Ultrastructural detection of photosensitizing molecules by fluorescence photoconversion of diaminobenzidine

Diaminobenzidine Photooxidation to Visualize Fluorescent Nanoparticles in Adhering Cultured Cells at Transmission Electron Microscopy

Visualizing nanoparticles made of organic material (e.g., polysaccharides, proteins, non-osmiophilic lipids) inside cells and tissues at transmission electron microscopy is a difficult task due to the intrinsic weak electron density of these nanoconstructs, which makes them hardly distinguishable in the biological environment. We describe here a simple protocol to apply photooxidation to fluorescently labeled nanoparticles administered to cultured cells in vitro. The conversion of the fluorescent signal into a granular electron-dense reaction product through light irradiation in the presence of diaminobenzidine makes the nanoparticles clearly visible at the ultrastructural level. Our procedure proved to be reliable with various fluorophores and may be applied to any cell type.

Enzyme-triggered deshielding of nanoparticles and positive-charge mediated lysosomal escape for chemo/photo-combination therapy

Smart nanoparticles with active-targeting, enzyme-triggered deshielding and positive-charge characteristics were fabricated for efficient chemo/photo-combination therapy.

Ultrastructural histochemistry in biomedical research: Alive and kicking

The high-resolution images provided by the electron microscopy has constituted a limitless source of information in any research field of life and materials science since the early Thirties of the last century. Browsing the scientific literature, electron microscopy was especially popular from the 1970’s to 80’s, whereas during the 90’s, with the advent of innovative molecular techniques, electron microscopy seemed to be downgraded to a subordinate role, as a merely descriptive technique. Ultra -structural histochemistry was crucial to promote the Renaissance of electron microscopy, when it became evident that a precise localization of molecules in the biological environment was necessary to fully understand their functional role. Nowadays, electron microscopy is still irreplaceable for ultrastructural morphology in basic and applied biomedical research, while the application of correlative light and electron microscopy and of refined ultrastructural histochemical techniques gives electron microscopy a central role in functional cell and tissue biology, as a really unique tool for high-resolution molecular biology in situ.

Visualizing endocytotic pathways at transmission electron microscopy via diaminobenzidine photo-oxidation by a fluorescent cell-membrane dye

The endocytotic pathway involves a complex, dynamic and interacting system of intracellular compartments. PKH26 is a fluorescent dye specific for long-lasting cell membrane labelling which has been successfully used for investigating cell internalization processes, at either flow cytometry or fluorescence microscopy. In the present work, diaminobenzidine photo-oxidation was tested as a procedure to detect PKH26 dye at transmission electron microscopy. Our results demonstrated that DAB-photo-oxidation is a suitable technique to specifically visualise this fluorescent dye at the ultrastructural level: the distribution of the granular dark reaction product perfectly matches the pattern of the fluorescence staining, and the electron density of the fine precipitates makes the signal evident and precisely detectable on the different subcellular compartments involved in the plasma membrane internalization routes.

Photoconversion of CFP to study neuronal tissue with electron microscopy

Being able to use versatile light microscopy on live or fixed samples followed by electron microscopy imaging for high resolution analyses is a challenging goal. The advantage is of course that tracing and localizing fluorescently labeled molecules yields great information about dynamic cellular processes, while electron microscopy of the same sample provides exquisite information about subcellular structures. Here, I describe the straightforward combination of both methods by photoconversion of diaminobenzidine (DAB) through cyan fluorescent protein (CFP) tagged proteins localized to the Golgi apparatus in primary hippocampal neurons.

The Histochem Cell Biol conspectus: the year 2013 in review

Herein, we provide a brief synopsis of all manuscripts published in Histochem Cell Biol in the year 2013. For ease of reference, we have divided the manuscripts into the following categories: Advances in Methodologies; Molecules in Health and Disease; Organelles, Subcellular Structures and Compartments; Golgi Apparatus; Intermediate Filaments and Cytoskeleton; Connective Tissue and Extracellular Matrix; Autophagy; Stem Cells; Musculoskeletal System; Respiratory and Cardiovascular Systems; Gastrointestinal Tract; Central Nervous System; Peripheral Nervous System; Excretory Glands; Kidney and Urinary Bladder; and Male and Female Reproductive Systems. We hope that the readership will find this annual journal synopsis of value and serve as a quick, categorized reference guide for “state-of-the-art” manuscripts in the areas of histochemistry, immunohistochemistry, and cell biology.

Tracing nanoparticles and photosensitizing molecules at transmission electron microscopy by diaminobenzidine photo-oxidation

During the last three decades, diaminobenzidine photo-oxidation has been applied in a variety of studies to correlate light and electron microscopy. Actually, when a fluorophore is excited by light, it can induce the oxidation of diaminobenzidine into an electron-dense osmiophilic product, which precipitates in close proximity to the fluorophore, thereby allowing its ultrastructural detection. This method has very recently been developed for two innovative applications: tracking the fate of fluorescently labeled nanoparticles in single cells, and detecting the subcellular location of photo-active molecules suitable for photodynamic therapy. These studies established that the cytochemical procedures exploiting diaminobenzidine photo-oxidation represent a reliable tool for detecting, inside the cells, with high sensitivity fluorescing molecules. These procedures are trustworthy even if the fluorescing molecules are present in very low amounts, either inside membrane-bounded organelles, or at the surface of the plasma membrane, or free in the cytosol. In particular, diaminobenzidine photo-oxidation allowed elucidating the mechanisms responsible for nanoparticles internalization in neuronal cells and for their escape from lysosomal degradation. As for the photo-active molecules, their subcellular distribution at the ultrastructural level provided direct evidence for the lethal multiorganelle photo-damage occurring after cell photo-sensitization. In addition, DAB photo-oxidized samples are suitable for the ultrastructural detection of organelle-specific molecules by post-embedding gold immunolabeling.

Simultaneous ultrastructural analysis of fluorochrome-photoconverted diaminobenzidine and gold immunolabelling in cultured cells

Diaminobenzidine photoconversion is a technique by which a fluorescent dye is transformed into a stably insoluble, brown, electrondense signal, thus enabling examination at both bright field light microscopy and transmission electron microscopy. In this work, a procedure is proposed for combining photoconversion and immunoelectron microscopy: in vitro cell cultures have been first submitted to photoconversion to analyse the intracellular fate of either fluorescent nanoparticles or photosensitizing molecules, then processed for transmission electron microscopy; different fixative solutions and embedding media have been used, and the ultrathin sections were finally submitted to post-embedding immunogold cytochemistry. Under all conditions the photoconversion reaction product and the target antigen were properly detected in the same section; Epon-embedded, osmicated samples required a pre-treatment with sodium metaperiodate to unmask the antigenic sites. This simple and reliable procedure exploits a single sample to simultaneously localise the photoconversion product and a variety of antigens allowing a specific identification of subcellular organelles at the ultrastructural level.