| 1. |
- Cavallaro, Sara, et al.
(author)
-
Comparison and optimization of nanoscale extracellular vesicle imaging by scanning electron microscopy for accurate size-based profiling and morphological analysis
- 2021
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In: Nanoscale Advances. - : Royal Society of Chemistry. - 2516-0230. ; 3:11, s. 3053-3063
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Journal article (peer-reviewed)abstract
- Nanosized extracellular vesicles (EVs) have been found to play a key role in intercellular communication, offering opportunities for both disease diagnostics and therapeutics. However, lying below the diffraction limit and also being highly heterogeneous in their size, morphology and abundance, these vesicles pose significant challenges for physical characterization. Here, we present a direct visual approach for their accurate morphological and size-based profiling by using scanning electron microscopy (SEM). To achieve that, we methodically examined various process steps and developed a protocol to improve the throughput, conformity and image quality while preserving the shape of EVs. The study was performed with small EVs (sEVs) isolated from a non-small-cell lung cancer (NSCLC) cell line as well as from human serum, and the results were compared with those obtained from nanoparticle tracking analysis (NTA). While the comparison of the sEV size distributions showed good agreement between the two methods for large sEVs (diameter > 70 nm), the microscopy based approach showed a better capacity for analyses of smaller vesicles, with higher sEV counts compared to NTA. In addition, we demonstrated the possibility of identifying non-EV particles based on size and morphological features. The study also showed process steps that can generate artifacts bearing resemblance with sEVs. The results therefore present a simple way to use a widely available microscopy tool for accurate and high throughput physical characterization of EVs.
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| 2. |
- Cavallaro, Sara, 1992-
(author)
-
Development of Techniques for Characterization, Detection and Protein Profiling of Extracellular Vesicles
- 2021
-
Doctoral thesis (other academic/artistic)abstract
- Nanosized extracellular vesicles (EVs, ∼30-2000 nm) have emerged as important mediators of intercellular communication, offering opportunities for both diagnostics and therapeutics. In particular, small EVs generated from the endolysosomal pathway (∼30-150 nm), referred to as exosomes, have attracted interest as a suitable biomarker for cancer diagnostics and treatment monitoring based on minimally invasive liquid biopsies. This is because exosomes carry valuable biological information (proteins, lipids, genetic material, etc.) reflecting their cells of origin. Using EVs as biomarkers or drug delivery agents in clinical applications requires a full understanding of their cellular origin, functions, and biological relevance. However, due to their small size and very high heterogeneity in molecular and physical features, the analysis of these vesicles is challenged by the limited detection ranges and/or accuracy of the currently available techniques. To overcome some of these challenges, this thesis focuses on developing different techniques for characterization, detection and protein profiling of EVs at both bulk and single particle levels. Specifically, the three methods investigated are scanning electron microscopy, electrokinetic sensing, and combined fluorescence - atomic force microscopy. First, a protocol for scanning electron microscopy imaging of EVs was optimized to improve the throughput and image quality of the method while preserving the shape of the vesicles. Application of the developed protocol for analysis of EVs from human serum showed the possibility to use scanning electron microscopy for morphological analysis and high-resolution size-based profiling of EVs over their entire size range. Comparison with nanoparticle tracking analysis, a commonly used technique for EV size estimation, showed a superior sensitivity of scanning electron microscopy for particles smaller than 70-80 nm. Moreover, the study showed process steps that can generate artifacts resembling sEVs and ways to minimize them. Secondly, a novel label-free electrokinetic sensor based on streaming current was developed, optimized and multiplexed for EV protein analysis at a bulk level. Using multiple microcapillary sensors functionalized with antibodies, the method showed the capacity for multiplexed detection of different surface markers on small EVs from non-small-cell lung cancer cells. The device performance in the multichannel configuration remained similar to the single-channel one in terms of noise, detection sensitivity, and reproducibility. The application of the technique for analysis of EVs isolated from lung cancer patients with different genomic alterations and after different applied treatments demonstrated the prospect of using EVs from liquid biopsies as a source of biomarker for cancer monitoring. Moreover, the results held promise for the application of the developed method in clinical settings. Finally, to increase the understanding of EV subpopulations and heterogeneity, a platform combining fluorescence and atomic force microscopy was developed for multiparametric analysis of EVs at a single particle level. The use of a precise spot identification approach and an efficient vesicle capture protocol allowed to study and correlate for the first time the membrane protein composition, size and mechanical properties (Young modulus) on individual small EVs. The application of the technique to vesicles isolated from different cell lines identified both common and cell line-specific EV subpopulations bearing distinct distributions of the analyzed parameters. For example, a sEV population co-expressing all the three analyzed proteins in relatively high abundance, yet having average diameters of <100 nm and relatively low Young moduli was found in all cell lines. The obtained results highlighted the possibility of using the developed platform to help decipher unsolved questions regarding EV biology.
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| 3. |
- Cavallaro, Sara, et al.
(author)
-
Multiparametric Profiling of Single Nanoscale Extracellular Vesicles by Combined Atomic Force and Fluorescence Microscopy : Correlation and Heterogeneity in Their Molecular and Biophysical Features
- 2021
-
In: Small. - : Wiley. - 1613-6810 .- 1613-6829. ; 17:14
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Journal article (peer-reviewed)abstract
- Being a key player in intercellular communications, nanoscale extracellular vesicles (EVs) offer unique opportunities for both diagnostics and therapeutics. However, their cellular origin and functional identity remain elusive due to the high heterogeneity in their molecular and physical features. Here, for the first time, multiple EV parameters involving membrane protein composition, size and mechanical properties on single small EVs (sEVs) are simultaneously studied by combined fluorescence and atomic force microscopy. Furthermore, their correlation and heterogeneity in different cellular sources are investigated. The study, performed on sEVs derived from human embryonic kidney 293, cord blood mesenchymal stromal and human acute monocytic leukemia cell lines, identifies both common and cell line-specific sEV subpopulations bearing distinct distributions of the common tetraspanins (CD9, CD63, and CD81) and biophysical properties. Although the tetraspanin abundances of individual sEVs are independent of their sizes, the expression levels of CD9 and CD63 are strongly correlated. A sEV population co-expressing all the three tetraspanins in relatively high abundance, however, having average diameters of <100 nm and relatively low Young moduli, is also found in all cell lines. Such a multiparametric approach is expected to provide new insights regarding EV biology and functions, potentially deciphering unsolved questions in this field.
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| 4. |
- Cavallaro, Sara, et al.
(author)
-
Multiplexed electrokinetic sensor for detection and therapy monitoring of extracellular vesicles from liquid biopsies of non-small-cell lung cancer patients
- 2021
-
In: Biosensors & bioelectronics. - : Elsevier. - 0956-5663 .- 1873-4235. ; 193
-
Journal article (peer-reviewed)abstract
- Liquid biopsies based on extracellular vesicles (EVs) represent a promising tool for treatment monitoring of tumors, including non-small-cell lung cancers (NSCLC). In this study, we report on a multiplexed electrokinetic sensor for surface protein profiling of EVs from clinical samples. The method detects the difference in the streaming current generated by EV binding to the surface of a functionalized microcapillary, thereby estimating the expression level of a marker. Using multiple microchannels functionalized with different antibodies in a parallel fluidic connection, we first demonstrate the capacity for simultaneous detection of multiple surface markers in small EVs (sEVs) from NSCLC cells. To investigate the prospects of liquid biopsies based on EVs, we then apply the method to profile sEVs isolated from the pleural effusion (PE) fluids of five NSCLC patients with different genomic alterations (ALK, KRAS or EGFR) and applied treatments (chemotherapy, EGFR- or ALKtyrosine kinase inhibitors). The vesicles were targeted against CD9, as well as EGFR and PD-L1, two treatment targets in NSCLC. The electrokinetic signals show detection of these markers on sEVs, highlighting distinct interpatient differences, e.g., increased EGFR levels in sEVs from a patient with EGFR mutation as compared to an ALK-fusion one. The sensors also detect differences in PD-L1 expressions. The analysis of sEVs from a patient prior and post ALK-TKI crizotinib treatment reveals significant increases in the expressions of some markers (EGFR and PD-L1). These results hold promise for the application of the method for tumor treatment monitoring based on sEVs from patient liquid biopsies.
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| 5. |
- Chung, Nguyen Xuan, et al.
(author)
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Optimized electrochemical breakdown etching using temporal voltage variation for formation of nanopores in a silicon membrane
- 2021
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In: Sensors and actuators. B, Chemical. - : Elsevier BV. - 0925-4005 .- 1873-3077. ; 331
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Journal article (peer-reviewed)abstract
- Dielectric breakdown etching is a well-known method of making nanopores on thin (similar to 50 nm) dielectric membranes. However, voltage driven translocation of biomolecules through such nanopores becomes extremely fast. For improved detection, for instance by the current blockage, a high-aspect-ratio nanopore could be beneficial for slowing down the translocation. High-aspect-ratio nanopore on silicon fabrication requires a well-controlled process and is dependent on specific crystal orientation, dopant type and resistivity of substrate. Therefore, an optimized method of processing high-aspect-ratio nanopores is necessary considering the advantage of a silicon membrane being able to be integrated with standard CMOS processing. Here, we present an optimized fabrication method for mass-producing a single and an array of nanopores on a thick (2 mu m) silicon device layer based on a silicon-on-insulator (SOI) wafer. A method of temporal voltage variation is exploited to optimize the etching parameters for the nanopore formation during electrochemical breakdown etching, diameters of nanopores around 12 nm have been achieved. Besides, the correlation between the parameters of etching and nanopore diameter is deduced. The processed high-aspect-ratio nanopore enables applications in single-molecule sensing such as DNA, exosomes, viruses, and protein markers. The developed process is inexpensive, fast and can be batch fabricated.
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| 6. |
- Ciobanu, V., et al.
(author)
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Large-Sized Nanocrystalline Ultrathin β-Ga2 O3 Membranes Fabricated by Surface Charge Lithography
- 2022
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In: Nanomaterials. - : MDPI AG. - 2079-4991. ; 12:4
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Journal article (peer-reviewed)abstract
- Large-sized 2D semiconductor materials have gained significant attention for their fascinat-ing properties in various applications. In this work, we demonstrate the fabrication of nanoperforated ultrathin β-Ga2 O3 membranes of a nanoscale thickness. The technological route includes the fabrication of GaN membranes using the Surface Charge Lithography (SCL) approach and subsequent thermal treatment in air at 900◦ C in order to obtain β-Ga2 O3 membranes. The as-grown GaN membranes were discovered to be completely transformed into β-Ga2 O3, with the morphology evolving from a smooth topography to a nanoperforated surface consisting of nanograin structures. The oxidation mechanism of the membrane was investigated under different annealing conditions followed by XPS, AFM, Raman and TEM analyses.
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| 7. |
- Fucikova, Anna, et al.
(author)
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The shell matters : one step synthesis of core-shell silicon nanoparticles with room temperature ultranarrow emission linewidth
- 2020
-
In: Faraday discussions. - : Royal Society of Chemistry (RSC). - 1359-6640 .- 1364-5498. ; 222:0, s. 135-148
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Journal article (peer-reviewed)abstract
- Here we present a one-step synthesis that provides silicon nanocrystals with a thin shell composed of a ceramic-like carbonyl based compound, embedded in a porous organosilicon film. The silicon nanocrystals were synthesised from hydrogen silsesquioxane molecules, modified with organic molecules containing carbonyl groups, which were annealed at 1000 degrees C in a slightly reducing 5% H-2 : 95% Ar atmosphere. The organic character of the shell was preserved after annealing due to trapping of organic molecules inside the HSQ-derived oxide matrix that forms during the annealing. The individual silicon nanocrystals, studied by single dot spectroscopy, exhibited a significantly narrower emission peak at room temperature (lowest linewidth similar to 17 meV) compared to silicon nanocrystals embedded in a silicon oxide shell (150 meV). Their emission linewidths are even significantly narrower than those of single CdSe quantum dots (>50 meV). It is hypothesized that the Si-core-thin shell structure of the nanoparticle is responsible for the unique optical properties. Its formation within one synthesis step opens new opportunities for silicon-based quantum dots. The luminescence from the produced nanocrystals covers a broad spectral range from 530-720 nm (1.7-2.3 eV) suggesting strong application potential for solar cells and LEDs, following the development of a suitable mass-fabrication protocol.
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| 8. |
- Gatty, Hithesh K., et al.
(author)
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Microfabricated Biosensor for Detection of Disease Biomarkers Based on Streaming Current Method
- 2023
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In: Intelligent Control, Robotics, and Industrial Automation - Proceedings of International Conference, RCAAI 2022. - : Springer Nature. ; , s. 715-723
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Conference paper (peer-reviewed)abstract
- A microfabricated biosensor based on the streaming current method is presented in this work. The microfabricated sensor consists of a silicon microchannel, which is enclosed with a glass capping to form a closed microchannel. The depth of the microchannel is approximately 10 µm in width and length varying from 50 to 100 µm. The silicon is etched using deep reactive ion etching (DRIE) to form a microchannel. For the capping of the channel, a glass wafer of type Borofloat is used and anodically bonded to the silicon wafer to form a closed microchannel. The microchannel is then functionalized to be specific to certain biomarkers which can be a potential biomarker for cancer, for example. The method used for detection is called the streaming current method. In this method, fluid is flown through the microchannel with high pressure close to six bars. The surface of the silicon is oxidized, which has a zeta potential of approximately 2.7. Depending on the type of fluid the charge concentration varies. By having a pressure in the channel, the charges get distributed as an anode and cathode at the inlet and outlet electrodes of the microfluidic channels. At a fixed potential, a streaming current is observed, which is proportional to the charge accumulated. The difference between the streaming current with and without the biomarker is correlated to the concentration. Hence, a biosensor based on the streaming current method can be realized, which could be used for potential cancer biomarker detection.
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| 9. |
- Gatty, Hithesh K., et al.
(author)
-
Wafer-level fabrication of individual solid-state nanopores for sensing single DNAs
- 2020
-
In: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 31:35
-
Journal article (peer-reviewed)abstract
- For biomolecule sensing purposes a solid-state nanopore platform based on silicon has certain advantages as compared to nanopores on other substrates such as graphene, silicon nitride, silicon oxide etc Capitalizing on the developed CMOS technology, nanopores on silicon are scalable without any requirement for additional processing, the devices are low cost and the process can be repeatable with a high yield. One of the essential requirements in biomolecule sensing is the ability of the nanopore to interact with the analyte. In this work, we present a method for processing high aspect ratio, single nanopores in the range of 10-30 nm in diameter and approximately 700 nm in length on a silicon-on-insulator (SOI) wafer. The presented method of manufacturing the high aspect ratio individual nanopores combines optical lithography and anisotropic KOH etching with a final electrochemical etching step to form the nanopores and is repeatable and can be processed in batches. We demonstrate electrical detection of dsDNA translocation, where the characteristic time of the process is in the millisecond range. We also analyse the translocation parameters and correlate the enhanced length of the nanopore to a longer translocation time as compared to other substrates.
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| 10. |
- Huang, Jing, 1987-, et al.
(author)
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Large-Area Transparent “Quantum Dot Glass” for Building-Integrated Photovoltaics
- 2022
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In: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 9:7, s. 2499-2509
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Journal article (peer-reviewed)abstract
- A concept of transparent “quantum dot glass”(TQDG) is proposed for a combination of a quantum dot(QD)-based glass luminescent solar concentrator (LSC) and itsedge-attached solar cells, as a type of transparent photovoltaics(TPVs) for building-integrated photovoltaics (BIPVs). Differentfrom conventional LSCs, which typically serve as pure opticaldevices, TQDGs have to fulfill requirements as both powergeneratingcomponents and building construction materials. In thiswork, we demonstrate large-area (400 cm2) TQDGs based onsilicon QDs in a triplex glass configuration. An overall powerconversion efficiency (PCE) of 1.57% was obtained with back-reflection for a transparent TQDG (average visible transmittance of84% with a color rendering index of 88 and a low haze ≤3%), contributing to a light utilization efficiency (LUE) of 1.3%, which isamong the top reported TPVs based on the LSC technology with similar size. Most importantly, these TQDGs are shown to havebetter thermal and sound insulation properties compared to normal float glass, as well as improved mechanical performance andsafety, which significantly pushes the TPV technology toward practical building integration. TQDGs simultaneously exhibit favorablephotovoltaic, aesthetic, and building envelope characteristics and can serve as a multifunctional material for the realization of nearlyzero-energy building concepts.
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| 11. |
- Nestoklon, Mikhail O., et al.
(author)
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Tight-binding calculations of the optical properties of Si nanocrystals in a SiO(2)matrix
- 2020
-
In: Faraday discussions. - : Royal Society of Chemistry (RSC). - 1359-6640 .- 1364-5498. ; 222:0, s. 258-273
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Journal article (peer-reviewed)abstract
- We develop an empirical tight binding approach for the modeling of the electronic states and optical properties of Si nanocrystals embedded in a SiO(2)matrix. To simulate the wide band gap SiO(2)matrix we use the virtual crystal approximation. The tight-binding parameters of the material with the diamond crystal lattice are fitted to the band structure of beta-cristobalite. This model of the SiO(2)matrix allows us to reproduce the band structure of real Si nanocrystals embedded in a SiO(2)matrix. In this model, we compute the absorption spectra of the system. The calculations are in an excellent agreement with experimental data. We find that an important part of the high-energy absorption is defined by the spatially indirect, but direct ink-space transitions between holes inside the nanocrystal and electrons in the matrix.
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| 12. |
- Sahu, Siddharth S., et al.
(author)
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Electrokinetic sandwich assay and DNA mediated charge amplification for enhanced sensitivity and specificity
- 2021
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In: Biosensors & bioelectronics. - : Elsevier BV. - 0956-5663 .- 1873-4235. ; 176
-
Journal article (peer-reviewed)abstract
- An electrical immuno-sandwich assay utilizing an electrokinetic-based streaming current method for signal transduction is proposed. The method records the changes in streaming current, first when a target molecule binds to the capture probes immobilized on the inner surface of a silica micro-capillary, and then when the detection probes interact with the bound target molecules on the surface. The difference in signals in these two steps constitute the response of the assay, which offers better target selectivity and a linear concentration dependent response for a target concentration within the range 0.2-100 nM. The proof of concept is demonstrated by detecting different concentrations of Immunoglobulin G (IgG) in both phosphate buffered saline (PBS) and spiked in E. coli cell lysate. A superior target specificity for the sandwich assay compared to the corresponding direct assay is demonstrated along with a limit of detection of 90 pM in PBS. The prospect of improving the detection sensitivity was theoretically analysed, which indicated that the charge contrast between the target and the detection probe plays a crucial role in determining the signal. This aspect was then experimentally validated by modulating the zeta potential of the detection probe by conjugating negatively charged DNA oligonucleotides. The length of the conjugated DNA was varied from 5 to 30 nucleotides, altering the zeta potential of the detection probe from -9.3 +/- 0.8 mV to -20.1 +/- 0.9 mV. The measurements showed a clear and consistent enhancement of detection signal as a function of DNA lengths. The results presented here conclusively demonstrate the role of electric charge in detection sensitivity as well as the prospect for further improvement. The study therefore is a step forward in developing highly selective and sensitive electrokinetic assays for possible application in clinical investigations.
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| 13. |
- Sahu, Siddharth S., et al.
(author)
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Exploiting Electrostatic Interaction for Highly Sensitive Detection of Tumor-Derived Extracellular Vesicles by an Electrokinetic Sensor
- 2021
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In: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 13:36, s. 42513-42521
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Journal article (peer-reviewed)abstract
- We present an approach to improve the detection sensitivity of a streaming current-based biosensor for membrane protein profiling of small extracellular vesicles (sEVs). The experimental approach, supported by theoretical investigation, exploits electrostatic charge contrast between the sensor surface and target analytes to enhance the detection sensitivity. We first demonstrate the feasibility of the approach using different chemical functionalization schemes to modulate the zeta potential of the sensor surface in a range -16.0 to -32.8 mV. Thereafter, we examine the sensitivity of the sensor surface across this range of zeta potential to determine the optimal functionalization scheme. The limit of detection (LOD) varied by 2 orders of magnitude across this range, reaching a value of 4.9 x 10(6) particles/mL for the best performing surface for CD9. We then used the optimized surface to profile CD9, EGFR, and PD-L1 surface proteins of sEVs derived from non-small cell lung cancer (NSCLC) cell-line H1975, before and after treatment with EGFR tyrosine kinase inhibitors, as well as sEVs derived from pleural effusion fluid of NSCLC adenocarcinoma patients. Our results show the feasibility to monitor CD9, EGFR, and PD-L1 expression on the sEV surface, illustrating a good prospect of the method for clinical application.
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| 14. |
- Sahu, Siddharth Sourabh, et al.
(author)
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Influence of molecular size and zeta potential in electrokinetic biosensing
- 2020
-
In: Biosensors & bioelectronics. - : Elsevier. - 0956-5663 .- 1873-4235. ; 152
-
Journal article (peer-reviewed)abstract
- Electrokinetic principles such as streaming current and streaming potential are extensively used for surface characterization. Recently, they have also been used in biosensors, resulting in enhanced sensitivity and simpler device architecture. Theoretical models regarding streaming current/potential studies of particle-covered surfaces have identified features such as the particle size, shape and surface charge to influence the electrokinetic signals and consequently, the sensitivity and effective operational regime of the biosensor. By using a set of well-characterized proteins with varying size and net surface charge, this article experimentally verifies the theoretical predictions about their influence on the sensor signal. Increasing protein size was shown to enhance the signal when their net surface charge was either opposite to that of the sensor surface, or close to zero, in agreement with the theoretical predictions. However, the effect gradually saturated as the protein size exceeded the coulomb screening length of the electrolyte. In contrast, the proteins containing the same type of charge as the surface showed little or no difference, except that the signal inverted. The magnitude of the surface charge was also shown to influence the signal. The sensitivity of the technique for protein detection varied over two orders of magnitude, depending upon the size and surface charge. Furthermore, the capacity of the electrokinetic method for direct electrical detection of various proteins, including those carrying little or no net electric charges, is demonstrated.
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| 15. |
- Stridfeldt, Fredrik, et al.
(author)
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Analyses of single extracellular vesicles from non-small lung cancer cells to reveal effects of epidermal growth factor receptor inhibitor treatments
- 2023
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In: Talanta. - : Elsevier BV. - 0039-9140 .- 1873-3573. ; 259
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Journal article (peer-reviewed)abstract
- Precision cancer medicine has changed the treatment landscape of non-small cell lung cancer (NSCLC) as illustrated by the introduction of tyrosine kinase inhibitors (TKIs) towards mutated epidermal growth factor receptor (EGFR). However, as responses to EGFR-TKIs are heterogenous among NSCLC patients, there is a need for ways to early monitor changes in treatment response in a non-invasive way e.g., in patient's blood samples. Recently, extracellular vesicles (EVs) have been identified as a source of tumor biomarkers which could improve on non-invasive liquid biopsy-based diagnosis of cancer. However, the heterogeneity in EVs is high. Putative biomarker candidates may be hidden in the differential expression of membrane proteins in a subset of EVs hard to identify using bulk techniques. Using a fluorescence-based approach, we demonstrate that a single-EV tech-nique can detect alterations in EV surface protein profiles. We analyzed EVs isolated from an EGFR-mutant NSCLC cell line, which is refractory to EGFR-TKIs erlotinib and responsive to osimertinib, before and after treatment with these drugs and after cisplatin chemotherapy. We studied expression level of five proteins; two tetraspanins (CD9, CD81), and three markers of interest in lung cancer (EGFR, programmed death-ligand 1 (PD-L1), human epidermal growth factor receptor 2 (HER2)). The data reveal alterations induced by the osimertinib treatment compared to the other two treatments. These include the growth of the PD-L1/HER2-positive EV population, with the largest increase in vesicles exclusively expressing one of the two proteins. The expression level per EV decreased for these markers. On the other hand, both the TKIs had a similar effect on the EGFR-positive EV population.
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| 16. |
- Zhou, Jingjian, et al.
(author)
-
Low-Cost Synthesis of Silicon Quantum Dots with Near-Unity Internal Quantum Efficiency
- 2021
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In: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 12:37, s. 8909-8916
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Journal article (peer-reviewed)abstract
- As a cost-effective batch synthesis method, Si quantum dots (QDs) with nearinfrared photoluminescence, high quantum yield (>50% in polymer nanocomposite), and nearunity internal quantum efficiency were fabricated from an inexpensive commercial precursor (triethoxysilane, TES), using optimized annealing and etching processes. The optical properties of such QDs are similar to those prepared from state-of-the-art precursors (hydrogen silsesquioxane, HSQ) yet featuring an order of magnitude lower cost. To understand the effect of synthesis parameters on QD optical properties, we conducted a thorough comparison study between common solid precursors: TES, HSQ, and silicon monoxide (SiO), including chemical, structural, and optical characterizations. We found that the structural nonuniformity and abundance of oxide inherent to SiO limited the resultant QD performance, while for TES-derived QDs this drawback can be avoided. The presented low-cost synthetic approach would significantly favor applications requiring high loading of good-quality Si QDs, such as light conversion for photovoltaics.
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| 17. |
- Zhou, Jingjian, 1993-
(author)
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Luminescent Silicon Nanocrystals: From Single Quantum Dot to Light-harvesting Devices
- 2022
-
Doctoral thesis (other academic/artistic)abstract
- Silicon (Si) serves as the basic material of the system-on-a-chip industry and photovoltaic panels nowadays. This is mostly thanks to its high abundance in the earth’s crust, thereby low cost, virtually non-toxicity, and superior stability. Nano-silicon, especially silicon quantum dots (Si QDs), is endowed by the quantum confinement effect with the ability to emit light efficiently under photoexcitation, different from the bulk counterpart. The bright photoluminescence (PL), first found in the 1990s, has paved the way for this nanomaterial to be applied for light conversions in the last decades, such as for biosensing/biolabeling, light emitting diodes and luminescent solar concentrators (LSCs). The latter is used to concentrate sunlight in the slab on the edge-attached solar cells by means of PL. This thesis, on the one hand, deepens the comprehension on the optical properties of Si QDs by single-dot spectroscopy; on the other hand, a low-cost mass synthesis of high-quality Si QDs is developed here, which favors high QD loading applications, demonstrated as large-area “quantum dot glass”. First, the photo-physics mechanism behind PL was studied by single-dot spectroscopy, excluding the QD size inhomogeneity in the ensemble measurements. A new method was developed to fabricate large-area (~mm2) isolated oxide-passivated Si QDs on a silicon-on-insulator wafer. Linearly polarized PLs were observed on those single dots. System-limited PL linewidths, ~250 μeV, were measured at 10 K on QDs here, indicating a good quality of oxide shell endowed by high temperature annealing. Based on this method, it is possible to modify the ambient optical environment of QDs without tenuous alignments. With Si QDs residing on a metal membrane with an oxide spacer, the PL yields of single dots were enhanced ~10 times in average compared to those residing outside the membrane. Next, we have achieved, for the first time, direct observation on the temperature-dependent radiative lifetimes on single ligand-passivated Si QDs. Most importantly, these single-dot PL decays can be well-fitted mono-exponentially, indicating trap-free dynamics, as opposite to oxide-passivated counterparts. Secondly, a chemical synthesis method of ligand-passivated Si QDs by using triethoxysilane (TES) as precursors is introduced. The quantum yield of as-synthesized Si QDs is ~40% in solution and ~55% in Si QDs/polymer nanocomposites. Such QDs have near-unity internal quantum efficiency both in the liquid and solid phase. With a comparably good quality of Si QDs, the QD cost of this TES method is about an order of magnitude less expensive than that of the established HSQ method. Finally, the application of Si QDs in photovoltaic devices was demonstrated. A 9 × 9 × 0.6 cm3 LSC device based on Si QDs was fabricated, delivering ~7.9% optical power conversion efficiency under one standard sun. This performance is very similar to the state of the art of direct-bandgap semiconductor QDs. To further expand the application area of this kind of transparent photovoltaic devices, a concept of transparent “quantum dot glass” (TQDG) is introduced, fulfilling requirements as both power-generating components and building construction materials. A 20 × 20 × 1 cm3 TQDG device was fabricated with the overall power conversion efficiency up to 1.57% and the average visible transmittance 84%. The light utilization efficiency (LUE) is 1.3%, which is among the top reported TPVs based on the LSC technology with a similar size. Moreover, to facilitate the characterization of large-area LSC-like light-harvesting devices a new concept of an “optical center” is introduced. A procedure of whole device PCE estimates from optical center excitation measurements with basic laboratory instruments was provided, with a negligible error to the measured one by the conventional method.
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| 18. |
- Zhou, Jingjian, et al.
(author)
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Photoluminescence Intensity Enhancement of Single Silicon Quantum Dots on a Metal Membrane with a Spacer
- 2020
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In: Physica Status Solidi (a) applications and materials science. - : WILEY-V C H VERLAG GMBH. - 1862-6300 .- 1862-6319. ; 217:4
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Journal article (peer-reviewed)abstract
- Silicon quantum dots (Si QDs) featuring high photoluminescence (PL) intensity are necessary for the realization of different photonic and photovoltaic devices, such as light-emitting diodes (LEDs) and luminescent solar concentrators (LSCs). Herein, Si QDs on a approximate to 100-200 nm thin silicon dioxide membrane with a metal back-coating are prepared. The dots are formed from the device layer of a silicon-on-insulator (SOI) wafer by etching and thermal oxidation. Aluminum is sputtered on the backside of the membrane, acting as a back-surface mirror, changing the local density of optical modes, as well as the local excitation field. The PL properties of such Si QDs are then characterized at the single-particle level. It is found that the PL yield of single Si QDs on the membrane is enhanced by approximately one order of magnitude, compared with that of Si QDs outside the membrane under the same excitation power. These results indicate that advances in nanofabrication can substantially improve the optical properties of Si QDs, thus paving the way for their application.
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| 19. |
- Zhou, Jingjian, et al.
(author)
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Wafer-scale fabrication of isolated luminescent silicon quantum dots using standard CMOS technology
- 2020
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In: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 31:50
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Journal article (peer-reviewed)abstract
- A wafer-scale fabrication method for isolated silicon quantum dots (Si QDs) using standard CMOS technology is presented. Reactive ion etching was performed on the device layer of a silicon-on-insulator wafer, creating nano-sized silicon islands. Subsequently, the wafer was annealed at 1100 degrees C for 1 h in an atmosphere of 5% H(2)in Ar, forming a thin oxide passivating layer due to trace amounts of oxygen. Isolated Si QDs covering large areas (similar to mm(2)) were revealed by photoluminescence (PL) measurements. The emission energies of such Si QDs can span over a broad range, from 1.3 to 2.0 eV and each dot is typically characterized by a single emission line at low temperatures. Most of the Si QDs exhibited a high degree of linear polarization along Si crystallographic directions [110] abd [(1) over bar 10]. In addition, system resolution-limited (250 mu eV) PL linewidths (full width at half maximum) were measured for several Si QDs at 10 K, with no clear correlation between emission energy and polarization. The initial part of PL decays was measured at room temperature for such oxide-embedded Si QDs, approximately several microseconds long. By providing direct access to a broad size range of isolated Si QDs on a wafer, this technique paves the way for the future fabrication of photonic structures with Si QDs, which can potentially be used as single-photon sources with a long coherence length.
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