Session Overview |
Tuesday, July 19 |
13:45 |
Single molecule and single particle manipulation with plasmonic thermofluidics
Fränzl Tobias, Leipzig University, Germany Tobias Thalheim, Leipzig University, Germany Desmond Quinn, Leipzig University, Germany * Frank Cichos, Leipzig University, Germany The manipulation of nano-objects at the microscale is of great technological significance to construct new functional materials, to manipulate tiny amounts of liquids, to reconfigure sensorial systems or to detect minute concentrations of analytes in medical screening. It is commonly approached by the generation of potential energy landscapes, for example, with optical fields or by using pressure driven microfluidics. We show that strong hydrodynamic boundary flows enable the trapping and manipulation of nano-objects near surfaces. These thermo-osmotic flows are induced by modulating the van der Waals interaction at a solid-liquid interface with optically generated temperature fields. Heat generation is provided by thin gold films or metallic nanostructures on a glass substrate, which enable localized but reconfigurable point optical heating. Convergent boundary flows with velocities of tens of micrometres per second are observed and substantiated by a quantitative physical model. We further show that these thermo-osmotic flows can be complemented with other thermally induced effects such as thermo-viscous and thermally induced depletion effects. Our findings have direct consequences for the field of plasmonic nano-tweezers as well as other thermo-plasmonic trapping schemes and pave the way for a general scheme of nanoscopic fluidic manipulation with thermally induced boundary flows |
14:00 |
Synthesis of hybrid Nanoparticles to target and sort Extracellular Vesicles as a diagnostic tool
* Mélanie Romain, ICB laboratory, France Daniel Guneysu, Femto-ST Institute, France Wilfrid Boireau, Femto-ST Institute, France Nadine Millot, ICB laboratory, France Extracellular vesicles (EVs) present a growing field of interest due to their ability for biological content transport during intercellular communication and their noteworthy release in biofluids, making them promising biomakers for diagnosis or therapeutic follow-up. However, it is very difficult to specifically target, isolate or characterize them because their circulation happens in complex samples (blood and other biological media) containing all subclass of EVs released continuously from different tissue/fluid cells. There, sub-populations of interests are minor and difficult to reach. This project aims to separate EVs sub-populations thanks to an acoustofluidic device combining microfluidic and electroacoustic modules capable of efficiently aligning and sorting submicron biological particles based on physico-chemical properties [1]. In order to refine sorting of the isolated sub-populations, targeted EVs will be spiked by hybrid nanoparticles (NPs), thus also facilitating EVs characterization. Gold nanoparticles are used for this purpose, and functionalized depending on the biomarkers of interests. A first linker grafting step is carried out with different mercapto alkyl carboxylic acids, leading to stable suspensions. Studies with UV-Visible spectroscopy and SPR assays enable to define the optimum grafting conditions for this step [2]. The next step of covalent conjugation of recognition biomolecules is carried out with different proteins: cytochrome C chosen to define grafting conditions on the NPs, and then various antibodies as anti-tetraspanins chosen to selectively target some EVs. RAMAN, UV-Visible and X-Ray photoelectron spectroscopies, DLS and zeta potential measurement, combined with SPR assays and TEM observations highlight the grafting of additional layers and maintained stability at each step of the synthesis. Then preliminary tests to study selective attachment in a complex media of the hybrid NPs to polymer microparticules, used as model EVs and functionalized with albumin or casein, show encouraging results as shown by UV-Vis spectroscopy and DLS. Further characterizations like AFM and TEM are required to confirm good selectivity of the targeting of NPs to targeted EVs. Future work should focus on targeting constitutive membrane proteins like tetraspanins on EVs from cells, before studying the targeting of pathology biomarkers like HSP70 or PDL1 on human EVs samples. 1. Chaalane, A., et al., Tunable Separation of Nanoparticles in a Continuous Flow Using Standing Surface Acoustic Wave. Sensors & Transducers Journal, 2019. 238(11): p. 72 - 79. 2. Dileseigres, A.S., Y. Prado, and O. Pluchery, How to Use Localized Surface Plasmon for Monitoring the Adsorption of Thiol Molecules on Gold Nanoparticles? Nanomaterials, 2022. 12(2). |
14:15 |
Exploiting the Interaction Between Live Escherichia coli and Citrate Au Nanoparticles to Form a Label-free Diagnostic Test for Bacterial Contamination
9. Biomedical applications of gold: sensors and devices * Camilla Gazzana, University of Technology Sydney, Australia Stella Valenzuela, University of Technology Sydney, Australia Andrew McDonagh, University of Technology Sydney, Australia Michael Cortie, University of Technology Sydney, Australia There is a continuing need for simple and cheap diagnostic kits for detection of bacterial contamination, for example in food or water. The objective of the present work is to demonstrate a simple label-free method of detection that is sensitive to E. coli, a common gram-negative pathogen. The technique used exploits the growth of live E.coli in a medium that also contains 24 nm diameter gold nanoparticles, and the results are read by visible light spectroscopy. Initially the Au colloid exhibits only the well-known single particle plasmon peak at about 530 nm, but addition of bacterial growth medium causes an agglomeration of the Au nanoparticles and the development of a broad second plasmon resonance peak at ~780 nm. Importantly, however, as the bacteria multiply in the mixture of Au colloid and growth medium, the height of the 780 nm peak is diminished at a rate that is in proportion to the original number of colony forming units (CFU) in the analyte. An overnight incubation of the sensor boosts the response by a factor of seven and would probably be required in any commercial application. The change in optical properties is clearly due to the live bacteria causing the agglomerated gold nanoparticles to aggregate and settle out. The mechanism must involve destruction of the stabilizing ligands on the Au nanoparticles, possibly via ingestion by, or secretions from, the live bacteria. This phenomenon, combined with the strong optical absorption of Au nanoparticle agglomerates, provides a sensing platform that can reliably detect live E.coli between 102 and 106 CFU/mL. The decay in the plasmon peak does not provide a useful signal for samples containing more than 106 CFU/mL but, in the range 106 to 108 CFU/mL, the overall attenuance of the suspension at 450 nm provides a complementary measure of bacterial concentration. When the two parameters (peak height and attenuance) are processed in combination, they provide a sensor that works between 102 to 108 CFU/mL of initial bacteria. A series of comparative tests showed that the technique works only for live E.coli and that dead E.coli do not trigger the response of the sensor, even if incubated overnight with the gold nanoparticles. The mechanism of this sensor is unusual since it depends both upon the manner in which live E.coli perturb the aggregation of the Au nanoparticles, and on the in situ multiplication of the live E.coli during the assay. The application of the technique to bacterial food pathogens besides E. coli remains an open question, however, and further exploration of both the mechanism and the range of species to which it applies could be worthwhile. In conclusion, the analysis described can be readily carried out on site for E.coli using relatively inexpensive materials and a low cost visible-light spectrometer. The method is both relatively sensitive and robust, and has the added advantage of only responding to live bacteria. |