Aptamer-functionalised magnetic particles for highly selective detection of urinary albumin in clinical samples of diabetic nephropathy and other kidney tract disease.

We report a new highly selective detection platform for human albumin (HA) in urine based on aptamer-functionalised magnetic particles. Magnetic separation and re-dispersion was utilised to expose the HA-bound particles to a methylene blue solution. A second magnetic collection step was then used to allow the methylene blue supernatant to be reduced at an unmodified screen-printed electrode. Since methylene blue adsorbs to HA, the reduction current fell in proportion to HA concentration. There was no interference from compounds such as dopamine, epinephrine, vanillylmandelic acid, normetanephrine, metanephrine and creatinine in artificial urine at the concentrations at which they would be expected to appear. A calibration equation was derived to allow for the effect of pH on the response. This enabled measurement to be made directly in clinical urine samples of varying pH. After optimisation of experimental parameters, the total assay time was 40 min and the limit of detection was between 0.93 and 1.16 μg mL, depending on the pH used. HA could be detected up to 400 μg mL, covering the range from normoalbuminuria to macroalbuminuria. Analysis of urine samples of patients, with diabatic nephropathy, type I & II diabetes mellitus and chronic kidney disease, from a local hospital showed good agreement with the standard urinary human albumin detection method.