Magnetic alginate hydrogel beads are one of the vastly reported magneto driven miniaturized nanocomposites that are used for multiple applications. In these beads, the magnetic phase is integrated to the polymer matrix by direct blending or in-situ nucleation to obtain magneto driven hydrogel matrix. However, these two types of beads, which were fabricated through two different protocols, show divergent stabilities in non-identical ionic density aqueous mediums. Significantly, the in-situ synthesized beads degrade rapidly showing low stability behaviour in neutral pH/ low ionic dense aqueous medium regardless their fabrication process have advantages compared to ex situ synthesis, like cheapness, one step and expeditious method. Generation of the ionic by-products inside of the bead while mineralizing the magnetic phase inside of the alginate hydrogel affects to increase the ionic density in in situ magnetic bead. Therefore, to stabilize the ionic density of the bead and the storage medium by reducing the ionic density in the bead, the water molecules penetrate inside of the bead through the alginate membrane only in low ionic denser aqueous mediums. Consequently, the bead starts to degrade when the crosslinking bond strength exceeds the maximum bead swelling due to the diffusing water load. On the other hand the in situ synthesised nanoparticles, exhibit a low particles size of ~ 3 nm when compared ex situ synthesised Fe3O4 nanoparticles u (~ 8 nm). This was due to the confinement of Fe3+ /Fe2+ in the alginate hydrogel matrix during the nucleation and growth of the Fe3O4 nanoparticles in the bead. Moreover, these in situ synthesized particles, in bead-b, showed a magnetite crystal phase with a low tendency to oxidise due to the alginate coating. Their magnetisation values, in combination with their low magnetic hysteresis, possibility of using these alginate beads for magneto-driven applications. However, to overcome low stability behaviour, a new protocol was introduced by modifying the in-situ beads by coating an extra alginate layer. This investigation provides with a fundamental framework to understand the properties of blended, ex-situ, and in-situ synthesised magnetic metal-oxide based alginate hydrogels. This study will direct the path to select the magnetic bead mode (ex-situ, in-situ, and modified in-situ) for different kinds of magneto-driven hydrogel applications.

Magneto driven colorimetric sensors provide remotely handling, guiding and manipulating capability when the sensors are integrated into the Lab-On-a Chip microfluidics systems. In this regard, the efficiency and the functionalities of the sensor scaffold are important and directly define the quality and the efficiency of the microfluidics system. Therefore, considering the sensing optical properties we have introduced a novel TiO2 nanotubes alginate scaffold for the detection of the artificial sweat biomarkers of lactate and glucose. The scaffold was fabricated by immobilising enzymatic catalytic assays of LOX/GOX and HRP with TMB chromophore in a TNT/alginate nanocomposite. A rapid colorimetric detection (blue colour optical signal read out) was observed for artificial sweat biomarkers in TNT/alginate hydrogel platform. Concerning the other reported scaffolds, TNT/alginate scaffold shows high loading capacity of the sensor assays and rapid optical readout recording due the contribution of hydrogel property and the superhydrophilicity of the TiO2 nanotubes. Moreover, the TNT/alginate scaffold has ability to integrate into a paper substrate (mostly used simple microfluidics device). High biological assay loadings and quick signal responses of our novel scaffold, opening new avenues to improve microfluidic paper-based analytical devices by the incorporation of alginate-based materials. Therefore, this biocompatible colorimetric biosensor scaffold is a promising platform to implement real time detection of sweat biomarkers in wearable devices.

Integration of magnetic properties to the TNT/alginate scaffold, by introducing magnetic phase (Fe3O4 nanoparticles or Fe particles) into the hydrogel matrix destroys the colorimetric sensing property of the scaffold since the interference of the intrinsic black color of the magnetic particles. However, we fabricated a Fe/ TNT/alginate scaffold containing of both magnetic and sensing properties, called Janus bead. In the novel fabrication process, the applied magnetic field while crosslinking the hydrogel, allowed to confine the superhydrophobic magnetic Fe particles to the depth of the hydrogel bead without interfering to the optical signal read out recording area. As well, the Janus bead exhibits soft magnetic properties while efficient biosensing ability. Further, colorimetric blood sensing is complicated due to the interference of the red color of the red coloration of the blood cells to the sensing scaffold. In our Janus bead, the hydrogel membrane acting as a red blood cells filter membrane and prevent the entrance of the red blood cells due to the smaller (below 1 micron) mesh size of the hydrogel membrane. The scaffold was tested to detect the blood glucose levels, and the expected response blue colour was generated successfully without interfering the red color, by proving the proposed hypothesis. Therefore, our Janus bead shows multiple functionalities of efficient nutrient biosensing, remote handling capability under the magnetic field and red blood cells filtering ability, is proposed as universal hydrogel scaffold for biosensing. As well, this miniaturized scaffold is introduced as a Lab-on-a-bead system to the microfluidics field.

With respect to the remote stimuli, exclusive superhydrophobobic magnetic particles system in microfluidics like magnetic liquid marbles, a new type of system was introduced, called magneto twister. The floating superhydrophobic magnetic particle collide layer water-air interface, incurves downwards with the water-solid/water-air interface under the magnetic field and the observed bending is more pronounced with the increase of the magnetic field value. The solid-water interface touched the depth of the water container with the increment of the magnetic field, making a stable flipped conical structured water interface, with a twister shape providing a stable magneto movable system. This magneto twister was used to manipulate water droplets in a water environment by just placing a water droplet over the twister and transporting the droplet with displacing the applied magnetic field, facilitating water droplet translocation in aqueous media. As well, this system successfully overcomes the instability and unexpected destruction behavior of the conventional magnetic liquid marble by providing a robust system while handling the droplets. Further, the applicability of the magnetic twister, as a magnetic plug to separate liquids inside of an open surface channel was successfully proved. Moreover, magnetic twister was used to collect and remove floating microplastic particles from the surface of the water. The twister, when close to a non-magnetic particle, formed a steep water-air interface slide capable to move the particle towards the twister, enabling the collection of particles. Then the translocating magnetic field induces to the movement of the twister removing the particles away. Therefore, this introduced magnetic twister opens up new pathways of using superhydrophobic magnetic nanoparticles in water-air interface assisted applications.

Superhydrophobic magnetic particles (C8-Fe) were applied to address one of the fundamental problems in microfluidics, the deposition of air bubbles in the surface of the aqueous channels. Low surface energy magnetic particles were used as a smart material to trap, collect and eliminate deposited air bubbles in aqueous systems, surfaces and microfluidic channels. The underwater superaerophilicity and the high magnetisation of the particles led to trap, manipulate and targeted removal of air bubbles without contaminating the aqueous sample, in a simple manner. This novel and versatile protocol secures bubble-free underwater surfaces or microfluidics channels. The air bubbles collection and the transportation capability was demonstrated for both bulk underwater surface system and inside of microfluidic channel by acquiring 98.9% bubble removing efficiency in the channel. This simple underwater air bubble manipulation and evacuation system will open up an easy and cheap way to address the air bubble contaminating issue without integrating any advanced tools and mechanisms.