University of California
San Diego

Departments of Nanoengineering
and Bioengineering

 

Alexander P. Hsiao

 

Current Research

Electric Field Directed Fabrication of Active Bio/Chem Sensors from Enzyme Linked Nanoparticles
Active transport atop an electrophoretic microarray allows for rapid concentration of nanoparticles onto individual electrode sites. We have previously demonstrated the fabrication of alternating layers of biotin and streptavidin derivatized nanoparticles on a CMOS microarray using electric field directed self-assembly. Our current research is focused on the construction of biological and chemical sensors using enzyme-linked nanoparticle layers. We believe that these nanoparticle layers will be superior to current surface bound sensors. The application of an electric field allows for rapid concentration of particles over individual electrode sites, allowing for efficient fabrication of enzyme-nanoparticle layers. Moreover, the increased surface area of multiple layers should enhance the recognition of analyte species. Our current method includes the alternate layering of glucose oxidase-avidin to 200nm biotin-polystyrene nanoparticles. Using the CMOS microarray we have fabricated constructs of up to 20 alternating layers of enzyme and nanoparticle. We further hope to activate these layers and observe chemiluminescence through the addition of glucose and luminol to the system, thereby producing a functional sensor. Furthermore, these structures can be customized to include multiple enzymes to allow for coupling between the layers as well as the incorporation of targeting or imaging moieties.  Future research will also include investigation into porous nanoparticles to allow for higher density packaging of enzymes as well as separate surface/internal chemistries.

Dielectrophoresis Directed Fabrication of DNA-Linked Nanoparticles
We have previously demonstrated the layering of DNA-linked 40nm particles in a DC electric field atop a CMOS microarray. The layering of particles was enabled by the complementary binding of biotinylated single-stranded DNA sequences attached to Neutravidin nanoparticles. I am now investigating the ability build layers by dielectrophoresis. Dielectrophoresis allows for the usage of higher conductivity buffers where DNA hybridization is more easily facilitated.

Electric Field Directed Fluorescence in situ hybridization
Currently, FISH performed on live cell samples requires lengthy overnight procedures and encounters problems with probe specificity. To enhance the efficiency and stringency of the process, the use of electric fields is being investigated to aid the transport of DNA probes into the cells. Moreover, electric fields can be used as an added level of stringency to remove nonspecific probe binding during wash steps. All together this should reduce the variability seen from sample to sample in current FISH procedures. I have successfully attached breast cancer cells to an electrode array and shown that DNA probes can be concentrated directly over electrodes where cells are fixed. We are currently testing a different electrode chip and will look in the future to fabricate our own design, which may include microchannels and electrodes on glass slides. Further investigation into the proper hybridization conditions will be carried out. This may be applied to a plethora of probes allowing for efficient and specific analysis of genes in cell samples.

Electric Field Directed Assembly of an Ordered Bio-functionalized Nanoparticle Array
(w/ K. Barbee in Prof. Huang’s group)