Chemical kinetics and fluorescence correlation spectroscopy

The dynamics of macromolecules, the subject of this symposium, are most directly studied by simply looking through a microscope and observing the molecular motion. With a microscope, we can resolve the size and shape of large particles, as well as monitor dynamic motion. For smaller particles, particularly single macromolecules, we cannot resolve the size or shape; but it is still possible to observe the motion, if we can make the particles appear as bright points of light sprinkled dilutely over a dark background. Siedentopf & Zsigmondy (1903) demonstrated this fact with a device which came to be called the ultramicroscope.

Applications of fluorescence correlation spectroscopy

The preceding paper by Douglas Magde has recounted the basic principles of Fluorescence Correlation Spectroscopy (FCS) as originally described (see Magde, Elson & Webb, 1972; Elson & Magde, 1974; Magde, Elson & Webb, 1974 Elson & Webb, 1975; referred to collectively as MEW), and has described the first application to chemical kinetics. In this paper I shall first illustrate the same principles of FCS with a simple graphical demonstration model based on the scheme for application to lateral diffusion in membranes as it was developed in our laboratory by Dr T. J. Herbert; I shall then proceed to discuss some current research in our group organized jointly with Professor E. L. Elson at Cornell.

Conjugation methods in immunofluorescence

We have described methods of labeling antibody preparations with FITC, TMRI, and RBI. The degree of labeling with FITC can be precisely controlled by using well-defined conjugation procedures and FITC of a known degree of purity. Our experience shows that relatively high F/P ratios of the order of 20 to 25 mug/mg are desirable for antibacterial conjugates. Many commercial preparations of rhodamine isothiocyanate are of very poor quality and are unsatisfactory for use in conjugate preparation. Therefore, one should analyze the rhodamine isothiocyanate product before preparing immune conjugates. Our experience indicates that very satisfactory conjugates of immune IgG or pure antibody can be prepared with TMRI of about 60% purity by using a dye-protein ratio of 20 mug/mg. The optimal dye-IgG ratio for labeling with RBI appears to be about two times that for labeling with TMRI because of the lower specific absorbance and fluorescence emission of RBI. Rhodamine conjugates may be preferred to FITC conjugates in certain situations where tissue autofluorescence interferes with the observation of the yellow-green emission of FITC. Furthermore, mixed rhodamine and FITC conjugates of different specificity can be used to great advantage in double-staining techniques that allow simultaneous screening for two antigenically different organisms on a single microscope slide.

Application of fluorescent antibody methods in the analysis of plaque samples

Direct FA staining for S mutans serotypes may be performed on smears made from plaque or strain isolates and on colonies attached to agar plates of black membrane filters. Staining with single conjugates directed to S mutans serotypes (a to e) as well as with polyvalent a-, b-, d-, f-fluorescein label and c-, e-rhodamine label conjugates indicate that serotype c is the most common. This is in agreement with many reports by other investigators. Cross-reactions with many S mutans conjugates occurred with organisms resembling Lancefield groups C and G streptococci.

Dibutyryl cyclic AMP-induced differentiation of epidermal cells in tissue culture

Histochemical and biochemical techniques have been used to compare the effects of dibutyryl cyclic AMP on epidermal cells and dermal cells in primary tissue culture. Rhodamin B staining showed only scattered positive cells in nontreated epidermal cells and a few contaminating keratinizing cell foci in both nontreated and treated dermal cell cultures. In contrast, treated epidermal cells stained strongly and had many keratinizing cell foci. A significant increase in histidine, cystine, and arginine incorporation was noted in epidermal cells treated with dibutyryl cyclic AMP as compared to untreated epidermal cells and to dermal cell cultures both treated and untreated. Dibutyryl cyclic AMP had no significant effect on leucine and phenylalanine incorporation. These results seem to suggest that the intracellular level of cyclic AMP not only controls the synthesis of DNA by epidermal cells in culture but also induces the process of differentiation toward keratinization.

[Random immunoglobulin. I. Use of chaotropicions and fluorescence quenching for quantitating the non-specific adsorption in the interaction of human IgG with rhodamine B]

It is shown that, when excited in the visible range, fluorescence of the dye may be either quenched or enhanced, from its initial value Fo, by addition of increasing "normal" immunoglobulin (IgGH7 S), depending if the solution is "non-chaotropic " (NaF 0,1 M) or "chaotropic" KI 1 M). Let F be the fluorescence obtained at concentration P in protein, then the plot of the quantity P.F/(FO-F)against the quantity P.F/(FO-F) gives a straight line; the zero ordinate of this is the inverse of the non-specific interaction equilibrium constant. Quenching of fluorescence by increase of temperature, and by increase of concentration of salt (KI) are also quantitatively dealed upon in order to testify that this non-specific interaction is of the "adsorption" type. Concentration of dye is 10-6M; concentration of protein is varied from 0,05 % to 0,5 %.

[Basic features in immunohistological technique (author's transl)]

Light and electron microscopic demonstration of antigens in tissue is possible by means of labelled antibodies. Direct and indirect immuno-fluorescence techniques and recently also the peroxidase method permit a broader application of this principle. The peroxidase technique has the advantage of requiring less equipment and of providing the possibility to obtain durable specimens. The fluorescence technique permits the association of fluorescence phenomena with certain tissue structures by means of secondary "staining", for instance localization of specific hormone production sites. This allows functional morphological deductions in healthy and pathological conditions. Flawless techniques and controls are required before a specific reaction can be acknowledged since auto-fluorescence phenomena as well as pseudo-specific and cross-reactions are sources of error leading to wrong conclusions. A standardization of methods must therefore be attempted.

Evaluation of a dual-staining method for acid-fast bacilli

A dual-staining procedure for acid-fast bacilli was found to have poor correlation with the Ziehl-Neelsen and auramine-rhodamine staining techniques.

[Direct determination of inorganic phosphor in serum and urine utilizing Rhodamin B (author's transl)]

A micromethod is described for the spectrophotometric determination of inorganic phosphate in serum and urine utilizing Rhodamin B as a dye (phosphomolybdat-Rhodamin B complex), Brij 35, and polyvinylpyrrolidon as catalyst. The procedure does not involve deproteinization and yields a stable complex in 20 min. The linearity is constant up to at least 9 mg Pi per 100 ml. It is both accurate (r = 0.972 in serum, r = 0.989 in urine, recovery in urine 98%) and precise (vk = 1.16% in the series). Bilirubin up to 10 mg/100 ml and serum protein do not interfere with the method.

Evaluation of six fluorescent protein stains for use in flow microfluorometry

Flow microfluorometric (FMF) analysis of stained cells has provided protein distribution histograms for large populations of cells. Spectral data and staining protocols were evaluated for six fluorescent protein dyes suggested for staining cells in liquid suspension. The requirements for dyes and/or staining protocol included minimal cell clumping and cell loss, near-optimal dye excitation at existing laser wavelengths, and tenacity of the dye/protein interaction. These criteria were best satisfied by fluorescein isothiocyanate (FITC) and rhodamine B isothiocyanate (RITC). Both fluorescamine and 8-aniline-1-naphthalene sulfonic acid (ANSA) showed potential applicability for use in systems where excitation wavelengths in the ultraviolet range are available. Protein staining with fluorescamine was extremely rapid. Brilliant sulfaflavine and 1-dimethyl-aminonaphthalene-5-sulfonyl chloride (DANSYL) were found unsatisfactory in these studies, since the former dye tended to diffuse from the cells, while the latter induced excessive cell clumping and cell loss. These techniques have application to immunofluorescence analysis and can also be profitably employed in dual-parameter analysis systems in connection with double-staining techniques for simultaneous DNA and protein analysis.

Tunable lasers in ophthalmology

The present status of laser application in clinical ophthalmology is breifly reviewed. The potentials of tunable dye lasers as retinal photocoagulators are discussed. Selective irradiation of ocular tissues over the full visible spectrum and the simplicity and reliability of recently developed waveguide lasers are the most attractive features of these lasers. Waveguide dye lasers have permitted to set up very compact and simple retinal photocoagulators, with improved output intensity stability and nearfield distribution uniformity. Preliminary results obtained with pulsed Rhodamine 6G laser show that good retinal photocoagulations are obtained at very low output energies.