Photobleaching of Methylene Blue in continuous wave thermal lens spectrometry

Lowe, Roger D.; Snook, Richard D.

doi:10.1039/an9931800613

Cited by 15 publications

(12 citation statements)

References 14 publications

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“…Photobleaching of MB has been studied in some detail, and the role of the triplet excited state has been recognized [ 38 , 39 ]. This dye fades relatively quickly when exposed to light, even in the absence of electron donors, and has been reported to retain a two-step process, involving intermediary formation of singlet oxygen, on exposure to visible light in aqueous solution [ 40 ].…”

Section: Discussionmentioning

confidence: 99%

Biogenic Gold Nanoparticles Decrease Methylene Blue Photobleaching and Enhance Antimicrobial Photodynamic Therapy

et al. 2021

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Antibiotic resistance is a growing concern that is driving the exploration of alternative ways of killing bacteria. Here we show that gold nanoparticles synthesized by the mycelium of Mucor plumbeus are an effective medium for antimicrobial photodynamic therapy (PDT). These particles are spherical in shape, uniformly distributed without any significant agglomeration, and show a single plasmon band at 522–523 nm. The nanoparticle sizes range from 13 to 25 nm, and possess an average size of 17 ± 4 nm. In PDT, light (from a source consisting of nine LEDs with a peak wavelength of 640 nm and FWMH 20 nm arranged in a 3 × 3 array), a photosensitiser (methylene blue), and oxygen are used to kill undesired cells. We show that the biogenic nanoparticles enhance the effectiveness of the photosensitiser, methylene blue, and so can be used to kill both Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria. The enhanced effectiveness means that we could kill these bacteria with a simple, small LED-based light source. We show that the biogenic gold nanoparticles prevent fast photobleaching, thereby enhancing the photoactivity of the methylene blue (MB) molecules and their bactericidal effect.

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Section: Discussionmentioning

confidence: 99%

Biogenic Gold Nanoparticles Decrease Methylene Blue Photobleaching and Enhance Antimicrobial Photodynamic Therapy

et al. 2021

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“…9,14,17 The setup comprises an excitation Ar + laser (Innova 90-6, Coherent, Palo Alto, CA) operated at 488.0 nm (170 mW in the sample, the beam waist 61.3 mm) and a HeNe probe laser (SP 106-1, Spectra-Physics, Eugene, OR; 632.8 nm, 5 mW in the sample; the beam size in the sample, 108.8 mm). The chopping frequency was low (4 Hz) to ensure the complete dissipation of the thermal-lens at the end of each steadystate excitation-cooling cycle.…”

Section: Instrumentalmentioning

confidence: 99%

“…Laser irradiation in thermooptical spectroscopy could not only provide a local increase in the temperature as a result of laser energy conversion into heat, but could also result in additional effects such as an increase in the reaction rate 9,[14][15][16] or a change in the energy balance of the kinetically controlled reactions, 13 emerging of laser-induced reactions, 11,12 photoinduced decomposition or isomerization, 17,18 or coagulation of metal nanoparticles. 19 On the other hand, products of light-induced or light-enhanced reactions affect the formation of thermal-lens element due to scattering or reabsorption of the radiation.…”

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confidence: 99%

Sensitivity Enhancement of Thermal-Lens Spectrometry Using Laser-Induced Precipitation

et al. 2009

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The possibility of thermal lensing of dynamically emerging light-absorbing layers at cell surfaces was investigated. Analyte accumulation at a cell surface determines long-term changes in the thermal-lens signal that was used as a source of analytical information to enhance sensitivity of thermal lensing. Considering the rate of accumulation as an additional analytical signal, we achieved a threefold decrease in the limits of detection for 4-aminoazobenzene to the level of 7 mM in a batch mode with the same level of reproducibility. The details of observed thermal-lens signal behavior in cells are discussed. The possibilities to use thermal-lens detection for 4-aminoazobenzene determination in quartz capillaries in flow mode were discussed and a drastic thermal-lens signal enhancement was discovered. The corresponding limit of detection for 4-aminoazobenzene in a flow mode is further decreased to the level of 3 mM.

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“…The consequent intensity changes in the probe beam are measured by a photodiode and provide the thermal lens signal. Among other applications, TLS has been widely used for sensitive detection of a wide class of species dissolved in dissimilar media [1][2][3][4][5][6][7][8][9] and for the study of different photodegradation processes [4,5]. When the excitation beam is highly focused onto a micrometric region of the sample the technique is called thermal lens microscopy (TLM), with the main advantage that very low amounts of samples can be characterized [6].…”

Section: Introductionmentioning

confidence: 99%

A comparison between thermal lens and conventional optical spectroscopy for monitoring of a photocatalytic process

et al. 2022

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We compare the thermal lens (TLS) and the optical transmission (OT) spectroscopy techniques to monitor the kinetic of a photocatalytic reaction. For this, an OT measurement facility was added to a TLS set-up. The TLS was implemented in a microspatial configuration named thermal lens microscopy (TLM). Methylene blue (MB) in Water solutions were used as test samples within a concentration range in which both techniques show good sensibility. Within this range, the limit of detection obtained by TLM was about one order of magnitude lower than that achieved by OT. The methylene blue concentration evolution with photocatalytic reaction time was measured with both techniques, showing a good agreement between their results. A ZnO thin film deposited on a glass substrate by the spray pyrolysis technique was used as catalyst, and the reaction was induced by UV-violet light.

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Photobleaching of Methylene Blue in continuous wave thermal lens spectrometry

Cited by 15 publications

References 14 publications

Biogenic Gold Nanoparticles Decrease Methylene Blue Photobleaching and Enhance Antimicrobial Photodynamic Therapy

Biogenic Gold Nanoparticles Decrease Methylene Blue Photobleaching and Enhance Antimicrobial Photodynamic Therapy

Sensitivity Enhancement of Thermal-Lens Spectrometry Using Laser-Induced Precipitation

A comparison between thermal lens and conventional optical spectroscopy for monitoring of a photocatalytic process

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