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Recent Progress and Applications of Thermal Lens Spectrometry and Photothermal Beam Deflection Techniques in Environmental Sensing
Mladen Franko, Leja Goljat, Mingqiang Liu, Hanna Budasheva, Mojca Žorž Furlan, Dorota Korte, 2023, original scientific article

Abstract: This paper presents recent development and applications of thermal lens microscopy (TLM) and beam deflection spectrometry (BDS) for the analysis of water samples and sea ice. Coupling of TLM detection to a microfluidic system for flow injection analysis (µFIA) enables the detection of microcystin-LR in waters with a four samples/min throughput (in triplicate injections) and provides an LOD of 0.08 µg/L which is 12-times lower than the MCL for microcystin-LR in water. µFIA-TLM was also applied for the determination of total Fe and Fe(II) in 3 µL samples of synthetic cloudwater. The LODs were found to be 100 nM for Fe(II) and 70 nM for total Fe. The application of µFIA-TLM for the determination of ammonium in water resulted in an LOD of 2.3 µM for injection of a 5 µL sample and TLM detection in a 100 µm deep microfluidic channel. For the determination of iron species in sea ice, the BDS was coupled to a diffusive gradient in the thin film technique (DGT). The 2D distribution of Fe(II) and total Fe on DGT gels provided by the BDS (LOD of 50 nM) reflected the distribution of Fe species in sea ice put in contact with DGT gels.
Keywords: thermal lens microscopy, beam deflection spectrometry, microfluidic system, microcystin-LR detection, iron species determination, ammonium detection
Published in RUNG: 03.01.2023; Views: 612; Downloads: 16
.pdf Full text (2,90 MB)

Hemichrome Determination by Thermal Lensing with Polyethylene Glycols for Signal Enhancement in Aqueous Solutions
Viktoriya Galimova, Mladen Franko, Mikhail Proskurnin, Mingqiang Liu, 2018, original scientific article

Abstract: The 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 spectro- photometry. 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.
Keywords: Hemoglobin, hemikrom, optotermična spektroskopija, etilenglikol, spektrometrija s toplotnimi lečami
Published in RUNG: 16.04.2018; Views: 3648; Downloads: 0
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Determination of Trace Cr(VI) with Diphenylcarbazide by μFIA–Thermal Lens Microscopy
Tatyana Gor’kova, Michail Proskurnina, Mingqiang Liu, Mladen Franko, 2016, original scientific article

Abstract: The optimum reaction parameters for the interaction of hexavalent chromium [Cr(VI)] with diphenylcarbazide in microfluidic chips (μFIA) with thermal-lens microscopic detection were selected. The characteristic feature of the applied flow scheme is the injection of the reagent into the stream containing the test metal, which enables in-field and real-time monitoring of Cr(VI) simply by flowing the sample continuously through the microchip. The limit of detection of Cr(VI) under the selected conditions (signal generating wavelength, 514.5 nm; excitation power, 100 mW; detection position, 10 cm downstream from the mixing zone of the microchip; flow rate 10 μL min–1; injection volume, 1.4 μL) is 15 ng mL–1 (2.9 × 10–7 mol L–1). The linear range is 40 ng mL–1 – 10 μg mL–1 with a relative standard deviation no higher than 10% in the concentration range 0.1–1 μg mL–1. The online monitoring by this scheme provides the possibility of up to 360 analyses per hour.
Keywords: Photothermal lensing, thermal-lens microscopic detection, microfluidic applications, μFIA, hexavalent chromium, diphenylcarbazide
Published in RUNG: 12.12.2016; Views: 3942; Downloads: 0
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Thermal lens microscopy : characterization and optimization
Mingqiang Liu, Mladen Franko, 2014, published scientific conference contribution

Keywords: mikroskopija, TLS, karakterizacija, optimizacija
Published in RUNG: 16.06.2016; Views: 4195; Downloads: 143
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Microfluidic flow injection thermal lens microscopy for high throughput and sensitive analysis of sub-μL samples
Mingqiang Liu, Sara Malovrh, Mladen Franko, 2016, original scientific article

Abstract: An analytical method combining microfluidic flow injection analysis (μFIA) with thermal lens microscopy (TLM) was developed for high throughput and sensitive analysis of sub-μL samples. Performance of the μFIA-TLM was validated for detection of hexavalent chromium [Cr(VI)] in water samples. At different sample injection volumes, detection positions and flow rates, influences of the reaction time and the diffusion of Cr-diphenylcarbazone (DPCO) complexes on the μFIA-TLM signal were investigated. Photodegradation of the Cr-DPCO complex was clearly observed when the absorbed photons per Cr-DPCO is above 1600. After optimization of the TLM with respect to rapid flows (up to 10 cm/s), we achieved a limit of detection of 0.6 ng/mL for Cr(VI) in a 50-μm deep channel. Impacts of interfering ions [V(V), Mo(VI), Fe(III)] on the Cr(VI) determination were found to be small. Cr(VI) in real samples from a cement factory were determined and found in good agreement with results of spectrophotometry. This μFIA-TLM shows advantages over its conventional counterpart, such as eliminating additional sample conditioning, reducing over 100 times the sample consumption to sub-μL and over 10 times the time required for one sample injection to a few seconds (up to 20 samples/min). The optimized μFIA-TLM setup can be applied for fast and sensitive analysis of nonfluoresent sub-μL samples in rapidly flowing mediums.
Keywords: Spektrometrija TLS, mikroskopija TLM, mikrofluidika, krom (VI)
Published in RUNG: 01.06.2016; Views: 4651; Downloads: 263
.pdf Full text (828,33 KB)

Thermal Lens Spectrometry: Still a Technique on the Horizon
Mingqiang Liu, Mladen Franko, 2016, published scientific conference contribution

Abstract: In this article the historical development of thermal lens spectrometry (TLS) is briefly reviewed for introduction. In continuation, the emphasis is on the recent progresses of TLS for measurements in ensembled sample cells and in microfluidic flow injection systems. Novel theories, instrumentations and their applications for high sample throughput environmental, chemical and biomedical analysis, particularly in micro space, are presented. Discussions are given on the limitations of present TLS systems, that open new horizons for future progress of this technique, which has already found place among routine techniques for chemical analysis. In the last part, proposals for the future development of TLS toward advanced applications in new research fields are presented.
Keywords: Thermal lens spectrometry, Microfluidic chip, Chemical analysis, Environmental monitoring, Biomedical assay
Published in RUNG: 17.05.2016; Views: 4408; Downloads: 0
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Development of a new microchip based ELISA platform for detection of NGAL : a biomarker of contrast-induced acute kidney injury
Mingqiang Liu, Mladen Franko, Tatjana Radovanović, 2014, published scientific conference contribution abstract

Keywords: ELISA, NGAL, TLM
Published in RUNG: 22.01.2015; Views: 5008; Downloads: 58
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