Ada-Ioana Bunea

Sensing based on the motion of enzyme-modified nanorods

Asymmetric modification with an enzyme confers nanorods an enhanced diffusive motion that is dependent on the concentration of the enzyme substrate. In turn, such a motion opens the possibility of determining the concentration of the enzyme substrate by measuring the diffusion coefficient of nanorods modified with the appropriate enzyme. Nanorods, with a Pt and a polypyrrole (PPy) segment, were fabricated. The PPy segment of such nanorods was then modified with glucose oxidase (GOx), glutamate oxidase (GluOx), or xanthine oxidase (XOD). Calibration curves, linking the diffusion coefficient of the oxidase-modified nanorods to the concentration of the oxidase substrate, were subsequently built. The oxidase-modified nanorods and their calibration curves were finally used to determine substrate concentrations both in simple aqueous solutions and in complex samples such as horse serum and cell culture media. Based on the obtained results we are confident that our motion-based approach to sensing can be developed to the point where different nanorods in a mixture simultaneously report on the concentration of different compounds with good temporal and spatial resolution.

Modification with hemeproteins increases the diffusive movement of nanorods in dilute hydrogen peroxide solutions

Nanorods were decorated with different hemeproteins that are able to convert hydrogen peroxide. When dispersed into hydrogen peroxide solutions, most of these nanorods are characterized by diffusion coefficients which increase with the concentration of hydrogen peroxide. Such a behaviour does not characterize unmodified nanorods.

Nanorods with Biocatalytically Induced Self‐Electrophoresis

Nanorods with motion enhanced through biocatalytically induced self‐electrophoresis are described. To obtain such nanorods, the polymer half of polypyrrole–gold (PPy‐Au) nanorods is decorated with horseradish peroxidase (HRP) and their metal half with cytochrome c (Cyt c). If such nanorods are suspended in enzymatically generated mixtures of O2⋅− and H2O2, the immobilized Cyt c is reduced by O2⋅−, and the immobilized HRP is oxidized by H2O2. As both hemeproteins are capable of direct electron transfer to/from solid substrates, the oxidized HRP is subsequently reduced with electrons received, through the nanorod, from the reduced Cyt c. The combined processes cause species from the electrical double layer of the nanorods to move from one end of the nanorod to the other, which powers the motion of the nanorods in the opposite direction. The diffusive motion of the hemeprotein‐modified nanorods is characterized by a diffusion coefficient 30 % larger in the presence of O2⋅− and H2O2 than in their absence. Unmodified nanorods do not show such behavior.

Nanobiophotonics using Light Robotics.

A confluence of developments is now ripe for the emergence of a new area within nanobiophotonics – Light Robotics – combining advances in microfabrication and optical micromanipulation together with intelligent control ideas from robotics and Fourier optics.

Optically fabricated and controlled microtool as a mobile heat source in microfluidics

Microfluidic systems have gained much interest in the past decade as they tremendously reduce sample volume requirements for investigating different phenomena and for various medical, pharmaceutical and defense applications. Rapid heat transfer and efficient diffusive material transport are among the benefits of miniaturization. These have been achieved so far by tediously designing and fabricating application-specific microfluidic chambers or by employing microdevices that can be difficult to integrate in microfluidic systems. In this work, we present the fabrication and functionalization via two-photon polymerization and physical vapor deposition of microstructures that serve as heat sources in microfluidic devices upon laser illumination. In contrast to other existing methods that rely on photo-thermal effects, our microtools are amenable to optical manipulation and can be actuated in specific locations where heat generation is desired. Heating effects manifest in the presence of a temperature gradient, induced fluid flow and the formation of microbubbles.

Rational design of light-controlled microrobots

Light Robotics is one of the newest progenies of the robotics family, bringing together advances in microfabrication and optical manipulation with intelligent control ideas from robotics and Fourier optics. The development of lightcontrollable microrobots capable of performing specific tasks at the microscale requires the ability to sculpt the two protagonists of the story: the light and the microrobots. Complex light sculpting for optical trapping has been in focus for over three decades, and its importance for controlling microscopic objects is well understood. Designing intricate microrobots for the task is a more recent development facilitated by state-of-the-art microfabrication techniques, and particularly by two-photon polymerization. The full 3D design freedom offered by two-photon polymerization opens the door for imagination, while at the same time bringing the responsibility of rationally designing microrobots tailored to specific tasks. In addition to shape and topology features, the surface chemistry of the microrobots can also help steer them towards specific applications. This paper will discuss strategies for the design and fabrication of light-controllable microrobots as a toolbox for biomedical applications.