Fluorescence spectroscopy and signalling from optically-tweezed aerosol droplets

Knox, Kerry J.; Symes, Rachel; Reid, Jonathan P.

doi:10.1016/j.cplett.2010.01.046

Cited by 9 publications

(5 citation statements)

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“…The laser powers at the droplet trapping position were estimated assuming a 35 AE 2% transmission efficiency of the microscope objective, measured from a dual-objective approach. 59 For the model calculations, the beam waist was taken as 4 mm, consistent with the results of Fig. 6(b) for a droplet radius of B 3850 nm and a trapping laser power of 30 mW.…”

Section: Retrieval Of the Imaginary Part Of The Refractive Indexmentioning

confidence: 96%

Retrieval of the complex refractive index of aerosol droplets from optical tweezers measurements

Miles

Walker

Burnham

et al. 2012

Phys. Chem. Chem. Phys.

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The cavity enhanced Raman scattering spectrum recorded from an aerosol droplet provides a unique fingerprint of droplet radius and refractive index, assuming that the droplet is homogeneous in composition. Aerosol optical tweezers are used in this study to capture a single droplet and a Raman fingerprint is recorded using the trapping laser as the source for the Raman excitation. We report here the retrieval of the real part of the refractive index with an uncertainty of ± 0.0012 (better than ± 0.11%), simultaneously measuring the size of the micrometre sized liquid droplet with a precision of better than 1 nm (< ± 0.05% error). In addition, the equilibrium size of the droplet is shown to depend on the laser irradiance due to optical absorption, which elevates the droplet temperature above that of the ambient gas phase. Modulation of the illuminating laser power leads to a modulation in droplet size as the temperature elevation is altered. By measuring induced size changes of <1 nm, we show that the imaginary part of the refractive index can be retrieved even when less than 10 × 10(-9) with an accuracy of better than ± 0.5 × 10(-9). The combination of these measurements allows the complex refractive index of a droplet to be retrieved with high accuracy, with the possibility of making extremely sensitive optical absorption measurements on aerosol samples and the testing of frequently used mixing rules for treating aerosol optical properties. More generally, this method provides an extremely sensitive approach for measuring refractive indices, particularly under solute supersaturation conditions that cannot be accessed by simple bulk-phase measurements.

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Section: Retrieval Of the Imaginary Part Of The Refractive Indexmentioning

confidence: 96%

Retrieval of the complex refractive index of aerosol droplets from optical tweezers measurements

Miles

Walker

Burnham

et al. 2012

Phys. Chem. Chem. Phys.

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“…According to such a hypothesis, any aerosol liquid droplet levitated in air would produce a supercooled liquid even below the relevant f p value irrespective of the nature of the liquid. Optical trapping chemistry of microdroplets levitated in air has been hitherto reported for water, ,− water/glycerol, − diethyl phthalate/glycerol, − and so forth; , however, most of the work has been conducted at ambient temperature and temperature ( T )-controlled experiments on an aerosol droplet are very limited, ,− , in particular, those below f p of a liquid. Therefore, a systematic study on T -controlled optical trapping of aerosol droplets in air is worth conducting to reveal supercooling behavior and the f p values of droplets levitated in air.…”

Section: Introductionmentioning

confidence: 99%

Optical Trapping–Microspectroscopy of Single Aerosol Microdroplets in Air: Supercooling of Dimethylsulfoxide Microdroplets

et al. 2020

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We report temperature (T = +22.5 ∼ −57.0 °C)-controlled optical trapping of single dimethylsulfoxide (DMSO) droplets with the diameter (d) of 7−15 μm in air. Optically levitated DMSO microdroplets containing 0.1 mol/dm 3 (=M) potassium iodide (KI) as an additive for reducing the vapor pressure of DMSO in air have been suggested to take supercooled liquid states even below the freezing temperature (f p ) of the bulk DMSO liquid (f p = +18.4 °C in the presence of 0.1 M KI) as seen in bright-field microscopic observations of the droplet. Clear evidence for supercooling of an aerosol DMSO microdroplet below f p has been obtained by in situ optical trapping−polarized Raman microspectroscopy of the droplet down to −14.9 °C. Analysis of the polarized Raman spectral data of an aerosol DMSO droplet (d = ∼10 μm) has demonstrated that the droplet at +22.5, +0.2, or −14.9 °C is characterized by the rotational relaxation time (τ rot ) of a DMSO molecule in the droplet being 1.95, 2.58, or 3.90 ps, respectively. On the basis of the τ rot values and the Stokes−Einstein equation (τ rot = 8πa 3 η/k B T where a, η, k B are the radius (1.883 Å) of a DMSO molecule, the viscosity in DMSO, and the Boltzmann constant, respectively), the η values in the DMSO microdroplet in air at +22.5, +0.2, or −14.9 °C have been estimated to be 2.39, 2.94, or 4.20 cP, respectively, while that of bulk DMSO liquid at +20.5 °C is 1.98 cP. We also report the T-dependence (+22.5 > T > −14.9 °C) of the viscosity in a single aerosol DMSO microdroplet (d = ∼10 μm) and the effects of aerosolization in air on the viscosity in DMSO.

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“…28 This was also followed by the first demonstration that fluorescence spectroscopy can be used to characterize optically trapped aerosol droplets. 29 • A demonstration that aerosol optical tweezers can be used in any one of three configurations: in the conventional inverted microscope configurations, in the non-inverted sense and in a horizontally propagating form. 23 • The extension of aerosol optical tweezers to low pressures and low temperatures.…”

Section: The Aerosol Optical Tweezers Toolboxmentioning

confidence: 99%

Optical manipulation of aerosol particle arrays

et al. 2011

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Aerosols play a crucial role in many areas of science, ranging from atmospheric chemistry and physics, to drug delivery to the lungs, combustion science and spray drying. The development of new methods to characterise the properties and dynamics of aerosol particles is of crucial importance if the complex role that particles play is to be more fully understood. Optical tweezers provide a valuable new tool to address fundamental questions in aerosol science. Single or multiple particles 1-15 μm in diameter can be manipulated over indefinite timescales using optical tweezing. Linear and non-linear Raman and fluorescence spectroscopies can be used to probe a particle's composition and size. In this paper we will report on the latest developments in the use of holographic optical trapping (HOT) to study aerosols. Although widely used to trap and manipulate arrays of particles in the condensed phase, the application of HOT to aerosols is still in its infancy. We will explore the opportunities provided by the formation of complex optical landscapes for controlling aerosol flow, for comparing the properties of multiple particles, for performing the first ever digital microfluidic operations in the aerosol phase and for examining interparticle interactions that can lead to coalescence/coagulation. Although aerosol coagulation is the primary process driving the evolution of particle size distributions, it remains very poorly understood. Using HOT, we can resolve the time-dependent motion of trapped particles and the light scattering from particles during the coalescence process.

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Fluorescence spectroscopy and signalling from optically-tweezed aerosol droplets

Cited by 9 publications

References 50 publications

Retrieval of the complex refractive index of aerosol droplets from optical tweezers measurements

Retrieval of the complex refractive index of aerosol droplets from optical tweezers measurements

Optical Trapping–Microspectroscopy of Single Aerosol Microdroplets in Air: Supercooling of Dimethylsulfoxide Microdroplets

Optical manipulation of aerosol particle arrays

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