Protein chip for the parallel quantification of high and low abundant biomarkers for sepsis.

We present herein a protein chip for diagnosis of sepsis that combines both a sandwich and a binding inhibition format in order to quantify high (CRP) and low abundant proteins (cytokines, PCT, neopterin) in parallel. Using the combined assay format the lowest detectable concentrations for CRP, IL-6, IL-8, IL-10, TNFα, PCT, and neopterin are 3 mg/L, 15 ng/L, 26 ng/L, 65 ng/L, 40 ng/L, 78 ng/L, and 0.46 µg/L. Four different combined assay formats are tested, using separate or joint incubation steps of analytes and detection antibodies. Yet, low limit of detection (LOD) and short processing time are contradictory: while the combined assay performed in a multistep protocol is extremely sensitive (e.g., the LOD for IL-6 is 15 ng/L), but more time-consuming (4 h), the all-in-one protocol takes only 2.5 h, but suffers from lower sensitivity compared with the multistep protocol (e.g., the LOD for IL-6 is up to 40 times enhanced). Reproducibility is good in both cases (CV 5-20%).

Trichoderma G protein-coupled receptors: functional characterisation of a cAMP receptor-like protein from Trichoderma atroviride.

Galpha subunits act to regulate vegetative growth, conidiation, and the mycoparasitic response in Trichoderma atroviride. To extend our knowledge on G protein signalling, we analysed G protein-coupled receptors (GPCRs). As the genome sequence of T. atroviride is not publicly available yet, we carried out an in silico exploration of the genome database of the close relative T. reesei. Twenty genes encoding putative GPCRs distributed over eight classes and additional 35 proteins similar to the Magnaporthe grisea PTH11 receptor were identified. Subsequently, four T. atroviride GPCR-encoding genes were isolated and affiliated to the cAMP receptor-like family by phylogenetic and topological analyses. All four genes showed lowest expression on glycerol and highest mRNA levels upon carbon starvation. Transcription of gpr3 and gpr4 responded to exogenously added cAMP and the shift from liquid to solid media. gpr3 mRNA levels also responded to the presence of fungal hyphae or cellulose membranes. Further characterisation of mutants bearing a gpr1-silencing construct revealed that Gpr1 is essential for vegetative growth, conidiation and conidial germination. Four genes encoding the first GPCRs described in Trichoderma were isolated and their expression characterized. At least one of these GPCRs is important for several cellular processes, supporting the fundamental role of G protein signalling in this fungus.

Xanthan/chitosan gold chip for metal enhanced protein biomarker detection.

Protein microarrays for disease diagnostics are required to accurately quantify analytes in the low pg/mL range. This task is hampered by weak signal strengths and too low detector sensitivity. Herein we present reflective gold chips coated with polyelectrolyte multilayers (PEMs) for signal enhancement in immunoassays for melanoma-relevant biomarkers. Among tested (semi)natural polysaccharides (xanthan, chitosan, carboxymethylcellulose, hyaluronic acid) PEMs composed of xanthan and chitosan performed best in terms of detection of low analyte concentrations (ED10), spot morphology, fluorescence background and variability (<10%). Fluorescence signals on gold slides with a 75 nm coating of seven crosslinked polyelectrolyte double layers were up to 50 times higher than on bare glass slides. In comparison to commercial substrates the signal to noise ratio is enhanced by up to factor 11. Furthermore sandwich assays for interleukins 6, 8, 10, tumour necrosis factor alpha (TNFα), vascular endothelial growth factor A (VEGF-A) and S100B show working ranges which cover significantly lower concentrations (up to 38-fold). Not limited to above assays the presented substrates, which combine a biocompatible interface with metal-based signal amplification, are a valuable tool in a variety of biosensor applications.

Aptamer-antibody on-chip sandwich immunoassay for detection of CRP in spiked serum.

This study describes a RNA aptamer-based biochip with high affinity and specificity for C-reactive protein (CRP). CRP, which exists in concentrations of 1-3mg/l in the serum of healthy patients, has been identified as a reliable biomarker for inflammation and as a potential marker for sepsis and tissue necrosis. The CRP-specific aptamer was covalently immobilized with its 5'-end on ARChip Epoxy. The detection of bound CRP was carried out optically using labelled secondary antibody in a sandwich format. Assay conditions were optimized with respect to the CRP binding buffer (buffer system, pH and additives) and Ca(2+) concentration (10 mM). Moreover, two sandwich immunoassay formats were tested, the one using dye-labelled antibodies and the other with biotin-modified antibodies/Dy647-labelled streptavidin. In comparison with an antibody-based chip assay, the aptamer chip is superior in terms of CRP measuring range (10 microg/l to 100mg/l) in human serum whereas antibody-based chips result in superior data reproducibility (CV of 8-15%). In contrast to antibody chips, aptamer microarrays provide the unique potential of detecting CRP in serum samples of low risk patients (1-3mg/l) as well as high risk patients (>500 mg/l), furthermore elevated CRP levels (20-350 mg/l) with acceptable recovery (70-130%) by including only one serum sample dilution step (1:100) for the complete measuring range.