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SnS Quantum Dot Molecular Imaging Probe and Piezoelectric Plate Sensor

Friday, June 7, 2019

2:00 PM-4:00 PM

BIOMED PhD Research Proposal

SnS Quantum Dot Molecular Imaging Probe and Piezoelectric Plate Sensor: Biomedical Engineering Through Innovative Aqueous Materials Synthesis

Song Han, PhD Candidate
School of Biomedical Engineering, Science and Health Systems
Drexel University

Wan Y. Shih, PhD
School of Biomedical Engineering, Science and Health Systems
Drexel University

Wei-Heng Shih, PhD
Department of Materials Science and Engineering
College of Engineering
Drexel University

Quantum dots (QDs) are fluorescent semiconducting nanoparticles that offer great potential for bioimaging because they are brighter than traditional fluorescent molecules. SnS QDs that emit near infrared (NIR) light are particularly advantageous because absorption and autofluorescence by the tissues are both minimal in the NIR range and SnS does not contain toxic elements that are prevalent in most known QDs. On the other hand, piezoelectric plate sensor (PEPS) is a unique sensor platform developed in Shih and Shih laboratory capable of genetic detection with polymerase chain reaction (PCR) sensitivity and specificity but without the need of gene isolation or amplification. What is in common between the aqueous synthesis of SnS QDs and that of the lead magnesium niobate (PMN) power that PEPSs are made from is the difficulty and complexity of these synthesis processes that rendered SnS QDs not stable and PEPS not reproducible.

The goal of this thesis is to investigate the aqueous synthesis processes of SnS QDs and that of PMN powder to achieve stable, aqueous SnS QD suspensions for NIR molecular imaging and reproducible PEPS for isolation-free and amplification-free genetic detections.

The challenge of using SnS for molecular bioimaging is that SnS dissolves in neutral pH in water. To stabilize SnS in water and make them biocompatible, we examined a novel aqueous approach that started with making cysteamine-capped SnS QDs in glycerol in acidic conditions, followed by stabilization by lengthening the capping molecules at neutral pH through repeated peptide bond formation with glycine and subsequent heat treatment at 200oC for 4 hr. SnS QDs were further made non-cytotoxic by complexing the positively charged SnS QDs with negatively charged 3-mercaptoprorionic acid (MPA). Ultrahigh signal-to noise ratio (S/N >31) NIR bioimaging was demonstrated using such charge-neutral NIR SnS QDs in targeting vascular endothelial growth factor (EGFR) on 3T3 cells and Tn antigen on HT29 cells.

The most challenging part of the initial PMN powder synthesis was a combustion step as a result of using ethylene glycol as the medium. The combustion step made the PMN powder finer, essential for making the freestanding film from which PEPSs were made. However, combustion also made the process uncontrollable and difficult to obtain reproducible PEPSs. In this study, we propose to achieve an aqueous synthesis route to achieve similarly fine PMN powder through mechanical particle size reduction and an innovative two-step crystallization schedule.  The repeatability of these steps are characterized by X-ray, particle size, sintering of the freestanding film, and PEPS temperature stability, and detection performances. Preliminary results showed that the newly fabricated PEPSs made by the aqueous synthesis routes detected anti-Tn antigen IgM in serum at a concentration 25,000 times lower than the comparing ELISA and detected DNA at 60 copies/ml as comparable to the PEPSs made from the combustion method. We will further carry out simultaneous hepatitis B virus (HBV) DNA and hepatitis C virus (HCV) RNA detection in patient sera in 30 min without isolation and amplification to illustrate the reliable performance of these newly fabricated PEPSs.

Contact Information

Ken Barbee

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