Evaluation of screen-printed gold on low-temperature co-fired ceramic as a substrate for the immobilization of electrochemical immunoassays

Functionalized Thick Film Impedance Sensors for Use in In Vitro Cell Culture

Multi-electrode arrays find application in electrophysiological recordings. The quality of the captured signals depends on the interfacial contact between electrogenic cells and the electronic system. Therefore, it requires reliable low-impedance electrodes. Low-temperature cofired ceramic technology offers a suitable platform for rapid prototyping of biological reactors and can provide both stable fluid supply and integrated bio-hardware interfaces for recordings in electrogenic cell cultures. The 3D assembly of thick film gold electrodes in in vitro bio-reactors has been demonstrated for neuronal recordings. However, especially when dimensions become small, their performance varies strongly. This work investigates the influence of different coatings on thick film gold electrodes with regard to their influence on impedance behavior. PEDOT:PSS layer, titanium oxynitride and laminin coatings are deposited on LTCC gold electrodes using different 2D and 3D MEA chip designs. Their impedance characteristics are compared and discussed. Titanium oxynitride layers emerged as suitable functionalization. Small 86-µm-electrodes have a serial resistance R_s of 32 kOhm and serial capacitance C_s of 4.1 pF at 1 kHz. Thick film gold electrodes with such coatings are thus qualified for signal recording in 3-dimensional in vitro cell cultures.

Micromechanical properties of biomedical hydrogel for application as microchannel elastomer

Polymers are believed to be the building blocks for the creation of the next generation of materials and devices in practically all areas of biomedical research. There are a number of polymers that are being employed in varied applications in microfluidic platform due to the tremendous possibilities for soft matter based elastomers especially in biomedical applications. Polymeric hydrogels have been used as building block in micro-confinements and for specified function such as flow control. The need exists to suitably determine the mechanical characteristics of gel-based materials for possible use as a microchannel elastomer. In this investigation, we describe synthesis procedure, morphological, wettability characterization of hydrogel elastomer synthesized by free-radical polymerization crosslinked over varying acrylamide composition for 10% w/v: 25% w/w, 15% w/v: 25% w/w, 20% w/v: 25% w/w and 25% w/v: 25% w/w respectively. Micromechanical properties such as surface morphology, wettability, and micro-rheological behaviour of hydrogel elastomer using standard protocols was undertaken to determine roughness, contact angle, loss modulus and storage modulus over varied cross-linking of the constituent monomers. The impact of these parameters on flow transport and microchannel structural stability is well delineated in this report. We established that polymeric hydrogel could be a candidate for whole microchannel elastomer with suitable application in areas of tissues and biomedical engineering to mimic native biological transport conduits.

A novel LTCC electrochemical cell construction and characterization: a detection compartment for portable devices

In this work we described for the first time the construction of a 25 μL electrochemical cell from low temperature co-fired ceramic (LTCC) material and carbon screen-printed electrode applicable in portable devices. Firstly, a carbon screen-printed electrode was prepared and characterized by cyclic voltammetry and scanning electron microscopy. Afterwards carbon polymeric film and metal pastes were dropped into the LTCC cell cavities in order to determine the device electrodes, and this arrangement was also electrochemically characterized. The great advantage of this promising device is the simple construction method and its widespread applicability in reusable portable devices.

Peptide separation through a CB[8]-mediated supramolecular trap-and-release process

We demonstrate a supramolecular peptide separation approach by the selective immobilization of peptides bearing an N-terminal tryptophan onto a CB[8]-modified gold substrate, followed by electrochemical release. The CB[8]-stabilized heteroternary complexes were characterized by (1)H NMR, ESI-MS, UV/vis, and fluorescence spectroscopy and cyclic voltammetry. Micropatterned CB[8]-modified gold substrates were found to trap only the recognizable N-tryptophan-containing peptides from a peptide mixture that could be visualized as green peptide arrays under fluorescence microscopy. Subsequently, the bound peptides were released from the modified substrates by the controlled single-electron reduction of viologen. The fully reversible trap-and-release process was repeated for 13 cycles, and the cumulative release profile of the dye-peptide conjugate was monitored by fluorescence spectroscopy, indicating that no degradation occurred.

Redox-magnetohydrodynamic microfluidics without channels and compatible with electrochemical detection under immunoassay conditions

A unique capability of redox-magnetohydrodynamics (redox-MHD) for handling liquids on a small scale was demonstrated. A 1.2 muL solution plug was pumped from an injection site to a detector without the need for a channel to direct the flow. The redox pumping species did not interfere with enzymatic activity in a solution compatible with enzyme-linked immunoassays. Alkaline phosphatase (AP), a common enzyme label, converted p-aminophenyl phosphate (PAPP) to p-aminophenol (PAP(R)) in the presence of 2.5 mM Ru(NH(3))(6)Cl(2) and 2.5 mM Ru(NH(3))(6) Cl(3), in 0.1 M Tris buffer (pH = 9). A solution plug containing PAPP (no AP) was pumped through the surrounding solution containing AP (no PAPP), and the enzymatically generated PAP(R) was easily detected and distinguishable electrochemically from the pumping species with square wave voltammetry down to 0.1 mM concentrations. The test device consisted of a silicon chip containing individually addressable microband electrodes, placed on a 0.5 T NdFeB permanent magnet with the field oriented perpendicular to the chip. A 8.0 mm wide x 15.5 mm long x 1.5 mm high volume of solution was contained by a poly(dimethylsiloxane) gasket and capped with a glass slide. A steady-state fluid velocity of approximately 30 mum/s was generated in a reinforcing flow configuration between oppositely polarized sets of pumping electrodes with approximately 2.1 muA.

Low-temperature co-fired ceramic microchannels with individually addressable screen-printed gold electrodes on four walls for self-contained electrochemical immunoassays

Microchannel devices were constructed from low-temperature co-fired ceramic (LTCC) materials with screen-printed gold (SPG) electrodes in three dimensions--on all four walls--for self-contained enzyme-linked immunosorbant assays with electrochemical detection. The microchannel confines the solution to a small volume, allowing concentration of electroactive enzymatically generated product and nearby electrodes provide high-speed and high-sensitivity detection: it also facilitates future integration with microfluidics. LTCC materials allow easy construction of three-dimensional structures compared with more traditional materials such as glass and polymer materials. Parallel processing of LTCC layers is more amenable to mass production and fast prototyping, compared with sequential processing for integrating multiple features into a single device. LTCC and SPG have not been reported previously as the basis for microchannel immunoassays, nor with integrated, individually addressable electrodes in three dimensions. A demonstration assay for mouse IgG at 5.0 ng/mL (3.3 × 10(-11) M) with electrochemical detection was achieved within a 1.8 cm long × 290 μm high × 130 μm wide microchannel (approximately 680 nL). Two of four SPG electrodes span the top and bottom walls and serve as the auxiliary electrode and the assay site, respectively. The other two (0.7 cm long × 97 μm wide) are centered lengthwise on the sidewalls of the channel. One serves as the working and the other as the pseudoreference electrode. The immunoassay components were immobilized at the bottom SPG region. Enzymatically generated p-aminophenol was detected at the internal working electrode within 15 s of introducing the enzyme substrate p-aminophenyl phosphate. A series of buffer rinses avoided nonspecific adsorption and false-positive signals.

Redox magnetohydrodynamic enhancement of stripping voltammetry: toward portable analysis using disposable electrodes, permanent magnets, and small volumes

The use of redox magnetohydrodynamics (MHD) to enhance the anodic stripping voltammetry (ASV) response of heavy metals has been investigated, with respect to achieving portability: disposable electrodes consisting of screen-printed carbon (SPC) on a low temperature co-fired ceramic (LTCC) substrate, small volumes, and permanent magnets. The analytes tested (Cd(2+), Cu(2+), and Pb(2+)) were codeposited on SPC with Hg(2+) to form a Hg thin film electrode. High concentrations of Fe(3+) were used to produce a high cathodic current which generates a significant Lorentz force in the presence of a magnetic field. This Lorentz force induces solution convection during the deposition step, enhancing the mass transport of analytes to the electrode and increasing their preconcentrated quantity in the mercury thin film. Therefore, larger ASV peaks and improved sensitivities are obtained, compared to analyses performed without a magnet. The effects on ASV signal of varying Hg(2+) concentration (0.10 and 1.0 mM), deposition time (10-600 s), and electrode surface roughness were investigated. In addition, analyses were performed using a real lake water matrix. By using the disposable LTCC-SPC working electrodes in small volumes (150 microL) and with small permanent magnets (0.78 T), peak areas were increased by 75% when compared to the signal obtained in the absence of a magnetic field. A limit of detection of 25 nM for Cd(2+) was observed with only a 1 min preconcentration time.