Optical scattering artifacts observed in the development of multiplexed surface enhanced Raman spectroscopy nanotag immunoassays

Here we describe scattering based signal suppression artifacts encountered while developing multiplex lateral flow (LF) immunoassay using surface enhanced Raman spectroscopy (SERS) "nanotags" as analyte labels. Using these SERS nanotags, we have produced a quantitative test for inflammation biomarkers that is transferable to the point of care (POC). The SERS assay shows similar performance when compared with a fluorescent nanoparticle POC test. Here, using cardiac and inflammation biomarkers, we highlight the need to carefully optimize the concentration of assay components when using SERS nanotags and a single-line multiplexing approach. We show that in certain circumstances the SERS signal may be suppressed, leading to a significant underestimation of the analyte concentrations. Using electron microscopy and optical spectroscopy, we demonstrate that the error in the measurement is associated with the light scattering properties of the nanotags. These findings will be applicable to other nanoparticle labels with high light scattering coefficients. Through careful modification of the assay to reduce the impact of light scattering, it is possible to produce quantitative assays, but potentially at the expense of multiplexing capability and assay sensitivity.

The diagnostic accuracy of different natriuretic peptides in the investigation of canine cardiac disease

OBJECTIVES

We aimed to validate and determine the accuracy of a new sandwich ELISA for canine N-terminal pro-B-type natriuretic peptide (NT-proBNP) in the discrimination of canine patients with cardiac disease from those with respiratory disease and to determine the effect of confounding variables on NT-proBNP concentrations.

METHODS

Validation studies for the new assay were undertaken. Concentrations of N-terminal atrial natriuretic peptide (NT-proANP) and NT-proBNP in both ethylenediaminetetraacetic acid (EDTA) plasma and serum were estimated in samples from 77 dogs at a laboratory blinded to the clinical status of the patient. The diagnostic accuracy of the each sample type and test was evaluated using receiver operating characteristic curves. The effect of age, gender and indicators of renal function was evaluated using a multivariate regression analysis.

RESULTS

Concentrations of NT-proBNP in both serum and plasma accurately discriminated dogs with respiratory disease from those with cardiac disease, with an optimum cut-off concentration of 210 pmol/l. NT-proBNP concentrations were unaffected by sample type. Increasing creatinine concentration is associated with increasing concentration of NT-proBNP. Age and gender were not found to have significant effects on natriuretic peptide concentrations in this population.

CLINICAL SIGNIFICANCE

Canine NT-proBNP appears to be a useful marker of the presence of cardiac disease, although concentrations must be interpreted in the light of the patient's renal function.

Clinical validation of a proANP 31-67 fragment ELISA in the diagnosis of heart failure in the dog

Atrial natriuretic peptide (ANP) is a polypeptide hormone found in increased concentrations in the plasma of dogs with heart failure. However, problems arise in using ANP as a diagnostic marker for heart failure because of its short half-life in plasma, proteolysis post-collection and the necessity for a radioimmunoassay. The diagnostic utility of a proANP 31-67 ELISA for the detection of heart failure in dogs was evaluated using plasma collected from 31 dogs with clinical and radiographic signs of heart failure and control samples from 40 dogs considered to be free of cardiac disease. Log proANP 31-67 levels were significantly higher in the heart failure group (P < 0.001). In this population of dogs, using a cut-off value of 1,750 fmol/ml, the sensitivity and specificity of the assay were 83.9 per cent and 97.5 per cent, respectively. Using a cut-off of 1,350 fmol/ml, the sensitivity and specificity were 93.5 per cent and 72.5 per cent, respectively. It is concluded that a proANP 31-67 fragment ELISA should prove to be a useful diagnostic aid in naturally occurring canine heart failure.

Visualization of Golgi apparatus in methacrylate embedded conifer embryo tissue using the monoclonal antibody JIM 84

Methacrylate embedding followed by resin removal has been used for the first time to visualize a membrane-associated antigen at the tissue level. Monoclonal antibody JIM 84 was used to stain the Golgi apparatus of gymnosperm (conifer) embryos by light microscope immunocytochemistry. Specificity of labelling was confirmed by electron microscope immunocytochemistry using LR-white resin. GA staining was evident in all stages of white spruce somatic embryo development from immature to mature. Some regions of the somatic embryos (e.g. root cap/suspensor region) stained more vigorously than other regions (hypocotyl/cotyledon end). GA also stained in roots of Monterey pine and Douglas fir. Unlike the situation in most angiosperms, JIM 84 antigen appears to be absent from the conifer plasma membrane. However, it appears to be present in representatives of both major classes of higher plants.