Thermal Lens Detection Research Articles

Microsphere-assisted enhanced photothermal lens detection integrated with digital holographic microscopy for 3D particle sensing and thermal diffusivity measurement

In this paper, we show that by extending the concept of “microsphere-assisted imaging” into thermal lens (TL) detection, enhancement of photothermal detection is achieved. Furthermore, by integration of TL detection and digital holographic microscopy (DHM), we provide simultaneous measurement of photothermal properties as well as complementary imaging of the sample. Simultaneous acquisition of photothermal properties and imaging is essential for characterization of a variety of samples in biochemistry, material science, and process technologies. TL is a sensitive methodology to detect low concentrations of analytes in low-loss samples, and DHM in the transmission mode is an effective technique for label-free, non-contact, and real-time imaging and measurement of phase objects, such as biomaterials. We demonstrate the usefulness of the TL-DHM integrated system by applying it for acquisition of photothermal maps of samples as well as obtaining their morphometrical information. Additionally, we measure the thermal diffusivity of polydimethylsiloxane because of the focusing effect of polystyrene microspheres. The system has the potential to be applied for a variety of objects including bio-samples and may be proposed as a bench-top characterization device.

An electrophoresis approach with online thermal lens detection to monitoring DNA surface coatings on gold nanoparticles

The coverage density of oligonucleotides on the surface of gold nanoparticles (AuNPs) is crucial for optimizing the sensitivity of AuNPs-based biosensors and evaluating the interactions between thiol-functionalized oligonucleotides and AuNPs. In this study, we report a novel approach based on a miniaturized gel electrophoresis chip (MGEC) integrated with online thermal lens detection for monitoring the amount of DNA on the surface of AuNPs. The microcontroller-based digitization board platform enables simultaneous measurement and recording of data. AuNPs were functionalized with a mixed thiol-terminated monolayer containing single stranded DNA at variable density, which is able to load binders for high sensitivity biorecognition. Due to high spatial and temporal resolution of the thermal lens detection system, our approach enables extremely small differences in the electrophoretic mobility of the particles to be resolved. Hence, small differences in the DNA surface density (55–275 nM) on the particles can be easily distinguished in short time (<6 min), not otherwise detectable using conventional UV–Vis spectrophotometers. In addition, the analytical capability of the proposed MGEC was validated measuring the low detection limit for standard AuNPs solutions using a 80 µL buffer, 100 µL gel, and a 37.5 V/cm electrical field. The result showed that the thermal lens signal linearly increased with the concentration of AuNPs over the range of 0.1–10 nM. The detection limit and relative standard deviation were 23 pM and 4%, respectively. We envisage that the system has potential as an advanced instrumental platform for designing biosensors in nanotechnology.

Hemichrome Determination by Thermal Lensing with Polyethylene Glycols for Signal Enhancement in Aqueous Solutions

ABSTRACTThe thermal lens technique is proposed for the determination of total hemoglobin in the form of reversible hemichrome. The conditions were optimized (concentration of sodium dodecyl sulfate, 2 mM) to attain the maximum sensitivity with the use of polyethylene glycols as signal enhancers. For polyethylene glycols with molecular weights 1500–35000 Da in a concentration range of 5–15% w/w (5–25 mM), the influence on thermal lens signal enhancement was estimated. It is shown that the use of 5% w/w polyethylene glycol 2000 provides the maximum increase in the thermal lens enhancement factor (by 40%) in comparison with unmodified aqueous solutions. The detection limit of iron(II) tris(1,10-phenanthrolinate) as a model system is 60 nM. Under these conditions, the thermal lens detection limit of hemichrome is 10 nM, which shows a 15-fold enhancement compared to spectrophotometry. Modification of the medium with polyethylene glycols decreases the limit of detection of hemichrome determination by 15% in comparison with unmodified aqueous solutions due to better reproducibility for the range of concentrations from 0.02 to 0.9 µM.

Thermal lens microscope sensitivity enhancement using a passive Fabry–Perot-type optical cavity

We developed a thermal lens microscope equipped with a passive optical cavity, which provides an optical feedback for the multiple pass of the probe laser beam to enhance sensitivity. Considering the maximum absorption peak for Fe(II) at 532 nm wavelength, we have achieved a 6.6-fold decrease in the limit of detection (LOD) to a level of 0.077 μg · l−1 without a cavity. The possibilities to use thermal lens detection combined with an optical resonator was proposed and a drastic thermal lens signal enhancement was achieved using very low excitation power. The corresponding LOD for Fe(II) was further decreased to the level of 0.006 μg · l−1 which represents an 85-fold decrease of the LOD value. This setup is a promising device, which can be applied as a sensitive tool for detecting chemical traces in small volumes of solutions.

Efficient thermal lens nanoparticle detection in a flow-focusing microfluidic device

A flow-focusing microfluidic device was fabricated for thermal lens nanoparticle detection. In this device, sample flow was first sandwiched by lateral z-axis sheath flows, and then by horizontal xy-plane sheath flows. The three-dimensional flow focus was visualized using an aqueous dye solution. Subsequently, 500-nm-sized red polystyrene particles were individually detected by the thermal lens detection method. When 1μL of sample solution containing 300 particles/μL was passed through the thermal lens detection point, 255±20 peaks corresponding to particles were observed.

Integrated Micro-Optics for Microfluidic Detection.

A method of embedding micro-optics into a microfluidic device was proposed and demonstrated. First, the usefulness of embedded right-angle prisms was demonstrated in microscope observation. Lateral-view microscopic observation of an aqueous dye flow in a 100-μm-sized microchannel was demonstrated. Then, the embedded right-angle prisms were utilized for multi-beam laser spectroscopy. Here, crossed-beam thermal lens detection of a liquid sample was applied to glucose detection.

Thermal lens detection of one and two‐color laser excitation of benzene in cryogenic liquid solutions

The thermal lens technique is applied to vibrational overtone spectroscopy of cryogenic solutions of benzene. The pump and probe thermal lens technique has been found to be very sensitive for detecting samples of low concentration in transparent liquefied gas solvents at low temperatures. The C–H fifth vibrational (Δυ = 6) overtone of benzene in liquefied ethane, krypton, and argon have been recorded at concentrations between 10 and 58 p.p.m. in a range of temperatures between 87 and 150 K. Experiments with one‐color laser excitation are sensitive enough to detect benzene at parts per million mole fraction. The dependence of the signal on the physical properties of the solvent and the excitation wavelength are shown. Finally, a thermal lens experiment with two‐color laser excitation is presented showing an increase in the magnitude of the peak absorption that will result in an increase of the limit of detection. A three‐level model to explain signal enhancement with respect to one‐color laser excitation under the same experimental conditions is presented. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Thread-based microfluidic three channel device in combination with thermal lens detection for the determination of copper and zinc

A new method involving a thread-based microfluidic three channel device in combination with thermal lens detection was developed for the sequential determination of Cu(ii) and Zn(ii).

Influences of Detection Pinhole and Sample Flow on Thermal Lens Detection in Microfluidic Systems

Thermal lens microscopy (TLM), due to its high temporal ( $${\sim }\mathrm{ms}$$ ) and spatial resolution ( $${\sim }\upmu \mathrm{m}$$ ), has been coupled to lab-on-chip chemistry for detection of a variety of compounds in chemical or biological fields. Due to the very short optical path length (usually below 100 $$\upmu \mathrm{m}$$ ) in a microchip, the sensitivity of TLM is unfortunately still 10 to 100 times lower than conventional TLS with 1 cm sample length. Optimization of the TLM optical configuration was made with respect to different pinhole aperture-to-beam size ratios for the best signal-to-noise ratio. In the static mode, the instrumental noise comes mainly from the shot noise of the probe beam when the chopper frequency is over 1 kHz or from the flicker noise of the probe beam at low frequencies. In the flowing mode, the flow-induced noise becomes dominant when the flow rate is high. At a given flow rate, fluids with a higher density and/or a higher viscosity will cause larger flow-induced noise. As an application, a combined microfluidic flow injection analysis ( $$\upmu \mathrm{FIA}$$ )–TLM device was developed for rapid determination of pollutants by colorimetric reactions. Hexavalent chromium [Cr(VI)] was measured as a model analyte. Analytical signals for 12 sample injections in 1 min have been recorded by the $${\upmu }$$ FIA–TLM. For injections of sub- $$\upmu $$ L samples into the microfluidic stream in a $$50\,\upmu \mathrm{m}$$ deep microchannel, a limit of detection of $$4\,\mathrm{ng}{\cdot }\mathrm{mL}^{-1}$$ was achieved for Cr(VI) in water at 60 mW excitation power.

Thermal lens detection in microfluidic chips

Main possibilities of thermal lens microscopy, a highly sensitive method of molecular absorption spectroscopy, in chemical analysis in microfluidic chips are shown.

Sensitivity Enhancement in Near-Field Photothermal-Lens Detection in Capillary Electrophoresis Using Laser-Induced Online Precipitation

This paper reports simultaneous photoinduced precipitation-based online preconcentration of target analytes at the inner walls in capillary zone electrophoresis (CZE) and surface-enhanced near-field crossed-beam photothermal-lens detection of the preconcentrated analytes. A simple technique using online readjustment of the optical scheme of the thermal-lens detector in the course of the separation for gaining optimum sensitivity for both water-soluble and precipitated analytes is proposed. It provides a considerable decrease in the limits of detection (LOD) with good concordance with the previously developed theoretical approach to this combination (D. A. Nedosekin, W. Faubel, M. A. Proskurnin, and U. Pyell, Talanta, 78, 682-690 (2009)). As a result, an enhancement of more than an order of magnitude in the limit of detection of the photoactive 4-aminoazobenzene compared to conventional thermal-lens detection in CZE is achieved while retaining very good sensitivity for unabsorbed analyte (Mordant Yellow 7). The application of the thermal-lens detector to the investigation of laser-induced reactions in flow in capillaries is discussed.

Extraction–thermal lens quantification of cobalt with Nitroso-R-Salt in two-phase aqueous systems with water-soluble polymer polyethylene glycol

A novel method is proposed for the extraction-thermal lens quantification of cobalt with Nitroso-R-Salt based on the distribution of the colored complex in a two-phase aqueous system on the basis of poly-ethylene glycol (PEG) and an ammonium sulfate solution followed by its thermal lens detection in the extract. The limit of detection is 0.3 μM (20 ng/mL); the lower limit of the analytical range is 0.7 μM (40 ng/mL); the relative standard deviation for the concentrations 1–50 μM makes 1–3% (n = 6, P = 0.95). In the determination of cobalt by spectrophotometry under the same conditions, the detection limit is 10 μM (0.6 μg/mL) and the lower limit of the analytical range is 40 μM (2.5 μg/mL). The precision of thermal lens measurements in PEG solutions is higher in comparison to that in aqueous ones because of the weaker interference of convection in aqueous solutions of PEG.

Thermal lens detection device

A thermal lens detection device was developed to realize an easy-to-use, portable and sensitive detector for nonfluorescent molecules. Two laser diodes (658 nm for excitation and 785 nm for probe) were made coaxial in an optical unit and were coupled to a single-mode optical fiber. On a microfluidic chip, a small holder for the optical fiber was fixed, and micro-lenses (numerical aperture of 0.2) were also integrated inside the holder. The micro-lenses were designed to realize an adequate chromatic aberration (50 μm), which was essential for sensitive thermal lens detection. Compared with conventional thermal lens detection systems which required very laborious and accurate optical alignment with the microchannel, the new device needed just attachment-detachment of the optical fiber, which was important for practical application. The lower limit of detection was 10 nM for nickel(II) phthalocyaninetetrasulfonic acid tetrasodium salt solutions (model sample), and the absorbance was 9 × 10(-6) AU. The absolute number of molecules detected was less than 200 zmol. The coefficient of variance for 5-time attachment-detachment of the optical probe was as small as 3.6%. The technical development allowed integration of the thermal lens detection devices inside a microsystem (e.g. enzyme-linked immuno-sorbent assay system), and practical microsystems were realized with sensitivities several-orders higher than absorptiometry.

Heterogeneous Thermal-Lens Immunoassay for Small Organic Compounds: Determination of 4-Aminophenol

4-Aminophenol was selected as a model hapten for thermal-lens detection in a heterogeneous indirect immunoassay for small organic compounds. The assay is based on the competition of the free hapten and 4-aminophenol labeled with tetramethyl rhodamine isothiocyanate (TRITC) for rabbit anti-4-aminophenol antibodies (4-AP-GA-BSA) immobilized on a transparent poly(ethylene terephthalate) plate. The amount of the colored analyte was directly measured by thermal lensing at the plate surface. The developed method is specific for 4-aminophenol. The limit of detection is 2 x 10(-7) M, which corresponds to the absolute amount of 3 x 10(-11) mol of 4-aminophenol. The sensitivities of the developed thermal-lens and fluorescence-based measurements of the immunoassay under the same conditions are in good agreement with the expected and discussed theoretical sensitivities of photothermal and fluorescence measurements.

Differential kinetic determination of cobalt and vanadium with thermal-lens monitoring

On the example of a model indicator reaction of oxidation of cobalt (II) and vanadium (IV) ions by a complex of iron (III) with 1,10-phenantroline, resulting in the formation of tris-(1,10-phenantroline) iron (II), an application of thermal-lens detection of analytical signal with differential kinetic methods is reported. For the simultaneous differential kinetic determination of cobalt (II) and vanadium (IV) with thermal-lens signal detection (514.5 nm, 35.5 mW), the achieved limit of detection (LOD) is 2 ng/ml for both metals, matching the respective values for individual determination. In comparison to spectrophotometric techniques, the effect of synergy, which reduces the sensitivity of detection in the system, is found to be negligible. In general, the sensitivity of differential kinetic determination of cobalt (II) and vanadium (IV) with thermal-lens registration of signal is superior to the analogous procedure with spectrophotometric control of the reaction velocity by two orders of magnitude.

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

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 microM 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 microM.

Electroinduced thermal lens spectrometry

A new technique for the generation of a thermal lens effect is considered. In this technique, the action of focused radiation from an inducing laser is replaced by an analogous action of electric current, which forms a thermal lens at a certain site of a liquid by the generation of a high local current density in a small liquid volume. The main regularities of this technique for thermal lens signal generation are considered, and an expression is derived to relate the detected signal (a relative change in probing radiation intensity at the detector) and the electrolyte concentration. A cell is proposed for electroinduced thermal lens detection. The dependence of the thermal lens signal on the applied voltage and on the concentration of the test electrolyte is determined for a model electrolyte (NaCl), and sensitivity characteristics are found to be consistent with theoretical estimations made in this work.

Effect of a solvent on the parameters of the analytical signal, detection limit, and analytical range of the determination in analytical thermal lens spectrometry

The effect of the main parameters of the solvents (water, acetone, methanol, ethanol, acetonitrile, dimethyl sulfoxide, dichloromethane, toluene, and chloroform) that are most frequently used in the analytical practice on the characteristics of the thermal lens effect (increase in temperature because of optical heating and in the size of the region involved in heating) and on the detection limit and the lower determination limit of the thermal lens determination was considered, and the criteria of the selection of the medium for thermal lens experiments were discussed. It was demonstrated that the gain in these characteristics of the thermal lens determination in the given medium in comparison with the aqueous medium does not necessarily coincide with the strength of the thermooptical effect in this medium. It was demonstrated that the optimum conditions of measurements in the thermal lens detection are controlled not only by the absorption of the analyte and the reagents, but also by the intrinsic absorption of the solvent. Recommendations were given on the selection of the solvent for analytical thermal lens spectrometry.

Overtone spectroscopy and thermal lens detection limit of methane in cryo-solutions

The overtone spectra of methane solutions from 5000 cm−1 to 17000 cm−1 in liquid nitrogen and liquid argon are presented. The region between 5000 and 15000 cm−1 has been measured using a Fourier transform spectrophotometer with methane concentrations between 0.41% and 37% in mole fraction. The thermal lens technique (TLS) was used to measure the fifth overtone, not observed with the Fourier transform spectrophotometer. For a fixed concentration, maximization of the TLS signal with low modulation frequency and high laser power of excitation is shown. Time-dependent signal profiles of single-beam thermal lens experiments are analysed with the parabolic and aberrant lens models. Fitting parameters are obtained from the time-dependent signals. The absorption coefficient of methane was calculated from the fitting parameters and thermo-optical properties of the solvent. The calculated absorption coefficient of the Δυ = 6 transition of methane is 1.7 × 10−3 cm−1, which is in good agreement with literature values. A limit of detection is calculated with measurements of the fifth overtone absorption of methane in liquid nitrogen for solutions of concentration from 0.012% to 0.36% in mole fraction. Calculated limits of detection are 54 ppm and 15 ppm according to two different definitions of limit of detection for the thermal lens technique.

Thermal diffusivity study of cheese fats by thermal lens detection

In this paper we used thermal lens spectrometry to determine the thermal diffusivity of cheese fats. We have used equal concentrations of cheese fats from oaxaca, chihuahua, gouda, manchego and mozzarella cheeses at 42°C temperature. The two lasers mismatched mode experimental configuration was used with a He-Ne laser, as a probe beam and an Ar + laser as the excitation one. The characteristic time constant of the transient thermal lens was obtained by fitting the theoretical expression to the experimental data in order to obtain the thermal diffusivity of the cheese fat samples. This measured thermal property may contribute to a better understanding of the cheese fats quality, which is very important in food industry.