Philipp S. Spuhler

Floating light-activated microelectrical stimulators tested in the rat spinal cord

Microelectrodes of neural stimulation utilize fine wires for electrical connections to driving electronics. Breakage of these wires and the neural tissue response due to their tethering forces are major problems encountered with long-term implantation of microelectrodes. The lifetime of an implant for neural stimulation can be substantially improved if the wire interconnects are eliminated. Thus, we proposed a floating light-activated microelectrical stimulator (FLAMES) for wireless neural stimulation. In this paradigm, a laser beam at near infrared (NIR) wavelengths will be used as a means of energy transfer to the device. In this study, microstimulators of various sizes were fabricated, with two cascaded GaAs p-i-n photodiodes, and tested in the rat spinal cord. A train of NIR pulses (0.2 ms, 50 Hz) was sent through the tissue to wirelessly activate the devices and generate the stimulus current. The forces elicited by intraspinal stimulation were measured from the ipsilateral forelimb with a force transducer. The largest forces were around 1.08 N, a significant level of force for the rat forelimb motor function. These in vivo tests suggest that the FLAMES can be used for intraspinal microstimulation even for the deepest implant locations in the rat spinal cord. The power required to generate a threshold arm movement was investigated as the laser source was moved away from the microstimulator. The results indicate that the photon density does not decrease substantially for horizontal displacements of the source that are in the same order as the beam radius. This gives confidence that the stimulation threshold may not be very sensitive to small displacement of the spinal cord relative to the spine-mounted optical power source.

Platform for in situ real-time measurement of protein-induced conformational changes of DNA

A platform for in situ and real-time measurement of protein-induced conformational changes in dsDNA is presented. We combine electrical orientation of surface-bound dsDNA probes with an optical technique to measure the kinetics of DNA conformational changes. The sequence-specific Escherichia coli integration host factor is utilized to demonstrate protein-induced bending upon binding of integration host factor to dsDNA probes. The effects of probe surface density on binding/bending kinetics are investigated. The platform can accommodate individual spots of microarrayed dsDNA on individually controlled, lithographically designed electrodes, making it amenable for use as a high throughput assay.

Quantification of surface etching by common buffers and implications on the accuracy of label-free biological assays

High throughput analyses in biochemical assays are gaining popularity in the post-genomic era. Multiple label-free detection methods are especially of interest, as they allow quantitative monitoring of biomolecular interactions. It is assumed that the sensor surface is stable to the surrounding medium while the biochemical processes are taking place. Using the Interferometric Reflectance Imaging Sensor (IRIS), we found that buffers commonly used in biochemical reactions can remove silicon dioxide, a material frequently used as the solid support in the microarray industry. Here, we report 53 pm to 731 pm etching of the surface silicon oxide over a 12-h period for several different buffers, including various concentrations of SSC, SSPE, PBS, TRIS, MES, sodium phosphate, and potassium phosphate buffers, and found that PBS and MES buffers are much more benign than the others. We observe a linear dependence of the etch depth over time, and we find the etch rate of silicon dioxide in different buffers that ranges from 2.73±0.76 pm/h in 1M NaCl to 43.54±2.95 pm/h in 6×SSC. The protective effects by chemical modifications of the surface are explored. We demonstrate unaccounted glass etching leading to erroneous results with label-free detection of DNA microarrays, and offer remedies to increase the accuracy of quantitative analysis.

In Vitro Testing of Floating Light Activated Micro-Electrical Stimulators

Chronic tissue response to microelectrode implants stands in the way as a major challenge to development of many neural prosthetic applications. The long term tissue response is mostly due to the movement of interconnects and the resulting mechanical stress between the electrode and the surrounding neural tissue. Remotely activated floating micro-stimulators are one possible method of eliminating the interconnects. As a method of energy transfer to the micro-stimulator, we proposed to use a laser beam at near infrared (NIR) wavelengths. FLAMES of various sizes were fabricated with integrated silicon PIN photodiodes. Sizes varied from 120 (Width) × 300 (Length) × 100 (Height) µm to 200 × 500 × 100µm. Devices were bench tested using 850nm excitation from a Ti:Sapphire laser. To test this method, the voltage field of the FLAMES was experimentally tested in saline solution pulsed with a NIR laser beam. The voltage generated is around 196mV in peak at the cathodic contact as a response to a single pulse. When a train of laser pulses was applied at 100Hz, the peak voltage at the cathodic contact remained around 141mV suggesting the feasibility of this approach for applications with pulse frequencies up to 100Hz.

Precisely controlled smart polymer scaffold for nanoscale manipulation of biomolecules.

We demonstrate the application of a novel smart surface to modulate the orientation of immobilized double stranded DNA (dsDNA) and the conformation of a polymer scaffold through variation in buffer pH and ionic strength. An amphoteric poly(dimethylacrylamide) based coating containing weak acrylamido acids and bases, which are copolymerized together with the neutral monomer, is covalently bound to the surface. The coating can be made to contain any desired amount of buffering and titrant ionogenic monomers, allowing control of the surface charge when the surface is bathed in a given buffer pH. Spectral self-interference fluorescence microscopy (SSFM) is utilized to precisely quantify both the DNA orientation and the polymer conformation with subnanometer resolution. It is possible to utilize the polymer scaffold to functionalize a variety of common materials used in microfabrication, making it a general purpose building block for the next generation of nanomachines and biosensors.

Addressable floating light activated micro-electrical stimulators for wireless neurostimulation

Stimulation of the central nervous system can be useful for treating neurological disorders. Wireless neurostimulating devices have the benefit that they can float in tissue and do not experience the sheering caused by tethering tension that non-wireless stimulators impose on connecting wires. An optically powered, logic controlled, CMOS microdevice that can decode telemetry data from an optical packet is a potential way of implementing wireless, addressable, microstimulators. Through the use of an optical packet, different devices can be addressed for stimulation, allowing spatially selective activation of neural tissue. This work presents the design and simulations of such a neural stimulation device, specifically an optically powered CMOS circuit that decodes telemetry data and determines whether it has been addressed.

Intraspinal stimulation with light activated micro-stimulators

Chronic tissue response to microelectrode implants stands in the way as a major challenge to development of many neural prosthetic applications. The long term tissue response is mostly due to the movement of interconnects and the resulting mechanical stress between the electrode and the surrounding neural tissue. Wireless microstimulators are a potential solution to the problem. As a method of energy transfer to the microstimulator, we propose to use a laser beam at near infrared (NIR) wavelengths. Microstimulators of various sizes were fabricated with two cascaded GaAs PIN photodiodes. The voltage field of the device was measured in saline solution as a response to an NIR laser source. The voltage in medium had a peak of around 190 mV above the cathodic contact and stayed flat for the duration of 0.2 ms pulse. In rats, microstimulators were inserted into the ventral horn of cervical spinal cord. A train of NIR pulses (0.2 ms, 100 Hz) were applied to wirelessly activate the devices. The forces generated due to stimulation of the motor neurons were measured from the ipsilateral forelimb with a force transducer. The largest force generated was around 0.9 N. The volume conductor and force measurements suggest that the floating light activated micro-electrical stimulator (FLAMES) approach is feasible for intraspinal stimulation.

Precise quantification and control of surface immobilized DNA orientation

We utilize spectral self-interference fluorescent microscopy (SSFM) to measure fluorophore height with sub-nm precision to precisely quantify DNA orientation and conformation. A novel polymeric 3D scaffold is used to functionalize the sensor surface and permits controlled orientation of the surface anchored DNA.

A platform for in situ real-time measurement of protein induced conformational changes of DNA

A platform for in situ and real-time measurement of protein induced conformational changes in dsDNA is presented. We demonstrate protein induced bending upon sequence specific binding of Integration Host Factor (IHF) to dsDNA probes.

Spectral Self-Interference Fluorescence Microscopy to Study Conformation of Biomolecules with Nanometer Accuracy

Despite the completion of the human genome sequencing, the revolution of personalized medicine still seems years away [1,2]. Although the Human Genome Project provides researchers with enormous amounts of genetic information, the genome is far more complex than the sequences it contains. Part of the reason is that DNA functions through critical interactions with proteins, such as genome packaging, epigenetic modifications, transcription, DNA replication, and DNA repair [3–7]. Since the idealized B-form DNA proposed more than 50 years ago by Watson and Crick, researchers have found that the conformation of DNA is naturally distorted and, depending on the particular sequence, DNA can be curved, tightly bent, or kinked [8–10]. These intrinsic variant conformations of DNA are recognized, stabilized, or even enhanced upon the formation of DNA–protein complexes CONTENTS