On-Chip Photoacoustics-Activated Cell Sorting (PA-ACS) for Label-Free and High-Throughput Detection and Screening of Microalgal Cells.

Microalgae play a crucial role in global carbon cycling as they convert carbon dioxide into various valuable macromolecules. Among them, Haematococcus pluvialis (H. pluvialis) is the richest natural source of astaxanthin (AXT), which is a valuable antioxidant, anti-inflammatory, and antiapoptosis agent. These benefits make AXT highly commercially valuable in pharmaceuticals, cosmetics, and nutritional industries. However, intrinsic genetic characteristics and extrinsic cultivation conditions influence biomass gains, leading to low productivity and extraction as the main techno-economic bottlenecks in this industry. Thus, detecting AXT in H. pluvialis is essential to determine the influence of multiple parameters on biocompound accumulation, enabling optimization of cultivation and enrichment of AXT-rich H. pluvialis cells. This work developed an opto-acousto-fluidic microplatform for detection, analysis, and sorting of microalgae. Via label-free monitoring and extraction of sample-induced ultrasonic signals, a photoacoustic microscopic system was proposed to provide a full-field visualization of AXT's content and distribution inside H. pluvialis cells. When employed as on-chip image-based flow cytometry, our microplatform can also offer high-throughput measurements of intracellular AXT in real time, which demonstrates similar results to conventional spectrophotometry methods and further reveals the heterogeneity of AXT content at the single-cell level. In addition, a solenoid valve-pump dual-mode cell sorter was integrated for effective sorting of cells with a maximum working frequency of 0.77 Hz, reducing the fluid response time by 50% in rising and 40-fold in recovery. The H. pluvialis cells which have more AXT accumulation (>30 µm in diameter) were 4.38-fold enriched with almost no dead empty and small green cells. According to the results, automated and reliable photoacoustics-activated cell sorting (PA-ACS) can screen AXT-rich cells and remove impurities at the terminal stage of cultivation, thereby increasing the effectiveness and purity of AXT extraction. The proposed system can be further adopted to enrich strains and mutants for the production of biofuels or other rare organic substances such as ß-carotene and lutein.

Automated assembly of high-density carbon fiber electrode arrays for single unit electrophysiological recordings.

Objective.Carbon fiber (CF) is good for chronic neural recording due to the small diameter (7µm), high Young's modulus, and low electrical resistance, but most high-density carbon fiber (HDCF) arrays are manually assembled with labor-intensive procedures and limited by the accuracy and repeatability of the operator handling. A machine to automate the assembly is desired.Approach.The HDCF array assembly machine contains: (1) a roller-based CF extruder, (2) a motion system with three linear and one rotary stages, (3) an imaging system with two digital microscope cameras, and (4) a laser cutter. The roller-based extruder automatically feeds single CF as raw material. The motion system aligns the CF with the array backend then places it. The imaging system observes the relative position between the CF and the backend. The laser cutter cuts off the CF. Two image processing algorithms are implemented to align the CF with the support shanks and circuit connection pads.Main results.The machine was capable of precisely handling 6.8µm carbon fiber electrodes (CFEs). Each electrode was placed into a 12µm wide trenches in a silicon support shank. Two HDCF arrays with 16 CFEs populated on 3 mm shanks (with 80µm pitch) were fully assembled. Impedance measurements were found to be in good agreement with manual assembled arrays. One HDCF array was implanted in the motor cortex in an anesthetized rat and was able to detect single unit activity.Significance.This machine can eliminate the manual labor-intensive handling, alignment and placement of single CF during assembly, providing a proof-of-concepts towards fully automated HDCF array assembly and batch production.

Open-source Toolkit: Benchtop Carbon Fiber Microelectrode Array for Nerve Recording.

Conventional peripheral nerve probes are primarily fabricated in a cleanroom, requiring the use of multiple expensive and highly specialized tools. This paper presents a cleanroom "light" fabrication process of carbon fiber neural electrode arrays that can be learned quickly by an inexperienced cleanroom user. This carbon fiber electrode array fabrication process requires just one cleanroom tool, a Parylene C deposition machine, that can be learned quickly or outsourced to a commercial processing facility at marginal cost. This fabrication process also includes hand-populating printed circuit boards, insulation, and tip optimization. The three different tip optimizations explored here (Nd:YAG laser, blowtorch, and UV laser) result in a range of tip geometries and 1 kHz impedances, with blowtorched fibers resulting in the lowest impedance. While previous experiments have proven laser and blowtorch electrode efficacy, this paper also shows that UV laser-cut fibers can record neural signals in vivo. Existing carbon fiber arrays either do not have individuated electrodes in favor of bundles or require cleanroom fabricated guides for population and insulation. The proposed arrays use only tools that can be used at a benchtop for fiber population. This carbon fiber electrode array fabrication process allows for quick customization of bulk array fabrication at a reduced price compared to commercially available probes.

Flexible High-Resolution Force and Dimpling Measurement System for Pia and Dura Penetration During In Vivo Microelectrode Insertion Into Rat Brain.

OBJECTIVE: Understanding the in vivo force and tissue dimpling during micro-electrode implantation into the brain are important for neuro-electrophysiology to minimize damage while enabling accurate placement and stable chronic extracellular electrophysiological recordings. Prior studies were unable to measure the sub-mN forces exerted during in vivo insertion of small electrodes. Here, we have investigated the in vivo force and dimpling depth profiles during brain surface membrane rupture (including dura) in anesthetized rats. METHODS: A µN-resolution cantilever beam-based measurement system was designed, built, and calibrated and adapted for in vivo use. A total of 244 in vivo insertion tests were conducted on 8 anesthetized rats with 121 through pia mater and 123 through dura and pia combined. RESULTS: Both microwire tip sharpening and diameter reduction reduced membrane rupture force (insertion force) and eased brain surface penetration. But dimpling depth and rupture force are not always strongly correlated. Multi-shank silicon probes showed smaller dimpling and rupture force per shank than single shank devices. CONCLUSION: A force measurement system with flexible range and µN-level resolution (up to 0.032 µN) was achieved and proved feasible. For both pia-only and dura-pia penetrations in anesthetized rats, the rupture force and membrane dimpling depth at rupture are linearly related to the microwire diameter. SIGNIFICANCE: We have developed a new system with both µN-level resolution and capacity to be used in vivo for measurement of force profiles of various neural interfaces into the brain. This allows quantification of brain tissue cutting and provides design guidelines for optimal neural interfaces.

Laser Sharpening of Carbon Fiber Microelectrode Arrays for Brain Recording.

Microwire microelectrode arrays (MEAs) are implanted in the brain for recording neuron activities to study the brain function. Among various microwire materials, carbon fiber stands out due to its small diameter (5-10 µm), relatively high Young's modulus, and low electrical resistance. Microwire tips in MEAs are often sharpened to reduce the insertion force and prevent the thin microwires from buckling. Currently, carbon fiber MEAs are sharpened by either torch burning, which limits the positions of wire tips to a water bath surface plane, or electrical discharge machining, which is difficult to implement to the nonelectrically conductive carbon fiber with parylene-C insulation. A laser-based carbon fiber sharpening method proposed in this study enables the fabrication of carbon fiber MEAs with sharp tips and custom lengths. Experiments were conducted to study effects of laser input voltage and transverse speed on carbon fiber tip geometry. Results of the tip sharpness and stripped length of the insulation as well as the electrochemical impedance spectroscopy measurement at 1 kHz were evaluated and analyzed. The laser input voltage and traverse speed have demonstrated to be critical for the sharp tip, short stripped length, and low electrical impedance of the carbon fiber electrode for brain recording MEAs. A carbon fiber MEA with custom electrode lengths was fabricated to validate the laser-based approach.