Active Sensing in Bees Through Antennal Movements Is Independent of Odor Molecule.

When sampling odors, many insects are moving their antennae in a complex but repeatable fashion. Previous studies with bees have tracked antennal movements in only two dimensions, with a low sampling rate and with relatively few odorants. A detailed characterization of the multimodal antennal movement patterns as function of olfactory stimuli is thus wanted. The aim of this study is to test for a relationship between the scanning movements and the properties of the odor molecule. We tracked several key locations on the antennae of bumblebees at high frequency and in three dimensions while stimulating the insect with puffs of 11 common odorants released in a low-speed continuous flow. Water and paraffin were used as negative controls. Movement analysis was done with the neural network Deeplabcut. Bees use a stereotypical oscillating motion of their antennae when smelling odors, similar across all bees, independently of the identity of the odors and hence their diffusivity and vapor pressure. The variability in the movement amplitude among odors is as large as between individuals. The main type of oscillation at low frequencies and large amplitude is triggered by the presence of an odor and is in line with previous work, as is the speed of movement. The second oscillation mode at higher frequencies and smaller amplitudes is constantly present. Antennae are quickly deployed when a stimulus is perceived, decorrelate their movement trajectories rapidly, and oscillate vertically with a large amplitude and laterally with a smaller one. The cone of airspace thus sampled was identified through the 3D understanding of the motion patterns. The amplitude and speed of antennal scanning movements seem to be function of the internal state of the animal, rather than determined by the odorant. Still, bees display an active olfactory sampling strategy. First, they deploy their antennae when perceiving an odor. Second, fast vertical scanning movements further increase the odorant capture rate. Finally, lateral movements might enhance the likelihood to locate the source of odor, similarly to the lateral scanning movement of insects at odor plume boundaries.

Oscillations for active sensing in olfaction: bioinspiration from insect antennal movements.

Crustacean and insect antennal scanning movements have been postulated to increase odorant capture but the exact mechanisms as well as measures of efficiency are wanting. The aim of this work is to test the hypothesis that an increase in oscillation frequency of a simplified insect antenna model translates to an increase of odorant capture, and to quantify by how much and through which mechanism. We approximate the antennal movements of bumblebees, quantified in a previous study, by a vertical oscillatory movement of a cylinder in a homogeneous horizontal flow with odorants. We test our multiphysics flow and mass transfer numerical model with dedicated experiments using particle image velocimetry. A new entire translating experimental measurement setup containing an oil tank enables us to work at appropriate Strouhal and Reynolds numbers. Increasing antennal oscillating frequency does increase the odorant capture rate, up to 200%, proving this behavior being active sensing. This result holds however only up to a critical frequency. A decrease of efficiency characterizes higher frequencies, due to molecules depletion within oversampled regions, themselves defined by overlaying boundary layers. Despite decades of work on thermal and mass transfer studies on oscillating cylinders, no analogy with published cases was found. This is due to the unique flow regimes studied here, resulting from the combination of organ small size and low frequencies of oscillations. A theory for such flow regimes is thus to be developed, with applications to fundamental research on animal perception up to bioinspired olfaction.

Pt particles functionalized on the molecular level as new nanocomposite materials for electrocatalysis.

A nanocomposite material consisting of platinum nanoparticles surrounded by an ionic conducting polymer dispersed on carbon Vulcan XC72 was synthesized. The aim of this nanocomposite material is to translate the triple-phase boundary to a molecular level in electrochemical systems involving a polymer electrolyte. The ionic conducting polymer is a poly(styrenesulfonic acid) (PSSA, or PSSNa in its sodium form) synthesized by atom-transfer radical polymerization. The polymer has a terminal thiol group to ensure bonding with platinum nanoparticles. The nanocomposite material (Pt-PSSA/C) exhibited thermal stability up to 160 °C and electrochemical stability up to 1 V versus RHE. Compared to a Pt/C catalyst, the nanocomposite catalyst has a lower active surface area but comparable catalytic activity for the oxygen reduction reaction. Furthermore, this nanocomposite material exhibits similar behavior in a fuel cell active layer without Nafion as a classical Pt/C catalyst with Nafion included in the active layer.

Solid-state dye-sensitized TiO(2) solar cells based on a sensitizer covalently wired to a hole conducting polymer.

We report on the molecular wiring efficiency of a ruthenium polypyridine complex acting as a sensitizer connected to a poly(3-hexyl)thiophene chain acting as hole transporting material. We have developed an efficient synthetic strategy to covalently connect via an ethanyl spacer a regioregular poly(3-hexyl)thiophene chain to a ruthenium complex. Solid-state dye-sensitized solar cells were prepared either with the latter system or with a similar ruthenium sensitizer but lacking the polymer chain (reference system). The comparison of the photocurrent-photovoltage characteristics of the cells recorded under AM1.5 indicates a two fold improvement of the overall photoconversion efficiencies when the sensitizer is grafted to the hole transporting material (eta = 0.27%) relative to the reference system (eta = 0.13%). The higher photovoltaic performance can be attributed to the better diffusion-like propagation of the holes from the sensitizer to the counter electrode through the covalently linked polythiophene chain.

Detection of degradation products of chemical warfare agents by highly porous molecularly imprinted microspheres.

The multiplication of terrorist actions in the recent events is alarming and the detection of chemical warfare agents (CWAs) has become one of the highest research priorities in the fields of security and public health. The biomimetic properties of molecularly imprinted polymers (MIPs) render them attractive for molecular recognition as well as sensing purposes. The degradation products of easily hydrolysable organophosphorus nerve agents such as pinacolyl methylphosphonate (PMP), a hydrolysis by-product of soman, are often used as templates in MIP synthesis. In this study, we describe the first example of PMP-imprinted polymer microspheres synthesized by precipitation polymerization. This one-step process involves methacrylic acid (MAA) as the monomer and divinylbenzene (DVB) as the cross-linker, in a toluene/acetonitrile mixture. Subsequent morphological characterizations of the PMP-imprinted particles show that they have diameters between 1 and 10 mum (as opposed to 4-5 mum for the non-imprinted microspheres), surface areas of up to 680 m(2) g(-1) and high porosities with pore sizes smaller than 2 nm. The present investigation also evidences the imprinting effect via batch binding experiments and reports on the use of a novel fluorescence-based methodology, where 4-methylumbelliferone (4MU) is utilised as a sensing agent to determine the PMP concentration in solution.

Ruthenium bis-terpyridine complexes connected to an oligothiophene unit for dry dye-sensitised solar cells.

The preparation of a series of new heteroleptic ruthenium complexes containing a 4'-phosphonic acid terpyridine and a terpyridine substituted in 4' position by a bithiophene or tert-thiophene are described. The UV-Vis absorption and emission spectra along the redox potentials of these complexes are reported. These new complexes were also tested as sensitizers in dry dye-sensitised solar cell using regioregular polyoctylthiophene as a solid hole conductor. It has been shown that the complexes substituted with thiophene chain exhibit poor photovoltaic efficiency most probably due to low electron injection efficiency. This latter property can be rationalised by the fact that the LUMO orbitals in these complexes are localised in the terpyridine substituted by the thiophene chain and not in the terpyridine phosphonic which is bonded to the TiO2 photoanode.