In this work, a recently proposed thermal lens instrument based on multi-pass probe beam concept is investigated and described as a multi-thermal-lens equivalent system. A simulation of the ...photothermal lens signal formation in a multi-thermal-lens equivalent configuration of the system is performed and validated by comparing the experimental signals of single, dual and ten-pass configurations to theoretically calculated values. The theoretically predicted enhancement of the signal is 9 to 10-fold for a weak thermal lens when comparing the ten-pass configuration with the conventional single-pass thermal lens system. Experimentally achieved signal enhancement in the ten-pass system is 8.3 for pure ethanol sample and between 8 and 9 for solutions with different concentrations of the Fe(II) - 1,10-Phenanthroline complex. Additionally, a value of 9.1 was calculated as the ratio of the slopes of the calibration lines obtained using the ten-pass and single-pass configurations. The achieved limit of detection for determination of Fe(II), in the ten-pass configuration, was 0.4 μgL−1, with a relative standard deviation around 4.5%, which compares favorably with previously reported results for TLS determination of Fe(II) in thin samples using low excitation power. For the multi-pass configuration the linear range of measurement is reduced when compared to the single-pass configuration. This is explained by the theoretical analysis of the photothermal signal under multi-pass condition, which shows the important contribution of nonlinear term in theoretical expression for the photothermal signal. The ten-pass configuration, which is presented and validated experimentally for the first time, offers important signal enhancement needed in recently developed TLS instruments with tunable, low power excitation sources.
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•Theoretical description of the multi-pass probe beam thermal lens concept is given for the first time.•The theoretical model is supported by experimental results.•Ten-pass configuration provides 8 to 9-fold signal enhancement as compared to single-pass configuration.•Detection of μgL−1 levels of Fe(II) was demonstrated, corresponding to absorbance of 8 × 10−6.•The multi-pass TLS system offers important enhancements needed in recently instruments with low power sources.
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•A novel gel electrophoresis with thermal lens detection biosensor was proposed.•Extremely small differences in the electrophoretic mobility of the particles can be resolved.•The ...developed sensor is highly sensitive and possesses a detection limit 0.023 nM.•The system enables acquiring results in remarkably shorter running times.•The presented approach can be of broad interest for effectively separating various biomolecules.
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.
Yb–Ce co-doped LSCAS glasses melted under a vacuum atmosphere are free of OH− radicals presenting downconversion luminescence of interest for solar cell application. Absorption spectra showed an ...ultraviolet–visible broad band related to the 2F5/2, 2F7/2 → 5d transitions of the Ce3+. Time-resolved luminescence evidenced energy transfer from Ce3+ to Yb3+, and the contour maps spectra showed a decrease in Ce3+ emission with the increase of Yb concentration. Thermal lens results evidenced an increase in heat generation, suggesting the occurrence of nonradiative transitions due to the formation of Yb2+ or Ce4+ ions. The observed emissions are attributed to energy transfer from Ce3+ or Yb2+ to two Yb3+ ions by quantum cutting mechanism, emission from Ce3+ at 520 nm, and predominantly, a phonon-assisted energy transfer from Ce3+ or Yb2+ to one Yb3+ ion.
•Ce–Yb co-doped low silica calcium aluminosilicate glasses were successfully developed.•The Yb3+ luminescence around 980–1030 nm increased due to downconversion process.•Thermal lens successfully allowed measuring energy transfer between Ce and Yb ions.•Ce–Yb LSCAS glasses are spectral converters for improving Si solar cell efficiency.
In the thermal lens experimental set-up we replaced the commonly employed pump laser by a halogen lamp, combined with an interference filter, providing a tuneable, nearly monochromatic pump source ...over the range of wavelengths 430–710 nm. Counter-propagating pump and probe beams are used and a 1 mm path-length sample cell together with the interference filter makes an optical cavity, providing amplification of the thermal lens signal, which leads to enhancement of the measurement sensitivity, and enables detection of absorbances on the order of 5 × 10−6. Amplified thermal lens signal allows us to replace the typical lock-in amplifier and digital oscilloscope with a silicon photodetector, Arduino, and a personal computer, offering the possibility for a compact, robust and portable device, useful for in-field absorption measurements in low concentration or weakly absorbing species. The use of a white light source for optical pumping, an interference filter for wavelength selection and direct diagnostic of the thermal lens signal increase the versatility of the instrument and simplifies substantially the experimental setup. Determination of Fe(II) concentrations at parts per billion levels was performed by the described white-light thermal lens spectrophotometer and the absorption spectrum for 50 μgL–1 Fe(II)-1,10-phenanthroline was well reproduced with an average measurement precision of 4%. The obtained limits of detection and quantitation of Fe(II) determination at 510 nm are 3 µgL−1 and 11 µgL−1, respectively. The calibration curve was linear in the concentration range of LOQ-500 µgL−1 with reproducibility between 2% and 6%, confirming that this instrument provides good spectrometric capabilities such as high sensitivity, tuneability and good reproducibility. In addition, the versatility of the instrument was demonstrated by recording the photothermal spectrum of gold nanostructured material and determination of excitation wavelength with most efficient optical to thermal energy conversion, which differs considerably (cca 100 nm) from the absorption maximum of the investigated sample.
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•A tuneable thermal lens spectrometer with an incoherent white light excitation was developed.•An optical cavity enables high sensitivity measurements at low excitation powers (7–17 mW, 430–710 nm).•The instrument provides good analytical performances such as high reproducibility, low LODs and tuneability.•Determination of Fe(II) concentrations at 11 μgL−1 levels (LOQ) can be performed.•Photothermal spectrum of a nanogold plasmonic material is presented.
In this work, a lithium tellurite glass (80TeO2− 20Li2O, in mol%) was synthesized and its optical properties were analyzed. This glass matrix has been extensively studied, mainly due to its highly ...nonlinear optical properties, but there have been no reports concerning its luminescence properties. To the best of our knowledge, this is the first observation of visible emission related to Te4+ centers in a lithium tellurite glass. A broad and intense emission band was centered at 650 nm and there was a broad excitation band in the UV–Vis region. The emission lifetime at room temperature was approximately 7.0 ± 0.2 µs and the fluorescence quantum efficiency was 63 ± 6%. These characteristics indicated that the system consisting of Te4+ centers in lithium tellurite glass is a good candidate as a phosphor material for various applications.
In this work we report on the absorption spectra of ethanol and water in the region 430–700 nm using a homemade halogen lamp-based photothermal lens spectrophotometer with a multipass probe-beam ...configuration. The spectra also include well resolved, higher absorption overtones. The instrument achieves high sensitivity due to multiple reflections within the optical cavity containing the sample. Finally, an Arduino board was used for collecting and digitizing the signal, thus enabling a more compact device.
•An optimization of Thermal Lens Spectrometry (TLS) experiment was made.•The TLS method is appropriate for permanganate quantification in water treatment application at neutral pH.•The Limits of ...Detection are 0.22 μM and 0.08 μM for distilled and tap water, respectively.
Although permanganate is a widely used oxidant in drinking water and wastewater treatment, only few spectrometric methods were proposed for measuring its concentration in water. The thermal lensing spectrometry (TLS) experiment was optimized and applied for the quantification of trace permanganate in water at neutral pH. Several parameters (probe beam waist position, confocal parameters and detector position) influencing the thermal lens (TL) signal were explored in order to optimize the geometry of mode-mismatched dual-beam experiment. Based on the obtained experimental and theoretical results, the TL signal reaches an amplitude that is two times larger than that obtained with the collimated method. As application of this experiment, I have measured the limit of detection (LOD) and quantification (LOQ) of permanganate in distilled and tap water without the need of reagents. The obtained results of LOD are 0.22 μM and 0.08 μM for distilled and tap water, respectively. These values are better than those obtained by the conventional absorption spectrometry method which is suitable for samples containing more than around 5.5 μM, and close to the LOD achieved by indirect spectrometric methods.
The determination of low concentration of iron in natural waters can be difficult due to the complexity of natural water, but primarily because it requires preconcentration of the sample with solvent ...extraction. In this work we report on results of thermal lens spectrometry (TLS) coupled to flow injection analysis (FIA) as a highly sensitive FIA-TLS method of iron detection. The concentration of iron redox species was determined using 1,10-phenanthroline (PHN), that forms stable complexes with Fe(II) ions which are characterized by an absorption maximum at 508 nm. The TLS system using a 633 nm probe laser and 530 nm pump laser beam was exploited for on-line detection in flow injection analysis, where a PHN solution was used as the carrier solution for FIA. The concentration of the complexing agent affects the quality of the TLS signal, and the optimal concentration was found at 1 mM PHN. The achieved limits of detection (LODs) for Fe(II) and total iron were 33 nM for Fe(II) and 21 nM for total iron concentration. The method was further validated by determining the linear concentration range, specificity in terms of analytical yield and by determining concentration of iron in a water sample from a local water stream.
Thermal lens spectrometry along with spectrophotometric titration were used to assess the composition of the complex of oxidized cytochrome
(ferricytochrome
) with 1,1',2,2'-tetraoleyl cardiolipin, ...which plays a key role in the initiation of apoptosis. Spectrophotometric titration was carried out for micromolar concentrations at which the complex is mainly insoluble, to assess the residual concentration in the solution and to estimate the solubility of the complex. Thermal lens spectrometry was used as a method of molecular absorption spectroscopy, which has two advantages over conventional optical transmission spectroscopy: the higher sensitivity of absorbance measurements and the possibility of studying the light absorption by chromophores and heat transfer in complex systems, such as living cells or tissues. Thermal lens measurements were carried out at nanomolar concentrations, where the complex is mainly in solution, i.e., under the conditions of its direct measurements. From the thermal lens measurements, the ratios of cytochrome
and cardiolipin in the complex were 50 at pH 7.4; 30 at pH 6.8; and 10 at pH 5.5, which fit well to the spectrophotometric data. The molecular solubility of the complex at pH 6.8-7.4 was estimated as 30 µmol/L.
•Silver stained protein bands in polyacrylamide gels are detected and analyzed by thermal lens spectrometry.•The self-built thermal lens sensor allows the detection of subnanogram protein ...quantities.•During measurement, soaking the gel in a medium containing methanol increases the signal strength.
Proteins separated by gel electrophoresis are commonly quantified by colorimetric analysis of the protein band stain intensity. For the most sensitive stain (silver), the minimal protein amount, needed for the optical visualization of the band, is around 1ng. This study investigates the use of thermal lens (TL) spectrometry for the quantification of subnanogram protein amounts. The developed dual laser TL sensor is set up in collinear geometry; it includes a HeNe probe beam, a 450nm diode laser pump beam, and a gel holder. After silver staining, the polyacrylamide gel is scanned by the sensor while kept soaked in water, and in 50% (v/v) methanol/water. During scanning, the TL signal of each band is recorded in function of its position. The TL sensor can detect protein amounts as low as 0.1ng in water, and 0.05ng in 50% methanol/water. The limit of detection ranges from 8 to 50pg, depending on the soaking medium and the staining strength. The theoretical results, predicting the sensitivity enhancement in methanol/water, are in agreement with the results. In conclusion, thermal lens spectrometry proves to be a valid method for the detection of subnanogram protein amounts in polyacrylamide gels, and its application can be extended to other soft gel matrices.
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