Design and optimisation of the resonant mirror, an optical biosensor, for the analysis of microalbuminuria in trauma patients

Abstract

Microalbuminuria is characterised by elevated levels of albumin in urine. It reflects localised increases in vascular permeability. Increases in vascular permeability occur as a result of inflammatory response to trauma or infection. Resonant mirror biosensors permit real time analysis of molecular interaction without the need for labelling either the receptor or the ligand. A resonant mirror-based assay was developed to detect albumin using anti human serum albumin antibody 0220-0704. Albumin standards were measured from 1-100 µg/ml to produce reproducible, linear calibration curves in a one-well assay format and from 2-32 µg/ml in a four-well format, which allows for the assay of control samples. The latter assay was used to detect albumin in human urine. Results were comparable with conventional methods and were reproducible. Secondly, a novel assay for creatinine was developed using the resonant mirror. Creatinine has a molecular weight below the detection limit of the device and so a response based on localised pH change, caused by the deamination of creatinine by creatinine deaminase was exploited. This novel application of the resonant mirror successfully detected creatinine at concentrations as low as 270µM. The inclusion of creatinine should permit correction for urine flow variation. The concept of using a resonant mirror for monitoring microalbuminuria has applications for analysis in trauma severity of patients. The exciting potential for this technology is the rapid, non-invasive, measurement of multiple medical markers in urine for use in clinical diagnosis.