Ultra-rapid colorimetric assay for protease detection using magnetic nanoparticle-based biosensors.

Sensitive protease detection methods often require time-consuming techniques and expensive instrumentation. To overcome this limitation, a novel, simple, sensitive and selective colorimetric detection approach was developed. This biosensing configuration was validated by the use of prostate specific antigen (PSA) protease as a model target. In this method, proteolytically active PSA capable of cleaving PSA substrates caused the release of black-colored magnetic carrier complexes, exposing the gold color sensor surface visible to the naked eye. The assay showed excellent sensitivity as well as specificity, capable of discriminating between different types of protease targets. The biosensor was able to quantitatively detect different PSA concentrations with a detection limit as low as 10 ng mL(-1). The sensor offers the possibility of developing a wash-less and cost-effective point-of-care device due to the simplicity of the probe immobilization process and the elimination of labeling and reporter molecules during the biosensing step.