Microsyringe Pump Research Articles

Dual Lab-in-Syringe Flow-Batch Platform for Automatic Fabric Disk Sorptive Extraction/Back-extraction as a Front End to Inductively Coupled Plasma Atomic Emission Spectrometry.

A novel dual lab-in-syringe flow-batch (D-LIS-FB) platform for automatic fabric-disk-in-syringe sorptive extraction followed by oxidative back-extraction as a front end to inductively coupled plasma atomic emission spectrometry (ICP-AES) is presented for the first time. Sol-gel poly(caprolactone)-poly(dimethylsiloxane)-poly(caprolactone)-coated polyester fabric disks were packed at the top of the glass barrel of a microsyringe pump as an alternative to column preconcentration. Herein lie multiple significant advantages including effectiveness, compactness, lower back-pressure, and lower time of analysis. Copper, lead, and cadmium were used as model analytes for the exploration of the capabilities of the developed platform. The online retained metal-diethyldithiophosphate complexes were eluted using diisopropyl ketone prior to atomization. Undesirable incompatibility of organic solvents for direct injection into the ICP-AES system was overcome ingeniously in a flow manner by oxidative back-extraction of the analytes utilizing a second lab-in-syringe setup. Following its optimization, the D-LIS-FB platform showed excellent linearity, in combination with good method precision (i.e., RSD < 3.4%) and trueness. Moreover, the limits of detection were 0.25 μg L-1 for Cd(II), 0.13 μg L-1 for Cu(II), and 0.37 μg L-1 for Pb(II), confirming the applicability of the proposed system for metal analysis at trace levels. As a proof-of-concept, the developed versatile system was utilized for the analysis of different environmental, food, and biological samples.

A Microfabricated Pistonless Syringe Pump Driven by Electro‐Conjugate Fluid with Leakless On/Off Microvalves (Small 15/2022)

Pistonless Syringe Pumps In article number 2106221, Joon-wan Kim and co-workers propose an on-chip microsyringe pump without mechanical sliding parts and with high power sources. As a liquid handing workstation is used for high throughput screening, the authors' micropumps integrated with other microfluidic devices by micro-electro-mechanical systems fabrication have the potential to perform the same function on a palm-sized device in the future.

An increase in spontaneous activity mediates visual habituation.

SUMMARYThe cerebral cortex is spontaneously active, but the function of this ongoing activity remains unclear. To test whether spontaneous activity encodes learned experiences, we measured the response of neuronal populations in mouse primary visual cortex with chronic two-photon calcium imaging during visual habituation to a specific oriented stimulus. We find that, during habituation, spontaneous activity increases in neurons across the full range of orientation selectivity, eventually matching that of evoked levels. This increase in spontaneous activity robustly correlates with the degree of habituation. Moreover, boosting spontaneous activity with two-photon optogenetic stimulation to the levels of visually evoked activity accelerates habituation. Our study shows that cortical spontaneous activity is linked to habituation, and we propose that habituation unfolds by minimizing the difference between spontaneous and stimulus-evoked activity levels. We conclude that baseline spontaneous activity could gate incoming sensory information to the cortex based on the learned experience of the animal.

A Microfabricated Pistonless Syringe Pump Driven by Electro-Conjugate Fluid with Leakless On/Off Microvalves.

In contrast to microfluidic devices, bulky syringe pumps are widely used to deliver a small amount of solution with high accuracy. Miniaturizing the syringe pump is difficult due to the scale effect in the microscale where the friction of the piston-cylinder is dominant and there are few high-power microactuators. To solve these problems, an on-chip microsyringe pump without mechanical sliding parts and with high power sources is proposed. The microsyringe pump utilizes the interface between water and oil (electro-conjugate fluid, ECF) instead of a piston and an electrohydrodynamic (EHD) flow driven by ECF in place of a linear actuator. ECF as a functional fluid has two capabilities: a) making the water-oil interface in microchannels and b) generating an active ECF flow at an applied voltage to withdraw and infuse aqueous solution by the interface. To control the flow direction, ECF-driven leakless on/off microvalves are also integrated. It is demonstrated that the proposed ECF microsyringe pump synchronized with the ECF on/off microvalves can control the withdrawing and infusing of aqueous solution with high resolution and precision. The experiments prove the feasibility of the microsyringe pump to be embedded as a module for the precise and linear control of flow rates in microfluidic devices.

Penta-Twinned Rh@Pt Core-Shell nanobranches with engineered shell thickness for reversible and active hydrogen redox electrocatalysis

Surface defects on electrocatalysts can effectively reduce reaction barriers and facilitate the kinetics of hydrogen evolution and oxidation reactions (HER/HOR). However, precisely engineering such surface structures remains a significant challenge. Herein, penta-twinned (PTw) Rh@Ptx core–shell nanobranches (NBs) with intense surface strains were facilely synthesized using PTw Rh NBs as the seeds for overgrowth of active Pt-shells. Through precisely regulating the supply of Pt precursor solution via a micro-syringe pump, the ultrathin Pt-shells conform to and replicate the twin defects of the PTw Rh seeds. Significantly, the shell thickness can be precisely controlled from 1.0, 2.0, and 3.8 to 5.0 atomic layers. Due to the integration of surface twinned defects, compressive strain and the core–shell ligand effect, these Rh@Ptx NBs exhibit superior hydrogen redox electrocatalytic performance compared to state-of-the-art Pt/C. Among the prepared materials, the Rh@Pt0.83 NBs with a 3.8 atomic layer Pt-shell showed the highest mass activity (2.36 A mgPt−1) and specific activity (6.55 mA cm−2) for HER at –0.07 V and presented the lowest overpotential (44 mV) at 10 mA cm−2, less than half the overpotential of the commercial Pt/C (98 mV). In terms of HOR, the Rh@Pt0.83 NBs showed a superior exchange current density (1.97 mA cm−2), approximately 7 times higher than that of Pt/C. Our work provides a facile method to synchronously engineer the Pt-shell thickness and surface defects of Rh@Pt core–shell nanocatalysts for the creation of robust and bifunctional hydrogen redox electrocatalysts.

Optimal Ratio of Wnt3a Expression in Human Mesenchymal Stem Cells Promotes Axonal Regeneration in Spinal Cord Injured Rat Model.

ObjectiveThrough our previous clinical trials, the demonstrated therapeutic effects of MSC in chronic spinal cord injury (SCI) were found to be not sufficient. Therefore, the need to develop stem cell agent with enhanced efficacy is increased. We transplanted enhanced Wnt3a-secreting human mesenchymal stem cells (hMSC) into injured spines at 6 weeks after SCI to improve axonal regeneration in a rat model of chronic SCI. We hypothesized that enhanced Wnt3a protein expression could augment neuro-regeneration after SCI. MethodsThirty-six Sprague-Dawley rats were injured using an Infinite Horizon (IH) impactor at the T9–10 vertebrae and separated into five groups : 1) phosphate-buffered saline injection (injury only group, n=7); 2) hMSC transplantation (MSC, n=7); 3) hMSC transfected with pLenti vector (without Wnt3a gene) transplantation (pLenti-MSC, n=7); 4) hMSC transfected with Wnt3a gene transplantation (Wnt3a-MSC, n=7); and 5) hMSC transfected with enhanced Wnt3a gene (1.7 fold Wnt3a mRNA expression) transplantation (1.7 Wnt3a-MSC, n=8). Six weeks after SCI, each 5×105 cells/15 µL at 2 points were injected using stereotactic and microsyringe pump. To evaluate functional recovery from SCI, rats underwent Basso-Beattie-Bresnahan (BBB) locomotor test on the first, second, and third days post-injury and then weekly for 14 weeks. Axonal regeneration was assessed using growth-associated protein 43 (GAP43), microtubule-associated protein 2 (MAP2), and neurofilament (NF) immunostaining. ResultsFourteen weeks after injury (8 weeks after transplantation), BBB score of the 1.7 Wnt3a-MSC group (15.0±0.28) was significantly higher than that of the injury only (10.0±0.48), MSC (12.57±0.48), pLenti-MSC (12.42±0.48), and Wnt3a-MSC (13.71±0.61) groups (p<0.05). Immunostaining revealed increased expression of axonal regeneration markers GAP43, MAP2, and NF in the Wnt3a-MSC and 1.7 Wnt3a-MSC groups. ConclusionOur results showed that enhanced gene expression of Wnt3a in hMSC can potentiate axonal regeneration and improve functional recovery in a rat model of chronic SCI.

Immunocytochemical Analysis of α-Tubulin Distribution Before and After Rapid Axopodial Contraction in the Centrohelid Raphidocystis contractilis

The centrohelid Raphidocystis contractilis is a heliozoan that has many radiating axopodia, each containing a bundle of microtubules. Although the rapid contraction of the axopodia at nearly a video rate (30 frames/s) is induced by mechanical stimuli, the mechanism underlying this phenomenon in R. contractilis has not yet been elucidated. In the present study, we described for the first time an adequate immunocytochemical fixation procedure for R. contractilis and the cellular distribution of α-tubulin before and after rapid axopodial contraction. We developed a flow-through chamber equipped with a micro-syringe pump that allowed the test solution to be injected at a flow rate below the threshold required to induce rapid axopodial contraction. Next, we used this injection method for evaluating the effects of different combinations of two fixatives (paraformaldehyde or glutaraldehyde) and two buffers (phosphate buffer or PHEM) on the morphological structure of the axopodia. A low concentration of glutaraldehyde in PHEM was identified as an adequate fixative for immunocytochemistry. The distribution of α-tubulin before and after rapid axopodial contraction was examined using immunocytochemistry and confocal laser scanning fluorescence microscopy. Positive signals were initially detected along the extended axopodia from the tips to the bases and were distributed in a non-uniform manner within the axopodia. Conversely, after the induction of a rapid axopodial contraction, these positive signals accumulated in the peripheral region of the cell. These results indicated that axopodial microtubules disassemble into fragments and/ or tubulin subunits during rapid axopodial contraction. Therefore, we hypothesize that the mechanism of extremely rapid axopodial contraction accompanied by cytoskeletal microtubule degradati

Low-cost fabrication of a polydimethylsiloxane (PDMS) microreactor using an improved Print-and-Peel (PAP) method and its performance testing in silver nanoparticle synthesis

Abstract A polydimethylsiloxane (PDMS) microreactor was fabricated using an improved Print-and-Peel (PAP) method. Its performance in terms of conversion was studied by observing the formation of silver (Ag) nanoparticles within the microreactor. Using an improvised LEGO® microsyringe pump, 0.001 M silver nitrate (AgNO3) and 0.002 M sodium borohydride (NaBH4) were introduced in the microchannels. Microreactor length and pumping speed were varied, and their effects on conversion were determined. Results showed that conversion increases with reactor length. Conversions in low speed (130 rad/s) were found to be higher than those in high speed (269 rad/s). Highest conversion of 32.52% was obtained for the 16-mm microreactor at low speed. The mean nanoparticle size of 24 nm measured through Scanning Electron Microscopy (SEM) is smaller than the range of 30 to 60 nm in the macroscale set-up. Spectrophotometric analysis showed that the particle size distribution in the microscale is narrower compared to that of the macroscale indicating the formation of more homogeneous and monodispersed nanoparticles in the microreactor. From the cost analysis, the cost of fabrication is fifty-fold less than that of commercial fabrication. Hence, the fabricated microreactor provides a competitive alternative for conventionally-produced microreactors

Fully Automated Electric-Field-Driven Liquid Phase Microextraction System with Renewable Organic Membrane As a Front End to High Performance Liquid Chromatography.

This article reports for the first time a programmable-flow-based mesofluidic platform that accommodates electric-field-driven liquid phase microextraction (μ-EME) in a fully automated mode. The miniaturized system is composed of a computer-controlled microsyringe pump and a multiposition rotary valve for handling aqueous and organic solutions at a low microliter volume and acts as a front-end to online liquid chromatographic separation. The organic membrane is automatically renewed and disposed of in every analytical cycle, thus minimizing analyte carry-over effects while avoiding analyst intervention. The proof-of-concept applicability of the automated mesofluidic device is demonstrated by the liquid chromatographic determination of nonsteriodal anti-inflammatory drugs in μ-EME processed complex samples (such as urine and influent wastewater) using online heart-cut approaches. Using 5 μL of 1-octanol, 7.5 μL of untreated sample and 7.5 μL of acceptor solution (25 mM NaOH), and 250 V for only 10 min in a stopped-flow mode, the extraction recoveries for the μ-EME of ibuprofen, ketoprofen, naproxen, and diclofenac exceed 40% in real samples. The flow-through system features moderately selective extraction regardless of the sample matrix constituents with repeatability values better than 13%.

Collection of cerebrospinal fluid from murine lateral ventricles for biomarker determination in mucopolysaccharidosis type IIIA

BackgroundCerebrospinal fluid (CSF) collection is currently the only feasible means to obtain biological fluid for the quantitative determination of biomarkers that may reflect disease activity within the brain. Studies in mouse models of human neurological disease benefit from ascertainment and subsequent analysis of brain tissue that is not afforded in human patients. The CSF provides a translational forum, however, due to the practical constraints presented by the mouse’s small size, CSF is often ignored in experimental mouse models. New methodHere we report a method for the controlled, precise and predictable collection of 10 μL of CSF from the lateral ventricles of adult mice using stereotaxic equipment and a micro-syringe pump. ResultsCollected CSF was clear and manifested the consistency of water and moreover, quantification of a disease-specific biomarker for the neurodegenerative disorder, mucopolysaccharidosis type IIIA (MPS IIIA) was possible in this small volume of CSF. In the naturally occurring mouse model of MPS IIIA, that faithfully recapitulates the human form of the disease, this biomarker was present at concentrations of >100 pmol/mL and undetectable in wild-type mice. Comparison with existing methodAdvantages of this method over the most commonly used cisterna magna collection technique include increased CSF sample volume (10 μL) and reduced blood contamination. ConclusionThe ability to collect CSF from mouse models of neurological disease enables a forum for translating research outcomes in experimental models to the human equivalent in which CSF collection is also possible.

Effects of the Numbers and the Shapes of Venting Slits on Intraocular Pressure after Baerveldt Glaucoma Drainage Implant

ABSTRACTPurpose: Venting slits are widely used as an effective method to avoid the high intraocular pressure (IOP) phase immediately after the implantation of non-valved glaucoma drainage devices. However, there have been no detailed reports comparing the types of needles used and the numbers of slits made. In this study we investigated the effects of different needle types and the number of venting slits.Methods: IOP was measured using a Keyence NR-600 transducer connected to the limbus of a pig eye with a 27G needle. A microsyringe pump was also connected to the corneal limbus using a 27 G needle to make a continuous perfusion system at the rate of 200 μl/hr. The silicone tube of a Baerveldt glaucoma drainage implant (BG101-350) was ligated near the plate and then implanted in the anterior chamber of the pig eye. The tube was covered with scleral tissue of another pig eye after 1 or 3 venting slits were created in the middle of the outer diameter using different types of needles (7–0 Vicryl®, 7–0 PDSⅡ®, 5–0 PDSⅡ®, 3–0 PDS Plus®). IOP measurement was started from 50 mmHg and then we monitored the chronological changes of IOP for 15 minutes.Results: The IOPs at 15 minutes after continuous perfusion with the venting slits made using 7–0 Vicryl needles were 29.0 ± 2.5 mmHg (1 slit) and 23.1 ± 8.3 mmHg (3 slits). The IOPs were 23.1 ± 3.1 mmHg and 23.5 ± 4.7 mmHg with 7–0 PDS needles (1 slit and 3 slits, respectively), 21.8 ± 2.2 mmHg and 20.8 ± 4.3 mmHg with 5–0 PDS needles (1 slit and 3 slits, respectively), and with 3–0 PDS needles they were 12.2 ± 3.0 mmHg for one slit and 13.2 ± 3.5 mmHg for 3 slits.Conclusions: Usage of a round (PDS) needles produces more predictable IOP than a spatulated (Vicryl) needle.

Nanostructured polyaniline based pipette tip solid phase extraction coupled with high-performance liquid chromatography for the selective determination of trace levels of three sulfonamides in honey and milk samples with the aid of experimental design methodology

In this study, a miniaturized solid-phase extraction based on 2-(hexyloxy) naphthalene-sulfate doped polyaniline polymer as a new nanostructured sorbent packed into a 200 μL pipette tip (PT-SPE) as a rapid and efficient method was developed for the simultaneous and selective extraction of three sulfonamide (SAs) antibiotics in aqueous solution. The resultant polymer was well characterized by FT-IR, UV–Vis., FESEM, EDX and XRD. In this strategy, the pipette tip containing the sorbent was matched to a syringe and the sample solution was loaded onto the sorbent using a microsyringe pump. The eluate was analyzed with high performance liquid chromatography using UV–Vis. spectrometry detection (HPLC/UV–Vis). In preliminary experiments, sample pH, sorbent dosage, sample volume and eluent volume were identified as critical variables affecting the solid phase micro-extraction of SAs by the developed sorbent. The response surface methodology (RSM) based on a rotatable central composite design (CCD) was employed for modeling the chromatographic peak areas of SAs as responses and optimized the effective extraction variables. This method is cost-effective because only 7.4 mg sorbent amount and 0.6 mL methanol as eluent were required for the extraction of analytes. The multiple response criteria were used to optimize simultaneous responses of the analytes using the desirability function. Under the optimal conditions, a good linear relationship between the peak areas and concentrations of the SAs was found in the range of 50–50,000 ng mL−1 with correlation coefficients above 0.999. The developed method was successfully applied to the analysis of SAs in milk, and honey samples.

Low-cost fabrication and performance testing of Polydimethylsiloxane (PDMS) micromixers using an improved print-and-Peel (PAP) method

The research presents different configurations of microfluidic mixers made from polydimethylsiloxane (PDMS) fabricated using an improved, low-cost print-and-peel (PAP) method. Processes, such as mixing, operated in the micro scale allow decreased equipment size-to-production capacity ratio and decreased energy consumption per unit product. In the study, saturated solutions of blue and yellow food dyes were introduced inside the channels using a LEGO® improvised microsyringe pump. Scanning Electron Microscopy (SEM) was used to determine the average depth of the fabricated micromixers which was found to be around 14 ¼m. The flows were observed and images were taken using a light microscope. The color intensities of the images were then measured using MATLAB®. From the relationship between color intensity and concentration, the mixing indices were calculated and found to be 0.9435 to 0.9941, which falls within the standard mixing index range (0.8 – 1.0) regardless of the flow rate and the configuration of the micromixer as verified through the two-way ANOVA. From the cost analysis, the cost of the device fabricated in this study is a hundred-fold less than expenses from standard fabrication procedures. Hence, the fabricated device provides an alternative for micromixers produced from expensive and conventional lithographic methods.

The Microbead Occlusion Model of Ocular Hypertension in Mice.

Glaucoma is a common optic neuropathy that leads to vision loss through the degeneration of retinal ganglion cells (RGCs) and their axons. RGC degeneration in glaucoma is associated with sensitivity to intraocular pressure (IOP) and elevated IOP (also known as ocular hypertension) is the primary modifiable risk factor. Ocular hypertension is the primary characteristic of rodent models for glaucoma research. Intracameral injection of microbeads has evolved as a preferred method of IOP elevation in rodents, particularly in mice. Here, we outline the protocol and method for the Microbead Occlusion Model in mice. We highlight the importance of anesthesia choice and the utilization of glass micropipettes in combination with a micromanipulator and microsyringe pump for the successful execution of the model.

Simultaneous extraction of acidic and basic drugs via on-chip electromembrane extraction

In the present work, a on-chip electromembrane extraction (CEME) was designed and employed for simultaneous extraction of mefenamic acid (MEF) and diclofenac (DIC), as acidic model analytes, and betaxolol (BET), as a basic model analyte, followed by HPLC-UV. The CEME consists of two polymethyl methacrylate (PMMA) parts which each part consists of two separated microfluidic channels. A polypropylene sheet membrane impregnated with an organic solvent was sandwiched between the parts. One of the parts was used as the flow path for the sample solution and the other one as holder for the acceptor phases. The separated microfluidic channels of the sample solution part were connected to each other using a small piece of a capillary tube and the sample solution was pumped through them by means of a micro-syringe pump. However, the acceptor phases of the acidic and basic analytes were separately kept stagnant in the two microfluidic channels during the extraction process. A d.c. potential was applied for migration of the analytes from sample solution through the organic membrane into the acceptor phases. All effective variables on the extraction efficiency of the analytes were optimized. Under the optimized conditions, preconcentration factors higher than 15 were achieved and the calibration curves were linear in the range of 10–500 μg L−1 (r2 > 0.9982). RSD% values (n = 4) and LODs were less than 7.1% and 5.0 μg L−1. The results demonstrated that CEME could efficiently be used for the simultaneous analysis of acidic and basic analytes in biological samples.

Investigation of High-Speed Erythrocyte Flow and Erythrocyte-Wall Impact in a Lab-on-a-Chip.

To better understand erythrocyte high-speed motion, collision characteristics, and collision-induced hemolysis probability in rotary blood pumps, a visual experimental investigation of high-speed erythrocyte flow and erythrocyte-wall collision in a lab-on-a-chip was performed. The erythrocyte suspension was driven by a microsyringe pump connected to the microchip, and the erythrocyte flow and erythrocyte-wall impact process were observed and imaged by an optical microscope and a high-speed camera. Two types of microchips with different impact surfaces (flat and curved) were employed. The motion and deformation features before and after collision were studied in detail. The results show that erythrocytes not only move along the flow direction in the flow plane but also rotate and roll in three-dimensional space. Erythrocytes keep discoid shape during the movement in the straight channel, but their deformations during collision are mainly classified into two types: erythrocyte structure is still stable and the erythrocyte performance can be ensured to a certain extent in the TypeA deformation, while the TypeB deformation makes the membrane more likely to fracture on the stretched side, increasing the probability of hemolysis. Furthermore, the movements and deformations of the erythrocytes after collision are analyzed and classified into two types: bouncing and slipping. Moreover, a simulation method for the flow in microchip was performed and validated through a comparison of the streamlines and experimental erythrocytes tracks, which can be further employed to predict the high-speed blood flow, associated with collision process in mechanical blood pump.

A glass capillary based microfluidic electromembrane extraction of basic degradation products of nitrogen mustard and VX from water

In this work, a glass capillary based microfluidic electromembrane extraction (μ-EME) was demonstrated for the first time. The device was made by connecting an auxillary borosilicate glass tubing (O.D. 3mm, I.D. 2mm) perpendicular to main borosilicate glass capillary just below one end of the capillary (O.D. 8mm, I.D. 1.2mm). It generated the distorted T-shaped device with inlet ‘1’ and inlet ‘2’ for the introduction of sample and acceptor solutions, respectively. At one end of this device (inlet ‘2’), a microsyringe containing acceptor solution along with hollow fiber (O.D. 1000μm) was introduced. This configuration creates the micro-channel between inner wall of glass capillary and outer surface of hollow fiber. Sample solution was pumped into the system through another end of glass capillary (inlet ‘1’), with a micro-syringe pump. The sample was in direct contact with the supported liquid membrane (SLM), consisted of 20% (w/w) di-(2-ethylhexyl)phosphate in 2-nitrophenyl octyl ether immobilized in the pores of the hollow fiber. In the lumen of the hollow fiber, the acceptor phase was present. The driving force for extraction was direct current (DC) electrical potential sustained over the SLM. Highly polar (logP=−2.5 to 1.4) basic degradation products of nitrogen mustard and VX were selected as model analytes. The influence of chemical composition of SLM, extraction time, voltage and pH of donor and acceptor phase were investigated. The model analytes were extracted from 10μL of pure water with recoveries ranging from 15.7 to 99.7% just after 3min of operation time. Under optimized conditions, good limits of detection (2–50ngmL−1), linearity (from 5–1000 to 100–1000ngmL−1), and repeatability (RSDs below 11.9%, n=3) were achieved. Applicability of the proposed μ-EME was proved by recovering triethanolamine (31.3%) from 10μL of five times diluted original water sample provided by the Organization for the Prohibition of Chemical Weapons during 28th official proficiency test.

Miniaturised medium pressure capillary liquid chromatography system with flexible open platform design using off-the-shelf microfluidic components

Trends towards portable analytical instrumentation of the last decades have not been equally reflected in developments of portable liquid chromatography (LC) instrumentation for rapid on-site measurements. A miniaturised medium pressure capillary LC (MPLC) system with gradient elution capability has been designed based on a flexible modular microfluidic system using primarily off-the-shelf low cost components to ensure wide accessibility to other analysts. The microfluidic platform was assembled on a breadboard and contained microsyringe pumps and switch valves, complemented with an injection valve and on-capillary detectors, all controlled by a PC. Four miniaturised microsyringe pumps, with 5, 20 and 100 μL syringe volume options, formed the basis of the pumping system. Two pairs of pumps were used for each mobile phase to create gradient elution capability. The two microsyringe pumps in each pairs were linked by two electrically operated microfluidic switching valves and both pairs of pumps were connected through a zero void volume cross-connector, thus providing a low hold-up volume for gradient formation. Sample was injected by a 20 nL nano-LC sampling valve, directly connected to a 18 cm long 100 μm i.d. Chromolith CapRod RP-18 monolithic capillary column. On-capillary LED-based UV–vis photometric detection was conducted through a piece of equal diameter fused silica capillary connected after the column. The performance of the portable LC system was evaluated theoretically and experimentally, including the maximum operating pressure, gradient mixing performance, and the performance of the detectors. The 5 μL microsyringe pump offered the best performance, with typical maximum operating pressures up to 11.4 ± 0.4 MPa (water) and gradient pumping repeatability of between 4 and 9% for gradients between 0.10% s−1 and 0.33% s−1. Test analytes of charged and uncharged dyes and pharmaceuticals of varying hydrophobicity showed typical RSD values of 0.7–1.4% and 3.3–4.8% in isocratic mode and 1.2–4.6% and 3.2–6.4% in gradient mode, respectively for retention time and peak area repeatability.

Note: Design and fabrication of a simple versatile microelectrochemical cell and its accessories.

A microelectrochemical cell housed in an optical microscope and custom-made accessories have been designed and fabricated, which allows performing spatially resolved corrosion measurements. The cell assembly was designed to directly integrate the reference electrode close to the capillary tip to avoid air bubbles. A hard disk along with an old optical microscope was re-engineered into a microgrinder, which made the vertical grinding of glass capillary tips very easy. A stepper motor was customized into a microsyringe pump to dispense a controlled volume of electrolyte through the capillary. A force sensitive resistor was used to achieve constant wetting area. The functionality of the developed instrument is demonstrated by studying μ-electrochemical behavior of worn surface on AA2014-T6 alloy.

Simultaneous Electrophysiological Recording and Micro-injections of Inhibitory Agents in the Rodent Brain.

Here we describe a method for the construction of a single-use "injectrode" using commercially accessible and affordable parts. A probing system was developed that allows for the injection of a drug while recording electrophysiological signals from the affected neuronal population. This method provides a simple and economical alternative to commercial solutions. A glass pipette was modified by combining it with a hypodermic needle and a silver filament. The injectrode is attached to commercial microsyringe pump for drug delivery. This results in a technique that provides real-time pharmacodynamics feedback through multi-unit extracellular signals originating from the site of drug delivery. As a proof of concept, we recorded neuronal activity from the superior colliculus elicited by flashes of light in rats, concomitantly with delivery of drugs through the injectrode. The injectrode recording capacity permits the functional characterization of the injection site favoring precise control over the localization of drug delivery. Application of this method also extends far beyond what is demonstrated here, as the choice of chemical substance loaded into the injectrode is vast, including tracing markers for anatomic experiments.