Single Quantum Dots-based Light Source: Near Field & Cellular Arrays Imaging

Sponsored by: NSF EPDT award, NSF IMR award, and Oak Ridge National Laboratory, Department of Energy.

The objective of this research is to develop a novel near-field scanning probe with sub-diffraction-limit resolution by directly fabricating nanometer sized light source on the tip, and to use the probe to characterize the distribution of multi-stage combinatorial directed nanovectors in tissues and living cells for tumor characterization and destruction.


The expected light source size is 10-50 nm, an order of magnitude smaller than that of a current NSOM.  The research will likely open many exciting opportunities in biomedical and industrial applications including near-field microscopy of sub-cellular structures, direct material patterning, ultra high-density data storage, and compact light-on-chip biosensors and biochips. The emission wavelength of the probe will cover the spectrum from near-UV to the visible range with imaging resolutions well beyond the diffraction limit.  The concept of “Nano-LED at-tip” using silicon technology was originated in the Zhang Lab in 2006.  The technology has attracted increased attention from both MEMS and Nanodevice communities as well as from materials and medical imaging researchers around the world.  The preliminary studies using Nano-LEDs made of doped silicon oxide, or light emitting quantum dots on a probe tip integrated with conventional NSOM (in collaboration with Professor David Vanden Bout, UT Austin, Biochemistry), have shown great promise.  It was the first time that apertureless images have been acquired with a light source embedded in a scanning probe tip.


We also demonstrated quantum dot based light emitting diodeson surfaces, fabricated by microcontactprinting of a well defined-geometry of CdSe/ZnS nanoparticles films onto p type silicon substrate.The structure of QD-based LEDs consists of multi-layers of inorganic materials: the combination of Au(thickness: 5nm) and Ag(12 nm) as the cathode or Al(20nm), ZnO:SnO2 (ratio 3:1, 40 nm) as the electron transporting layer, CdSe/ZnS particles as the light emission layer, 1 nm SiO2 as an energy barrier layer, and p-silicon as the hole transporting layer. The creation of quantum dot monolayer can be done at room temperature using microcontact printing via PDMS.

Patterning technique enables site-controlled patterning and controlled feature size of light emitting area with greater accuracy. We utilize a stamping technique for patterning colloidal QDs with well-defined geometry. It is possible to accurately define multicolor light sources on a single substrate, which open up the possibilities for creating microsystems for imaging and sensing cancer cell lines. We have imaged, MDA 435 cancer cell samples excited by the quantum dot based inorganic light emitting diodes on silicon to demonstrate the capabilities of the device created.