A comparison of methods to assess cell mechanical properties.

The mechanical properties of cells influence their cellular and subcellular functions, including cell adhesion, migration, polarization, and differentiation, as well as organelle organization and trafficking inside the cytoplasm. Yet reported values of cell stiffness and viscosity vary substantially, which suggests differences in how the results of different methods are obtained or analyzed by different groups. To address this issue and illustrate the complementarity of certain approaches, here we present, analyze, and critically compare measurements obtained by means of some of the most widely used methods for cell mechanics: atomic force microscopy, magnetic twisting cytometry, particle-tracking microrheology, parallel-plate rheometry, cell monolayer rheology, and optical stretching.

DNA Computing Systems Activated by Electrochemically-triggered DNA Release from a Polymer-brush-modified Electrode Array.

An array of four independently wired indium tin oxide (ITO) electrodes was used for electrochemically stimulated DNA release and activation of DNA-based Identity, AND and XOR logic gates. Single-stranded DNA molecules were loaded on the mixed poly(,-di-methylaminoethyl methacrylate) (PDMAEMA)/poly-(methacrylic acid) (PMAA) brush covalently attached to the ITO electrodes. The DNA deposition was performed at pH 5.

Nanoreactors based on DNAzyme-functionalized magnetic nanoparticles activated by magnetic field.

A new biomimetic nanoreactor design, MaBiDz, is presented based on a copolymer brush in combination with superparamagnetic nanoparticles. This cellular nanoreactor features two species of magnetic particles, each functionalized with two components of a binary deoxyribozyme system. In the presence of a target mRNA analyte and a magnetic field, the nanoreactor is assembled to form a biocompartment enclosed by the polymeric brush that enables catalytic function of the binary deoxyribozyme with enhanced kinetics.

Magnetic Field-Activated Sensing of mRNA in Living Cells.

Detection of specific mRNA in living cells has attracted significant attention in the past decade. Probes that can be easily delivered into cells and activated at the desired time can contribute to understanding translation, trafficking and degradation of mRNA. Here we report a new strategy termed magnetic field-activated binary deoxyribozyme (MaBiDZ) sensor that enables both efficient delivery and temporal control of mRNA sensing by magnetic field.

AFM study shows prominent physical changes in elasticity and pericellular layer in human acute leukemic cells due to inadequate cell-cell communication.

Biomechanical properties of single cells in vitro or ex vivo and their pericellular interfaces have recently attracted a lot of attention as a potential biophysical (and possibly prognostic) marker of various diseases and cell abnormalities. At the same time, the influence of the cell environment on the biomechanical properties of cells is not well studied. Here we use atomic force microscopy to demonstrate that cell-cell communication can have a profound effect on both cell elasticity and its pericellular coat.

An Enzyme-based 1:2 Demultiplexer Interfaced with an Electrochemical Actuator.

An enzyme-based 1:2 demultiplexer is designed in a flow system composed of three cells where each one is modified with a different enzyme: hexokinase, glucose dehydrogenase and glucose-6-phosphate dehydrogenase. The Input signal activating the biocatalytic cascade is represented by glucose, while the Address signal represented by ATP is responsible for directing the Input signal to one of the output channels, depending on the logic value of the Address. The biomolecular 1:2 demultiplexer is extended to include two electrochemical actuators releasing entrapped DNA molecules in the active output channel.

Biophysical differences between chronic myelogenous leukemic quiescent and proliferating stem/progenitor cells.

The treatment of chronic myeloid leukemia (CML), a clonal myeloproliferative disorder has improved recently, but most patients have not yet been cured. Some patients develop resistance to the available tyrosine kinase treatments. Persistence of residual quiescent CML stem cells (LSCs) that later resume proliferation is another common cause of recurrence or relapse of CML.

Bioelectronic Interface Connecting Reversible Logic Gates Based on Enzyme and DNA Reactions.

It is believed that connecting biomolecular computation elements in complex networks of communicating molecules may eventually lead to a biocomputer that can be used for diagnostics and/or the cure of physiological and genetic disorders. Here, a bioelectronic interface based on biomolecule-modified electrodes has been designed to bridge reversible enzymatic logic gates with reversible DNA-based logic gates. The enzyme-based Fredkin gate with three input and three output signals was connected to the DNA-based Feynman gate with two input and two output signals-both representing logically reversible computing elements.

Diffusion of Oligonucleotides from within Iron-Cross-Linked, Polyelectrolyte-Modified Alginate Beads: A Model System for Drug Release.

An analytical model to describe diffusion of oligonucleotides from stable hydrogel beads is developed and experimentally verified. The synthesized alginate beads are Fe(3+) -cross-linked and polyelectrolyte-doped for uniformity and stability at physiological pH. Data on diffusion of oligonucleotides from inside the beads provide physical insights into the volume nature of the immobilization of a fraction of oligonucleotides due to polyelectrolyte cross-linking, that is, the absence of a surface-layer barrier in this case.

Substance Release Triggered by Biomolecular Signals in Bioelectronic Systems.

A new approach to bioelectronic Sense-and-Act systems was developed with the use of modified electrodes performing sensing and substance-releasing functions. The sensing electrode was activated by biomolecular/biological signals ranging from small biomolecules to proteins and bacterial cells. The activated sensing electrode generated reductive potential and current, which stimulated dissolution of an Fe(3+)-cross-linked alginate matrix on the second connected electrode resulting in the release of loaded biochemical species with different functionalities.

Towards early detection of cervical cancer: Fractal dimension of AFM images of human cervical epithelial cells at different stages of progression to cancer.

Unlabelled: We used AFM HarmoniX modality to analyse the surface of individual human cervical epithelial cells at three stages of progression to cancer, normal, immortal (pre-malignant) and carcinoma cells. Primary cells from 6 normal strains, 6 cancer, and 6 immortalized lines (derived by plasmid DNA-HPV-16 transfection of cells from 6 healthy individuals) were tested. This cell model allowed for good control of the cell phenotype down to the single cell level, which is impractical to attain in clinical screening tests (ex-vivo).

Bridging the Two Worlds: A Universal Interface between Enzymatic and DNA Computing Systems.

Molecular computing based on enzymes or nucleic acids has attracted a great deal of attention due to the perspectives of controlling living systems in the way we control electronic computers. Enzyme-based computational systems can respond to a great variety of small molecule inputs. They have the advantage of signal amplification and highly specific recognition.

A bioelectronic system for insulin release triggered by ketone body mimicking diabetic ketoacidosis in vitro.

A bioelectronic system composed of two modified electrodes, one activated in the presence of ketone bodies, a biomarker of diabetic ketoacidosis, and another releasing insulin upon receiving a signal, was designed and tested in vitro to operate as a Sense-and-Act device. The functional integration of biomarker-sensing and insulin-releasing electrodes represents a step to a theranostic system with autonomous operation.

Enzyme-based logic gates switchable between OR, NXOR and NAND Boolean operations realized in a flow system.

The enzyme-based system performing a biocatalytic cascade reaction was realized in a flow device and was used to mimic Boolean logic operations. Chemical inputs applied to the system resulted in the activation of additional reaction steps, allowing the reversible switch of the logic operations between OR, NXOR and NAND gates for processing of two other biomolecular inputs.

If cell mechanics can be described by elastic modulus: study of different models and probes used in indentation experiments.

Here we investigated the question whether cells, being highly heterogeneous objects, could be described with the elastic modulus (effective Young's modulus) in a self-consistent way. We performed a comparative analysis of the elastic modulus derived from the indentation data obtained with atomic force microscopy (AFM) on human cervical epithelial cells (both normal and cancerous). Both sharp (cone) and dull (2500-nm radius sphere) AFM probes were used.

Activation of a biocatalytic electrode by removing glucose oxidase from the surface--application to signal triggered drug release.

A biocatalytic electrode activated by pH signals was prepared with a multilayered nanostructured interface including PQQ-dependent glucose dehydrogenase (PQQ-GDH) directly associated with the conducting support and glucose oxidase (GOx) located on the external interface. GOx was immobilized through a pH-signal-cleavable linker composed of an iminobiotin/avidin complex. In the presence of GOx, glucose was intercepted at the external interface and biocatalytically oxidized without current generation, thus keeping the electrode in its nonactive state.

Model system for targeted drug release triggered by immune-specific signals.

A new sense-and-act system was realized by integrating a biocatalytic/bioaffinity electrode responding to immune signals represented by an antibody and a polymer-modified electrode loaded with drug-mimicking species. The release of the drug-mimicking species was achieved specifically in response to a signal antibody, thus demonstrating for the first time an immune-induced drug-releasing process. The present approach promises new options for future applications in controlled drug release and personalized medicine.

Majority and minority gates realized in enzyme-biocatalyzed systems integrated with logic networks and interfaced with bioelectronic systems.

Biocatalytic reactions operating in parallel and resulting in reduction of NAD(+) or oxidation of NADH were used to mimic 3-input majority and minority logic gates, respectively. The substrates corresponding to the enzyme reactions were used as the input signals. When the input signals were applied at their high concentrations, defined as logic 1 input values, the corresponding biocatalytic reactions were activated, resulting in changes of the NADH concentration defined as the output signal.

Enzymatic filter for improved separation of output signals in enzyme logic systems towards 'sense and treat' medicine.

The major challenge for the application of autonomous medical sensing systems is the noise produced by non-zero physiological concentrations of the sensed target. If the level of noise is high, then a real signal indicating abnormal changes in the physiological levels of the analytes might be hindered. Inevitably, this could lead to wrong diagnostics and treatment, and would have a negative impact on human health.

Quantitative study of the elastic modulus of loosely attached cells in AFM indentation experiments.

When measuring the elastic (Young's) modulus of cells using AFM, good attachment of cells to a substrate is paramount. However, many cells cannot be firmly attached to many substrates. A loosely attached cell is more compliant under indenting.

Ultrabright fluorescent mesoporous silica nanoparticles for prescreening of cervical cancer.

Unlabelled: We report on the first functional use of recently introduced ultrabright fluorescent mesoporous silica nanoparticles, which are functionalized with folic acid, to distinguish cancerous and precancerous cervical epithelial cells from normal cells. The high brightness of the particles is advantageous for fast and reliable identification of both precancerous and cancerous cells. Normal and cancer cells were isolated from three healthy women and three cancer patients.

Method for quantitative measurements of the elastic modulus of biological cells in AFM indentation experiments.

Here we overview and further develop a quantitative method to measure mechanics of biological cells in indentation experiments, which is based on the use of atomic force microscopy (AFM). We demonstrate how the elastic modulus of the cell body should be measured when the cellular brush is taken into account. The brush is an essential inelastic part of the cell, which surrounds all eukaryotic (the brush is mostly microvilli and glycocalyx) and gram-negative prokaryotic cells (the brush is polysaccharides).