Minimal Dead Volume Research Articles

NanoRidge filters: Fabrication strategies and performance optimization for nano-scale microfluidic particle filtration.

Filters with high throughput, minimal dead volume, and greater sensitivity to particle size are needed, which traditional benchtop filtration cannot provide. Leveraging microfabrication techniques developed by the electronics and optics industries, the filters presented here feature a unique serpentine "NanoRidge" structure, offering a continuous filtration gap spanning over three meters on a compact 4 × 14.5 mm2 footprint. This design provides more precise size filtration cut-offs and consistent flow paths compared to traditional membrane filtration systems. Despite challenges associated with glass substrate deformation impacting uniform filter gap sizes, the study provides valuable insights into the development of NanoRidge filters (NRFs) for enhancing filtration efficiency in preparatory techniques and sample analysis. This study describes the fabrication and testing of these new filter types and directly compares the performance to traditional membrane filters using the metrics of particle size cut-off (the smallest difference in particle size which can be filtered vs passed) and particle loss. The NanoRidge filters were characterized using imaging (during fabrication, post-fabrication and use, fluorescent particles captured and small molecule dye), pressure and flow measurements, and a series of particle sizes "filter or pass" studies. Particle capacity (100-250 nm) ranged from 5 × 108 to 7 × 109 in 1 ml samples at a flow rate of 100 μl/min with backpressure in the range of 1-3 Bar. The optimized fabrication procedure for the 150 nm NRF yielded a small particle recovery of 95% while also achieving a large particle filtration of 73%. High filtration efficiency was also proven in the final 60 and 80 nm NRF fabrication procedures at 96% and 91%, respectively.

Management of refined and personalized newborn blood specimen collection

BackgroundIatrogenic blood loss is an important cause of neonatal anemia. In this study, a spreadsheet tool was developed to reduce blood collection, providing a new idea for the prevention of iatrogenic blood loss in newborns. MethodsBased on hematocrit, minimum test volume and dead volume, a new tool was to calculate the minimum blood collection volume and the number of containers required for the test portfolio. We collected data from October 2022 to October 2023 from Xiamen Maternal and Child Health Hospital for analysis and validation. ResultsDuring this year, there were 16,434 patients and 13,696 plasma/serological samples in the neonatology department. Among them, there were 8 test combinations of greater than 1%, and 9490 samples in total. According to the hospital manual, the recommended amount of blood collection is 27,534 ml and 9490 containers. Through the analysis of this tool, total blood collection was 8864.77 ml, marked qnantity of upward containers (closest level to the calculated blood collection volume) was 10301 ml, and the amount of containers was 8835, which decreased by 67.8%, 62.58% and 6.9% respectively. Besides, if the hematocrit information cannot be obtained in advance and the high hematocrit is calculated as 0.8, the recommended amount of blood collection is 14334.3 ml, and the marked amount of the upward container markering is 17340 ml, decreasing by 47.9% and 37.02% respectively. ConclusionWe have developed an auxiliary tool that can manage neonatal blood specimen collection in a fine and personalized way and can be applied among different laboratory instruments by parameters modification.

Abstract 1044: Low-cost, high-sensitivity InSituPlex® mIF assays on the Parhelia Omni-Stainer™

Abstract Background: Multiplex immunofluorescence (mIF) is an important tool for extracting complex phenotypic information from normal or diseased tissues, and provides accurate and predictive insights on the tissue microenvironment faster. For patient samples in translational and clinical research, high sensitivity, specificity, and reproducibility are critical; however, throughput and cost considerations are also important in designing clinical studies. Enabling an easy-to-use high-performance assay such as InSituPlex® on robust and affordable auto-stainers like the Parhelia Omni-Stainer™ can allow researchers to gain a deeper understanding of the tissue micro-environment through high-quality multiplexed biomarker detection in a fraction of the time and cost. Methods: We performed Ultivue InSituPlex® assays with OmniVUE™ panels using the Parhelia Omni-Stainer™, a low-cost, high-throughput tissue auto-stainer with reduced requirements for reagents with a minimal dead volume. We compared the whole-slide staining performance across replicates using human tonsil and tumor tissue arrays across multiple independent runs over multiple days. The stained slides were scanned using the Zeiss AxioScan.Z1 high-throughput imaging system, and image batches were processed using Ultivue’s UltiStacker.AI and UltiAnalyzer.AI software. Results: Tighter temperature control of the slide in the Omni-Stainer supports optimal InSituPlex® signal amplification. Intra-run and inter-day analysis on serial sections of human tonsil and tumor tissue arrays demonstrated a high degree of consistency in InSituPlex® assay performance, specifically with marker-specific signal intensities and cell densities. The Omni-Stainer facilitates the use of low reagent volumes at each step of the assay due to its efficient reagent use, thus lowering the cost of reagents per slide. Conclusions: This study demonstrated a fast, simple and robust workflow to perform high-performance InSituPlex® mIF assays on the low-cost, high-throughput Parhelia Omni-Stainer™. Ultivue’s configurable OmniVUE™ mIF panels can be run on the Omni-Stainer with reduced associated reagent costs per slide. This workflow can support larger clinical and translational studies in a more cost-effective fashion, leading to in-depth analysis of tissue microenvironment through highly precise multiplexed biomarker detection. Citation Format: Kevin Hwang, Lauren Duro, Alex Veith, Nelson Wedin, Nikolay Samusik, Je H. Lee. Low-cost, high-sensitivity InSituPlex® mIF assays on the Parhelia Omni-Stainer™ [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1044.

On-column capillary suppressor for open tubular ion chromatography

BackgroundSuppressors with different dead volumes are required to match different suppressed ion chromatography systems. Especially for suppressed open tubular ion chromatography (SOTIC), the dead volume is a critical parameter. Both connection tubes between open tubular (OT) columns and suppressors and the dead volumes of the suppressors should be as short/small as possible to minimize peak dispersion. Suppressors with different dead volumes are required to match the various suppressed ion chromatography systems that operate at low flow rates 20–200 nL/min. ResultsWe describe three designs of on-column capillary suppressors for SOTIC: (A) on-column electrodialytic suppressor prepared by making small cracks on the cycloolefin polymer (COP) capillary at targeted locations, (B) on-column electrodialytic suppressor built on a polyether ether ketone (PEEK) capillary by removing the wall materials at target locations, (C) on-column chemical suppressor based on a single cut on a PEEK capillary at a targeted location a single cut on a PEEK capillary at a targeted location. The on-column electrodialytic suppressors work in two different modes with suppression voltage applied in co-current and counter-current direction to the eluent flow. Because of very narrow column inner diameter (i.d.), up to several hundred volts were required to suppress the hydroxide eluent, but it was found the there was a >90% loss of analytes in the suppressor accompanied with a high noise level after on-column electrodialytic suppression. Theoretical analysis reveals that high suppression voltage significantly affects the retention of specific analytes by electromigration. Further analysis indicated that the electrodialytic on-column suppressor in co-current mode would behave totally different from traditional suppressors. The on-column chemical suppression, with minimum dead volume of 0.27 nL, provides fairly well suppression of low hydroxide eluent without analyte loss in the suppressor. In design C, an efficiency of 47000 ± 1800 plates/m for Cl−, corresponding to a peak volume of 17.9 ± 0.7 nL, was obtained when separating five anion mixture (0.5 mM each) in the 25 μm i.d. AS18 latex coated PEEK OT column with an injection of 7.3 nL. Theoretical calculation revealed that a column efficiency loss of ≤3% would result in a cylindrical chemical suppression channel and thus it is taken as the acceptable dispersion contribution originating from the on-column chemical suppressor. SignificanceDifferent on-column suppressors have been designed on OT columns with i.d.s less than 30 μm. Two electrodialytic on-column suppressor designs with eluent flow parallel to the direction of electric field were proposed and tested. The eluent flow rate, analytes’ retention behavior, resistance of suppression channel, current-voltage relationship, and working principles in both co-current and counter-current were experimentally investigated and comprehensively discussed. It was found that although the on-column electrodialytic suppressions (Design A and B) are not feasible in practice, the electrodialytic on-column suppressor on co-current mode has a potential of being used as an enriching capillary column for analyte ions. Design C provides fairly well chemical suppression. Theoretical calculation indicates that the loss of column efficiency can be controlled within 3%.

A transient flow reactor for rapid gas switching at atmospheric pressure.

Herein, we present a design for a transient flow reactor system with high detection sensitivity and minimal dead volume, such that it is capable of sub-second switching of the gas stream flowing through a catalytic bed. We demonstrate the reactor's capabilities for step transient, pulse, and stream oscillation experiments using the model system of CO oxidation over Pd catalysts, and we find that we are able to precisely model step transients for CO oxidation using a pseudo-homogenous-packed bed reactor model. The design principles leading to minimal gas hold-up time and increased sensitivity that are described in this paper can be implemented into existing flow reactor designs with minimal cost, providing a readily accessible alternative to the existing transient instrumentation.

Teeth and bones micro-slurries introduction to MIP OES for elements simultaneous quantification

This study aims development of new, rapid and direct method for simultaneous multi-elemental determination in micro-volume slurried samples of teeth and bones.The method proposed allow for direct, without prior sample decomposition, injection of 15 μL of slurries (Bone Meal NIST 1486, deciduous human and dog teeth) into microwave induced plasma optical emission spectrometer (MIP OES) and determination of Ca, Cu, Fe, K, Mg, Mn, Na, Pb, Sr and Zn. The optimization procedures were undertaken (univariate and simplex methods) to achieve the best values of parameters influencing the analytical signals. Minimum dead volume, high nebulization and slurry transport efficiency were obtained by using on-axis low-volume spray chamber/v-groove pneumatic nebulizer interface for 15 μL slurry injection in discontinues mode (at 1.2 mL min−1 pump speed).Analytical parameters of the proposed method were assessed by determination of the limits of detection (LODs), absolute detection limit and precision (RSDs). The obtained LODs were appropriate (in the range of mg/kg) for the determination of the elements in the standard reference material (Bone Meal NIST 1486) for validation procedure and successful application in two real samples (deciduous human and dog teeth).

Discrete micro-volume suspension injection to microwave induced plasma for simultaneous determination of cadmium and lead pre-concentrated on multiwalled carbon nanotubes in optical emission spectrometry

A discrete sample introduction system (DSIS) for the direct micro-volume nanomaterials (NMs) suspension injection has been developed toward the simultaneous determination of Cd and Pb pre-concentrated (by dispersive micro solid-phase extraction (DMSPE)) on oxidized multiwalled carbon nanotubes (MWCNTs) to microwave induced plasma optical emission spectrometry (DMSPE-DSIS-MIP OES). On-axis low-volume spray chambers with flow focusing micro nebulizer (continues mode) and v-groove type pneumatic nebulizer (discontinues mode) for microliter-volume suspension introduction were tested.A univariate approach and the simplex optimization procedure were used to achieve optimized conditions and derive analytical figures of merit. Minimum dead volume, high nebulization and suspension transport efficiency were obtained by using miniaturized spray chamber/v-groove pneumatic nebulizer interface for 10 μL suspension injection in discontinues mode (at 0.5 mL min−1 pump speed).Analytical performance of DMSPE-DSIS-MIP OES method was characterized by determination of the limits of detection (0.7 and 0.1 ng mL−1 for Cd and Pb, respectively) and precision ranged from 6% to 8%. Quantitative data obtained for water reference materials (ERM-CA011b and SRM 1643e) were in good agreement, according to the t-test, for a confidence level of 95%, with the corresponding reference values, proving the potential of this analysis system for trace analysis via MIP OES. The proposed method had been successfully applied for the determination of Cd and Pb in water real samples.

Petrel Probe: An Integrated In Situ Sampling and Injection Interface for Fast, High-Efficiency Liquid Chromatography-Mass Spectrometry Analysis.

Herein, we describe an in situ analysis probe, Petrel probe, highly integrating multiple functions of in situ sampling, in situ sample injection, high-performance liquid chromatography (HPLC) separation, and mass spectrometry (MS) electrospray. The Petrel probe was fabricated based on a single capillary, which consists of a micrometer-sized hole for sampling, a packed column for LC separation, and a tapered tip for MS electrospray. The design of the Petrel probe was optimized to obtain higher structural strength, and a polytetrafluoroethylene (PTFE) chip was used for sealing the probe-sampling hole to meet the high-pressure (∼30 MPa) requirement of LC manifold. On the basis of the Petrel probe, we developed a novel valveless LC injection method, that is, the probe pressing microamount in situ (PPMI) injection method, which performs sample injection by pressing the probe-sampling hole on the PTFE chip, using the mobile phase to dissolve the sample dry spot in the sampling area on the chip, and injecting it into the LC column under high-pressure conditions for separation and subsequent MS analysis. The LC-MS system with the PPMI injection method exhibits rapid injection and separation speed, as well as minimum injection dead volume. It can yield a high separation efficiency comparable to those of conventional HPLC systems. The present system was optimized using standard peptide samples, and four peptides were separated within 11 min in a probe with an effective column length of 5 cm, achieving the highest theoretical plate number up to ∼5,500,000/m. The system was also applied in the separation of cytochrome C digest to demonstrate its separation ability for complex samples, and 21 peptides were detected in 8 min with an amino-acid coverage of 83%.

A Sensitive and Portable Deep-UV Absorbance Detector with a Microliter Gas Cell Compatible with Micro GC

Deep-UV absorption spectrometry for detection of toxic airborne gases, for instance, Benzene, Toluene, Ethylbenzene, and Xylenes (BTEX) has drawn considerable attention owing to its high sensitivity and reliability. However, the development of a deep-UV absorbance detector having good sensitivity, portability, and a low-volume gas cell with applicability for a micro Gas Chromatography (μGC) is challenging. Herein we present a novel, self-referenced, and portable deep-UV absorbance detector with a microliter (275 μL) gas cell having minimal dead volume. It has excellent compatibility with μGC for detection of individual BTEX components in a mixed sample at a sub-ppm level. The design consists of the latest, portable, and cost-effective optical and electronic components, i.e., deep-UV LED, hollow-core waveguide, and photodiodes. The detector directly measures the absorbance values in volts using an integrated circuit with a log-ratio amplifier. The prototype was tested with direct injection of toluene-N2 (1.5 ppm to 50 ppm) and good linearity (R2 = 0.99) with a limit of detection of 196 ppb was obtained. The absorbance detector with μGC setup was tested with a BTEX mixture in N2 at different GC column temperatures. All the BTEX species were sequentially separated and detected with an individual peak for a concentration range of 2.5 ppm to 10 ppm.

Fluid pressure heterogeneity during fluid flow in rocks: new laboratory measurement device and method

SUMMARY We present a new type of transducer capable of measuring local pore fluid pressure in jacketed rock samples under elevated confining pressure conditions. The transducers are passive (strain-gauge based), of small size (7 mm in diameter at the contact with the rock and around 10 mm in length), and have minimal dead volume (a few mm3). The transducers measure the differential pressure between the confining fluid and the internal pore pressure. The design is easily adaptable to tune the sensitivity and working pressure range up to several hundred megapascals. An array of four such transducers was tested during hydrostatic pressurization cycles on Darley Dale sandstone and Westerly granite. The prototypes show very good linearity up to 80 MPa with maximum deviations of the order of 0.25 MPa, regardless of the combination of pore and confining pressure. Multiple internal pore pressure measurements allow us to quantify the local decrease in permeability associated with faulting in Darley Dale sandstone, and also prove useful in tracking the development of pore pressure fronts during transient flow in low permeability Westerly granite.

Layer-by-layer fabrication of 3D hydrogel structures using open microfluidics.

Patterned deposition and 3D fabrication techniques have enabled the use of hydrogels for a number of applications including microfluidics, sensors, separations, and tissue engineering in which form fits function. Devices such as reconfigurable microvalves or implantable tissues have been created using lithography or casting techniques. Here, we present a novel open-microfluidic patterning method that utilizes surface tension forces to form hydrogel layers on top of each other, into a patterned 3D structure. We use a patterning device to form a temporary open microfluidic channel on an existing gel layer, allowing the controlled flow of unpolymerized gel in device-regions. After layer gelation and device removal, the process can be repeated iteratively to create multi-layered 3D structures. The use of open-microfluidic and surface tension-based methods to define the shape of each individual layer enables patterning to be performed with a simple pipette and with minimal dead-volume. Our method is compatible with unmodified (native) biological hydrogels, and other non-biological materials with precursor fluid properties compatible with capillary flow. With our open-microfluidic layer-by-layer fabrication method, we demonstrate the capability to build agarose, type I collagen, and polymer-peptide 3D structures featuring asymmetric designs, multiple components, overhanging features, and cell-laden regions.

Centrifugal Step Emulsification: How Buoyancy Enables High Generation Rates of Monodisperse Droplets.

We demonstrate that buoyancy in centrifugal step emulsification enables substantially higher generation rates of monodisperse droplets compared to pressure driven set-ups. Step emulsification in general can produce droplets in comparatively simple systems (only one moving liquid) with a low CV of <5% in droplet diameter and with a minimum dead volume. If operated below a critical capillary number, the droplet diameter is defined by geometry and surface forces only. Above that critical capillary number, however, jetting occurs, leading to an increased droplet diameter and CV. Consequently, generation rates of monodisperse droplets are limited in pressure-driven systems. In this paper, we show that centrifugal step emulsification can overcome this limitation by applying sufficient buoyancy to the system. The buoyancy, induced by the centrifugal field and a density difference of the continuous and disperse phase, supports droplet necking by pulling the forming droplet away from the nozzle. The influence of buoyancy is studied using specific microfluidic designs that allow for supplying different buoyancies to the same droplet generation rates. For a droplet diameter of 100 μm, droplet generation at rates above 2.8k droplets per second and nozzle were reached, which is an increase of more than a factor of 8 in comparison to pressure-driven systems.

Enhanced Microchip Electrophoresis Separations Combined with Electrochemical Detection Utilizing a Capillary Embedded in Polystyrene.

The ability to use microchip-based electrophoresis for fast, high-throughput separations provides researchers with a tool for close-to real time analysis of biological systems. While PDMS-based electrophoresis devices are popular, the separation efficiency is often an issue due to the hydrophobic nature of PDMS. In this study, a hybrid microfluidic capillary device was fabricated to utilize the positive features of PDMS along with the electrophoretic performance of fused silica. A capillary loop was embedded in a polystyrene base that can be coupled with PDMS microchannels at minimal dead volume interconnects. A method for cleaning out the capillaries after a wet-polishing step was devised through the use of 3D printed syringe attachment. By comparing the separation efficiency of fluorescein and CBI-glycine with both a PDMS-based serpentine device and the embedded capillary loop device, it was shown that the embedded capillary loop device maintained higher theoretical plates for both analytes. A Pd decoupler with a carbon or Pt detection electrode were embedded along with the loop allowing integration of the electrophoretic separation with electrochemical detection. A series of catecholamines were separated to show the ability to resolve similar analytes and detect redox active species. The release of dopamine and norepinephrine from PC 12 cells was also analyzed showing the compatibility of these improved microchip separations with high ionic cell buffers associated with cell culture.

A robust and extendable sheath flow interface with minimal dead volume for coupling CE with ESI-MS

In this paper, we describe a robust sheath flow-based CE-MS interface with minimal interface dead volume based on an extended pattern. A 20µm i.d. × 90µm o.d. fused-silica capillary with a chemically-etched thin-wall tip (30µm o.d.) was used as the separation capillary as well as electrospray emitter, and a 200µm i.d. × 375µm o.d. capillary with a tapered tip (40µm o.d.) was used as the sheath flow capillary. An extendable sheath-flow interface mode was adopted by decreasing the thickness of separation capillary tip and extending the separation capillary tip out from the sheath flow capillary tip, and allowing the sheath flow to be transferred to the separation capillary tip along its outer surface, forming a surface sheath flow to mix with sample flow at the separation capillary tip. Such a strategy could significantly reduce the interface dead volume and thus improve the CE separation efficiency and detection sensitivity, as well as evidently enhance the working reliability of the CE-MS interface. We investigated various factors affecting the interface performance, including capillary extending distance, emitter diameters, sheath flow capillary shape, and sheath flow rate. Under the optimized conditions, a minimal interface dead volume of ca. 4pL was obtained which is the smallest one compared with previously-reported sheath flow-based CE-MS interfaces. The feasibility and applicability of the present CE-MS interface were demonstrated in the separation of a peptide mixture with high separation efficiency of 2.07–3.38µm plate heights and good repeatabilities (< 6.1% RSD, n = 5). We except such a simple and robust interface could provide a possible solution for the development of commercial CE-MS interfaces differing from the currently-used ones, and has the potentials to be applied in routine analytical laboratories for various studies such as proteomics, metabolomics, or single cell analysis.

Extending the upper temperature range of gas chromatography with all-silicon microchip columns using a heater/clamp assembly

Miniaturization of gas chromatography (GC) instrumentation is of interest because it addresses current and future issues relating to compactness, portability and field application. While incremental advancements continue to be reported in GC with columns fabricated in microchips (referred to in this paper as “microchip columns”), the current performance is far from acceptable. This lower performance compared to conventional GC is due to factors such as pooling of the stationary phase in corners of non-cylindrical channels, adsorption of sensitive compounds on incompletely deactivated surfaces, shorter column lengths and less than optimum interfacing to injector and detector. In this work, a GC system utilizing microchip columns was developed that solves the latter challenge, i.e., microchip interfacing to injector and detector. A microchip compression clamp was constructed to heat the microchip (i.e., primary heater), and seal the injector and detector fused silica interface tubing to the inlet and outlet ports of the microchip channels with minimum extra-column dead volume. This clamp allowed occasional operation up to 375°C and routine operation up to 300°C. The compression clamp was constructed of a low expansion alloy, Kovar™, to minimize leaking due to thermal expansion mismatch at the interface during repeated thermal cycling, and it was tested over several months for more than one hundred injections without forming leaks. A 5.9m long microcolumn with rectangular cross section of 158μm×80μm, which approximately matches a 100μm i.d. cylindrical fused silica column, was fabricated in a silicon wafer using deep reactive ion etching (DRIE) and high temperature fusion bonding; finally, the channel was coated statically with a 1% vinyl, 5% phenyl, 94% methylpolysiloxane stationary phase. High temperature separations of C10-C40 n-alkanes and a commercial diesel sample were demonstrated using the system under both temperature programmed GC (TPGC) and thermal gradient GC (TGGC) conditions. TGGC analysis of a complex essential oil sample was also demonstrated. Addition of a secondary heater and polyimide insulation proved to be helpful in achieving the desired elution temperature without having to raise the primary heater temperature above 300°C for high boiling point compounds.

General-Purpose, Parallel and Reversible Microfluidic Interconnects

The packaging of microfluidic chips is a limiting factor in their ease of use and widespread application. A simple and versatile casting procedure to fabricate a parallel minimal dead-volume connector using polydimethylsiloxane elastomers without the application of any adhesive materials is demonstrated. The interconnections reversibly join standard-sized teflon, glass, or plastic tubing to modular microfluidic systems with minimal dead volume for biological and chemical applications. Parallel port connectors with 18 and 35 channels have been developed to illustrate the applicability of this novel universal fluidic interface to the large-scale integration of microfluidic (chip) devices, which will scale without problem to 100 parallel channels. The advantages of this novel interface are evaluated in relation to a comprehensive classification and analysis of other world to chip interconnection technologies.

Development of interface for online coupling of micro-fluidic chip-based photo-micro-reactor/ultrasonic nebulization with microwave induced plasma spectrometry and its application in simultaneous determination of inorganic trace elements in biological materials

A novel analysis online system based on direct coupling of micro-fluidic μchip-based photo-micro-reactor/ultrasonic nebulization (μchip-UV/MR/USN) to microwave induced plasma-optical emission spectrometry (MIP OES) for simultaneous determination of inorganic trace elements in human body fluids and water samples was developed. A univariate approach and the simplex optimization procedure were used to achieve optimized conditions and derive analytical figures of merit. Minimum dead volume, high photo-decomposition and nebulization efficiency and high sample transport efficiency were obtained by using this interface. The experimental concentration detection limits for simultaneous determination, calculated as the concentration giving a signal equal to three times the standard deviation of the blank (LOD, 3σblank criterion, peak height) were 30, 6, 1, 2, 10, 2, 7, 5, 8, 10, 9 and 30μgL−1 for Ba, Ca, Cd, Cu, Fe, Li, Mg, Mn, Pb, Sr, Zn and C, respectively. Repeatability expressed as the relative standard deviations (RSD, n=6) for the target elements ranged from 4% to 8%. Quantitative data obtained for Seronorm urine and water reference materials were in good agreement with the corresponding reference values, proving the potential of this analysis system for multi-element trace analysis via MIP OES. The proposed method had been successfully applied for the determination of inorganic trace elements in urine, mineral water and implant fluid samples. The developed method is quite suitable for routine analysis of inorganic trace elements in biological and environmental fields and precious biological samples such as implant fluids.

Pneumatic microvalve-based hydrodynamic sample injection for high-throughput, quantitative zone electrophoresis in capillaries.

A hybrid microchip/capillary electrophoresis (CE) system was developed to allow unbiased and lossless sample loading and high-throughput repeated injections. This new hybrid CE system consists of a poly(dimethylsiloxane) (PDMS) microchip sample injector featuring a pneumatic microvalve that separates a sample introduction channel from a short sample loading channel, and a fused-silica capillary separation column that connects seamlessly to the sample loading channel. The sample introduction channel is pressurized such that when the pneumatic microvalve opens briefly, a variable-volume sample plug is introduced into the loading channel. A high voltage for CE separation is continuously applied across the loading channel and the fused-silica capillary separation column. Analytes are rapidly separated in the fused-silica capillary, and following separation, high-sensitivity MS detection is accomplished via a sheathless CE/ESI-MS interface. The performance evaluation of the complete CE/ESI-MS platform demonstrated that reproducible sample injection with well controlled sample plug volumes could be achieved by using the PDMS microchip injector. The absence of band broadening from microchip to capillary indicated a minimum dead volume at the junction. The capabilities of the new CE/ESI-MS platform in performing high-throughput and quantitative sample analyses were demonstrated by the repeated sample injection without interrupting an ongoing separation and a linear dependence of the total analyte ion abundance on the sample plug volume using a mixture of peptide standards. The separation efficiency of the new platform was also evaluated systematically at different sample injection times, flow rates, and CE separation voltages.

Microfluidic impact printer with interchangeable cartridges for versatile non-contact multiplexed micropatterning

Biopatterning has been increasingly used for well-defined cellular microenvironment, patterned surface topology, and guided biological cues; however, it meets challenges on biocompatibility, thermal and chemical sensitivity, as well as limited availability of reagents. In this paper, we aim at combining the desired features from non-contact inkjet printing and dot-matrix impact printing to establish a versatile multiplexed micropatterning platform, referred to as Microfluidic Impact Printer (MI-Printer), for emerging biomedical applications. Using this platform, we can achieve the distinct features of no cross-contamination, sub-microliter ink loading with a minimal dead volume, high-throughput printing, biocompatible non-contact processing, sequential patterning with self-alignment, wide adaptability for complex media (e.g., cell suspension or colloidal solutions), interchangeable/disposable cartridge design, and simple assembly and configuration, all highly desirable towards laboratory-based research and development. Specifically, the printing resolution of the MI-printer platform has been experimentally characterized and theoretically analysed. Optimal printing resolution of 80 μm has been repeatedly obtained. Furthermore, two useful functions of the MI-printer, multiplexed printing and combinatorial printing, have been experimentally demonstrated with less than 10 μm misalignment. Moreover, molecular and biological patterning, utilizing the multiplexed and combinatorial printing, has been implemented to illustrate the utility of this versatile printing technique for emerging biomedical applications.

&lt;b&gt;Methylene blue adsorption from glycerol solution onto the acicular habit of &amp;alpha;-goethite&lt;/b&gt;

The mechanism of methylene blue adsorption onto the surface of synthetic acicular habit of &alpha;-goethite from glycerol solution has been studied through batch experiment at 25, 30 and 35 0C in a glass cell of minimal dead volume. To describe the adsorption results, an attempt was made to fit the data to the Langmuir, Freundlich, Temkin and Dubinin equations. It was evident that adsorption capacity increased rapidly from 4.7 to 27.2 x 10-5 M for the equilibrium concentration of 0.13 to 1.90 x 10-5 M at 25 oC to a maximum of 33.1 x 10-5 M for 30 oC for equilibrium concentration of 2.74 M. Drop in the height of the plateau was observed and remained unchanged for 35 oC, and a maximum appeared in each isotherm before plateau. The adsorption process was found to be exothermic with an estimated mean entropy change of 23.84 kJ/mol. Also, an initial estimation of the surface acidity was made and it has been suggested that the surface of this mineral is heterogeneous if the location of these sites are presumed to be the adsorption sites identified as Lewis and Bronsted acid types. Furthermore, thermodynamic parameters ∆H, ∆G and ∆S for the adsorption were determined from the data and some features of the adsorption mechanism were enumerated on the basis of reaction scheme that incorporates simple adsorption phase exchange at the glycerol/&alpha;-FeOOH interface.KEY WORDS: Surface interface, Crystal habit, Heterogeneity, Micropore volume&nbsp;&nbsp;Bull. Chem. Soc. Ethiop. 2011, 25(1), 25-35.&nbsp;