The difficulty in localizing specific cellular proteins by immuno-electron microscopy techniques limits applications of electron microscopy to cell biology. We found that in vivo immunogold labeling improves epitope accessibility, ultrastructural preservation and three-dimensional visualization, and allows correlated light and electron microscopy. We detected large-scale chromatin folding motifs within intact interphase nuclei of CHO cells and visualized the ultrastructure of DNA replication 'factories' labeled with GFP-proliferating cell nuclear antigen (PCNA).

The limited research that exists in the area of prior learning assessment (PLA) has tended to be descriptive and conceptual in nature. Where empirical studies have been done, they have focussed mainly on PLA as a means of credentialing rather than as a learning experience. Furthermore, there has been very little empirical research into the educational effectiveness of PLA from the student’s point of view. This empirical study used a qualitative approach to investigate the perceptions of a focus group of 32 adult learners who were engaged in portfolio-based PLA in an open and distance education university. The study explored students’ initial expectations of PLA, what they think they got out of the process, and the extent to which these perceived benefits of PLA would extend to other adult students. The study examined the question of whether PLA operates as a motivator or as a selection mechanism and concluded that there was evidence for both factors. Further results indicated that, in general, PLA learners were surprised to find they had been engaged in a learning process. The study concludes that PLA can be an effective educational opportunity for certain kinds of adult learners, but it should not be taken as a panacea.

The enzymatic conversion of an organic substrate to an intensely colored, insoluble reaction product is widely used as a detection method in immunohistochemistry [1], and has also been used for in situ hybridization detection [2]. Although widely used, it is not ideal for all applications. Diffusion of the products may limit resolution, and the continuous nature of the staining may obscure the underlying cellular structure. Contrast with other cellular stains may be less than desired, an issue which has been addressed by the recent development of nickel-based enhancement reagents that bind to the diaminobenzidine reaction product to give a darker signal [3]. Some applications also require higher sensitivity than is possible with direct enzymatic staining; this is usually achieved through an amplification method such as the polymerase chain reaction [4] or catalytic deposition of haptenated substrates such as biotinylated tyramides [5]. However, this adds substantially to the length and complexity of the procedure, and may also be subject to diffusion of the amplified products.

Gold clusters are gold compounds with a core of gold atoms and organic groups covalently bound to the surface gold atoms. An example is undecagold, Au11(P(C6H5)3)7, whose structure was solved by x-ray crystallography using 3-dimensional crystals. These differ from colloidal gold, which are suspensions of metal particles, usually formed by metal ion reduction; although the particles may be approximately the same size, they vary due to the statistical process of formation. Gold clusters are compounds with a definite formula, and should all be perfectly identical. However, it is known that there is a family of stable gold cluster compounds, such as Au6, Au11, Au13, AU55, Au67, etc. In a given preparation of gold clusters, there is usually some mixture of these, thus leading to some size variation. Methods such as gel filtration column chromatography and ultrafiltration can be used to separate most of these species, so that relatively pure preparations may be achieved.

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