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Research

DNA Sensor Chip with Integrated Plasmon Resonators, Micro-optics and Microfluidics

Institution: Draper Laboratory
Investigators: Jonathan Bernstein, David Carter, Farhad Hakimi, Mark Mescher

In this research task, a microfluidic chip will be developed that will enable the fast detection and identification of single molecules of DNA, without the need for PCR (polymerase chain reaction).

In the device under development, a microfluidic system will flow single molecules of DNA through an array of metallic nanoparticles, which will be fabricated on an optical waveguide.  The waveguide will excite the surface plasmon resonance, leading to intense fields in the gaps between the metal nanoparticles.  These fields will excite fluorescence from the tagged biomolecules, which will then be collected by a microscope objective.  The greatly reduced excitation volume will lead to a dramatic improvement in the signal-to-noise ratio, compared to traditional diffraction-limited approaches.

sensor chip

Metallic Nanoparticle Arrays for Fluorescence Excitation

Institution: Harvard University, Division of Engineering and Applied Sciences
Investigator: Professor Ken Crozier
Postdoctoral Researcher: Dr Tian Yang

Surface plasmons enable the sub-wavelength confinement and resonant enhancement of optical fields.  This presents an opportunity for improving the signal-to-noise ratio (SNR) in single biomolecule detection, through reduced excitation volume and enhanced fluorescence provided by intense local optical fields.  In this project, we are investigating the design of plasmon resonator structures based on metal nanoparticle chains, for the application of biomolecule detection.

array

Microfabricated Probes for Ultra-high Spatial Resolution Measurements of Field Distributions

Institution: Harvard University, Division of Engineering and Applied Sciences
Investigator: Professor Ken Crozier
Graduate Student Researcher: Yanshu Zou

Progress in the development of metal nanoparticle arrays for the sub-wavelength confinement of optical fields is dependent on tools for the measurement of optical (i.e. electric) field distributions with very high spatial resolution.  Currently, the most widespread method for this purpose is the tapered optical fiber near-field scanning optical microscope (NSOM).  An optical fiber is tapered to form a sharp tip, and the sides are coated with aluminum, leaving a ~50-100 nm opening at the end of the tip.  However, these tips are not sharp enough for the measurement of the fields in the ~20-50 nm gaps of the plasmonic structures under investigation by the Center (see "2. Metallic Nanoparticle Arrays").  In this task, we will develop new probes for NSOM based on the combination of plasmonics with atomic force microscopy.

Diblock Copolymer Fabrication and Characterization of Metallic Nanostructures

Institution: University of Massachusetts at Amherst, Physics Department
Investigators: Professor Mark Tuominen and Professor Marc Achermann

The widespread use of plasmonic nanostructures in MEMS applications will require that them to be conveniently manufacturable and compatible with conventional processing steps.  To achieve this, nanoporous array templates derived from diblock copolymer films will be used as a deposition or etch mask to produce arrays of silver or gold nanoscale plasmonic elements.  We will utilize recently developed techniques for producing 10-20 nm scale metal cylinders, dots, rings, and holes in metal films.

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In the plasmonic fluorescence sensor investigated by the Center, the fluorescent emitters are in close proximity to metal nanostructures.  As a result of antenna effects, the metal nanostructure can locally enhance electric fields, which can dramatically increase the emission efficient of the emitter, thereby increasing sensor performance.  However, it is well known that the emission of a dipole in the close proximity of a metal surface can be significantly quenched as a result of its interaction with free electrons in the metal.  Our goal will be to design and build a plasmonic sensor that exploits field enhancement effects while keeping quenching effects minimal by controlling the distance between metal and emitter.

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Metallic Nanoparticle Optical Fiber Sensor

Institution: Harvard University, Division of Engineering and Applied Sciences
Investigator: Professor Federico Capasso
Graduate Student Researchers: Ertugrul Cubukcu, Jenny Smythe

In this project, a new probe for Surface-Enhanced Raman Scattering (SERS) will be demonstrated.  The probe will consist of an optical fiber, with an array of metallic nanoparticles fabricated on the end face.  Light from a diode laser will be coupled in to the optical fiber.  The intense localized near fields of the metallic nanostructures ("antennas") will produce giant enhancement of the SERS cross section of molecules in the immediate vicinity of the fiber.  The optical fiber will allow remote positioning within a microfluidic lab-on-a-chip for the detection of biological molecules at ultra-low concentrations.

Sensor

Nanohole Array Sensor with Integrated Asynchronous, Partitioned, Microfluidic Sample Delivery

Institution: Harvard Medical School
Investigators: Dale Larson and James Hogle

In this project, we will develop a nanohole array biosensor for the detection and characterization of interactions between viruses and membrane-bound receptors at the single particle (virus) level.  The detector combines a simple system for preparing receptor-decorated artificial membranes with a nanohole array sensor technology.

The project will demonstrate the detection of single poliovirus particle binding to membrane bound receptors.  The real-time characterization of receptor-mediated conformational changes in poliovirus that results from insertion of viral sequences at the single particle level will be monitored.  Nanohole array sensor prototypes with integrated microfluidic manifolds will be demonstrated.

nanosensor