Temperature-regulated gold nanoparticle sensors for immune chromatographic rapid test kits with reproducible sensitivity: a study.

Immune-chromatographic kits are being used since several years in the rapid detection of infectious diseases. It is also called the lateral flow technique, and is used for antigen or antibody detection. There are a series of steps involved in the development of these immune-chromatographic test kits. Still, the preparation of gold nanoparticles (AuNPs) is an important quality variable for the immune-chromatographic test kit sensitivity. The immune chromatographic test must be specific in detection for specific antigen and antibody; this implies that the test kit should not show a false result. Secondly, the test kit should be sensitive enough to give a readable result, and the intensity of the test line should increase or decrease with the concentration of an analytic sample. Various factors can influence the performance of a test. Temperature differences in AuNPs preparation can alter the assay kinetics and contribute to assay variability. Other factors such as assay components, manufacturing processes and reagent variation also contribute to assay precision and accuracy. It is important to note that assay reproducibility is the combined effect of individual sources of variability. The authors have synthesized AuNPs by immediately controlling the reaction temperature. Different batches of Malaria rapid test kit were developed and the test kit sensitivity was analysed. It was found that test kits designed with temperature-controlled AuNPs sensor had reproducible uniformity in terms of batch to batch sensitivity than AuNPs synthesized by conventional Turkevich and Fern process.

Optical Density Optimization of Malaria Pan Rapid Diagnostic Test Strips for Improved Test Zone Band Intensity.

For the last few decades, the immunochromatographic assay has been used for the rapid detection of biological markers in infectious diseases in humans and animals The assay, also known as lateral flow assay, is utilized for the detection of antigen or antibody in human infectious diseases. There are a series of steps involved in the development of these immuno-chromatographic test kits, from gold nano colloids preparation to nitrocellulose membrane coating (NCM). These tests are mostly used for qualitative assays by a visual interpretation of results. For the interpretation of the results, the color intensity of the test zone is therefore very significant. Herein, the study was performed on a malaria antigen test kit. Several studies have reported the use of gold nanoparticles (AuNPs) with varying diameters and its binding with various concentrations of protein in order to optimize tests. However, none of these studies have reported how to fix (improve) test zone band intensity (color), if different sized AuNPs were synthesized during a reaction and when conjugated equally with same amount of protein. Herein, different AuNPs with average diameter ranging from 10 nm to 50 nm were prepared and conjugated equally with protein concentration of 150 µg/mL with KD = 1.0 × 10-3. Afterwards, the developed kits' test zone band intensity for all different sizes AuNPs was fixed to the same band level (high) by utilization of an ultraviolet-visible spectrophotometer. The study found that the same optical density (OD) has the same test zone band intensity irrespective of AuNP size. This study also illustrates the use of absorption maxima (λ max) techniques to characterize AuNPs and to prevent wastage of protein while developing immunochromatographic test kits.