Electroactive micro and nanowells for optofluidic storage

This paper reports an optofluidic architecture which enables reversible trapping, detection and long term storage of spectrally multiplexed semiconductor quantum dot cocktails in electrokinetically active wells ranging in size from 200nm to 5μm. Here we describe the microfluidic delivery of these cocktails, fabrication method and principal of operation for the wells, and characterize the readout capabilities, storage and erasure speeds, internal spatial signal uniformity and potential storage density of the devices. We report storage and erase speeds of less than 153ms and 30ms respectively and the ability to provide 6-bit storage in a single 200nm well through spectral and intensity multiplexing. Furthermore, we present a novel method for enabling passive long term storage of the quantum dots in the wells by transporting them through an agarose gel matrix. We envision that this technique could find eventual application in fluidic memory or display devices

Electroactive nanowells for spectrographic fluidic memory

Current optical storage devices such as DVDs have their read/write capabilities fundamentally restricted by the diffraction limit of light. We present an optofluidic architecture for storing cocktails of colloidal quantum dots in electroactive nanowell structures. One application of these devices is the development of a fluidic memory approach which could enable the generation, reading and erasing of multiple bit information packages on single light diffraction limited data marks by spectral and intensity multiplexing of quantum dot cocktails. Here we focus on the development of the electroactive nanowell trapping architecture. Briefly, we have shown that by applying an electric potential between a top and bottom Indium Tin Oxide (ITO) electrodes, particles ranging from 5μm polystyrene spheres to 5nm quantum dots suspended in solution can be attracted, stored and rejected from a targeted well structure by electrokinetic actuation. Nanowells 100 nm in diameter and 1 μm deep were fabricated by depositing silicon and a small oxide thin film on top of an ITO cover slip, patterning the wells on electron beam resist followed by a series of dry etching steps that leave the ITO substrate exposed in the well sites. When the quantum dots are electrokinetically transported to their sensing sites, they are then excited by a UV-blue light, and their discrete fluorescent signal is captured by a fiber spectrometer. Data erasure can be selectively performed by reversing the polarity of the field and ejecting the quantum dots from the nanowell data marks

Electrokinetically Active Nanowells

In this research I developed a new form of microfluidic transport technique that exploits electrokinetic phenomena in discrete micro and nanometer sized wells. Through the use of these "Electroactive Nanowells", I have been able to demonstrate the reversible trapping of micro and nanoscale objects in discrete locations, enabled a new form of microfluidic memory and used a modified version of this technique to generate a wireless drug delivery system for the control of flying insects. The outcome of this research is threefold: First, it establishes a low power device that can increase the speed of traditional microwell screening techniques by four orders of magnitude in an easy to fabricate setup. The second outcome is the development of the first high density microfluidic memory, which can store up to 6 bits of material storage in single 200 nanometer wells; providing a 6 order magnitude increase in storage density over traditional microfluidic storage devices. Third, I exploited the essential transport physics of this approach to enable a wireless and implantable drug delivery system capable of dispensing various chemicals on demand; and applied it to the of chemically directed control of live micro air vehicles. Fourth, I present a flexible version of this drug delivery system by using only polymers in the fabrication process

Surface characterization of nanoparticles using near-field light scattering

The effect of nanoparticle surface coating characteristics on colloidal stability in solution is a critical parameter in understanding the potential applications of nanoparticles, especially in biomedicine. Here we explored the modification of the surface of poly(ethylene glycol)-coated superparamagnetic iron oxide nanoparticles (PEG-SPIOs) with the synthetic pseudotannin polygallol via interpolymer complexation (IPC). Changes in particle size and zeta potential were indirectly assessed via differences between PEG-SPIOs and IPC-SPIOs in particle velocity and scattering intensity using near-field light scattering. The local scattering intensity is correlated with the distance between the particle and waveguide, which is affected by the size of the particle (coating thickness) as well as the interactions between the particle and waveguide (related to the zeta potential of the coating). Therefore, we report here the use of near-field light scattering using nanophotonic force microscopy (using a NanoTweezerTM instrument, Halo Labs) to determine the changes that occurred in hydrated particle characteristics, which is accompanied by an analytical model. Furthermore, we found that altering the salt concentration of the suspension solution affected the velocity of particles due to the change of dielectric constant and viscosity of the solution. These findings suggest that this technique is suitable for studying particle surface changes and perhaps can be used to dynamically study reaction kinetics at the particle surface