Biomedical subjects

T A Camesano

Publications and source records attributed to T A Camesano.

3 recordsLinked to original sources

PubMed2005

On the importance of precise calibration techniques for an atomic force microscope.

Proper calibration of any instrument is vital to an investigator's ability to compare laboratory experiments, as well as to draw quantitative relations between experimental results and the real world. For the atomic force microscope, knowledge of quantities such as the probe spring constant, the piezoactuator voltage/height response, and the probe radius of curvature is necessary when transforming raw data into height, separation and force. These parameters are also prerequisites when applying mathematical models to the collected data. In this communication, we adapt existing techniques of quantifying these parameters to our equipment and show differences between the adjusted parameters and those provided by the manufacturer. The total statistical uncertainty attributable to these parameters was calculated as > 1500% using the manufacturers' values. After adjustment, this contribution drops to approximately 20%. The combined effect of quantifying these parameters, which had previously not been explored in concert, demonstrates the necessity of properly understanding one's equipment in order to generate reproducible and credible experimental results.

Calibration↗

PubMed2003

Polysaccharide properties probed with atomic force microscopy.

In recent years, polysaccharides have been extensively studied using atomic force microscopy (AFM). Owing to its high lateral and vertical resolutions and ability to measure interaction forces in liquids at pico- or nano-Newton level, the AFM is an excellent tool for characterizing biopolymers. The first imaging studies showed the morphology of polysaccharides, but gradually more quantitative image analysis techniques were developed as the AFM grew easier to use in aqueous liquids and in non-contact modes. Recently, AFM has been used to stretch polysaccharides and characterize their physicochemical properties by application of appropriate polymer stretching models, using a technique called single-molecule force spectroscopy. From application of such models as the wormlike chain, freely jointed chain, extensible-freely jointed chain, etc., properties such as the contour length, persistence length and segment elasticity or spring constant can be calculated for polysaccharides. The adhesion between polysaccharides and surfaces has been quantified with AFM, and this application is particularly useful for studying polysaccharides on microbial and other types of cells, because their adhesion is controlled by biopolymer characteristics. This review presents a synthesis of the theory and techniques currently in use to probe the physicochemical properties of polysaccharides with AFM.

Animals↗

PubMed2001

Single molecule study of xanthan conformation using atomic force microscopy.

Conformations of individual macromolecules of the biopolymer xanthan were investigated using atomic force microscopy (AFM). Xanthan from very dilute solutions (1 ppm) was allowed to adsorb onto freshly cleaved mica and examined using tapping mode AFM under ambient conditions. The secondary structure of xanthan was probed by heating the polymer and gradually cooling, which denatured and renatured the polymer. When salt was present, renatured xanthan formed a double helical structure, consistent with the structure of native xanthan. In pure water, renaturation was not complete as what appeared to be single helical structures were observed. The number-average contour length (L(n)) of the polymer in its single helical state was 1651 nm. In the double helical state, induced by the addition of salt, L(n) decreased to 450 nm (in 0.5 M KCl). The chains also became less rigid as salt was added. The persistence length decreased from 417 nm in pure water to approximately 150 nm in 0.1 or 0.5 M KCl. This indicated a trend toward more flexible molecules when salt was present. Calculations of end-to-end distances based on equilibrium and projected conformations confirmed that the xanthan chain conformation on the mica surface was at equilibrium and was therefore representative of the conformation of xanthan in solution. The single-molecule AFM technique eliminates one common bias of solution techniques, which is the determination of an average signal between aggregates and dissolved molecules. It is thus a useful complement to solution-based methods for determining physical-chemical properties of biopolymers.

Carbohydrate Conformation↗