Bernardo Cordovez

Trapping and storage of particles in electroactive microwells

The authors describe electroactive microwells which exploit highly localized electrokinetic effects in order to actively concentrate, confine, store, and reject particles in well defined geometries. In this letter the authors present experimental results demonstrating repeatable trapping and repulsion of polystyrene particles in wells ranging in diameter from 6 to 20 µm in the presence of a superimposed pressure driven flow. A comprehensive finite element model is developed to describe the transport physics involved in the attraction and repulsion processes. Immediate applications include active cell trapping, particle concentration and unlabeled sensing.

A nanotweezer system for evanescent wave excited surface enhanced Raman spectroscopy (SERS) of single nanoparticles

We experimentally demonstrate the integration of near-field optical tweezers with surface enhanced Raman scattering (SERS) spectroscopy by using the optical evanescent wave from a silicon nitride waveguide to trap single shell-isolated metallic nanoparticles (NPs) and simultaneously excite SERS signals of Raman reporter molecules adsorbed on the surface of the trapped metallic NPs. Both evanescent wave excited Stokes and anti-Stokes SERS spectra of waveguide trapped single silver (Ag) NPs were acquired, which were compared to their far-field SERS spectra. We investigated the trapping of bare and shell-isolated metallic NPs and determined that the addition of a shell to the metallic NPs minimized particle-induced laser damage to the waveguide, which allowed for the stable acquisition of the SERS spectra. This work realizes a new nanophotonic approach, which we refer to as near-field light scattering Raman (NLS-Raman), for simultaneous near-field optical trapping and SERS characterization of single metallic NPs.

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 5microm. 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.

The molecular nanotweezer: nanomanipulation taken to new lows

By exploiting near field optical forces, the Molecular NanoTweezer can trap the smallest nanoparticles yet reported inluding individual proteins and quantum dots. This breakthrough is being commercialized and will produce the first system to allow for direct optical manipulation of biologically relevant nanoparticles. This breakthrough is being commercialized and will produce the first system to allow direct optical manipulation of biological nanoparticles. The Molecular NanoTweezer overcomes the lower size limit imposed by diffraction (the limit of traditional optical tweezers) by using waveguides and optical resonators patterned on silicon chips that produce near field optical forces. In this talk, we will discuss current and future applications of this technology, including surface-tether-free immunoassays. We will finalize our talk by briefly overviewing the commercialization efforts.

Spectrographic fluidic memory using electroactive nanowell arrays

We present an optofluidic memory architecture that enables the reading and erasing of multiple bit information packages on single light diffraction limited data marks by exploiting spectral and intensity multiplexing of colloidal quantum dot cocktails.

Optofluidic Surface Enhanced Raman Scattering Chip for Detection of Dengue Virus

In this work we describe the development of an optofluidic device for surface enhanced Raman scattering (SERS) based detection of biological pathogens. The chip exploits the use of electro-active microwells which serve to both physically concentrate the Raman enhancers and to reduce the total analysis time through a unique electrokinetically driven on-chip mixing effect. To quantify the concentration performance of the device we use 44 nm polystyrene particles at low electric field strength (between 1.00–2.00 V) and demonstrate close to 90% concentration saturation within 2.5 s. We demonstrate the mixing capability through the enhanced detection of dengue virus serotype 2 (DENV-2). With DENV-2, we successfully detected the SERS signals with a limit of detection of 30 pM.Copyright

Optofluidics: Fluidics Enabling Optics and Optics Enabling Fluidics

Optical devices which incorporate liquids as a fundamental part of the structure can be traced at least as far back as the 18th century where rotating pools of mercury were proposed as a simple technique to create smooth mirrors for use in reflecting telescopes. Modern microfluidic and nanofluidics has enabled the development of a present day equivalent of such devices centered on the marriage of fluidics and optics which we refer to as “Optofluidics.” In this review paper we will present an overview of our approach to the development of three different optofluidic devices. In the first of these we will demonstrate how the fusion of novel nanophotonic structures with micro- and nanofluidic networks can be used to perform ultrasensitive, label free biomolecular analysis. This will be done in the context of our newly developed devices for screening of Dengue and Influenza virus RNA. For the second class of device I will discuss and demonstrate how optical forces (scattering, adsorption and polarization) in solid and liquid core nanophotonic structures can be used to drive novel microfluidic processes. Some of the advanced analytical, numerical and experimental techniques used to investigate and design these systems will be discussed as well as issues relating to integration and their fabrication.Copyright

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.

Electro-active nanowell structures for sensing and optofluidic applications

Here we describe the development of ldquoelectroactiverdquo nanowells which exploit extremely localized electrokinetic effects in order to guide and confine nanoparticles into targeted nanostructures. Applications for the devices include sensing and optofluidically adaptable photonics.

Terahertz microfluidics for on-chip detection and identification of biomolecular compositions and conformations

In this paper, the authors demonstrated that microfluidic devices can be used to perform on-chip THz spectroscopy of biomolecules and chemical agents with high signal-to-noise ratios