated transport of silver chloride (AgCl) particles in fish skin

Electron-dense nano-particles in aqueous suspension were administered by immersion into the epidermis of fish using ultrasound in the therapeutic range. Enhanced permeability of the tissues to the particles was achieved by acoustic cavitation, which induced a controlled level of necrosis in the outer cell layers, and by non-cavitational exposures, which widened intercellular spaces of non-necrosed tissue in deeper regions of the epidermis. Both particle concentration and penetration depth were quantified using transmission electron microscopy. While cavitation-induced perforation was necessary for particles to penetrate into the tissues, non-cavitational exposures during immersions increased the particle flux towards the skin surface, as well as the diffusion rate of the particles within the epidermis and their depth of penetration. The technique described above may potentially be applied for non-stressful, mass-administration of substances into aquatic animals, as well as the relatively new field of ultrasound-facilitated delivery in moist epithelial tissues in humans.

Analytical findings in a fatal poisoning with silver compound

A 69-year-old male radio technician drank an unknown amount of a liquid and died within 5 h at a hospital. Mainly silver, potassium, and calcium, among other substances, were found in the residue of the liquid from the empty bottle by means of the spectrographic method (30.7% silver and 25.5% potassium using atomic absorption spectometry [AAS] method). The toxicological analysis of the postmortem material for silver performed by the flame AAS method (stomach, 2.43 micrograms/g; intestines, 1.12 micrograms/g; liver, 6.29 micrograms/g; kidney, 4.85 micrograms/g; spleen, 30.1 micrograms/g; heart, 10.8 micrograms/g; lung, 14.8 micrograms/g; and brain, 0.61 microgram/g) confirmed fatal silver compound poisoning. The results were verified by the standard additions technique and recovery examination. However, no increase in the potassium concentrations was observed in the postmortem material. There have been no data in available literature on the distribution of silver in tissues in people after oral administration of silver salts.

Safety issues related to the use of silver fluoride in paediatric dentistry

Due to its exceedingly high fluoride content, 40% silver fluoride solution has the potential to cause fluorosis when used in young children. In vitro testing conducted in the present investigation indicates that application of 40% silver fluoride to deep carious lesions or its use as a 'spot' application agent could result in 3 to 4 mg of fluoride reaching the systemic circulation. As scientifically-based clinical trials on the safety of 40% silver fluoride have not been conducted, it would be appropriate for it to be withdrawn from further clinical use until proper testing and evaluation have been carried out. In view of the possibility that lower strength solutions of silver fluoride (1-4%) may be just as effective as 40% in 'arresting' deep caries, testing should focus on such solutions, particularly as the potential for toxicity from their fluoride content would be reduced by a factor of 10-40.