Quantum Dot (Epitaxial) Biosensor
We have been investigating an innovative technological approach for biosensing based on the use of arrays of epitaxial quantum dots (eQD) previously known for their applications in advanced communication devices such as QD lasers. The goal is to develop a commercially viable (cost-effective) eQD device for the rapid detection and typing of human viral and bacterial pathogens. Our initial focus is on the Influenza A biosensor, but other human pathogens will be addressed with the eQD platform technology. This multidisciplinary project is carried out in collaboration with researchers from the Faculty of Engineering, Faculty of Sciences and Faculty of Medicine (Department of Microbiology and Infectious Diseases and Department of Pharmacology), as well as with some researchers from Canadian and non-Canadian Universities and government laboratories. The activity is supported by the Canadian Institute of Health Research, Université de Sherbrooke and the Canada Research Chair in Quantum Semiconductors program.
Semiconductor nanocrystals, also known as colloidal quantum dots (cQD’s) provide a unique opportunity for research on detection and monitoring of various biomolecular material systems. Due to their size comparable to biomolecules and some viruses (see The Scale of Things) and due to their unique optical, electrical and magnetic properties, cQD’s are thought to have potential as attractive luminescent and detection enhancing (or enabling) probes for in-vivo diagnostics (e.g., imaging), therapy (e.g., drug delivery) and sensing applications. Today, CdSe coated with ZnS are probably the most known and investigated cQD’s, although other colloidal nanocrystals of both II-VI and III-V groups have been the subject of an ongoing worldwide investigation. Development of cQD’s compatible with different bio-environments or functionalized for adsorption of specific biomolecules has challenged the efforts of researchers involved in this domain of nanoscience and biotechnology. For instance, critical to the bright and stable photoluminescence (PL) of cQD’s is the ability to minimize the role of surface defects (traps), which are the source of the PL quenching signal through non-radiative recombination centers (NRRC). Surface trap related intermittence in PL emission, also known as blinking, has been commonly observed from cQD’s. Such behaviour could impose significant limitations on the successful use of cQD’s for biosensing or single biomolecule imaging. The neutralization of surface defects requires the development of ever elusive surface passivation methods. In addition, the free-standing nature of cQD’s makes it difficult to implement otherwise powerful dry methods of processing such as laser-assisted etching and surface functionalization.
The above mentioned problems related to the technology of cQD’s have inspired us to investigate an alternative method of using quantum dots for bio-detection that is based on the application of arrays of epitaxially grown quantum dots (eQD’s). It is known that eQD’s do not suffer from the blinking effect. Furthermore, eQD’s can be processed with specialty tools that would be impractical for cQD’s, allowing to tune the emission wavelength of an individual eQD or groups of eQD’s and to carry out selective area surface passivation/functionalization for the immobilization of different antibodies or DNA biomoieties.