One-step assay for optical prostate specific antigen detection using magnetically engineered responsive thin film.

We report a novel and very simple method for the detection of proteolytically-active prostate specific antigen (PSA) at a very low concentration using a self-assembled monolayer (SAM) of magnetic beads conjugated with peptide. The application of surface plasmon resonance (SPR) allows real-time optical characterization of the constructed recognition monolayer. This set-up is also capable of rapid monitoring of PSA samples through an instantaneous detection of medium refractive index shift induced by the enzymatic cleavage of the peptide and the dissociation of free magnetic beads. The results showed the ability of our SPR sensor to detect PSA within a short time (few minutes to 30 min) with high sensitivity (100 pg/ml) and specificity. Thanks to the elimination of washing and blocking steps, as well as the signal amplification and labeling procedures, this approach can be implemented in other miniaturized configurations such as screen printed electrode and biochip array amenable to low-cost point-of-care devices.

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.

A novel and rapid assay for HIV-1 protease detection using magnetic bead mediation.

A simple sensing assay was established for label-free detection of HIV-1 protease. HIV-1 protease peptide substrate conjugated to magnetic beads via its N-terminus is directly fixed onto the sensor gold surface through the sulphur atom of cysteine. Surface plasmon resonance (SPR) was used to study the peptide substrate cleavage efficiency of the protease with magnetic beads of different sizes (1 µm and 30 nm). Cyclic voltammetry and faradic impedance spectroscopy were employed in order to characterize the functionalized gold electrode. It was found that the nano-sized beads are a more efficient sensing probe for the protease. Electrochemical biosensing showed a gradual decrease in charge transfer resistance after injection of the HIV-1 protease. The experimental data established a detection limit of 10 pg/ml, as well as demonstrated a drug screening assay. This HIV-1 protease biosensor represents a new detection approach which will lead to low-cost point-of-care devices for sensitive HIV-1 diagnosis, as well as high-throughput drug screening platforms.

Wash-less and highly sensitive assay for prostate specific antigen detection.

A novel, simple and facile biosensor for prostate specific antigen (PSA) detection was constructed. In this method, proteolytically active PSA is capable of cleaving PSA substrate-magnetic carrier complexes. Electrochemical analysis of the sensor layer showed a significant decrease in impedance signal after proteolysis has occurred, whereas a positive change in impedance was observed using a negative control substrate, indicating the specificity of our detection mechanism. The biosensor has the ability to monitor PSA concentrations ranging from 1 pg ml(-1) to 1 µg ml(-1) with a detection limit as low as 1 pg 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.