The limit of detection in transversal photothermal deflection spectroscopy with light scattering samples

The limit of detection for the 4,6 dinitro-orthocresol (DNOC) pesticide, including small latex particles as light scattering samples in water as suspending medium, has been determined for the transversal photothermal deflection technique. The results where compared to conventional spectrophotometry. In the photothermal deflection experiments performed with a continuous Ar⁺-excitation beam (=363.8 nm) a LOD of 0.8 g/l is achieved for the DNOC in water.Awarded poster prize     

"ENERGY"-DEPENDENT QUENCHING OF CHLOROPHYLL FLUORESCENCE and THERMAL ENERGY DISSIPATION IN INTACT LEAVES DURING INDUCTION OF PHOTOSYNTHESIS

Abstract— Intact leaves, previously adapted to darkness for a prolonged period of time, were suddenly illuminated with a strong, photosynthetically saturating, white light (ca 1500 μmol m⁻² s^_1), resulting in the rapid establishment of a large energy-dependent chlorophyll fluorescence quenching (q_E) as shown by in vivo fluorescence measurements with a pulse amplitude modulation technique. Two different photothermal methods, photoacoustic spectroscopy and photothermal deflection spectroscopy, were used to monitor thermal deactivation of excited pigments during the dark-light transitions. The in vivo photothermal signals measured with both techniques were shown to remain constant during induction of photosynthesis under high light conditions, suggesting that, in contrast to current hypotheses, energy-dependent quenching q_E is not associated with significant changes in thermal dissipation of absorbed light energy in the chloroplasts. When photosynthesis was induced with a low-intensity modulated light, a noticeable decrease in the heat emission yield was observed resulting from the progressive activation of the competing photochemical processes.     

Comparison of collinear and transverse photothermal deflection spectroscopy for trace analysis of pesticides in water

Summary A fiber optic modified photothermal deflection spectrometer (PTDS) was developed and tested for trace analysis of pesticides in water. A UV argon laser beam (=363.8 nm) was delivered to a sample cuvette either directly, or through a multimode optical fiber of 400 m core diameter. The HeNe-probe laser beam was guided to the same sample cuvette by a monomode optical fiber of 5 m core diameter and focussed not only transverse within an angle of 90°, but also collinear within an angle of approximately 0° to the Ar⁺-excitation beam. In transverse dual beam experiments a limit of detection (LOD) of 400 ppt for the pesticide DNOC (4,6-dinitroorthocresol) was achieved. The LODs for 2,4-dinitrophenol, dinoseb and dinosebacetate were 2 ppb, 18 pbb and 6 ppb, respectively. These LODs obtained with the transverse PTDS are up to 2 orders of magnitudes lower than the values taken with the Cary 2400 spectrophotometer. In collinear PTDS experiments with the pesticide dinosebacetate the enhancement factor of the LOD is about 4, when compared to the transverse PTDS using 1×1 cm² diameter sample cuvettes.     

Use of photothermal deflection spectrometry (PDS) for studies of analytes in aqueous solutions

Summary A crossed-beam photothermal deflection spectrophotometer (PDS) instrument was built, evaluated and applied to the determination of lanthanide neodymium. A dye laser filled with rhodamine 6 G and pumped by an argon ion laser at 514 nm was operated with outputs between 4 and 500 mW at the cuvette position and chopped at 2 Hz. The deflection of a He-Ne probe laser beam, crossing the exciting dye laser, was measured by a two-dimensional position sensitive device and two lock-in amplifiers. The setup was evaluated with a solid carbon sample and the liquids toluene and Nd³⁺/HClO₄.A calibration curve for Nd³⁺ in HClO₄ was obtained and the limit of detection (LOD) for Nd³⁺ was determined to be 2·10^–6 mol/l. This LOD is, on the one hand, by 2 orders of magnitudes lower than the value obtained with the Cary 2400 spectrophotometer and, on the other hand, this transverse PDS technique is highly competitive to collinear thermal lensing and laser-induced photoacoustic spectroscopy.     

Low-Cost Colorimetric Measurement of Phosphate Trace Levels in Water and in Soil Solutions by the Collinear Photothermal Beam Deflection Method

Abstract

The collinear photothermal beam deflection technique with a c.w. AlGaAs semi-conductor diode laser (790nm) and He-Ne laser (630 nm) used as the pump and probe beam, respectively, has been combined with the molybdenum blue colorimetry to measure the level of orthophosphate in water and in soil solutions. A detection sensitivity of 0.1 mmol/m³ of PO^3- ₄ has been achieved with the present set-up.     

基于共轭聚合物的纳米粒子用于肿瘤的近红外二区荧光成像及光热治疗

为提高生物组织荧光成像质量以及对肿瘤的高效光热治疗,设计合成了一种新型的窄带隙共轭聚合物(BDT-TTQ),并通过纳米沉积的方式将聚合物制备成水溶性纳米粒子(BDT-TTQ NPs).该共轭聚合物纳米粒子在1000~1200 nm近红外二区范围具有较好的吸收,在1064 nm的激发光下能实现1200~1400 nm的近红外二区荧光成像. BDT-TTQ NPs纳米粒子粒径分布较窄,形貌呈规则的球形且分散均匀,具有好的生物相容性.该纳米粒子既可以在体外实现较高的近红外二区荧光成像穿透深度,又可以实现对小鼠活体血管的高清晰度的近红外二区荧光成像.此外,BDT-TTQ NPs纳米粒子在1064 nm激光下展现出优异的光热转换效率,具有较高的光毒性,对体外的肿瘤细胞以及小鼠的异质瘤具有高的光热杀伤能力.     

LyP-1 peptide-functionalized gold nanoprisms for SERRS imaging and tumor growth suppressing by PTT induced-hyperthermia

The gold nanoprisms (GNPs) have exhibited special plasmonic properties for biomedical applications because of their unique shapes and dimensions. Based on their optical performance, the NIR dye IR780 not only enabled the GNPs-based nanosystem as SERRS nanoparticles for Raman-encoded molecular imaging, but also enhanced the plasmonic photothermal property by laser irradiation. Meanwhile, the GNPs/IR780-Lyp-1 by introduction of tumor-homing peptide segment LyP-1, which presents high affinity to p32 protein, demonstrated the increased enrichment in tumor region and enhanced photothermal therapy efficacy.     

Trace analysis of pollutants in water using the photothermal interferometry as HPLC detector

A new procedure including high performance liquid chromatography in combination with photothermal interference spectroscopy as detection device (HPLC/PIS) has been proposed, optimized and its figures of merit for pesticide residue analysis are shown. The flowing sample under study is set in one arm of a Mach-Zehnder interferometer, and its refractive index is modulated by a periodically chopped continuous wave argon ion laser. As chopper, an acousto optical modulator has been introduced to switch the excitation laser beam between different lines (457 nm, 488 nm, 514 nm) simultaneously. Thus a multi component analysis can be realized either by using an HPLC-system in front of the PIS device or by a multi line Ar⁺-laser, directly. The limit of detection of the HPLC/PIS system reached 71 g/l of the pesticide di-nitro-ortho-cresol (DNOC).     

Magnification in excess of 100-times of the microscopic photothermal lensing signal from solute molecules by two-color excitation with continuous-wave lasers.

A microscopic photothermal lensing measurement under two-color continuous-wave laser excitation was performed to investigate a signal enhancement owing to the transient absorption by photoexcited solute molecules in liquid solutions. An intensity-modulated 409 nm laser beam and an un-modulated 532 nm laser beam were used for excitation, and a 670 nm probe beam was used for detecting the modulation amplitude of thermal lensing signals generated with a microscopic objective lens focusing laser beams into a capillary flow cell of 0.1 mm optical path length. The amplitude of the modulated signal increased as the power of the un-modulated laser beam increased, and a 143-times magnification was observed for an iso-propanol solution of naphthacene having 4.6 x 10(-4) absorbance at 409 nm and a negligible absorbance at 532 nm. A four-level model explaining the signal enhancement is proposed, and an important role of the transient absorption by photoexcited molecules is discussed.     

Thermal conductivity analysis of polymeric crystal by mirage effect

Photothermal Techniques are based on the conversion of the modulated light energy into heat within the sample. Using the Photothermal Probe Beam Technique, where the analysis of a laser beam deflected by the mirage effect near the sample leads to the thermal properties of this sample, we have determined the three components of the thermal conductivity tensor of an orthorhombic polydiacetylene single crystal. A numerical simulation of the probe beam deflection is also presented and compared to the experimental data.     

Thermohydrogel Containing Melanin for Photothermal Cancer Therapy

Melanin is an effective absorber of light and can extend to near infrared (NIR) regions. In this study, a natural melanin is presented as a photothermal therapeutic agent (PTA) because it provides a good photothermal conversion efficiency, shows biodegradability, and does not induce long‐term toxicity during retention in vivo. Poloxamer solution containing melanin (Pol–Mel) does not show any precipitation and shows sol–gel transition at body temperature. After irradiation from 808 nm NIR laser at 1.5 W cm⁻² for 3 min, the photothermal conversion efficiency of Pol–Mel is enough to kill cancer cells in vitro and in vivo. The tumor growth of mice bearing CT26 tumors treated with Pol–Mel injection and laser irradiation is suppressed completely without recurrence postirradiation. All these results indicate that Pol–Mel can become an attractive PTA for photothermal cancer therapy.

     

Photothermal microscopy applied to the study of polymer composites

It is proposed to transfer the capabilities of a high sensitivity photothermal technique, developed by the group and widely used in the study of thermal properties of ceramics, metals and glass, to the study of polymer composites. The technique uses a sensing beam for the measurement of the thermal response of the sample due to local effects induced by heating with a modulated pump laser. With a simple spatial sweep of the beams on the sample surface, information on a micrometric scale of the thermal diffusivity of the material, distribution of phases and pores is obtained. Post-process analysis allows calculating average values of relevant properties such as thermal diffusivity, degree of crystallinity and distribution of aggregates. These measurements are performed at low laser powers (of the order of micro watts) avoiding the damage of the studied samples and turning this technique into a powerful tool of non-destructive characterization.     

Small-angle optical deflection from collinear configuration for sensitive detection in microfluidic systems

This paper describes a novel detection system based on small-angle optical deflection from the collinear configuration of a microfluidic chip. In this system, the incident light beam was focused on the microchannel through the edge of a lens, resulting in a small deflection angle that deviated 20° from the collinear configuration. The emitted fluorescence was collected through the center of the same lens and delivered to a photomultiplier tube in the vertical direction; the reflection light of the chip plate was kept away from the detector. In contrast to traditional confocal and nonconfocal laser-induced fluorescence detection systems, background levels resulting from scattered excitation light, reflection and refraction from the microchip was significantly eliminated. Significant enhancement of the signal-to-noise ratio was obtained by shaping a laser beam that combined an attenuator with a spectral filter to optimize laser power and the dimensions of the laser beam. FITC and FITC-labeled amino acid were used as model analytes to demonstrate the performance sensitivity, separation efficiency, and reproducibility of this detection system by using a hybrid polydimethylsiloxane/glass microfluidic device. The limit of detection of FITC was estimated to be 2 pM (0.55 zmol) (S/N = 3). Furthermore, the single cell analysis for the determination of intracellular glutathione in a single 3T3 mouse fibroblast cell was demonstrated. The results suggest that the proposed optical arrangements will be promising for development of sensitive, low-cost microfluidic systems.     

Large increase in the heat transfer through monolayers detected by beam deflection

We report the application of photothermal beam deflection for studying heat transfer across the liquid/ gas interface covered with surfactant monolayers. Laser-induced Marangoni convection was generated on the surface of an absorbing aqueous solution with and without a monolayer. The change in heat transfer to the air was monitored by the deflection of a probe beam propagating close to the solution surface. A large increase in the deflection as well as in the air temperature for monolayer-covered surfaces was observed. A film-balance study showed that the magnitude of deflection increases as a function of monolayer compression.     

Cavity ring-down spectroscopy measurements of single aerosol particle extinction. I. The effect of position of a particle within the laser beam on extinction

A continuous wave distributed feedback diode laser operating in the near infrared at wavelengths close to 1650 nm has been used to measure the extinction of light by single aerosol particles. The technique of optical feedback cavity ring-down spectroscopy (CRDS) was used for measurement of CRDS events at a repetition rate of 1.25 kHz. This very high repetition rate enabled multiple measurements of the extinction of light by single aerosol particles for the first time and demonstrated the dependence of light scattering on the position of a particle within the laser beam. A model is proposed to explain quantitatively this phenomenon. The minimum detectable dimensionless extinction coefficient epsilonmin was determined to be 3x10(-6). Extinction values obtained for single spherical polymer beads from a monodisperse sample of particles of diameter of 4 microm are in near-quantitative agreement with the values calculated by the Mie scattering theory. The deviations from the Mie theory expected for measurement of extinction by CRDS using a continuous wave laser are discussed in the companion paper.     

Time-Resolved Studies of Light Propagation in Crassula and Phaseolus Leaves

Abstract— Time-resolved transmittance was used to extract in vivo optical properties of leaves of green plants experimentally. In time-resolved transmittance measurements an ultrashort light pulse is directed onto the surface of the object and the transmitted light is measured with a time resolution in the range of picoseconds. A table-top terawatt laser was used to generate 200 fs light pulses at 790 nm with a repetition rate of 10 Hz. The light pulses were focused through a cuvette filled with water to produce white light pulses and optical filters were placed in the beam path to select the wavelength of the light focused onto the leaf surface. The time profiles of the light transmitted through the leaves was recorded with a streak camera having a time resolution of about 2.5 ps. Results from Crassula falcata and Phaseolus vulgaris studied at 550, 670 and 740 nm are reported. The three selected wavelength regions represent medium, high and a low absorption of light, respectively. A library of curves was generated using Monte Carlo simulation, and the absorption and scattering coefficients were extracted by comparison of experimental curves with this library. Our results suggest that in the case of the thin (200 μm) Phaseolus leaves and certainly in the case of the thick (4 mm) Crassula leaves, light scattering plays an important role in light transport through the leaf and should also affect light flux in these leaves.     

Trace analysis of pollutants in water using the photothermal interferometry as HPLC detector

A new procedure including high performance liquid chromatography in combination with photothermal interference spectroscopy as detection device (HPLC/PIS) has been proposed, optimized and its figures of merit for pesticide residue analysis are shown. The flowing sample under study is set in one arm of a Mach-Zehnder interferometer, and its refractive index is modulated by a periodically chopped continuous wave argon ion laser. As chopper, an acousto optical modulator has been introduced to switch the excitation laser beam between different lines (457 nm, 488 nm, 514 nm) simultaneously. Thus a multi component analysis can be realized either by using an HPLC-system in front of the PIS device or by a multi line Ar(+)-laser, directly. The limit of detection of the HPLC/PIS system reached 71 microg/l of the pesticide di-nitro-ortho-cresol (DNOC).     

Synthesis of a Near‐Infrared BODIPY Dye for Bioimaging and Photothermal Therapy

The development of robust photothermal agents for near‐infrared (NIR) imaging is a great challenge. Herein, we report the design and synthesis of a new photothermal agent, based on the aza‐boron‐dipyrromethene framework (azaBDP). This compound possessed excellent photostability and high photothermal‐conversion efficiency (50 %) under NIR laser irradiation. When the photothermal properties of this compound were utilized for tumor inhibition, stable long‐term fluorescence was observed in living animals. Photothermal treatment efficiently suppressed tumor growth, as evidenced by in vitro and in vivo experiments. Furthermore, NIR emission could be detected by using an imaging system and therapeutic self‐monitoring was achieved by using NIR imaging.     

A Water‐Soluble,NIR‐Absorbing Quaterrylenediimide Chromophore for Photoacoustic Imaging and Efficient Photothermal Cancer Therapy

Precision phototheranostics, including photoacoustic imaging and photothermal therapy, requires stable photothermal agents. Developing such agents with high stability and high photothermal conversion efficiency (PTCE) remains a considerable challenge. Herein, we introduce a new photothermal agent based on water‐soluble quaterrylenediimide (QDI) that can self‐assemble into nanoparticles (QDI‐NPs) in aqueous solution. Incorporating polyethylene glycol (PEG) into the QDI core significantly enhances both physiological stability and biocompatibility of QDI‐NPs. The highly photostable QDI‐NPs offer advantages including intense absorption in the near‐infrared (NIR) and high PTCE of up to 64.7±4 %. This is higher than that of commercial indocyanine green (ICG). Their small size (ca. 10 nm) enables sustained retention in deep tumor sites and also proper clearance from the body. QDI‐NPs allow high‐resolution photoacoustic imaging and efficient 808 nm laser‐triggered photothermal therapy of cancer in vivo.