Porous silicon based photoluminescence immunosensor for rapid and highly-sensitive detection of Ochratoxin A.

A rapid and low cost photoluminescence (PL) immunosensor for the determination of low concentrations of Ochratoxin A (OTA) has been developed. This immunosensor was based on porous silicon (PSi) and modified by antibodies against OTA (anti-OTA). PSi layer was fabricated by metal-assisted chemical etching (MACE) procedure. Main structural parameters (pore size, layer thickness, morphology and nanograins size) and composition of PSi were investigated by means of X-Ray diffraction (XRD), scanning electron microscopy (SEM) and Raman spectroscopy. PL-spectroscopy of PSi was performed at room temperature and showed a wide emission band centered at 680 ± 20nm. Protein A was covalently immobilized on the surface of PSi, which in next steps was modified by anti-OTA and BSA in this way a anti-OTA/Protein-A/PSi structure sensitive towards OTA was designed. The anti-OTA/Protein-A/PSi-based immunosensors were tested in a wide range of OTA concentrations from 0.001 upto 100ng/ml. Interaction of OTA with anti-OTA/Protein-A/PSi surface resulted in the quenching of photoluminescence in comparison to bare PSi. The limit of detection (LOD) and the sensitivity range of anti-OTA/Protein-A/PSi immunosensors were estimated. Association constant and Gibbs free energy for the interaction of anti-OTA/Protein-A/PSi with OTA were calculated and analyzed using the interaction isotherms. Response time of the anti-OTA/Protein-A/PSi-based immunosensor toward OTA was in the range of 500-700s. These findings are very promising for the development of highly sensitive, and potentially portable immunosensors suitable for fast determination of OTA in food and beverages.

Gold coated porous silicon nanocomposite as a substrate for photoluminescence-based immunosensor suitable for the determination of Aflatoxin B1.

A rapid and low cost photoluminescence (PL) immunosensor for the determination of low concentrations of Aflatoxin B1 (AFB1) has been developed. This immunosensor was based on porous silicon (PSi) covered by thin gold layer (Au) and modified by antibodies against AFB1 (anti-AFB1). PSi layer was formed on silicon substrate, then the surface of PSi was covered by 30nm layer of gold (PSi/Au) using electrochemical and chemical deposition methods and in such ways PSi/Au(El.) and PSi/Au(Chem.) structures were formed, respectively. In order to find PSi/Au the most efficiently suitable for PL-based sensor design, structure several different PSi/Au(El.) and PSi/Au(Chem.) structures were designed while using different conditions for electrochemical or chemical deposition of gold layer. It was shown that during the formation of PSi/Au structure crystalline Au nanoparticles uniformly coated the surface of the PSi pores. PL spectroscopy of PSi/Au nanocomposites was performed at room temperature and it showed a wide emission band centered at 700nm. Protein A was covalently immobilized on the surface of PSi/Au(El.) and PSi/Au(Chem.) forming PSi/Au(El.)/Protein-A and PSi/Au(Chem.)/Protein-A structures, respectively. In the next step PSi/Au(El.)/Protein-A and PSi/Au(Chem.)/Protein-A structures were modified by anti-AFB1 and in such way a structures (PSi/Au(El.)/Protein-A/anti-AFB1 and PSi/Au(Chem.)/Protein-A/anti-AFB1) sensitive towards AFB1 were designed. The PSi/Au(El.)/Protein-A/anti-AFB1- and PSi/Au(Chem.)/Protein-A/anti-AFB1-based immunosensors were tested in a wide range of AFB1 concentrations from 0.001 upon 100ng/ml. Interaction of AFB1 with PSi/Au(El.)/Protein-A/anti-AFB1- and PSi/Au(Chem.)/Protein-A/anti-AFB1-based structures resulted PL quenching. The highest sensitivity towards AFB1 was determined for PSi/Au(El.)/Protein-A/anti-AFB1-based immunosensor and it was in the range of 0.01-10ng/ml. The applicability of PSi/Au-based structures as new substrates suitable for PL-based immunosensors is discussed.