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12 pages, 2762 KB

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Enhancing Double-Beam Laser Tweezers Raman Spectroscopy (LTRS) for the Photochemical Study of Individual Airborne Microdroplets

by Jovanny A. Gómez Castaño, Luc Boussekey, Jean P. Verwaerde, Myriam Moreau and Yeny A. Tobón

Molecules 2019, 24(18), 3325; https://doi.org/10.3390/molecules24183325 - 12 Sep 2019

Cited by 10 | Viewed by 4447

Abstract

A new device and methodology for vertically coupling confocal Raman microscopy with optical tweezers for the in situ physico- and photochemical studies of individual microdroplets (Ø ≤ 10 µm) levitated in air is presented. The coupling expands the spectrum of studies performed with individual particles using laser tweezers Raman spectroscopy (LTRS) to photochemical processes and spatially resolved Raman microspectroscopy on airborne aerosols. This is the first study to demonstrate photochemical studies and Raman mapping on optically levitated droplets. By using this configuration, photochemical reactions in aerosols of atmospheric interest can be studied on a laboratory scale under realistic conditions of gas-phase composition and relative humidity. Likewise, the distribution of photoproducts within the drop can also be observed with this setup. The applicability of the coupling system was tested by studying the photochemical behavior of microdroplets (5 µm < Ø < 8 µm) containing an aqueous solution of sodium nitrate levitated in air and exposed to narrowed UV radiation (254 ± 25 nm). Photolysis of the levitated NaNO₃ microdroplets presented photochemical kinetic differences in comparison with larger NaNO₃ droplets (40 µm < Ø < 80 µm), previously photolyzed using acoustic traps, and heterogeneity in the distribution of the photoproducts within the drop. Full article

(This article belongs to the Special Issue Practical Applications of Molecular Spectroscopy)

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14 pages, 4026 KB

Open AccessArticle

Microfluidic Cultivation and Laser Tweezers Raman Spectroscopy of E. coli under Antibiotic Stress

by Zdeněk Pilát, Silvie Bernatová, Jan Ježek, Johanna Kirchhoff, Astrid Tannert, Ute Neugebauer, Ota Samek and Pavel Zemánek

Sensors 2018, 18(5), 1623; https://doi.org/10.3390/s18051623 - 18 May 2018

Cited by 43 | Viewed by 9690

Abstract

Analyzing the cells in various body fluids can greatly deepen the understanding of the mechanisms governing the cellular physiology. Due to the variability of physiological and metabolic states, it is important to be able to perform such studies on individual cells. Therefore, we developed an optofluidic system in which we precisely manipulated and monitored individual cells of Escherichia coli. We tested optical micromanipulation in a microfluidic chamber chip by transferring individual bacteria into the chambers. We then subjected the cells in the chambers to antibiotic cefotaxime and we observed the changes by using time-lapse microscopy. Separately, we used laser tweezers Raman spectroscopy (LTRS) in a different micro-chamber chip to manipulate and analyze individual cefotaxime-treated E. coli cells. Additionally, we performed conventional Raman micro-spectroscopic measurements of E. coli cells in a micro-chamber. We found observable changes in the cellular morphology (cell elongation) and in Raman spectra, which were consistent with other recently published observations. The principal component analysis (PCA) of Raman data distinguished between the cefotaxime treated cells and control. We tested the capabilities of the optofluidic system and found it to be a reliable and versatile solution for this class of microbiological experiments. Full article

(This article belongs to the Special Issue Applications of Raman Spectroscopy in Sensors)

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11 pages, 6110 KB

Open AccessArticle

Probing the Kinetic Anabolism of Poly-Beta-Hydroxybutyrate in Cupriavidus necator H16 Using Single-Cell Raman Spectroscopy

by Zhanhua Tao, Lixin Peng, Pengfei Zhang, Yong-Qing Li and Guiwen Wang

Sensors 2016, 16(8), 1257; https://doi.org/10.3390/s16081257 - 8 Aug 2016

Cited by 14 | Viewed by 8033

Abstract

Poly-beta-hydroxybutyrate (PHB) can be formed in large amounts in Cupriavidus necator and is important for the industrial production of biodegradable plastics. In this investigation, laser tweezers Raman spectroscopy (LTRS) was used to characterize dynamic changes in PHB content—as well as in the contents of other common biomolecule—in C. necator during batch growth at both the population and single-cell levels. PHB accumulation began in the early stages of bacterial growth, and the maximum PHB production rate occurred in the early and middle exponential phases. The active biosynthesis of DNA, RNA, and proteins occurred in the lag and early exponential phases, whereas the levels of these molecules decreased continuously during the remaining fermentation process until the minimum values were reached. The PHB content inside single cells was relatively homogenous in the middle stage of fermentation; during the late growth stage, the variation in PHB levels between cells increased. In addition, bacterial cells in various growth phases could be clearly discriminated when principle component analysis was performed on the spectral data. These results suggest that LTRS is a valuable single-cell analysis tool that can provide more comprehensive information about the physiological state of a growing microbial population. Full article

(This article belongs to the Special Issue Applications of Raman Spectroscopy in Biosensors)

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