Nanoscale Photonics

From single molecule nanofluidics to light-matter interaction in nanostructures

by Siddharth Ghosh
Doctoral thesis
Date of Examination:2016-08-15
Date of issue:2017-08-14
Advisor:Prof. Dr. Jörg Enderlein
Referee:Prof. Dr. Jörg Enderlein
Referee:Prof. Dr. Peter Jomo Walla
Persistent Address: http://dx.doi.org/10.53846/goediss-6398

 

 

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Abstract

English

Detecting single nanometre scale objects and studying them in a controlled manner in solution is still a difficult task due to diffusion. We demonstrate one-dimensional nanofluidic flows of single molecules by confining diffusion in two spatial dimensions. A high-throughput nanofabrication process was developed using electron-beam lithography, reactive ion etching, and shadow-angle- electron-beam deposition to prepare the required nanofluidic devices. We used the device to detect single organic dye molecules, nanodots, and small DNA molecules using two-foci fluorescence correlation spectroscopy. Fluorescence is frequently exploited in single molecule detection. In this thesis, a non-toxic fluorescent nanomaterial called carbon nanodots (CNDs) is studied using a fluorescence and elec- tron correlative microscopy approach. We find that CNDs are single photon emitters in the visible range. A strong electron-phonon coupling is observed in their photoluminescence. The light- matter interaction at atomic scale of CNDs is not well understood. We study the optical behaviour of CNDs using a time-dependent density-functional tight binding method. A type of CND studied in this thesis is graphene quantum dots. Their optical behaviour is strongly dependent on the edge properties, functional groups, and the total number of atoms. We envision that single molecule nanofluidics will impact the biomedical research and diagnos- tics by enabling the study of protein-protein interactions and detecting single molecule level onset of any disease. The CNDs studied here have already been used in super-resolution microscopy with potential to replace the toxic quantum dots for labelling. Our theoretical findings on CNDs answer towards their optical and electronic properties. These are useful for the development of single photon quantum detectors and optoelectronic devices. Overall, the results presented here should have applications in biomedical sciences, optoelectronics, and quantum information tech- nologies.
Keywords: Single molecule; nanofluidics; fluorescence; spectroscopy; graphene; carbon nanodots; light-matter interactions; nanophotonics; nanoscale photonics; DFTB; Time-dependent density functional theory; nanofabrications; two-foci fluorescence correlation spectroscopy; 2f-FCS
 
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