Rapid assembly of mixed thiols for toll-like receptor-based electrochemical pathogen sensing.

Herein, we describe a rapid and facile fabrication of electrochemical sensors utilizing two different toll-like receptor (TLR) proteins as biorecognition elements to detect bacterial pathogen associated molecular patterns (PAMPs). Using potential-assisted self-assembly, binary mixtures of 11-mercaptoundecanoic acid (MUA) and 6-mercapto-1-hexanol (MCH), or MUA and an in-house synthesized zwitterionic sulfobetaine thiol (DPS) were assembled on a gold working electrode within 5 minutes, which is >200 times shorter than other TLR sensors' preparation time. Electrochemical methods and X-ray photoelectron microscopy were used to characterize the SAM layers.

Integration of complementary split-ring resonators into digital microfluidics for manipulation and direct sensing of droplet composition.

This paper demonstrates the integration of complementary split-ring resonators (CSSRs) with digital microfluidics (DMF) sample manipulation for passive, on-chip radio-frequency (RF) sensing. Integration is accomplished by having the DMF and the RF-sensing components share the same ground plane: by designing the RF-resonant openings directly into the ground plane of a DMF device, both droplet motion and sensing are achieved, adding a new on-board detection mode for use in DMF. The system was modelled to determine basic features and to balance various factors that need to be optimized to maintain both functionalities (DMF-enabled droplet movement and RF detection) on the same chip.

Electrochemical Determination of Fentanyl Using Carbon Nanofiber-Modified Electrodes.

In this work, we report the direct electrochemical oxidation of fentanyl using commercial screen-printed carbon electrodes (SPCEs) modified with carboxyl-functionalized carbon nanofibers (fCNFs). CNFs have surface chemistry and reactivity similar to carbon nanotubes (CNTs), yet they are easier to produce and are of a lower cost than CNTs. By monitoring the current produced during the electrochemical oxidation of fentanyl, variables such as fCNF loading, fentanyl accumulation time, electrolyte pH, and differential pulse voltammetry parameters were optimized.

A Molecularly Imprinted Sol-Gel Electrochemical Sensor for Naloxone Determination.

A molecularly imprinted sol-gel is reported for selective and sensitive electrochemical determination of the drug naloxone (NLX). The sensor was developed by combining molecular imprinting and sol-gel techniques and electrochemically grafting the sol solution onto a functionalized multiwall carbon nanotube modified indium-tin oxide (ITO) electrode. The sol-gel layer was obtained from acid catalyzed hydrolysis and condensation of a solution composed of triethoxyphenylsilane (TEPS) and tetraethoxysilane (TES).

Investigation of Capillary Filling Dynamics of Multicomponent Fluids in Straight and Periodically Constricted Microchannels.

An extensive study of capillary flow of fluids with various viscosities in straight and periodically constricted microchannels with different surface wettability is presented. Capillary filling speed in hydrophilic, less hydrophilic, and hydrophobic microchannels were experimentally monitored and compared with the Washburn theoretical model. For all liquids, a linear relationship was found between the square of propagation distance and time, which is expected for Newtonian fluids.

Nanostructured nickel oxide electrodes for non-enzymatic electrochemical glucose sensing.

Nanostructured nickel (Ni) and nickel oxide (NiO) electrodes were fabricated on Ni foils using the glancing angle deposition (GLAD) technique. Cyclic voltammetry and amperometry showed the electrodes enable non-enzymatic electrochemical determination of glucose in strongly alkaline media. Under optimized conditions of NaOH concentration and working potential (~ 0.

An impedimetric biosensor for E. coli O157:H7 based on the use of self-assembled gold nanoparticles and protein G.

Two kinds of electrochemical impedimetric biosensors for the detection of E. coli O157:H7 are described and compared. They were fabricated using self-assembled layers of thiolated protein G (PrG-thiol) on (i) planar gold electrodes and (ii) gold nanoparticles (Au NPs) modified gold electrodes.

Evaluation of protein separation mechanism and pore size distribution in colloidal self-assembled nanoparticle sieves for on-chip protein sizing.

The separation behavior of 6.5-66 kDa proteins in silica particle array-based sieves formed by colloidal self-assembly in microchips is reported across a pore size range of 22-103 nm. The protein separation and resolution improves markedly with decreasing pore size.

Size-based proteins separation using polymer-entrapped colloidal self-assembled nanoparticles on-chip.

We report on a facile method to stabilize colloidal self-assembled (CSA) nanoparticles packed in microchannels for high speed size-based separation of proteins. Silica nanoparticles, self-assembled in a network of microfluidic channels, were stabilized with a methacrylate polymer prepared in situ through photopolymerization. The entrapment conditions were investigated to minimize the effect of the polymer matrix on the structure of the packing and the separation properties of the CSA beds.

A regenerating ultrasensitive electrochemical impedance immunosensor for the detection of adenovirus.

We report on the development of a regenerable sensitive immunosensor based on electrochemical impedance spectroscopy for the detection of type 5 adenovirus. The multi-layered immunosensor fabrication involved successive modification steps on gold electrodes: (i) modification with self-assembled layer of 1,6-hexanedithiol to which gold nanoparticles were attached via the distal thiol groups, (ii) formation of self-assembled monolayer of 11-mercaptoundecanoic acid onto the gold nanoparticles, (iii) covalent immobilization of monoclonal anti-adenovirus 5 antibody, with EDC/NHS coupling reaction on the nanoparticles, completing the immunosensor. The immunosensor displayed a very good detection limit of 30 virus particles/ml and a wide linear dynamic range of 10(5).

A regenerating self-assembled gold nanoparticle-containing electrochemical impedance sensor.

We report on the development of an electrochemical reductive desorption protocol for repeated regeneration of gold electrodes modified with multi-layers of self-assembled surfaces for use in electrochemical sensing. The gold electrodes were first modified with 1,6-hexanedithiol to which gold nanoparticles were attached in a subsequent modification step. Attachment of thiolated single-stranded nucleic acid oligomers to the gold nanoparticles completed the electrochemical sensor.

Multiplexed electrokinetic sample fractionation, preconcentration and elution for proteomics.

Both 6 and 8-channel integrated microfluidic sample pretreatment devices capable of performing "in space" sample fractionation, collection, preconcentration and elution of captured analytes via sheath flow assisted electrokinetic pumping are described. Coatings and monolithic polymer beds were developed for the glass devices to provide cationic surface charge and anodal electroosmotic flow for delivery to an electrospray emitter tip. A mixed cationic ([2-(methacryloyloxy)ethyl] trimethylammonium chloride) (META) and hydrophobic butyl methacrylate-based monolithic porous polymer, photopolymerized in the 6- or 8-fractionation channels, was used to capture and preconcentrate samples.

Integrated electrokinetic sample fractionation and solid-phase extraction in microfluidic devices.

A microfluidic device that performs "in space" sample fractionation, collection, and preconcentration for proteomics is described. Effluents from a 2.75 mm long fractionation channel, focused via sheath flow, were sequentially delivered into an array of 36-collection channels containing monolithic polymer beds for SPE.

Tunable thick polymer coatings for on-chip electrophoretic protein and peptide separation.

We report a variety of procedures for fabricating confinement-induced polymer coatings, used to eliminate non-specific protein adsorption and to control electroosmotic flow for microchip capillary electrophoresis. The coating strategy generates relatively thick polymer wall coatings (100-700 nm) and can easily be tuned by adjusting the monomer concentration. 2-hydroxyethyl methacrylate (HEMA) polymer coating, photopatterned in microfluidic channels, effectively reduced protein non-specific adsorption and rendered high efficiency (N/m=∼3 × 10⁶) for protein separation.

On-chip solid phase extraction and enzyme digestion using cationic PolyE-323 coatings and porous polymer monoliths coupled to electrospray mass spectrometry.

We evaluate the compatibility and performance of polymer monolith solid phase extraction beds that incorporate cationic charge, with a polycationic surface coating, PolyE-323, fabricated within microfluidic glass chips. The PolyE-323 is used to reduce protein and peptide adsorption on capillary walls during electrophoresis, and to create anodal flow for electrokinetically driven nano-electrospray ionization mass spectrometry. A hydrophobic butyl methacrylate-based monolithic porous polymer was copolymerized with an ionizable monomer, [2-(methacryloyloxy)ethyl] trimethylammonium chloride to form a polymer monolith for solid phase extraction that also sustains anodal electroosmotic flow.

Microchannels filled with diverse micro- and nanostructures fabricated by glancing angle deposition.

The integration of porous structures into microchannels is known to enable unique and useful separations both in electrophoresis and chromatography. Etched pillars and other nanostructures have received considerable interest in recent years as a platform for creating microchannels with pores tailored to specific applications. We present a versatile method for integration of three-dimensionally sculptured nano- and micro-structures into PDMS microchannels.

Multifunctional protein processing chip with integrated digestion, solid-phase extraction, separation and electrospray.

We describe a microfluidic device in which integrated tryptic digestion, SPE, CE separation and electrospray ionization for MS are performed. The chip comprised of 10 × 30 μm channels for CE, and two serially connected 150 μm deep, 800 μm wide channels packed with 40 to 60 μm diameter beads, loaded with either immobilized trypsin, reversed-phase packing or both. On-chip digestion of cytochrome c using the trypsin bed showed complete consumption of the protein in 3 min, in contrast to the 2 h required for conventional solution phase tryptic digestion.

Microfluidic devices for electrokinetic sample fractionation.

We present three generations of microchip-based "in-space" sample fractionators and collectors for use in proteomics. The basic chip design consisted of a single channel for CE separation of analytes that then intersects a fractionation zone feed into multiple high aspect ratio microchannels for fractionation of separated components. Achievements of each generation are discussed in relation to important design criteria.

Matrix-free laser desorption/ionization mass spectrometry using silicon glancing angle deposition (GLAD) films.

Glancing angle deposition (GLAD) was used to fabricate nanostructured silicon (Si) thin films with highly controlled morphology for use in laser desorption/ionization mass spectrometry (DIOS-MS). Peptides, drugs and metabolites in the mass range of 150-2500 Da were readily analyzed. The best performance was obtained with 500 nm thick films deposited at a deposition angle of 85 degrees .

Capillary electrochromatography with packed bead beds in microfluidic devices.

Microchip-based bead-packed columns for electrochromatography are described for several types of stationary phases. Chromatography columns 2 mm in length were used for the separation of proteins and peptides by size- and ion-exchange modes of separation, respectively. In size-exclusion electrochromatograpgy, FITC-IgG and FITC-insulin were baseline resolved in less than 10 s, with efficiencies of up to 139,000 plates/m for FITC-insulin.

Microchip-based capillary electrochromatography using packed beds.

Integration of a packed column onto a microchip for performance of capillary electrochromatography (CEC) is described. The quartz device incorporated a cross-injector, and a double weir trapping design for formation of 1, 2 and 5 mm long CEC columns. Three fluorescent dyes were baseline-resolved with plate numbers of 330,(330,000 plates/m; height equivalent to a theoretical plate, H = 3.

An integrated solid-phase extraction system for sub-picomolar detection.

A microchip structure etched on a glass substrate for packed column solid-phase extraction (SPE) and capillary electrochromatography (CEC) is described. A 200 microm long, octadecylsilane (ODS) packed column was secured using two different approaches: solvent lock or polymer entrapment. The former method was utilized for SPE while the latter approach was applied for CEC.