Determination of minute amounts of ATP by flow injection analysis using enzyme amplification reactions and fluorescence detection

HB-EGF synthesis and release induced by cholesterol depletion of human epidermal keratinocytes is controlled by extracellular ATP and involves both p38 and ERK1/2 signaling pathways

The heparin-binding EGF-like growth factor (HB-EGF) is an autocrine/paracrine keratinocyte growth factor, which binds to the epidermal growth factor (EGF) receptor family and plays a critical role during the re-epithelialization of cutaneous wound by stimulating the keratinocytes proliferation and migration. In this study, cellular stressing condition in autocrine cultures of human keratinocytes was induced by cholesterol depletion using methyl-beta-cyclodextrin (MβCD). MβCD treatment induces the expression and the release of HB-EGF. By analysis of the culture media, large amounts of cellular ATP were measured particularly after 1 h of MβCD treatment. To investigate whether ATP contributes to the expression of HB-EGF, the nonhydrolyzable ATP analogue, ATP-γ-S, was used to mimic the extracellular ATP released. We report that keratinocytes stimulated with ATP-γ-S induce HB-EGF expression and activate EGFR and ERK1/2. Using an antagonist of P2 purinergic receptors, we demonstrate that HB-EGF synthesis induced by lipid rafts disruption is dependent on ATP interaction with P2 purinergic receptors. Moreover, our data suggest that both MAPKs p38 and ERK1/2 are involved together or independently in the regulation of HB-EGF gene expression. These findings provide new insight into the signaling pathway by which HB-EGF is expressed after lipid rafts disruption. In summary, after lipid raft disruption, keratinocytes release large amount of extracellular ATP. ATP induces HB-EGF synthesis and release by interacting with the P2 purinergic receptor and through p38 and ERK1/2 signaling in response to a challenging environment. A release of ATP acts as an early stress response in keratinocytes.

A novel electro-optical sensor format with generic applicability for exploitation with NAD(P) dependent enzymes

This paper describes the development of a novel optically interrogated enzyme electrode with generic applicability for NAD(P) dependent enzymes. The example reported here employs a multi-enzyme pathway comprising the enzymes pyruvate kinase, hexokinase, glucose-6-phosphate dehydrogenase and diaphorase. The final substrate of this pathway, dichlorophenol indophenol (DCPIP), was immobilised within an ultra-thin polymer film of o-phenylenediamine, itself electrochemically polymerised onto a conductive gold coating on the surface of a support polyethylene sheet. Dichlorophenol indophenol (DCPIP) absorbs within the visible region of the spectrum with a lambda(max) approximately 600 nm. When reduced, the molar absorption coefficient at this wavelength decreases significantly and DCPIP effectively becomes colourless (DCPIPH(3)). Ultra-thin layers of gold (<10 nm thickness) exhibit an optical absorption minimum at wavelengths of approximately 520 nm and therefore light within this region of the spectrum may be transmitted with relative ease through the polymer/gold/polyethylene optrode. Results presented within this paper show how this electro-optical sensor may be used to determine concentrations of adenosine triphosphate (ATP) within a sample. In the presence of ATP a colour change from blue to colourless was observed for DCPIP when the assay was performed in solution. However, when DCPIP was immobilised within a polymeric film onto the surface of gold coated electrodes, a colour change from blue to red was observed corresponding to a third redox state of DCPIP (DCPIPH).

Biosensors based on flow-through systems

When combined with biosensors as the sensing element microdialysis and flow injection analysis (FIA) systems become sophisticated tools for handling analytical processes. In particular a FIA system offers a high degree of automation together with high reproducibility and small sample volumes, whereas the biosensor, allows selective and sensitive measurements of the various analytes. Here we describe first a miniaturised microdialysis flow-through system developed for glucose determination, then we focus on amperometric immunosensors and on microbial sensors. In the former, antibodies against low molecular weight environmental contaminants or against high molecular weight proteins are responsible for analyte detection, whereas the latter use immobilised microorganisms as the recognising element for monitoring water pollutants.

Development of an amperometric flow injection immunoanalysis system for the determination of the herbicide 2,4-dichlorophenoxyacetic acid in water

An amperometric flow injection immunoanalysis (FIIA) system based on an immunoreactor with immobilized biocomponents on a silica surface has been developed for the determination of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D). In the antigen coating mode the hapten was immobilized and monoclonal primary antibody against 2,4-D together with alkaline phosphatase (AP)-labelled secondary antibody were used as sensing elements in a titration assay. In the antibody coating mode a biotinylated monoclonal antibody was immobilized on the surface of the immunoreactor and a 2,4-D-AP-conjugate was used for detection. For electrochemical measurements p-aminophenol enzymatically generated from p-aminophenyl phosphate was oxidized at a carbon working electrode at +150 mV versus Ag/AgCl. The system enabled the determination of 2,4-D in drinking water samples in the range from 0.2 to 70 micrograms/l. The whole system was computer controlled with a measuring time of 12 min for one determination.

Principles and applications of flow injection analysis in biosensors

In practical applications biosensors are often forced to operate under less than optimal conditions. Because of their construction, and the physical processes and chemical reactions involved in their operation, compromise conditions are frequently required to synchronize all events taking place. Therefore, and in order to implement functions such as periodic calibration, conditioning and possible regeneration of the biosensor, and, very importantly, to yield the freedom to select the optimum detection means, it is advantageous to use these devices in a flow-through mode, particularly by employing the flow injection (FI) approach. The capacity of FI, as offering itself as a complementary facility to augment the performance of biosensors, and in many cases as an attractive alternative, is demonstrated by reference to selected examples, comprising assays based on enzymatic procedures with optical and thermal detection procedures, and via description of a recently introduced technique for immunoassays, termed flow injection renewable surface immunoassays, which promises to entail powerful potentials and to yield compatible or better economy of operation than existing approaches.