A new fluorescence-based methodology for studying bioaerosol scavenging processes using a hyperspectral LIF-LIDAR remote sensing system.

This paper presents a novel experimental approach to in-situ study of atmospheric phenomena such as nucleation scavenging by biological seeds, bio-droplet dehydration, and bioaerosol's particle scavenging by raindrops. Our methodology is based on the analysis of the dynamical changes of fluorescence signal. We use a remote sensing system based on a homebuilt hyperspectral laser induced fluorescence (LIF) Lidar to measure the transient back-fluorescence and backscattering signals. The spectral line shape of the transient fluorescence associated with an aerosolized tryptophan solution was first analyzed in the laboratory. It then used to study bioaerosol phase transitions between wet and dry conditions. The experiments were first conducted in a dynamic aerosol cell where we repetitively create and monitor the droplets containing bioaerosol cloud starting from its early formation till its total evaporation. The LIF-Lidar was used to simultaneously measure back-fluorescence, scattering and transmission. These measurements were synchronized with the generation of droplets containing bioaerosol and with the monitoring of aerosol's size distribution and ambient conditions. A novel optical receiver design was used to simultaneously detect both back-fluorescence polarization components. Results showed that along with droplet's evaporation process, bioaerosol's fluorescence spectrum exhibit a blue shift, known as the dynamic Stokes-shifts, of ∼2000 cm-1 and an increase in its fluorescence anisotropy. To the best of our knowledge, this is the first report of fluorescence Stokes-shifts and anisotropy within microdroplets containing a biological solution due to wet-dry phase transitions. This method was also used to quantify scavenging of biological particle by raindrops from 100 m. It shows that valuable information can be derived from analyzing the fluorescence spectrum of bioaerosol within a cloud and demonstrate the potential of a LIF-LIDAR remote system to perform in-situ studies of scavenging processes.

A multiple-method comparative study using GC-MS, AMDIS and in-house-built software for the detection and identification of "unknown" volatile organic compounds in breath.

The human respiratory system is a highly complex matrix that exhales many volatile organic compounds (VOCs). Breath-exhaled VOCs are often "unknowns" and possess low concentrations, which make their analysis, peak digging and data processing challenging. We report a new methodology, applied in a proof-of-concept experiment, for the detection of VOCs in breath. For this purpose, we developed and compared four complementary analysis methods based on solid-phase microextraction and thermal desorption (TD) tubes with two GC-mass spectrometer (MS) methods. Using eight model compounds, we obtained an LOD range of 0.02-20 ng/ml. We found that in breath analysis, sampling the exhausted air from Tedlar bags is better when TD tubes are used, not only because of the preconcentration but also due to the stability of analytes in the TD tubes. Data processing (peak picking) was based on two data retrieval approaches with an in-house script written for comparison and differentiation between two populations: sick and healthy. We found it best to use "raw" AMDIS deconvolution data (.ELU) rather than its NIST (.FIN) identification data for comparison between samples. A successful demonstration of this method was conducted in a pilot study (n = 21) that took place in a closed hospital ward (Covid-19 ward) with the discovery of four potential markers. These preliminary findings, at the molecular level, demonstrate the capabilities of our method and can be applied in larger and more comprehensive experiments in the omics world.

Structural elucidation of phenidate analogues via the ESI-MS/MS spectra of their sodium adduct ions.

The identification of phenidate new psychoactive substances (NPS) by implementing MS (Mass spectrometry) techniques is a challenging task. Phenidate analogues present information-poor mass spectra, both in GC-EI-MS and LC-ESI-MS/MS of the protonated molecules [M+H]+, with a high abundance fragment/product ion representing the secondary amine-containing residue. This lack of EI-MS and ESI-MS/MS information is attributed to the strong tendency of the amine residue to stabilize the positive charge and leads to unavoidable ambiguity in the identification process. Moreover, thermal decomposition of these compounds occurs in the injection port and/or on the column under standard GC conditions. Herein, we demonstrate how structural information can be attained instantaneously through the LC-ESI-MS/MS fragmentation of the accompanied sodium adducts [M+Na]+. The sodium cation alters the charge distribution during ESI-MS/MS fragmentation, generating a major product ion corresponding to the Na+ adduction of the carbonyl group, providing new structural information of the main core of phenidate derivatives (alkylaryl acetate/acetic acid), enabling their reliable structural elucidation. This quick, simple and easy technique can be implemented to confirm the identity or identify various structurally related phenidate analogues in forensic toxicology and doping analysis without the need for sample handling.

Nonmechanical Conductance Switching in a Molecular Tunnel Junction.

We present a molecular junction composed of a donor (polyacetylene strands) and an acceptor (malononitrile) connected together via a benzene ring and coupled weakly to source and drain electrodes on each side, for which a gate electrode induces intramolecular charge transfer, switching reversibly the character of conductance. Using a new brand of density functional theory, for which orbital energies are similar to the quasiparticle energies, we show that the junction displays a single, gate-tunable differential conductance channel in a wide energy range. The gate field must align parallel to the displacement vector between donors and acceptor to affect their potential difference; for strong enough fields, spontaneous intramolecular electron transfer occurs. This event radically affects conductance, reversing the charge of carriers, enabling a spin-polarized current channel. We discuss the physical principles controlling the operation of the junction and find interplay of quantum interference, charging, Coulomb blockade, and electron-hole binding energy effects. We expect that this switching behavior is a generic property for similar donor-acceptor systems of sufficient stability.