Josias Basil Wacker

Increasing the efficiency of lanthanide luminescent bioprobes: bioconjugated silica nanoparticles as markers for cancerous cells

The lanthanide binuclear helicate [Ln2(LC2)3] has been embedded into bare and NH2-functionalized silica nanoparticles (NPs) using water-in-oil microemulsion technique. TEM analysis reveals both [Ln2(LC2)3]@SiO2 and [Ln2(LC2)3]@SiO2/NH2 nanoparticles having a spherical morphology and being monodispersed with an average size of 55 ± 5 and 90 ± 10 nm, respectively. The energy of the ligand triplet state, ∼21800 cm−1 ([Gd2(LC2)3]@NP), does not change upon incorporation into silica nanoparticles and is optimal for sensitizing EuIII luminescence. As a consequence, [Eu2(LC2)3]@SiO2 and [Eu2(LC2)3]@SiO2/NH2 NPs display red emission due to characteristic 5D0 → 7FJ (J = 0–4) transitions with absolute quantum yield reaching 28% for the latter. NH2-functionalized NPs have then been conjugated with avidin (NP-avidin) or goat anti-mouse IgG antibody (NP-IgG) to test them as luminescent biomarkers. Time-resolved microscopy of immunocytochemical assays involving recognition of mucin-like proteins expressed on breast cancer MCF-7 cells by the 5D10 monoclonal antibody confirms that the NP-IgG bioprobe displays specific luminescent signal with signal-to-noise ratio ≈20% higher than the one obtained for the bioconjugate of molecular [Eu2(LC2(COOH))3] with IgG. In addition, immunoassays using a streptavidin-coated plate and the NP-IgG probe are able to detect 15 ng mL−1 of the biotinylated 5D10 antibody with a signal-to-noise ratio of 100.

Anisotropic Magnetic Porous Assemblies of Oxide Nanoparticles Interconnected Via Silica Bridges for Catalytic Application

We report the microfluidic chip-based assembly of colloidal silanol-functionalized silica nanoparticles using monodisperse water-in-oil droplets as templates. The nanoparticles are linked via silica bridges, thereby forming superstructures that range from doublets to porous spherical or rod-like micro-objects. Adding magnetite nanoparticles to the colloid generates micro-objects that can be magnetically manipulated. We functionalized such magnetic porous assemblies with horseradish peroxidase and demonstrate the catalytic binding of fluorescent dye-labeled tyramide over the complete effective surface of the superstructure. Such nanoparticle assemblies permit easy manipulation and recovery after a heterogeneous catalytic process while providing a large surface similar to that of the individual nanoparticles.

Microfluidic chip for monitoring Ca2+ transport through a confluent layer of intestinal cells

The absorption of dietary calcium through the intestinal barrier is essential for maintaining health in general and especially of the bone system. We propose a microfluidic model that studies free calcium (Ca2+) transport through a confluent monolayer of Caco-2 cells. The latter were cultured on a porous membrane that was positioned in between a top and bottom microfluidic chamber. Fresh cell culture medium was continuously supplied into the device at a flow rate of 5 nL s−1 and the culture progress of the cell monolayer was continuously monitored using integrated Transepithelial Electrical Resistance (TEER) electrodes. The electrical measurements showed that the Caco-2 monolayer formed a dense and tight barrier in 5 days. The transported free Ca2+ from the top microfluidic chamber to the basolateral side of the cell monolayer was measured using the calcium-sensitive dye fura-2. This is a ratiometric dye which exhibits an excitation spectrum shift from 340 nm to 380 nm, when it binds to Ca2+ with an emission peak at 510 nm. Therefore, the concentration of free Ca2+ is proportional to the ratio of fluorescence emissions obtained by exciting at 340 nm and 380 nm. The barrier function of the cell monolayer was evaluated by a measured rate of Ca2+ transport through the monolayer that was 5 times lower than that through the bare porous membrane. The continuous perfusion of cell nutrients and the resultant mechanical shear on the cell surface due to the fluid flow are two key factors that would narrow the gap between the in vivo and in vitro conditions. These conditions significantly enhance the Caco-2 cell culture model for studying nutrients bioavailability.

Grafting submicron titania particles with gold nanoparticles using droplet microfluidics

A microfluidic method to synthesize gold–titania nanocomposites is presented. Porous TiO2 particles are first loaded with a reducing agent and then suspended in water and mixed with chloroauric acid (HAuCl4) in a droplet-by-droplet manner on a microfluidic chip. The procedure allows strongly reducing the amount of reagents and easy control of the reaction.

A microfluidic process for on-chip formation of assemblies of oxide nanoparticles

We report the continuous growth of spherical assemblies of silica and titania nanoparticles, which were pre-activated to produce hydroxyl/peroxy groups on their surface, by flowing a colloid-in-dioctyl phthalate emulsion into a polydimethylsiloxane microfluidic chip, which is held at a temperature of 120–130 °C. When the colloidal microdroplets enter the chip, the instantaneous heating results in vapour-based convective agitation and emulsion breakup, leading to microdroplet fusion and subsequent merging of their nanoparticle content. This progressively results in a robust large assembly obtained after sintering at 600 °C owing to strong chemical interparticle bonds.

On-chip synthesis of silica nanoparticle assemblies with controlled shape and size

We describe the assembly of silica nanoparticles into superstructures with controlled shape and size. The individual nanoparticles are chemically linked to each other via silica bridges, thus providing high mechanical stability to the assembly. Key to control the size and shape of the assemblies is the confinement of the nanoparticles in highly monodisperse microdroplets that are produced in a microfluidic chip. Exploiting the high surface-to-volume ratio of the assemblies, we show an enzymatic reaction on them. To control the position of the assemblies in a microfluidic environment, we embed superparamagnetic nanoparticles into them, which allows us to move the assemblies with a simple hand magnet.