11. Applications of Thermal Lens Microscopy in Microfluidic SystemsMladen Franko, 2016, published scientific conference contribution abstract (invited lecture) Abstract: Detection in microfluidic systems requires highly sensitive analytical methods, because of the very short optical interaction length, which is usually in the range of 100 μm or shorter. Furthermore, the amounts of analytes in detection volumes are extremely small (femto- or attomoles). Thermal lens spectrometry and particularly thermal lens microscopy (TLM) appear as techniques of choice for detection in microfluidic and lab-on-a-chip systems, since they enable measurements of absorbance’s or absorbance changes as low as 10-7. In addition to ultra-high sensitivity, TLM offers high spatial resolution (≈1 μm) and sufficient temporal resolution (ms range), which is required for studies of processes in microfluidic systems.
Recent development of TLM theory and instrumentation lead to experimental confirmations of the effects of microfluidic flows on the TLM signal, which affects the sensitivity. On the other hand, these observations have enabled optimization of TLM instruments [1]. As a result of these advancements, applications of TLM were extended from simple laminar flows [2], to highly complex systems such as Tylor-type flows, where TLM detection provided data for description of diffusion processes in n-octane/methanol binary liquid systems [3]. The major streamline of TLM applications was however focused on the development of vanguard analytical systems [4], which are needed in various fields of chemical analysis, including food safety and quality control, environmental monitoring as well as biomedical research and diagnostics. Such systems are used as sample screening systems (sample filters or selectors) when the information is needed quickly to make immediate decisions in relation to the analytical problem. They provide simplicity (e.g. little or no sample pre-treatment), low cost, rapid and reliable response, and frequently give just binary responses. However, their major weakness is low metrological quality of results. Therefore, uncertainties of up to 5–15% are usually accepted as a toll for rapidity and simplicity, which are essential even though in contradiction with conventional analytical concepts. With the objective of developing new vanguard analytical systems, a relevant goal is to exploit the advantages offered by microfluidic lab-on-a-chip systems on one hand, and TLM detection on the other. In such combinations, the FIA approach simplifies sample handling (e.g. volume measurements) and transport to the detector, while microfluidic lab-on-a-chip technology can facilitate and speed up processes including colorimetric reactions, antigen–antibody or enzyme–substrate interactions in bioanalytical systems, and even extraction and preconcentration steps by introducing continuous flow processing and micro unit operations in chemical analysis [2]. High sensitivity of TLM in such systems offers low limits of detection, which also contribute to low uncertainties that are typically below 10%. An important advantage of microfluidic systems lies in the fact that small dimensions of such systems, which consist of capillaries and micro reactors with dimensions about 10 to 100 μm, significantly reduce the molecular diffusion time, which is inversely proportional to the second power of distance. For example, the time required for completion of an ELISA immunoassay for NGAL a biomarker of acute kidney failure was reduced from four hours to only 30 mins. [5, 6] when transferring the assay into a microfluidic system, while maintaining or even improving the sensitivity. Even more evident improvement in sample throughput (reduction of analysis time from 10 hours to 30 minutes) was achieved for determination of antibodies for human papilloma virus (anti L1 HPV 16) in blood plasma, after immobilizing adequate pseudovirions as antigens on magnetic nanobeads [6]. Other health-related applications include detection of toxins, such as microcystin, or carcinogenic substances such as Cr(VI), which offers improved limits of detection as compared to spectrophotometry as well as sample throughput, which can reach 20 samples/min. [7].
[1] M. Liu and M. Franko, Crit. Rev. Anal. Chem. 44, 328-353 (2014).
[2] T. Kitamori, M. Tokeshi, A. Hibara, and K. Sato, Anal. Chem. 76, 52A-60A (2004).
[3] M. Lubej, U. Novak, M. Liu, M. Martelanc, M. Franko and I. Plazl, Lab Chip (2015) DOI:10.1039/c4lc01460j.
[4] M. Valcárcel and B. Lendl. Trends Anal. Chem. 23, 527-534 (2004).
[5] T. Radovanović, M. Liu, P. Likar, M. Klemenc and M. Franko, Int. J. Thermophys. (2014) DOI:10.1007/s10765-014-1699-9.
[6] T. Radovanović, Dissertation, University of Nova Gorica (2016).
[7] M. Franko, M. Liu, A. Boškin, A. Delneri, and M.A. Proskurnin, Anal. Sci. 32, 23-30 (2016).
Keywords: Spektrometrija TLM, mikrofluidni sistemi, biomarkerji, alergeni, pesticidi, acetilholinesteraza
Published in RUNG: 07.11.2016; Views: 6922; Downloads: 45
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12. Optimized frequency dependent photothermal beam deflection spectroscopyMladen Franko, Dorota Korte, Humberto Cabrera, 2016, original scientific article Abstract: In the paper the optimization of the experimental setup for photothermal beam deflection spectrometry is performed by analyzing the influence of its geometrical parameters (detector and sample position, probe beam radius and its waist position etc) on the detected signal. Furthermore,
the effects of fluid’s thermo-optical properties, for optimized geometrical configuration, on the
measurement sensitivity and uncertainty determination of sample thermal properties is also studied.
The examined sample is a recently developed CuFeInTe3 material. Results show, that it is a complex problem to choose the proper geometrical configuration as well as
sensing fluid to enhance the sensitivity of the method. A signal enhancement is observed at low modulation frequencies by placing the sample in acetonitrile (ACN), while at high modulation frequencies the sensitivity is higher for measurements made in air. For both, detection in air and
acetonitrile the determination of CuFeInTe3 thermal properties is performed. The determined values of thermal diffusivity and thermal conductivity are (0.048 ± 0.002) × 10−4 m2 s−1 and 4.6 ± 0.2 W m−1 K−1 and (0.056 ± 0.005) × 10−4 m2 s−1 and 4.8 ± 0.4 W m−1 K−1 for ACN and air,
respectively. It is seen, that the determined values agree well within the range of their measurement uncertainties for both cases, although the measurement uncertainty is two times lower for the measurements in ACN providing more accurate results. The analysis is performed by the use of
recently developed theoretical description based on the complex geometrical optics. It is also shown, how the presented work fits into the current status of photothermal beam deflection spectroscopy.
Keywords: Optitermi, na spektrometrija, toplotna difuzivnost, toplotna prevodnost, polprevodniki, vpliv topila
Published in RUNG: 07.11.2016; Views: 6301; Downloads: 0
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13. Identifikacija, porazdelitev in vezavne oblike železa v rižu (Oryza sativa L.) z rentgensko absorpcijsko in emisijsko mikro-spektroskopijoBojan Šuc, 2016, undergraduate thesis Abstract: V diplomskem delu smo raziskali vezavne oblike železa v različnih delih korenin riža s kombinacijo rentgenske absorpcijske spektroskopije in mikroskopije z metodo mikro-XANES. S tem smo želeli izboljšati razumevanje vnosa železovih spojin v rastline riža (Oryza sativa L.) na tkivnem nivoju. Rastline riža so bile vzgojene v hidroponskem sistemu z dodanim železom Fe2+ (kot FeSO4). Spektri mikro-XANES na absorpcijskem robu K železa so bili pomerjeni na prečnih rezinah korenin, zamrznjenih v tekočem dušiku, na žarkovni liniji ID21 sinhrotrona ESRF v Grenoblu v fluorescenčnem načinu. Pri analizi spektrov mikro-XANES smo preučili uporabnost metode linearnega kombiniranja referenčnih spektrov XANES železa izmerjenih na nizu referenčnih dvo- in trivalentnih železovih spojin. Rezultati so pokazali, da je možno s to metodo v rastlinskih vzorcih jasno ločiti med dvo- in trivalentnimi železovimi kompleksi in določiti njihov delež z natančnostjo ±1%. Prevladujoča valenca železa v vzorcih korenin je Fe3+. Prepoznavanje in razločevanje različnih železovih kompleksov je manj natančno. Natančnost pri določanju deleža različnih trivalentnih železovih kompleksov je med 10% in 30%. Nekaterih železovih kompleksov s to metodo ni mogoče razločiti med sabo, ker se njihovi spektri XANES premalo razlikujejo. Kot najpogostejše železove komplekse v koreninah riža smo prepoznali Fe2+-fitat med dvovalentnimi spojinami, med trivalentnimi pa: železov oksid/hidroxid Goethit α-FeOOH Fe3+-citrat in Fe3+-fitat. Na natančnost pri razločevanju železovih spojin znatno vplivajo statistični šum in sistematske napake v izmerjenih spektrih mikro-XANES. Rezultati razmerij med dvo- in trivalentnimi železovimi kompleksi v različnih delih korenin kažejo, da se rastline riža zaščitijo pred strupenim toksičnim dvovalentnim železom tako, da ga oksidirajo in tvorijo tako imenovani plak, oziroma oborino, s čimer omejijo vnos dvovalentnega železa.
Keywords: Rentgenska absorpcijska spektrometrija, riž, železo, mikro-XANES, metoda linearnega kombiniranja referenčnih spektrov
Published in RUNG: 06.09.2016; Views: 9718; Downloads: 255
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15. Microfluidic flow injection thermal lens microscopy for high throughput and sensitive analysis of sub-μL samplesMingqiang 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: 6516; Downloads: 277
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16. Oxidation as a pre-step in determination of organophosphorus compounds by the AChe-TLS bioassayMojca Bavcon Kralj, Polonca Trebše, Mladen Franko, 2006, original scientific article Keywords: analizna kemija, analitska kemija, bioanalitske tehnike, organofosfatni pesticidi, oksidacija, učinkovitost kemijske oksidacije, kemijska analiza, plinska kromatografija na masno detekcijo, GC-MS, spektrometrija na osnovi termičnih leč, AChE-TLS, NBS
Published in RUNG: 15.10.2013; Views: 7954; Downloads: 35
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