Photothermal Interference Research Articles

Ultra-wide range and wavelength fixed trace gas detection technology based on single chamber multiplexing

The all-fiber photo-thermal interference (PTI) system based on hollow-core photonic crystal fiber (HC-PCF) has the advantages of wide dynamic range, ultra-sensitivity, and small volume, which is of great significance in gas trace analysis. Most of the previous PTI systems obtain the relationship between gas concentration and phase modulation by wavelength scanning and extracting the second harmonic signal absorbed by the gas. However, the residual modulation caused by the asynchronism between wavelength and modulation signal seriously affects the signal-to-noise ratio (SNR) and dynamic detection range of the system. In addition, wavelength scanning has limitations for detecting gas with irregular absorption lines. This paper proposes an all-fiber photo-thermal interference system with pump intensity external modulation. The system is not limited by the gas absorption line and has a high SNR. The factors affecting the dynamic range of the system are analyzed theoretically and experimentally. It is verified that increasing the injection gas pressure can significantly increase the detection limit of the system compared with increasing the pump light power. The redshift of the pump light can dramatically increase the detection limit of the system. A C2H2 gas trace system with the pump wavelength redshifted to 1530.41 nm was demonstrated. The detection lower limit of 9.24 ppm and an extensive dynamic detection range of five orders of magnitude were obtained.

Photothermal interference urease-powered polydopamine nanomotor for enhanced propulsion and synergistic therapy

Enzyme-powered nanomotors with active motion have opened a new door in design of biocompatible drug delivery systems for cancer treatment. However, the movement of them still faces huge challenges due to the viscous physiological environment. To address this issue, we developed a photothermal interference (PTI) urease-modified polydopamine (PDA) nanomotor (PDA@HSA@Ur) for deeper-penetration of doxorubicin (DOX) through improved motion. The urease-powered nanomotors can generate self-propulsion via catalyzing decomposition of biocompatible urea into carbon dioxide and ammonia through a self-diffusiophoretic. Meanwhile, when exposed to near-infrared (NIR) laser, the increased temperature of tumors microenvironment from nanomotors can not only induce tumor cell apoptosis but also enhance the biocatalytic activity of urease to improve the motion of nanomotors. Compared to the nanomotors propelled only by urea, PTI nanomotors realize highly effective self-propulsion with improved cellular uptake in vitro. Furthermore, PTI nanomotors display an enhanced anticancer efficiency owing to synergistic photothermal and chemotherapy effect. The PTI reported in this manuscript is the first to provide a thermally assisted method for highly efficient cancer treatment with urease-powered nanomotors in a complex physiological environment through enhanced motion and synergistic therapy.

Photoacoustic detection of photothermal heterodyning: a method for determination of chromophore distances in aqueous solution

When two different chromophores placed close to each other in water are optically excited by continuous light beams with intensities modulated at two different frequencies, the temperature change from heat diffusing from one chromophore affects the magnitude of the thermal expansion coefficient in the region of the other chromophore, owing to the fact that the thermal expansion coefficient of water increases with temperature. Therefore, in addition to two separate linear photoacoustic emission at the sites of each chromophore, the oscillating variations in the thermal expansion coefficient of water means that a heterodyned photoacoustic effect will be generated at the sum and difference of the two modulation frequencies. It is shown here theoretically that the destructive photothermal interference between two chromophores, occurring at certain frequencies for a specific inter-chromophore distance, will give rise to amplitude nulls and thus drastic phase changes in the heterodyned photoacoustic waves, which hints a method that is capable of determining distances between the two chromophores and acts as a photoacoustic analog of Förster resonance energy transfer.

Environmental impacts on the gonadotropic system in female Atlantic salmon (Salmo salar) during vitellogenesis: Photothermal effects on pituitary gonadotropins, ovarian gonadotropin receptor expression, plasma sex steroids and oocyte growth

The gonadotropic system and ovarian growth and development were studied during vitellogenesis in female Atlantic salmon subjected to either simulated natural photoperiod and ambient water temperature (NL-amb), or an accelerating photoperiod (short day of LD8:16 from May 10) combined with either warmed (ca 2°C above ambient; 8L-warm) or cooled water (ca 2°C below ambient; 8L-cold) from May to September.Monthly samples were collected from 10 females/group for determination of transcript levels of pituitary gonadotropin subunits (fshb and lhb) and ovarian gonadotropin receptors (fshr and lhr), plasma sex steroids (testosterone: T and estradiol-17β: E2), gonadosomatic index (GSI) and oocyte size.Short day in combination with either warmed or cooled water induced an earlier increase in pituitary fshb and lhb levels compared with NL-amb controls, and advanced ovarian growth and the seasonal profiles of T, E2. By contrast only minor effects were seen of the photothermal treatments on ovarian fshr and lhr.The 8L-cold had earlier increase in fshb, lhb and E2, but similar oocyte and gonadal growth as 8L-warm, suggesting that the 8L-cold group tried to compensate for the lower water temperature during the period of rapid gonadal growth by increasing fshb and E2 production.Both the 8L-warm and 8L-cold groups showed incomplete ovulation in a proportion of the females, possibly due to the photoperiod advancement resulting in earlier readiness of spawning occurring at a higher ambient temperature, or due to some reproductive dysfunction caused by photothermal interference with normal neuroendocrine regulation of oocyte development and maturation.

Single metallic nanoparticle imaging for protein detection in cells.

We performed a visualization of membrane proteins labeled with 10-nm gold nanoparticles in cells, using an all-optical method based on photothermal interference contrast. The high sensitivity of the method and the stability of the signals allows 3D imaging of individual nanoparticles without the drawbacks of photobleaching and blinking inherent to fluorescent markers. A simple analytical model is derived to account for the measurements of the signal amplitude and the spatial resolution. The photothermal interference contrast method provides an efficient, reproducible, and promising way to visualize low amounts of proteins in cells by optical means.

Imaging single metal nanoparticles in scattering media by photothermal interference contrast

We have developed a photothermal method for far-field optical detection of nanometer-sized metal particles, combining high-frequency modulation and polarization interference contrast. We can image gold colloids down to 5 nm in diameter, with a signal-to-noise ratio higher than 10. This is a considerable improvement over commonly used optical methods based on resonance plasmon scattering which, for background reasons, are limited to particles of more than about 40 nm in diameter. By adding 300 nm latex spheres in the sample, we also show that in addition to its intrinsic sensitivity, our photothermal method is totally insensitive to non-absorbing scatterers.

On-column indirect photothermal interference detection for capillary zone electrophoresis.

An indirect photothermal interference detection method, which is based on the diffraction of a probe laser beam by a capillary tube, for detecting metal cations separated by capillary zone electrophoresis (CZE) is described. In this capillary photothermal interference detector, a 2 mW He-Ne probe laser is employed to provide the probe beam and an 18 mW He-Ne pump laser is used to supply the pump beam. Factors that contribute to the noise and signal in indirect photothermal interference detection in CZE, such as the noise from the scattered light caused by both the probe beam and the pump laser beam, and effects of the concentration of ethanol and NaCl on the separation efficiency, were studied. The effect of scattered light can be reduced effectively with the configuration constraints investigated for photothermal capillary absorption measurements. With Methylene Blue added to carrier electrolyte as an absorber, three typical metal cations (KI, CuII and AlIII) were separated using this system. For CuII, a 2.1 x 10(-7) mol l-1 concentration detection limit (S/N = 2) without preconcentration and a 1.02 x 10(-17) mol detection limit as absolute amount were measured, considering the optical sampling volume estimated to be 50 pl, and 1.99 x 10(6) theoretical plates were observed on the laboratory-made CE system. It was demonstrated that indirect photothermal interference detection is suitable for small capillaries and a large ionic strength range for CE analysis.

Studies of the residual absorption of a Bi2Sr2CaCu2O8+? single crystal at THz frequencies

We measured the residual absorption of a Bi2Sr2 CaCu2 O8+δ single crystal at low temperature in the frequency range between 0.6 THz and 4.2 THz using a new method, photothermal interference spectroscopy. By combining with reflectivity data obtained with a Fourier-transform IR spectrometer (frequency range: 3 THz to 100 THz) we have calculated the dynamical conductivity using a Kramers-Kronig-transformation. The results are compared with calculations of the far infrared conductivity and show qualitative features expected for a superconductor with nodes in the gap.

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).

Measurements of the residual absorption of high tc superconductors at THz-frequencies using the photothermal interference spectroscopy

For the measurement of the absorptivity of a sample a modulated FIR beam is focused on the sample leading due to absorption to a periodic modulation of the temperature of the sample and of a layer of the adjacent gas. This temperature change is detected by the use of a two beam interferometer. We report about measurements of the low temperature residual absorption of thin YBaCuO films on SrTiO3, and MgO and of a BiSCCO single crystal. We find that the absorptivity at low temperature, which follows a frequency squared behaviour at microwave frequencies up to 100 GHz, shows a plateau in the frequency range between 0.6 THz and 4 THz.

Low-temperature IR-reflectivity of superconducting Bi-2212 single crystals with different oxygen contents

We report on low temperature infrared reflectivity measurements of Bi2Sr2CaCu2O8+δ single crystals (Bi-2212) with two different oxygen contents having Tc values of 91 K for an optimally-doped crystal and 73 K for an over-doped crystal. The reflectivity of the optimally-doped sample at low temperature (10 K) was near unity in the range between 150 cm-1 and 400 cm-1 and for the over-doped sample noticeably smaller. The results for the optimally-doped sample are similar to results of other IR-reflectivity measurements on Bi-2212 single crystals. For the over-doped crystal we additionally determined the absorptivity in the range of 20 cm-1 and 140 cm-1 by photothermal interference spectroscopy.

Analytical characterization of laser photothermal transient deformation spectrometry

The radiationless relaxation process of excited molecules has developed as the basis for many laser photothermal spectroscopies. For example, laser photoacoustic spectrometry, laser thermal lens spectrometry, laser photothermal deflection spectrometry, laser photothermal refraction spectrometry and laser photothermal interference spectrometry have been applied to analytical chemistry and evolved into a kind of high sensitivity and high space resolution absorption spectrometries.

Study of the submillimeter absorptivity of high T c superconductors by photothermal interference spectroscopy

We report on the study of the submillimeter absorptivity of high-Tc superconductors by a new method, the photothermal interference spectroscopy. Absorption in a sample leads to a temperature change of the sample and, by heat transfer, also of a gas volume adjacent to the sample and to a change of refractive index in the gas volume that we detect by an interferometric method. We demonstrate the feasibility of the method by determination of the absorptivity of high-Tc superconducting YBa2Cu3O7−δ samples for submillimeter radiation at a frequency near 1 THz. The absorptivity shows a peak at Tc, that is most likely due to fluctuation effects, a strong drop below Tc and a finite value at low temperatures, with a peak near 15 K.