Recent Progress and Applications of Thermal Lens Spectrometry and Photothermal Beam Deflection Techniques in Environmental Sensing.

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.

Synthesis and Characterization of MWCNT-COOH/Fe3O4 and CNT-COOH/Fe3O4/NiO Nanocomposites: Assessment of Adsorption and Photocatalytic Performance.

In this study the adsorption and photodegradation capabilities of modified multi-walled carbon nanotubes (MWCNTs), using tartrazine as a model pollutant, is demonstrated. MWCNT-COOH/Fe3O4 and MWCNT-COOH/Fe3O4/NiO nanocomposites were prepared by precipitation of metal oxides in the presence of MWCNTs. Their properties were examined by X-ray diffraction in powder (XRD), Fourier-transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), Raman spectroscopy, synchrotron-based Scanning PhotoElectron Microscopy (SPEM), and Brunauer-Emmett-Teller (BET) analysis. It was found that the optimal adsorption conditions were pH 4 for MWCNT-COOH/Fe3O4 and pH 3 for MWCNT-COOH/Fe3O4/NiO, temperature 25 °C, adsorbent dose 1 g L-1, initial concentration of tartrazine 5 mg L-1 for MWCNT-COOH/Fe3O4 and 10 mg L-1 for MWCNT-COOH/Fe3O4/NiO and contact time 5 min for MWCNT-COOH/Fe3O4/NiO and 15 min for MWCNT-COOH/Fe3O4. Moreover, the predominant degradation process was elucidated simultaneously, with and without simulated sunlight irradiation, using thermal lens spectrometry (TLS) and UV-Vis absorption spectrophotometry. The results indicated the prevalence of the photodegradation mechanism over adsorption from the beginning of the degradation process.

Through-Plane and In-Plane Thermal Diffusivity Determination of Graphene Nanoplatelets by Photothermal Beam Deflection Spectrometry.

In this work, in-plane and through-plane thermal diffusivities and conductivities of a freestanding sheet of graphene nanoplatelets are determined using photothermal beam deflection spectrometry. Two experimental methods were employed in order to observe the effect of load pressures on the thermal diffusivity and conductivity of the materials. The in-plane thermal diffusivity was determined by the use of a slope method supported by a new theoretical model, whereas the through-plane thermal diffusivity was determined by a frequency scan method in which the obtained data were processed with a specifically developed least-squares data processing algorithm. On the basis of the determined values, the in-plane and through-plane thermal conductivities and their dependences on the values of thermal diffusivity were found. The results show a significant difference in the character of thermal parameter dependence between the two methods. In the case of the in-plane configuration of the experimental setup, the thermal conductivity decreases with the increase in thermal diffusivity, whereas with the through-plane variant, the thermal conductivity increases with an increase in thermal diffusivity for the whole range of the loading pressure used. This behavior is due to the dependence of heat propagation on changes introduced in the graphene nano-platelets structure by compression.

Nanobody-Dependent Detection of Microcystis aeruginosa by ELISA and Thermal Lens Spectrometry.

Nanobodies against cell surface antigens of toxic cyanobacteria Microcystis aeruginosa were recovered by whole-cell biopanning of a naïve phage display library of nanobodies. Six unique sequences were identified and three sub-cloned and purified as fusion immunoreagents together with either green fluorescent protein or AviTag to be used for diagnostics. The yields of nanobody constructs were in the range of 5-10 mg/l and their specificity and sensitivity was initially evaluated by immunofluorescence and by fluorescent enzyme-linked immunosorbent assay (ELISA) using fluorescent nanobodies. The ELISA data confirmed the nanobody specificity but showed that the saturation of the fluorescence signal already in the presence of few hundreds of cells limited the dynamic range of the method. As an alternative, Avi-tagged nanobodies were used in combination with streptavidin-linked horseradish peroxidase for developing a diagnostic colorimetric cell ELISA, the limit-of-detection of which was 3.2 and 4.5 cells/ml for the two tested cyanobacteria strains, whereas the linear range of the assay was expanded from 10 to 10,000 cells. The fluorescent nanobodies were finally exploited for quantifying cyanobacteria by thermal lens spectrometry (TLS) that enabled to reach a limit-of-detection of 1.2 cells/ml and provided a linear range of measurement between 0 and 10,000 cells. No cross-reactivity with unrelated microalgae was detected and both colorimetric ELISA and TLS provided a linear range of detection of few logs. The data indicate that nanobodies are suitable capture reagents and that both TLS and colorimetric ELISA are reliable to monitor variations of cyanobacteria populations.

Determination of Dissolved Iron Redox Species in Freshwater Sediment using DGT Technique Coupled to BDS.

In this work we have developed a novel method for determination of iron redox species by the use of diffusive gradients in thin-film (DGT) technique coupled to photothermal beam deflection spectroscopy (BDS). The combination of both methods achieved low limit of detection (LOD) of 0.14 µM for Fe (II) ions. The total Fe concentration determined in the Vrtojbica river sediment (Slovenia, Rozna Dolina, 5000 Nova Gorica) was 49.3 µgL-1. The Fe (II) and Fe (III) concentration amounted to 12.8 µgL-1 and 39.9 µgL-1, respectively. Such an approach opens new opportunities for monitoring the content of iron species in natural waters and sediments and provides highly sensitive chemical analysis and an accurate qualitative and quantitative characteristic of the materials under study.