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3 pages, 188 KiB

Open AccessEditorial

Special Issue “Applications of Photoacoustic Spectroscopy”

by Cristina Popa, Ana Maria Bratu and Mioara Petrus

Molecules 2020, 25(21), 5116; https://doi.org/10.3390/molecules25215116 - 04 Nov 2020

Cited by 1 | Viewed by 2065

Abstract

Photoacoustic spectroscopy is one of the most exciting areas of research in physics and chemistry, covering a broad range of applications from agricultural to biological, including atmospheric monitoring, space science, and air-quality measurements to security and workplace surveillance, in addition to its great [...] Read more.

Photoacoustic spectroscopy is one of the most exciting areas of research in physics and chemistry, covering a broad range of applications from agricultural to biological, including atmospheric monitoring, space science, and air-quality measurements to security and workplace surveillance, in addition to its great potential in preclinical and clinical biomedical applications [...] Full article

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

Research

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19 pages, 6442 KiB

Open AccessArticle

Nanostructured Thin Coatings Containing Anthriscus sylvestris Extract with Dual Bioactivity

by Irina Negut, Valentina Grumezescu, Alexandru Mihai Grumezescu, Alexandra Cătălina Bîrcă, Alina Maria Holban, Iuliana Urzica, Sorin Marius Avramescu, Bianca Gălățeanu and Ariana Hudiță

Molecules 2020, 25(17), 3866; https://doi.org/10.3390/molecules25173866 - 25 Aug 2020

Cited by 6 | Viewed by 2492

Abstract

Plant extracts are highly valuable pharmaceutical complexes recognized for their biological properties, including antibacterial, antifungal, antiviral, antioxidant, anticancer, and anti-inflammatory properties. However, their use is limited by their low water solubility and physicochemical stability. In order to overcome these limitations, we aimed to [...] Read more.

Plant extracts are highly valuable pharmaceutical complexes recognized for their biological properties, including antibacterial, antifungal, antiviral, antioxidant, anticancer, and anti-inflammatory properties. However, their use is limited by their low water solubility and physicochemical stability. In order to overcome these limitations, we aimed to develop nanostructured carriers as delivery systems for plant extracts; in particular, we selected the extract of Anthriscus sylvestris (AN) on the basis of its antimicrobial effect and antitumor activity. In this study, AN-extract-functionalized magnetite (Fe₃O₄@AN) nanoparticles (NPs) were prepared by the co-precipitation method. The purpose of this study was to synthesize and investigate the physicochemical and biological features of composite coatings based on Fe₃O₄@AN NPs obtained by matrix-assisted pulsed laser evaporation technique. In this respect, laser fluence and drop-casting studies on coatings were performed. The physical and chemical properties of laser-synthesized coatings were investigated by scanning electron microscopy, while Fourier transform infrared spectroscopy comparative analysis was used for determining the chemical structure and functional integrity. Relevant data regarding the presence of magnetic nanoparticles as the only crystalline phase and the size of nanoparticles were obtained by transmission electron microscopy. The in vitro toxicity assessment of the Fe₃O₄@AN showed significant cytotoxic activity against human adenocarcinoma HT-29 cells after prolonged exposure. Antimicrobial results demonstrated that Fe₃O₄@AN coatings inhibit microbial colonization and biofilm formation in clinically relevant bacteria species and yeasts. Such coatings are useful, natural, and multifunctional solutions for the development of tailored medical devices and surfaces. Full article

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

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18 pages, 3118 KiB

Open AccessArticle

Multivariate Analysis of Photoacoustic Spectra for the Detection of Short-Chained Hydrocarbon Isotopologues

by Alain Loh and Marcus Wolff

Molecules 2020, 25(9), 2266; https://doi.org/10.3390/molecules25092266 - 11 May 2020

Cited by 9 | Viewed by 2603

Abstract

We report, to our knowledge, the first optical detection scheme for short-chained hydrocarbon isotopologues. The sensor system is based on photoacoustic spectroscopy (PAS). Two continuous wave, thermoelectrically cooled, distributed feedback interband cascade lasers (DFB-ICLs) with emission wavelengths around 3.33 and 3.38 μm, respectively, [...] Read more.

We report, to our knowledge, the first optical detection scheme for short-chained hydrocarbon isotopologues. The sensor system is based on photoacoustic spectroscopy (PAS). Two continuous wave, thermoelectrically cooled, distributed feedback interband cascade lasers (DFB-ICLs) with emission wavelengths around 3.33 and 3.38 μm, respectively, served as light sources. The investigations comprised the main stable carbon isotopologues of methane (¹²CH₄, ¹³CH₄), ethane (¹²CH₃-¹²CH₃, ¹³CH₃-¹²CH₃, ¹³CH₃-¹³CH₃), and propane (¹²CH₃-¹²CH₂-¹²CH₃, ¹³CH₃-¹²CH₂-¹²CH₃). They were selected because of their importance for numerous applications from climate and planetary research to natural gas exploration. Multiple measurements of single components in nitrogen and synthetic mixtures were conducted at room temperature and atmospheric pressure. Depending on the investigated hydrocarbon isotopologue, detection limits ranging from 0.043 ppmv to 3.4 ppmv were achieved. For a selective concentration determination, multivariate analysis (MVA) was applied. Partial least-squares regression (PLSR) was used to calculate concentrations from the PA spectra. The implementation of MVA has shown that the PA setup in principle works reliably and that the selective concentration determination of short-chained hydrocarbon isotopologues is possible. Full article

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

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14 pages, 3131 KiB

Open AccessArticle

Spectroscopic Characterization of Emulsions Generated with a New Laser-Assisted Device

by Andra Dinache, Tatiana Tozar, Adriana Smarandache, Ionut Relu Andrei, Simona Nistorescu, Viorel Nastasa, Angela Staicu, Mihail-Lucian Pascu and Mihaela Oana Romanitan

Molecules 2020, 25(7), 1729; https://doi.org/10.3390/molecules25071729 - 09 Apr 2020

Cited by 22 | Viewed by 3112

Abstract

This paper presents a spectroscopic study of emulsions generated with a laser-assisted device. Fourier transform infrared (FTIR), Raman and UV–Vis–NIR reflectance spectra of emulsions, recorded before and after exposure to laser radiation were used to characterize the effect of laser irradiation. The paper [...] Read more.

This paper presents a spectroscopic study of emulsions generated with a laser-assisted device. Fourier transform infrared (FTIR), Raman and UV–Vis–NIR reflectance spectra of emulsions, recorded before and after exposure to laser radiation were used to characterize the effect of laser irradiation. The paper also presents a comparison between the calculated IR spectra and the experimental FTIR spectra of an emulsion’s components. FTIR measurements allowed the identification of absorption bands specific to each of the emulsions’ components. Moreover, it enabled the observation of destabilization of the emulsion in real-time. Raman spectroscopy allowed the observation of the modifications at a molecular level, by identifying the vibrations of the representative functional groups and the polymerization of sodium tetradecyl sulfate (STS) molecules by analyzing the evolution of the carbonyl band. UV–Vis–NIR reflectance spectra of emulsions before and after exposure to laser radiation showed that the physical characteristics of the emulsions changed during irradiation—the dimensions of the droplets decreased, leading to an emulsion with a better time stability. These results proved that the employed spectroscopy techniques were powerful tools in emulsion analysis. Full article

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

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10 pages, 1915 KiB

Open AccessArticle

The Analysis of Lead Phytotoxicity in Seeds Using CO₂ Laser Photoacoustic Spectroscopy

by Cristina Popa, Ana Maria Bratu, Mioara Petrus and Mihaela Bacalum

Molecules 2020, 25(7), 1637; https://doi.org/10.3390/molecules25071637 - 02 Apr 2020

Cited by 6 | Viewed by 2026

Abstract

Lead (Pb) is the most prevalent heavy metal pollutant in the natural environment. Pb is not a fundamental element for plants, but they absorb it when it is present in their environment, having no known physiological activity. The aim of our research was [...] Read more.

Lead (Pb) is the most prevalent heavy metal pollutant in the natural environment. Pb is not a fundamental element for plants, but they absorb it when it is present in their environment, having no known physiological activity. The aim of our research was to evaluate the efficacy of laser photoacoustic spectroscopy as a tool to monitor changes induced by Pb in plant respiration by highlighting two molecular markers (C₂H₄ and CO₂). To better understand Pb phytotoxicity, we monitored the plantlets evolution as well as the morphology of the root cells. Firstly, we showed that the treatment hinders the plantlet’s development. Furthermore, using laser photoacoustic spectroscopy, we found a decrease in the concentration of C₂H₄ and CO₂ vapors measured in the respiration of treated plants. Finally, fluorescence microscopy results showed that in Pb treated plantlets, the cell roots morphology is clearly altered as compared with the untreated ones. All the results are well correlated and can help further in understanding Pb phytotoxicity. Full article

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

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10 pages, 2256 KiB

Open AccessArticle

The Assessment of Carbon Dioxide Dissociation Using a Single-Mode Microwave Plasma Generator

by George Mogildea, Marian Mogildea, Cristina Popa and Gabriel Chiritoi

Molecules 2020, 25(7), 1558; https://doi.org/10.3390/molecules25071558 - 28 Mar 2020

Cited by 9 | Viewed by 3572

Abstract

This paper focuses on the dissociation of carbon dioxide (CO₂) following the absorption processes of microwave radiation by noncontact metal wire (tungsten). Using a microwave plasma generator (MPG) with a single-mode cavity, we conducted an interaction of microwaves with a noncontact [...] Read more.

This paper focuses on the dissociation of carbon dioxide (CO₂) following the absorption processes of microwave radiation by noncontact metal wire (tungsten). Using a microwave plasma generator (MPG) with a single-mode cavity, we conducted an interaction of microwaves with a noncontact electrode in a CO₂ atmosphere. High energy levels of electromagnetic radiation are generated in the focal point of the MPG’s cylindrical cavity. The metal wires are vaporized and ionized from this area, subsequently affecting the dissociation of CO_2. The CO₂ dissociation is highlighted through plasma characterization and carbon monoxide (CO) quantity determination. For plasma characterization, we used an optical emission spectroscopy method (OES), and for CO quantity determination, we used a gas analyzer instrument. Using an MPG in the CO₂ atmosphere, we obtained a high electron temperature of the plasma and a strong dissociation of CO₂. After 20 s of the interaction between microwaves and noncontact electrodes, the quantity of CO increased from 3 ppm to 1377 ppm (0.13% CO). This method can be used in space applications to dissociate CO₂ and refresh the atmosphere of closed spaces. Full article

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

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10 pages, 2977 KiB

Open AccessArticle

Compact and Highly Sensitive NO₂ Photoacoustic Sensor for Environmental Monitoring

by Yufeng Pan, Lei Dong, Xukun Yin and Hongpeng Wu

Molecules 2020, 25(5), 1201; https://doi.org/10.3390/molecules25051201 - 07 Mar 2020

Cited by 37 | Viewed by 3627

Abstract

A nitrogen dioxide (NO₂) photoacoustic sensor for environmental monitoring was developed using a low-cost high-power laser diode emitting at 450 nm. A compact low-noise photoacoustic detection module was designed to reduce the sensor size and to suppress noise. A LabVIEW-based control [...] Read more.

A nitrogen dioxide (NO₂) photoacoustic sensor for environmental monitoring was developed using a low-cost high-power laser diode emitting at 450 nm. A compact low-noise photoacoustic detection module was designed to reduce the sensor size and to suppress noise. A LabVIEW-based control system was employed for the sensor. The parameters of the sensor were studied in detail in terms of laser power and operating pressure. The linearity of the sensor response with laser power and NO₂ concentration confirms that saturation does not occur. At atmospheric pressure, a 3σ detection limit of 250 ppt (part per trillion by volume) was achieved with a 1-s averaging time, which corresponds to the specific detectivity of 3.173 × 10⁻⁹ W cm⁻¹ Hz^−1/2. A 72 h outdoor continuous on-line monitoring of environmental NO₂ was implemented to demonstrate the reliability and validity of the developed NO₂ sensor. Full article

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

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9 pages, 1400 KiB

Open AccessFeature PaperArticle

Fluorescence and Time-Delayed Lasing during Single Laser Pulse Excitation of a Pendant mm-Sized Dye Droplet

by Mihai Boni, Ionut Relu Andrei, Mihail Lucian Pascu and Angela Staicu

Molecules 2019, 24(24), 4464; https://doi.org/10.3390/molecules24244464 - 05 Dec 2019

Cited by 7 | Viewed by 2970

Abstract

Fluorescence and lasing emission that are produced separately in time during excitation laser pulse for an mm-sized Rhodamine 6G dye-water droplet are reported. The droplet acts as a quasi-spherical closed optical resonator and due to multiple internal reflections, the resonant amplified emission is [...] Read more.

Fluorescence and lasing emission that are produced separately in time during excitation laser pulse for an mm-sized Rhodamine 6G dye-water droplet are reported. The droplet acts as a quasi-spherical closed optical resonator and due to multiple internal reflections, the resonant amplified emission is delayed with respect to fluorescence emission. Measurements of the temporal evolution of the droplet’s emission were performed by varying the signal acquisition gate width and gate delay with respect to the pumping pulse. The droplet emission spectra are structured in two bands which appear one after the other in time: first, the fluorescence emission band which follows pumping laser pulse time shape and then a second band, the lasing band, placed at shorter wavelengths and formed in time after the peak of the pumping laser pulse intensity, on the pulse tail. The lasing threshold pumping intensity is much lower than those for typical dye lasers. Full article

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

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Review

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17 pages, 2077 KiB

Open AccessReview

Advances in Mid-Infrared Spectroscopy-Based Sensing Techniques for Exhaled Breath Diagnostics

by Ramya Selvaraj, Nilesh J. Vasa, S. M. Shiva Nagendra and Boris Mizaikoff

Molecules 2020, 25(9), 2227; https://doi.org/10.3390/molecules25092227 - 09 May 2020

Cited by 58 | Viewed by 5860

Abstract

Human exhaled breath consists of more than 3000 volatile organic compounds, many of which are relevant biomarkers for various diseases. Although gas chromatography has been the gold standard for volatile organic compound (VOC) detection in exhaled breath, recent developments in mid-infrared (MIR) laser [...] Read more.

Human exhaled breath consists of more than 3000 volatile organic compounds, many of which are relevant biomarkers for various diseases. Although gas chromatography has been the gold standard for volatile organic compound (VOC) detection in exhaled breath, recent developments in mid-infrared (MIR) laser spectroscopy have led to the promise of compact point-of-care (POC) optical instruments enabling even single breath diagnostics. In this review, we discuss the evolution of MIR sensing technologies with a special focus on photoacoustic spectroscopy, and its application in exhaled breath biomarker detection. While mid-infrared point-of-care instrumentation promises high sensitivity and inherent molecular selectivity, the lack of standardization of the various techniques has to be overcome for translating these techniques into more widespread real-time clinical use. Full article

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

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25 pages, 721 KiB

Open AccessFeature PaperReview

Applications of Near Infrared Photoacoustic Spectroscopy for Analysis of Human Respiration: A Review

by Dan C. Dumitras, Mioara Petrus, Ana-Maria Bratu and Cristina Popa

Molecules 2020, 25(7), 1728; https://doi.org/10.3390/molecules25071728 - 09 Apr 2020

Cited by 45 | Viewed by 4735

Abstract

In this review, applications of near-infrared photoacoustic spectroscopy are presented as an opportunity to evaluate human respiration because the measurement of breath is fast, intact and simple to implement. Recently, analytical methods for measuring biomarkers in exhaled air have been extensively developed. With [...] Read more.

In this review, applications of near-infrared photoacoustic spectroscopy are presented as an opportunity to evaluate human respiration because the measurement of breath is fast, intact and simple to implement. Recently, analytical methods for measuring biomarkers in exhaled air have been extensively developed. With laser-based photoacoustic spectroscopy, volatile organic compounds can be identified with high sensitivity, at a high rate, and with very good selectivity. The literature review has shown the applicability of near-infrared photoacoustic spectroscopy to one of the problems of the real world, i.e., human health. In addition, the review will consider and explore different breath sampling methods for human respiration analysis. Full article

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

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