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Colloidal Synthesis and Solution Coating for Piezoelectric Ceramics and Fluorescent Nanoparticles: Materials, Fabrication, and Applications

Wan Y. Shih and Wei-Heng Shih

School of Biomedical Engineering, Science, and Health Systems, and Department of Materials Science & Engineering, Drexel University, Philadelphia, PA 19104; Email: shihwh@drexel.edu

Modification of interparticle separation in the nanometer range plays a crucial role in the properties of colloidal suspensions. We have developed a nanocoating method that modifies the surface chemistry of ceramic powders. The nanocoating enhances the chemical and thermal stability of the powders, improves the consolidation and rheological properties of the slurries, increases the homogeneous distribution of processing additives, and lowers the sintering temperatures of the green compacts. As an example, the coating of Mg(OH)2 layer on Nb2O5 particles facilitates the direct, one-step, sintering of perovskite lead magnesium niobate (PMN) ceramics below 1000ºC. Furthermore the coating approach is used to generate highly reactive lead magnesium niobate-lead titanate (PMN-PT) freestanding films that have enhanced piezoelectric response at high electric field. We have also performed the antimony (Sb) doping studies for Na0.5K0.5)NbO3-LiNbO3 (NKN-LN) solid solutions using the precursor coating approach. We obtained a d33 coefficient of 240 pC/N and a high dielectric constant of 1000 at 1 kHz at 4% Sb without CIP.

The piezoelectric materials that we developed were used to fabricate miniaturized, highly piezoelectric microcantilever sensor (PEMS) that offers the advantages of in-situ, direct, and simple electrical detection and better capabilities to withstand damping in aqueous environment. Binding of antigens to the antibody immobilized on the cantilever surface increases the cantilever’s mass and reduces its resonance frequency, which is detected by monitoring the resonance frequency shift. Demonstration of in-situ detection of cells, proteins, and specific antigen-antibody binding have been shown using lead zirconate titanate (PZT)/stainless steel cantilevers of less than 0.5 mm in length with better than 10-14 g/Hz detection sensitivity for proteins including prostate specific antigen (PSA) and human epidermal growth factor receptor 2 (HER2), and bioagent (anthrax spore). Furthermore, we have developed PEMS in the scale of micron using semiconductor microfabrication technique capable of better than 10-16 g/Hz sensitivity.

More recently, the colloidal approach was also used to develop an aqueous process for quantum dots (QDs) which are semiconductor nanocrystals that exhibit distinctive photoluminescence properties due to quantum confinement effect. Through an environmentally friendly aqueous method, cadmium sulfide (CdS) and non-heavy metal zinc sulfide (ZnS) QDs capped with molecules that could be directly conjugated were synthesized with size smaller than 5 nm. As a fluorescence imaging and tracking tool, the application of aqueous QDs in biomedical systems was also investigated.

Wei-Heng Shih received a B.Sc. in physics in 1976 from Tsinghua University in Taiwan and completed his Ph.D. degree in Physics in 1984 from Ohio State University. He joined the Department of Materials Science and Engineering at Drexel University in 1991 and was promoted to Professor in 2003. His research has covered a wide range of areas of materials science and engineering including colloidal processing of ceramics; sol-gel processing of microporous and mesoporous ceramic powders; and chemical treatment of combustion wastes. His current research interests are fabrication, characterization and design of piezoelectric cantilever sensors for biomedical applications and the development of environmentally friendly synthesis of photoluminescent nanocrystalline particles (quantum dots). Prof. Shih has one patent, and five patents and seven provisional patents in application. He received the 1999 Edward C. Henry Electronics Division Best Paper Award from The American Ceramic society. In Drexel University, he has received several awards including the Faculty Achievement Award, Professor of the Year, and the Research Achievement Award. He has been inducted to Drexel’s 106 Club.

Wan Y. Shih, Associate Professor of School of Biomedical Engineering, Science, and Health Systems, Drexel University. She received her BS in Physics from Tsinghua University, Taiwan, and her Ph.D in Physics from Ohio State University, Columbus, Ohio. Her broad research areas include ferroelectricity, colloids, piezoelectric materials and sensors. She has one patent, and five patents and seven provisional patents in application. Her work on “Electromechanical Behavior of PZT-Brass Unimorphs,” J. Am. Ceram. Soc. 82[7], 1733-1740 (1999), won the 1999 Edward C. Henry Electronics Division Best Paper Award of the American Ceramic Society. Her current research is focused on the piezoelectric