Enzymatic Nanocomposites with Radio Frequency Field-Modulated Activity.

The control over enzymatic activity by physical stimuli is of interest to many applications in medicine, biotechnology, synthetic biology, and nanobionics. Although the main focus has been on optically responsive systems, alternative strategies to modulate the enzymatic activity of hybrid systems are needed. Here we describe a radiofrequency (RF) field controlled catalytic activity of an enzymatic sol-gel composite. Specifically, the activity of bovine carbonic anhydrase entrapped in sol-gel-derived magnetite (enzyme@ferria) composite was accelerated by a factor of 460% compared to its initial value, by applying the RF field of 937 A/m, with fast response time. This acceleration is reversible and its magnitude controllable. An acceleration mechanism, based on RF-induced heating of the magnetite by the Néel relaxation effect, is proposed and proven. The entrapment within a sol-gel matrix solves the problem of enhancing activity by heating without denaturing the enzyme. RF-controlled enzymatic composites can be potentially applied as biological RF sensors or to control biochemical reactions within living organisms.

The controllable destabilization route for synthesis of low cytotoxic magnetic nanospheres with photonic response.

We present a new approach for obtaining magnetic nanospheres with tunable size and high magnetization. The method is implemented via controllable destabilization of a stable magnetite hydrosol with glycerol, leading to the formation of aggregates followed by their stabilization with the citrate shell. This inexpensive, simple and easily scalable approach required no special equipment. The obtained samples were characterized by high stability and magnetization over 80 emu/g. Effects of synthetic conditions on physicochemical properties of nanospheres were monitored by hydrodynamic size, zeta potential, and polydispersity of magnetite aggregates. The size of the resulting aggregates varied between 650 nm and 40 nm, and the zeta potential from +30 mV to -43 mV by changing the ratio of the reagents. Under optimal conditions the clusters with a diameter of 80 nm were produced with a narrow size distribution ±3 nm. These characteristics allowed for optical response to the external magnetic field, thereby producing a magnetic photon liquid. Due to biocompatibility of the reagents used in the synthesis the nanospheres evoked a negligible cytotoxicity for human non-malignant and tumor cell lines. These results make new materials valuable in photonics and biomedicine.