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Keywords = profluorescent nitroxide

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16 pages, 1810 KiB  
Article
Application of a Fluorescent Probe for the Online Measurement of PM-Bound Reactive Oxygen Species in Chamber and Ambient Studies
by Reece Brown, Svetlana Stevanovic, Zachary Brown, Mingfu Cai, Shengzhen Zhou, Wei Song, Xinming Wang, Branka Miljevic, Jun Zhao, Steven Bottle and Zoran Ristovski
Sensors 2019, 19(20), 4564; https://doi.org/10.3390/s19204564 - 21 Oct 2019
Cited by 3 | Viewed by 3197
Abstract
This manuscript details the application of a profluorescent nitroxide (PFN) for the online quantification of radical concentrations on particulate matter (PM) using an improved Particle Into Nitroxide Quencher (PINQ). A miniature flow-through fluorimeter developed specifically for use with the 9,10-bis(phenylethynyl)anthracene-nitroxide (BPEAnit) probe was [...] Read more.
This manuscript details the application of a profluorescent nitroxide (PFN) for the online quantification of radical concentrations on particulate matter (PM) using an improved Particle Into Nitroxide Quencher (PINQ). A miniature flow-through fluorimeter developed specifically for use with the 9,10-bis(phenylethynyl)anthracene-nitroxide (BPEAnit) probe was integrated into the PINQ, along with automated gas phase corrections through periodic high efficiency particle arrestor (HEPA) filtering. The resulting instrument is capable of unattended sampling and was operated with a minimum time resolution of 2.5 min. Details of the fluorimeter design and examples of data processing are provided, and results from a chamber study of side-stream cigarette smoke and ambient monitoring campaign in Guangzhou, China are presented. Primary cigarette smoke was shown to have both short-lived (t1/2 = 27 min) and long-lived (t1/2 = indefinite) PM-bound reactive oxygen species (ROS) components which had previously only been observed in secondary organic aerosol (SOA). Full article
(This article belongs to the Special Issue Fluorescence-Based Sensors)
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Figure 1

Figure 1
<p>(<b>a</b>) Simplified cross-section of the microfluidic cell showing the assembly of key components. The cells outer dimensions are 30 × 30 × 48 mm. Notably, the liquid flow-path is a continuous cylinder throughout the entire illuminated path, significantly reducing the entrapment of bubbles inside the cell. (<b>b</b>) The assembly of the full fluorimeter illustrating the connections between the fluorescence cell, CPS450 laser and USB2000+ spectrometer.</p> Full article ">Figure 2
<p>The typical fluorescence response measured for the 9,10-bis(phenylethynyl)anthracene-nitroxide (BPEAnit) probe with the flow-through fluorimeter for a total phase and gas phase sample. The response wavelengths averaged for the measurement of the primary and secondary peaks are indicated by the blue and red shaded regions, respectively. The large third peak centred on 450 nm is the laser used as the excitation source.</p> Full article ">Figure 3
<p>(<b>a–c</b>) The calibration plots for the three flow-through fluorimeters constructed and tested. (<b>a</b>) and (<b>b</b>) use USB2000+ series spectrometers, whilst (<b>c</b>) uses a newer FLAME spectrometer with temperature stabilization. The flame spectrometer is more adept at measuring very low concentrations, although these are far below those measured when integrated into the Particle Into Nitroxide Quencher (PINQ).</p> Full article ">Figure 4
<p>(<b>a</b>) The raw fluorescence response of the PINQ sample over time for side-stream cigarette smoke in a chamber. The alternating signal is caused by switching between filtered and unfiltered air. Sharp spikes in the signal are caused by bubbles in the sample line. The total and gas phase data points coloured indicate the data points averaged to generate the next plot in the figure. (<b>b</b>) The de-bubbled, trimmed and averaged plateaus and corresponding standard error of the alternating signal which correspond to the total and gas phase. (<b>c</b>) The final particle phase reactive oxygen species (ROS) concentration with standard error calculated by subtracting the interpolated gas phase from the total phase after correcting for background fluorescence and converting the signal to equivalent concentrations of BPEAnit-Me per cubic meter of air.</p> Full article ">Figure 5
<p>The ROS data, normalized by its initial value and corrected for mass losses, along with two different fitted curves to the ROS data using different assumptions of ROS decay. (<b>a</b>) shows a fit which assumes that all ROS present have a single half-life, with a value calculated from the fit of 120 min with a 95% confidence interval (CI)(110,140). This model does not fit well at low or high elapsed times. (<b>b</b>) shows a fit which assumes there are two subsets of ROS, in which the second set has a lifetime which is effectively infinite over the measurement period. The half-life of the short-lived ROS using this model is 27 min with a 95% CI(23,31).</p> Full article ">Figure 6
<p>(<b>a</b>) shows a day period of analysed PINQ data collected at a rooftop site measuring ambient background aerosol in Guangzhou, China. (<b>b</b>) shows the hourly average organic mass concentration measured by the time-of-flight Aerosol Chemical Speciation Monitor (TOF-ACSM). (<b>c</b>) gives the NO<sub>3</sub> mass measured by the TOF-ACSM. (<b>d</b>) shows the hourly total particulate matter (PM)<sub>2.5</sub> mass concentration measured by the BAM-1020.</p> Full article ">
18 pages, 1834 KiB  
Article
Profluorescent Fluoroquinolone-Nitroxides for Investigating Antibiotic–Bacterial Interactions
by Anthony D. Verderosa, Rabeb Dhouib, Kathryn E. Fairfull-Smith and Makrina Totsika
Antibiotics 2019, 8(1), 19; https://doi.org/10.3390/antibiotics8010019 - 4 Mar 2019
Cited by 10 | Viewed by 5639
Abstract
Fluorescent probes are widely used for imaging and measuring dynamic processes in living cells. Fluorescent antibiotics are valuable tools for examining antibiotic–bacterial interactions, antimicrobial resistance and elucidating antibiotic modes of action. Profluorescent nitroxides are ‘switch on’ fluorescent probes used to visualize and monitor [...] Read more.
Fluorescent probes are widely used for imaging and measuring dynamic processes in living cells. Fluorescent antibiotics are valuable tools for examining antibiotic–bacterial interactions, antimicrobial resistance and elucidating antibiotic modes of action. Profluorescent nitroxides are ‘switch on’ fluorescent probes used to visualize and monitor intracellular free radical and redox processes in biological systems. Here, we have combined the inherent fluorescent and antimicrobial properties of the fluoroquinolone core structure with the fluorescence suppression capabilities of a nitroxide to produce the first example of a profluorescent fluoroquinolone-nitroxide probe. Fluoroquinolone-nitroxide (FN) 14 exhibited significant suppression of fluorescence (>36-fold), which could be restored via radical trapping (fluoroquinolone-methoxyamine 17) or reduction to the corresponding hydroxylamine 20. Importantly, FN 14 was able to enter both Gram-positive and Gram-negative bacterial cells, emitted a measurable fluorescence signal upon cell entry (switch on), and retained antibacterial activity. In conclusion, profluorescent nitroxide antibiotics offer a new powerful tool for visualizing antibiotic–bacterial interactions and researching intracellular chemical processes. Full article
(This article belongs to the Special Issue From the Southern Hemisphere: Research on Resistance, Antibiotics and Treatments)
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Figure 1

Figure 1
<p>(<b>A</b>) The fluorescent antibiotic BOCILLIN <sup>TM</sup> FL penicillin (BOCILLIN-FL), an example of a fluorophore covalently linked to an antibiotic; (<b>B</b>) an example of a profluorescent nitroxide, based on the boron-dipyrromethene (BODIPY) fluorophore [<a href="#B17-antibiotics-08-00019" class="html-bibr">17</a>].</p> Full article ">Figure 2
<p>Absorption and fluorescence emission spectra of FN <b>14</b> (absorbance (<b><span style="color:red">—</span></b>), fluorescence (<b><span style="color:red">- -</span></b>)); FM <b>17</b> (absorbance (<b><span style="color:#4472C4">—</span></b>), fluorescence (<b><span style="color:#4472C4">- -</span></b>)). Measured in H<sub>2</sub>O, λ<sub>ex</sub> = 340 nm and 9 µM for both FN <b>14</b> and FM <b>17</b>.</p> Full article ">Figure 3
<p>Integrated fluorescence as a function of time for the reduction of FN <b>14</b> to its corresponding hydroxylamine derivative <b>20</b> with 1000 equivalents of sodium ascorbate. Hydroxylamine <b>20</b> (<span style="color:#4472C4">•</span>); FM <b>17</b> (<span style="color:red">•</span>). Measured in H<sub>2</sub>O with λ<sub>ex</sub> = 340 nm.</p> Full article ">Figure 4
<p>Graph of the relationship between fluorescence intensity of FM <b>17</b> and solution pH. Measured in H<sub>2</sub>O and excited at λ<sub>ex</sub> = 340 nm.</p> Full article ">Figure 5
<p>Fluorescence and brightfield overlay micrographs of bacterial cells treated with FN <b>14</b> or FM <b>17</b>. (<b>A</b>) Medium (0.9% NaCl) containing FN <b>14</b> (600 µM); (<b>B</b>) FN <b>14</b> (600 µM) and <span class="html-italic">P. aeruginosa</span>; (<b>C</b>) FN <b>14</b> (600 µM) and <span class="html-italic">E. coli</span>; (<b>D</b>) FN <b>14</b> (150 µM) and <span class="html-italic">S. aureus</span>; (<b>E</b>) FN <b>14</b> (150 µM) and <span class="html-italic">E. faecalis</span> cells; (<b>F</b>) Medium (0.9% NaCl) containing FM <b>17</b> (600 µM); (<b>G</b>) FM <b>17</b> (600 µM) and <span class="html-italic">P. aeruginosa</span>; (<b>H</b>) FM <b>17</b> (600 µM) and <span class="html-italic">E. coli</span>; (<b>I</b>) FM <b>17</b> (600 µM) and <span class="html-italic">S. aureus</span>; (<b>J</b>) FM <b>17</b> (600 µM) and <span class="html-italic">E. faecalis</span>. Scale bars are 5 µM in length.</p> Full article ">Scheme 1
<p>Synthetic route to fluoroquinolone-nitroxide (FN) compounds <b>14</b>–<b>16</b> and their corresponding methoxyamines <b>17</b>–<b>19</b>. Reagents and conditions: (<b>a</b>) cat. Pd(OAc)<sub>2</sub>, BINAP, Cs<sub>2</sub>CO<sub>3</sub>, THF, 65 °C, 72 h; (<b>b</b>) 2 M NaOH, MeOH, 50 °C, overnight.</p> Full article ">Scheme 2
<p>Reduction of FN <b>14</b> to its corresponding hydroxylamine derivative <b>20</b> with 1000 equivalents sodium ascorbate. Reagents and conditions: (<b>a</b>) Sodium ascorbate, H<sub>2</sub>O, 30 min., Room Temperature (RT).</p> Full article ">
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