Ravi Gaikwad

Detection of surface brush on biological cells in vitro with atomic force microscopy

Observation of a brush on the cell surface with the atomic force microscopy (AFM) in vitro is reported. The number of methods to study brushes that coat living cells is limited despite their biological importance. Moreover, it is important to take into account the brush layer when studying cell mechanics. Here the authors present an AFM method to detect the length and grafting density of the brush on viable cells with resolution that considerably surpasses any existing method. The authors demonstrate this method using cultured human cervical epithelial cells, but it can be applied to any type of cell.

Silica Nanoparticles to Polish Tooth Surfaces for Caries Prevention

Although silica particles have been used for tooth polishing, polishing with nanosized particles has not been reported. Here we hypothesize that such polishing may protect tooth surfaces against the damage caused by cariogenic bacteria, because the bacteria can be easily removed from such polished surfaces. This was tested on human teeth ex vivo. The roughness of the polished surfaces was measured with atomic force microscopy (AFM). A considerably lower nanometer-scale roughness was obtained when silica nanoparticles were used to polish the tooth surfaces, as compared with conventional polishing pastes. Bacterial attachment to the dental surfaces was studied for Streptococcus mutans, the most abundant cariogenic bacteria. We demonstrated that it is easier to remove bacteria from areas polished with silica nanoparticles. The results demonstrate the advantage of using silica nanoparticles as abrasives for tooth polishing.

Towards Nonspecific Detection of Malignant Cervical Cells with Fluorescent Silica Beads

To date, the methods for detection of cancer cells are mostly based on traditional techniques used in biology, such as visual identification of malignant changes, cell-growth analysis, specific ligand-receptor labeling, or genetic tests. Despite being well developed, these methods are either insufficiently accurate or require a lengthy complicated analysis. A search for alternative methods for the detection of cancer cells may be a fruitful approach. Proposed here is a novel method for the detection of cancer cells in vitro, which is based on nonspecific adhesion of silica beads to cells. First, atomic force microscopy is used to study the adhesion of single silica beads to malignant and normal cells cultured from human cervix. It is found that adhesion depends on the time of contact, and can be statistically different for malignant and normal cells. Using these data, an optical method utilizing fluorescent silica beads is developed, which is based on detection of the difference in the number of adherent particles. The method is tested using primary cells cultured from cervical tissues of three healthy individuals and three patients with cervical cancer. The method shows sufficiently high sensitivity for cancer to make it interesting to perform further statistical tests.

Detection of cancerous cervical cells using physical adhesion of fluorescent silica particles and centripetal force.

Here we describe a non-traditional method to identify cancerous human cervical epithelial cells in a culture dish based on physical adhesion between silica beads and cells. It is a simple optical fluorescence-based technique which detects the relative difference in the amount of fluorescent silica beads physically adherent to surfaces of cancerous and normal cervical cells. The method utilizes the centripetal force gradient that occurs in a rotating culture dish. Due to the variation in the balance between adhesion and centripetal forces, cancerous and normal cells demonstrate clearly distinctive distributions of the fluorescent particles adherent to the cell surface over the culture dish. The method demonstrates higher adhesion of silica particles to normal cells compared to cancerous cells. The difference in adhesion was initially observed by atomic force microscopy (AFM). The AFM data were used to design the parameters of the rotational dish experiment. The optical method that we describe is much faster and technically simpler than AFM. This work provides proof of the concept that physical interactions can be used to accurately discriminate normal and cancer cells.

Surface dominant photoresponse of multiferroic BiFeO3 nanowires under sub-bandgap illumination

A surface dominant sub-bandgap photo-carrier generation has been observed in multiferroic BiFeO3 (BFO) nanowires, which is mainly attributed to the depopulation of surface states that exist within the bandgap. Mapping of surface potential using Kelvin probe force microscopy (KPFM) further supports the depopulation of surface states in BFO nanowires under sub-bandgap illumination. The mechanism of photovoltage generation in BFO nanowires is investigated by measuring the photoresponse with local illumination of visible laser pulses at different positions of the BFO nanowires. Interestingly, large photovoltage signals were observed when the laser spot was focused close to contact electrodes, showing a position dependent effect of photoresponse in the BFO nanowires. The sub-bandgap excitation of surface states in multiferroic nanowires offers potential new strategies for application in photovoltaic devices.

Atomic force microscopy characterization of corneocytes: effect of moisturizer on their topology, rigidity, and friction.

Background/purpose: Atomic force microscopy (AFM) is a novel technique for skin characterization.

A novel in vitro stripping method to study geometry of corneocytes with fluorescent microscopy: example of aging skin.

Background/purpose: To develop modification of stripping method allowing high‐resolution fluorescent visualization of corneocytes of human skin in vitro. To validate the method, the measured corneocyte areas on skin flakes are collected from individuals of different ages.

Atomic Force Microscopy Helps to Develop Methods for Physical Detection of Cancerous Cells

Humans are still far from defeating cancer. Early detection of cancer will decrease fatality from this disease. Traditional methods of identification of cancerous cells are mainly based on regular techniques used in biology, such as visual identification of maligant changes, cell growth analysis, specific ligand-receptor labeling, or genetic tests. After many years of research, these methods are still either insufficiently accurate or require a lengthy complicated analysis. It has been recently shown that the atomic force microscopy (AFM) method can be useful in the search for alternative methods for a reliable detection of cancer cells. Here we describe the atomic force microscopy (AFM) study of malignant and normal cells cultured from human cervix. Studying adhesion of AFM probes to both of these types of cells, we found that the adhesion can be statistically different. This finding allows us to propose two novel methods for detection cancer cells by using fluorescent silica beads. The methods show high sensitivity to detect cancer in-vitro. Nevertheless, more statistical data will be needed to determine the actual accuracy of the methods.