Nanosensing 

Quantum dots are able to improve fluorescent assays by offering a number of benefits over traditional organic fluorophores, such as high brightness, longer fluorescence lifetime, better photostability, as well as narrow and symmetric emission spectrum. The excitation spectrum of quantum dots extends far into the UV region and hence multiple quantum dots can be excited with a single light source. This unique property make them an exceptional fluorescence resonance energy transfer (FRET) donor because of the aacceptor spectral bleed-through can be easily avoided.

 

The evergrowing interest in quantum dots also prompts studies on their non-photoluminescence properties, such as electrohydrodynamic, electrochemical, and photoelectrical properties. These new phenomena have been adopted in new molecular sensing strategy.

Our research focuses on the application of quantum dots as smart molecular probe for diagnostics and biosensing.

QD-FRET

A quantum dot fluorescent energy transfer (QD-FRET) smart nanosensor. The sensor is turned on in the presence of the target of interest. In the absence of the target, only one emission peak at 605 nm is observed upon the excitation by 488 nm excitation source. In the presence of the target, an additional emission at 670 nm arises accompanied by decreased emission at 605 nm.

QEMSA

We report a new phenomenon where the electrophoretic mobility of a QD-DNA nanoassembly can be precisely and predictably modulated by the degree of surface DNA conjugation. This phenomenon forms the basis of a nanoassay called quantum dot electrophoretic mobility shift assay (QEMSA) that is able to accurately quantify DNA. QEMSA maps DNA quantity into an electrophoretic mobility shift. Each streptavidin-functionalized QD acts as an electrophoretic nanotether, gathering biotin-tagged DNA from solution to form a QD-DNA nanoassembly. DNA amount is determined by measuring the relative speed at which the QD-DNA nanoassemblies migrate.

Single Molecule Detection

We use single molecule spectroscopy as an ultrasensitive detection platform for diagnostics and biosensing in combination with various molecular sensing strategies. 

Detection of DNA point mutation. The mutation site is identified and labeled by ligation reaction. The presence of mutation is indicated by coincident fluorescent burst detected by single molecule spectroscopy. Left: wide type. Right: mutant.

Nanoprocessing

We have taken a conceptually different approach to silica DNA extraction by developing a novel thermoplastic substrate containing a hierarchical layering of microscale folds and nanoscale silica lamella. The material’s nonporous, high-surface area structure protects DNA from shear force-induced ragmentation by harboring it in a condensed, tentacle conformation that enables the extraction of vast amounts of ultrahigh-molecular-weight (UHMW) DNA. The material is fabricated by a simple heat shrinking process, which lead to a hierarchical layering of microscale polyolefin folds and nanoscale silica lamella that can act as a high-surface-area, low-shear substrate for DNA extraction.