Microelectrode arrays for neural interface devices that are made of biocompatible thin-film polymer are expected to have extended functional lifetime because the flexible material may minimize adverse tissue response caused by micromotion. However, their flexibility prevents them from being accurately inserted into neural tissue. This article demonstrates a method to temporarily attach a flexible microelectrode probe to a rigid stiffener using biodissolvable polyethylene glycol (PEG) to facilitate precise, surgical insertion of the probe. A unique stiffener design allows for uniform distribution of the PEG adhesive along the length of the probe. Flip-chip bonding, a common tool used in microelectronics packaging, enables accurate and repeatable alignment and attachment of the probe to the stiffener. The probe and stiffener are surgically implanted together, then the PEG is allowed to dissolve so that the stiffener can be extracted leaving the probe in place. Finally, an in vitro test method is used to evaluate stiffener extraction in an agarose gel model of brain tissue. This approach to implantation has proven particularly advantageous for longer flexible probes (>3 mm). It also provides a feasible method to implant dual-sided flexible probes. To date, the technique has been used to obtain various in vivo recording data from the rat cortex. Video LinkThe video component of this article can be found at

The rapid growth and development in biodetection technology has largely been driven by the emergence of new and deadly infectious diseases and the realization of biological warfare as new means of terrorism. [1,2] To address the need for portable, multiplex biodetection systems, we report here a novel biosensing platform using engineered nanowires as an alternative substrate for sandwich immunoassays (Figure 1 A). The nanowires are built through submicrometer layering of different metals by electrodeposition within a porous alumina template. [3,4] A variety of metals can be deposited: in this study, we employed stripes of gold, silver, and nickel. Owing to the permutations in which the metals can be deposited, a large number of unique yet easily identifiable encoded nanowires can be included in a multiplex array format.Image processing of an optical reflectance image can enable the stripe pattern to be identified rapidly, while fluorescence images report information on the degree of binding between the antibody-conjugated nanowires and a fluorophore-tagged antigen target. Such nanowires have been utilized to efficiently detect and report both DNA hybridization and immunoassay processes. [5,6] Herein, we demonstrate the feasibility of using multistriped metallic nanowires (Figure 1 A) in a suspended format to enable rapid and sensitive single and multiplex immunoassays for biowarfare agent simulants.Both the hybridization and kinetics of the capture of the target analyte in solution favor the nanowires over conventional fixed array-based formats. The incorporation of an appropriate ferromagnetic metallic component, for example, Ni, enables the nanoparticles to be manipulated by using magnetic fields. [7][8][9][10] To demonstrate the capability of directly detecting potential biological warfare agents in both clinical and environmental samples, a reagent set of three antigens generally accepted for use in simulating actual biothreat agents was chosen. The three nonpathogenic simulants include 1) Bacillus globigii (Bg) spores to simulate Bacillus anthracis and other bacterial species, 2) RNA MS2 bacteriophage to simulate Variola (virus for smallpox) and other pathogenic viruses, and 3) ovalbumin (Ova) protein to simulate protein toxins such as ricin or botulinum toxin. Besides the relative handling safety of these simulants, they were also chosen to reflect the variation in target sizes, ranging from large bacterial spores ( % 2 mm) to small protein molecules ( % 2 nm). Figure 1. A) Analogy between a conventional barcode and a metallic stripeencoded nanowire (diameter % 250 nm; length % 6 mm). Ni segments (50 nm) are deposited at both ends on the magnetic nanowire (not drawn to scale). B) Schematic of the sandwich immunoassay performed on a nanowire. C) Post-assay reflectance and fluorescence readout of the nanowires. The identity of the antigen present can be easily identified from the stripe pattern of the nanowires; for example, the fluorescently lit nanowire to which anti-Bg spore Ab was attached has a stripe pa...

Metallic nanoparticles suspended in aqueous solutions, and functionalized with chemical and biological surface coatings, are important elements in basic and applied nanoscience research. Many applications require an understanding of the electrokinetic or colloidal properties of such particles. In this paper we describe the results of experiments to measure the zeta potential of metallic nanorod particles in aqueous saline solutions, including the effects of pH, ionic strength, metallic composition, and surface functionalization state. Particle substrates tested include gold, silver, and palladium monometallic particles as well as gold/silver bimetallic particles. Surface functionalization conditions included 11-mercaptoundecanoic acid (MUA), mercaptoethanol (ME), and mercaptoethanesulfonic acid (MESA) self-assembled monolayers (SAMs), as well as MUA layers subsequently derivatized with proteins. Zeta potential data for typical charge-stabilized polystyrene particles are also presented for comparison. Experimental data are compared with theory. The results of these studies are useful in predicting and controlling the aggregation, adhesion, and transport of functionalized metallic nanoparticles within microfluidic devices and other systems.

Abstract-Flexible polymer probes are expected to enable extended interaction with neural tissue by minimizing damage from micromotion and reducing inflammatory tissue response. However, their flexibility prevents them from being easily inserted into the tissue. This paper describes an approach for temporarily attaching a silicon stiffener with biodissolvable polyethylene glycol (PEG) so that the stiffener can be released from the probe and extracted shortly after probe placement. A novel stiffener design with wicking channels, along with flipchip technology, enable accurate alignment of the probe to the stiffener, as well as uniform distribution of the PEG adhesive. Insertion, extraction, and electrode function were tested in both agarose gel and a rat brain. Several geometric and material parameters were tested to minimize probe displacement during stiffener extraction. We demonstrated average probe displacement of 28 ± 9 µm.

In vitro brain-on-a-chip platforms hold promise in many areas including: drug discovery, evaluating effects of toxicants and pathogens, and disease modelling. A more accurate recapitulation of the intricate organization of the brain in vivo may require a complex in vitro system including organization of multiple neuronal cell types in an anatomically-relevant manner. Most approaches for compartmentalizing or segregating multiple cell types on microfabricated substrates use either permanent physical surface features or chemical surface functionalization. This study describes a removable insert that successfully deposits neurons from different brain areas onto discrete regions of a microelectrode array (MEA) surface, achieving a separation distance of 100 μm. The regional seeding area on the substrate is significantly smaller than current platforms using comparable placement methods. The non-permanent barrier between cell populations allows the cells to remain localized and attach to the substrate while the insert is in place and interact with neighboring regions after removal. The insert was used to simultaneously seed primary rodent hippocampal and cortical neurons onto MEAs. These cells retained their morphology, viability, and function after seeding through the cell insert through 28 days in vitro (DIV). Co-cultures of the two neuron types developed processes and formed integrated networks between the different MEA regions. Electrophysiological data demonstrated characteristic bursting features and waveform shapes that were consistent for each neuron type in both mono- and co-culture. Additionally, hippocampal cells co-cultured with cortical neurons showed an increase in within-burst firing rate (p = 0.013) and percent spikes in bursts (p = 0.002), changes that imply communication exists between the two cell types in co-culture. The cell seeding insert described in this work is a simple but effective method of separating distinct neuronal populations on microfabricated devices, and offers a unique approach to developing the types of complex in vitro cellular environments required for anatomically-relevant brain-on-a-chip devices.