Liquid Marble Photosensor.

A liquid marble is a liquid droplet coated by a hydrophobic powder. The liquid marble does not wet adjacent surfaces and therefore can be manipulated as a dry soft body. A Belousov-Zhabotinsky (BZ) reaction is an oscillatory chemical reaction exhibiting waves of oxidation. We demonstrate how to make a photo-sensor from BZ medium liquid marbles. We insert electrodes into a liquid marble, prepared from BZ solution and coated with polyethylene powder. The electrodes record a potential difference which oscillates due to oxidation wave-fronts crossing the electrodes. When the BZ marble is illuminated by a light source, the oxidation wave-fronts are hindered and, thus, the electrical potential recorded ceases to oscillate. We characterise several types of responses of BZ marble photosensors to various stimuli, and provide explanations of the recorded activity. BZ liquid marble photosensors may find applications in the fields of liquid electronics, soft robotics and unconventional computing.

Neuromorphic Liquid Marbles with Aqueous Carbon Nanotube Cores.

Neuromorphic computing devices attempt to emulate features of biological nervous systems through mimicking the properties of synapses toward implementing the emergent properties of their counterparts, such as learning. Inspired by recent advances in the utilization of liquid marbles (LMs, microliter quantities of fluid coated in hydrophobic powder) for the creation of unconventional computing devices, we describe the development of LMs with neuromorphic properties through the use of copper coatings and 1.0 mg mL-1 carbon nanotube (CNT)-containing fluid cores. Experimentation was performed through sandwiching the LMs between two cup-style electrodes and stimulating them with repeated dc pulses at 3.0 V. Our results demonstrate that "entrainment" of CNT-filled copper LMs via periodic pulses can cause their electrical resistance to rapidly switch between high to low resistance profiles upon inverting the polarity of stimulation: the reduction in resistance between high and low profiles was approximately 88% after two rounds of entrainment. This effect was found to be reversible through reversion to the original stimulus polarity and was strengthened by repeated experimentation, as evidenced by a mean reduction in time to switching onset of 43%. These effects were not replicated in nanotube solutions not bound inside LMs. Our electrical characterization also reveals that nanotube-filled LMs exhibit pinched loop hysteresis IV profiles consistent with the description of memristors. We conclude by discussing the applications of this technology to the development of unconventional computing devices and the study of emergent characteristics in biological neural tissue.

Mapping outcomes of liquid marble collisions.

Liquid marbles (LMs) have many promising roles in the ongoing development of microfluidics, microreactors, bioreactors, and unconventional computing. In many of these applications, the coalescence of two LMs is either required or actively discouraged, therefore it is important to study liquid marble collisions and establish parameters which enable the desired collision outcome. Recent reports on LM coalescence have focused on either two mobile LMs colliding, or an accelerating LM hitting a sessile LM with a backstop. A further possible scenario is the impact of a mobile LM against a non-supported static LM. This paper investigates such a collision, using high-speed videography for single-frame analysis. Multiple collisions were undertaken whilst varying the modified Weber number (We*) and offset ratios (X*). Parameter ranges of 1.0 < We* < 1.4 and 0.0 < X* < 0.1, resulted in a coalescence rate of approximately 50%. Whereas, parameter ranges X* > 0.25, and We* < 0.95 or We* > 1.55 resulted in 100% non-coalescence. Additionally, observations of LMs moving above a threshold velocity of 0.6 m s-1 have revealed a new and unusual deformation. Comparisons of the outcome of collisions whilst varying both the LM volume and the powder grain size have also been made, revealing a strong link. The results of this work provide a deeper understanding of LM coalescence, allowing improved control when designing future collision experiments.

Evaporation, Lifetime, and Robustness Studies of Liquid Marbles for Collision-Based Computing.

Liquid marbles (LMs) have recently attracted interest for use as cargo carriers in digital microfluidics and have successfully been implemented as signal carriers in collision-based unconventional computing circuits. Both application domains require LMs to roll over substantial distances and to survive a certain number of collisions without degrading. To evaluate the lifetime of LMs being subjected to movement and impact stresses, we have selected four types of coating to investigate: polytetrafluoroethylene (PTFE), ultrahigh density polyethylene (PE), Ni, and a mixture of Ni with PE (Ni-PE). Hierarchies of robustness have been constructed which showed that pure PE LMs survived the longest when stationary and in motion. Pure PTFE LMs were shown to be the least resilient to multiple impacts. The PTFE coating provided minimal protection against evaporative losses for small LM volumes (2 and 5 µL) however, larger LMs (10 µL) were shown to have good evaporative stabilities when stationary. Conversely, PE LMs showed a remarkable ability to withstand multiple impacts and were also stable when considering just passive evaporation. Hybrid Ni-PE LMs exhibited more resilience to multiple impacts compared to Ni LMs. Thus, when designing LM devices, it is paramount to determine impact pathways and select appropriate coating materials.

pH Oscillating System for Molecular Computation as a Chemical Turing Machine.

It has previously been demonstrated that native chemical Turing machines can be constructed by exploiting the nonlinear dynamics of the homogeneous oscillating Belousov-Zhabotinsky reaction. These Turing machines can perform word recognition of a Chomsky type 1 context sensitive language (CSL), demonstrating their high computing power. Here, we report on a chemical Turing machine that has been developed using the H2O2-H2SO4-SO3 2--CO3 2- pH oscillating system. pH oscillators are different to bromate oscillators in two key ways: the proton is the autocatalytic agent, and at least one of the reductants is always fully consumed in each turnover-meaning the system has to be operated as a flow reactor. Through careful design, we establish a system that can also perform Chomsky type 1 CSL word recognition and demonstrate its power through the testing of a series of in-language and out-of-language words.

Marimo actuated rover systems.

BACKGROUND: The potential to directly harness photosynthesis to make actuators, biosensors and bioprocessors has been previously demonstrated in the literature. Herein, this capability has been expanded to more advanced systems - Marimo Actuated Rover Systems (MARS) - which are capable of autonomous, solar powered, movement. RESULTS: We demonstrate this ability is both a practical and viable alternative to conventional mobile platforms for exploration and dynamic environmental monitoring. Prototypes have been successfully tested to measure their speed of travel and ability to automatically bypass obstacles. Further, MARS is electromagnetically silent, thus avoiding the background noise generated by conventional electro/mechanical platforms which reduces instrument sensitivity. The cost of MARS is significantly lower than platforms based on conventional technology. CONCLUSIONS: An autonomous, low-cost, lightweight, compact size, photosynthetically powered rover is reported. The potential for further system enhancements are identified and under development.

Exploring the symbol processing 'time interval' parametric constraint in a Belousov-Zhabotinsky operated chemical Turing machine.

Chemical reactions are powerful molecular recognition machines. This power has been recently harnessed to build actual instances of each class of experimentally realizable computing automata, using exclusively small-molecule chemistry (i.e. without requiring biomolecules). The most powerful of them, a programmable Turing machine, uses the Belousov-Zhabotinsky oscillatory chemistry, and accepts/rejects input sequences through a dual oscillatory and thermodynamic output signature. The time interval between the aliquots representing each letter of the input is the parameter that determines the time it takes to run the computation. Here, we investigate this critical performance parameter, and its effect not only on the computation speed, but also on the robustness of the accept/reject oscillatory and thermodynamic criteria. Our work demonstrates that the time interval is a non-trivial design parameter, whose choice should be made with great care. The guidelines we provide can be used in the optimization of the speed, robustness, and energy efficiency of chemical automata computations.

On resistance switching and oscillations in tubulin microtubule droplets.

HYPOTHESIS: Tubulin is a key protein of the cytoskeleton, forming networks of microtubules (MTs). These networks are vital for many aspects of a cell, including intra-cellular transport. It has been suggested by others that this network could be responsible for sub-cellular information processing, which naturally raises the question of whether such a system could be exploited for more artificial constructs. In this endeavour, this paper studies the electrical properties of Taxol-stabilised MT ensembles. EXPERIMENTS: Electrical experiments were conducted on samples containing MTs. Measurements were made using iridium-coated needle electrodes on a droplet. Cyclic voltammetry was performed, by sweeping through a DC voltage range of [-1.2,+1.2] V. AC measurements were also taken, between 1 kHZ and 10 MHz, and with a DC bias. Separately, pulse train stimulation were conducted, with an amplitude of 0.5 V and duration of 1 ms. FINDINGS: Cyclic voltammetry experiments reveal that the MT droplets act as electrical switches, under the experimental conditions. This is partly revealed in a substantial hysteresis. The stimulation of a MT droplet with a positive fast-impulse resulted in oscillation of the droplet's resistance, not observed in control experiments. Taxol-stabilised MT samples proved to be mem-resistive/mem-inductive, therefore the history of their electrical characterisation is able to change their response and behaviour. If the history of electrical stimuli is the same, so is the response. These findings pave a way towards future designs of MT-based sensing and computing devices, including data storage featuring liquid states.

Contactless sensing of liquid marbles for detection, characterisation & computing.

Liquid marbles (LMs) are of growing interest in many fields, including microfluidics, microreactors, sensors, and signal carriers. The generation of LMs is generally performed manually, although there has recently been a burst of publications involving 'automatic marble makers'. The characteristics of a LM is dependent on many things, including how it is generated, it is therefore important to be able to characterise LMs once made. Here is presented a novel contactless LM sensor, constructed on a PCB board with a comb-like structure of 36 interlacing electrical traces, 100 µm wide and 100 µm apart. This cheap, scalable, and easy to use sensor exploits the inherent impedance (comprised of the electrical resistance, capacitive reactance and inductive reactance) of different LMs. With it, parameters of a LM can be easily determined, without interfering with the LM. These parameters are (1) particle size of the LM coating, (2) the concentration of a NaCl solution used as the LM core, and (3) the volume of the LM. Additionally, due to the comb-like nature of the sensor, the accurate positioning (down to the inter-trace spacing) of the LM can be ascertained. The new sensor has been shown to work under both static and dynamic (mobile) conditions. The capacitance of a LM was recorded to be 0.10 pF, which compares well with the calculated value of 0.12 pF.

Marimo machines: oscillators, biosensors and actuators.

BACKGROUND: The green algae balls (Aegagropila linnaei), known as Marimo, are large spherical colonies of live photosynthetic filaments, formed by rolling water currents in freshwater lakes. Photosynthesis therein produces gas bubbles that can attach to the Marimo, consequently changing its buoyancy. This property allows them to float in the presence of light and sink in its absence. RESULTS: We demonstrate that this ability can be harnessed to make actuators, biosensors and bioprocessors (oscillator, logic gates). Factors affecting Marimo movement have been studied to enable the design, construction and testing of working prototypes. CONCLUSIONS: A novel actuator design is reported, incorporating an enhanced bubble retention system and the design and optimisation of a bio-oscillator is demonstrated. A range of logic gates (or, and, nor, nand, xor) implementable with Marimo have been proposed.

Thermal switch of oscillation frequency in Belousov-Zhabotinsky liquid marbles.

External control of oscillation dynamics in the Belousov-Zhabotinsky (BZ) reaction is important for many applications including encoding computing schemes. When considering the BZ reaction, there are limited studies dealing with thermal cycling, particularly cooling, for external control. Recently, liquid marbles (LMs) have been demonstrated as a means of confining the BZ reaction in a system containing a solid-liquid interface. BZ LMs were prepared by rolling 50 µl droplets in polyethylene (PE) powder. Oscillations of electrical potential differences within the marble were recorded by inserting a pair of electrodes through the LM powder coating into the BZ solution core. Electrical potential differences of up to 100 mV were observed with an average period of oscillation ca 44 s. BZ LMs were subsequently frozen to -1°C to observe changes in the frequency of electrical potential oscillations. The frequency of oscillations reduced upon freezing to 11 mHz cf. 23 mHz at ambient temperature. The oscillation frequency of the frozen BZ LM returned to 23 mHz upon warming to ambient temperature. Several cycles of frequency fluctuations were able to be achieved.

Liquid Marble Actuator for Microfluidic Logic Systems.

A mechanical flip-flop actuator has been developed that allows for the facile re-routing and distribution of liquid marbles (LMs) in digital microfluidic devices. Shaped loosely like a triangle, the actuating switch pivots from one bistable position to another, being actuated by the very low mass and momentum of a LM rolling under gravity (~4 × 10-6 kg ms-1). The actuator was laser-cut from cast acrylic, held on a PTFE coated pivot, and used a PTFE washer. Due to the rocking motion of the switch, sequential LMs are distributed along different channels, allowing for sequential LMs to traverse parallel paths. This distributing effect can be easily cascaded, for example to evenly divide sequential LMs down four different paths. This lightweight, cheap and versatile actuator has been demonstrated in the design and construction of a LM-operated mechanical multiplication device - establishing its effectiveness. The actuator can be operated solely by gravity, giving it potential use in point-of-care devices in low resource areas.