Implantable retinal prosthetic devices consisting of microelectrode arrays are being built in attempts to restore vision. Current retinal prostheses use metal planar electrodes. We are developing a novel electro-neural interface using carbon nanotube (CNT) bundles as flexible, protruding microelectrodes. We have synthesized vertically self-assembled, multi-walled CNT bundles by thermal chemical vapor deposition. Using conventional silicon-based micro-fabrication processes, these CNT bundles were integrated onto pre-patterned circuits. CNT protruding electrodes have significant potentials in providing safer stimulation for retinal prostheses. They could also act as recording units to sense electrical and chemical activities in neural systems for fundamental neuroscience research.
Miniaturized, portable and robust sensing systems are required for the development of integrated biological analysis systems and their application to clinical diagnostics. This work uses vertical cavity surface emitting lasers (VCSELs), optical emission filters and PIN photodetectors to realize monolithically integrated, near infrared, fluorescence detection systems. The integration of these micro technologies with biochip applications will drastically reduce cost and allow for parallel sensing architectures, which is particularly useful for flow channel arrays such as in capillary array electrophoresis. This paper focuses on the fabrication of integrated fluorescence sensors. Fabrication procedures have been developed to realize intracavity contacted VCSELs and low noise photodetectors, such as selective AlGaAs wet etching and via planarization. A reflow process with positive photoresist has been developed to provide via electrical contacts and to optically isolate the photodetector from the light source. Three-dimensional microstructures can be simply made by this reflow technique. Optical simulations predict that a detection sensitivity lower than 10000 molecules per 104μm2 sample area. Single molecule detection may be possible in certain sensing architectures.
As biological analysis systems scale to smaller dimensions, the realization of small and portable biosensors becomes increasingly important. The innovation of integrated fluorescence sensors is now possible due to the development of optoelectronics over the past decade. We present the monolithic integration of vertical cavity surface emitting lasers, PIN photo-detectors and optical emission filters to be used as a fluorescence sensor. The integration will drastically reduce cost and size of fluorescence detection systems. Also, parallel sensing architectures of more than one hundred channels will be possible. The sensor will be utilized for near-IR fluorescence detection. This spectral range is compatible with standard AlGaAs optoelectronic technology and will also reduce background fluorescence from complex bio-fluids such as blood. PIN heterostructure photodetectors have been fabricated and tested. Photodetector experiments show extremely low dark current of less than 500fA/mm, quantum efficiency greater than 85 percent and linear detector response. Optical simulations predict a detection sensitivity lower than 10000 fluorescent molecules in a detection area of 104 micrometers 2.