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L McDonnell

Publications and source records attributed to L McDonnell.

At least 19 recordsLinked to original sources
PubMed2005

Improving immunoassays based on the analysis of scanning force microscopy images.

Scanning force microscopy has been demonstrated to be an effective binding event detection step for immunoassays. In its simplest form--analysing small area images--the detection limit of the scanning force microscopic immunoassay (SFMIA) has been shown to be comparable to existing techniques. In the present work, we have examined how the performance of image analysis-based SFMIA can be improved. Firstly, we have used a surface analysis parameter that increases linearly with the concentration of binding events. This parameter--the surface area ratio--is the ratio of the surface area after antigen binding to the surface area of the original biospecific surface. With this parameter, SFMIA images can be rapidly analysed and converted into assay units. Secondly, we have demonstrated that by using silicon wafer supports that carry fiducial marks we can relocate to very high accuracy onto the biospecific surfaces and identify the changes due to antigen binding. By relocating in this manner the signal to noise ratio of the technique is enhanced. Thirdly, from simulations we have determined the SFM tip size and image area that optimizes the immunoassay sensitivity.

Animals↗
PubMed2004

Atomic force microscopy of BHK-21 cells: an investigation of cell fixation techniques.

The atomic force microscope (AFM) has been used to image a wide variety of biological samples, including cultured cells, in air. Whilst cultured cells have been prepared for AFM analysis using a variety of matrices and fixatives, a definitive study of sample preparation and its effects on cell morphology has not, as far as the authors are aware, previously been reported. Although a considerable number of cell fixatives exist, no single fixative is ideal for all investigations. Prior to the performance of specialised techniques, such as atomic force microscopy of cultured cells in air, the cell fixation method must be investigated and optimised. The fixative abilities of 2% paraformaldehyde-lysine-periodate, 0.25% glutaraldehyde, paraformaldehyde-glutaraldehyde, 4% phosphate-buffered formal saline, 1% formaldehyde, methanol:acetone, formal saline, 4% paraformaldehyde and ethanol:acetic acid were assessed in this study. A qualitative assessment system was used to evaluate the efficacy of the above fixatives using conventional fixation criteria (i.e. the presence of fibroblastic morphology consistent with optical microscopy and the absence of fixation artifacts). The optimal fixative was identified as 4% paraformaldehyde, which was capable of providing optically consistent images of BHK-21 (fibroblastic) cells, whose heights remained within the measurement capability of the AFM instrument used in this study.

Animals↗
PubMed2004

Atomic force microscopy analysis of enveloped and non-enveloped viral entry into, and egress from, cultured cells.

Since its invention, the atomic force microscope has been used to image a wide variety of biological samples, including viruses. Viral entry into, and egress from, cultured cells has been extensively studied using numerous scientific techniques and to a limited extent using atomic force microscopy. One of the main structural differences that can exist between viruses is the absence, or presence, of an envelope and this factor has consequences for the mode of viral entry and egress. In this study, the entry into, and egress from, cultured cells of enveloped and non-enveloped viruses were investigated using atomic force microscopy. No significant cell surface changes were observed following infection with enveloped or non-enveloped viruses. Although roughness analysis of viral entry revealed cell smoothing post-infection, no differences between the roughness values of enveloped and non-enveloped viral entry were observed. Line analysis of viral entry revealed minor differences between cells infected with an enveloped rather than a non-enveloped virus. These differences may represent a distinction between the uptake processes of enveloped and non-enveloped viruses. Studies of viral egress revealed that infected cells were undergoing cytopathic changes. Whilst topographic, height and roughness differences clearly occurred between virally- and mock-infected cells, no significant differences were elucidated between enveloped and non-enveloped viral egress.

Animals↗
PubMed2004

A method for measuring the size distribution of latex particles by scanning force microscopy.

A methodology has been developed to accurately determine the size distribution of latex particles using the scanning force microscope (SFM). Unlike other workers, who have generally measured the lateral dimensions of monolayers of latex particles using a global quantification method, we have measured the heights of individual latex particles located at the edges of latex monolayers that were immobilised onto mica substrates. In agreement with other work, we noted that the edges of monolayers of latex particles provided stable and reproducible scanning force imaging. Whilst SFM imaging noise, image processing artifacts, tip/sample forces and variations in the mica substrate are sources of measurement error that should not be overlooked, our experience has been that the variation over time of the sensitivity of the Z actuator is the greatest potential uncertainty in determining the heights of latex particles. The methodology that we used requires frequent calibration of the Z actuator of the SFM, typically before and after two or three images, in order to ensure that the uncertainties in the Z sensitivity are known and minimised. This methodology was developed for an SFM instrument that was equipped with open loop piezoelectric actuators following a careful study of the behaviour of those actuators. Using this methodology, we have measured the size distributions of populations of 300-400 latex particles from each of several different latex samples, with the maximum variation in the Z-actuator calibration experienced during the measurement of a sample being less than 2%, often about 1% and occasionally better still. In so doing, we have demonstrated that SFMs equipped with open loop actuators can be used for high confidence quantitative measurements of step heights.

Journal Article↗
PubMed2002

Immobilisation of Semliki forest virus for atomic force microscopy.

Semliki Forest virus (SFV), an alphavirus, is a single-stranded positive-sense RNA virus. The RNA genome is surrounded by a protein shell known as the capsid which itself is surrounded by a lipid envelope of host cell origin. In this study, SFV strain L10 enveloped virus and its capsid were immobilised onto silicon wafer supports which had been pre-coated with a monolayer of the relevant anti-viral antibody. After drying, the samples were imaged in air, using non-contact mode atomic force microscopy (AFM). Quantification of the AFM images has revealed that both the strain L10 enveloped virus and capsid collapse when immobilised in this manner. The capsid undergoes more significant collapse compared to the enveloped virus. The dimensions of the immobilised enveloped virus and capsid have been compared to a model where the free spherical particles collapse into ellipsoids during immobilisation. For the immobilised capsid the dimensions are consistent with this model whereas for the enveloped virus the model is less effective. The dimensions of the enveloped virus appear to be affected by the antibody used for immobilisation.

Animals↗
PubMed2001

Quantification of red blood cells using atomic force microscopy.

For humans the sizes and shapes of their red blood cells are important indicators of well being. In this study, the feasibility of using the atomic force microscope (AFM) to provide the sizes and shapes of red blood cells has been investigated. An immobilisation procedure has been developed that enabled red blood cells to be reliably imaged by contact AFM in air. The shapes of the red blood cells were readily apparent in the AFM images. Various cell quantification parameters were investigated, including thickness, width, surface area and volume. Excellent correlation was found between the AFM-derived immobilised mean cell volume (IMCV) parameter and the mean cell volume (MCV) parameter used in current haematological practice. The correlation between MCV and IMCV values has validated the immobilisation procedure by demonstrating that the significant cell shrinkage that occurs during immobilisation and drying does not introduce quantification artifacts. Reliable IMCV values were obtained by quantifying 100 red blood cells and this typically required 3-5 AFM images of 100 microm x 100 microm area. This work has demonstrated that the AFM can provide in a single test the red blood cell size and shape data needed in the assessment of human health.

Anemia, Macrocytic↗
PubMed1993

Skeinoid fibers.

Explore the source record for details and available documents.

Adult↗
PubMed1990

Altitude sickness.

Altitude sickness is a clinical syndrome that occurs with abrupt ascents to altitudes of 3000 metres and above. Symptoms include headache, malaise, fatigue, dizziness, anorexia, nausea and vomiting, and oliguria. At higher altitudes more severe illness resulting from pulmonary oedema or cerebral oedema can occur.

Altitude Sickness↗
PubMed1989

Breathing management: a simple stress and pain reduction strategy for use on a pediatric service.

A review of the pediatric literature on pain and stress reducing strategies is followed by a description of a breathing management and relaxation technique. Its use as a pain coping method is illustrated by two cases on a pediatric service. The positive responses of stress affected patients suggests that this approach can be effective in reducing feelings of panic and anxiety as a reaction to pain and the anticipation of pain.

Adaptation, Psychological↗
PubMed1986

The oxidation of tryptamine by the two forms of monoamine oxidase in human tissues.

The selective monoamine oxidase inhibitors clorgyline and (-)-deprenyl have been used to determine the activities of monoamine oxidase-A and -B towards tryptamine in several human tissues. The results were compared with those obtained with the A-form-selective substrate 5-hydroxytryptamine, the B-form-selective substrate 2-phenethylamine and the common substrate tyramine. Tryptamine was found to be a substrate for both forms of the enzyme in human liver, kidney cortex and medulla and in seven different brain regions. The Km values of the two forms towards this substrate were similar in all the human tissues examined but the maximum velocities differed. Thus the A-form would contribute approximately 50% of the total monoamine oxidase activity towards this substrate in human cerebral cortex, whereas it would contribute about 60% in kidney cortex and medulla and 75% in liver. These results suggest that both forms of monoamine oxidase would contribute to the metabolism of tryptamine in human tissues and are difficult to reconcile with suggestions that tryptamine excretion may provide a simple index of monoamine oxidase-A inhibition.

Brain↗
PubMed1983

CEA-like material in cytosols from human breast carcinomas. Correlation with biochemical and pathologic parameters.

CEA-like material was found in 51 of 62 primary human breast carcinomas and in only 2 of 12 fibroadenomas. Levels of carcinoma CEA-like material correlated weakly with cytoplasmic estradiol receptor levels, total cytosol estrogens, and cytosol progesterone. Levels of CEA-like material showed no significant correlation with carcinoma stage, grade, cellularity, size or histologic type. Levels, however, correlated inversely with lymphocyte infiltration.

Adenofibroma↗