Alsu I. Zamaleeva

Layer-by-layer coating of bacteria with noble metal nanoparticles for surface-enhanced Raman scattering

A simple layer-by-layer method to coat the bacterial cells with gold and silver nanoparticles (AuNPs and AgNPs) for the acquisition of surface-enhanced Raman scattering (SERS) spectra is reported. First, the bacteria cell wall is coated with poly (allylamine hydrochloride) (PAH), a positively charged polymer, and then with citrate reduced Au or AgNPs. In order to increase the stability of the coating, another layer of PAH is prepared on the surface. The SEM and AFM images indicate that the nanoparticles are in the form of both isolated and aggregated nanoparticles on the bacterial wall. The coating of bacterial cells with AgNPs or AuNPs not only serves for their preparation for SERS measurement but also helps to visualize the coated of bacterial cells under the ordinary white-light microscope objective due to efficient light-scattering properties of Au and AgNPs. A comparative study single versus aggregates of bacterial cells is also demonstrated for possible single bacterial detection with SERS. The two bacteria that differ in shape and cell wall biochemical structure, Escherichia coli and Staphylococcus cohnii, Gram-negative and -positive, respectively, are used as models. The preliminary results reveal that the approach could be used for single bacterial cell identification.

Living Fungi Cells Encapsulated in Polyelectrolyte Shells Doped with Metal Nanoparticles

We report the layer-by-layer coating of living fungi cells (Saccharomyces cerevisiae and Trichoderma asperellum) with polyelectrolytes poly(allylamine hydrochloride)/sodium poly(styrene sulfonate) and bovine serum albumin/DNA and citrate-stabilized gold and silver nanoparticles. It was found that the nanoparticles were effectively incorporated between oppositely charged polyelectrolyte layers, modifying the topography and the roughness of cell walls. The formation of large aggregates of nanoparticles on the cell walls of encapsulated cells was shown. It was found that the encapsulated cells preserved their viability and the shells were soft enough to allow the growth of mycelium. The surface-enhanced Raman scattering (SERS) was used to investigate the biochemical environments of the gold and silver nanoparticles immobilized on the surface of T. asperellum conidia. The SERS spectra from encapsulated conidia and polyelectrolytes indicate that both gold and silver nanoparticles interact with cell walls from different locations, and nanoparticle-polyelectrolyte interaction is limited. The approach described in this paper might have potential applications in modification of living cells.

Interfacing living unicellular algae cells with biocompatible polyelectrolyte-stabilised magnetic nanoparticles.

Green algae are a promising platform for the development of biosensors and bioelectronic devices. Here we report a reliable single-step technique for the functionalisation of living unicellular green algae Chlorella pyrenoidosa with biocompatible 15 nm superparamagnetic nanoparticles stabilised with poly(allylamine hydrochloride). The magnetised algae cells can be manipulated and immobilised using external permanent magnets. The distribution of the nanoparticles on the cell walls of C. pyrenoidosa was studied by optical and fluorescence microscopy, TEM, SEM and EDX spectroscopy. The viability and the magnetic properties of the magnetised algae are studied in comparison with the native cells. The technique may find a number of potential applications in biotechnology and bioelectronics.

Polyelectrolyte-mediated assembly of multiwalled carbon nanotubes on living yeast cells.

Here we report the three-dimensional assembly of carbon nanotubes on the polyelectrolyte-coated living Saccharomyces cerevisiae cells using the polyelectrolyte-mediated layer-by-layer approach. Synthetic polyelectrolytes poly(allylamine hydrochloride) and poly(sodium 4-styrenesulfonate) were layer-by-layer deposited on the surfaces of the yeast cells followed by the deposition of water-soluble oxidized multiwalled carbon nanotubes (MWNTs) and an additional outermost polyelectrolyte bilayer. This resulted in the fabrication of polyelectrolyte/nanotubes composite coatings on the cell walls of the yeast cells, which could be clearly seen using the conventional optical microscopy. Transmission and scanning electron microscopy was applied to further investigate the composite coatings. Viability of the encapsulated cells was confirmed using the intercellular esterase activity test. Finally, electrochemical studies using voltammetry and electrochemical impedance measurements were performed, indicating that the composite polyelectrolytes/MWNTs coatings sufficiently affect the electron mediation between the encapsulated yeast cells and the artificial electron acceptor, making it possible to distinguish between living and dead cells. The technique described here may find potential application in the development of microelectronic devices, core-shell and hollow composite microparticles, and electrochemical cell-based biosensors.

A Direct Technique for Magnetic Functionalization of Living Human Cells

Functionalized living cells are regarded as effective tools in directed cell delivery and tissue engineering. Here we report the facile functionalization of viable isolated HeLa cells with superparamagnetic cationic nanoparticles via a single-step biocompatible process. Nanoparticles are localized on the cellular membranes and do not penetrate into the cytoplasm. The magnetically responsive cells are viable and able to colonize and grow on substrates. Magnetically facilitated microorganization of functionalized cells into viable living clusters is demonstrated. We believe that the technique described here may find a number of potential applications in cell-based therapies and in development of whole-cell biosensors.

A whole-cell amperometric herbicide biosensor based on magnetically functionalised microalgae and screen-printed electrodes

We report the fabrication of an amperometric whole-cell herbicide biosensor based on magnetic retention of living cells functionalised with magnetic nanoparticles (MNPs) on the surface of a screen-printed electrode. We demonstrate that Chlorella pyrenoidosa microalgae cells coated with biocompatible MNPs and retained on the electrode with a permanent magnet act as a sensing element for the fast detection of herbicides. The magnetic functionalisation does not affect the viability and photosynthesis activity-mediated triazine herbicide recognition in microalgae. The current of ferricyanide ion was recorded during alternating illumination periods and biosensor fabricated was used to detect atrazine (from 0.9 to 74 µM) and propazine (from 0.6 to 120 µM) (the limits of detection 0.7 and 0.4 µM, respectively). We believe that the methodology presented here can be widely used in fabrication of a number of whole cell biosensors since it allows for efficient and reversible cells immobilisation and does not affect the cellular metabolism.

CHAPTER 3:Direct Deposition of Nanomaterials onto Cells

Nanomaterials and nanoscale tools have been successfully utilized in diverse biological systems over the past decades. Integrating nanomaterials with living cells attracts considerable interest because it may be possible to provide new functions, control cell phenotype and fate, and also to create cell–nanomaterial hybrids with desirable properties. In this chapter we describe strategies and methods for the direct deposition of nanomaterials onto cells for extracellular surface functionalisation. We emphasize the importance of the cell surface properties and their interactions with nanomaterials. We also discuss the different approaches to deposit nanomaterials onto cells by either aiming at a homogeneous coating of the cells with different types of nanomaterials or ligand-specific binding of nanoparticles to extracellular biomolecules. The importance of the cell viability during the process of nanomaterials deposition, which depends on the field of application, is discussed. We also present some of the recent studies focused on the development of new smart materials for cell surface functionalization, fabrication of 3D nanoparticle–cell hybrids, and utilization of nanomodified cells in emerging technologies.