Dmytro O. Volkov

Ultrabright fluorescent mesoporous silica nanoparticles.

The first successful approach to synthesizing ultrabright fluorescent mesoporous silica nanoparticles is reported. Fluorescent dye is physically entrapped inside nanochannels of a silica matrix created during templated sol-gel self-assembly. The problem of dye leakage from open channels is solved by incorporation of hydrophobic groups in the silica matrix. This makes the approach compatible with virtually any dye that can withstand the synthesis. The method is demonstrated using the dye Rhodamine 6G. The obtained 40-nm silica particles are about 30 times brighter than 30-nm coated water-soluble quantum dots. The particles are substantially more photostable than the encapsulated organic dye itself.

Ultrabright fluorescent mesoporous silica particles

Recent self-assembly of ultra-bright fluorescent colloidal mesoporous (nanoporous) silica particles is highlighted. The particles can be up to two others of magnitude brighter than polymeric particles of comparable size assembled with quantum dots. Comparing with the maximum fluorescence of free dye in the same volume, the particles can show fluorescence which is higher by more than three orders of magnitude. We discuss the nature of the high brightness of these particles, existing problems, potential applications and prospects.

Logic Networks Based on Immunorecognition Processes

The biochemical system logically processing biochemical signals using immune-specific and biocatalytic reactions was designed, and the generated output signals were analyzed by AFM and optical means. Different patterns of immune signals resulted in the formation of various interfacial structures followed by biocatalytic reactions activated by the next set of biochemical inputs. The developed approach to multisignal biosensing allows qualitative evaluation of the biochemical information in terms of YES-NO, providing the base for novel molecular-level logic analysis of complex patterns of biochemical signals. Application of AFM to read out the structures generated on the interface could potentially lead to substantial miniaturization of the immune logic systems.

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.

Atomic force microscopy study of immunosensor surface to scale down the size of ELISA-type sensors

Here we describe the use of atomic force microscopy (AFM) to study the nanoscale mechanics of the molecular layers of a popular immunosensor, ELISA (enzyme-linked immunosorbent assay) type. We characterize the sensor surface in terms of brush length and grafting density of the molecular layers. The obtained data demonstrated that a reliable reading of the immunosignal (a suggested dimensionless combination of brush length and grafting density) can be attained from an area as small as approximately 3 microm(2). This is approximately 4 million times smaller compared to typical ELISA sensors. The immunosensor described is composed of a molecular mix of two different antigens. Intriguingly, we find that AFM can reliably distinguish between having the immunosignal from either antibody and from both antibodies together. This was impossible to get by using standard optical detection methods.

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.