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Intrinsic blinking characteristics of single colloidal CdSe-CdS/ZnS core-multishell quantum dots
KTH, Centres, Science for Life Laboratory, SciLifeLab.ORCID iD: 0000-0002-2442-1809
KTH, Centres, Science for Life Laboratory, SciLifeLab.
Swedish Natl Forens Ctr, SE-58194 Linkoping, Sweden..
Swedish Natl Forens Ctr, SE-58194 Linkoping, Sweden..
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2019 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 3, article id 035404Article in journal (Refereed) Published
Abstract [en]

Fluorescence blinking of single colloidal semiconductor quantum dots (QDs) has been extensively studied, and several sophisticated models have been proposed. In this work, we derive Heisenberg equations of motion to carefully study principal transition processes, i.e., photoexcitation, energy relaxation, impact ionization and Auger recombination, radiative and nonradiative recombinations, and tunneling between core states and surface states, of the electron-hole pair in single CdSe-CdS/ZnS core-multishell QDs and show that the on-state probability density distribution of the QD fluorescence obeys the random telegraph signal theory because of the random radiative recombination of the photoexcited electron-hole pair in the QD core, while the off-state probability density distribution obeys the inverse power law distribution due to the series of random walks of the photoexcited electron in the two-dimensional surface-state network after the electron tunnels from the QD core to the QD surface. These two different blinking characteristics of the single QD are resolved experimentally by properly adjusting the optical excitation power and the bin time.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC , 2019. Vol. 99, no 3, article id 035404
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-241317DOI: 10.1103/PhysRevB.99.035404ISI: 000454766400012Scopus ID: 2-s2.0-85059881217OAI: oai:DiVA.org:kth-241317DiVA, id: diva2:1282543
Note

QC 20190125

Available from: 2019-01-25 Created: 2019-01-25 Last updated: 2019-10-20Bibliographically approved
In thesis
1. Fluorescent quantum dots and graphene-based sensors for forensic applications
Open this publication in new window or tab >>Fluorescent quantum dots and graphene-based sensors for forensic applications
2019 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

A key emerging concept within the forensic sciences today areportable measurementdevices, where a much more efficient usage of the resources involved with crime-solving is possible if confirmatory measurements can be realised directly at a crimescene with such devices. Today, the majority of the presently used methods duringcriminal investigation at a crime scene involves measurements of a presumptivenature, which is a vital tool as it enables the screening of samples. In this thesis,the overarching goal is the development of tool kits for the analysis of biosampleson-site at a crime scene. This is mainly investigated through two routes: theusage of Quantum Dots (QDs) as a recognition element in sensory applications andfabrication of a graphene-based device for the detection of illicit drugs.The investigations conducted for the studies presented in this thesis focuses onsensory applications with a forensic detection scheme in mind: study I reveals in-trinsic properties of QDs to better understand sensing mechanisms upon bindinginteractions; study II demonstrates the fabrication of a graphene-based device forthe detection of illicit drugs; study III showcases the functionalised and bioconju-gated of QDs for a specific investigation into a biological process; study IV furtherthe investigation into the possible side-effects of QDs on biological specimens.In study I we numerically and experimentally investigate the intrinsic blinkingcharacteristics of CdSe-CdS/ZnS QDs. This includes a thorough examination of theexperimental parameters of the measurement setup: the bin time and excitationpower. Different mechanisms between the off- and on-state probability distributionsare found, wherein the on-state follows the random telegraph signal theory and theoff-state follows the inverse power law distribution.In study II, the detection of illicit drugs (amphetamine and cocaine) is achievedthrough graphene-based sensors processed to contain metal electrodes with superioradhesion and low contact resistance. The construction of a microfluidic system isfurther realised for a detection of molecules based on non-covalent interactions.With this system, a wavelength-dependent photoactivity for amphetamine and arange of its chemical analogs is demonstrated. A molecule dependent interactionwith the graphene surface is shown of the graphene surface either in the form ofp-doping (cocaine) or n-doping (amphetamine).Study III investigates the endocytic pathway of the vascular cell adhesionmolecule 1 (VCAM1) in Human Umbilical Vein Endothelial Cells (HUVECs) in-iiiivABSTRACTduced by Tumor Necrosis Factorα(TNFα) with the usage of 3-Mercaptopropionicacid coated (3MPA)-QDs and 5-Carboxyfluorescein (5FAM) functionalised and la-belled with VCAM1 binding peptides, respectively. Internalisation of the VCAM1molecules into lysosomes is shown with light microscopy through observations ofdifferent pathways of the 5FAM labelled peptides and functionalised QDs.In study IV we investigate the adverse effects of 3MPA-QDs on the humanairway epithelium by an examination of the calcium response in lung cells upon astimulation with QDs. The cellular response to the deposition of QDs is observedwith light microscopy and electrical measurements as a global increase of Ca2+in the epithelial layers and a transient decrease in the electrical response. Theseobservations imply that the influx of calcium caused by the QD deposition is inducedby mechanical stressIn an additional ongoing study, the age determination of dried blood spotsare investigated with the usage of protein markers commonly found in the blood.Human serum (HS) is spiked with a marker of interest to mimic those of normallevels in adult human males. After which the HS is allowed to undergo an ageingprocess in a 96 well plate and further analysed in terms of the enzymatic activitywith commercially available kits. The preliminary test results show that there is ameasurable change of activity dependenton the utilised marker that may act as abasis for the age determination of dried blod spots

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2019. p. 119
Series
TRITA-SCI-FOU ; 2019:42
Keywords
Graphene, Quantum Dots, Blood, Forensics, Drugs
National Category
Natural Sciences Nano Technology
Research subject
Biological Physics
Identifiers
urn:nbn:se:kth:diva-262750 (URN)978-91-7873-307-1 (ISBN)
Presentation
2019-10-18, Pascal, Tomtebodavägen 23a, Solna, 10:00 (English)
Opponent
Supervisors
Funder
Swedish Foundation for Strategic Research , Forskningsinstitutsdoktorand 2015
Note

Examinator: Professor Björn Önfelt

Available from: 2019-10-21 Created: 2019-10-20 Last updated: 2019-10-21Bibliographically approved

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Fu, YingJussi, Johnny IsraelssonBrismar, Hjalmar

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