Towards slime mould chemical sensor: Mapping chemical inputs onto electrical potential dynamics of Physarum Polycephalum

Plasmodium of slime mould Physarum polycephalum is a large single celled organism visible unaided by the eye. This slime mould is capable of optimising the shape of its protoplasmic networks in spatial configurations of attractants and repellents. Such adaptive behaviour can interpreted as computation. When exposed to attractants and repellents, Physarum changes patterns of its electrical activity. We experimentally derived a unique one-to-one mapping between a range of selected bioactive chemicals and patterns of oscillations of the slime mould's extracellular electrical potential. This direct and rapid change demonstrates detection of these chemicals in a similar manner to a biological contactless chemical sensor. We believe results could be used in future designs of slime mould based chemical sensors and computers. © 2013 Elsevier B.V

Sensory fusion in Physarum polycephalum and implementing multi-sensory functional computation

Surface electrical potential and observational growth recordings were made of a protoplasmic tube of the slime mould Physarum polycephalum in response to a multitude of stimuli with regards to sensory fusion or multisensory integration. Each stimulus was tested alone and in combination in order to evaluate for the first time the effect that multiple stimuli have on the frequency of streaming oscillation. White light caused a decrease in frequency whilst increasing the temperature and applying a food source in the form of oat flakes both increased the frequency. Simultaneously stimulating P. polycephalum with light and oat flake produced no net change in frequency, while combined light and heat stimuli showed an increase in frequency smaller than that observed for heat alone. When the two positive stimuli, oat flakes and heat, were combined, there was a net increase in frequency similar to the cumulative increases caused by the individual stimuli. Boolean logic gates were derived from the measured frequency change. © 2014

Liquid marble interaction gate for collision-based computing

© 2017 Elsevier Ltd Liquid marbles are microliter droplets of liquid, encapsulated by self-organized hydrophobic particles at the liquid/air interface. They offer an efficient approach for manipulating liquid droplets and compartmentalizing reactions in droplets. Digital fluidic devices employing liquid marbles might benefit from having embedded computing circuits without electronics and moving mechanical parts (apart from the marbles). We present an experimental implementation of a collision gate with liquid marbles. Mechanics of the gate follows principles of Margolus’ soft-sphere collision gate. Boolean values of the inputs are given by the absence (FALSE) or presence (TRUE) of a liquid marble. There are three outputs: two outputs are trajectories of undisturbed marbles (they only report TRUE when just one marble is present at one of the inputs), one output is represented by trajectories of colliding marbles (when two marbles collide they lose their horizontal momentum and fall), this output reports TRUE only when two marbles are present at inputs. Thus the gate implements AND and AND-NOT logical functions. We speculate that by merging trajectories representing AND-NOT output into a single channel one can produce a one-bit half-adder. Potential design of a one-bit full-adder is discussed, and the synthesis of both a pure nickel metal and a hybrid nickel/polymer liquid marble is reported

Transfer function of protoplasmic tubes of Physarum polycephalum

The slime mould Physarum polycephalum is a large single celledmyxomycete; its plasmodium consists of tubes which extend to find sources of food. It has been previously shown that the tubes are conductive with a resistance of approximately 3MV, and have been used in basic DC circuits. Hybrid slime mould-electronic circuits have been proposed, using the protoplasmic tubes, grown between agar, as Physarum wires. This paper aims to evaluate the electrical properties of the protoplasmic tubes with respect to analogue and digital waveforms. The Physarum wires act as low pass filters with a mean cut off frequency of 19 kHz (SD 9 KHz); they have a 12.1 dB/decade roll-off (SD 1.9 dB/decade). Mean attenuation across the band-pass range is �6 dB (S.D. 4.5 dB). The mechanism for the frequency dependant attenuation is unknown however a combination of protoplasmic electrolyte and the cytoskeletal structure is the most likely cause. The tubes last approximately 2 weeks before forming adry sclerotia, when they cease being conductive and is the prevalent limiting factor of their practical use; this is caused by dehydration and lack of nutrition, a limitation which may be overcome. The potential for Physarum wires in hybrid circuits is strengthened; while previous circuits were simple DC circuits, this work demonstrates that they may be used as electronic components or wires in both digital and analogue circuits or even as a computing component in analogue computers

The importance of methane breath testing: A review

Sugar malabsorption in the bowel can lead to bloating, cramps, diarrhea and other symptoms of irritable bowel syndrome as well as affecting absorption of other nutrients. The hydrogen breath test is now a well established noninvasive test for assessing malabsorption of sugars in the small intestine. However, there are patients who can suffer from the same spectrum of malabsorption issues but who produce little or no hydrogen, instead producing relatively large amounts of methane. These patients will avoid detection with the traditional breath test for malabsorption based on hydrogen detection. Likewise the hydrogen breath test is an established method for small intestinal bacterial overgrowth (SIBO) diagnoses. Therefore, a number of false negatives would be expected for patients who solely produce methane. Usually patients produce either hydrogen or methane, and only rarely there are significant co-producers, as typically the methane is produced at the expense of hydrogen by microbial conversion of carbon dioxide. Various studies show that methanogens occur in about a third of all adult humans; therefore, there is significant potential for malabsorbers to remain undiagnosed if a simple hydrogen breath test is used. As an example, the hydrogen-based lactose malabsorption test is considered to result in about 5-15% false negatives mainly due to methane production. Until recently methane measurements were more in the domain of research laboratories, unlike hydrogen analyses which can now be undertaken at a relatively low cost mainly due to the invention of reliable electrochemical hydrogen sensors. More recently, simpler lower cost instrumentation has become commercially available which can directly measure both hydrogen and methane simultaneously on human breath. This makes more widespread clinical testing a realistic possibility. The production of small amounts of hydrogen and/or methane does not normally produce symptoms, whereas the production of higher levels can lead to a wide range of symptoms ranging from functional disorders of the bowel to low level depression. It is possible that excess methane levels may have more health consequences than excess hydrogen levels. This review describes the health consequences of methane production in humans and animals including a summary of the state of the art in detection methods. In conclusion, the combined measurement of hydrogen and methane should offer considerable improvement in the diagnosis of malabsorption syndromes and SIBO when compared with a single hydrogen breath test. © 2013 IOP Publishing Ltd

Development of a sensor system for the early detection of soft rot in stored potato tubers

A number of sensor types were fabricated and tested for their electrical resistance changes to compounds known to be evolved by potato tubers with soft rot caused by the bacterium Erwinia carotovora. On the basis of these tests, three sensors were selected for incorporation into a prototype device. The device was portable and could be used without computer control after threshold values and sensor settling criteria had been downloaded. The prototype was assessed for its discriminating power under simulated storage conditions. The device was capable of detecting one tuber with soft rot in 100 kg of sound tubers in a simulated storage crate. The device was also able to detect a tuber inoculated with E. carotovora, but without visible signs of soft rot, within 10 kg of sound tubers. The same system was able to follow the progression of the disease in a tuber stored amongst 10 kg of sound tubers when operated at 4 °C and 85% relative humidity (conditions typical of a refrigerated storage facility)

Gas chromatography-mass spectrometry analyses of volatile organic compounds from potato tubers inoculated with Phytophthora infestans or Fusarium coeruleum

Volatile organic compounds (VOCs) collected from potato tubers inoculated with Phytophthora infestans (late blight), Fusarium coeruleum (dry rot) or sterilized distilled water (as a control) were analysed using gas chromatography-mass spectrometry (GC-MS) and gas chromatography-flame ionization detection (GC-FID). A total of 52 volatiles were identified by GC-MS in the headspaces above P. infestans- and F. coeruleum-inoculated tubers after incubation for 42 days in the dark at 10°C. Of these VOCs, the six most abundant were common to both pathogens. These were benzothiazole (highest abundance), 2-ethyl-1-hexanol (second highest abundance), and at approximately equal third abundance, hexanal, 2-methylpropanoic acid-2,2-dimethyl-1-(2-hydroxy-1-methylethyl)-propyl ester, 2-methylpropanoic acid-3-hydroxy-2,4,4-trimethyl-pentyl ester and phenol. In addition, styrene also occurred at approximately equal third abundance in the headspace of F. coeruleum-inoculated tubers, but at lower abundance in the headspace of P. infestans-inoculated tubers. Some VOCs were specific to each pathogen. Butanal, 3-methylbutanal, undecane and verbenone were found at low levels only in the headspace of tubers inoculated with P. infestans, while 2-pentylfuran and copaene were found only in the headspace of tubers inoculated with F. coeruleum. Additionally GC-FID analysis identified ethanol and 2-propanol in the liquid exudate from both P. infestans- and F. coeruleum-inoculated tubers after incubation for 35 days, and in the headspace after incubation for 42 days. These data provide key information for developing a sensor-based early warning system for the detection of postharvest diseases in stored potato tubers